Acousto-Optic–Based Wavelength-Comb-Swept Laser for Extended Displacement Measurements

PubMed Central

Park, Nam Su; Chun, Soo Kyung; Han, Ga-Hee; Kim, Chang-Seok

2017-01-01

We demonstrate a novel wavelength-comb-swept laser based on two intra-cavity filters: an acousto-optic tunable filter (AOTF) and a Fabry-Pérot etalon filter. The AOTF is used for the tunable selection of the output wavelength with time and the etalon filter for the narrowing of the spectral linewidth to extend the coherence length. Compared to the conventional wavelength-swept laser, the acousto-optic–based wavelength-comb-swept laser (WCSL) can extend the measureable range of displacement measurements by decreasing the sensitivity roll-off of the point spread function. Because the AOTF contains no mechanical moving parts to select the output wavelength acousto-optically, the WCSL source has a high wavenumber (k) linearity of R2 = 0.9999 to ensure equally spaced wavelength combs in the wavenumber domain. PMID:28362318

Modern retinal laser therapy

PubMed Central

Kozak, Igor; Luttrull, Jeffrey K.

2014-01-01

Medicinal lasers are a standard source of light to produce retinal tissue photocoagulation to treat retinovascular disease. The Diabetic Retinopathy Study and the Early Treatment Diabetic Retinopathy Study were large randomized clinical trials that have shown beneficial effect of retinal laser photocoagulation in diabetic retinopathy and have dictated the standard of care for decades. However, current treatment protocols undergo modifications. Types of lasers used in treatment of retinal diseases include argon, diode, dye and multicolor lasers, micropulse lasers and lasers for photodynamic therapy. Delivery systems include contact lens slit-lamp laser delivery, indirect ophthalmocope based laser photocoagulation and camera based navigated retinal photocoagulation with retinal eye-tracking. Selective targeted photocoagulation could be a future alternative to panretinal photocoagulation. PMID:25892934

Predictive modeling, simulation, and optimization of laser processing techniques: UV nanosecond-pulsed laser micromachining of polymers and selective laser melting of powder metals

NASA Astrophysics Data System (ADS)

Criales Escobar, Luis Ernesto

One of the most frequently evolving areas of research is the utilization of lasers for micro-manufacturing and additive manufacturing purposes. The use of laser beam as a tool for manufacturing arises from the need for flexible and rapid manufacturing at a low-to-mid cost. Laser micro-machining provides an advantage over mechanical micro-machining due to the faster production times of large batch sizes and the high costs associated with specific tools. Laser based additive manufacturing enables processing of powder metals for direct and rapid fabrication of products. Therefore, laser processing can be viewed as a fast, flexible, and cost-effective approach compared to traditional manufacturing processes. Two types of laser processing techniques are studied: laser ablation of polymers for micro-channel fabrication and selective laser melting of metal powders. Initially, a feasibility study for laser-based micro-channel fabrication of poly(dimethylsiloxane) (PDMS) via experimentation is presented. In particular, the effectiveness of utilizing a nanosecond-pulsed laser as the energy source for laser ablation is studied. The results are analyzed statistically and a relationship between process parameters and micro-channel dimensions is established. Additionally, a process model is introduced for predicting channel depth. Model outputs are compared and analyzed to experimental results. The second part of this research focuses on a physics-based FEM approach for predicting the temperature profile and melt pool geometry in selective laser melting (SLM) of metal powders. Temperature profiles are calculated for a moving laser heat source to understand the temperature rise due to heating during SLM. Based on the predicted temperature distributions, melt pool geometry, i.e. the locations at which melting of the powder material occurs, is determined. Simulation results are compared against data obtained from experimental Inconel 625 test coupons fabricated at the National Institute for Standards & Technology via response surface methodology techniques. The main goal of this research is to develop a comprehensive predictive model with which the effect of powder material properties and laser process parameters on the built quality and integrity of SLM-produced parts can be better understood. By optimizing process parameters, SLM as an additive manufacturing technique is not only possible, but also practical and reproducible.

Controlling laser emission by selecting crystal orientation

NASA Astrophysics Data System (ADS)

Chen, Lijuan; Han, Shujuan; Wang, Zhengping; Wang, Jiyang; Zhang, Huanjin; Yu, Haohai; Han, Shuo; Xu, Xinguang

2013-01-01

Based on the anisotropy of laser crystal, we demonstrate a method of adjusting laser emission by selecting crystal orientation. When the light propagating direction varies from a to c axis of Nd:LiGd(MoO4)2 crystal, emission wavelength exhibits a sensitive change of 1061 nm → 1061/1062 + 1068 nm → 1068 nm. The experimental discipline is well explained by a theoretical study of simulating on the spatial distribution of stimulated emission cross-section. This letter manifests that the laser property along non-principal-axis direction is also valuable for research and application, which breaks through the traditional custom of using laser materials processed along principal-axis.

Photoacoustic Spectroscopy with Quantum Cascade Lasers for Trace Gas Detection

PubMed Central

Elia, Angela; Di Franco, Cinzia; Lugarà, Pietro Mario; Scamarcio, Gaetano

2006-01-01

Various applications, such as pollution monitoring, toxic-gas detection, non invasive medical diagnostics and industrial process control, require sensitive and selective detection of gas traces with concentrations in the parts in 109 (ppb) and sub-ppb range. The recent development of quantum-cascade lasers (QCLs) has given a new aspect to infrared laser-based trace gas sensors. In particular, single mode distributed feedback QCLs are attractive spectroscopic sources because of their excellent properties in terms of narrow linewidth, average power and room temperature operation. In combination with these laser sources, photoacoustic spectroscopy offers the advantage of high sensitivity and selectivity, compact sensor platform, fast time-response and user friendly operation. This paper reports recent developments on quantum cascade laser-based photoacoustic spectroscopy for trace gas detection. In particular, different applications of a photoacoustic trace gas sensor employing a longitudinal resonant cell with a detection limit on the order of hundred ppb of ozone and ammonia are discussed. We also report two QC laser-based photoacoustic sensors for the detection of nitric oxide, for environmental pollution monitoring and medical diagnostics, and hexamethyldisilazane, for applications in semiconductor manufacturing process.

Single-mode fiber laser based on core-cladding mode conversion.

PubMed

Suzuki, Shigeru; Schülzgen, Axel; Peyghambarian, N

2008-02-15

A single-mode fiber laser based on an intracavity core-cladding mode conversion is demonstrated. The fiber laser consists of an Er-doped active fiber and two fiber Bragg gratings. One Bragg grating is a core-cladding mode converter, and the other Bragg grating is a narrowband high reflector that selects the lasing wavelength. Coupling a single core mode and a single cladding mode by the grating mode converter, the laser operates as a hybrid single-mode laser. This approach for designing a laser cavity provides a much larger mode area than conventional large-mode-area step-index fibers.

The selective and efficient laser ion source and trap project LIST for on-line production of exotic nuclides

NASA Astrophysics Data System (ADS)

Wendt, Klaus; Gottwald, Tina; Hanstorp, Dag; Mattolat, Christoph; Raeder, Sebastian; Rothe, Sebastian; Schwellnus, Fabio; Havener, Charles; Lassen, Jens; Liu, Yuan

2010-02-01

Laser ion sources based on resonant excitation and ionization of atoms are well-established tools for selective and efficient production of radioactive ion beams. A recent trend is the complementary installation of reliable state-of-the-art all solid-state Ti:Sapphire laser systems. To date, 35 elements of the Periodic Table are available at laser ion sources by using these novel laser systems, which complements the overall accessibility to 54 elements including use of traditional dye lasers. Recent progress in the field concerns the identification of suitable optical excitation schemes for Ti:Sapphire laser excitation as well as technical developments of the source in respect to geometry, cavity material as well as by incorporation of an ion guide system in the form of the laser ion source trap LIST.

Correlation of the ionisation response at selected points of IC sensitive regions with SEE sensitivity parameters under pulsed laser irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gordienko, A V; Mavritskii, O B; Egorov, A N

2014-12-31

The statistics of the ionisation response amplitude measured at selected points and their surroundings within sensitive regions of integrated circuits (ICs) under focused femtosecond laser irradiation is obtained for samples chosen from large batches of two types of ICs. A correlation between these data and the results of full-chip scanning is found for each type. The criteria for express validation of IC single-event effect (SEE) hardness based on ionisation response measurements at selected points are discussed. (laser applications and other topics in quantum electronics)

Ray tracing method for simulation of laser beam interaction with random packings of powders

NASA Astrophysics Data System (ADS)

Kovalev, O. B.; Kovaleva, I. O.; Belyaev, V. V.

2018-03-01

Selective laser sintering is a technology of rapid manufacturing of a free form that is created as a solid object by selectively fusing successive layers of powder using a laser. The motivation of this study is due to the currently insufficient understanding of the processes and phenomena of selective laser melting of powders whose time scales differ by orders of magnitude. To construct random packings from mono- and polydispersed solid spheres, the algorithm of their generation based on the discrete element method is used. A numerical method of ray tracing is proposed that is used to simulate the interaction of laser radiation with a random bulk packing of spherical particles and to predict the optical properties of the granular layer, the extinction and absorption coefficients, depending on the optical properties of a powder material.

The choice: Welding with CO2 or Nd:YAG lasers

NASA Astrophysics Data System (ADS)

Leong, Keng H.

The recent commercial availability of multi-kilowatt Nd:YAG lasers has opened new avenues for rapid laser processing as well as intensified the competition (cost effectiveness) between CO2 and Nd:YAG laser systems. Vendors offering Nd:YAG laser systems may claim lower operating costs (than CO2) and fiberoptic beam delivery flexibility while CO2 systems vendors may emphasize lower capital cost and well established processing requirements and experience. The capital and operating costs of a laser system are impacted by demand and supply economics and technological advances. Frequently the total cost of a workcell using a laser for processing has to be considered rather than the laser system alone. Consequently it is not very practical to approach the selection of a laser system based on its capital cost and estimated operating cost only. This presentation describes a more pragmatic approach to aid the user in the selection of the optimal multi-kilowatt laser system for a particular processing requirement with emphasis on welding. CO2 laser systems are well established on the factory floor. Consequently, emphasis is given to the comparative application of Nd:YAG lasers, process requirements and performance. Requirements for the laser welding of different metals are examined in the context of hardware (laser system and beam delivery) selection and examples of welding speeds that can be achieved using CO2 and Nd:YAG lasers are examined.

Selective IR multiphoton dissociation of molecules in a pulsed gas-dynamically cooled molecular flow interacting with a solid surface as an alternative to low-energy methods of molecular laser isotope separation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Makarov, G N; Petin, A N

2016-03-31

We report the results of studies on the isotope-selective infrared multiphoton dissociation (IR MFD) of SF{sub 6} and CF{sub 3}I molecules in a pulsed, gas-dynamically cooled molecular flow interacting with a solid surface. The productivity of this method in the conditions of a specific experiment (by the example of SF{sub 6} molecules) is evaluated. A number of low-energy methods of molecular laser isotope separation based on the use of infrared lasers for selective excitation of molecules are analysed and their productivity is estimated. The methods are compared with those of selective dissociation of molecules in the flow interacting with amore » surface. The advantages of this method compared to the low-energy methods of molecular laser isotope separation and the IR MPD method in the unperturbed jets and flows are shown. It is concluded that this method could be a promising alternative to the low-energy methods of molecular laser isotope separation. (laser separation of isotopes)« less

Short Wavelength Laser/Materials Interactions

DTIC Science & Technology

1989-12-20

lasterials interaction phenomena and effects, and 4) materials evaluation. The program has led to major advances in science-based understanding of...3.0 RESULTS 5 3.1 MATERIALS SELECTION and CHARACTERIZATION 5 3.2 DEVELOPMENT of NEW INSTRUMENTATION 8 3.2.1 Laser Sources 8 3.2.2 Multiwavelength ...high temperature during laser irradiation. The program has led to major advances in science-based understanding of materials performance under extreme

Robust generation of Fourier-synthesized laser fields and their estimation of the optical phase by using quantum control of molecular tunneling ionization

NASA Astrophysics Data System (ADS)

Yoshida, Tsuyoshi; Saito, Naoaki; Ohmura, Hideki

2018-03-01

Intense (5.0 × 1012 W cm-2) nanosecond Fourier-synthesized laser fields consisting of fundamental, second-, third-, and fourth-harmonic light generated by an interferometer-free Fourier-synthesized laser field generator induce orientation-selective ionization based on directionally asymmetric molecular tunneling ionization (TI). The laser field generator ensures adjustment-free operation, high stability, and high reproducibility. Phase-sensitive, orientation-selective molecular TI provides a simple way to estimate the relative phase differences between the fundamental light and each harmonic by data-fitting analysis. This application of Fourier-synthesized laser fields will facilitate not only lightwave engineering but also the control of matter.

Diode-based additive manufacturing of metals using an optically-addressable light valve.

PubMed

Matthews, Manyalibo J; Guss, Gabe; Drachenberg, Derrek R; Demuth, James A; Heebner, John E; Duoss, Eric B; Kuntz, Joshua D; Spadaccini, Christopher M

2017-05-15

Selective Laser Melting (SLM) of metal powder bed layers, whereby 3D metal objects can be printed from a digital file with unprecedented design flexibility, is spurring manufacturing innovations in medical, automotive, aerospace and textile industries. Because SLM is based on raster-scanning a laser beam over each layer, the process is relatively slow compared to most traditional manufacturing methods (hours to days), thus limiting wider spread use. Here we demonstrate the use of a large area, photolithographic method for 3D metal printing, using an optically-addressable light valve (OALV) as the photomask, to print entire layers of metal powder at once. An optical sheet of multiplexed ~5 kW, 20 ms laser diode and ~1 MW, 7 ns Q-switched laser pulses are used to selectively melt each layer. The patterning of near infrared light is accomplished by imaging 470 nm light onto the transmissive OALV, which consists of polarization-selective nematic liquid crystal sandwiched between a photoconductor and transparent conductor for switching.

Laser/Optical Data Base Products: Evaluation and Selection.

ERIC Educational Resources Information Center

Nicholls, Paul Travis

1988-01-01

The practical advice for the evaluation of laser/optical data disk materials (e.g., CD-ROM) is based on a review of the relevant literature. An evaluation framework is outlined and collection development tools and sources of published reviews are identified. (34 references) (Author/CLB)

Comparisons of selected laser beam power missions to conventionally powered missions

NASA Technical Reports Server (NTRS)

Bozek, John M.; Oleson, Steven R.; Landis, Geoffrey A.; Stavnes, Mark W.

1993-01-01

Earth-based laser sites beaming laser power to space assets have shown benefits over competing power system concepts for specific missions. Missions analyzed in this report that show benefits of laser beam power are low Earth orbit (LEO) to geosynchronous Earth orbit (GEO) transfer, LEO to low lunar orbit (LLO) cargo missions, and lunar-base power. Both laser- and solar-powered orbit-transfer vehicles (OTV's) make a 'tug' concept viable, which substantially reduces cumulative initial mass to LEO in comparison to chemical propulsion concepts. Lunar cargo missions utilizing laser electric propulsion from Earth-orbit to LLO show substantial mass saving to LEO over chemical propulsion systems. Lunar-base power system options were compared on a landed-mass basis. Photovoltaics with regenerative fuel cells, reactor-based systems, and laser-based systems were sized to meet a generic lunar-base power profile. A laser-based system begins to show landed mass benefits over reactor-based systems when proposed production facilities on the Moon require power levels greater than approximately 300 kWe. Benefit/cost ratios of laser power systems for an OTV, both to GEO and LLO, and for a lunar base were calculated to be greater than 1.

Laser altimetry simulator. Version 3.0: User's guide

NASA Technical Reports Server (NTRS)

Abshire, James B.; Mcgarry, Jan F.; Pacini, Linda K.; Blair, J. Bryan; Elman, Gregory C.

1994-01-01

A numerical simulator of a pulsed, direct detection laser altimeter has been developed to investigate the performance of space-based laser altimeters operating over surfaces with various height profiles. The simulator calculates the laser's optical intensity waveform as it propagates to and is reflected from the terrain surface and is collected by the receiver telescope. It also calculates the signal and noise waveforms output from the receiver's optical detector and waveform digitizer. Both avalanche photodiode and photomultiplier detectors may be selected. Parameters of the detected signal, including energy, the 50 percent rise-time point, the mean timing point, and the centroid, can be collected into histograms and statistics calculated after a number of laser firings. The laser altimeter can be selected to be fixed over the terrain at any altitude. Alternatively, it can move between laser shots to simulate the terrain profile measured with the laser altimeter.

Vanderbilt free-electron-laser project in biomedical and materials research. Annual report, 1 February 1987-31 January 1988

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haglund, R.F.; Tolk, N.H.

The Medical Free Electron Laser Program was awarded to develop, construct and operate a free-electron laser facility dedicated to biomedical and materials studies, with particular emphases on: fundamental studies of absorption and localization of electromagnetic energy on and near material surfaces, especially through electronic and other selective, non-statistical processes; non-thermal photon-materials interactions (e.g., electronic bond-breaking or vibrational energy transfer) in physical and biological materials as well as in long-wavelength biopolymer dynamics; development of FEL-based methods to study drug action and to characterize biomolecular properties and metabolic processes in biomembranes; clinical applications in otolaryngology, neurosurgery, ophthalmology and radiology stressing the usemore » of the laser for selective laser-tissue, laser-cellular and laser-molecule interactions in both therapeutic and diagnostic modalities.« less

High-Temperature Tolerance in Multi-Scale Cermet Solar-Selective Absorbing Coatings Prepared by Laser Cladding.

PubMed

Pang, Xuming; Wei, Qian; Zhou, Jianxin; Ma, Huiyang

2018-06-19

In order to achieve cermet-based solar absorber coatings with long-term thermal stability at high temperatures, a novel single-layer, multi-scale TiC-Ni/Mo cermet coating was first prepared using laser cladding technology in atmosphere. The results show that the optical properties of the cermet coatings using laser cladding were much better than the preplaced coating. In addition, the thermal stability of the optical properties for the laser cladding coating were excellent after annealing at 650 °C for 200 h. The solar absorptance and thermal emittance of multi-scale cermet coating were 85% and 4.7% at 650 °C. The results show that multi-scale cermet materials are more suitable for solar-selective absorbing coating. In addition, laser cladding is a new technology that can be used for the preparation of spectrally-selective coatings.

A 532 nm Chaotic Fiber Laser Transmitter for Underwater Lidar

DTIC Science & Technology

2013-04-23

passes through unaffected. 3.1.1.2 Ring Lasers as Oscillators The simplest form of laser is a called a Fabry - Perot laser, in which two reflectors are...insufficient to drive the gain amplifier, and so the circulator-based design was scrapped in favor of the Fabry - Perot , whose efficiency was far better...Bidirectional Ring and Fabry - Perot Lasers The Fabry - Perot laser used two matched FBGs to create a wavelength-selective resonator cavity. First single- and

Lasers and wound healing.

PubMed

Nemeth, A J

1993-10-01

The advances in laser surgery over the past decade have been remarkable and have significantly altered the management of a host of dermatologic disorders. This article focuses on the CO2 laser as a cutting and vaporization tool and reviews the features that distinguish CO2 laser-induced wounds from those created by a scalpel. Tissue welding, wound management after skin treatment with the visible light lasers based on the principle of selective photothermolysis, as well as the controversial field of low-energy laser therapy (biostimulation) are also addressed.

Algal Biomass Analysis by Laser-Based Analytical Techniques—A Review

PubMed Central

Pořízka, Pavel; Prochazková, Petra; Prochazka, David; Sládková, Lucia; Novotný, Jan; Petrilak, Michal; Brada, Michal; Samek, Ota; Pilát, Zdeněk; Zemánek, Pavel; Adam, Vojtěch; Kizek, René; Novotný, Karel; Kaiser, Jozef

2014-01-01

Algal biomass that is represented mainly by commercially grown algal strains has recently found many potential applications in various fields of interest. Its utilization has been found advantageous in the fields of bioremediation, biofuel production and the food industry. This paper reviews recent developments in the analysis of algal biomass with the main focus on the Laser-Induced Breakdown Spectroscopy, Raman spectroscopy, and partly Laser-Ablation Inductively Coupled Plasma techniques. The advantages of the selected laser-based analytical techniques are revealed and their fields of use are discussed in detail. PMID:25251409

Microstructure and Magnetic Properties of Magnetic Material Fabricated by Selective Laser Melting

NASA Astrophysics Data System (ADS)

Jhong, Kai Jyun; Huang, Wei-Chin; Lee, Wen Hsi

Selective Laser Melting (SLM) is a powder-based additive manufacturing which is capable of producing parts layer-by-layer from a 3D CAD model. The aim of this study is to adopt the selective laser melting technique to magnetic material fabrication. [1]For the SLM process to be practical in industrial use, highly specific mechanical properties of the final product must be achieved. The integrity of the manufactured components depend strongly on each single laser-melted track and every single layer, as well as the strength of the connections between them. In this study, effects of the processing parameters, such as the space distance of surface morphology is analyzed. Our hypothesis is that when a magnetic product is made by the selective laser melting techniques instead of traditional techniques, the finished component will have more precise and effective properties. This study analyzed the magnitudes of magnetic properties in comparison with different parameters in the SLM process and compiled a completed product to investigate the efficiency in contrast with products made with existing manufacturing processes.

Oxygen measurement by multimode diode lasers employing gas correlation spectroscopy.

PubMed

Lou, Xiutao; Somesfalean, Gabriel; Chen, Bin; Zhang, Zhiguo

2009-02-10

Multimode diode laser (MDL)-based correlation spectroscopy (COSPEC) was used to measure oxygen in ambient air, thereby employing a diode laser (DL) having an emission spectrum that overlaps the oxygen absorption lines of the A band. A sensitivity of 700 ppm m was achieved with good accuracy (2%) and linearity (R(2)=0.999). For comparison, measurements of ambient oxygen were also performed by tunable DL absorption spectroscopy (TDLAS) technique employing a vertical cavity surface emitting laser. We demonstrate that, despite slightly degraded sensitivity, the MDL-based COSPEC-based oxygen sensor has the advantages of high stability, low cost, ease-of-use, and relaxed requirements in component selection and instrument buildup compared with the TDLAS-based instrument.

A review on powder-based additive manufacturing for tissue engineering: selective laser sintering and inkjet 3D printing

PubMed Central

Shirazi, Seyed Farid Seyed; Gharehkhani, Samira; Mehrali, Mehdi; Yarmand, Hooman; Metselaar, Hendrik Simon Cornelis; Adib Kadri, Nahrizul; Osman, Noor Azuan Abu

2015-01-01

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powder-based material systems. Hence, the latest state of knowledge available on the use of AM powder-based techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article. PMID:27877783

A review on powder-based additive manufacturing for tissue engineering: selective laser sintering and inkjet 3D printing.

PubMed

Shirazi, Seyed Farid Seyed; Gharehkhani, Samira; Mehrali, Mehdi; Yarmand, Hooman; Metselaar, Hendrik Simon Cornelis; Adib Kadri, Nahrizul; Osman, Noor Azuan Abu

2015-06-01

Since most starting materials for tissue engineering are in powder form, using powder-based additive manufacturing methods is attractive and practical. The principal point of employing additive manufacturing (AM) systems is to fabricate parts with arbitrary geometrical complexity with relatively minimal tooling cost and time. Selective laser sintering (SLS) and inkjet 3D printing (3DP) are two powerful and versatile AM techniques which are applicable to powder-based material systems. Hence, the latest state of knowledge available on the use of AM powder-based techniques in tissue engineering and their effect on mechanical and biological properties of fabricated tissues and scaffolds must be updated. Determining the effective setup of parameters, developing improved biocompatible/bioactive materials, and improving the mechanical/biological properties of laser sintered and 3D printed tissues are the three main concerns which have been investigated in this article.

IGZO TFT-based circuit with tunable threshold voltage by laser annealing

NASA Astrophysics Data System (ADS)

Huang, Xiaoming; Yu, Guang; Wu, Chenfei

2017-11-01

In this work, a high-performance inverter based on amorphous indium-gallium-zinc oxide thin-film transistors (TFTs) has been fabricated, which consists of a driver TFT and a load TFT. The threshold voltage (Vth) of the load TFT can be tuned by applying an area-selective laser annealing. The transfer curve of the load TFT shows a parallel shift into the negative bias direction upon laser annealing. Based on x-ray photoelectron spectroscopy analyses, the negative Vth shift can be attributed to the increase of oxygen vacancy concentration within the device channel upon laser irradiation. Compared to the untreated inverter, the laser annealed inverter shows much improved switching characteristics, including a large output swing range which is close to full swing, as well as an enhanced output voltage gain. Furthermore, the dynamic performance of ring oscillator based on the laser-annealed inverter is improved.

Diode-based additive manufacturing of metals using an optically-addressable light valve

DOE PAGES

Matthews, Manyalibo J.; Guss, Gabe; Drachenberg, Derrek R.; ...

2017-05-10

We present that Selective Laser Melting (SLM) of metal powder bed layers, whereby 3D metal objects can be printed from a digital file with unprecedented design flexibility, is spurring manufacturing innovations in medical, automotive, aerospace and textile industries. Because SLM is based on raster-scanning a laser beam over each layer, the process is relatively slow compared to most traditional manufacturing methods (hours to days), thus limiting wider spread use. Here we demonstrate the use of a large area, photolithographic method for 3D metal printing, using an optically-addressable light valve (OALV) as the photomask, to print entire layers of metal powdermore » at once. An optical sheet of multiplexed ~5 kW, 20 ms laser diode and ~1 MW, 7 ns Q-switched laser pulses are used to selectively melt each layer. Finally, the patterning of near infrared light is accomplished by imaging 470 nm light onto the transmissive OALV, which consists of polarization-selective nematic liquid crystal sandwiched between a photoconductor and transparent conductor for switching.« less

Rapid prototyping of 2D glass microfluidic devices based on femtosecond laser assisted selective etching process

NASA Astrophysics Data System (ADS)

Kim, Sung-Il; Kim, Jeongtae; Koo, Chiwan; Joung, Yeun-Ho; Choi, Jiyeon

2018-02-01

Microfluidics technology which deals with small liquid samples and reagents within micro-scale channels has been widely applied in various aspects of biological, chemical, and life-scientific research. For fabricating microfluidic devices, a silicon-based polymer, PDMS (Polydimethylsiloxane), is widely used in soft lithography, but it has several drawbacks for microfluidic applications. Glass has many advantages over PDMS due to its excellent optical, chemical, and mechanical properties. However, difficulties in fabrication of glass microfluidic devices that requires multiple skilled steps such as MEMS technology taking several hours to days, impedes broad application of glass based devices. Here, we demonstrate a rapid and optical prototyping of a glass microfluidic device by using femtosecond laser assisted selective etching (LASE) and femtosecond laser welding. A microfluidic droplet generator was fabricated as a demonstration of a microfluidic device using our proposed prototyping. The fabrication time of a single glass chip containing few centimeter long and complex-shaped microfluidic channels was drastically reduced in an hour with the proposed laser based rapid and simple glass micromachining and hermetic packaging technique.

Lead extraction by selective operation of a nanosecond-pulsed 355nm laser

NASA Astrophysics Data System (ADS)

Herzog, Amir; Bogdan, Stefan; Glikson, Michael; Ishaaya, Amiel A.; Love, Charles

2016-03-01

Lead extraction (LE) is necessary for patients who are suffering from a related infection, or in opening venous occlusions that prevent the insertion of additional lead. In severe cases of fibrous encapsulation of the lead within a vein, laser-based cardiac LE has become one of the foremost methods of removal. In cases where the laser radiation (typically at 308 nm wavelength) interacts with the vein wall rather than with the fibrotic lesion, severe injury and subsequent bleeding may occur. Selective tissue ablation was previously demonstrated by a laser operating in the UV regime; however, it requires the use of sensitizers (e.g.: tetracycline). In this study, we present a preliminary examination of efficacy and safety aspects in the use of a nanosecond-pulsed solid-state laser radiation, at 355 nm wavelength, guided in a catheter consisting of optical fibers, in LE. Specifically, we demonstrate a correlation between the tissue elasticity and the catheter advancement rate, in ex-vivo experiments. Our results indicate a selectivity property for specific parameters of the laser radiation and catheter design. The selectivity is attributed to differences in the mechanical properties of the fibrotic tissue and a normal vein wall, leading to a different photomechanical response of the tissue's extracellular matrix. Furthermore, we performed successful in-vivo animal trials, providing a basic proof of concept for using the suggested scheme in LE. Selective operation using a 355 nm laser may reduce the risk of blood vessel perforation as well as the incidence of major adverse events.

Single Step Laser Transfer and Laser Curing of Ag NanoWires: A Digital Process for the Fabrication of Flexible and Transparent Microelectrodes.

PubMed

Zacharatos, Filimon; Karvounis, Panagiotis; Theodorakos, Ioannis; Hatziapostolou, Antonios; Zergioti, Ioanna

2018-06-19

Ag nanowire (NW) networks have exquisite optical and electrical properties which make them ideal candidate materials for flexible transparent conductive electrodes. Despite the compatibility of Ag NW networks with laser processing, few demonstrations of laser fabricated Ag NW based components currently exist. In this work, we report on a novel single step laser transferring and laser curing process of micrometer sized pixels of Ag NW networks on flexible substrates. This process relies on the selective laser heating of the Ag NWs induced by the laser pulse energy and the subsequent localized melting of the polymeric substrate. We demonstrate that a single laser pulse can induce both transfer and curing of the Ag NW network. The feasibility of the process is confirmed experimentally and validated by Finite Element Analysis simulations, which indicate that selective heating is carried out within a submicron-sized heat affected zone. The resulting structures can be utilized as fully functional flexible transparent electrodes with figures of merit even higher than 100. Low sheet resistance (<50 Ohm/sq) and high visible light transparency (>90%) make the reported process highly desirable for a variety of applications, including selective heating or annealing of nanocomposite materials and laser processing of nanostructured materials on a large variety of optically transparent substrates, such as Polydimethylsiloxane (PDMS).

Waveguide-based optical chemical sensor

DOEpatents

Grace, Karen M [Ranchos de Taos, NM; Swanson, Basil I [Los Alamos, NM; Honkanen, Seppo [Tucson, AZ

2007-03-13

The invention provides an apparatus and method for highly selective and sensitive chemical sensing. Two modes of laser light are transmitted through a waveguide, refracted by a thin film host reagent coating on the waveguide, and analyzed in a phase sensitive detector for changes in effective refractive index. Sensor specificity is based on the particular species selective thin films of host reagents which are attached to the surface of the planar optical waveguide. The thin film of host reagents refracts laser light at different refractive indices according to what species are forming inclusion complexes with the host reagents.

Laser Sintering Technology and Balling Phenomenon.

PubMed

Oyar, Perihan

2018-02-01

The aim of this review was to evaluate the balling phenomenon which occurs typically in Selective Laser Sintering (SLS). The balling phenomenon is a typical SLS defect, and observed in laser sintered powder, significantly reduces the quality of SLS, and hinders the further development of SLS Technology. Electronic database searches were performed using Google Scholar. The keywords "laser sintering, selective laser sintering, direct metal laser melting, and balling phenomenon" were searched in title/abstract of publications, limited to December 31, 2016. The inclusion criteria were SLS, balling phenomenon, some alloys (such as Cr-Co, iron, stainless steel, and Cu-based alloys) mechanical properties, microstructure and bond strength between metal-ceramic crown, laboratory studies, full text, and in English language. A total of 100 articles were found the initial search and yielded a total of 50 studies, 30 of which did not fulfill the inclusion criteria and were therefore excluded. In addition, 20 studies were found by screening the reference list of all included publications. Finally, 40 studies were selected for this review. The method in question is regulated by powder material characteristics and the conditions of laser processing. The procedure of formation, affecting factors, and the mechanism of the balling effect are very complex.

Qualification and Selection of Flight Diode Lasers for Space Applications

NASA Technical Reports Server (NTRS)

Liebe, Carl C.; Dillon, Robert P.; Gontijo, Ivair; Forouhar, Siamak; Shapiro, Andrew A.; Cooper, Mark S.; Meras, Patrick L.

2010-01-01

The reliability and lifetime of laser diodes is critical to space missions. The Nuclear Spectroscopic Telescope Array (NuSTAR) mission includes a metrology system that is based upon laser diodes. An operational test facility has been developed to qualify and select, by mission standards, laser diodes that will survive the intended space environment and mission lifetime. The facility is situated in an electrostatic discharge (ESD) certified clean-room and consist of an enclosed temperature-controlled stage that can accommodate up to 20 laser diodes. The facility is designed to characterize a single laser diode, in addition to conducting laser lifetime testing on up to 20 laser diodes simultaneously. A standard laser current driver is used to drive a single laser diode. Laser diode current, voltage, power, and wavelength are measured for each laser diode, and a method of selecting the most adequate laser diodes for space deployment is implemented. The method consists of creating histograms of laser threshold currents, powers at a designated current, and wavelengths at designated power. From these histograms, the laser diodes that illustrate a performance that is outside the normal are rejected and the remaining lasers are considered spaceborne candidates. To perform laser lifetime testing, the facility is equipped with 20 custom laser drivers that were designed and built by California Institute of Technology specifically to drive NuSTAR metrology lasers. The laser drivers can be operated in constant-current mode or alternating-current mode. Situated inside the enclosure, in front of the laser diodes, are 20 power-meter heads to record laser power throughout the duration of lifetime testing. Prior to connecting a laser diode to the current source for characterization and lifetime testing, a background program is initiated to collect current, voltage, and resistance. This backstage data collection enables the operational test facility to have full laser diode traceablity.

Airborne and spaceborne lasers for terrestrial geophysical sensing; Proceedings of the Meeting, Los Angeles, CA, Jan. 14, 15, 1988

NASA Technical Reports Server (NTRS)

Allario, Frank (Editor)

1988-01-01

The present conference on airborne and spaceborne remote sensing laser applications discusses topics in atmospheric and geophysical sciences-related sensors, lidar and DIAL component and subsystem technologies, and coherent laser experiments and semiconductor laser technologies. Attention is given to airborne lidar measurement of aerosols, a ground-based injection-locked pulsed TEA laser for wind measurements, chemical/biological agent standoff detection methods, lidars for wind shear erosion, laser tuning to selected gas absorption lines in the atmosphere, the NASA lidar-in-space technology experiment, and the Laser Atmospheric Wind Sounder.

Selective Removal of Natural Occlusal Caries by Coupling Near-infrared Imaging with a CO2 Laser

PubMed Central

Tao, You-Chen; Fried, Daniel

2011-01-01

Laser removal of dental hard tissue can be combined with optical, spectral or acoustic feedback systems to selectively ablate dental caries and restorative materials. Near-infrared (NIR) imaging has considerable potential for the optical discrimination of sound and demineralized tissue. Last year we successfully demonstrated that near-IR images can be used to guide a CO2 laser ablation system for the selective removal of artificial caries lesions on smooth surfaces. The objective of this study was to test the hypothesis that two-dimensional near-infrared images of natural occlusal caries can be used to guide a CO2 laser for selective removal. Two-dimensional NIR images were acquired at 1310-nm of extracted human molar teeth with occlusal caries. Polarization sensitive optical coherence tomography (PS-OCT) was also used to acquire depth-resolved images of the lesion areas. An imaging processing module was developed to analyze the NIR imaging output and generate optical maps that were used to guide a CO2 laser to selectively remove the lesions at a uniform depth. Post-ablation NIR images were acquired to verify caries removal. Based on the analysis of the NIR images, caries lesions were selectively removed with a CO2 laser while sound tissues were conserved. However, the removal rate varied markedly with the severity of decay and multiple passes were required for caries removal. These initial results are promising but indicate that the selective removal of natural caries is more challenging than the selective removal of artificial lesions due to varying tooth geometry, the highly variable organic/mineral ratio in natural lesions and more complicated lesion structure. PMID:21909225

Selective removal of natural occlusal caries by coupling near-infrared imaging with a CO II laser

NASA Astrophysics Data System (ADS)

Tao, You-Chen; Fried, Daniel

2008-02-01

Laser removal of dental hard tissue can be combined with optical, spectral or acoustic feedback systems to selectively ablate dental caries and restorative materials. Near-infrared (NIR) imaging has considerable potential for the optical discrimination of sound and demineralized tissue. Last year we successfully demonstrated that near-IR images can be used to guide a CO2 laser ablation system for the selective removal of artificial caries lesions on smooth surfaces. The objective of this study was to test the hypothesis that two-dimensional near-infrared images of natural occlusal caries can be used to guide a CO2 laser for selective removal. Two-dimensional NIR images were acquired at 1310-nm of extracted human molar teeth with occlusal caries. Polarization sensitive optical coherence tomography (PS-OCT) was also used to acquire depth-resolved images of the lesion areas. An imaging processing module was developed to analyze the NIR imaging output and generate optical maps that were used to guide a CO2 laser to selectively remove the lesions at a uniform depth. Post-ablation NIR images were acquired to verify caries removal. Based on the analysis of the NIR images, caries lesions were selectively removed with a CO2 laser while sound tissues were conserved. However, the removal rate varied markedly with the severity of decay and multiple passes were required for caries removal. These initial results are promising but indicate that the selective removal of natural caries is more challenging than the selective removal of artificial lesions due to varying tooth geometry, the highly variable organic/mineral ratio in natural lesions and more complicated lesion structure.

Selective Removal of Natural Occlusal Caries by Coupling Near-infrared Imaging with a CO(2) Laser.

PubMed

Tao, You-Chen; Fried, Daniel

2008-03-01

Laser removal of dental hard tissue can be combined with optical, spectral or acoustic feedback systems to selectively ablate dental caries and restorative materials. Near-infrared (NIR) imaging has considerable potential for the optical discrimination of sound and demineralized tissue. Last year we successfully demonstrated that near-IR images can be used to guide a CO(2) laser ablation system for the selective removal of artificial caries lesions on smooth surfaces. The objective of this study was to test the hypothesis that two-dimensional near-infrared images of natural occlusal caries can be used to guide a CO(2) laser for selective removal. Two-dimensional NIR images were acquired at 1310-nm of extracted human molar teeth with occlusal caries. Polarization sensitive optical coherence tomography (PS-OCT) was also used to acquire depth-resolved images of the lesion areas. An imaging processing module was developed to analyze the NIR imaging output and generate optical maps that were used to guide a CO(2) laser to selectively remove the lesions at a uniform depth. Post-ablation NIR images were acquired to verify caries removal. Based on the analysis of the NIR images, caries lesions were selectively removed with a CO(2) laser while sound tissues were conserved. However, the removal rate varied markedly with the severity of decay and multiple passes were required for caries removal. These initial results are promising but indicate that the selective removal of natural caries is more challenging than the selective removal of artificial lesions due to varying tooth geometry, the highly variable organic/mineral ratio in natural lesions and more complicated lesion structure.

Laser Materials Processing for NASA's Aerospace Structural Materials

NASA Technical Reports Server (NTRS)

Nagarathnam, Karthik; Hunyady, Thomas A.

2001-01-01

Lasers are useful for performing operations such as joining, machining, built-up freeform fabrication, and surface treatment. Due to the multifunctional nature of a single tool and the variety of materials that can be processed, these attributes are attractive in order to support long-term missions in space. However, current laser technology also has drawbacks for space-based applications. Specifically, size, power efficiency, lack of robustness, and problems processing highly reflective materials are all concerns. With the advent of recent breakthroughs in solidstate laser (e.g., diode-pumped lasers) and fiber optic technologies, the potential to perform multiple processing techniques in space has increased significantly. A review of the historical development of lasers from their infancy to the present will be used to show how these issues may be addressed. The review will also indicate where further development is necessary to realize a laser-based materials processing capability in space. The broad utility of laser beams in synthesizing various classes of engineering materials will be illustrated using state-of-the art processing maps for select lightweight alloys typically found on spacecraft. Both short- and long-term space missions will benefit from the development of a universal laser-based tool with low power consumption, improved process flexibility, compactness (e.g., miniaturization), robustness, and automation for maximum utility with a minimum of human interaction. The potential advantages of using lasers with suitable wavelength and beam properties for future space missions to the moon, Mars and beyond will be discussed. The laser processing experiments in the present report were performed using a diode pumped, pulsed/continuous wave Nd:YAG laser (50 W max average laser power), with a 1064 nm wavelength. The processed materials included Ti-6AI-4V, Al-2219 and Al-2090. For Phase I of this project, the laser process conditions were varied and optimized to see the effects on melt-quenching, cladding/alloying (using the pre-placed powder technique), and cutting. Key parameters such laser power, pulse repetition frequency, process speed, and shield gas flow and the observed process characteristics such as plasma formation during laser/material interaction, have been reported for all experimental runs. Preliminary materials characterization of select samples was carried out using various microscopy, diffraction, spectroscopy and microhardness test methods, and reported. Select nitridation results of Ti-6AI-4V using nitrogen assist gas indicated the successful formation of hard titanium nitrides with much higher hardness (2180 kg/sq mm). A cost-effective and simple powder delivery system has been successfully fabricated for the further experimentation in Phase H.

A real-time spectroscopic sensor for monitoring laser welding processes.

PubMed

Sibillano, Teresa; Ancona, Antonio; Berardi, Vincenzo; Lugarà, Pietro Mario

2009-01-01

In this paper we report on the development of a sensor for real time monitoring of laser welding processes based on spectroscopic techniques. The system is based on the acquisition of the optical spectra emitted from the laser generated plasma plume and their use to implement an on-line algorithm for both the calculation of the plasma electron temperature and the analysis of the correlations between selected spectral lines. The sensor has been patented and it is currently available on the market.

Dispersion-based Fresh-slice Scheme for Free-Electron Lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guetg, Marc

The Fresh-slice technique improved the performance of several Self-Amplified Spontaneous Emission Free-Electron laser schemes by granting selective control on the temporal lasing slice without spoiling the other electron bunch slices. So far, the implementation required a special insertion device to create the beam yaw, called dechirper. We demonstrate a novel scheme to enable Freshslice operation based on electron energy chirp and orbit dispersion that can be implemented at any free-electron laser facility without additional hardware.

Novel diode-based laser system for combined transcutaneous monitoring and computer-controlled intermittent treatment of jaundiced neonates

NASA Astrophysics Data System (ADS)

Hamza, Mostafa; El-Ahl, Mohammad H. S.; Hamza, Ahmad M.

2001-06-01

The high efficacy of laser phototherapy combined with transcutaneous monitoring of serum bilirubin provides optimum safety for jaundiced infants from the risk of bilirubin encephalopathy. In this paper the authors introduce the design and operating principles of a new laser system that can provide simultaneous monitoring and treatment of several jaundiced babies at one time. The new system incorporates diode-based laser sources oscillating at selected wavelengths to achieve both transcutaneous differential absorption measurements of bilirubin concentration in addition to the computer controlled intermittent laser therapy through a network of optical fibers. The detailed description and operating characteristics of this system are presented.

Tunable thulium-doped fiber laser based on an abrupt-tapered in-fiber interferometer

NASA Astrophysics Data System (ADS)

Hernández-Arriaga, M. V.; Durán-Sánchez, M.; Ibarra-Escamilla, B.; Álvarez-Tamayo, R. I.; Santiago-Hernández, H.; Bello-Jiménez, M.; Kuzin, E. A.

2017-11-01

An experimental study of an all-fiber tunable thulium-doped fiber laser based on an abrupt-tapered in-fiber interferometer is presented. A microfiber filter with length of 6 mm and diameter of 20 μm is used to achieve single laser wavelength tuning in a range of 19.4 nm and dual-wavelength laser operation at 1761.8 and 1793.4 nm with a channel spacing of 31.6 nm. The abrupt-tapered structure allows multi-modal interference at the air-cladding interface. The proposed in-fiber interferometer exhibits characteristics of low cost and simple fabrication, making it suitable for practical applications in wavelength filtering and wavelength selection in all-fiber lasers.

Free-jet feasibility study of a thermal acoustic shield concept for AST/VCE application-dual stream nozzles. Comprehensive data report. Volume 2: Laser velocimeter and suppressor. Base pressure data

NASA Technical Reports Server (NTRS)

Janardan, B. A.; Brausch, J. F.; Price, A. O.

1984-01-01

Acoustic and diagnostic data that were obtained to determine the influence of selected geometric and aerodynamic flow variables of coannular nozzles with thermal acoustic shields are summarized in this comprehensive data report. A total of 136 static and simulated flight acoustic test points were conducted with 9 scale-model nozzles. Aerodynamic laser velocimeter measurements were made for four selected plumes. In addition, static pressure data in the chute base region of the suppressor configurations were obtained to assess the influence of the shield stream on the suppressor base drag.

Broadband atomic-layer MoS₂ optical modulators for ultrafast pulse generations in the visible range.

PubMed

Zhang, Yuxia; Yu, Haohai; Zhang, Rui; Zhao, Gang; Zhang, Huaijin; Chen, Yanxue; Mei, Liangmo; Tonelli, Mauro; Wang, Jiyang

2017-02-01

Visible lasers are a fascinating regime, and their significance is illustrated by the 2014 Noble prizes in physics and chemistry. With the development of blue laser diodes (LDs), the LD-pumped solid-state visible lasers become a burgeoning direction today. Constrained by the scarce visible optical modulators, the solid-state ultrafast visible lasers are rarely realized. Based on the bandgap structure and optoelectronic properties of atomic-layer MoS₂, it can be proposed that MoS₂ has the potential as a visible optical modulator. Here, by originally revealing layer-dependent nonlinear absorption of the atomic-layer MoS₂ in the visible range, broadband atomic-layer MoS₂ optical modulators for the visible ultrafast pulse generation are developed and selected based on the proposed design criteria for novel two-dimensional (2D) optical modulators. By applying the selected MoS₂ optical modulators in the solid-state praseodymium lasers, broadband mode-locked ultrafast lasers from 522 to 639 nm are originally realized. We believe that this Letter should promote the development of visible ultrafast photonics and further applications of 2D optoelectronic materials.

Towards novel compact laser sources for non-invasive diagnostics and treatment

NASA Astrophysics Data System (ADS)

Rafailov, Edik U.; Litvinova, Karina S.; Sokolovski, Sergei G.

2015-08-01

An important field of application of lasers is biomedical optics. Here, they offer great utility for diagnosis, therapy and surgery. For the development of novel methods of laser-based biomedical diagnostics careful study of light propagation in biological tissues is necessary to enhance our understanding of the optical measurements undertaken, increase research and development capacity and the diagnostic reliability of optical technologies. Ultimately, fulfilling these requirements will increase uptake in clinical applications of laser based diagnostics and therapeutics. To address these challenges informative biomarkers relevant to the biological and physiological function or disease state of the organism must be selected. These indicators are the results of the analysis of tissues and cells, such as blood. For non-invasive diagnostics peripheral blood, cells and tissue can potentially provide comprehensive information on the condition of the human organism. A detailed study of the light scattering and absorption characteristics can quickly detect physiological and morphological changes in the cells due to thermal, chemical, antibiotic treatments, etc [1-5]. The selection of a laser source to study the structure of biological particles also benefits from the fact that gross pathological changes are not induced and diagnostics make effective use of the monochromatic directional coherence properties of laser radiation.

New laser system for highly sensitive clinical pulse oximetry

NASA Astrophysics Data System (ADS)

Hamza, Mostafa; Hamza, Mohammad

1996-04-01

This paper describes the theory and design of a new pulse oximeter in which laser diodes and other compact laser sources are used for the measurement of oxygen saturation in patients who are at risk of developing hypoxemia. The technique depends upon illuminating special sites of the skin of the patient with radiation from modulated laser sources at selected wavelengths. The specific laser wavelengths are chosen based on the absorption characteristics of oxyhemoglobin, reduced hemoglobin and other interfering sources for obtaining more accurate measurements. The laser radiation transmitted through the tissue is detected and signal processing based on differential absorption laser spectroscopy is done in such a way to overcome the primary performance limitations of the conventionally used pulse oximetry. The new laser pulse oximeter can detect weak signals and is not affected by other light sources such as surgical lamps, phototherapy units, etc. The detailed description and operating characteristics of this system are presented.

Study on the characteristic and application of DFB semiconductor lasers under optical injection for microwave photonics

NASA Astrophysics Data System (ADS)

Pu, Tao; Wang, Wei wei

2018-01-01

In order to apply optical injection effect in Microwave Photonics system, The red-shift effect of the cavity mode of the DFB semiconductor laser under single-frequency optical injection is studied experimentally, and the red-shift curve of the cavity mode is measured. The wavelength-selective amplification property of the DFB semiconductor laser under multi-frequency optical injection is also investigated, and the gain curves for the injected signals in different injection ratios are measured in the experiment. A novel and simple structure to implement a single-passband MPF with wideband tunability based on the wavelength-selective amplification of a DFB semiconductor laser under optical injection is proposed and experimentally demonstrated. MPFs with center frequency tuned from 13 to 41 GHz are realized in the experiment. A wideband and frequency-tunable optoelectronic oscillator based on a directly modulated distributed feedback (DFB) semiconductor laser under optical injection is proposed and experimentally demonstrated. By optical injection, the relaxation oscillation frequency of the DFB laser is enhanced and its high modulation efficiency makes the loop oscillate without the necessary of the electrical filter. An experiment is performed; microwave signals with frequency tuned from 5.98 to 15.22 GHz are generated by adjusting the injection ratio and frequency detuning between the master and slave lasers.

Preheat effect on titanium plate fabricated by sputter-free selective laser melting in vacuum

NASA Astrophysics Data System (ADS)

Sato, Yuji; Tsukamoto, Masahiro; Shobu, Takahisa; Yamashita, Yorihiro; Yamagata, Shuto; Nishi, Takaya; Higashino, Ritsuko; Ohkubo, Tomomasa; Nakano, Hitoshi; Abe, Nobuyuki

2018-04-01

The dynamics of titanium (Ti) melted by laser irradiation was investigated in a synchrotron radiation experiment. As an indicator of wettability, the contact angle between a selective laser melting (SLM) baseplate and the molten Ti was measured by synchrotron X-rays at 30 keV during laser irradiation. As the baseplate temperature increased, the contact angle decreased, down to 28° at a baseplate temperature of 500 °C. Based on this result, the influence of wettability of a Ti plate fabricated by SLM in a vacuum was investigated. It was revealed that the improvement of wettability by preheating suppressed sputtering generation, and a surface having a small surface roughness was fabricated by SLM in a vacuum.

Advanced Laser-Based Techniques for Gas-Phase Diagnostics in Combustion and Aerospace Engineering.

PubMed

Ehn, Andreas; Zhu, Jiajian; Li, Xuesong; Kiefer, Johannes

2017-03-01

Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics.

Reverse spontaneous laser line sweeping in ytterbium fiber laser

NASA Astrophysics Data System (ADS)

Navratil, P.; Peterka, P.; Honzatko, P.; Kubecek, V.

2017-03-01

Self-induced laser line sweeping of various regimes of sweep direction is reported for an experimental ytterbium fiber laser. The regimes involve sweeping from shorter to longer wavelengths (1076~\\text{nm}\\to 1083 nm)—so-called normal self-sweeping; from longer to shorter wavelengths (1079~\\text{nm}\\to 1073 nm)—so-called reverse self-sweeping; and a mixed regime in which a precarious balance of the normal and reverse sweeping exists and the sweep direction can change between consecutive sweeps. The regimes of sweeping were selected by changing the pump wavelength only. A detailed explanation of this sweep direction dynamics is presented based on a semi-empirical model. This model also provides a way to predict the sweep direction of fiber lasers based on other rare-earth-doped laser media.

KrF laser-induced OH fluorescence imaging in a supersonic combustion tunnel

NASA Technical Reports Server (NTRS)

Quagliaroli, T. M.; Laufer, G.; Hollo, S. D.; Krauss, R. H.; Whitehurst, R. B., III; Mcdaniel, J. C., Jr.

1992-01-01

Planar fluorescence images of OH in a continuous-flow, electrical-resistively heated, high enthalpy, hydrogen-air combustion tunnel, induced by a tunable KrF laser, were recorded. These images were compared to previously recorded fluorescence images induced by a doubled-dye laser under similar conditions. Images induced by the doubled-dye laser system demonstrated a severe distortion caused by absorption and fluorescence trapping. By contrast, images of the fluorescence induced by the tunable KrF laser retained the symmetry properties of the flow. Based on signal-to-noise ratio measurements the yield of the fluorescence induced by the doubled-dye laser is larger than the fluorescence yield induced by the KrF laser. The measurements in the present facility of OH fluorescence induced by the KrF laser were limited by the photon-statistical noise. Based 2 on this result, doubled-dye laser systems are recommended for OH imaging in small and OH lean (less than 10 exp 15/cu cm) facilities. KrF lasers should be selected otherwise.

Dual-wavelength quantum cascade laser for trace gas spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jágerská, J.; Tuzson, B.; Mangold, M.

2014-10-20

We demonstrate a sequentially operating dual-wavelength quantum cascade laser with electrically separated laser sections, emitting single-mode at 5.25 and 6.25 μm. Based on a single waveguide ridge, this laser represents a considerable asset to optical sensing and trace gas spectroscopy, as it allows probing multiple gas species with spectrally distant absorption features using conventional optical setups without any beam combining optics. The laser capability was demonstrated in simultaneous NO and NO{sub 2} detection, reaching sub-ppb detection limits and selectivity comparable to conventional high-end spectroscopic systems.

Cascade conical refraction for annular pumping of a vortex Nd:YAG laser and selective excitation of low- and high-order Laguerre–Gaussian modes

NASA Astrophysics Data System (ADS)

Wu, Yongxiao; Wang, Zhongyang; Chen, Sanbin; Shirakwa, Akira; Ueda, Ken-ichi; Li, Jianlang

2018-05-01

We proposed an efficient and vortex Nd:YAG laser for selective lasing of low- and high-order vortex modes, in which multiple-ring pump light was originated from cascaded conical refraction of multiple biaxial crystals. In our proof of concept demonstration, we used two-crystal cascade conical refraction to generate two-ring pump light; the mutual intensity ratio and relative separation of the inner ring and outer ring were controlled by rotating the second biaxial crystal and by moving the imaging lens, respectively. As a result, we obtained selective excitation of Laguerre–Gaussian (LG01 and LG03) vortex modes in the end-pump Nd:YAG laser. For LG01-mode output, the laser power reached 439 mW with 52.5% slope efficiency; for LG03-mode output, the laser power reached 160 mW with 41.3% slope efficiency. Our results revealed that the multiple-ring pumping technique based on cascaded conical refraction would pave the way for realization of the efficient and switchable excitation of low- and high-order LG modes in an end-pumped solid-state laser.

Spatial-mode switchable ring fiber laser based on low mode-crosstalk all-fiber mode MUX/DEMUX

NASA Astrophysics Data System (ADS)

Ren, Fang; Yu, Jinyi; Wang, Jianping

2018-05-01

We report an all-fiber ring laser that emits linearly polarized (LP) modes based on the intracavity all-fiber mode multiplexer/demultiplexer (MUX/DEMUX). Multiple LP modes in ring fiber laser are generated by taking advantage of mode MUX/DEMUX. The all-fiber mode MUX/DEMUX are composed of cascaded mode-selective couplers (MSCs). The output lasing mode of the ring fiber laser can be switched among the three lowest-order LP modes by employing combination of a mode MUX and a simple N × 1 optical switch. The slope efficiencies, optical spectra and mode profiles are measured.

Laser-assisted selective fusing of thermal sprayed Ni-based self-fluxing alloys by using high-power diode lasers

NASA Astrophysics Data System (ADS)

Chun, Eun-Joon; Kim, Min-Su; Nishikawa, Hiroshi; Park, Changkyoo; Suh, Jeong

2018-03-01

Fusing treatment of Ni-based self-fluxing alloys (Metco-16C and 1276F) was performed using high-power diode lasers to control the temperature of the substrate's surface in real time. The effects of the fusing treatment temperature on the microstructural change and hardness distribution were also investigated. For Metco-16C and 1276F, the macrostructural inhomogeneity (voids) within the thermal sprayed layer decreased considerably as the fusing temperature increased. For both self-fluxing alloys, the optimal temperature for fusing was approximately 1423 K (for Metco-16C) and 1373 K (for 1276F), both of which are within the solid state temperature range; these temperatures maximize the alloy hardness together with the macrostructural homogeneity. In this temperature range, the microstructure consists of a lamellar-structured matrix phase with fine (<5 μm) carbides and borides. Selective fusing for a thermal sprayed layer 0.2-0.5 mm in thickness could be successfully achieved in a high-power diode laser system.

Selection of the most influential factors on the water-jet assisted underwater laser process by adaptive neuro-fuzzy technique

NASA Astrophysics Data System (ADS)

Nikolić, Vlastimir; Petković, Dalibor; Lazov, Lyubomir; Milovančević, Miloš

2016-07-01

Water-jet assisted underwater laser cutting has shown some advantages as it produces much less turbulence, gas bubble and aerosols, resulting in a more gentle process. However, this process has relatively low efficiency due to different losses in water. It is important to determine which parameters are the most important for the process. In this investigation was analyzed the water-jet assisted underwater laser cutting parameters forecasting based on the different parameters. The method of ANFIS (adaptive neuro fuzzy inference system) was applied to the data in order to select the most influential factors for water-jet assisted underwater laser cutting parameters forecasting. Three inputs are considered: laser power, cutting speed and water-jet speed. The ANFIS process for variable selection was also implemented in order to detect the predominant factors affecting the forecasting of the water-jet assisted underwater laser cutting parameters. According to the results the combination of laser power cutting speed forms the most influential combination foe the prediction of water-jet assisted underwater laser cutting parameters. The best prediction was observed for the bottom kerf-width (R2 = 0.9653). The worst prediction was observed for dross area per unit length (R2 = 0.6804). According to the results, a greater improvement in estimation accuracy can be achieved by removing the unnecessary parameter.

Direct chemical-analysis of uv laser-ablation products of organic polymers by using selective ion monitoring mode in gas-chromatography mass-spectrometry

USGS Publications Warehouse

Cho, Yirang; Lee, H.W.; Fountain, S.T.; Lubman, D.M.

1994-01-01

Trace quantities of laser ablated organic polymers were analyzed by using commercial capillary column gas chromatography/mass spectrometry; the instrument was modified so that the laser ablation products could be introduced into the capillary column directly and the constituents of each peak in the chromatogram were identified by using a mass spectrometer. The present study takes advantage of the selective ion monitoring mode for significantly improving the sensitivity of the mass spectrometer as a detector, which is critical in analyzing the trace quantities and confirming the presence or absence of the species of interest in laser ablated polymers. The initial composition of the laser ablated polymers was obtained by using an electron impact reflectron time-of-flight mass spectrometer and the possible structure of the fragments observed in the spectra was proposed based on the structure of the polymers.

Investigating the CO 2 laser cutting parameters of MDF wood composite material

NASA Astrophysics Data System (ADS)

Eltawahni, H. A.; Olabi, A. G.; Benyounis, K. Y.

2011-04-01

Laser cutting of medium density fibreboard (MDF) is a complicated process and the selection of the process parameters combinations is essential to get the highest quality cut section. This paper presents a means for selecting the process parameters for laser cutting of MDF based on the design of experiments (DOE) approach. A CO 2 laser was used to cut three thicknesses, 4, 6 and 9 mm, of MDF panels. The process factors investigated are: laser power, cutting speed, air pressure and focal point position. In this work, cutting quality was evaluated by measuring the upper kerf width, the lower kerf width, the ratio between the upper kerf width to the lower kerf width, the cut section roughness and the operating cost. The effect of each factor on the quality measures was determined. The optimal cutting combinations were presented in favours of high quality process output and in favours of low cutting cost.

Novel diode laser-based sensors for gas sensing applications

NASA Technical Reports Server (NTRS)

Tittel, F. K.; Lancaster, D. G.; Richter, D.

2000-01-01

The development of compact spectroscopic gas sensors and their applications to environmental sensing will be described. These sensors employ mid-infrared difference-frequency generation (DFG) in periodically poled lithium niobate (PPLN) crystals pumped by two single-frequency solid state lasers such as diode lasers, diode-pumped solid state, and fiber lasers. Ultrasensitive, highly selective, and real-time measurements of several important atmospheric trace gases, including carbon monoxide, nitrous oxide, carbon dioxide, formaldehyde [correction of formaldehye], and methane, have been demonstrated.

Selective Laser Sintering of Conductive Inks for Inkjet Printing Based on Nanoparticle Compositions with Organic Silver Salts

NASA Astrophysics Data System (ADS)

Titkov, A. I.; Gadirov, R. M.; Nikonov, S. Yu.; Odod, A. V.; Solodova, T. A.; Kurtсevich, A. E.; Kopylova, T. N.; Yukhin, Yu. M.; Lyakhov, N. Z.

2018-02-01

Inkjet ink based on silver nanoparticles with sizes of 11.1 ± 2.4 nm has been developed. Test images are printed on a laboratory inkjet printer, followed by sintering the printed patterns with a diode laser having a wavelength of 453 nm. The structure and electrical properties of the resulting films are studied depending on the parameters of laser sintering. It is found that under optimal conditions, an electrically conductive film with a low resistivity of 12.2 μΩ· cm can be formed.

Lithographic wavelength control of an external cavity laser with a silicon photonic crystal cavity-based resonant reflector.

PubMed

Liles, Alexandros A; Debnath, Kapil; O'Faolain, Liam

2016-03-01

We report the experimental demonstration of a new design for external cavity hybrid lasers consisting of a III-V semiconductor optical amplifier (SOA) with fiber reflector and a photonic crystal (PhC)-based resonant reflector on SOI. The silicon reflector is composed of an SU8 polymer bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and side-mode suppression ratios of more than 25 dB.

Laser Photoradiation Therapy For Neonatal Jaundice

NASA Astrophysics Data System (ADS)

Hamza, Mostafa; Hamza, Mohammad

1987-04-01

This paper describes our leading experience in the clinical application of laser in the treatment of neonatal jaundice. Currently, the irradiation of jaundiced infants during neonatal life to fluorescent light is the most common treatment of neonatal hyperbilirubinemia. The authors have investigated the photodegradation of bilirubin by laser in vitro and in Gunn rats before embarking on its clinical application in the treatment of jaundice in the new born child. This work was done to study the theraputic effect of laser compared to the currently used phototherapy in the treatment of neonatal jaundice. We selected 16 full term neonates with jaundice to be the subject of this study. The neonates of the study were devided into two groups. The first group was treated with continuous phototherapy . The second group recieved photoradiation therapy with gas laser The laser used was a CW argon-ion laser tuned to oscillate at 488.0 nm wavelength. This wavelength selection was based on our previous studies on the effect of laser irradiation of Gunn rats at different wavelengths. Comparison of the results of both methods of treatment will be reported in detail. The advantages and limitations of laser photoradiation therapy for neonatal jaundice will be discussed.

Inducing Stable α + β Microstructures during Selective Laser Melting of Ti-6Al-4V Using Intensified Intrinsic Heat Treatments

PubMed Central

Barriobero-Vila, Pere; Gussone, Joachim; Haubrich, Jan; Sandlöbes, Stefanie; Da Silva, Julio Cesar; Cloetens, Peter; Schell, Norbert; Requena, Guillermo

2017-01-01

Selective laser melting is a promising powder-bed-based additive manufacturing technique for titanium alloys: near net-shaped metallic components can be produced with high resource-efficiency and cost savings. For the most commercialized titanium alloy, namely Ti-6Al-4V, the complicated thermal profile of selective laser melting manufacturing (sharp cycles of steep heating and cooling rates) usually hinders manufacturing of components in a one-step process owing to the formation of brittle martensitic microstructures unsuitable for structural applications. In this work, an intensified intrinsic heat treatment is applied during selective laser melting of Ti-6Al-4V powder using a scanning strategy that combines porosity-optimized processing with a very tight hatch distance. Extensive martensite decomposition providing a uniform, fine lamellar α + β microstructure is obtained along the building direction. Moreover, structural evidence of the formation of the intermetallic α2-Ti3Al phase is provided. Variations in the lattice parameter of β serve as an indicator of the microstructural degree of stabilization. Interconnected 3D networks of β are generated in regions highly affected by the intensified intrinsic heat treatment applied. The results obtained reflect a contribution towards simultaneous selective laser melting-manufacturing and heat treatment for fabrication of Ti-6Al-4V parts. PMID:28772630

Investigation of Laser Welding of Ti Alloys for Cognitive Process Parameters Selection.

PubMed

Caiazzo, Fabrizia; Caggiano, Alessandra

2018-04-20

Laser welding of titanium alloys is attracting increasing interest as an alternative to traditional joining techniques for industrial applications, with particular reference to the aerospace sector, where welded assemblies allow for the reduction of the buy-to-fly ratio, compared to other traditional mechanical joining techniques. In this research work, an investigation on laser welding of Ti⁻6Al⁻4V alloy plates is carried out through an experimental testing campaign, under different process conditions, in order to perform a characterization of the produced weld bead geometry, with the final aim of developing a cognitive methodology able to support decision-making about the selection of the suitable laser welding process parameters. The methodology is based on the employment of artificial neural networks able to identify correlations between the laser welding process parameters, with particular reference to the laser power, welding speed and defocusing distance, and the weld bead geometric features, on the basis of the collected experimental data.

Investigation of Laser Welding of Ti Alloys for Cognitive Process Parameters Selection

PubMed Central

2018-01-01

Laser welding of titanium alloys is attracting increasing interest as an alternative to traditional joining techniques for industrial applications, with particular reference to the aerospace sector, where welded assemblies allow for the reduction of the buy-to-fly ratio, compared to other traditional mechanical joining techniques. In this research work, an investigation on laser welding of Ti–6Al–4V alloy plates is carried out through an experimental testing campaign, under different process conditions, in order to perform a characterization of the produced weld bead geometry, with the final aim of developing a cognitive methodology able to support decision-making about the selection of the suitable laser welding process parameters. The methodology is based on the employment of artificial neural networks able to identify correlations between the laser welding process parameters, with particular reference to the laser power, welding speed and defocusing distance, and the weld bead geometric features, on the basis of the collected experimental data. PMID:29677114

Rapid and Selective Removal of Composite From Tooth Surfaces With a 9.3 μm CO2 Laser Using Spectral Feedback

PubMed Central

Chan, Kenneth H.; Hirasuna, Krista; Fried, Daniel

2015-01-01

Objective Dental composite restorative materials are color matched to the tooth and are difficult to remove by mechanical means without excessive removal or damage to peripheral enamel and dentin. Lasers are ideally suited for selective ablation to minimize healthy tissue loss when replacing existing restorations, sealants, or removing composite adhesives such as residual composite left after debonding orthodontic brackets. Methods In this study, a carbon dioxide laser operating at 9.3-μm with a pulse duration of 10–20-microsecond and a pulse repetition rate of ~200 Hz was integrated with a galvanometer based scanner and used to selectively remove composite from tooth surfaces. Spectra of the plume emission were acquired after each laser pulse and used to differentiate between the ablation of dental enamel or composite. Microthermocouples were used to monitor the temperature rise in the pulp chamber during composite removal. The composite was placed on tooth buccal and occlusal surfaces and the carbon dioxide laser beam was scanned across the surface to selectively remove the composite without excessive damage to the underlying sound enamel. The residual composite and the damage to the underlying enamel was evaluated using optical microscopy. Results The laser was able to rapidly remove composite from tooth buccal and occlusal surfaces with minimal damage to the underlying sound enamel and without excessive heat accumulation in the tooth. Conclusion This study demonstrated that composite can be selectively removed from tooth surfaces at clinically relevant rates using a CO2 laser operating at 9.3-μm with high pulse repetition rates with minimal heat deposition and damage to the underlying enamel. PMID:21956630

Rapid and selective removal of composite from tooth surfaces with a 9.3 µm CO2 laser using spectral feedback.

PubMed

Chan, Kenneth H; Hirasuna, Krista; Fried, Daniel

2011-09-01

Dental composite restorative materials are color matched to the tooth and are difficult to remove by mechanical means without excessive removal or damage to peripheral enamel and dentin. Lasers are ideally suited for selective ablation to minimize healthy tissue loss when replacing existing restorations, sealants, or removing composite adhesives such as residual composite left after debonding orthodontic brackets. In this study, a carbon dioxide laser operating at 9.3-µm with a pulse duration of 10-20-microsecond and a pulse repetition rate of ∼200 Hz was integrated with a galvanometer based scanner and used to selectively remove composite from tooth surfaces. Spectra of the plume emission were acquired after each laser pulse and used to differentiate between the ablation of dental enamel or composite. Microthermocouples were used to monitor the temperature rise in the pulp chamber during composite removal. The composite was placed on tooth buccal and occlusal surfaces and the carbon dioxide laser beam was scanned across the surface to selectively remove the composite without excessive damage to the underlying sound enamel. The residual composite and the damage to the underlying enamel was evaluated using optical microscopy. The laser was able to rapidly remove composite from tooth buccal and occlusal surfaces with minimal damage to the underlying sound enamel and without excessive heat accumulation in the tooth. This study demonstrated that composite can be selectively removed from tooth surfaces at clinically relevant rates using a CO(2) laser operating at 9.3-µm with high pulse repetition rates with minimal heat deposition and damage to the underlying enamel. Copyright © 2011 Wiley-Liss, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matthews, Manyalibo J.; Guss, Gabe; Drachenberg, Derrek R.

We present that Selective Laser Melting (SLM) of metal powder bed layers, whereby 3D metal objects can be printed from a digital file with unprecedented design flexibility, is spurring manufacturing innovations in medical, automotive, aerospace and textile industries. Because SLM is based on raster-scanning a laser beam over each layer, the process is relatively slow compared to most traditional manufacturing methods (hours to days), thus limiting wider spread use. Here we demonstrate the use of a large area, photolithographic method for 3D metal printing, using an optically-addressable light valve (OALV) as the photomask, to print entire layers of metal powdermore » at once. An optical sheet of multiplexed ~5 kW, 20 ms laser diode and ~1 MW, 7 ns Q-switched laser pulses are used to selectively melt each layer. Finally, the patterning of near infrared light is accomplished by imaging 470 nm light onto the transmissive OALV, which consists of polarization-selective nematic liquid crystal sandwiched between a photoconductor and transparent conductor for switching.« less

Selective determination of arginine-containing and tyrosine-containing peptides using capillary electrophoresis and laser-induced fluorescence detection.

PubMed

Cobb, K A; Novotny, M V

1992-01-01

The use of two different amino acid-selective fluorogenic reagents for the derivatization of peptides is investigated. One such scheme utilizes a selective reaction of benzoin with the guanidine moiety to derivatize arginine residues occurring in a peptide. The second scheme involves the formylation of tyrosine, followed by reaction with 4-methoxy-1,2-phenylenediamine. The use of capillary electrophoresis and laser-induced fluorescence detection allows enhanced efficiencies and sensitivities to be obtained for the separations of either arginine- or tyrosine-containing peptides. A helium-cadmium laser (325 nm) is ideally suited for the laser-based detection system due to a close match of the excitation maxima of derivatized peptides from both reactions. A detection limit of 270 amol is achieved for model arginine-containing peptides, while the detection limit for model tyrosine-containing peptides is measured at 390 amol. Both derivatization reactions are found to be useful for high-sensitivity peptide mapping applications in which only the peptides containing the derivatized amino acids are detected.

Soviet chemical laser research: pulsed lasers. Report for 1963--1970

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ksander, Y.

1971-11-01

The document reviews Soviet work on pulsed chemical lasers published in the open litarature in 1963-1970. Whereas U. S. research combines the approaches of physics, quantum electrodynamics, and aerodynamics, Soviet laser research is heavily (and expertly) oriented to understanding the chemical reactions. They prefer pulsed to cw systems, concentrating on kinetics of vibrationally excited diatomic systems. The documents describe gas lasers with discharge, photolytic, and other initiation and includes research on HN/sub 3/ + CO/sub 2/ mixtures, and means of controlling reaction rates by resonant coupling and selective heating. The report also proposes a laser based on photorecombination of atoms.

Metasurface-assisted orbital angular momentum carrying Bessel-Gaussian Laser: proposal and simulation.

PubMed

Zhou, Nan; Wang, Jian

2018-05-23

Bessel-Gaussian beams have distinct properties of suppressed diffraction divergence and self-reconstruction. In this paper, we propose and simulate metasurface-assisted orbital angular momentum (OAM) carrying Bessel-Gaussian laser. The laser can be regarded as a Fabry-Perot cavity formed by one partially transparent output plane mirror and the other metasurface-based reflector mirror. The gain medium of Nd:YVO 4 enables the lasing wavelength at 1064 nm with a 808 nm laser serving as the pump. The sub-wavelength structure of metasurface facilitates flexible spatial light manipulation. The compact metasurface-based reflector provides combined phase functions of an axicon and a spherical mirror. By appropriately selecting the size of output mirror and inserting mode-selection element in the laser cavity, different orders of OAM-carrying Bessel-Gaussian lasing modes are achievable. The lasing Bessel-Gaussian 0 , Bessel-Gaussian 01 + , Bessel-Gaussian 02 + and Bessel-Gaussian 03 + modes have high fidelities of ~0.889, ~0.889, ~0.881 and ~0.879, respectively. The metasurface fabrication tolerance and the dependence of threshold power and output lasing power on the length of gain medium, beam radius of pump and transmittance of output mirror are also discussed. The obtained results show successful implementation of metasurface-assisted OAM-carrying Bessel-Gaussian laser with favorable performance. The metasurface-assisted OAM-carrying Bessel-Gaussian laser may find wide OAM-enabled communication and non-communication applications.

Laser focal profiler based on forward scattering of a nanoparticle

NASA Astrophysics Data System (ADS)

Ota, Taisuke

2018-03-01

A laser focal intensity profiling method based on the forward scattering from a nanoparticle is demonstrated for in situ measurements using a laser focusing system with six microscope objective lenses with different numerical apertures ranging from 0.15 to 1.4. The measured profiles showed Airy disc patterns although their rings showed some imperfections due to aberrations and misalignment of the test system. The dipole radiation model revealed that the artefact of this method was much smaller than the influence of the deterioration in the experimental system; a condition where no artefact appears was predicted based on proper selection of measurement angles.

Arrangement for damping the resonance in a laser diode

NASA Technical Reports Server (NTRS)

Katz, J.; Yariv, A.; Margalit, S. (Inventor)

1985-01-01

An arrangement for damping the resonance in a laser diode is described. This arrangement includes an additional layer which together with the conventional laser diode form a structure (35) of a bipolar transistor. Therein, the additional layer serves as the collector, the cladding layer next to it as the base, and the active region and the other cladding layer as the emitter. A capacitor is connected across the base and the collector. It is chosen so that at any frequency above a certain selected frequency which is far below the resonance frequency the capacitor impedance is very low, effectively shorting the base to the collector.

Office-based Management of Recurrent Respiratory Papilloma.

PubMed

Motz, Kevin M; Hillel, Alexander T

2016-06-01

This review will highlight the indications and benefits of office-based therapy for recurrent respiratory papillomatosis (RRP) and discuss the utilization of photo-dynamic lasers and adjuvant medical therapy in office-based settings. Office-based management of RRP allows for more timely interventions, is preferred by the majority of patients, and negates the risk of general anesthesia. Current literature argues for the utilization of KTP laser over CO 2 laser for office-based treatment of RRP. Medical therapies for RRP are limited, but agents such as bevacizumab are promising and have been shown to reduce disease burden. Medical therapies that can induce disease remission are still needed. Office-based procedures save time and healthcare expenses compared to like procedures in the operating room. However, the increased frequency for office-based procedures predicts similar overall healthcare costs for office-based and OR laser excision of RRP. Office-based management of RRP is a feasible and well-tolerated strategy in appropriately selected patients with adequate local anesthesia.

Fiber laser welding of nickel based superalloy Inconel 625

NASA Astrophysics Data System (ADS)

Janicki, Damian M.

2013-01-01

The paper describes the application of single mode high power fiber laser (HPFL) for the welding of nickel based superalloy Inconel 625. Butt joints of Inconel 625 sheets 0,8 mm thick were laser welded without an additional material. The influence of laser welding parameters on weld quality and mechanical properties of test joints was studied. The quality and mechanical properties of the joints were determined by means of tensile and bending tests, and micro hardness tests, and also metallographic examinations. The results showed that a proper selection of laser welding parameters provides non-porous, fully-penetrated welds with the aspect ratio up to 2.0. The minimum heat input required to achieve full penetration butt welded joints with no defect was found to be 6 J/mm. The yield strength and ultimate tensile strength of the joints are essentially equivalent to that for the base material.

Microwave photonic filter using multiwavelength Brillouin-erbium fiber laser with double-Brillouin-frequency shift

DOE Office of Scientific and Technical Information (OSTI.GOV)

Loh, K. K.; Yeo, K. S.; Shee, Y. G.

2015-04-24

A microwave photonic filter based on double-Brillouin-frequency spaced multiwavelength Brillouin-erbium fiber laser (BEFL) is experimentally demonstrated. The filter selectivity can be easily adjusted by tuning and apodizing the optical taps generated from the multiwavelength BEFL. Reconfiguration of different frequency responses are demonstrated.

Transient Infrared Measurement of Laser Absorption Properties of Porous Materials

NASA Astrophysics Data System (ADS)

Marynowicz, Andrzej

2016-06-01

The infrared thermography measurements of porous building materials have become more frequent in recent years. Many accompanying techniques for the thermal field generation have been developed, including one based on laser radiation. This work presents a simple optimization technique for estimation of the laser beam absorption for selected porous building materials, namely clinker brick and cement mortar. The transient temperature measurements were performed with the use of infrared camera during laser-induced heating-up of the samples' surfaces. As the results, the absorbed fractions of the incident laser beam together with its shape parameter are reported.

Multifunctional gold nanorods for selective plasmonic photothermal therapy in pancreatic cancer cells using ultra-short pulse near-infrared laser irradiation.

PubMed

Patino, Tania; Mahajan, Ujjwal; Palankar, Raghavendra; Medvedev, Nikolay; Walowski, Jakob; Münzenberg, Markus; Mayerle, Julia; Delcea, Mihaela

2015-03-12

Gold nanorods (AuNRs) have attracted considerable attention in plasmonic photothermal therapy for cancer treatment by exploiting their selective and localized heating effect due to their unique photophysical properties. Here we describe a strategy to design a novel multifunctional platform based on AuNRs to: (i) specifically target the adenocarcinoma MUC-1 marker through the use of the EPPT-1 peptide, (ii) enhance cellular uptake through a myristoylated polyarginine peptide (MPAP) and (iii) selectively induce cell death by ultra-short near infrared laser pulses. We used a biotin-avidin based approach to conjugate EPPT-1 and MPAP to AuNRs. Dual-peptide (EPPT-1+MPAP) labelled AuNRs showed a significantly higher uptake by pancreatic ductal adenocarcinoma cells when compared to their single peptide or avidin conjugated counterparts. In addition, we selectively induced cell death by ultra-short near infrared laser pulses in small target volumes (∼1 μm3), through the creation of plasmonic nanobubbles that lead to the destruction of a local cell environment. Our approach opens new avenues for conjugation of multiple ligands on AuNRs targeting cancer cells and tumors and it is relevant for plasmonic photothermal therapy.

Removal of sulfur compounds from diesel using ArF laser and oxygen.

PubMed

Gondal, M A; Siddiqui, M N; Al-Hooshani, K

2013-01-01

A laser-based technique for deep desulfurization of diesel and other hydrocarbon fuels by removal of dimethyldibenzothiophene (DMDBT), a persistent sulfur contaminant in fuel oils has been developed. We report a selective laser excitation of DMDBT in diesel and model compounds such as n-hexane in a reaction chamber under oxygen environment where oxidative reactions can take place. ArF laser emitting at 193 nm was employed for excitation of oxygen and DMDBT, while for process optimization, the laser energy was varied from 50 to 200 mJ/cm(2). The laser-irradiated DMDBT solution under continuous oxygen flow was analyzed by UV absorption spectrometer to determine the photochemical oxidative degradation of DMDBT. In just 5 min of laser irradiation time, almost 95% DMDBT was depleted in a diesel containing 200 ppm of DMDBT. This article provides a new method for the removal of sulfur compounds from diesel by laser based photochemical process.

Fully Solution-Processable Fabrication of Multi-Layered Circuits on a Flexible Substrate Using Laser Processing

PubMed Central

Ji, Seok Young; Choi, Wonsuk; Jeon, Jin-Woo; Chang, Won Seok

2018-01-01

The development of printing technologies has enabled the realization of electric circuit fabrication on a flexible substrate. However, the current technique remains restricted to single-layer patterning. In this paper, we demonstrate a fully solution-processable patterning approach for multi-layer circuits using a combined method of laser sintering and ablation. Selective laser sintering of silver (Ag) nanoparticle-based ink is applied to make conductive patterns on a heat-sensitive substrate and insulating layer. The laser beam path and irradiation fluence are controlled to create circuit patterns for flexible electronics. Microvia drilling using femtosecond laser through the polyvinylphenol-film insulating layer by laser ablation, as well as sequential coating of Ag ink and laser sintering, achieves an interlayer interconnection between multi-layer circuits. The dimension of microvia is determined by a sophisticated adjustment of the laser focal position and intensity. Based on these methods, a flexible electronic circuit with chip-size-package light-emitting diodes was successfully fabricated and demonstrated to have functional operations. PMID:29425144

Single-mode SOA-based 1kHz-linewidth dual-wavelength random fiber laser.

PubMed

Xu, Yanping; Zhang, Liang; Chen, Liang; Bao, Xiaoyi

2017-07-10

Narrow-linewidth multi-wavelength fiber lasers are of significant interests for fiber-optic sensors, spectroscopy, optical communications, and microwave generation. A novel narrow-linewidth dual-wavelength random fiber laser with single-mode operation, based on the semiconductor optical amplifier (SOA) gain, is achieved in this work for the first time, to the best of our knowledge. A simplified theoretical model is established to characterize such kind of random fiber laser. The inhomogeneous gain in SOA mitigates the mode competition significantly and alleviates the laser instability, which are frequently encountered in multi-wavelength fiber lasers with Erbium-doped fiber gain. The enhanced random distributed feedback from a 5km non-uniform fiber provides coherent feedback, acting as mode selection element to ensure single-mode operation with narrow linewidth of ~1kHz. The laser noises are also comprehensively investigated and studied, showing the improvements of the proposed random fiber laser with suppressed intensity and frequency noises.

Selecting laser eye protectors - a helping hand

NASA Astrophysics Data System (ADS)

Gappenach, Catherine; Krüger, Jörg; Offenhäuser, Friedrich; Pintaske, Sabine; Krauß, Hans-Joachim

2015-10-01

The European laser safety standards EN 207, EN 208, and EN 12254 each contain an annex B, which serves as a guidance for the selection of products. These annexes are informative only and are therefore not binding. As there are a variety of hazard scenarios, it is not recommended to change these annexes to a normative status, through which they would become mandatory. Instead, it is recommended to allow users to apply their own skills and know-how in selecting appropriate products, justifying where and why they deviate from the guidance in the standards. This paper explains the background on which the guidance for selection in the annexes of the standards is based and shows physically meaningful leeway.

Development of selective laser treatment techniques using mid-infrared tunable nanosecond pulsed laser.

PubMed

Ishii, Katsunori; Saiki, Masayuki; Hazama, Hisanao; Awazu, Kunio

2010-01-01

Mid-infrared (MIR) laser with a specific wavelength can excite the corresponding biomolecular site to regulate chemical, thermal and mechanical interactions to biological molecules and tissues. In laser surgery and medicine, tunable MIR laser irradiation can realize the selective and less-invasive treatments and the special diagnosis by vibrational spectroscopic information. This paper showed a novel selective therapeutic technique for a laser angioplasty of atherosclerotic plaques and a laser dental surgery of a carious dentin using a MIR tunable nanosecond pulsed laser.

Wavelength adjustability of frequency conversion light of Yb-doped fiber laser based on FBGs

NASA Astrophysics Data System (ADS)

Dobashi, Kazuma; Tomihari, Yasuhiro; Imai, Koichi; Hirohashi, Junji; Makio, Satoshi

2018-02-01

We focused on wavelength conversion of simple and compact CW Yb-Doped fiber laser based on FBGs with wavelength adjustable function. By controlling temperatures of FBGs in fiber laser, it was possible to tune oscillated wavelength from 1064.101 nm to 1064.414 nm with more than 20 W in CW operation mode. Based on this fundamental light, frequency converted light (SHG and THG) were generated by utilizing two PP:Mg-SLT devises. We obtained more than 3 W of SHG light with tuning range of 150 pm and more than 35 mW of THG with tuning range of 100 pm. By selecting FBG grating and QPM grating properly, we can realize adjustable wavelength laser with the same scheme from 1040 nm to 1090 nm and their SHG/THG. With this combination of FBG based fiber laser and QPM devices, it is possible to tune the wavelength just by temperature tuning without any changes of beam shape and beam pointing.

Moving Object Localization Based on UHF RFID Phase and Laser Clustering

PubMed Central

Fu, Yulu; Wang, Changlong; Liang, Gaoli; Zhang, Hua; Ur Rehman, Shafiq

2018-01-01

RFID (Radio Frequency Identification) offers a way to identify objects without any contact. However, positioning accuracy is limited since RFID neither provides distance nor bearing information about the tag. This paper proposes a new and innovative approach for the localization of moving object using a particle filter by incorporating RFID phase and laser-based clustering from 2d laser range data. First of all, we calculate phase-based velocity of the moving object based on RFID phase difference. Meanwhile, we separate laser range data into different clusters, and compute the distance-based velocity and moving direction of these clusters. We then compute and analyze the similarity between two velocities, and select K clusters having the best similarity score. We predict the particles according to the velocity and moving direction of laser clusters. Finally, we update the weights of the particles based on K clusters and achieve the localization of moving objects. The feasibility of this approach is validated on a Scitos G5 service robot and the results prove that we have successfully achieved a localization accuracy up to 0.25 m. PMID:29522458

Methods and devices based on brillouin selective sideband amplification

NASA Technical Reports Server (NTRS)

Yao, X. Steve (Inventor)

2003-01-01

Opto-electronic devices and techniques using Brillouin scattering to select a sideband in a modulated optical carrier signal for amplification. Two lasers respectively provide a carrier signal beam and a Brillouin pump beam which are fed into an Brillouin optical medium in opposite directions. The relative frequency separation between the lasers is adjusted to align the frequency of the backscattered Brillouin signal with a desired sideband in the carrier signal to effect a Brillouin gain on the sideband. This effect can be used to implement photonic RF signal mixing and conversion with gain, conversion from phase modulation to amplitude modulation, photonic RF frequency multiplication, optical and RF pulse generation and manipulation, and frequency-locking of lasers.

Net shaped high performance oxide ceramic parts by selective laser melting

NASA Astrophysics Data System (ADS)

Yves-Christian, Hagedorn; Jan, Wilkes; Wilhelm, Meiners; Konrad, Wissenbach; Reinhart, Poprawe

An additive manufacturing technique (AM) for ceramics, based on Al2O3-ZrO2 powder by means of Selective Laser Melting (SLM) is presented. Pure ceramic powder is completely melted by a laser beam yielding net-shaped specimens of almost 100% densities without any post-processing. Possible crack formation during the build-up process due to thermal stresses is prevented by a high-temperature preheating of above 1600 ∘C. Specimens with fine-grained nano-sized microstructures and flexural strengths of above 500 MPa are produced. The new technology allows for rapid freeform manufacture of complex net-shaped ceramics, thus, exploiting the outstanding mechanical and thermal properties for high-end medical and engineering disciplines.

Communication: Determining the structure of the N{sub 2}Ar van der Waals complex with laser-based channel-selected Coulomb explosion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Chengyin, E-mail: cywu@pku.edu.cn; Liu, Yunquan; Gong, Qihuang

2014-04-14

We experimentally reconstructed the structure of the N{sub 2}Ar van der Waals complex with the technique of laser-based channel-selected Coulomb explosion imaging. The internuclear distance between the N{sub 2} center of mass and the Ar atom, i.e., the length of the van der Waals bond, was determined to be 3.88 Å from the two-body explosion channels. The angle between the van der Waals bond and the N{sub 2} principal axis was determined to be 90° from the three-body explosion channels. The reconstructed structure was contrasted with our high level ab initio calculations. The agreement demonstrated the potential application of laser-basedmore » Coulomb explosion in imaging transient molecular structure, particularly for floppy van der Waals complexes, whose structures remain difficult to be determined by conventional spectroscopic methods.« less

Tunable multi-wavelength fiber lasers based on an Opto-VLSI processor and optical amplifiers.

PubMed

Xiao, Feng; Alameh, Kamal; Lee, Yong Tak

2009-12-07

A multi-wavelength tunable fiber laser based on the use of an Opto-VLSI processor in conjunction with different optical amplifiers is proposed and experimentally demonstrated. The Opto-VLSI processor can simultaneously select any part of the gain spectrum from each optical amplifier into its associated fiber ring, leading to a multiport tunable fiber laser source. We experimentally demonstrate a 3-port tunable fiber laser source, where each output wavelength of each port can independently be tuned within the C-band with a wavelength step of about 0.05 nm. Experimental results demonstrate a laser linewidth as narrow as 0.05 nm and an optical side-mode-suppression-ratio (SMSR) of about 35 dB. The demonstrated three fiber lasers have excellent stability at room temperature and output power uniformity less than 0.5 dB over the whole C-band.

Distributed feedback fiber laser based on a fiber Bragg grating inscribed using the femtosecond point-by-point technique

NASA Astrophysics Data System (ADS)

Skvortsov, M. I.; Wolf, A. A.; Dostovalov, A. V.; Vlasov, A. A.; Akulov, V. A.; Babin, S. A.

2018-03-01

A distributed feedback (DFB) fiber laser based on a 32-mm long pi-phase-shifted fiber Bragg grating inscribed using the femtosecond point-by-point technique in a single-mode erbium-doped optical fiber (CorActive EDF-L 1500) is demonstrated. The lasing power of the DFB laser reaches 0.7 mW at a wavelength of 1550 nm when pumped with a laser diode at a wavelength of 976 nm and power of 525 mW. The width of the lasing spectrum is 17 kHz. It is shown that the pi-phase-shifted fiber Bragg grating fs-inscribed in a non-PM fiber provides the selection of the single polarization mode of the DFB laser. DFB laser formation in a highly doped non-photosensitive optical fiber (CoreActive SCF-ER60-8/125-12) is also demonstrated.

Surface-selective laser sintering of thermolabile polymer particles using water as heating sensitizer

NASA Astrophysics Data System (ADS)

Antonov, E. N.; Krotova, L. I.; Minaev, N. V.; Minaeva, S. A.; Mironov, A. V.; Popov, V. K.; Bagratashvili, V. N.

2015-11-01

We report the implementation of a novel scheme for surface-selective laser sintering (SSLS) of polymer particles, based on using water as a sensitizer of laser heating and sintering of particles as well as laser radiation at a wavelength of 1.94 μm, corresponding to the strong absorption band of water. A method of sintering powders of poly(lactide-co-glycolide), a hydrophobic bioresorbable polymer, after modifying its surface with an aqueous solution of hyaluronic acid is developed. The sintering thresholds for wetted polymer are by 3 - 4 times lower than those for sintering in air. The presence of water restricts the temperature of the heated polymer, preventing its thermal destruction. Polymer matrices with a developed porous structure are obtained. The proposed SSLS method can be applied to produce bioresorbable polymer matrices for tissue engineering.

Two-dimensional angular energy spectrum of electrons accelerated by the ultra-short relativistic laser pulse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borovskiy, A. V.; Galkin, A. L.; Department of Physics of MBF, Pirogov Russian National Research Medical University, 1 Ostrovitianov Street, Moscow 117997

The new method of calculating energy spectra of accelerated electrons, based on the parameterization by their initial coordinates, is proposed. The energy spectra of electrons accelerated by Gaussian ultra-short relativistic laser pulse at a selected angle to the axis of the optical system focusing the laser pulse in a low density gas are theoretically calculated. The two-peak structure of the electron energy spectrum is obtained. Discussed are the reasons for its appearance as well as an applicability of other models of the laser field.

Tunable dual-wavelength fiber laser based on an MMI filter in a cascaded Sagnac loop interferometer

NASA Astrophysics Data System (ADS)

Ma, Lin; Kang, Zexin; Qi, Yanhui; Jian, Shuisheng

2014-04-01

A widely tunable dual-wavelength erbium-doped fiber laser based on a cascaded Sagnac loop interferometer incorporating a multimode interference filter is proposed and experimentally demonstrated in this paper. The mode selection is implemented by using the cascaded Sagnac loop interferometer with two segments of polarization maintaining fibers, and the wavelength tuning was achieved by using the refractive index characteristic of multimode interference effects. The tunable dual-wavelength fiber laser has a wavelength tuning of about 40 nm with a signal-to-noise ratio of more than 50 dB.

Graphene based widely-tunable and singly-polarized pulse generation with random fiber lasers

PubMed Central

Yao, B. C.; Rao, Y. J.; Wang, Z. N.; Wu, Y.; Zhou, J. H.; Wu, H.; Fan, M. Q.; Cao, X. L.; Zhang, W. L.; Chen, Y. F.; Li, Y. R.; Churkin, D.; Turitsyn, S.; Wong, C. W.

2015-01-01

Pulse generation often requires a stabilized cavity and its corresponding mode structure for initial phase-locking. Contrastingly, modeless cavity-free random lasers provide new possibilities for high quantum efficiency lasing that could potentially be widely tunable spectrally and temporally. Pulse generation in random lasers, however, has remained elusive since the discovery of modeless gain lasing. Here we report coherent pulse generation with modeless random lasers based on the unique polarization selectivity and broadband saturable absorption of monolayer graphene. Simultaneous temporal compression of cavity-free pulses are observed with such a polarization modulation, along with a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a broadly-tunable repetition rate across three orders of magnitude up to 3 MHz, and a singly-polarized pulse train at 41 dB extinction ratio, about an order of magnitude larger than conventional pulsed fiber lasers. Moreover, our graphene-based pulse formation also demonstrates robust pulse-to-pulse stability and wide-wavelength operation due to the cavity-less feature. Such a graphene-based architecture not only provides a tunable pulsed random laser for fiber-optic sensing, speckle-free imaging, and laser-material processing, but also a new way for the non-random CW fiber lasers to generate widely tunable and singly-polarized pulses. PMID:26687730

Graphene based widely-tunable and singly-polarized pulse generation with random fiber lasers.

PubMed

Yao, B C; Rao, Y J; Wang, Z N; Wu, Y; Zhou, J H; Wu, H; Fan, M Q; Cao, X L; Zhang, W L; Chen, Y F; Li, Y R; Churkin, D; Turitsyn, S; Wong, C W

2015-12-21

Pulse generation often requires a stabilized cavity and its corresponding mode structure for initial phase-locking. Contrastingly, modeless cavity-free random lasers provide new possibilities for high quantum efficiency lasing that could potentially be widely tunable spectrally and temporally. Pulse generation in random lasers, however, has remained elusive since the discovery of modeless gain lasing. Here we report coherent pulse generation with modeless random lasers based on the unique polarization selectivity and broadband saturable absorption of monolayer graphene. Simultaneous temporal compression of cavity-free pulses are observed with such a polarization modulation, along with a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a broadly-tunable repetition rate across three orders of magnitude up to 3 MHz, and a singly-polarized pulse train at 41 dB extinction ratio, about an order of magnitude larger than conventional pulsed fiber lasers. Moreover, our graphene-based pulse formation also demonstrates robust pulse-to-pulse stability and wide-wavelength operation due to the cavity-less feature. Such a graphene-based architecture not only provides a tunable pulsed random laser for fiber-optic sensing, speckle-free imaging, and laser-material processing, but also a new way for the non-random CW fiber lasers to generate widely tunable and singly-polarized pulses.

Influence of temperature on the spectral characteristics of semiconductor lasers in the visible range

NASA Astrophysics Data System (ADS)

Adamov, A. A.; Baranov, M. S.; Khramov, V. N.

2018-04-01

The results of studies on the effect of temperature on the output spectral characteristics of continuous semiconductor lasers of the visible range are presented. The paper presents the results of studying the spectral-optical radiation parameters of semiconductor lasers, their coherence lengths, and the dependence of the position of the spectral peak of the wavelength on temperature. This is necessary for the selection of the most optimal laser in order to use it for medical ophthalmologic diagnosis. The experiment was carried out using semiconductor laser modules based on a laser diode. The spectra were recorded by using a two-channel automated spectral complex based on the MDR-23 monochromator. Spectral dependences on the temperature of semiconductor lasers are obtained, in the range from 300 to 370 K. The possibility of determining the internal damage to the stabilization of laser modules without opening the case is shown, but only with the use of their spectral characteristics. The obtained data allow taking into account temperature characteristics and further optimization of parameters of such lasers when used in medical practice, in particular, in ophthalmologic diagnostics.

Optimization of the fiber laser parameters for local high-temperature impact on metal

NASA Astrophysics Data System (ADS)

Yatsko, Dmitrii S.; Polonik, Marina V.; Dudko, Olga V.

2016-11-01

This paper presents the local laser heating process of surface layer of the metal sample. The aim is to create the molten pool with the required depth by laser thermal treatment. During the heating the metal temperature at any point of the molten zone should not reach the boiling point of the main material. The laser power, exposure time and the spot size of a laser beam are selected as the variable parameters. The mathematical model for heat transfer in a semi-infinite body, applicable to finite slab, is used for preliminary theoretical estimation of acceptable parameters values of the laser thermal treatment. The optimization problem is solved by using an algorithm based on the scanning method of the search space (the zero-order method of conditional optimization). The calculated values of the parameters (the optimal set of "laser radiation power - exposure time - spot radius") are used to conduct a series of natural experiments to obtain a molten pool with the required depth. A two-stage experiment consists of: a local laser treatment of metal plate (steel) and then the examination of the microsection of the laser irradiated region. According to the experimental results, we can judge the adequacy of the ongoing calculations within the selected models.

Bleaching of tattooed skin phantoms by series of laser shots

NASA Astrophysics Data System (ADS)

Shubnyy, Andrey G.; Zhigarkov, Vyacheslav S.; Yusupov, Vladimir I.; Sviridov, Alexander P.; Bagratashvili, Victor N.

2018-04-01

The bleaching of polyacrylamide tattooed skin-mimicking phantoms by a series of laser pulses in a single session is studied. It is shown that compared to the single-pulse procedures tattoo removal by series of laser pulses allows not only for reducing the necessary laser fluence, but also for improving the degree of bleaching. The dynamics of formation and dissolution of microscopic gas bubbles in tattooed skin phantoms exposed to laser radiation is also studied. A laser-induced tattoo bleaching mechanism is suggested, based on the process of selective photo-thermolysis of pigmented particles in conditions where the thermal conductivity of the medium surrounding the particles is decreased because of the microbubbles formed therein.

Infrared laser spectroscopic trace gas sensing

NASA Astrophysics Data System (ADS)

Sigrist, Markus

2016-04-01

Chemical sensing and analyses of gas samples by laser spectroscopic methods are attractive owing to several advantages such as high sensitivity and specificity, large dynamic range, multi-component capability, and lack of pretreatment or preconcentration procedures. The preferred wavelength range comprises the fundamental molecular absorption range in the mid-infared between 3 and 15 μm, whereas the near-infrared range covers the (10-100 times weaker) higher harmonics and combination bands. The availability of near-infrared and, particularly, of broadly tunable mid-infrared sources like external cavity quantum cascade lasers (EC-QCLs), interband cascade lasers (ICLs), difference frequency generation (DFG), optical parametric oscillators (OPOs), recent developments of diode-pumped lead salt semiconductor lasers, of supercontinuum sources or of frequency combs have eased the implementation of laser-based sensing devices. Sensitive techniques for molecular absorption measurements include multipass absorption, various configurations of cavity-enhanced techniques such as cavity ringdown (CRD), or of photoacoustic spectroscopy (PAS) including quartz-enhanced (QEPAS) or cantilever-enhanced (CEPAS) techniques. The application requirements finally determine the optimum selection of laser source and detection scheme. In this tutorial talk I shall discuss the basic principles, present various experimental setups and illustrate the performance of selected systems for chemical sensing of selected key atmospheric species. Applications include an early example of continuous vehicle emission measurements with a mobile CO2-laser PAS system [1]. The fast analysis of C1-C4 alkanes at sub-ppm concentrations in gas mixtures is of great interest for the petrochemical industry and was recently achieved with a new type of mid-infrared diode-pumped piezoelectrically tuned lead salt vertical external cavity surface emitting laser (VECSEL) [2]. Another example concerns measurements on short-lived species like nitrous acid (HONO) with a QCL-based QEPAS system where the small gas sampling volume and hence short gas residence time are of particular importance [3]. A true analysis of gas mixtures has been performed with a widely tunable DFG system in a medical application that could also be adapted to atmospheric species [4]. It is demonstrated that a laser-based narrowband system with broad tunability combined with an appropriate detection scheme is feasible for the chemical analysis of multi-component gas mixtures even with an a priori unknown composition. Most recent examples will further confirm the great potential of infrared laser-based devices for trace species sensing. References 1. D. Marinov and M.W. Sigrist: "Monitoring of road-traffic emission with mobile photoacoustic system", Photochem. and Photobiol. Sciences 2, 774-778 (2003) 2. J.M. Rey, M. Fill, F. Felder and M.W. Sigrist: "Broadly tunable mid-infrared VECSEL for multiple components hydrocarbons gas sensing", Appl. Phys. B 117, 935-939 (2014) 3. H. Yi, R. Maamary, X. Gao, M.W. Sigrist, E. Fertein, and W. Chen: "Short-lived species detection of nitrous acid by external-cavity quantum cascade laser based quartz-enhanced photoacoustic absorption spectroscopy", Appl. Phys. Lett. 106, 101109 (2015) 4. M. Gianella and M.W. Sigrist: "Chemical Analysis of Surgical Smoke by Infrared Laser Spectroscopy", Appl. Phys. B 109, 485-496 (2012)

Spatial filter with volume gratings for high-peak-power multistage laser amplifiers

NASA Astrophysics Data System (ADS)

Tan, Yi-zhou; Yang, Yi-sheng; Zheng, Guang-wei; Shen, Ben-jian; Pan, Heng-yue; Liu, Li

2010-08-01

The regular spatial filters comprised of lens and pinhole are essential component in high power laser systems, such as lasers for inertial confinement fusion, nonlinear optical technology and directed-energy weapon. On the other hand the pinhole is treated as a bottleneck of high power laser due to harmful plasma created by the focusing beam. In this paper we present a spatial filter based on angular selectivity of Bragg diffraction grating to avoid the harmful focusing effect in the traditional pinhole filter. A spatial filter consisted of volume phase gratings in two-pass amplifier cavity were reported. Two-dimensional filter was proposed by using single Pi-phase-shifted Bragg grating, numerical simulation results shown that its angular spectrum bandwidth can be less than 160urad. The angular selectivity of photo-thermorefractive glass and RUGATE film filters, construction stability, thermal stability and the effects of misalignments of gratings on the diffraction efficiencies under high-pulse-energy laser operating condition are discussed.

All-Fiber Configuration Laser Self-Mixing Doppler Velocimeter Based on Distributed Feedback Fiber Laser.

PubMed

Wu, Shuang; Wang, Dehui; Xiang, Rong; Zhou, Junfeng; Ma, Yangcheng; Gui, Huaqiao; Liu, Jianguo; Wang, Huanqin; Lu, Liang; Yu, Benli

2016-07-27

In this paper, a novel velocimeter based on laser self-mixing Doppler technology has been developed for speed measurement. The laser employed in our experiment is a distributed feedback (DFB) fiber laser, which is an all-fiber structure using only one Fiber Bragg Grating to realize optical feedback and wavelength selection. Self-mixing interference for optical velocity sensing is experimentally investigated in this novel system, and the experimental results show that the Doppler frequency is linearly proportional to the velocity of a moving target, which agrees with the theoretical analysis commendably. In our experimental system, the velocity measurement can be achieved in the range of 3.58 mm/s-2216 mm/s with a relative error under one percent, demonstrating that our novel all-fiber configuration velocimeter can implement wide-range velocity measurements with high accuracy.

In-fiber modal interferometer based on multimode and double cladding fiber segments for tunable fiber laser applications

NASA Astrophysics Data System (ADS)

Prieto-Cortés, P.; Álvarez-Tamayo, R. I.; Durán-Sánchez, M.; Castillo-Guzmán, A.; Salceda-Delgado, G.; Ibarra-Escamilla, B.; Kuzin, E. A.; Barcelata-Pinzón, A.; Selvas-Aguilar, R.

2018-02-01

We report an in-fiber structure based on the use of a multimode fiber segment and a double cladding fiber segment, and its application as spectral filter in an erbium-doped fiber laser for selection and tuning of the laser line wavelength. The output transmission of the proposed device exhibit spectrum modulation of the input signal with free spectral range of 21 nm and maximum visibility enhanced to more than 20 dB. The output spectrum of the in-fiber filter is wavelength displaced by bending application which allows a wavelength tuning of the generated laser line in a range of 12 nm. The use of the proposed in-fiber structure is demonstrated as a reliable, simple, and low-cost wavelength filter for tunable fiber lasers design and optical instrumentation applications.

Mode Selection for a Single-Frequency Fiber Laser

NASA Technical Reports Server (NTRS)

Liu, Jian

2010-01-01

A superstructured fiber-grating-based mode selection filter for a single-frequency fiber laser eliminates all free-space components, and makes the laser truly all-fiber. A ring cavity provides for stable operations in both frequency and power. There is no alignment or realignment required. After the fibers and components are spliced together and packaged, there is no need for specially trained technicians for operation or maintenance. It can be integrated with other modules, such as telescope systems, without extra optical alignment due to the flexibility of the optical fiber. The filter features a narrow line width of 1 kHz and side mode suppression ratio of 65 dB. It provides a high-quality laser for lidar in terms of coherence length and signal-to-noise ratio, which is 20 dB higher than solid-state or microchip lasers. This concept is useful in material processing, medical equipment, biomedical instrumentation, and optical communications. The pulse-shaping fiber laser can be directly used in space, airborne, and satellite applications including lidar, remote sensing, illuminators, and phase-array antenna systems.

Fabrication of a 20.5-inch-diameter segmented silicon annular optic prototype for the ROMA program

NASA Astrophysics Data System (ADS)

Hassell, Frank R.; Groark, Frank M.

1995-10-01

Recent advancements in single crystal silicon material science and fabrication capabilities and very low absorption (VLA) multi-layer dielectric coating technology have led to the development of uncooled, large aperture, high power mirrors for high energy laser (HEL) systems. Based on this success, a segmented single-crystal silicon substrate concept has been selected as the baseline fabrication approach for uncooled 1.2 meter diameter resonator annular optics for the Alpha space based high energy laser. The objective of this Resonator Optics Materials Assessment (ROMA) task was to demonstrate all of the key fabrication processes required to fabricate the full sized annular optics for the Alpha space based high energy laser. This paper documents the fabrication of a half-scale annular optic prototype (AOP) of the Alpha laser rear cone.

Utilization of selected laser-ablation-based diagnostic methods for study of elemental distribution in various solid samples

NASA Astrophysics Data System (ADS)

Kaiser, J.; Novotný, K.; Hrdlička, A.; Malina, R.; Novotný, J.; Prochazka, D.; Petrilak, M.; Krajcarová, L.; Vítková, G.; Kučerová, P.

2010-12-01

Here we report on the recent developments and upgrades of our Laser-Induced Breakdown Spectroscopy setups and their different modification for high-resolution mapping. Mapping capabilities of Laser-Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry are compared. The applied improvements as an autofocus algorithm, together with the realization of double-pulse LIBS or combination of LIBS by Laser-Induced Fluorescence Spectroscopy (LIFS) with technique are detailed. The signal enhancement obtained by double-pulse approach is demonstrated. The state of the art on development of portable remote LIBS apparatus is also presented.

Robotic Laser Coating Removal System

DTIC Science & Technology

2008-08-01

9 3.2 SELECTION OF TEST PLATFORM/FACILITY .................................. 9 3.3 TEST PLATFORM/FACILITY HISTORY...lasers are 4 efficient in converting electrical energy to coherent radiation and, thus, have widespread industrial use. In order to select an...completion of this evaluation a 6 kW CO2 laser from Rofin-Sinar was selected for use in the RLCRS. This laser provided the highest quality laser

Diode laser based resonance ionization mass spectrometric measurement of strontium-90

NASA Astrophysics Data System (ADS)

Bushaw, B. A.; Cannon, B. D.

1997-10-01

A diode laser based scheme for the isotopically selective excitation and ionization of strontium is presented. The double-resonance excitation 5s 21S 0→5s5p 3P 1→5s6s 3S 1 is followed by photoionization at 488 nm. The isotope shifts and hyperfine structure in the resonance transitions have been accurately measured for the stable isotopes and 90Sr, with the measurement of the 90Sr shifts using sub-pg samples. Analytical tests, using graphite crucible atomization, demonstrated 90Sr detection limits of 0.8 fg and overall (optical+mass spectrometer) isotopic selectivity of >10 10 against stable strontium.

Lasers for tattoo removal: a review.

PubMed

Choudhary, Sonal; Elsaie, Mohamed L; Leiva, Angel; Nouri, Keyvan

2010-09-01

Tattoos have existed and have been used as an expression of art by man for ages-and so have the techniques to remove them. Lasers based on the principle of selective photothermolysis are now being used to remove black as well as colorful tattoos with varying successes. The commonly used lasers for tattoo removal are the Q-switched 694-nm ruby laser, the Q-switched 755-nm alexandrite laser, the 1,064-nm Nd:YAG laser, and the 532-nm Nd:YAG laser. Newer techniques and methods are evolving in tattoo removal with lasers. Choosing the right laser for the right tattoo color is necessary for a successful outcome. Our review aims to understand the principles of laser tattoo removal and their applications for different types and colors of tattoos. The review also highlights the complications that can occur such as dyspigmentation, allergic reactions, epidermal debris, ink darkening, and so on, in this process and how to prevent them.

Numerical analysis of fundamental mode selection of a He-Ne laser by a circular aperture

NASA Astrophysics Data System (ADS)

He, Xin; Zhang, Bin

2011-11-01

In the He-Ne laser with an integrated cavity made of zerodur, the inner face performance of the gain tube is limited by the machining techniques, which tends to influence the beam propagation and transverse mode distribution. In order to improve the beam quality and select out the fundamental mode, an aperture is usually introduced in the cavity. In the process of laser design, the Fresnel-Kirchhoff diffraction integral equation is adopted to calculate the optical field distributions on each interface. The transit matrix is obtained based on self-reproducing principle and finite element method. Thus, optical field distribution on any interface and field loss of each transverse mode could be acquired by solving the eigenvalue and eigenvector of the transit matrix. For different-sized apertures in different positions, we could get different matrices and corresponding calculation results. By comparing these results, the optimal size and position of the aperture could be obtained. As a result, the feasibility of selecting fundamental mode in a zerodur He-Ne laser by a circular aperture has been verified theoretically.

Selective Two-Photon Absorptive Resonance Femtosecond-Laser Electronic-Excitation Tagging (STARFLEET) Velocimetry in Flow and Combustion Diagnostics

NASA Technical Reports Server (NTRS)

Jiang, Naibo; Halls, Benjamin R.; Stauffer, Hans U.; Roy, Sukesh; Danehy, Paul M.; Gord, James R.

2016-01-01

Selective Two-Photon Absorptive Resonance Femtosecond-Laser Electronic-Excitation Tagging (STARFLEET), a non-seeded ultrafast-laser-based velocimetry technique, is demonstrated in reactive and non-reactive flows. STARFLEET is pumped via a two-photon resonance in N2 using 202.25-nm 100-fs light. STARFLEET greatly reduces the per-pulse energy required (30 µJ/pulse) to generate the signature FLEET emission compared to the conventional FLEET technique (1.1 mJ/pulse). This reduction in laser energy results in less energy deposited in the flow, which allows for reduced flow perturbations (reactive and non-reactive), increased thermometric accuracy, and less severe damage to materials. Velocity measurements conducted in a free jet of N2 and in a premixed flame show good agreement with theoretical velocities and further demonstrate the significantly less-intrusive nature of STARFLEET.

Two-Photon Laser-Induced Fluorescence O and N Atoms for the Study of Heterogeneous Catalysis in a Diffusion Reactor

NASA Technical Reports Server (NTRS)

Pallix, Joan B.; Copeland, Richard A.; Arnold, James O. (Technical Monitor)

1995-01-01

Advanced laser-based diagnostics have been developed to examine catalytic effects and atom/surface interactions on thermal protection materials. This study establishes the feasibility of using laser-induced fluorescence for detection of O and N atom loss in a diffusion tube to measure surface catalytic activity. The experimental apparatus is versatile in that it allows fluorescence detection to be used for measuring species selective recombination coefficients as well as diffusion tube and microwave discharge diagnostics. Many of the potential sources of error in measuring atom recombination coefficients by this method have been identified and taken into account. These include scattered light, detector saturation, sample surface cleanliness, reactor design, gas pressure and composition, and selectivity of the laser probe. Recombination coefficients and their associated errors are reported for N and O atoms on a quartz surface at room temperature.

Computational Simulation of Thermal and Spattering Phenomena and Microstructure in Selective Laser Melting of Inconel 625

NASA Astrophysics Data System (ADS)

Özel, Tuğrul; Arısoy, Yiğit M.; Criales, Luis E.

Computational modelling of Laser Powder Bed Fusion (L-PBF) processes such as Selective laser Melting (SLM) can reveal information that is hard to obtain or unobtainable by in-situ experimental measurements. A 3D thermal field that is not visible by the thermal camera can be obtained by solving the 3D heat transfer problem. Furthermore, microstructural modelling can be used to predict the quality and mechanical properties of the product. In this paper, a nonlinear 3D Finite Element Method based computational code is developed to simulate the SLM process with different process parameters such as laser power and scan velocity. The code is further improved by utilizing an in-situ thermal camera recording to predict spattering which is in turn included as a stochastic heat loss. Then, thermal gradients extracted from the simulations applied to predict growth directions in the resulting microstructure.

Comparison of aged polyamide powders for selective laser sintering

NASA Astrophysics Data System (ADS)

Martínez, A.; Ibáñez, A.; Sánchez, A.; León, M. A.

2012-04-01

Selective Laser Sintering (SLS) is an additive manufacturing technology in which a three-dimensional object is manufactured layer by layer by melting powder materials with heat generated from a CO2 laser. However, a disadvantage of sintered materials is that the unsintered powder material during the process can be reused only a limited number of cycles, as during the heating phase in the sintering chamber the material remains at a temperature near the fusion point for a certain period of time and lose properties. This work shows the study of two polyamides (PA12)-based powders used in SLS with the aim of understanding the modification of their properties mainly with the temperature and the time at which they are exposed during the processing.

Technology Assessment of Laser-Assisted Materials Processing in Space

NASA Technical Reports Server (NTRS)

Nagarathnam, Karthik; Taminger, Karen M. B.

2001-01-01

Lasers are useful for performing operations such as joining, machining, built-up freeform fabrication, shock processing, and surface treatments. These attributes are attractive for the supportability of longer-term missions in space due to the multi-functionality of a single tool and the variety of materials that can be processed. However, current laser technology also has drawbacks for space-based applications, specifically size, power efficiency, lack of robustness, and problems processing highly reflective materials. A review of recent laser developments will be used to show how these issues may be reduced and indicate where further improvement is necessary to realize a laser-based materials processing capability in space. The broad utility of laser beams in synthesizing various classes of engineering materials will be illustrated using state-of-the art processing maps for select lightweight alloys typically found on spacecraft. With the advent of recent breakthroughs in diode-pumped solid-state lasers and fiber optic technologies, the potential to perform multiple processing techniques is increasing significantly. Lasers with suitable wavelengths and beam properties have tremendous potential for supporting future space missions to the moon, Mars and beyond.

Setup for functional cell ablation with lasers: coupling of a laser to a microscope.

PubMed

Sweeney, Sean T; Hidalgo, Alicia; de Belle, J Steven; Keshishian, Haig

2012-06-01

The selective removal of cells by ablation is a powerful tool in the study of eukaryotic developmental biology, providing much information about their origin, fate, or function in the developing organism. In Drosophila, three main methods have been used to ablate cells: chemical, genetic, and laser ablation. Each method has its own applicability with regard to developmental stage and the cells to be ablated, and its own limitations. The primary advantage of laser-based ablation is the flexibility provided by the method: The operations can be performed in any cell pattern and at any time in development. Laser-based techniques permit manipulation of structures within cells, even to the molecular level. They can also be used for gene activation. However, laser ablation can be expensive, labor-intensive, and time-consuming. Although live cells can be difficult to image in Drosophila embryos, the use of vital fluorescent imaging methods has made laser-mediated cell manipulation methods more appealing; the methods are relatively straightforward. This article provides the information necessary for setting up and using a laser microscope for lasesr ablation studies.

Perspectives of powerful laser technique for medicine

NASA Astrophysics Data System (ADS)

Konov, Vitali I.; Prokhorov, Alexander M.; Shcherbakov, Ivan A.

1991-11-01

The optimum laser-system parameters are being selected for several types of surgical operations using ablation techniques. The choice is based on the specific demands of the operation performed, knowledge of the ablation laws, limitations on laser-beam intensity which come from the necessity to transport high-intensity light through flexible fiber, and the peculiarities of different laser systems. At present it is more expedient to develop laser medical setups oriented to the solution of one task or a limited number of problems. The choice of a concrete installation should be based on the investigation results of interaction of radiation with biological tissues and its transmission through the fiber, the analysis of the level of development of laser and fiber technique, specificity of the operation, and compatibility of laser facilitates and traditional medical equipment. The paper illustrates such an approach by way of several concrete examples and notes the corresponding laser systems, which were developed or are in the developmental stage in the General Physics Institute of the USSR Academy of Sciences and in organizations connected with the Institute.

Interferometric optical online dosimetry for selective retina treatment (SRT)

NASA Astrophysics Data System (ADS)

Stoehr, Hardo; Ptaszynski, Lars; Fritz, Andreas; Brinkmann, Ralf

2007-07-01

Selective retina treatment (SRT) is a new laser based method to treat retinal diseases associated with disorders of the retinal pigment epithelium (RPE). Applying microsecond laser pulses tissue damage spatially confined to the retinal pigment epithelium (RPE) is achieved. The RPE cell damage is caused by transient microbubbles emerging at the strongly absorbing melanin granules inside the RPE cells. Due to the spatial confinement to the RPE the photoreceptors can be spared and vision can be maintained in the treated retinal areas. A drawback for effective clinical SRT is that the laser induced lesions are ophthalmoscopically invisible. Therefore, a real-time feedback system for dosimetry is necessary in order to avoid undertreatment or unwanted collateral damage to the adjacent tissue. We develop a dosimetry system which uses optical interferometry for the detection of the transient microbubbles. The system is based on an optical fiber interferometer operated with a laser diode at 830nm. We present current results obtained with a laser slit lamp using porcine RPE explants in vitro and complete porcine eye globes ex vivo. The RPE cell damage is determined by Calcein fluorescence viability assays. With a threshold criterium for RPE cell death derived from the measured interferometric signal transients good agreement with the results of the viability assays is achieved.

Laser based in-situ and standoff detection of chemical warfare agents and explosives

NASA Astrophysics Data System (ADS)

Patel, C. Kumar N.

2009-09-01

Laser based detection of gaseous, liquid and solid residues and trace amounts has been developed ever since lasers were invented. However, the lack of availability of reasonably high power tunable lasers in the spectral regions where the relevant targets can be interrogated as well as appropriate techniques for high sensitivity, high selectivity detection has hampered the practical exploitation of techniques for the detection of targets important for homeland security and defense applications. Furthermore, emphasis has been on selectivity without particular attention being paid to the impact of interfering species on the quality of detection. Having high sensitivity is necessary but not a sufficient condition. High sensitivity assures a high probability of detection of the target species. However, it is only recently that the sensor community has come to recognize that any measure of probability of detection must be associated with a probability of false alarm, if it is to have any value as a measure of performance. This is especially true when one attempts to compare performance characteristics of different sensors based on different physical principles. In this paper, I will provide a methodology for characterizing the performance of sensors utilizing optical absorption measurement techniques. However, the underlying principles are equally application to all other sensors. While most of the current progress in high sensitivity, high selectivity detection of CWAs, TICs and explosives involve identifying and quantifying the target species in-situ, there is an urgent need for standoff detection of explosives from safe distances. I will describe our results on CO2 and quantum cascade laser (QCL) based photoacoustic sensors for the detection of CWAs, TICs and explosives as well the very new results on stand-off detection of explosives at distances up to 150 meters. The latter results are critically important for assuring safety of military personnel in battlefield environment, especially from improvised explosive devices (IEDs), and of civilian personnel from terrorist attacks in metropolitan areas.

Enabling Laser and Lidar Technologies for NASA's Science and Exploration Mission's Applications

NASA Technical Reports Server (NTRS)

Singh, Upendra N.; Kavaya, Michael J.

2005-01-01

NASA s Laser Risk Reduction Program, begun in 2002, has achieved many technology advances in only 3.5 years. The recent selection of several lidar proposals for Science and Exploration applications indicates that the LRRP goal of enabling future space-based missions by lowering the technology risk has already begun to be met.

Advances in Laser/Lidar Technologies for NASA's Science and Exploration Mission's Applications

NASA Technical Reports Server (NTRS)

Singh, Upendra N.; Kavaya, Michael J.

2005-01-01

NASA's Laser Risk Reduction Program, begun in 2002, has achieved many technology advances in only 3.5 years. The recent selection of several lidar proposals for Science and Exploration applications indicates that the LRRP goal of enabling future space-based missions by lowering the technology risk has already begun to be met.

Laser effects based optimal laser parameter identifications for paint removal from metal substrate at 1064 nm: a multi-pulse model

NASA Astrophysics Data System (ADS)

Han, Jinghua; Cui, Xudong; Wang, Sha; Feng, Guoying; Deng, Guoliang; Hu, Ruifeng

2017-10-01

Paint removal by laser ablation is favoured among cleaning techniques due to its high efficiency. How to predict the optimal laser parameters without producing damage to substrate still remains challenging for accurate paint stripping. On the basis of ablation morphologies and combining experiments with numerical modelling, the underlying mechanisms and the optimal conditions for paint removal by laser ablation are thoroughly investigated. Our studies suggest that laser paint removal is dominated by the laser vaporization effect, thermal stress effect and laser plasma effect, in which thermal stress effect is the most favoured while laser plasma effect should be avoided during removal operations. Based on the thermodynamic equations, we numerically evaluated the spatial distribution of the temperature as well as thermal stress in the paint and substrate under the irradiation of laser pulse at 1064 nm. The obtained curves of the paint thickness vs. threshold fluences can provide the reference standard of laser parameter selection in view of the paint layer with different thickness. A multi-pulse model is proposed and validated under a constant laser fluence to perfectly remove a thicker paint layer. The investigations and the methods proposed here might give hints to the efficient operations on the paint removal and lowering the risk of substrate damages.

Features and dosimetry of laser-inflicted retina injuries induced by short laser pulses

NASA Astrophysics Data System (ADS)

Pustovalov, Victor K.

1996-04-01

Energy absorption, heat transfer, thermodenaturation under the action of laser radiation pulse on pigmented spherical granules in heterogeneous laminated biotissues are investigated on the base of mathematical simulation. The possibility of selective interaction between short radiation pulses and pigmented retina biotissues is noted which results in the formation of thermodenaturation microregions inside and near the melanosomes. These denaturation microregions can originate in the eye biotissue under laser radiation intensities less than about 2 - 4 times the threshold ones determined ophthalmoscopically. These microdamages can appear without being detected by the standard ophthalmoscopical methods.

[Gas pipeline leak detection based on tunable diode laser absorption spectroscopy].

PubMed

Zhang, Qi-Xing; Wang, Jin-Jun; Liu, Bing-Hai; Cai, Ting-Li; Qiao, Li-Feng; Zhang, Yong-Ming

2009-08-01

The principle of tunable diode laser absorption spectroscopy and harmonic detection technique was introduced. An experimental device was developed by point sampling through small multi-reflection gas cell. A specific line near 1 653. 7 nm was targeted for methane measurement using a distributed feedback diode laser as tunable light source. The linearity between the intensity of second harmonic signal and the concentration of methane was determined. The background content of methane in air was measured. The results show that gas sensors using tunable diode lasers provide a high sensitivity and high selectivity method for city gas pipeline leak detection.

3.1 W narrowband blue external cavity diode laser

NASA Astrophysics Data System (ADS)

Peng, Jue; Ren, Huaijin; Zhou, Kun; Li, Yi; Du, Weichuan; Gao, Songxin; Li, Ruijun; Liu, Jianping; Li, Deyao; Yang, Hui

2018-03-01

We reported a high-power narrowband blue diode laser which is suitable for subsequent nonlinear frequency conversion into the deep ultraviolet (DUV) spectral range. The laser is based on an external cavity diode laser (ECDL) system using a commercially available GaN-based high-power blue laser diode emitting at 448 nm. Longitudinal mode selection is realized by using a surface diffraction grating in Littrow configuration. The diffraction efficiency of the grating was optimized by controlling the polarization state of the laser beam incident on the grating. A maximum optical output power of 3.1 W in continuous-wave operation with a spectral width of 60 pm and a side-mode suppression ratio (SMSR) larger than 10 dB at 448.4 nm is achieved. Based on the experimental spectra and output powers, the theoretical efficiency and output power of the subsequent nonlinear frequency conversion were calculated according to the Boyd- Kleinman theory. The single-pass conversion efficiency and output power is expected to be 1.9×10-4 and 0.57 mW, respectively, at the 3.1 W output power of the ECDL. The high-power narrowband blue diode laser is very promising as pump source in the subsequent nonlinear frequency conversion.

Phase-locking of combination-cylinder discharge CO2 laser

NASA Astrophysics Data System (ADS)

Xu, Yonggen

2014-05-01

A new type of laser resonator is presented to obtained good coherent beam and the parameters of the laser beam are calculated. The principle of phase-locking is described based on the injection-locking, the properties of the injected beam in the resonator are studied in detail. The output beam from output mirror is an annular laser beam with zero central intensity. An analytical expression for the annular laser beam through the ABCD optical system is derived. Typical numerical examples are calculated to confirm our analytical results. It is shown that the good coherent beam can be obtained through phase-locking, and the central intensity of annular beam through ABCD optical system will become maximum when the parameters of laser beam are selected reasonably.

Rapid prototyped porous nickel–titanium scaffolds as bone substitutes

PubMed Central

Hoffmann, Waldemar; Bormann, Therese; Rossi, Antonella; Müller, Bert; Schumacher, Ralf; Martin, Ivan; Wendt, David

2014-01-01

While calcium phosphate–based ceramics are currently the most widely used materials in bone repair, they generally lack tensile strength for initial load bearing. Bulk titanium is the gold standard of metallic implant materials, but does not match the mechanical properties of the surrounding bone, potentially leading to problems of fixation and bone resorption. As an alternative, nickel–titanium alloys possess a unique combination of mechanical properties including a relatively low elastic modulus, pseudoelasticity, and high damping capacity, matching the properties of bone better than any other metallic material. With the ultimate goal of fabricating porous implants for spinal, orthopedic and dental applications, nickel–titanium substrates were fabricated by means of selective laser melting. The response of human mesenchymal stromal cells to the nickel–titanium substrates was compared to mesenchymal stromal cells cultured on clinically used titanium. Selective laser melted titanium as well as surface-treated nickel–titanium and titanium served as controls. Mesenchymal stromal cells had similar proliferation rates when cultured on selective laser melted nickel–titanium, clinically used titanium, or controls. Osteogenic differentiation was similar for mesenchymal stromal cells cultured on the selected materials, as indicated by similar gene expression levels of bone sialoprotein and osteocalcin. Mesenchymal stromal cells seeded and cultured on porous three-dimensional selective laser melted nickel–titanium scaffolds homogeneously colonized the scaffold, and following osteogenic induction, filled the scaffold’s pore volume with extracellular matrix. The combination of bone-related mechanical properties of selective laser melted nickel–titanium with its cytocompatibility and support of osteogenic differentiation of mesenchymal stromal cells highlights its potential as a superior bone substitute as compared to clinically used titanium. PMID:25383165

Lunar Observer Laser Altimeter observations for lunar base site selection

NASA Technical Reports Server (NTRS)

Garvin, James B.; Bufton, Jack L.

1992-01-01

One of the critical datasets for optimal selection of future lunar landing sites is local- to regional-scale topography. Lunar base site selection will require such data for both engineering and scientific operations purposes. The Lunar Geoscience Orbiter or Lunar Observer is the ideal precursory science mission from which to obtain this required information. We suggest that a simple laser altimeter instrument could be employed to measure local-scale slopes, heights, and depths of lunar surface features important to lunar base planning and design. For this reason, we have designed and are currently constructing a breadboard of a Lunar Observer Laser Altimeter (LOLA) instrument capable of acquiring contiguous-footprint topographic profiles with both 30-m and 300-m along-track resolution. This instrument meets all the severe weight, power, size, and data rate limitations imposed by Observer-class spacecraft. In addition, LOLA would be capable of measuring the within-footprint vertical roughness of the lunar surface, and the 1.06-micron relative surface reflectivity at normal incidence. We have used airborne laser altimeter data for a few representative lunar analog landforms to simulate and analyze LOLA performance in a 100-km lunar orbit. We demonstrate that this system in its highest resolution mode (30-m diameter footprints) would quantify the topography of all but the very smallest lunar landforms. At its global mapping resolution (300-m diameter footprints), LOLA would establish the topographic context for lunar landing site selection by providing the basis for constructing a 1-2 km spatial resolution global, geodetic topographic grid that would contain a high density of observations (e.g., approximately 1000 observations per each 1 deg by 1 deg cell at the lunar equator). The high spatial and vertical resolution measurements made with a LOLA-class instrument on a precursory Lunar Observer would be highly synergistic with high-resolution imaging datasets, and will allow for direct quantification of critical slopes, heights, and depths of features visible in images of potential lunar base sites.

Comparison of bond strength and surface morphology of dental enamel for acid and Nd-YAG laser etching

NASA Astrophysics Data System (ADS)

Parmeswearan, Diagaradjane; Ganesan, Singaravelu; Ratna, P.; Koteeswaran, D.

1999-05-01

Recently, laser pretreatment of dental enamel has emerged as a new technique in the field of orthodontics. However, the changes in the morphology of the enamel surface is very much dependent on the wavelength of laser, emission mode of the laser, energy density, exposure time and the nature of the substance absorbing the energy. Based on these, we made a comparative in vitro study on laser etching with acid etching with reference to their bond strength. Studies were conducted on 90 freshly extracted, non carious, human maxillary or mandibular anteriors and premolars. Out of 90, 60 were randomly selected for laser irradiation. The other 30 were used for conventional acid pretreatment. The group of 60 were subjected to Nd-YAG laser exposure (1060 nm, 10 Hz) at differetn fluences. The remaining 30 were acid pretreated with 30% orthophosphoric acid. Suitable Begg's brackets were selected and bound to the pretreated surface and the bond strength were tested using Instron testing machine. The bond strength achieved through acid pretreatment is found to be appreciably greater than the laser pretreated tooth. Though the bond strength achieved through the acid pretreated tooth is found to be significantly greater than the laser pretreated specimens, the laser pretreatement is found to be successful enough to produce a clinically acceptable bond strength of > 0.60 Kb/mm. Examination of the laser pre-treated tooth under SEM showed globule formation which may produce the mechanical interface required for the retention of the resin material.

New perspectives in laser analytics: Resonance-enhanced multiphoton ionization in a Paul ion trap combined with a time-of-flight mass spectrometer

NASA Astrophysics Data System (ADS)

Bisling, Peter; Heger, Hans Jörg; Michaelis, Walfried; Weitkamp, Claus; Zobel, Harald

1995-04-01

A new laser analytical device has been developed that is based on resonance-enhanced multiphoton ionization in the very center of a radio-frequency quadrupole ion trap. Applications in speciation anlaysis of biological and enviromental samples and in materials science will all benefit from laser-optical selectivity in the resonance excitation process, combined with mass-spectropic sensivity which is further enhanced by the ion accumulation and storage capability.

Wavelength-controlled external-cavity laser with a silicon photonic crystal resonant reflector

NASA Astrophysics Data System (ADS)

Gonzalez-Fernandez, A. A.; Liles, Alexandros A.; Persheyev, Saydulla; Debnath, Kapil; O'Faolain, Liam

2016-03-01

We report the experimental demonstration of an alternative design of external-cavity hybrid lasers consisting of a III-V Semiconductor Optical Amplifier with fiber reflector and a Photonic Crystal (PhC) based resonant reflector on SOI. The Silicon reflector comprises a polymer (SU8) bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and sidemode suppression ratio of more than 25 dB.

High quality proton beams from hybrid integrated laser-driven ion acceleration systems

NASA Astrophysics Data System (ADS)

Sinigardi, Stefano; Turchetti, Giorgio; Rossi, Francesco; Londrillo, Pasquale; Giove, Dario; De Martinis, Carlo; Bolton, Paul R.

2014-03-01

We consider a hybrid acceleration scheme for protons where the laser generated beam is selected in energy and angle and injected into a compact linac, which raises the energy from 30 to 60 MeV. The laser acceleration regime is TNSA and the energy spectrum is determined by the cutoff energy and proton temperature. The dependence of the spectrum on the target properties and the incidence angle is investigated with 2D PIC simulations. We base our work on widely available technologies and on laser with a short pulse, having in mind a facility whose cost is approximately 15 M €. Using a recent experiment as the reference, we choose the laser pulse and target so that the energy spectrum obtained from the 3D PIC simulation is close to the one observed, whose cutoff energy was estimated to be over 50 MeV. Laser accelerated protons in the TNSA regime have wide energy spectrum and broad divergence. In this paper we compare three transport lines, designed to perform energy selection and beam collimation. They are based on a solenoid, a quadruplet of permanent magnetic quadrupoles and a chicane. To increase the maximum available energy, which is actually seen as an upper limit due to laser properties and available targets, we propose to inject protons into a small linac for post-acceleration. The number of selected and injected protons is the highest with the solenoid and lower by one and two orders of magnitude with the quadrupoles and the chicane respectively. Even though only the solenoid enables achieving to reach a final intensity at the threshold required for therapy with the highest beam quality, the other systems will be very likely used in the first experiments. Realistic start-to-end simulations, as the ones reported here, are relevant for the design of such experiments.

Subsurface femtosecond tissue alteration: selectively photobleaching macular degeneration pigments in near retinal contact.

PubMed

Manevitch, Zakhariya; Lewis, Aaron; Levy, Carol; Zeira, Evelyne; Banin, Eyal; Manevitch, Alexandra; Khatchatouriants, Artium; Pe'er, Jacob; Galun, Eithan; Hemo, Itzhak

2012-06-14

This paper uses advances in the ultrafast manipulation of light to address a general need in medicine for a clinical approach that can provide a solution to a variety of disorders requiring subsurface tissue manipulation with ultralow collateral damage. Examples are age-related macular degeneration (AMD), fungal infections, tumors surrounded by overlying tissue, cataracts, etc. Although lasers have revolutionized the use of light in clinical settings, most lasers employed in medicine cannot address such problems of depth-selective tissue manipulation. This arises from the fact that they are mostly based on one photon based laser tissue interactions that provide a cone of excitation where the energy density is sufficiently high to excite heat or fluorescence in the entire cone. Thus, it is difficult to excite a specific depth of a tissue without affecting the overlying surface. However, the advent of femtosecond (fs) lasers has caused a revolution in multiphoton microscopy (Zipfel et al. Nat. Biotechnol. 2003, 21, 1369-1377; Denk et al. Science 1990, 248, 73-76) and fabrication (Kawata et al. Nature 2001, 412, 697-698). With such lasers, the photon energy density is only high enough for multiphoton processes in the focal volume, and this opens a new direction to address subsurface tissue manipulation. Here we show in an AMD animal model, Ccr2 KO knockout mutant mice, noninvasive, selective fs two-photon photobleaching of pigments associated with AMD that accumulate under and in ultraclose proximity to the overlying retina. Pathological evidence is presented that indicates the lack of collateral damage to the overlying retina or other surrounding tissue.

All-Fiber Configuration Laser Self-Mixing Doppler Velocimeter Based on Distributed Feedback Fiber Laser

PubMed Central

Wu, Shuang; Wang, Dehui; Xiang, Rong; Zhou, Junfeng; Ma, Yangcheng; Gui, Huaqiao; Liu, Jianguo; Wang, Huanqin; Lu, Liang; Yu, Benli

2016-01-01

In this paper, a novel velocimeter based on laser self-mixing Doppler technology has been developed for speed measurement. The laser employed in our experiment is a distributed feedback (DFB) fiber laser, which is an all-fiber structure using only one Fiber Bragg Grating to realize optical feedback and wavelength selection. Self-mixing interference for optical velocity sensing is experimentally investigated in this novel system, and the experimental results show that the Doppler frequency is linearly proportional to the velocity of a moving target, which agrees with the theoretical analysis commendably. In our experimental system, the velocity measurement can be achieved in the range of 3.58 mm/s–2216 mm/s with a relative error under one percent, demonstrating that our novel all-fiber configuration velocimeter can implement wide-range velocity measurements with high accuracy. PMID:27472342

Enhancing Surface Finish of Additively Manufactured Titanium and Cobalt Chrome Elements Using Laser Based Finishing

NASA Astrophysics Data System (ADS)

Gora, Wojciech S.; Tian, Yingtao; Cabo, Aldara Pan; Ardron, Marcus; Maier, Robert R. J.; Prangnell, Philip; Weston, Nicholas J.; Hand, Duncan P.

Additive manufacturing (AM) offers the possibility of creating a complex free form object as a single element, which is not possible using traditional mechanical machining. Unfortunately the typically rough surface finish of additively manufactured parts is unsuitable for many applications. As a result AM parts must be post-processed; typically mechanically machined and/or and polished using either chemical or mechanical techniques (both of which have their limitations). Laser based polishing is based on remelting of a very thin surface layer and it offers potential as a highly repeatable, higher speed process capable of selective area polishing, and without any waste problems (no abrasives or liquids). In this paper an in-depth investigation of CW laser polishing of titanium and cobalt chrome AM elements is presented. The impact of different scanning strategies, laser parameters and initial surface condition on the achieved surface finish is evaluated.

Double wedge prism based beam deflector for precise laser beam steering

NASA Astrophysics Data System (ADS)

Tyszka, Krzysztof; Dobosz, Marek; Bilaszewski, Tomasz

2018-02-01

Aiming to increase laser beam pointing stability required in interferometric measurements, we designed a laser beam deflector intended for active laser beam stabilization systems. The design is based on two wedge-prisms: the deflecting wedge driven by a tilting piezo-platform and the fixed wedge to compensate initial beam deflection. Our design allows linear beam steering, independently in the horizontal or vertical direction, with resolution of less than 1 μrad in a range of more than 100 μrad, and no initial deflection of the beam. Moreover, the ratio of the output beam deflection angle and the wedge tilt angle is less than 0.1; therefore, the noise influence is significantly reduced in comparison to standard mirror-based deflectors. The theoretical analyses support the designing process and can serve as a guide to wedge-prism selection. The experimental results are in agreement with theory and confirm the advantages of the presented double wedge system.

Super-contrast photoacoustic resonance imaging

NASA Astrophysics Data System (ADS)

Gao, Fei; Zhang, Ruochong; Feng, Xiaohua; Liu, Siyu; Zheng, Yuanjin

2018-02-01

In this paper, a new imaging modality, named photoacoustic resonance imaging (PARI), is proposed and experimentally demonstrated. Being distinct from conventional single nanosecond laser pulse induced wideband PA signal, the proposed PARI method utilizes multi-burst modulated laser source to induce PA resonant signal with enhanced signal strength and narrower bandwidth. Moreover, imaging contrast could be clearly improved than conventional single-pulse laser based PA imaging by selecting optimum modulation frequency of the laser source, which originates from physical properties of different materials beyond the optical absorption coefficient. Specifically, the imaging steps is as follows: 1: Perform conventional PA imaging by modulating the laser source as a short pulse to identify the location of the target and the background. 2: Shine modulated laser beam on the background and target respectively to characterize their individual resonance frequency by sweeping the modulation frequency of the CW laser source. 3: Select the resonance frequency of the target as the modulation frequency of the laser source, perform imaging and get the first PARI image. Then choose the resonance frequency of the background as the modulation frequency of the laser source, perform imaging and get the second PARI image. 4: subtract the first PARI image from the second PARI image, then we get the contrast-enhanced PARI results over the conventional PA imaging in step 1. Experimental validation on phantoms have been performed to show the merits of the proposed PARI method with much improved image contrast.

Selective Emitter Pumped Rare Earth Laser

NASA Technical Reports Server (NTRS)

Chubb, Donald L. (Inventor); Patton, Martin O. (Inventor)

2001-01-01

A selective emitter pumped rare earth laser provides an additional type of laser for use in many laser applications. Rare earth doped lasers exist which are pumped with flashtubes or laser diodes. The invention uses a rare earth emitter to transform thermal energy input to a spectral band matching the absorption band of a rare earth in the laser in order to produce lasing.

Technologies for thermal management of mid-IR Sb-based surface emitting lasers

NASA Astrophysics Data System (ADS)

Perez, J.-P.; Laurain, A.; Cerutti, L.; Sagnes, I.; Garnache, A.

2010-04-01

In this paper, for the first time to our knowledge, we report and demonstrate the technological steps dedicated to thermal management of antimonide-based surface emitting laser devices grown by molecular beam epitaxy. Key points of the technological process are firstly the bonding of the structure on the SiC host substrate and secondly the GaSb substrate removal to leave the Sb-based membrane. The structure design (etch stop layer, metallic mirror, etc), bonding process (metallic bonding via solid-liquid interdiffusion) and GaSb substrate removal process (selective wet-chemical etchants, etc) are presented. Optical characterizations together with external-cavity VCSEL laser emission at 2.3 µm at room temperature in continuous wave are presented.

SELECTIVE TRACE ENRICHMENT BY IMMUNOAFFINITY CAPILLARY ELECTROCHROMATOGRAPHY ON-LINE WITH CAPILLARY ZONE ELECTROPHORESIS - LASER-INDUCED FLUORESCENCE

EPA Science Inventory

Limited by the lack of a sensitive, universal detector, many capillary-based liquid-phase separation techniques might benefit from techniques that overcome modest concentration sensitivity by preconcentrating large injection volumes. The work presented employs selective solid-ph...

LASER BIOLOGY AND MEDICINE: Laser analysis of the 13C/12C isotope ratio in CO2 in exhaled air

NASA Astrophysics Data System (ADS)

Stepanov, E. V.

2002-11-01

Tunable diode lasers (TDLs) are applied to the diagnostics of gastroenterological diseases using respiratory tests and preparations enriched with the stable 13C isotope. This method of the analysis of the 13C/12C isotope ratio in CO2 in exhaled air is based on the selective measurement of the resonance absorption at the vibrational — rotational structure of 12CO2 and 13CO2. The CO2 transmission spectra in the region of 4.35 μm were measured with a PbEuSe double-heterostructure TDL. The accuracy of carbon isotope ratio measurements in CO2 of exhaled air performed with the TDL was ~0.5%. The data of clinical tests of the developed laser-based analyser are presented.

Switchable multiwavelength erbium-doped photonic crystal fiber ring laser based on a length of polarization-maintaining photonic crystal fiber

NASA Astrophysics Data System (ADS)

Cheng, Jianqun; Ruan, Shuangchen

2011-11-01

A switchable multi-wavelength Erbium-doped photonic crystal fiber (ED-PCF) ring laser based on a length of polarization-maintaining photonic crystal fiber(PM-PCF) is presented and demonstrated experimentally. A segment of ED-PCF is used as linear gain medium in the resonant cavity. Due to the polarization hole burning (PHB) caused by the PM-PCF and a polarization controller (PC), the laser can operate in stable dual- or triple- wavelength modes at room temperature. The optical signal-to-noise ratio (OSNR) of the laser without any wavelength-selective components is greater than 30 dB. The amplitude variations of lasing peaks in ten minutes are less than 0.26dB for two different operating modes.

Switchable multiwavelength erbium-doped photonic crystal fiber ring laser based on a length of polarization-maintaining photonic crystal fiber

NASA Astrophysics Data System (ADS)

Cheng, Jianqun; Ruan, Shuangchen

2012-03-01

A switchable multi-wavelength Erbium-doped photonic crystal fiber (ED-PCF) ring laser based on a length of polarization-maintaining photonic crystal fiber(PM-PCF) is presented and demonstrated experimentally. A segment of ED-PCF is used as linear gain medium in the resonant cavity. Due to the polarization hole burning (PHB) caused by the PM-PCF and a polarization controller (PC), the laser can operate in stable dual- or triple- wavelength modes at room temperature. The optical signal-to-noise ratio (OSNR) of the laser without any wavelength-selective components is greater than 30 dB. The amplitude variations of lasing peaks in ten minutes are less than 0.26dB for two different operating modes.

Narrow line width dual wavelength semiconductor optical amplifier based random fiber laser

NASA Astrophysics Data System (ADS)

Shawki, Heba A.; Kotb, Hussein E.; Khalil, Diaa

2018-02-01

A novel narrow line-width Single longitudinal mode (SLM) dual wavelength random fiber laser of 20 nm separation between wavelengths of 1530 and 1550 nm is presented. The laser is based on Rayleigh backscattering in a standard single mode fiber of 2 Km length as distributed mirrors, and a semiconductor optical amplifier (SOA) as the optical amplification medium. Two optical bandpass filters are used for the two wavelengths selectivity, and two Faraday Rotator mirrors are used to stabilize the two lasing wavelengths against fiber random birefringence. The optical signal to noise ratio (OSNR) was measured to be 38 dB. The line-width of the laser was measured to be 13.3 and 14 KHz at 1530 and 1550 nm respectively, at SOA pump current of 370 mA.

Spacecraft hazard avoidance utilizing structured light

NASA Technical Reports Server (NTRS)

Liebe, Carl Christian; Padgett, Curtis; Chapsky, Jacob; Wilson, Daniel; Brown, Kenneth; Jerebets, Sergei; Goldberg, Hannah; Schroeder, Jeffrey

2006-01-01

At JPL, a <5 kg free-flying micro-inspector spacecraft is being designed for host-vehicle inspection. The spacecraft includes a hazard avoidance sensor to navigate relative to the vehicle being inspected. Structured light was selected for hazard avoidance because of its low mass and cost. Structured light is a method of remote sensing 3-dimensional structure of the proximity utilizing a laser, a grating, and a single regular APS camera. The laser beam is split into 400 different beams by a grating to form a regular spaced grid of laser beams that are projected into the field of view of an APS camera. The laser source and the APS camera are separated forming the base of a triangle. The distance to all beam intersections of the host are calculated based on triangulation.

Switchable narrow linewidth fiber laser with LP11 transverse mode output

NASA Astrophysics Data System (ADS)

Shen, Ya; Ren, Guobin; Yang, Yuguang; Yao, Shuzhi; Wu, Yue; Jiang, Youchao; Xu, Yao; Jin, Wenxing; Zhu, Bofeng; Jian, Shuisheng

2018-01-01

We experimentally demonstrate a switchable narrow linewidth single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser with LP11 transverse mode output. The laser is based on a mode selective all-fiber fused coupler which is composed of a single-mode fiber (SMF) and a two-mode fiber (TMF). By controlling the polarization state of the output light, the laser can provide narrow linewidth SLM output with LP11 transverse mode at two specific wavelengths, which correspond to two transmission peaks of the chirped moiré fiber grating (CMFBG). The 20 dB linewidth of the fiber laser for each wavelength is approximately 7.2 and 6.4 kHz.

Mode-locked solid state lasers using diode laser excitation

DOEpatents

Holtom, Gary R [Boston, MA

2012-03-06

A mode-locked laser employs a coupled-polarization scheme for efficient longitudinal pumping by reshaped laser diode bars. One or more dielectric polarizers are configured to reflect a pumping wavelength having a first polarization and to reflect a lasing wavelength having a second polarization. An asymmetric cavity provides relatively large beam spot sizes in gain medium to permit efficient coupling to a volume pumped by a laser diode bar. The cavity can include a collimation region with a controlled beam spot size for insertion of a saturable absorber and dispersion components. Beam spot size is selected to provide stable mode locking based on Kerr lensing. Pulse durations of less than 100 fs can be achieved in Yb:KGW.

Moving target detection in flash mode against stroboscopic mode by active range-gated laser imaging

NASA Astrophysics Data System (ADS)

Zhang, Xuanyu; Wang, Xinwei; Sun, Liang; Fan, Songtao; Lei, Pingshun; Zhou, Yan; Liu, Yuliang

2018-01-01

Moving target detection is important for the application of target tracking and remote surveillance in active range-gated laser imaging. This technique has two operation modes based on the difference of the number of pulses per frame: stroboscopic mode with the accumulation of multiple laser pulses per frame and flash mode with a single shot of laser pulse per frame. In this paper, we have established a range-gated laser imaging system. In the system, two types of lasers with different frequency were chosen for the two modes. Electric fan and horizontal sliding track were selected as the moving targets to compare the moving blurring between two modes. Consequently, the system working in flash mode shows more excellent performance in motion blurring against stroboscopic mode. Furthermore, based on experiments and theoretical analysis, we presented the higher signal-to-noise ratio of image acquired by stroboscopic mode than flash mode in indoor and underwater environment.

Laser-activated protein solder for peripheral nerve repair

NASA Astrophysics Data System (ADS)

Trickett, Rodney I.; Lauto, Antonio; Dawes, Judith M.; Owen, Earl R.

1995-05-01

A 100 micrometers core optical fiber-coupled 75 mW diode laser operating at a wavelength of 800 nm has been used in conjunction with a protein solder to stripe weld severed rat tibial nerves, reducing the long operating time required for microsurgical nerve repair. Welding is produced by selective laser denaturation of the albumin based solder which contains the dye indocyanine green. Operating time for laser soldering was 10 +/- 5 min. (n equals 20) compared to 23 +/- 9 min. (n equals 10) for microsuturing. The laser solder technique resulted in patent welds with a tensile strength of 15 +/- 5 g, while microsutured nerves had a tensile strength of 40 +/- 10 g. Histopathology of the laser soldered nerves, conducted immediately after surgery, displayed solder adhesion to the outer membrane with minimal damage to the inner axons of the nerves. An in vivo study is under way comparing laser solder repaired tibial nerves to conventional microsuture repair. At the time of submission 15 laser soldered nerves and 7 sutured nerves were characterized at 3 months and showed successful regeneration with compound muscle action potentials of 27 +/- 8 mV and 29 +/- 8 mW respectively. A faster, less damaging and long lasting laser based anastomotic technique is presented.

[Special application of matrix-assisted laser desorption ionization time-of-flight mass spectrometry in clinical microbiological diagnostics].

PubMed

Nagy, Erzsébet; Abrók, Marianna; Bartha, Noémi; Bereczki, László; Juhász, Emese; Kardos, Gábor; Kristóf, Katalin; Miszti, Cecilia; Urbán, Edit

2014-09-21

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry as a new possibility for rapid identification of bacteria and fungi revolutionized the clinical microbiological diagnostics. It has an extreme importance in the routine microbiological laboratories, as identification of the pathogenic species rapidly will influence antibiotic selection before the final determination of antibiotic resistance of the isolate. The classical methods for identification of bacteria or fungi, based on biochemical tests, are influenced by many environmental factors. The matrix-assisted laser desorption ionization time-of-flight mass spectrometry is a rapid method which is able to identify a great variety of the isolated bacteria and fungi based on the composition of conserved ribosomal proteins. Recently several other applications of the method have also been investigated such as direct identification of pathogens from the positive blood cultures. There are possibilities to identify bacteria from the urine samples in urinary tract infection or from other sterile body fluids. Using selective enrichment broth Salmonella sp from the stool samples can be identified more rapidly, too. The extended spectrum beta-lactamase or carbapenemase production of the isolated bacteria can be also detected by this method helping the antibiotic selection in some cases. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry based methods are suitable to investigate changes in deoxyribonucleic acid or ribonucleic acid, to carry out rapid antibiotic resistance determination or other proteomic analysis. The aim of this paper is to give an overview about present possibilities of using this technique in the clinical microbiological routine procedures.

Studies on the optogalvanic effect and isotope-selective excitation of ytterbium in a hollow cathode discharge lamp using a pulsed dye laser.

PubMed

Kumar, Pankaj; Kumar, Jitendra; Prakash, Om; Saini, Vinod K; Dixit, Sudhir K; Nakhe, Shankar V

2013-09-01

This paper presents studies on the pulsed optogalvanic effect and isotope-selective excitation of Yb 555.648 nm (0 cm(-1) → 17 992.007 cm(-1)) and 581.067 nm (17 992.007 cm(-1) → 35 196.98 cm(-1)) transitions, in a Yb/Ne hollow cathode lamp. The Yb atoms were excited by narrow linewidth (500-1000 MHz) Rh110 and Rh6G dye based pulsed lasers. Optogalvanic signal inversion for ground state transition at 555.648 nm was observed beyond a hollow cathode discharge current of 8.5 mA, in contrast to normal optogalvanic signal at 581.067 nm up to maximum current of 14 mA. The isotope-selective excitation studies of Yb were carried out by recording Doppler limited optogalvanic signals as a function of dye laser wavelength. For the 581.067 nm transition, three even isotopes, (172)Yb, (174)Yb, and (176)Yb, and one odd isotope, (171)Yb, were clearly resolved. These data were compared with selective isotope excitation by 10 MHz linewidth continuous-wave dye laser. For 555.648 nm transition, isotopes were not clearly resolved, although isotope peaks of low modulation were observed.

New horizons in selective laser sintering surface roughness characterization

NASA Astrophysics Data System (ADS)

Vetterli, M.; Schmid, M.; Knapp, W.; Wegener, K.

2017-12-01

Powder-based additive manufacturing of polymers and metals has evolved from a prototyping technology to an industrial process for the fabrication of small to medium series of complex geometry parts. Unfortunately due to the processing of powder as a basis material and the successive addition of layers to produce components, a significant surface roughness inherent to the process has been observed since the first use of such technologies. A novel characterization method based on an elastomeric pad coated with a reflective layer, the Gelsight, was found to be reliable and fast to characterize surfaces processed by selective laser sintering (SLS) of polymers. With help of this method, a qualitative and quantitative investigation of SLS surfaces is feasible. Repeatability and reproducibility investigations are performed for both 2D and 3D areal roughness parameters. Based on the good results, the Gelsight is used for the optimization of vertical SLS surfaces. A model built on laser scanning parameters is proposed and after confirmation could achieve a roughness reduction of 10% based on the S q parameter. The Gelsight could be successfully identified as a fast, reliable and versatile surface topography characterization method as it applies to all kind of surfaces.

A Multi-Wavelength IR Laser for Space Applications

NASA Technical Reports Server (NTRS)

Li, Steven X.; Yu, Anthony W.; Sun, Xiaoli; Fahey, Molly E.; Numata, Kenji; Krainak, Michael A.

2017-01-01

We present a laser technology development with space flight heritage to generate laser wavelengths in the near- to mid-infrared (NIR to MIR) for space lidar applications. Integrating an optical parametric crystal to the LOLA (Lunar Orbiter Laser Altimeter) laser transmitter design affords selective laser wavelengths from NIR to MIR that are not easily obtainable from traditional diode pumped solid-state lasers. By replacing the output coupler of the LOLA laser with a properly designed parametric crystal, we successfully demonstrated a monolithic intra-cavity optical parametric oscillator (iOPO) laser based on all high technology readiness level (TRL) subsystems and components. Several desired wavelengths have been generated including 2.1 microns, 2.7 microns and 3.4 microns. This laser can also be used in trace-gas remote sensing, as many molecules possess their unique vibrational transitions in NIR to MIR wavelength region, as well as in time-of-flight mass spectrometer where desorption of samples using MIR laser wavelengths have been successfully demonstrated.

A multi-wavelength IR laser for space applications

NASA Astrophysics Data System (ADS)

Li, Steven X.; Yu, Anthony W.; Sun, Xiaoli; Fahey, Molly E.; Numata, Kenji; Krainak, Michael A.

2017-05-01

We present a laser technology development with space flight heritage to generate laser wavelengths in the near- to midinfrared (NIR to MIR) for space lidar applications. Integrating an optical parametric crystal to the LOLA (Lunar Orbiter Laser Altimeter) laser transmitter design affords selective laser wavelengths from NIR to MIR that are not easily obtainable from traditional diode pumped solid-state lasers. By replacing the output coupler of the LOLA laser with a properly designed parametric crystal, we successfully demonstrated a monolithic intra-cavity optical parametric oscillator (iOPO) laser based on all high technology readiness level (TRL) subsystems and components. Several desired wavelengths have been generated including 2.1 µm, 2.7 μm and 3.4 μm. This laser can also be used in trace-gas remote sensing, as many molecules possess their unique vibrational transitions in NIR to MIR wavelength region, as well as in time-of-flight mass spectrometer where desorption of samples using MIR laser wavelengths have been successfully demonstrated

Design and implementation of a laser-based absorption spectroscopy sensor for in situ monitoring of biomass gasification

NASA Astrophysics Data System (ADS)

Viveros Salazar, David; Goldenstein, Christopher S.; Jeffries, Jay B.; Seiser, Reinhard; Cattolica, Robert J.; Hanson, Ronald K.

2017-12-01

Research to demonstrate in situ laser-absorption-based sensing of H2O, CH4, CO2, and CO mole fraction is reported for the product gas line of a biomass gasifier. Spectral simulations were used to select candidate sensor wavelengths that optimize sensitive monitoring of the target species while minimizing interference from other species in the gas stream. A prototype sensor was constructed and measurements performed in the laboratory at Stanford to validate performance. Field measurements then were demonstrated in a pilot scale biomass gasifier at West Biofuels in Woodland, CA. The performance of a prototype sensor was compared for two sensor strategies: wavelength-scanned direct absorption (DA) and wavelength-scanned wavelength modulation spectroscopy (WMS). The lasers used had markedly different wavelength tuning response to injection current, and modern distributed feedback lasers (DFB) with nearly linear tuning response to injection current were shown to be superior, leading to guidelines for laser selection for sensor fabrication. Non-absorption loss in the transmitted laser intensity from particulate scattering and window fouling encouraged the use of normalized WMS measurement schemes. The complications of using normalized WMS for relatively large values of absorbance and its mitigation are discussed. A method for reducing adverse sensor performance effects of a time-varying WMS background signal is also presented. The laser absorption sensor provided measurements with the sub-second time resolution needed for gasifier control and more importantly provided precise measurements of H2O in the gasification products, which can be problematic for the typical gas chromatography sensors used by industry.

The application of image processing in the measurement for three-light-axis parallelity of laser ranger

NASA Astrophysics Data System (ADS)

Wang, Yang; Wang, Qianqian

2008-12-01

When laser ranger is transported or used in field operations, the transmitting axis, receiving axis and aiming axis may be not parallel. The nonparallelism of the three-light-axis will affect the range-measuring ability or make laser ranger not be operated exactly. So testing and adjusting the three-light-axis parallelity in the production and maintenance of laser ranger is important to ensure using laser ranger reliably. The paper proposes a new measurement method using digital image processing based on the comparison of some common measurement methods for the three-light-axis parallelity. It uses large aperture off-axis paraboloid reflector to get the images of laser spot and white light cross line, and then process the images on LabVIEW platform. The center of white light cross line can be achieved by the matching arithmetic in LABVIEW DLL. And the center of laser spot can be achieved by gradation transformation, binarization and area filter in turn. The software system can set CCD, detect the off-axis paraboloid reflector, measure the parallelity of transmitting axis and aiming axis and control the attenuation device. The hardware system selects SAA7111A, a programmable vedio decoding chip, to perform A/D conversion. FIFO (first-in first-out) is selected as buffer.USB bus is used to transmit data to PC. The three-light-axis parallelity can be achieved according to the position bias between them. The device based on this method has been already used. The application proves this method has high precision, speediness and automatization.

Comparative study of diode-pumped alkali vapor laser and exciplex-pumped alkali laser systems and selection principal of parameters

NASA Astrophysics Data System (ADS)

Huang, Wei; Tan, Rongqing; Li, Zhiyong; Han, Gaoce; Li, Hui

2017-03-01

A theoretical model based on common pump structure is proposed to analyze the output characteristics of a diode-pumped alkali vapor laser (DPAL) and XPAL (exciplex-pumped alkali laser). Cs-DPAL and Cs-Ar XPAL systems are used as examples. The model predicts that an optical-to-optical efficiency approaching 80% can be achieved for continuous-wave four- and five-level XPAL systems with broadband pumping, which is several times the pumped linewidth for DPAL. Operation parameters including pumped intensity, temperature, cell's length, mixed gas concentration, pumped linewidth, and output coupler are analyzed for DPAL and XPAL systems based on the kinetic model. In addition, the predictions of selection principal of temperature and cell's length are also presented. The concept of the equivalent "alkali areal density" is proposed. The result shows that the output characteristics with the same alkali areal density but different temperatures turn out to be equal for either the DPAL or the XPAL system. It is the areal density that reflects the potential of DPAL or XPAL systems directly. A more detailed analysis of similar influences of cavity parameters with the same areal density is also presented.

Observing interactions between DNA bases using ion dip spectroscopy.

NASA Astrophysics Data System (ADS)

Vries Mattanjah, De

2002-03-01

We investigate biomolecular building blocks and their clusters with each other and with water on a single molecular level. The motivation is the need to distinguish between intrinsic molecular properties and those that result from the biological environment. This is achieved by a combination of laser desorption and jet cooling, applied to aromatic amino acids, small peptides containing those, purine bases and nucleosides. This approach is coupled with a number of gas phase laser spectroscopic techniques. We will present results for DNA bases guanine, adenine, cytosine, and their derivatives, for which we obtained tautomer selected vibronic spectra. Capitalizing on these results we use these bases as chromophores to study interactions in single base pairs, obtained by formation of clusters of laser desorbed bases in a supersonic beam. For analysis we employ both UV/UV and IR/UV ion-dip spectroscopy, the results of which we compare with ab initio calculations.

Supercontinuum white light lasers for flow cytometry

PubMed Central

Telford, William G.; Subach, Fedor V.; Verkhusha, Vladislav V.

2009-01-01

Excitation of fluorescent probes for flow cytometry has traditionally been limited to a few discrete laser lines, an inherent limitation in our ability to excite the vast array of fluorescent probes available for cellular analysis. In this report, we have used a supercontinuum (SC) white light laser as an excitation source for flow cytometry. By selectively filtering the wavelength of interest, almost any laser wavelength in the visible spectrum can be separated and used for flow cytometric analysis. The white light lasers used in this study were integrated into a commercial flow cytometry platform, and a series of high-transmission bandpass filters used to select wavelength ranges from the blue (~480 nm) to the long red (>700 nm). Cells labeled with a variety of fluorescent probes or expressing fluorescent proteins were then analyzed, in comparison with traditional lasers emitting at wavelengths similar to the filtered SC source. Based on a standard sensitivity metric, the white light laser bandwidths produced similar excitation levels to traditional lasers for a wide variety of fluorescent probes and expressible proteins. Sensitivity assessment using fluorescent bead arrays confirmed that the SC laser and traditional sources resulted in similar levels of detection sensitivity. Supercontinuum white light laser sources therefore have the potential to remove a significant barrier in flow cytometric analysis, namely the limitation of excitation wavelengths. Almost any visible wavelength range can be made available for excitation, allowing access to virtually any fluorescent probe, and permitting “fine-tuning” of excitation wavelength to particular probes. PMID:19072836

Selective Laser Sintering of Nano Al2O3 Infused Polyamide

PubMed Central

Warnakula, Anthony; Singamneni, Sarat

2017-01-01

Nano Al2O3 polyamide composites are evaluated for processing by selective laser sintering. A thermal characterization of the polymer composite powders allowed us to establish the possible initial settings. Initial experiments are conducted to identify the most suitable combinations of process parameters. Based on the results of the initial trials, more promising ranges of different process parameters could be identified. The post sintering characterization showed evidence of sufficient inter-particle sintering and intra-layer coalescence. While the inter-particle coalescence gradually improved, the porosity levels slightly decreased with increasing laser power. The nano-filler particles tend to agglomerate around the beads along the solid tracks, possibly due to Van der Walls forces. The tensile stress results showed an almost linear increase with increasing nano-filler content. PMID:28773220

Could adverse effects and complications of selective laser trabeculoplasty be decreased by low-power laser therapy?

PubMed

Paiva, Alexandre de Carvalho Mendes; da Fonseca, Adenilson de Souza

2017-11-30

Selective laser trabeculoplasty (SLT) has been used for treatment of primary open-angle glaucoma, ocular hypertension, pigmenter and pseudoexfoliative glaucoma being considered a low-risk procedure. Therefore, transitory and permanent adverse effects have been reported, including corneal changes, subclinical edema, and reduction in endothelial cells and in central corneal thickness. Despite rarer, serious corneal complications after SLT can be permanent and lead to visual impairment, central corneal haze, opacity and narrowing. The mechanism involves increase of vasoactive and chemotactic cytokines causing inflammatory infiltrate, destruction of stromal collagen by fibroblasts and increase of matrix metalloproteinases type 2, which impair reepithelization. SLT also increases free radical production and reduces antioxidant enzymes, resulting in endothelium damages. Low-power laser therapy (LPLT) has been used in regenerative medicine based on its biostimulatory and anti-inflammatory effects. Biostimulation occurs through the interaction of laser photons with cytochrome C oxidase enzyme, which activates intracellular biochemical cascades causing synthesis of a number of molecules related to anti-inflammatory, regenerative effects, pain relief and reduction in edema. It has been showed that LPLT reduces gene expression related to pro-inflammatory cytokines and matrix metalloproteinases, and it increases expression of growth factors related to its proliferative and healing actions. Although radiations emitted by low-power lasers are considered safe and able to induce therapeutic effects, researches based on experimental models for glaucoma could bring important data if LPLT could be an alternative approach to improve acceptation for patients undergoing SLT.

Gelatin based on Power-gel.TM. as solders for Cr.sup.4+laser tissue welding and sealing of lung air leak and fistulas in organs

DOEpatents

Alfano, Robert R.; Tang, Jing; Evans, Jonathan M.; Ho, Peng Pei

2006-04-25

Laser tissue welding can be achieved using tunable Cr.sup.4+ lasers, semiconductor lasers and fiber lasers, where the weld strength follows the absorption spectrum of water. The use of gelatin and esterified gelatin as solders in conjunction with laser inducted tissue welding impart much stronger tensile and torque strengths than albumin solders. Selected NIR wavelength from the above lasers can improve welding and avoid thermal injury to tissue when used alone or with gelatin and esterified gelatin solders. These discoveries can be used to enhance laser tissue welding of tissues such as skin, mucous, bone, blood vessel, nerve, brain, liver, pancreas, spleen, kidney, lung, bronchus, respiratory track, urinary tract, gastrointestinal tract, or gynecologic tract and as a sealant for pulmonary air leaks and fistulas such as intestinal, rectal and urinary fistulas.

Scanning pattern angle effect on the resulting properties of selective laser sintered monolayers of Cu-Sn-Ni powder

NASA Astrophysics Data System (ADS)

Sabelle, Matías; Walczak, Magdalena; Ramos-Grez, Jorge

2018-01-01

Laser-based layer manufacturing of metals, also known as additive manufacturing, is a growing research field of academic and industrial interest. However, in the associated laser-driven processes (i.e. selective laser sintering (SLS) or melting (SLM)), optimization of some parameters has not been fully explored. This research aims at determining how the angle of laser scanning pattern (i.e. build orientation) in SLS affects the mechanical properties and structure of an individual Cu-Sn-Ni alloy metallic layer sintered in the process. Experiments consist in varying the angle of the scanning pattern (0°, 30°, 45° 60° and 90° relative to the transverse dimension of the piece), at constant scanning speed and laser beam power, producing specimens of different thicknesses. A noticeable effect of the scan angle on the mechanical strength and degree of densification of the sintered specimens is found. Thickness of the resulting monolayer correlates negatively with increasing scan angle, whereas relative density correlates positively. A minimum porosity and maximum UTS are found at the angle of 60°. It is concluded that angle of the scanning pattern angle plays a significant role in SLS of metallic monolayers.

Normal-mode selectivity in ultrafast Raman excitations in C60

NASA Astrophysics Data System (ADS)

Zhang, G. P.; George, Thomas F.

2006-01-01

Ultrafast Raman spectra are a powerful tool to probe vibrational excitations, but inherently they are not normal-mode specific. For a system as complicated as C60 , there is no general rule to target a specific mode. A detailed study presented here aims to investigate normal-mode selectivity in C60 by an ultrafast laser. To accurately measure mode excitation, we formally introduce the kinetic-energy-based normal-mode analysis which overcomes the difficulty with the strong lattice anharmonicity and relaxation. We first investigate the resonant excitation and find that mode selectivity is normally difficult to achieve. However, for off-resonant excitations, it is possible to selectively excite a few modes in C60 by properly choosing an optimal laser pulse duration, which agrees with previous experimental and theoretical findings. Going beyond the phenomenological explanation, our study shines new light on the origin of the optimal duration: The phase matching between the laser field and mode vibration determines which mode is strongly excited or suppressed. This finding is very robust and should be a useful guide for future experimental and theoretical studies in more complicated systems.

Normal mode selectivity in ultrafast Raman excitations in C60

NASA Astrophysics Data System (ADS)

Zhang, Guoping; George, Thomas F.

2006-05-01

Ultrafast Raman spectra are a powerful tool to probe vibrational excitations, but inherently they are not normal-mode specific. For a system as complicated as C60, there is no general rule to target a specific mode. A detailed study presented here aims to investigate normal mode selectivity in C60 by an ultrafast laser. To accurately measure mode excitation, we formally introduce the kinetic energy-based normal mode analysis which overcomes the difficulty with the strong lattice anharmonicity and relaxation. We first investigate the resonant excitation and find that mode selectivity is normally difficult to achieve. However, for off-resonant excitations, it is possible to selectively excite a few modes in C60 by properly choosing an optimal laser pulse duration, which agrees with previous experimental and theoretical findings. Going beyond the phenomenological explanation, our study shines new light on the origin of the optimal duration: The phase matching between laser field and mode vibration determines which mode is strongly excited or suppressed. This finding is very robust and may be a useful guide for future experimental and theoretical studies in more complicated systems.

On the role of heat and mass transfer into laser processability during selective laser melting AlSi12 alloy based on a randomly packed powder-bed

NASA Astrophysics Data System (ADS)

Wang, Lianfeng; Yan, Biao; Guo, Lijie; Gu, Dongdong

2018-04-01

A newly transient mesoscopic model with a randomly packed powder-bed has been proposed to investigate the heat and mass transfer and laser process quality between neighboring tracks during selective laser melting (SLM) AlSi12 alloy by finite volume method (FVM), considering the solid/liquid phase transition, variable temperature-dependent properties and interfacial force. The results apparently revealed that both the operating temperature and resultant cooling rate were obviously elevated by increasing the laser power. Accordingly, the resultant viscosity of liquid significantly reduced under a large laser power and was characterized with a large velocity, which was prone to result in a more intensive convection within pool. In this case, the sufficient heat and mass transfer occurred at the interface between the previously fabricated tracks and currently building track, revealing a strongly sufficient spreading between the neighboring tracks and a resultant high-quality surface without obvious porosity. By contrast, the surface quality of SLM-processed components with a relatively low laser power notably weakened due to the limited and insufficient heat and mass transfer at the interface of neighboring tracks. Furthermore, the experimental surface morphologies of the top surface were correspondingly acquired and were in full accordance to the calculated results via simulation.

Five-Channel Infrared Laser Absorption Spectrometer for Combustion Product Monitoring Aboard Manned Spacecraft

NASA Technical Reports Server (NTRS)

Briggs, Ryan M.; Frez, Clifford; Borgentun, Carl E.; Bagheri, Mahmood; Forouhar, Siamak; May, Randy D.

2014-01-01

Continuous combustion product monitoring aboard manned spacecraft can prevent chronic exposure to hazardous compounds and also provides early detection of combustion events. As future missions extend beyond low-Earth orbit, analysis of returned environmental samples becomes impractical and safety monitoring should be performed in situ. Here, we describe initial designs of a five-channel tunable laser absorption spectrometer to continuously monitor combustion products with the goal of minimal maintenance and calibration over long-duration missions. The instrument incorporates dedicated laser channels to simultaneously target strong mid-infrared absorption lines of CO, HCl, HCN, HF, and CO2. The availability of low-power-consumption semiconductor lasers operating in the 2 to 5 micron wavelength range affords the flexibility to select absorption lines for each gas with maximum interaction strength and minimal interference from other gases, which enables the design of a compact and mechanically robust spectrometer with low-level sensitivity. In this paper, we focus primarily on absorption line selection based on the availability of low-power single-mode semiconductor laser sources designed specifically for the target wavelength range.

In-situ sequential laser transfer and laser reduction of graphene oxide films

NASA Astrophysics Data System (ADS)

Papazoglou, S.; Petridis, C.; Kymakis, E.; Kennou, S.; Raptis, Y. S.; Chatzandroulis, S.; Zergioti, I.

2018-04-01

Achieving high quality transfer of graphene on selected substrates is a priority in device fabrication, especially where drop-on-demand applications are involved. In this work, we report an in-situ, fast, simple, and one step process that resulted in the reduction, transfer, and fabrication of reduced graphene oxide-based humidity sensors, using picosecond laser pulses. By tuning the laser illumination parameters, we managed to implement the sequential printing and reduction of graphene oxide flakes. The overall process lasted only a few seconds compared to a few hours that our group has previously published. DC current measurements, X-Ray Photoelectron Spectroscopy, X-Ray Diffraction, and Raman Spectroscopy were employed in order to assess the efficiency of our approach. To demonstrate the applicability and the potential of the technique, laser printed reduced graphene oxide humidity sensors with a limit of detection of 1700 ppm are presented. The results demonstrated in this work provide a selective, rapid, and low-cost approach for sequential transfer and photochemical reduction of graphene oxide micro-patterns onto various substrates for flexible electronics and sensor applications.

Pump and probe spectroscopy with continuous wave quantum cascade lasers.

PubMed

Kirkbride, James M R; Causier, Sarah K; Dalton, Andrew R; Weidmann, Damien; Ritchie, Grant A D

2014-02-07

This paper details infra-red pump and probe studies on nitric oxide conducted with two continuous wave quantum cascade lasers both operating around 5 μm. The pump laser prepares a velocity selected population in a chosen rotational quantum state of the v = 1 level which is subsequently probed using a second laser tuned to a rotational transition within the v = 2 ← v = 1 hot band. The rapid frequency scan of the probe (with respect to the molecular collision rate) in combination with the velocity selective pumping allows observation of marked rapid passage signatures in the transient absorption profiles from the polarized vibrationally excited sample. These coherent transient signals are influenced by the underlying hyperfine structure of the pump and probe transitions, the sample pressure, and the coherent properties of the lasers. Pulsed pump and probe studies show that the transient absorption signals decay within 1 μs at 50 mTorr total pressure, reflecting both the polarization and population dephasing times of the vibrationally excited sample. The experimental observations are supported by simulation based upon solving the optical Bloch equations for a two level system.

Data acquisition and path selection decision making for an autonomous roving vehicle

NASA Technical Reports Server (NTRS)

Frederick, D. K.; Shen, C. N.; Yerazunis, S. W.

1976-01-01

Problems related to the guidance of an autonomous rover for unmanned planetary exploration were investigated. Topics included in these studies were: simulation on an interactive graphics computer system of the Rapid Estimation Technique for detection of discrete obstacles; incorporation of a simultaneous Bayesian estimate of states and inputs in the Rapid Estimation Scheme; development of methods for estimating actual laser rangefinder errors and their application to date provided by Jet Propulsion Laboratory; and modification of a path selection system simulation computer code for evaluation of a hazard detection system based on laser rangefinder data.

Nanosecond laser scribing of CIGS thin film solar cell based on ITO bottom contact

NASA Astrophysics Data System (ADS)

Kuk, Seungkuk; Wang, Zhen; Fu, Shi; Zhang, Tao; Yu, Yi Yin; Choi, JaeMyung; Jeong, Jeung-hyun; Hwang, David J.

2018-03-01

Cu(In,Ga)Se2 (CIGS) thin films, a promising photovoltaic architecture, have mainly relied on Molybdenum for the bottom contact. However, the opaque nature of Molybdenum (Mo) poses limitations in module level fabrication by laser scribing as a preferred method for interconnect. We examined the P1, P2, and P3 laser scribing processes on CIGS photovoltaic architecture on the indium tin oxide (ITO) bottom contact with a cost-effective nanosecond pulsed laser of 532 nm wavelength. Laser illuminated from the substrate side, enabled by the transparent bottom contact, facilitated selective laser energy deposition onto relevant interfaces towards high-quality scribing. Parametric tuning procedures are described in conjunction with experimental and numerical investigation of relevant mechanisms, and preliminary mini-module fabrication results are also presented.

Mid infrared quantum cascade laser operating in pure amplitude modulation for background-free trace gas spectroscopy.

PubMed

Bidaux, Yves; Bismuto, Alfredo; Patimisco, Pietro; Sampaolo, Angelo; Gresch, Tobias; Strubi, Gregory; Blaser, Stéphane; Tittel, Frank K; Spagnolo, Vincenzo; Muller, Antoine; Faist, Jérôme

2016-11-14

We present a single mode multi-section quantum cascade laser source composed of three different sections: master oscillator, gain and phase section. Non-uniform pumping of the QCL's gain reveals that the various laser sections are strongly coupled. Simulations of the electronic and optical properties of the laser (based on the density matrix and scattering matrix formalisms, respectively) were performed and a good agreement with measurements is obtained. In particular, a pure modulation of the laser output power can be achieved. This capability of the device is applied in tunable-laser spectroscopy of N₂O where background-free quartz enhanced photo acoustic spectral scans with nearly perfect Voigt line shapes for the selected absorption line are obtained.

Degenerate band edge laser

NASA Astrophysics Data System (ADS)

Veysi, Mehdi; Othman, Mohamed A. K.; Figotin, Alexander; Capolino, Filippo

2018-05-01

We propose a class of lasers based on a fourth-order exceptional point of degeneracy (EPD) referred to as the degenerate band edge (DBE). EPDs have been found in parity-time-symmetric photonic structures that require loss and/or gain; here we show that the DBE is a different kind of EPD since it occurs in periodic structures that are lossless and gainless. Because of this property, a small level of gain is sufficient to induce single-frequency lasing based on a synchronous operation of four degenerate Floquet-Bloch eigenwaves. This lasing scheme constitutes a light-matter interaction mechanism that leads also to a unique scaling law of the laser threshold with the inverse of the fifth power of the laser-cavity length. The DBE laser has the lowest lasing threshold in comparison to a regular band edge laser and to a conventional laser in cavities with the same loaded quality (Q ) factor and length. In particular, even without mirror reflectors the DBE laser exhibits a lasing threshold which is an order of magnitude lower than that of a uniform cavity laser of the same length and with very high mirror reflectivity. Importantly, this novel DBE lasing regime enforces mode selectivity and coherent single-frequency operation even for pumping rates well beyond the lasing threshold, in contrast to the multifrequency nature of conventional uniform cavity lasers.

Resonator design and performance estimation for a space-based laser transmitter

NASA Astrophysics Data System (ADS)

Agrawal, Lalita; Bhardwaj, Atul; Pal, Suranjan; Kamalakar, J. A.

2006-12-01

Development of a laser transmitter for space applications is a highly challenging task. The laser must be rugged, reliable, lightweight, compact and energy efficient. Most of these features are inherently achieved by diode pumping of solid state lasers. Overall system reliability can further be improved by appropriate optical design of the laser resonator besides selection of suitable electro-optical and opto-mechanical components. This paper presents the design details and the theoretically estimated performance of a crossed-porro prism based, folded Z-shaped laser resonator. A symmetrically pumped Nd: YAG laser rod of 3 mm diameter and 60 mm length is placed in the gain arm with total input peak power of 1800 W from laser diode arrays. Electro-optical Q-switching is achieved through a combination of a polarizer, a fractional waveplate and LiNbO 3 Q-switch crystal (9 x 9 x 25 mm) placed in the feedback arm. Polarization coupled output is obtained by optimizing azimuth angle of quarter wave plate placed in the gain arm. Theoretical estimation of laser output energy and pulse width has been carried out by varying input power levels and resonator length to analyse the performance tolerances. The designed system is capable of meeting the objective of generating laser pulses of 10 ns duration and 30 mJ energy @ 10 Hz.

Tungsten disulphide based all fiber Q-switching cylindrical-vector beam generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, J.; Yan, K.; Zhou, Y.

2015-11-09

We proposed and demonstrated an all fiber passively Q-switching laser to generate cylindrical-vector beam, a two dimensional material, tungsten disulphide (WS{sub 2}), was adopted as a saturable absorber inside the laser cavity, while a few-mode fiber Bragg grating was used as a transverse mode-selective output coupler. The repetition rate of the Q-switching output pulses can be varied from 80 kHz to 120 kHz with a shortest duration of 958 ns. Attributed to the high damage threshold and polarization insensitivity of the WS{sub 2} based saturable absorber, the radially polarized beam and azimuthally polarized beam can be easily generated in the Q-switching fiber laser.

Selective ablation of sub- and supragingival calculus with a frequency-doubled Alexandrite laser

NASA Astrophysics Data System (ADS)

Rechmann, Peter; Hennig, Thomas

1995-05-01

In a preceding trial the absorption characteristics of subgingival calculus were calculated using fluorescence emission spectroscopy (excitation laser: N2-laser, wavelength 337 nm, pulse duration 4 ns). Subgingival calculus seems to contain chromophores absorbing in the ultraviolet spectral region up to 420 nm. The aim of the actual study was the ablation of sub- and supragingival calculus using a frequency doubled Alexandrite-laser (wavelength 377 nm, pulse duration 100 ns, repetition rate 110 Hz). Extracted human teeth presenting sub- and supragingival calculus were irradiated perpendicular to their axis with a laser fluence of 1 Jcm-2. Using a standard application protocol calculus was irradiated at the enamel surface, at the junction between enamel and root, and at the root surface (located on dentin or on cementum). During the irradiation procedure an effective water cooling-system was engaged. For light microscopical investigations undecalcified histological sections were prepared after treatment. The histological sections revealed that a selective and total removal of calculus is possible at all locations without ablation of healthy enamel, dentin or cementum. Even low fluences provide us with a high effectiveness for the ablation of calculus. Thus, based on different absorption characteristics and ablation thresholds, engaging a frequency doubled Alexandrite-laser a fast and, even more, a selective ablation of sub- and supragingival calculus is possible without adverse side effects to the surrounding tissues. Even more, microbial dental plaque can be perfectly removed.

Defects diagnosis in laser brazing using near-infrared signals based on empirical mode decomposition

NASA Astrophysics Data System (ADS)

Cheng, Liyong; Mi, Gaoyang; Li, Shuo; Wang, Chunming; Hu, Xiyuan

2018-03-01

Real-time monitoring of laser welding plays a very important role in the modern automated production and online defects diagnosis is necessary to be implemented. In this study, the status of laser brazing was monitored in real time using an infrared photoelectric sensor. Four kinds of braze seams (including healthy weld, unfilled weld, hole weld and rough surface weld) along with corresponding near-infrared signals were obtained. Further, a new method called Empirical Mode Decomposition (EMD) was proposed to analyze the near-infrared signals. The results showed that the EMD method had a good performance in eliminating the noise on the near-infrared signals. And then, the correlation coefficient was developed for selecting the Intrinsic Mode Function (IMF) more sensitive to the weld defects. A more accurate signal was reconstructed with the selected IMF components. Simultaneously, the spectrum of selected IMF components was solved using fast Fourier transform, and the frequency characteristics were clearly revealed. The frequency energy of different frequency bands was computed to diagnose the defects. There was a significant difference in four types of weld defects. This approach has been proved to be an effective and efficient method for monitoring laser brazing defects.

New approaches in clinical application of laser-driven ionizing radiation

NASA Astrophysics Data System (ADS)

Hideghéty, Katalin; Szabó, Rita Emilia; Polanek, Róbert; Szabó, Zoltán.; Brunner, Szilvia; Tőkés, Tünde

2017-05-01

The planned laser-driven ionizing beams (photon, very high energy electron, proton, carbon ion) at laser facilities have the unique property of ultra-high dose rate (>Gy/s-10), short pulses, and at ELI-ALPS high repetition rate, carry the potential to develop novel laser-driven methods towards compact hospital-based clinical application. The enhanced flexibility in particle and energy selection, the high spatial and time resolution and extreme dose rate could be highly beneficial in radiotherapy. These approaches may increase significantly the therapeutic index over the currently available advanced radiation oncology methods. We highlight two nuclear reactionbased binary modalities and the planned radiobiology research. Boron Neutron Capture Therapy is an advanced cell targeted modality requiring 10B enriched boron carrier and appropriate neutron beam. The development of laser-based thermal and epithermal neutron source with as high as 1010 fluence rate could enhance the research activity in this promising field. Boron-Proton Fusion reaction is as well as a binary approach, where 11B containing compounds are accumulated into the cells, and the tumour selectively irradiated with protons. Due to additional high linear energy transfer alpha particle release of the BPFR and the maximum point of the Bragg-peak is increased, which result in significant biological effect enhancement. Research at ELI-ALPS on detection of biological effect differences of modified or different quality radiation will be presented using recently developed zebrafish embryo and rodent models.

On-sky performance of the tip-tilt correction system for GLAS using an EMCCD camera

NASA Astrophysics Data System (ADS)

Skvarč, Jure; Tulloch, Simon

2008-07-01

Adaptive optics systems based on laser guide stars still need a natural guide star (NGS) to correct for the image motion caused by the atmosphere and by imperfect telescope tracking. The ability to properly compensate for this motion using a faint NGS is critical to achieve large sky coverage. For the laser guide system (GLAS) on the 4.2 m William Herschel Telescope we designed and tested in the laboratory and on-sky a tip-tilt correction system based on a PC running Linux and an EMCCD technology camera. The control software allows selection of different centroiding algorithms and loop control methods as well as the control parameters. Parameter analysis has been performed using tip-tilt only correction before the laser commissioning and the selected sets of parameters were then used during commissioning of the laser guide star system. We have established the SNR of the guide star as a function of magnitude, depending on the image sampling frequency and on the dichroic used in the optical system; achieving a measurable improvement using full AO correction with NGSes down to magnitude range R=16.5 to R=18. A minimum SNR of about 10 was established to be necessary for a useful correction. The system was used to produce 0.16 arcsecond images in H band using bright NGS and laser correction during GLAS commissioning runs.

The development of heterogeneous materials based on Ni and B4C powders using a cold spray and stratified selective laser melting technologies

NASA Astrophysics Data System (ADS)

Filippov, A. A.; Fomin, V. M.; Buzyurkin, A. E.; Kosarev, V. F.; Malikov, A. G.; Orishich, A. M.; Ryashin, N. S.

2018-01-01

The work is dedicated to the creation of new ceramic-composite materials based on boron carbide, nickel and using a laser welding in order to obtain three dimensional objects henceforth. The perspective way of obtaining which has been suggested by the authors combined two methods: cold spray technology and subsequent laser post-treatment. At this stage, the authors focused on the interaction of the laser with the substance, regardless of the multi-layer object development. The investigated material of this work was the metal-ceramic mixture based on boron carbide, which has high physical and mechanical characteristics, such as hardness, elastic modulus, and chemical resistance. The nickel powder as a binder and different types of boron carbide were used. The ceramic content varied from 30 to 70% by mass. Thin ceramic layers were obtained by the combined method and cross-sections of different seams were studied. It was shown that the most perspective layers for additive manufacturing could be obtained from cold spray coatings with ceramic concentrations more than 50% by weight treated when laser beam was defocused (thermal-conductive laser mode).

Reflectors and tuning elements for widely-tunable GaAs-based sampled grating DBR lasers

NASA Astrophysics Data System (ADS)

Brox, O.; Wenzel, H.; Della Case, P.; Tawfieq, M.; Sumpf, B.; Weyers, M.; Knigge, A.

2018-02-01

Widely-tunable lasers without moving parts are attractive light sources for sensors in industry and biomedicine. In contrast to InP based sampled grating (SG) distributed Bragg reflector (DBR) diode lasers which are commercially available, shorter wavelength GaAs SG-DBR lasers are still under development. One reason is the difficulty to integrate gratings with coupling coefficients that are high enough for functional grating bursts with lengths below 10 μm. Recently we have demonstrated > 20 nm wide quasi-continuous tuning with a GaAs based SG-DBR laser emitting around 975 nm. Wavelength selective reflectors are realized with SGs having different burst periods for the front and back mirrors. Thermal tuning elements (resistors) which are placed on top of the SG allow the control of the spectral positions of the SG reflector combs and hence to adjust the Vernier mode. In this work we characterize subsections of the developed SG-DBR laser to further improve its performance. We study the impact of two different vertical structures (with vertical far field FWHMs of 41° and 24°) and two grating orders on the coupling coefficient. Gratings with coupling coefficients above 350 cm-1 have been integrated into SG-DBR lasers. We also examine electronic tuning elements (a technique which is typically applied in InP based SG-DBR lasers and allows tuning within nanoseconds) and discuss the limitations in the GaAs material system

Experimental study of a VBG-based Tm : YLF slab laser at different output coupler parameters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, X M; Ding, Y; Dai, T Y

2015-04-30

The performance of a Tm : YLF slab laser is studied at different output coupler parameters. Use is made of a 20-mm-long a-cut slab crystal doped with 2.5 at. % thulium ions. With a volume Bragg grating and a Fabry – Perot etalon, the selected output wavelength of this Tm : YLF slab laser is 1908 nm. For the optimised output coupler with a transmission of 20% and a radius of curvature of 300 mm, the output power exceeds 74.1 W and the slope efficiency with respect to the absorbed pump power reaches 48.4%. In addition, the beam quality ofmore » the Tm : YLF slab laser is improved. (lasers)« less

Dimensional processing of composite materials by picosecond pulsed ytterbium fiber laser

NASA Astrophysics Data System (ADS)

Kotov, S. A.

2017-12-01

In this paper, an experimental study of laser dimensional processing of thermoset carbon fiber reinforced plastics with a thickness of 2 and 3 mm was performed. In the process of work test rig setup based on picosecond pulsed fiber laser with 1.06 microns wavelength and 30 W average power was developed. Experimental tests were carried out at the maximum average power, with laser beam moved by a galvanometric mirrors system. Cutting tests were executed with different scanning velocity, using different laser modes, number of repetitions, hatching distance and focal plane position without process gas. As a result of the research recommendations for the selection processing mode parameters, providing minimal heat affected zone, good kerf geometry and high cutting speed were produced.

Laser-based nanoengineering of surface topographies for biomedical applications

NASA Astrophysics Data System (ADS)

Schlie, Sabrina; Fadeeva, Elena; Koroleva, Anastasia; Ovsianikov, Aleksandr; Koch, Jürgen; Ngezahayo, Anaclet; Chichkov, Boris. N.

2011-04-01

In this study femtosecond laser systems were used for nanoengineering of special surface topographies in silicon and titanium. Besides the control of feature sizes, we demonstrated that laser structuring caused changes in material wettability due to a reduced surface contact area. These laser-engineered topographies were tested for their capability to control cellular behavior of human fibroblasts, SH-SY5Y neuroblastoma cells, and MG-63 osteoblasts. We found that fibroblasts reduced cell growth on the structures, while the other cell types proliferated at the same rate. These findings make laser-surface structuring very attractive for biomedical applications. Finally, to explain the results the correlation between topography and the biophysics of cellular adhesion, which is the key step of selective cell control, is discussed.

Selective laser sintering of cermet mixtures Ti and B4C

NASA Astrophysics Data System (ADS)

Filippov, A. A.; Fomin, V. M.; Malikov, A. G.; Orishich, A. M.

2016-10-01

The work is dedicated to the creation of a new heterogeneous ceramic-composite materials based on boron carbide and titanium, using a laser, in order to further layer-growing 3D products from these materials. The paper discussed two methods for obtaining ceramic-composite material: laser sintering of boron carbide powder and a metal-melting the powder mixture. We study the microstructure of the samples at various energy process modes. An attempt was made to justify the applicability of the regime used for the cultivation of layered products.

Photonic structures in diamond based on femtosecond UV laser induced periodic surface structuring (LIPSS).

PubMed

Granados, Eduardo; Martinez-Calderon, Miguel; Gomez, Mikel; Rodriguez, Ainara; Olaizola, Santiago M

2017-06-26

We study the fabrication of photonic surface structures in single crystal diamond by means of highly controllable direct femtosecond UV laser induced periodic surface structuring. By appropriately selecting the excitation wavelength, intensity, number of impinging pulses and their polarization state, we demonstrate emerging high quality and fidelity diamond grating structures with surface roughness below 1.4 nm. We characterize their optical properties and study their potential for the fabrication of photonic structure anti-reflection coatings for diamond Raman lasers in the near-IR.

Practical issues in laser cleaning of stone and painted artefacts: optimisation procedures and side effects

NASA Astrophysics Data System (ADS)

Pouli, Paraskevi; Oujja, Mohamed; Castillejo, Marta

2012-02-01

In the last twenty years lasers have acquired an important role in the study and the preservation of Cultural Heritage (CH) objects and Monuments, as they have effectively illuminated a number of complex diagnostic and restoration problems. Their unique properties have enabled their use in a wide range of conservation applications, since they ensure interventions with precise control, material selectivity and immediate feedback. Surface cleaning, based on laser ablation, is a delicate, critical and irreversible process, which, given the multitude of materials that may be present on a CH object and the often fragile or precarious condition of the original surfaces, is fraught with many potential complications. Therefore it is crucial to choose the best possible laser cleaning methodology for each individual case, which involves optimising the laser parameters according to material properties, as well as the thorough knowledge of the ablation mechanisms involved. In this context the systematic investigation and elucidation of potential damage or side effects occurring upon cleaning is essential, as it delineates the possibilities and limitations of laser ablation and allows the fine-tuning of the operating parameters for a successful cleaning intervention. This paper is an overview of studies investigating the mechanisms which are responsible for the laser-induced discoloration effects. Emphasis is given on the yellowing coloration observed on stonework upon infrared (IR) ablation of pollution encrustations, while the various theories introduced to approach the different physical and/or chemical processes and mechanisms responsible for such side effects are discussed. In this respect the different laser cleaning methodologies, which are based on the use of laser systems with different pulse durations and wavelength characteristics, introduced in order to rectify or prevent discoloration on stonework are presented. In parallel, the darkening phenomena which occur upon laser irradiation of painted surfaces are also considered. Studies on series of model paints performed in order to understand the sensitivity of pigments to laser irradiation are critically reviewed. In this respect the importance of the optimal wavelength and pulse-duration selection for a safe and controlled laser cleaning intervention is also addressed.

Laser additive manufacturing of 3D meshes for optical applications.

PubMed

Essa, Khamis; Sabouri, Aydin; Butt, Haider; Basuny, Fawzia Hamed; Ghazy, Mootaz; El-Sayed, Mahmoud Ahmed

2018-01-01

Selective laser melting (SLM) is a widely used additive manufacturing process that can be used for printing of intricate three dimensional (3D) metallic structures. Here we demonstrate the fabrication of titanium alloy Ti-6Al-4V alloy based 3D meshes with nodally-connected diamond like unit cells, with lattice spacing varying from 400 to 1000 microns. A Concept Laser M2 system equipped with laser that has a wavelength of 1075 nm, a constant beam spot size of 50μm and maximum power of 400W was used to manufacture the 3D meshes. These meshes act as optical shutters / directional transmitters and display interesting optical properties. A detailed optical characterisation was carried out and it was found that these structures can be optimised to act as scalable rotational shutters with high efficiencies and as angle selective transmission screens for protection against unwanted and dangerous radiations. The efficiency of fabricated lattice structures can be increased by enlarging the meshing size.

Laser additive manufacturing of 3D meshes for optical applications

PubMed Central

Essa, Khamis; Sabouri, Aydin; Butt, Haider; Basuny, Fawzia Hamed; Ghazy, Mootaz

2018-01-01

Selective laser melting (SLM) is a widely used additive manufacturing process that can be used for printing of intricate three dimensional (3D) metallic structures. Here we demonstrate the fabrication of titanium alloy Ti–6Al–4V alloy based 3D meshes with nodally-connected diamond like unit cells, with lattice spacing varying from 400 to 1000 microns. A Concept Laser M2 system equipped with laser that has a wavelength of 1075 nm, a constant beam spot size of 50μm and maximum power of 400W was used to manufacture the 3D meshes. These meshes act as optical shutters / directional transmitters and display interesting optical properties. A detailed optical characterisation was carried out and it was found that these structures can be optimised to act as scalable rotational shutters with high efficiencies and as angle selective transmission screens for protection against unwanted and dangerous radiations. The efficiency of fabricated lattice structures can be increased by enlarging the meshing size. PMID:29414982

Studies for aluminum photoionization in hot cavity for the selective production of exotic species projecta)

NASA Astrophysics Data System (ADS)

Scarpa, D.; Vasquez, J.; Tomaselli, A.; Grassi, D.; Biasetto, L.; Cavazza, A.; Corradetti, S.; Manzolaro, M.; Montano, J.; Andrighetto, A.; Prete, G.

2012-02-01

Selective production of exotic species (SPES) is an ISOL-based accelerator facility that will be built in the Legnaro INFN Laboratory (Italy), intended to provide an intense neutron-rich radioactive ion beams obtained by proton induced fission of an uranium carbide target. Beside this main target, a silicon carbide (SiC) target will the first to be used to deliver some p-rich beams. This target will validate also the functionality of the SPES facility with aluminum beam as result of hitting SiC target with protons. In the past off-line studies on laser photoionization of aluminum have performed in Pavia Spectroscopy Laboratory and in Laboratori Nazionali di Legnaro where, recently, a XeCl excimer laser was installed in order to test the laser ionization in the SPES hot cavity. Results are promising to justify further studies with this technique, aiming a better characterization of the SPES ion extraction capability under laser photoionization.

Method and apparatus for aligning a solar concentrator using two lasers

DOEpatents

Diver Jr., Richard Boyer

2003-07-22

A method and apparatus are provided for aligning the facets of a solar concentrator. A first laser directs a first laser beam onto a selected facet of the concentrator such that a target board positioned adjacent to the first laser at approximately one focal length behind the focal point of the concentrator is illuminated by the beam after reflection thereof off of the selected facet. A second laser, located adjacent to the vertex of the optical axis of the concentrator, is used to direct a second laser beam onto the target board at a target point thereon. By adjusting the selected facet to cause the first beam to illuminate the target point on the target board produced by the second beam, the selected facet can be brought into alignment with the target point. These steps are repeated for other selected facets of the concentrator, as necessary, to provide overall alignment of the concentrator.

Narrow-linewidth tunable laser working at 633 nm suitable for industrial interferometry

NASA Astrophysics Data System (ADS)

Minh, Tuan Pham; Hucl, Václav; Čížek, Martin; Mikel, Břetislav; Hrabina, Jan; Řeřucha, Šimon; Číp, Ondřej; Lazar, Josef

2015-05-01

Semiconductor lasers found a foothold in many fields of human activities, mainly thanks to its small size, low cost and high energy efficiency. Recent methods for accurate distance measurement in industrial practice use principles of laser interferometry, which are based on lasers operating in the visible spectrum. When the laser beam is visible the alignment of the industrial interferometer makes the measuring process easier. Traditional lasers for these purposes for many decades - HeNe gas laser - have superb coherence properties but small tunable range. On the other hand laser diodes are very useful lasers but only if the active layer of the semiconductor equips with a passive selective element that will increase the quality of their own resonator and also prevents the structure of its higher longitudinal modes. The main aim of the work is a design of the laser source based on a new commercial available laser diode with Distributed Bragg Reflector structure, butterfly package and fibre coupled output. The ultra-low noise injection current source, stable temperature controller and supply electronic equipment were developed with us and experimentally tested with this laser for the best performances required of the industrial interferometry field. The work also performs a setup for frequency noise properties investigation with an unbalanced fibre based Mach-Zehnder interferometer and 10 m long fibre spool inserted in the reference arm. The work presents the way to developing the narrow-linewidth operation the DBR laser with the wide tunable range up to more than 1 nm of the operation wavelength at the same time. Both capabilities predetermine this complex setup for the industrial interferometry application as they are the long distance surveying or absolute scale interferometry.

Laser Research and Development Studies for Laser Guide Star Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pennington, D.; Beach, R.; Ebbers, C.

2000-02-23

In this paper we consider two CW solid state laser approaches to a 589 nm LGS system. Both are based on the technique of sum-frequency generation, but differ in the cavity architecture. Both technologies are very promising and are worth of further consideration. This preliminary proposal is intended to encompass both designs. A down select shall be performed early in the project execution to focus on the most promising option. The two design options consist of: (1) A dual-frequency resonator with intra-cavity doubling in LB0 offers the promise of a simple architecture and may scale more easily to high power.more » This design has been shown to be highly reliable, efficient and high power when used in frequency-doubled Nd:YAG lasers for programs at LLNL and in commercial products. The challenge in this design is the demonstration of a high power13 18 nm oscillator with adequate suppression of the 1064 nm line. (2) A MOPA based design uses commercial low power oscillators to produce both wavelengths, then amplifies the wavelengths before doubling. This design requires the demonstration of a 1318 nm amplifier, though the design is scaled from a kW CW amplifier already delivered to a customer at a different wavelength. The design must also demonstrate high power scaling of sum-frequency generation in the relatively new nonlinear material, PPLN. The first step in the process would be to further evaluate the two conceptual options for technical feasibility, cost and constructability. Then a down selection to one design would be conducted. Finally, R&D on that design would then proceed. Minimal testing should be required for this selection. The majority of the funding received would be allocated to development of the design selected.« less

Laser-activated solid protein bands for peripheral nerve repair: an vivo study.

PubMed

Lauto, A; Trickett, R; Malik, R; Dawes, J M; Owen, E R

1997-01-01

Severed tibial nerves in rats were repaired using a novel technique, utilizing a semiconductor diode-laser-activated protein solder applied longitudinally across the join. Welding was produced by selective laser denaturation of solid solder bands containing the dye indocyanine green. An in vivo study, using 48 adult male Wistar rats, compared conventional microsuture-repaired tibial nerves with laser solder-repaired nerves. Nerve repairs were characterised immediately after surgery and after 3 months. Successful regeneration with average compound muscle action potentials of 2.5 +/- 0.5 mV and 2.7 +/- 0.3 mV (mean and standard deviation) was demonstrated for the laser-soldered nerves and the sutured nerves, respectively. Histopathology confirmed comparable regeneration of axons in laser- and suture-operated nerves. The laser-based nerve repair technique was easier and faster than microsuture repair, minimising manipulation damage to the nerve.

High-resolution monochromatic x-ray imaging system based on spherically bent crystals.

PubMed

Aglitskiy, Y; Lehecka, T; Obenschain, S; Bodner, S; Pawley, C; Gerber, K; Sethian, J; Brown, C M; Seely, J; Feldman, U; Holland, G

1998-08-01

We have developed an improved x-ray imaging system based on spherically curved crystals. It is designed and used for diagnostics of targets ablatively accelerated by the Nike KrF laser. A spherically curved quartz crystal (d = .?, R = mm) has been used to produce monochromatic backlit images with the He-like Si resonance line (1865 eV) as the source of radiation. The spatial resolution of the x-ray optical system is 1.7 mum in selected places and 2-3 mum over a larger area. Time-resolved backlit monochromatic images of polystyrene planar targets driven by the Nike facility have been obtained with a spatial resolution of 2.5 mum in selected places and 5 mum over the focal spot of the Nike laser.

The efficacy of selective calculus ablation at 400 nm: comparison to conventional calculus removal methods

NASA Astrophysics Data System (ADS)

Schoenly, Joshua E.; Seka, Wolf; Romanos, Georgios; Rechmann, Peter

A desired outcome of scaling and root planing is the complete removal of calculus and infected root tissue and preservation of healthy cementum for rapid healing of periodontal tissues. Conventional periodontal treatments for calculus removal, such as hand instrument scaling and ultrasonic scaling, often deeply scrape the surface of the underlying hard tissue and may leave behind a smear layer. Pulsed lasers emitting at violet wavelengths (specifically, 380 to 400 nm) are a potential alternative treatment since they can selectively ablate dental calculus without ablating pristine hard tissue (i.e., enamel, cementum, and dentin). In this study, light and scanning electron microscopy are used to compare and contrast the efficacy of in vitro calculus removal for several conventional periodontal treatments (hand instruments, ultrasonic scaler, and Er:YAG laser) to calculus removal with a frequency-doubled Ti:sapphire (λ = 400 nm). After calculus removal, enamel and cementum surfaces are investigated for calculus debris and damage to the underlying hard tissue surface. Compared to the smear layer, grooves, and unintentional hard tissue removal typically found using these conventional treatments, calculus removal using the 400-nm laser is complete and selective without any removal of pristine dental hard tissue. Based on these results, selective ablation from the 400-nm laser appears to produce a root surface that would be more suitable for successful healing of periodontal tissues.

Coupling of metal-organic frameworks-containing monolithic capillary-based selective enrichment with matrix-assisted laser desorption ionization-time-of-flight mass spectrometry for efficient analysis of protein phosphorylation.

PubMed

Li, Daojin; Yin, Danyang; Chen, Yang; Liu, Zhen

2017-05-19

Protein phosphorylation is a major post-translational modification, which plays a vital role in cellular signaling of numerous biological processes. Mass spectrometry (MS) has been an essential tool for the analysis of protein phosphorylation, for which it is a key step to selectively enrich phosphopeptides from complex biological samples. In this study, metal-organic frameworks (MOFs)-based monolithic capillary has been successfully prepared as an effective sorbent for the selective enrichment of phosphopeptides and has been off-line coupled with matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) for efficient analysis of phosphopeptides. Using š-casein as a representative phosphoprotein, efficient phosphorylation analysis by this off-line platform was verified. Phosphorylation analysis of a nonfat milk sample was also demonstrated. Through introducing large surface areas and highly ordered pores of MOFs into monolithic column, the MOFs-based monolithic capillary exhibited several significant advantages, such as excellent selectivity toward phosphopeptides, superb tolerance to interference and simple operation procedure. Because of these highly desirable properties, the MOFs-based monolithic capillary could be a useful tool for protein phosphorylation analysis. Copyright © 2016 Elsevier B.V. All rights reserved.

LIBS spectra of multi-component Al, Fe, Cu alloys and composite materials used for selected elements of armament and munition

NASA Astrophysics Data System (ADS)

Ostrowski, R.; Skrzeczanowski, W.; Rycyk, A.; CzyŻ, K.; Sarzyński, A.; Strzelec, M.; Jach, K.; Świerczyński, R.

2017-10-01

Spectral investigations in the UV-VIS range of selected Al, Cu, and Fe alloys and composite materials were performed using LIBS technique. The investigated objects were typical rifle cartridges, mortars, rocket launchers and samples of different type steel, Cu and Al alloys, as well as composite materials of special chemical composition. Two Nd:YAG lasers were applied: a short 4 ns, 60 mJ Brio Quantel/BigSky laser (1064 nm) and a long pulse 200/400 (up to 1000) µs ({ 2/4 up to 10 J) laser (1064 nm) constructed at the Institute of Optoelectronics MUT. This spectrochemical analysis was possible for Al, Cu, and Fe alloys objects for both lasers, and in case of composites only if the samples were irradiated by short laser pulse since in the experiment with the long pulse, all composite materials spectra, in general, were very similar to each other - they imitated a grey/black body spectra. For metal alloys in experiments with a short laser pulse only atomic spectra were observed while for long microsecond laser pulses molecular transitions have been registered for Al alloys. Electron temperatures of plasma created on different materials for short and long laser pulses were found on the base of Boltzmann plots. Temperatures are clearly higher for plasmas generated with a short laser pulse which results from much higher laser power density on the sample surface for short pulse and not from fluence which is 20-40 times larger for long pulse.

Investigation of the High-Cycle Fatigue Life of Selective Laser Melted and Hot Isostatically Pressed Ti-6Al-4v

DTIC Science & Technology

2015-03-26

INVESTIGATION OF THE HIGH -CYCLE FATIGUE LIFE OF SELECTIVE LASER MELTED AND HOT ISOSTATICALLY PRESSED TI-6AL-4V THESIS Kevin D. Rekedal...ENY-MS-15-M-212 INVESTIGATION OF THE HIGH -CYCLE FATIGUE LIFE OF SELECTIVE LASER MELTED AND HOT ISOSTATICALLY PRESSED TI-6AL-4V THESIS...AFIT-ENY-MS-15-M-212 INVESTIGATION OF THE HIGH -CYCLE FATIGUE LIFE OF SELECTIVE LASER MELTED AND HOT ISOSTATICALLY PRESSED TI-6AL-4V

Theory and simulation of multi-channel interference (MCI) widely tunable lasers.

PubMed

Chen, Quanan; Lu, Qiaoyin; Guo, Weihua

2015-07-13

A novel design of an InP-based monolithic widely tunable laser, multi-channel interference (MCI) laser, is proposed and presented for the first time. The device is comprised of a gain section, a common phase section and a multi-channel interference section. The multi-channel interference section contains a 1x8 splitter based on cascaded 1 × 2 multi-mode interferometers (MMIs) and eight arms with unequal length difference. The rear part of each arm is integrated with a one-port multi-mode interference reflector (MIR). Mode selection of the MCI laser is realized by the constructive interference of the lights reflected back by the eight arms. Through optimizing the arm length difference, a tuning range of more than 40 nm covering the whole C band, a threshold current around 11.5 mA and an side-mode-suppression-ratio (SMSR) up to 48 dB have been predicted for this widely tunable laser. Detailed design principle and numerical simulation results are presented.

Quantum entanglement in strong-field ionization

NASA Astrophysics Data System (ADS)

Majorosi, Szilárd; Benedict, Mihály G.; Czirják, Attila

2017-10-01

We investigate the time evolution of quantum entanglement between an electron, liberated by a strong few-cycle laser pulse, and its parent ion core. Since the standard procedure is numerically prohibitive in this case, we propose a method to quantify the quantum correlation in such a system: we use the reduced density matrices of the directional subspaces along the polarization of the laser pulse and along the transverse directions as building blocks for an approximate entanglement entropy. We present our results, based on accurate numerical simulations, in terms of several of these entropies, for selected values of the peak electric-field strength and the carrier-envelope phase difference of the laser pulse. The time evolution of the mutual entropy of the electron and the ion-core motion along the direction of the laser polarization is similar to our earlier results based on a simple one-dimensional model. However, taking into account also the dynamics perpendicular to the laser polarization reveals a surprisingly different entanglement dynamics above the laser intensity range corresponding to pure tunneling: the quantum entanglement decreases with time in the over-the-barrier ionization regime.

Tunable and switchable dual-wavelength single polarization narrow linewidth SLM erbium-doped fiber laser based on a PM-CMFBG filter.

PubMed

Yin, Bin; Feng, Suchun; Liu, Zhibo; Bai, Yunlong; Jian, Shuisheng

2014-09-22

A tunable and switchable dual-wavelength single polarization narrow linewidth single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser based on polarization-maintaining chirped moiré fiber Bragg grating (PM-CMFBG) filter is proposed and demonstrated. For the first time as we know, the CMFBG inscribed on the PM fiber is applied for the wavelength-tunable and-switchable dual-wavelength laser. The PM-CMFBG filter with ultra-narrow transmission band (0.1 pm) and a uniform polarization-maintaining fiber Bragg grating (PM-FBG) are used to select the laser longitudinal mode. The stable single polarization SLM operation is guaranteed by the PM-CMFBG filter and polarization controller. A tuning range of about 0.25 nm with about 0.075 nm step is achieved by stretching the uniform PM-FBG. Meanwhile, the linewidth of the fiber laser for each wavelength is approximate 6.5 and 7.1 kHz with a 20 dB linewidth, which indicates the laser linewidth is approximate 325 Hz and 355 Hz FWHM.

Comparative study of DPAL and XPAL systems and selection principal of parameters

NASA Astrophysics Data System (ADS)

Huang, Wei; Tan, Rongqing; Li, Zhiyong; Han, Gaoce; Li, Hui

2016-10-01

A theoretical model based on common pump structure is proposed to analyze the laser output characteristics of DPAL (Diode pumped alkali vapor laser) and XPAL (Exciplex pumped alkali laser) in this paper. The model predicts that an optical-to-optical efficiency approaching 80% can be achieved for continuous-wave four- and five-XPAL systems with broadband pumping which is several times of pumped linewidth for DPAL. Operation parameters including pumped intensity, temperature, cell' s length, mixed gas concentration, pumped linewidth and output mirror reflectivity are analyzed for DPAL and XPAL systems basing on the kinetic model. The result shows a better performance in Cs-Ar XPAL laser with requirements of relatively high Ar concentration, high pumped intensity and high temperature. Comparatively, for Cs-DPAL laser, lower temperature and lower pumped intensity should be acquired. In addition, the predictions of selection principal of temperature and cell's length are also presented. The conception of the equivalent "alkali areal density" is proposed in this paper. It is defined as the product of the alkali density and cell's length. The result shows that the output characteristics of DPAL (or XPAL) system with the same alkali areal density but different temperatures turn out to be equal. It is the areal density that reflects the potential of DPAL or XPAL systems directly. A more detailed analysis of similar influences of cavity parameters with the same areal density is also presented. The detailed results of continuous-wave DPAL and XPAL performances as a function of pumped laser linewidth and mixed gas pressure are presented along with an analysis of influences of output coupler.

A new method of building footprints detection using airborne laser scanning data and multispectral image

NASA Astrophysics Data System (ADS)

Luo, Yiping; Jiang, Ting; Gao, Shengli; Wang, Xin

2010-10-01

It presents a new approach for detecting building footprints in a combination of registered aerial image with multispectral bands and airborne laser scanning data synchronously obtained by Leica-Geosystems ALS40 and Applanix DACS-301 on the same platform. A two-step method for building detection was presented consisting of selecting 'building' candidate points and then classifying candidate points. A digital surface model(DSM) derived from last pulse laser scanning data was first filtered and the laser points were classified into classes 'ground' and 'building or tree' based on mathematic morphological filter. Then, 'ground' points were resample into digital elevation model(DEM), and a Normalized DSM(nDSM) was generated from DEM and DSM. The candidate points were selected from 'building or tree' points by height value and area threshold in nDSM. The candidate points were further classified into building points and tree points by using the support vector machines(SVM) classification method. Two classification tests were carried out using features only from laser scanning data and associated features from two input data sources. The features included height, height finite difference, RGB bands value, and so on. The RGB value of points was acquired by matching laser scanning data and image using collinear equation. The features of training points were presented as input data for SVM classification method, and cross validation was used to select best classification parameters. The determinant function could be constructed by the classification parameters and the class of candidate points was determined by determinant function. The result showed that associated features from two input data sources were superior to features only from laser scanning data. The accuracy of more than 90% was achieved for buildings in first kind of features.

Numerical investigation of vessel heating using a copper vapor laser and a pulsed dye laser in treating vascular skin lesions

NASA Astrophysics Data System (ADS)

Pushkareva, A. E.; Ponomarev, I. V.; Isaev, A. A.; Klyuchareva, S. V.

2018-02-01

A computer simulation technique was employed to study the selective heating of a tissue vessel using emission from a pulsed copper vapor laser and a pulsed dye laser. The depth and size of vessels that could be selectively and safely removed were determined for the lasers under examination.

Application of tissue mesodissection to molecular cancer diagnostics.

PubMed

Krizman, David; Adey, Nils; Parry, Robert

2015-02-01

To demonstrate clinical application of a mesodissection platform that was developed to combine advantages of laser-based instrumentation with the speed/ease of manual dissection for automated dissection of tissue off standard glass slides. Genomic analysis for KRAS gene mutation was performed on formalin fixed paraffin embedded (FFPE) cancer patient tissue that was dissected using the mesodissection platform. Selected reaction monitoring proteomic analysis for quantitative Her2 protein expression was performed on FFPE patient tumour tissue dissected by a laser-based instrument and the MilliSect instrument. Genomic analysis demonstrates highly confident detection of KRAS mutation specifically in lung cancer cells and not the surrounding benign, non-tumour tissue. Proteomic analysis demonstrates Her2 quantitative protein expression in breast cancer cells dissected manually, by laser-based instrumentation and by MilliSect instrumentation (mesodissection). Slide-mounted tissue dissection is commonly performed using laser-based instruments or manually scraping tissue by scalpel. Here we demonstrate that the mesodissection platform as performed by the MilliSect instrument for tissue dissection is cost-effective; it functions comparably to laser-based dissection and which can be adopted into a clinical diagnostic workflow. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Multifunctional gold nanorods for selective plasmonic photothermal therapy in pancreatic cancer cells using ultra-short pulse near-infrared laser irradiation

NASA Astrophysics Data System (ADS)

Patino, Tania; Mahajan, Ujjwal; Palankar, Raghavendra; Medvedev, Nikolay; Walowski, Jakob; Münzenberg, Markus; Mayerle, Julia; Delcea, Mihaela

2015-03-01

Gold nanorods (AuNRs) have attracted considerable attention in plasmonic photothermal therapy for cancer treatment by exploiting their selective and localized heating effect due to their unique photophysical properties. Here we describe a strategy to design a novel multifunctional platform based on AuNRs to: (i) specifically target the adenocarcinoma MUC-1 marker through the use of the EPPT-1 peptide, (ii) enhance cellular uptake through a myristoylated polyarginine peptide (MPAP) and (iii) selectively induce cell death by ultra-short near infrared laser pulses. We used a biotin-avidin based approach to conjugate EPPT-1 and MPAP to AuNRs. Dual-peptide (EPPT-1 + MPAP) labelled AuNRs showed a significantly higher uptake by pancreatic ductal adenocarcinoma cells when compared to their single peptide or avidin conjugated counterparts. In addition, we selectively induced cell death by ultra-short near infrared laser pulses in small target volumes (~1 μm3), through the creation of plasmonic nanobubbles that lead to the destruction of a local cell environment. Our approach opens new avenues for conjugation of multiple ligands on AuNRs targeting cancer cells and tumors and it is relevant for plasmonic photothermal therapy.Gold nanorods (AuNRs) have attracted considerable attention in plasmonic photothermal therapy for cancer treatment by exploiting their selective and localized heating effect due to their unique photophysical properties. Here we describe a strategy to design a novel multifunctional platform based on AuNRs to: (i) specifically target the adenocarcinoma MUC-1 marker through the use of the EPPT-1 peptide, (ii) enhance cellular uptake through a myristoylated polyarginine peptide (MPAP) and (iii) selectively induce cell death by ultra-short near infrared laser pulses. We used a biotin-avidin based approach to conjugate EPPT-1 and MPAP to AuNRs. Dual-peptide (EPPT-1 + MPAP) labelled AuNRs showed a significantly higher uptake by pancreatic ductal adenocarcinoma cells when compared to their single peptide or avidin conjugated counterparts. In addition, we selectively induced cell death by ultra-short near infrared laser pulses in small target volumes (~1 μm3), through the creation of plasmonic nanobubbles that lead to the destruction of a local cell environment. Our approach opens new avenues for conjugation of multiple ligands on AuNRs targeting cancer cells and tumors and it is relevant for plasmonic photothermal therapy. Electronic supplementary information (ESI) available: Size distribution histograms of the hydrodynamic diameter and ζ-potential of functionalized and CTAB stabilized AuNRs. Characterization of TR-AV functionalized AuNRs after 48 h at 4 °C. The ζ-potential of TR-AV functionalized AuNRs and CTAB stabilized AuNRs. The ζ-potential of peptide-conjugated AuNRs in water. See DOI: 10.1039/c5nr00114e

Microstructure of selective laser melted CM247LC nickel-based superalloy and its evolution through heat treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Divya, V.D., E-mail: dv272@cam.ac.uk; Muñoz-Moreno, R.; Messé, O.M.D.M.

2016-04-15

The selective laser melting of high temperature alloys is of great interest to the aerospace industry as it offers the prospect of producing more complex geometries than can be achieved with other manufacturing methods. In this study, the microstructure of the nickel-based superalloy, CM247LC, has been characterised following selective laser melting and after a post deposition heat treatment below the γ′ solvus temperature. In the as-deposited state, scanning electron microscopy with electron backscatter diffraction revealed a fine, cellular microstructure with preferential alignment of 〈001〉 along the build direction. A high dislocation density was seen at the periphery of the cells,more » indicating substantial localised deformation of the material. Fine primary MC carbides were also observed in the inter-cellular regions. High-resolution transmission electron microscopy identified the occurrence of very fine γ′ precipitates, approximately 5 nm in diameter, dispersed within the gamma phase. After heat treatment, the elongated cell colonies were observed to partially coalesce, accompanied by a decrease in dislocation density, producing columnar grains along the build direction. Cuboidal γ′ precipitates approximately 500 nm in diameter were observed to form in the recrystallised grains, accompanied by larger γ′ precipitates on the grain boundaries.« less

Strained-layer indium gallium arsenide-gallium arsenide- aluminum galium arsenide photonic devices by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Osowski, Mark Louis

With the arrival of advanced growth technologies such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD), research in III-V compound semiconductor photonic devices has flourished. Advances in fabrication processes have allowed the realization of high-performance quantum well lasers which emit over a wide spectral range and operate with low threshold currents. As a result, semiconductor lasers are presently employed in a wide variety of applications, including fiber-optic telecommunications, optical spectroscopy, solid-state laser pumping, and photonic integrated circuits. The work in this dissertation addresses three photonic device structures which are currently receiving a great deal of attention in the research community: integrable quantum well laser devices, distributed feedback (DFB) laser devices, and quantum wire arrays. For the realization of the integrable and integrated photonic devices described-in Chapter 2, a three-step selective-area growth technique was utilized. The selective epitaxy process was used to produce discrete buried-heterostructure Fabry Perot lasers with threshold currents as low as 2.6 mA. Based on this process, broad- spectrum edge-emitting superluminescent diodes are demonstrated which display spectral widths of over 80 nm. In addition, the monolithic integration of a multiwavelength emitter is demonstrated in which two distinct laser sources are coupled into a single output waveguide. The dissertation also describes the development of a single-growth-step ridge waveguide DFB laser. The DFB laser utilizes an asymmetric cladding waveguide structure to enhance the interaction of the optical mode with the titanium surface metal to promote single frequency emission via gain coupling. These lasers exhibit low threshold currents (11 mA), high side mode suppression ratios (50 dB), and narrow linewidths (45 kHz). In light of the substantial performance advantages of quantum well lasers relative to double heterostructure lasers, extensive efforts have been directed toward producing quantum wire systems. In view of this, the final subject of this dissertation details the fabrication and characterization of quantum wire arrays by selective-area MOCVD. The method employs a silicon dioxide grating mask with sub-micron oxide dimensions to achieve selective deposition of high-quality buried layers in the open areas of the patterned substrate. This allows the fabrication of embedded nanostructures in a single growth step, and the crystallographic nature of the growth allows for control of their lateral size. Using this process, the growth of strained InGaAs wires with a lateral dimension of less than 50 nm are obtained. Subsequent characterization by photoluminescence, scanning electron microscopy and transmission electron microscopy is also presented.

In-situ formation of Ni4Ti3 precipitate and its effect on pseudoelasticity in selective laser melting additive manufactured NiTi-based composites

NASA Astrophysics Data System (ADS)

Gu, Dongdong; Ma, Chenglong

2018-05-01

Selective laser melting (SLM) additive manufacturing technology was applied to synthesize NiTi-based composites via using ball-milled Ti, Ni, and TiC mixed powder. By transmission electron microscope (TEM) characterization, it indicated that the B2 (NiTi) matrix was obtained during SLM processing. In spite of more Ti content (the Ti/Ni ratio >1), a mass of Ni-rich intermetallic compounds containing Ni4Ti3 with nanostructure features and eutectic Ni3Ti around in-situ Ti6C3.75 dendrites were precipitated. Influence of the applied laser volume energy density (VED) on the morphology and content of Ni4Ti3 precipitate was investigated. Besides, nanoindentation test of the matrix was performed in order to assess pseudoelastic recovery behavior of SLM processed NiTi-based composites. At a relatively high VED of 533 J/mm3, the maximum pseudoelastic recovery was obtained due to the lowest content of Ni4Ti3 precipitates. Furthermore, the precipitation mechanism of in-situ Ni4Ti3 was present based on the redistribution of titanium element and thermodynamics analysis, and then the relationship of Ni4Ti3 precipitate, VED and pseudoelastic recovery behavior was also revealed.

Laser particle sorter

DOEpatents

Martin, J.C.; Buican, T.N.

1987-11-30

Method and apparatus are provided for sorting particles, such as biological particles. A first laser is used to define an optical path having an intensity gradient which is effective to propel the particles along the path but which is sufficiently weak that the particles are not trapped in an axial direction. A probe laser beam is provided for interrogating the particles to identify predetermined phenotypical characteristics of the particles. A second laser beam is provided to intersect the driving first laser beam, wherein the second laser beam is activated by an output signal indicative of a predetermined characteristic. The second laser beam is switchable between a first intensity and a second intensity, where the first intensity is effective to displace selected particles from the driving laser beam and the second intensity is effective to propel selected particles along the deflection laser beam. The selected particles may then be propelled by the deflection beam to a location effective for further analysis. 2 figs.

Laser particle sorter

DOEpatents

Martin, John C.; Buican, Tudor N.

1989-01-01

Method and apparatus for sorting particles, such as biological particles. A first laser defines an optical path having an intensity gradient which is effective to propel the particles along the path but which is sufficiently weak that the particles are not trapped in an axial direction. A probe laser beam interrogates the particles to identify predetermined phenotypical characteristics of the particles. A second laser beam intersects the driving first laser beam, wherein the second laser beam is activated by an output signal indicative of a predetermined characteristic. The second laser beam is switchable between a first intensity and a second intensity, where the first intensity is effective to displace selected particles from the driving laser beam and the second intensity is effective to propel selected particles along the deflection laser beam. The selected particles may then be propelled by the deflection beam to a location effective for further analysis.

Threshold parameters of the mechanisms of selective nanophotothermolysis with gold nanoparticles

NASA Astrophysics Data System (ADS)

Pustovalov, Victor; Zharov, Vladimir

2008-02-01

Photothermal-based effects in and around gold nanoparticles under action of short (nano, pico- and femtosecond) laser pulses are analyzed with focus on photoacoustic effects due to the thermal expansion of nanoparticles and liquid around them, thermal protein denaturation, explosive liquid vaporization, melting and evaporation of nanoparticle, optical breakdown initiated by nanoparticles and accompanied to shock waves and explosion (fragmentation) of gold nanoparticles. Characteristic parameters for these processes such as the temperature and laser intensity thresholds are summarized to provide basis for comparison of different mechanisms of selective nanophotothermolysis of different targets (e.g., cancer cells, bacteria, viruses, fungi, and helminths).

Database for LDV Signal Processor Performance Analysis

NASA Technical Reports Server (NTRS)

Baker, Glenn D.; Murphy, R. Jay; Meyers, James F.

1989-01-01

A comparative and quantitative analysis of various laser velocimeter signal processors is difficult because standards for characterizing signal bursts have not been established. This leaves the researcher to select a signal processor based only on manufacturers' claims without the benefit of direct comparison. The present paper proposes the use of a database of digitized signal bursts obtained from a laser velocimeter under various configurations as a method for directly comparing signal processors.

Thermal Model of Laser-Induced Eye Damage

DTIC Science & Technology

1974-10-08

Identify by. block ntber) Ocular Damage Laser Effect3 Thermal Model Temperature Rise Prediction Retinal, Corneal, Lenticular Damage 20. ABSTR ACT (CoIfn...routine available to predict retinal or lenticular beam characteristics based on beam de- scripton at the cornea and distance of the last beam waist 5...used are selected for minimal aberrations of the astigmatic kind and that coma is negligible because of nearly axial "illumination. Secondly, the thermal

Nanoparticle Selective Laser Processing for a Flexible Display Fabrication

NASA Astrophysics Data System (ADS)

Seung Hwan Ko,; Heng Pan,; Daeho Lee,; Costas P. Grigoropoulos,; Hee K. Park,

2010-05-01

To demonstrate a first step for a novel fabrication method of a flexible display, nanomaterial based laser processing schemes to demonstrate organic light emitting diode (OLED) pixel transfer and organic field effect transistor (OFET) fabrication on a polymer substrate without using any conventional vacuum or photolithography processes were developed. The unique properties of nanomaterials allow laser induced forward transfer of organic light emitting material at low laser energy while maintaining good fluorescence and also allow high resolution transistor electrode patterning at plastic compatible low temperature. These novel processes enable an environmentally friendly and cost effective process as well as a low temperature manufacturing sequence to realize inexpensive, large area, flexible electronics on polymer substrates.

Layered surface structure of gas-atomized high Nb-containing TiAl powder and its impact on laser energy absorption for selective laser melting

NASA Astrophysics Data System (ADS)

Zhou, Y. H.; Lin, S. F.; Hou, Y. H.; Wang, D. W.; Zhou, P.; Han, P. L.; Li, Y. L.; Yan, M.

2018-05-01

Ti45Al8Nb alloy (in at.%) is designed to be an important high-temperature material. However, its fabrication through laser-based additive manufacturing is difficult to achieve. We present here that a good understanding of the surface structure of raw material (i.e. Ti45Al8Nb powder) is important for optimizing its process by selective laser melting (SLM). Detailed X-ray photoelectron spectroscopy (XPS) depth profiling and transmission electron microscopy (TEM) analyses were conducted to determine the surface structure of Ti45Al8Nb powder. An envelope structure (∼54.0 nm in thickness) was revealed for the powder, consisting of TiO2 + Nb2O5 (as the outer surface layer)/Al2O3 + Nb2O5 (as the intermediate layer)/Al2O3 (as the inner surface layer)/Ti45Al8Nb (as the matrix). During SLM, this layered surface structure interacted with the incident laser beam and improved the laser absorptivity of Ti45Al8Nb powder by ∼32.21%. SLM experiments demonstrate that the relative density of the as-printed parts can be realized to a high degree (∼98.70%), which confirms good laser energy absorption. Such layered surface structure with appropriate phase constitution is essential for promoting SLM of the Ti45Al8Nb alloy.

Compact Mach-Zehnder interferometer based on photonic crystal fiber and its application in switchable multi-wavelength fiber laser

NASA Astrophysics Data System (ADS)

Chen, Weiguo; Lou, Shuqin; Wang, Liwen; Li, Honglei; Guo, Tieying; Jian, Shuisheng

2009-08-01

The compact Mach-Zehnder interferometer is proposed by splicing a section of photonic crystal fiber (PCF) and two pieces of single mode fiber (SMF) with the air-holes of PCF intentionally collapsed in the vicinity of the splices. The depedence of the fringe spacing on the length of PCF is investigated. Based on the Mach-Zehnder interferometer as wavelength-selective filter, a switchable dual-wavelength fiber ring laser is demonstrated with a homemade erbiumdoped fiber amplifier (EDFA) as the gain medium at room temperature. By adjusting the states of the polarization controller (PC) appropriately, the laser can be switched among the stable single-and dual -wavelength lasing operations by exploiting polarization hole burning (PHB) effect.

Determination of phosphorus in steel by the combined technique of laser induced breakdown spectrometry with laser induced fluorescence spectrometry

NASA Astrophysics Data System (ADS)

Kondo, Hiroyuki; Hamada, Naoya; Wagatsuma, Kazuaki

2009-09-01

Laser induced breakdown spectrometry (LIBS) combined with laser induced fluorescence spectrometry (LIFS) has been applied for detection of trace-level phosphorus in steel. The plasma induced by irradiation of Nd:YAG laser pulse for ablation was illuminated by the 3rd harmonic of Ti:Sapphire laser tuned to one of the resonant lines for phosphorus in the wavelength region of 253-256 nm. An excitation line for phosphorus was selected to give the highest signal-to-noise ratio. Fluorescence signals, P213.62 and P214.91 nm, were observed with high selectivity at the contents as low as several tens µg g - 1 . Fluorescence intensities were in a good linear correlation with the contents. Fluorescence intensity ratio of a collisionally assisted line (213.62 nm) to a direct transition line (214.91 nm) was discussed in terms of the analytical conditions and experimental results were compared with a calculation based on rate equations. Since the fluorescence signal light in the wavelength range longer than 200 nm can be transmitted relatively easily, even through fiber optics of moderate length, LIBS/LIFS would be a versatile technique in on-site applications for the monitoring of phosphorus contents in steel.

Nd:YOV4 laser surface texturing on DLC coating: Effect on morphology, adhesion, and dry wear behavior

NASA Astrophysics Data System (ADS)

Surfaro, Maria; Giorleo, Luca; Montesano, Lorenzo; Allegri, Gabriele; Ceretti, Elisabetta; La Vecchia, Giovina Marina

2018-05-01

The surface of structural components is usually subjected to higher stresses, greater wear or fatigue damage, and more direct environmental exposure than the inner parts. For this reason, the interest to improve superficial properties of items is constantly increasing in different fields as automotive, electronic, biomedical, etc. Different approaches can be used to achieve this goal: case hardening by means of superficial heat treatments like carburizing or nitriding, deposition of thin or thick coatings, roughness modification, etc. Between the available technologies to modify components surface, Laser Surface Texturing (LST) has already been recognized in the last decade as a process, which improves the tribological properties of various parts. Based on these considerations the aim of the present research work was to realize a controlled laser texture on a Diamond-like Carbon (DLC) thin coating (about 3 µm thick) without damaging both the coating itself and the substrate. In particular, the effect of laser process parameters as marking speed and loop cycle were investigated in terms of texture features modifications. Both qualitative and quantitative analyses of the texture were executed by using a scanning electron microscope and a laser probe system to select the proper laser parameters. Moreover, the effect of the selected texture on the DLC nanohardness, adhesion and wear behavior was pointed out.

Novel space-time trellis codes for free-space optical communications using transmit laser selection.

PubMed

García-Zambrana, Antonio; Boluda-Ruiz, Rubén; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

2015-09-21

In this paper, the deployment of novel space-time trellis codes (STTCs) with transmit laser selection (TLS) for free-space optical (FSO) communication systems using intensity modulation and direct detection (IM/DD) over atmospheric turbulence and misalignment fading channels is presented. Combining TLS and STTC with rate 1 bit/(s · Hz), a new code design criterion based on the use of the largest order statistics is here proposed for multiple-input/single-output (MISO) FSO systems in order to improve the diversity order gain by properly chosing the transmit lasers out of the available L lasers. Based on a pairwise error probability (PEP) analysis, closed-form asymptotic bit error-rate (BER) expressions in the range from low to high signal-to-noise ratio (SNR) are derived when the irradiance of the transmitted optical beam is susceptible to moderate-to-strong turbulence conditions, following a gamma-gamma (GG) distribution, and pointing error effects, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Obtained results show diversity orders of 2L and 3L when simple two-state and four-state STTCs are considered, respectively. Simulation results are further demonstrated to confirm the analytical results.

Laser-assisted selection and passaging of human pluripotent stem cell colonies.

PubMed

Terstegge, Stefanie; Rath, Barbara H; Laufenberg, Iris; Limbach, Nina; Buchstaller, Andrea; Schütze, Karin; Brüstle, Oliver

2009-09-10

The derivation of somatic cell products from human embryonic stem cells (hESCs) requires a highly standardized production process with sufficient throughput. To date, the most common technique for hESC passaging is the manual dissection of colonies, which is a gentle, but laborious and time-consuming process and is consequently inappropriate for standardized maintenance of hESC. Here, we present a laser-based technique for the contact-free dissection and isolation of living hESCs (laser microdissection and pressure catapulting, LMPC). Following LMPC treatment, 80.6+/-8.7% of the cells remained viable as compared to 88.6+/-1.7% of manually dissected hESCs. Furthermore, there was no significant difference in the expression of pluripotency-associated markers when compared to the control. Flow cytometry revealed that 83.8+/-4.1% of hESCs isolated by LMPC expressed the surface marker Tra-1-60 (control: 83.9+/-3.6%). In vitro differentiation potential of LMPC treated hESCs as determined by embryoid body formation and multi-germlayer formation was not impaired. Moreover, we could not detect any overt karyotype alterations as a result of the LMPC process. Our data demonstrate the feasibility of standardized laser-based passaging of hESC cultures. This technology should facilitate both colony selection and maintenance culture of pluripotent stem cells.

Acousto-Optic Q-Switched Fiber Laser-Based Intra-Cavity Photoacoustic Spectroscopy for Trace Gas Detection

PubMed Central

Zhang, Qinduan; Chang, Jun; Wang, Zongliang; Wang, Fupeng; Qin, Zengguang

2017-01-01

We proposed a new method for gas detection in photoacoustic spectroscopy based on acousto-optic Q-switched fiber laser by merging a transmission PAS cell (resonant frequency f0 = 5.3 kHz) inside the fiber laser cavity. The Q-switching was achieved by an acousto-optic modulator, achieving a peak pulse power of ~679 mW in the case of the acousto-optic modulation signal with an optimized duty ratio of 10%. We used a custom-made fiber Bragg grating with a central wavelength of 1530.37 nm (the absorption peak of C2H2) to select the laser wavelength. The system achieved a linear response (R2 = 0.9941) in a concentration range from 400 to 7000 ppmv, and the minimum detection limit compared to that of a conventional intensity modulation system was enhanced by 94.2 times. PMID:29295599

High-speed laser anemometry based on spectrally resolved Rayleigh scattering

NASA Technical Reports Server (NTRS)

Seasholtz, Richard G.

1991-01-01

Laser anemometry in unseeded flows based on the measurement of the spectrum of Rayleigh scattered laser light is reviewed. The use of molecular scattering avoids the well known problems (particle lag, biasing effects, seed generation, seed injection) of seeded flows. The fundamental limits on velocity measurement accuracy are determined using maximum likelihood methods. Measurement of the Rayleigh spectrum with scanning Fabry-Perot interferometers is analyzed and accuracy limits are established for both single pass and multipass configurations. Multipass configurations have much higher selectivity and are needed for measurements where there is a large amount of excess noise caused by stray laser light. It is shown that Rayleigh scattering is particularly useful for supersonic and hypersonic flows. The results of the analysis are compared with measurements obtained with a Rayleigh scattering diagnostic developed for study of the exhaust plume of a small hydrogen-oxygen rocket, where the velocities are in the range of 1000 to 5000 m/sec.

Humidity sensor based on intracavity sensing of fiber ring laser

NASA Astrophysics Data System (ADS)

Shi, Jia; Xu, Wei; Xu, Degang; Wang, Yuye; Zhang, Chao; Yan, Chao; Yan, Dexian; He, Yixin; Tang, Longhuang; Zhang, Weihong; Yao, Jianquan

2017-10-01

A humidity sensor based on the intracavity sensing of a fiber ring laser is proposed and experimentally demonstrated. In the fiber ring laser, a humidity-sensitive fiber-optic multimode interferometer (MMI), fabricated by the single-mode-no-core-single-mode (SNCS) fiber coated with Agarose, works as the wavelength-selective filter for intracavity wavelength-modulated humidity sensing. The experiment shows that the lasing wavelength of the fiber laser has a good linear response to ambient humidity from 35%RH to 95%RH. The humidity sensitivity of -68 pm/%RH is obtained with a narrow 3 dB bandwidth less than 0.09 nm and a high signal-to-noise ratio (SNR)  ˜60 dB. The time response of the sensor has been measured to be as fast as 93 ms. The proposed sensor possesses a good stability and low temperature cross-sensitivity.

Expression microdissection adapted to commercial laser dissection instruments

PubMed Central

Hanson, Jeffrey C; Tangrea, Michael A; Kim, Skye; Armani, Michael D; Pohida, Thomas J; Bonner, Robert F; Rodriguez-Canales, Jaime; Emmert-Buck, Michael R

2016-01-01

Laser-based microdissection facilitates the isolation of specific cell populations from clinical or animal model tissue specimens for molecular analysis. Expression microdissection (xMD) is a second-generation technology that offers considerable advantages in dissection capabilities; however, until recently the method has not been accessible to investigators. This protocol describes the adaptation of xMD to commonly used laser microdissection instruments and to a commercially available handheld laser device in order to make the technique widely available to the biomedical research community. The method improves dissection speed for many applications by using a targeting probe for cell procurement in place of an operator-based, cell-by-cell selection process. Moreover, xMD can provide improved dissection precision because of the unique characteristics of film activation. The time to complete the protocol is highly dependent on the target cell population and the number of cells needed for subsequent molecular analysis. PMID:21412274

Acousto-Optic Q-Switched Fiber Laser-Based Intra-Cavity Photoacoustic Spectroscopy for Trace Gas Detection.

PubMed

Zhang, Qinduan; Chang, Jun; Wang, Qiang; Wang, Zongliang; Wang, Fupeng; Qin, Zengguang

2017-12-25

We proposed a new method for gas detection in photoacoustic spectroscopy based on acousto-optic Q-switched fiber laser by merging a transmission PAS cell (resonant frequency f ₀ = 5.3 kHz) inside the fiber laser cavity. The Q-switching was achieved by an acousto-optic modulator, achieving a peak pulse power of ~679 mW in the case of the acousto-optic modulation signal with an optimized duty ratio of 10%. We used a custom-made fiber Bragg grating with a central wavelength of 1530.37 nm (the absorption peak of C₂H₂) to select the laser wavelength. The system achieved a linear response (R² = 0.9941) in a concentration range from 400 to 7000 ppmv, and the minimum detection limit compared to that of a conventional intensity modulation system was enhanced by 94.2 times.

Low-photon-number optical switch and AND/OR logic gates based on quantum dot-bimodal cavity coupling system.

PubMed

Ma, Shen; Ye, Han; Yu, Zhong-Yuan; Zhang, Wen; Peng, Yi-Wei; Cheng, Xiang; Liu, Yu-Min

2016-01-11

We propose a new scheme based on quantum dot-bimodal cavity coupling system to realize all-optical switch and logic gates in low-photon-number regime. Suppression of mode transmission due to the destructive interference effect is theoretically demonstrated by driving the cavity with two orthogonally polarized pulsed lasers at certain pulse delay. The transmitted mode can be selected by designing laser pulse sequence. The optical switch with high on-off ratio emerges when considering one driving laser as the control. Moreover, the AND/OR logic gates based on photon polarization are achieved by cascading the coupling system. Both proposed optical switch and logic gates work well in ultra-low energy magnitude. Our work may enable various applications of all-optical computing and quantum information processing.

Low-photon-number optical switch and AND/OR logic gates based on quantum dot-bimodal cavity coupling system

PubMed Central

Ma, Shen; Ye, Han; Yu, Zhong-Yuan; Zhang, Wen; Peng, Yi-Wei; Cheng, Xiang; Liu, Yu-Min

2016-01-01

We propose a new scheme based on quantum dot-bimodal cavity coupling system to realize all-optical switch and logic gates in low-photon-number regime. Suppression of mode transmission due to the destructive interference effect is theoretically demonstrated by driving the cavity with two orthogonally polarized pulsed lasers at certain pulse delay. The transmitted mode can be selected by designing laser pulse sequence. The optical switch with high on-off ratio emerges when considering one driving laser as the control. Moreover, the AND/OR logic gates based on photon polarization are achieved by cascading the coupling system. Both proposed optical switch and logic gates work well in ultra-low energy magnitude. Our work may enable various applications of all-optical computing and quantum information processing. PMID:26750557

Direct printing of microstructures by femtosecond laser excitation of nanocrystals in solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shou, Wan; Pan, Heng, E-mail: hp5c7@mst.edu

2016-05-23

We report direct printing of micro/sub-micron structures by femtosecond laser excitation of semiconductor nanocrystals (NCs) in solution. Laser excitation with moderate intensity (10{sup 11}–10{sup 12} W/cm{sup 2}) induces 2D and 3D deposition of CdTe nanocrystals in aqueous solution, which can be applied for direct printing of microstructures. It is believed that laser irradiation induces charge formation on nanocrystals leading to deposition. Furthermore, it is demonstrated that the charged nanocrystals can respond to external electrical bias, enabling a printing approach based on selective laser induced electrophoretic deposition. Finally, energy dispersive X-ray analysis of deposited structures shows oxidation occurs and deposited structure mainlymore » consists of Cd{sub x}O.« less

Organic holographic polymer dispersed liquid crystal distributed feedback laser from different diffraction orders

NASA Astrophysics Data System (ADS)

Liu, Minghuan; Liu, Yonggang; Zhang, Guiyang; Peng, Zenghui; Li, Dayu; Ma, Ji; Xuan, Li

2016-11-01

Holographic polymer dispersed liquid crystal (HPDLC) based distributed feedback (DFB) lasers were prepared with poly (-methoxy-5-(2‧-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) film as the active medium layer. The HPDLC grating film was fabricated via holographic induced photopolymerization. The pure film spectra of MEH-PPV and the amplified spontaneous emission (ASE) spectrum were investigated. The laser device was single-longitudinal mode operation. The tunability of the HPDLC DFB laser was achieved by selecting different grating periods. The lasing performances were also characterized and compared from different diffraction orders. The lasing threshold increased with the diffraction order and the third order laser possessed the largest conversion efficiency in this device. The experimental results were in good agreement with the theoretical calculations.

Online, efficient and precision laser profiling of bronze-bonded diamond grinding wheels based on a single-layer deep-cutting intermittent feeding method

NASA Astrophysics Data System (ADS)

Deng, Hui; Chen, Genyu; He, Jie; Zhou, Cong; Du, Han; Wang, Yanyi

2016-06-01

In this study, an online, efficient and precision laser profiling approach that is based on a single-layer deep-cutting intermittent feeding method is described. The effects of the laser cutting depth and the track-overlap ratio of the laser cutting on the efficiency, precision and quality of laser profiling were investigated. Experiments on the online profiling of bronze-bonded diamond grinding wheels were performed using a pulsed fiber laser. The results demonstrate that an increase in the laser cutting depth caused an increase in the material removal efficiency during the laser profiling process. However, the maximum laser profiling efficiency was only achieved when the laser cutting depth was equivalent to the initial surface contour error of the grinding wheel. In addition, the selection of relatively high track-overlap ratios of laser cutting for the profiling of grinding wheels was beneficial with respect to the increase in the precision of laser profiling, whereas the efficiency and quality of the laser profiling were not affected by the change in the track-overlap ratio. After optimized process parameters were employed for online laser profiling, the circular run-out error and the parallelism error of the grinding wheel surface decreased from 83.1 μm and 324.6 μm to 11.3 μm and 3.5 μm, respectively. The surface contour precision of the grinding wheel significantly improved. The highest surface contour precision for grinding wheels of the same type that can be theoretically achieved after laser profiling is completely dependent on the peak power density of the laser. The higher the laser peak power density is, the higher the surface contour precision of the grinding wheel after profiling.

Investigation into the influence of laser energy input on selective laser melted thin-walled parts by response surface method

NASA Astrophysics Data System (ADS)

Liu, Yang; Zhang, Jian; Pang, Zhicong; Wu, Weihui

2018-04-01

Selective laser melting (SLM) provides a feasible way for manufacturing of complex thin-walled parts directly, however, the energy input during SLM process, namely derived from the laser power, scanning speed, layer thickness and scanning space, etc. has great influence on the thin wall's qualities. The aim of this work is to relate the thin wall's parameters (responses), namely track width, surface roughness and hardness to the process parameters considered in this research (laser power, scanning speed and layer thickness) and to find out the optimal manufacturing conditions. Design of experiment (DoE) was used by implementing composite central design to achieve better manufacturing qualities. Mathematical models derived from the statistical analysis were used to establish the relationships between the process parameters and the responses. Also, the effects of process parameters on each response were determined. Then, a numerical optimization was performed to find out the optimal process set at which the quality features are at their desired values. Based on this study, the relationship between process parameters and SLMed thin-walled structure was revealed and thus, the corresponding optimal process parameters can be used to manufactured thin-walled parts with high quality.

Design, development, and field testing of Infrared Heterodyne Radiometer (IHR) for remote profiling of tropospheric and stratospheric species

NASA Technical Reports Server (NTRS)

Lange, R.; Savage, M.; Peyton, B.

1981-01-01

The performance of a dual-channel infrared heterodyne radiometer, designed to remotely monitor the concentration and vertical distribution of selected atmospheric species, is described. Ground based solar viewing measurement using the IHR were performed at selected laser transitions for ammonia (NH3 and ozone O3). Flight tests were conducted aboard the Galileo II, NASA Ames CV-990, on the Latitude Survey Mission. Ozone was the selected atmospheric species for the airborne flight measurements because of the scientific interest in this atmospheric species, the availability of in situ monitors, the coordinated ozone measurements, and the availability of ground truth data. The IHS was operated in the solar viewing mode to determine ozone distributions in the stratosphere and in the nadir viewing mode to determine the ozone distribution in the troposphere. Airborne atmospheric propagation measurements also were carried out at selected CO2 laser transitions.

Selective laser ablation of carious lesions using simultaneous scanned near-IR diode and CO2 lasers

NASA Astrophysics Data System (ADS)

Chan, Kenneth H.; Fried, Daniel

2017-02-01

Previous studies have established that carious lesions can be imaged with high contrast using near-IR wavelengths coincident with high water absorption, namely 1450-nm, without the interference of stains. It has been demonstrated that computer-controlled laser scanning systems utilizing IR lasers operating at high pulse repetition rates can be used for serial imaging and selective removal of caries lesions. In this study, a point-to-point scanning system was developed integrating a 1450-nm diode laser with the CO2 ablation laser. This approach is advantageous since it does not require an expensive near-IR camera. In this pilot study, we demonstrate the feasibility of a combined NIR and IR laser system for the selective removal of carious lesions.

Selective Laser Ablation of Carious Lesions using Simultaneous Scanned Near-IR Diode and CO2 Lasers.

PubMed

Chan, Kenneth H; Fried, Daniel

2017-01-28

Previous studies have established that carious lesions can be imaged with high contrast using near-IR wavelengths coincident with high water absorption, namely 1450-nm, without the interference of stains. It has been demonstrated that computer-controlled laser scanning systems utilizing IR lasers operating at high pulse repetition rates can be used for serial imaging and selective removal of caries lesions. In this study, a point-to-point scanning system was developed integrating a 1450-nm diode laser with the CO 2 ablation laser. This approach is advantageous since it does not require an expensive near-IR camera. In this pilot study, we demonstrate the feasibility of a combined NIR and IR laser system for the selective removal of carious lesions.

Laser engines operating by resonance absorption. [thermodynamic feasibility study

NASA Technical Reports Server (NTRS)

Garbuny, M.; Pechersky, M. J.

1976-01-01

Basic tutorial article on the thermodynamic feasibility of laser engines at the present state of the art. Three main options are considered: (1) laser power applied externally to a heat reservoir (boiler approach); (2) internal heating of working fluid by resonance absorption; and (3) direct conversion of selective excitation into work. Only (2) is considered practically feasible at present. Basic concepts and variants, efficiency relations, upper temperature limits of laser engines, selection of absorbing gases, engine walls, bleaching, thermodynamic cycles of optimized laser engines, laser-powered turbines, laser heat pumps are discussed. Photon engines and laser dissociation engines are also considered.

Multiple-Diode-Laser Gas-Detection Spectrometer

NASA Technical Reports Server (NTRS)

Webster, Christopher R.; Beer, Reinhard; Sander, Stanley P.

1988-01-01

Small concentrations of selected gases measured automatically. Proposed multiple-laser-diode spectrometer part of system for measuring automatically concentrations of selected gases at part-per-billion level. Array of laser/photodetector pairs measure infrared absorption spectrum of atmosphere along probing laser beams. Adaptable to terrestrial uses as monitoring pollution or control of industrial processes.

Narrow-band injection seeding of a terahertz frequency quantum cascade laser: Selection and suppression of longitudinal modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nong, Hanond, E-mail: Nong.Hanond@rub.de; Markmann, Sergej; Hekmat, Negar

2014-09-15

A periodically poled lithium niobate (PPLN) crystal with multiple poling periods is used to generate tunable narrow-bandwidth THz pulses for injection seeding a quantum cascade laser (QCL). We demonstrate that longitudinal modes of the quantum cascade laser close to the gain maximum can be selected or suppressed according to the seed spectrum. The QCL emission spectra obtained by electro-optic sampling from the quantum cascade laser, in the most favorable case, shows high selectivity and amplification of the longitudinal modes that overlap the frequency of the narrow-band seed. Proper selection of the narrow-band THz seed from the PPLN crystal discretely tunesmore » the longitudinal mode emission of the quantum cascade laser. Moreover, the THz wave build-up within the laser cavity is studied as a function of the round-trip time. When the seed frequency is outside the maximum of the gain spectrum the laser emission shifts to the preferential longitudinal mode.« less

Narrowband 1.5-{mu}m Bragg filter based on a polymer waveguide with a laser-written refractive-index grating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sokolov, Viktor I; Panchenko, Vladislav Ya; Seminogov, V N

We report the fabrication of narrowband frequency-selective filters for the 1.5-{mu}m telecom window, which include a single-mode polymer waveguide with a submicron Bragg grating inscribed by a helium-cadmium laser. The filters have a reflectance R > 98 % and a nearly rectangular reflection band with a bandwidth {Delta}{lambda}{approx}0.4nm. They can be used as components of optical multiplexers/demultiplexers for combining and separating signals in high-speed dense wavelength-division multiplexed optical fibre communication systems. (laser components)

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Laser microphotoacoustic sensor of ammonia traces in the atmosphere

NASA Astrophysics Data System (ADS)

Serebryakov, D. V.; Morozov, I. V.; Kosterev, A. A.; Letokhov, V. S.

2010-02-01

A microphotoacoustic highly selective sensor of ammonia is built. Main attention is paid to the operation mechanism of the acoustic sensor based on a quartz tuning fork. The optimal dimensions and configuration of the acoustic resonator are determined, which made it possible to increase the sensor sensitivity by two—three times compared to the sensitivity of the existing devices. The detector sensitivity for ammonia was 60ppb (0.05 mg m-3) for the measurement time of 10s and a 25-mW, 1.53-μm laser beam in the acoustic resonator.

Toward automated selective retina treatment (SRT): an optical microbubble detection technique

NASA Astrophysics Data System (ADS)

Seifert, Eric; Park, Young-Gun; Theisen-Kunde, Dirk; Roh, Young-Jung; Brinkmann, Ralf

2018-02-01

Selective retina therapy (SRT) is an ophthalmological laser technique, targeting the retinal pigment epithelium (RPE) with repetitive microsecond laser pulses, while causing no thermal damage to the neural retina, the photoreceptors as well as the choroid. The RPE cells get damaged mechanically by microbubbles originating, at the intracellular melanosomes. Beneficial effects of SRT on Central Serous Retinopathy (CSR) and Diabetic Macula Edema (DME) have already been shown. Variations in the transmission of the anterior eye media and pigmentation variation of RPE yield in intra- and inter- individual thresholds of the pulse energy required for selective RPE damage. Those selective RPE lesions are not visible. Thus, dosimetry-systems, designed to detect microbubbles as an indicator for RPE cell damage, are demanded elements to facilitate SRT application. Therefore, a technique based on the evaluation of backscattered treatment light has been developed. Data of 127 spots, acquired during 10 clinical treatments of CSR patients, were assigned to a RPE cell damage class, validated by fluorescence angiography (FLA). An algorithm has been designed to match the FLA based information. A sensitivity of 0.9 with a specificity close to 1 is achieved. The data can be processed within microseconds. Thus, the process can be implemented in existing SRT lasers with an automatic pulse wise increasing energy and an automatic irradiation ceasing ability to enable automated treatment close above threshold to prevent adverse effects caused by too high pulse energy. Alternatively, a guidance procedure, informing the treating clinician about the adequacy of the actual settings, is possible.

Breath analysis using external cavity diode lasers: a review

NASA Astrophysics Data System (ADS)

Bayrakli, Ismail

2017-04-01

Most techniques that are used for diagnosis and therapy of diseases are invasive. Reliable noninvasive methods are always needed for the comfort of patients. Owing to its noninvasiveness, ease of use, and easy repeatability, exhaled breath analysis is a very good candidate for this purpose. Breath analysis can be performed using different techniques, such as gas chromatography mass spectrometry (MS), proton transfer reaction-MS, and selected ion flow tube-MS. However, these devices are bulky and require complicated procedures for sample collection and preconcentration. Therefore, these are not practical for routine applications in hospitals. Laser-based techniques with small size, robustness, low cost, low response time, accuracy, precision, high sensitivity, selectivity, low detection limit, real-time, and point-of-care detection have a great potential for routine use in hospitals. In this review paper, the recent advances in the fields of external cavity lasers and breath analysis for detection of diseases are presented.

Influence of small particles inclusion on selective laser melting of Ti-6Al-4V powder

NASA Astrophysics Data System (ADS)

Gong, Haijun; Dilip, J. J. S.; Yang, Li; Teng, Chong; Stucker, Brent

2017-12-01

The particle size distribution and powder morphology of metallic powders have an important effect on powder bed fusion based additive manufacturing processes, such as selective laser melting (SLM). The process development and parameter optimization require a fundamental understanding of the influence of powder on SLM. This study introduces a pre-alloyed titanium alloy Ti-6Al-4V powder, which has a certain amount of small particles, for SLM. The influence of small particle inclusion is investigated through microscopy of surface topography, elemental and microstructural analysis, and mechanical testing, compared to the Ti-6Al-4V powder provided by SLM machine vendor. It is found that the small particles inclusion in Ti-6Al-4V powder has a noticeable effect on extra laser energy absorption, which may develop imperfections and deteriorate the SLM fatigue performance.

Narrowband diode laser pump module for pumping alkali vapors.

PubMed

Rotondaro, M D; Zhdanov, B V; Shaffer, M K; Knize, R J

2018-04-16

We describe a method of line narrowing and frequency-locking a diode laser stack to an alkali atomic line for use as a pump module for Diode Pumped Alkali Lasers. The pump module consists of a 600 W antireflection coated diode laser stack configured to lase using an external cavity. The line narrowing and frequency locking is accomplished by introducing a narrowband polarization filter based on magneto-optical Faraday effect into the external cavity, which selectively transmits only the frequencies that are in resonance with the 6 2 S 1/2 → 6 2 P 3/2 transition of Cs atoms. The resulting pump module has demonstrated that a diode laser stack, which lases with a line width of 3 THz without narrowbanding, can be narrowed to 10 GHz. The line narrowed pump module produced 518 Watts that is 80% of the power generated by the original broadband diode laser stack.

A sulfur hexafluoride sensor using quantum cascade and CO2 laser-based photoacoustic spectroscopy.

PubMed

Rocha, Mila; Sthel, Marcelo; Lima, Guilherme; da Silva, Marcelo; Schramm, Delson; Miklós, András; Vargas, Helion

2010-01-01

The increase in greenhouse gas emissions is a serious environmental problem and has stimulated the scientific community to pay attention to the need for detection and monitoring of gases released into the atmosphere. In this regard, the development of sensitive and selective gas sensors has been the subject of several research programs. An important greenhouse gas is sulphur hexafluoride, an almost non-reactive gas widely employed in industrial processes worldwide. Indeed it is estimated that it has a radiative forcing of 0.52 W/m(2). This work compares two photoacoustic spectrometers, one coupled to a CO(2) laser and another one coupled to a Quantum Cascade (QC) laser, for the detection of SF(6). The laser photoacoustic spectrometers described in this work have been developed for gas detection at small concentrations. Detection limits of 20 ppbv for CO(2) laser and 50 ppbv for quantum cascade laser were obtained.

Manufacturing the Gas Diffusion Layer for PEM Fuel Cell Using a Novel 3D Printing Technique and Critical Assessment of the Challenges Encountered

PubMed Central

Singamneni, Sarat; Ramos, Maximiano; Al-Jumaily, Ahmed M

2017-01-01

The conventional gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells incorporates a carbon-based substrate, which suffers from electrochemical oxidation as well as mechanical degradation, resulting in reduced durability and performance. In addition, it involves a complex manufacturing process to produce it. The proposed technique aims to resolve both these issues by an advanced 3D printing technique, namely selective laser sintering (SLS). In the proposed work, polyamide (PA) is used as the base powder and titanium metal powder is added at an optimised level to enhance the electrical conductivity, thermal, and mechanical properties. The application of selective laser sintering to fabricate a robust gas diffusion substrate for PEM fuel cell applications is quite novel and is attempted here for the first time. PMID:28773156

Manufacturing the Gas Diffusion Layer for PEM Fuel Cell Using a Novel 3D Printing Technique and Critical Assessment of the Challenges Encountered.

PubMed

Jayakumar, Arunkumar; Singamneni, Sarat; Ramos, Maximiano; Al-Jumaily, Ahmed M; Pethaiah, Sethu Sundar

2017-07-14

The conventional gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells incorporates a carbon-based substrate, which suffers from electrochemical oxidation as well as mechanical degradation, resulting in reduced durability and performance. In addition, it involves a complex manufacturing process to produce it. The proposed technique aims to resolve both these issues by an advanced 3D printing technique, namely selective laser sintering (SLS). In the proposed work, polyamide (PA) is used as the base powder and titanium metal powder is added at an optimised level to enhance the electrical conductivity, thermal, and mechanical properties. The application of selective laser sintering to fabricate a robust gas diffusion substrate for PEM fuel cell applications is quite novel and is attempted here for the first time.

Additive Manufacturing of Al-12Si Alloy Via Pulsed Selective Laser Melting

NASA Astrophysics Data System (ADS)

Chou, R.; Milligan, J.; Paliwal, M.; Brochu, M.

2015-03-01

Additive manufacturing (AM) of metallic materials is experiencing a research and commercialization craze in almost all industrial sectors. However, to date, AM has been limited to a small numbers of alloys. With respect to aluminum, two alloys received some attention: Al-12Si and Al-10Si-1Mg. In both cases, fully dense components have been achieved using a continuous-wave selective laser melting system. In this article, a new approach of selective laser melting using a pulsed-laser source as opposed to a continuous-wave laser is proposed. Pulse selective laser melting (P-SLM) would allow for greater control over the heat input and thus further optimization possibilities of the microstructure. P-SLM was demonstrated using the Al-12Si system. Si refinement below 200 nm was achieved throughout the component. Density up to 95% and high hardness of above 135 HV were obtained. The solidification mechanism is also explained.

Process observation in fiber laser-based selective laser melting

NASA Astrophysics Data System (ADS)

Thombansen, Ulrich; Gatej, Alexander; Pereira, Milton

2015-01-01

The process observation in selective laser melting (SLM) focuses on observing the interaction point where the powder is processed. To provide process relevant information, signals have to be acquired that are resolved in both time and space. Especially in high-power SLM, where more than 1 kW of laser power is used, processing speeds of several meters per second are required for a high-quality processing results. Therefore, an implementation of a suitable process observation system has to acquire a large amount of spatially resolved data at low sampling speeds or it has to restrict the acquisition to a predefined area at a high sampling speed. In any case, it is vitally important to synchronously record the laser beam position and the acquired signal. This is a prerequisite that allows the recorded data become information. Today, most SLM systems employ f-theta lenses to focus the processing laser beam onto the powder bed. This report describes the drawbacks that result for process observation and suggests a variable retro-focus system which solves these issues. The beam quality of fiber lasers delivers the processing laser beam to the powder bed at relevant focus diameters, which is a key prerequisite for this solution to be viable. The optical train we present here couples the processing laser beam and the process observation coaxially, ensuring consistent alignment of interaction zone and observed area. With respect to signal processing, we have developed a solution that synchronously acquires signals from a pyrometer and the position of the laser beam by sampling the data with a field programmable gate array. The relevance of the acquired signals has been validated by the scanning of a sample filament. Experiments with grooved samples show a correlation between different powder thicknesses and the acquired signals at relevant processing parameters. This basic work takes a first step toward self-optimization of the manufacturing process in SLM. It enables the addition of cognitive functions to the manufacturing system to the extent that the system could track its own process. The results are based on analyzing and redesigning the optical train, in combination with a real-time signal acquisition system which provides a solution to certain technological barriers.

The δ2H and δ18O of tap water from 349 sites in the United States and selected territories

USGS Publications Warehouse

Coplen, Tyler B.; Landwehr, Jurate M.; Qi, Haiping; Lorenz, Jennifer M.

2013-01-01

Because the stable isotopic compositions of hydrogen (δ2H) and oxygen (δ18O) of animal (including human) tissues, such as hair, nail, and urine, reflect the δ2H and δ18O of water and food ingested by an animal or a human and because the δ2H and δ18O of environmental waters vary geographically, δ2H and δ18O values of tap water samples collected in 2007-2008 from 349 sites in the United States and three selected U.S. territories have been measured in support of forensic science applications, creating one of the largest databases of tap water δ2H and δ18O values to date. The results of replicate isotopic measurements for these tap water samples confirm that the expanded uncertainties (U = 2μc) obtained over a period of years by the Reston Stable Isotope Laboratory from δ2H and δ18O dual-inlet mass spectrometric measurements are conservative, at ±2‰ and ±0.2 ‰, respectively. These uncertainties are important because U.S. Geological Survey data may be needed for forensic science applications, including providing evidence in court cases. Half way through the investigation, an isotope-laser spectrometer was acquired, enabling comparison of dual-inlet isotope-ratio mass spectrometric results with isotope-laser spectrometric results. The uncertainty of the laser-based δ2H measurement results for these tap water samples is comparable to the uncertainty of the mass spectrometric method, with the laser-based method having a slightly lower uncertainty. However, the δ18O uncertainty of the laser-based method is more than a factor of ten higher than that of the dual-inlet isotoperatio mass spectrometric method.

Experimental phase-space-based optical amplification of scar modes.

PubMed

Michel, C; Tascu, S; Doya, V; Aschiéri, P; Blanc, W; Legrand, O; Mortessagne, F

2012-04-01

Wave billiards which are chaotic in the geometrical limit are known to support nongeneric spatially localized modes called scar modes. The interaction of the scar modes with gain has been recently investigated in optics in microcavity lasers and vertical-cavity surface-emitting lasers. Exploiting the localization properties of scar modes in their wave-analogous phase-space representation, we report experimental results of scar mode selection by gain in a doped D-shaped optical fiber.

Comparative Evaluation of Effects of Laser Modalities on Shear Bond Strengths of Veneering Porcelains to Laser Sintered Substructures: An In Vitro Study.

PubMed

Gorler, Oguzhan; Saygin, Aysegul Goze

2017-06-01

Laser modalities and direct metal laser sintering (DMLS) have a potential to enhance micromechanical bonding between dental super- and infrastructures. However, the effect of different manufacturing methods on the metal-ceramic bond strength needs further evaluation. We investigated the effect of surface treatment with Er:YAG, Nd:YAG, and Ho:YAG lasers on the shear bond strength (SBS) of high-fusion dental porcelains (Vita and G-Ceram) to infrastructures prepared with DMLS in vitro settings. Study specimens (n = 128) were randomly divided into study subsets (n = 8), considering treatment types applied on the surface of infrastructures, including sandblasting and selected laser modalities; infrastructure types as direct laser sintered (DLS) and Ni-Cr based; and superstructure porcelains as Vita and G-Ceram. The SBS test was performed to assess the effectiveness of surface modifications that were also examined with a stereo microscope. Considering laser procedure types, the highest SBS values were obtained by Er:YAG laser, followed by, with a decreasing efficiency, Ho:YAG laser and sandblasting procedures, and Nd:YAG laser procedure (p < 0.05). Nd:YAG laser decreases the bonding of Vita and G-Ceram in all the infrastructures compared with sandblasting. Considering porcelains, the highest SBS values were obtained by Vita (p < 0.05). Considering infrastructures, the highest SBS values were obtained by DMLS procedure (p < 0.05). The laser procedures caused surface irregularities as revealed by the stereo microscopic examination. In current experimental settings, Er:YAG laser applied to DLS infrastructure veneered with Vita porcelain increases bonding strength more distinctly, and Nd:YAG laser applied to Ni-Cr-based infrastructure veneered with G-Ceram porcelain alters bonding strength unfavorably.

Chromatic energy filter and characterization of laser-accelerated proton beams for particle therapy

NASA Astrophysics Data System (ADS)

Hofmann, Ingo; Meyer-ter-Vehn, Jürgen; Yan, Xueqing; Al-Omari, Husam

2012-07-01

The application of laser accelerated protons or ions for particle therapy has to cope with relatively large energy and angular spreads as well as possibly significant random fluctuations. We suggest a method for combined focusing and energy selection, which is an effective alternative to the commonly considered dispersive energy selection by magnetic dipoles. Our method is based on the chromatic effect of a magnetic solenoid (or any other energy dependent focusing device) in combination with an aperture to select a certain energy width defined by the aperture radius. It is applied to an initial 6D phase space distribution of protons following the simulation output from a Radiation Pressure Acceleration model. Analytical formula for the selection aperture and chromatic emittance are confirmed by simulation results using the TRACEWIN code. The energy selection is supported by properly placed scattering targets to remove the imprint of the chromatic effect on the beam and to enable well-controlled and shot-to-shot reproducible energy and transverse density profiles.

Automatic variable selection method and a comparison for quantitative analysis in laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Duan, Fajie; Fu, Xiao; Jiang, Jiajia; Huang, Tingting; Ma, Ling; Zhang, Cong

2018-05-01

In this work, an automatic variable selection method for quantitative analysis of soil samples using laser-induced breakdown spectroscopy (LIBS) is proposed, which is based on full spectrum correction (FSC) and modified iterative predictor weighting-partial least squares (mIPW-PLS). The method features automatic selection without artificial processes. To illustrate the feasibility and effectiveness of the method, a comparison with genetic algorithm (GA) and successive projections algorithm (SPA) for different elements (copper, barium and chromium) detection in soil was implemented. The experimental results showed that all the three methods could accomplish variable selection effectively, among which FSC-mIPW-PLS required significantly shorter computation time (12 s approximately for 40,000 initial variables) than the others. Moreover, improved quantification models were got with variable selection approaches. The root mean square errors of prediction (RMSEP) of models utilizing the new method were 27.47 (copper), 37.15 (barium) and 39.70 (chromium) mg/kg, which showed comparable prediction effect with GA and SPA.

Selective removal of natural caries lesions from dentin and tooth occlusal surfaces using a diode-pumped Er:YAG laser

NASA Astrophysics Data System (ADS)

Jew, Jamison; Chan, Kenneth H.; Darling, Cynthia L.; Fried, Daniel

2017-02-01

Selective removal of caries lesions with high precision is best accomplished using lasers operating at high pulse repetition rates utilizing small spot sizes. Conventional flash-lamp pumped Er:YAG lasers are poorly suited for this purpose, but new diode-pumped solid-state (DPSS) Er:YAG lasers have become available operating at high pulse repetition rates. Microradiography was used to determine the mineral content of the demineralized dentin of 200-μm thick sections with natural caries lesions prior to laser ablation. The purpose of this study was to explore the use of a DPSS Er:YAG laser for the selective removal of demineralized dentin and natural occlusal lesions on extracted teeth.

Stress assisted selective ablation of ITO thin film by picosecond laser

NASA Astrophysics Data System (ADS)

Farid, Nazar; Chan, Helios; Milne, David; Brunton, Adam; M. O'Connor, Gerard

2018-01-01

Fast selective pattering with high precession on 175 nm ITO thin film with IR ps lasers is investigated. Ablation parameters are optimized with detailed studies on the scribed depth, topography, and particle generation using AFM and SEM. A comparison of 10 and 150 ps laser revealed that the shorter pulse (10 ps) laser is more appropriate in selective and partial ablation; up to 20 nm resolution for controlled depth with multipulses having energy below the damage threshold is demonstrated. The experimental results are interpreted to involve stress assisted ablation mechanism for the 10 ps laser while thermal ablation along with intense melting occurs for 150 ps laser. The transition between these regimes is estimated to occur at approximately 30 ps.

Influence of Selective Laser Melting Processing Parameters of Co-Cr-W Powders on the Roughness of Exterior Surfaces

NASA Astrophysics Data System (ADS)

Baciu, M. A.; Baciu, E. R.; Bejinariu, C.; Toma, S. L.; Danila, A.; Baciu, C.

2018-06-01

Selective Laser Melting (SLM) represents an Additive Manufacturing method widely used in medical practice, mainly in dental medicine. The powder of 59% Co, 25% Cr, 2.5% W alloy (Starbond CoS Powder 55, S&S Scheftner C, Germany) was processed (SLM) on a Realizer SLM 50 device (SLM Solution, Germany). After laser processing and simple sanding with Al2O3 or two-phase sanding (Al2O3 and glass balls), measurements of surface roughness were conducted. This paper presents the influences exercised by laser power (P = 60 W, 80 W and 100 W), the scanning speed (vscan = 333 mm/s, 500 mm/s and 1000 mm/s) and exposure time (te = 20 µs, 40 µs and 60 µs) on the roughness of surfaces obtained by SLM processing. Based on the experimental results obtained for roughness (Ra), some recommendations regarding the choice of favorable combinations among the values of technological parameters under study in order to obtain the surface quality necessary for subsequent applications of the processed parts (SLM) have been made.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirkbride, James M. R.; Causier, Sarah K.; Dalton, Andrew R.

This paper details infra-red pump and probe studies on nitric oxide conducted with two continuous wave quantum cascade lasers both operating around 5 μm. The pump laser prepares a velocity selected population in a chosen rotational quantum state of the v = 1 level which is subsequently probed using a second laser tuned to a rotational transition within the v = 2 ← v = 1 hot band. The rapid frequency scan of the probe (with respect to the molecular collision rate) in combination with the velocity selective pumping allows observation of marked rapid passage signatures in the transient absorptionmore » profiles from the polarized vibrationally excited sample. These coherent transient signals are influenced by the underlying hyperfine structure of the pump and probe transitions, the sample pressure, and the coherent properties of the lasers. Pulsed pump and probe studies show that the transient absorption signals decay within 1 μs at 50 mTorr total pressure, reflecting both the polarization and population dephasing times of the vibrationally excited sample. The experimental observations are supported by simulation based upon solving the optical Bloch equations for a two level system.« less

High-power, cladding-pumped all-fiber laser with selective transverse mode generation property.

PubMed

Li, Lei; Wang, Meng; Liu, Tong; Leng, Jinyong; Zhou, Pu; Chen, Jinbao

2017-06-10

We demonstrate, to the best of our knowledge, the first cladding-pumped all-fiber oscillator configuration with selective transverse mode generation based on a mode-selective fiber Bragg grating pair. Operating in the second-order (LP 11 ) mode, maximum output power of 4.2 W is obtained with slope efficiency of about 38%. This is the highest reported output power of single higher-order transverse mode generation in an all-fiber configuration. The intensity distribution profile and spectral evolution have also been investigated in this paper. Our work suggests the potential of realizing higher power with selective transverse mode operation based on a mode-selective fiber Bragg grating pair.

Laser-induced fluorescence method for on-line molecular isotopologues of iodine-127, iodine-129, iodine-131 detected in gaseous media using a tunable diode laser

NASA Astrophysics Data System (ADS)

Kireev, S. V.; Shnyrev, S. L.; Sobolevsky, I. V.

2016-06-01

The letter reports on the development of a laser-induced fluorescence method for on-line selective measurement of 127I2, 129I2, 131I2, 129I127I, 127I131I, 129I131I isotopologue concentrations in gaseous media. The method is based on the excitation of molecular iodine isotopologues’ fluorescence by tunable diode laser (632-637 nm) radiation at three or four wavelengths corresponding to the 127I2, 131I2, 129I127I, 129I131I absorption line centers. Boundary relations for concentrations of simultaneously measured iodine isotopologues is about 10-5-10-6.

Flexible metal patterning in glass microfluidic structures using femtosecond laser direct-write ablation followed by electroless plating

NASA Astrophysics Data System (ADS)

Xu, Jian; Midorikawa, Katsumi; Sugioka, Koji

2014-03-01

A simple and flexible technique for integrating metal micropatterns into glass microfluidic structures based on threedimensional femtosecond laser microfabrication is presented. Femtosecond laser direct writing followed by thermal treatment and successive chemical etching allows us to fabricate three-dimensional microfluidic structures such as microchannels and microreservoirs inside photosensitive glass. Then, the femtosecond laser direct-write ablation followed by electroless metal plating enables space-selective deposition of patterned metal films on desired locations of internal walls of the fabricated microfluidic structures. The developed technique is applied to integrate a metal microheater into a glass microchannel to control the temperature of liquid samples in the channel, which can be used as a microreactor for enhancement of chemical reactions.

Using laser-induced breakdown spectroscopy on vacuum alloys-production process for elements concentration analysis

NASA Astrophysics Data System (ADS)

Zhao, Tianzhuo; Fan, Zhongwei; Lian, Fuqiang; Liu, Yang; Lin, Weiran; Mo, Zeqiang; Nie, Shuzhen; Wang, Pu; Xiao, Hong; Li, Xin; Zhong, Qixiu; Zhang, Hongbo

2017-11-01

Laser-induced breakdown spectroscopy (LIBS) utilizing an echelle spectrograph-ICCD system is employed for on-line analysis of elements concentration in a vacuum induction melting workshop. Active temperature stabilization of echelle spectrometer is implemented specially for industrial environment applications. The measurement precision is further improved by monitoring laser parameters, such as pulse energy, spatial and temporal profiles, in real time, and post-selecting laser pulses with specific pulse energies. Experimental results show that major components of nickel-based alloys are stable, and can be well detected. By using internal standard method, calibration curves for chromium and aluminum are obtained for quantitative determination, with determination coefficient (relative standard deviation) to be 0.9559 (< 2.2%) and 0.9723 (< 2.8%), respectively.

Laser-assisted treatment of dentinal hypersensitivity: a literature review

PubMed Central

Biagi, Roberto; Cossellu, Gianguido; Sarcina, Michele; Pizzamiglio, Ilaria Tina; Farronato, Giampietro

2015-01-01

Summary The purpose of this literature review was to evaluate the effectiveness of the laser-assisted treatment of dentinal hypersensitivity. A review with inclusion and exclusion criteria was performed from January 2009 to December 2014 with electronic data-bases: MedLine via PubMed, Science Direct and Cochrane Library. Research of paper magazines by hand was not considered. Forty-three articles were selected between literature reviews, in vitro studies, clinical trials, pilot and preliminary studies. The items were divided into laser-used groups for an accurate description, and then the reading of results into various typologies. Laser-assisted treatment reduces dentinal hypersensitivity-related pain, but also a psychosomatic component must be considered, so further studies and more suitable follow-ups are necessary. PMID:26941892

Monitoring spacecraft atmosphere contaminants by laser absorption spectroscopy

NASA Technical Reports Server (NTRS)

Steinfeld, J. I.

1976-01-01

Laser-based spectrophotometric methods which have been proposed for the detection of trace concentrations of gaseous contaminants include Raman backscattering (LIDAR) and passive radiometry (LOPAIR). Remote sensing techniques using laser spectrometry are presented and in particular a simple long-path laser absorption method (LOLA), which is capable of resolving complex mixtures of closely related trace contaminants at ppm levels is discussed. A number of species were selected for study which are representative of those most likely to accumulate in closed environments, such as submarines or long-duration manned space flights. Computer programs were developed which will permit a real-time analysis of the monitored atmosphere. Estimates of the dynamic range of this monitoring technique for various system configurations, and comparison with other methods of analysis, are given.

Formation of periodic surface structures on dielectrics after irradiation with laser beams of spatially variant polarisation: a comparative study

NASA Astrophysics Data System (ADS)

Papadopoulos, Antonis; Skoulas, Evangelos; Tsibidis, George D.; Stratakis, Emmanuel

2018-02-01

A comparative study is performed to explore the periodic structure formation upon intense femtosecond-pulsed irradiation of dielectrics with radially and azimuthally polarised beams. Laser conditions have been selected appropriately to produce excited carriers with densities below the optical breakdown threshold in order to highlight the role of phase transitions in surface modification mechanisms. The frequency of the laser-induced structures is calculated based on a theoretical model that comprises estimation of electron density excitation, heat transfer, relaxation processes, and hydrodynamics-related mass transport. The influence of the laser wavelength in the periodicity of the structures is also unveiled. The decreased energy absorption for azimuthally polarised beams yields periodic structures with smaller frequencies which are more pronounced as the number of laser pulses applied to the irradiation spot increases. Similar results are obtained for laser pulses of larger photon energy and higher fluences. All induced periodic structures are oriented parallel to the laser beam polarisation.

Mid-IR laser system for advanced neurosurgery

NASA Astrophysics Data System (ADS)

Klosner, M.; Wu, C.; Heller, D. F.

2014-03-01

We present work on a laser system operating in the near- and mid-IR spectral regions, having output characteristics designed to be optimal for cutting various tissue types. We provide a brief overview of laser-tissue interactions and the importance of controlling certain properties of the light beam. We describe the principle of operation of the laser system, which is generally based on a wavelength-tunable alexandrite laser oscillator/amplifier, and multiple Raman conversion stages. This configuration provides robust access to the mid-IR spectral region at wavelengths, pulse energies, pulse durations, and repetition rates that are attractive for neurosurgical applications. We summarize results for ultra-precise selective cutting of nerve sheaths and retinas with little collateral damage; this has applications in procedures such as optic-nerve-sheath fenestration and possible spinal repair. We also report results for cutting cornea, and dermal tissues.

Treating vascular lesions.

PubMed

Astner, Susanne; Anderson, R Rox

2005-01-01

The treatment of acquired vascular lesions is one of the most commonly requested and performed cutaneous laser procedures. Furthermore, every year, 40,000 children are born in the United States each with congenital vascular lesions and malformations. Laser treatment of vascular lesion is based on the principle of selective photothermolysis, conceived in the 1980s. A variety of different lasers and light sources have since been used in the treatment of vascular lesions: lasers with wavelengths between green and yellow, near infrared lasers, and broadband light sources. Despite limitations, this remains the treatment of choice today. This publication addresses acquired and congenital vascular lesions as different entities and proposes a separation of vascular lesions into those that can easily be treated from those where clearance is difficult. Different treatment modalities and the various endpoints of individual vascular lesions will be discussed.

Energy spectrum and thermal properties of a terahertz quantum-cascade laser based on the resonant-phonon depopulation scheme

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khabibullin, R. A., E-mail: khabibullin@isvch.ru; Shchavruk, N. V.; Klochkov, A. N.

The dependences of the electronic-level positions and transition oscillator strengths on an applied electric field are studied for a terahertz quantum-cascade laser (THz QCL) with the resonant-phonon depopulation scheme, based on a cascade consisting of three quantum wells. The electric-field strengths for two characteristic states of the THz QCL under study are calculated: (i) “parasitic” current flow in the structure when the lasing threshold has not yet been reached; (ii) the lasing threshold is reached. Heat-transfer processes in the THz QCL under study are simulated to determine the optimum supply and cooling conditions. The conditions of thermocompression bonding of themore » laser ridge stripe with an n{sup +}-GaAs conductive substrate based on Au–Au are selected to produce a mechanically stronger contact with a higher thermal conductivity.« less

In situ process monitoring in selective laser sintering using optical coherence tomography

NASA Astrophysics Data System (ADS)

Gardner, Michael R.; Lewis, Adam; Park, Jongwan; McElroy, Austin B.; Estrada, Arnold D.; Fish, Scott; Beaman, Joseph J.; Milner, Thomas E.

2018-04-01

Selective laser sintering (SLS) is an efficient process in additive manufacturing that enables rapid part production from computer-based designs. However, SLS is limited by its notable lack of in situ process monitoring when compared with other manufacturing processes. We report the incorporation of optical coherence tomography (OCT) into an SLS system in detail and demonstrate access to surface and subsurface features. Video frame rate cross-sectional imaging reveals areas of sintering uniformity and areas of excessive heat error with high temporal resolution. We propose a set of image processing techniques for SLS process monitoring with OCT and report the limitations and obstacles for further OCT integration with SLS systems.

[Research progress in CoCr metal-ceramic alloy fabricated by selective laser melting].

PubMed

Yan, X; Lin, H

2018-02-09

Cobalt-chromium alloys have been applied to dental porcelain fused to metal (PFM) restorations over the past decades owing to their excellent corrosion resistance, good biocompatibility and low price. The production of CoCr metal-ceramic restorations has always been based on traditional lost-wax casting techniques. However, in recent years, selective laser melting (SLM) is becoming more and more highly valued by dental laboratories and dental practitioners due to its individuation, precision and efficiency. This paper mainly reviews the recent researches on the production process of copings, microstructure, mechanical property, metal-ceramic bond strength, fit of copings, corrosion resistance and biocompatibility of SLM CoCr metal-ceramic alloy.

Fabrication of a terahertz quantum-cascade laser with a double metal waveguide based on multilayer GaAs/AlGaAs heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khabibullin, R. A., E-mail: khabibullin@isvch.ru; Shchavruk, N. V.; Pavlov, A. Yu.

2016-10-15

The Postgrowth processing of GaAs/AlGaAs multilayer heterostructures for terahertz quantumcascade lasers (QCLs) are studied. This procedure includes the thermocompression bonding of In–Au multilayer heterostructures with a doped n{sup +}-GaAs substrate, mechanical grinding, and selective wet etching of the substrate, and dry etching of QCL ridge mesastripes through a Ti/Au metallization mask 50 and 100 μm wide. Reactive-ion-etching modes with an inductively coupled plasma source in a BCl{sub 3}/Ar gas mixture are selected to obtain vertical walls of the QCL ridge mesastripes with minimum Ti/Au mask sputtering.

Two-photon excitation of nitric oxide fluorescence as a temperature indicator in unsteady gas-dynamic processes

NASA Technical Reports Server (NTRS)

Mckenzie, R. L.; Gross, K. P.

1980-01-01

A laser induced fluorescence technique, suitable for measuring fluctuating temperatures in cold turbulent flows containing very low concentrations of nitric oxide is described. Temperatures below 300 K may be resolved with signal to noise ratios greater than 50 to 1 using high peak power, tunable dye lasers. The method relies on the two photon excitation of selected ro-vibronic transitions. The analysis includes the effects of fluorescence quenching and shows the technique to be effective at all densities below ambient. Signal to noise ratio estimates are based on a preliminary measurement of the two photon absorptivity for a selected rotational transition in the NO gamma (0,0) band.

Laser-activated protein bands for peripheral nerve repair

NASA Astrophysics Data System (ADS)

Lauto, Antonio; Trickett, Rodney I.; Malik, Richard; Dawes, Judith M.; Owen, Earl R.

1996-01-01

A 100 micrometer core optical fiber-coupled 75 mW diode laser operating at a wavelength of 800 nm has been used in conjunction with a protein solder to stripe weld severed rat tibial nerves, reducing the long operating time required for microsurgical nerve repair. Welding is produced by selective laser denaturation of the protein based solder which contains the dye indocyanine green. Operating time for laser soldering was 10 plus or minus 5 min. (n equals 24) compared to 23 plus or minus 9 min (n equals 13) for microsuturing. The laser solder technique resulted in patent welds with a tensile strength of 15 plus or minus 5 g, while microsutured nerves had a tensile strength of 40 plus or minus 10 g. Histopathology of the laser soldered nerves, conducted immediately after surgery, displayed solder adhesion to the outer membrane with minimal damage to the inner axons of the nerves. An in vivo study, with a total of fifty-seven adult male wistar rats, compared laser solder repaired tibial nerves to conventional microsuture repair. Twenty-four laser soldered nerves and thirteen sutured nerves were characterized at three months and showed successful regeneration with average compound muscle action potentials (CMAP) of 2.4 plus or minus 0.7 mV and 2.7 plus or minus 0.8 mV respectively. Histopathology of the in vivo study, confirmed the comparable regeneration of axons in laser and suture operated nerves. A faster, less damaging and long lasting laser based anastomotic technique is presented.

Real-time laser cladding control with variable spot size

NASA Astrophysics Data System (ADS)

Arias, J. L.; Montealegre, M. A.; Vidal, F.; Rodríguez, J.; Mann, S.; Abels, P.; Motmans, F.

2014-03-01

Laser cladding processing has been used in different industries to improve the surface properties or to reconstruct damaged pieces. In order to cover areas considerably larger than the diameter of the laser beam, successive partially overlapping tracks are deposited. With no control over the process variables this conduces to an increase of the temperature, which could decrease mechanical properties of the laser cladded material. Commonly, the process is monitored and controlled by a PC using cameras, but this control suffers from a lack of speed caused by the image processing step. The aim of this work is to design and develop a FPGA-based laser cladding control system. This system is intended to modify the laser beam power according to the melt pool width, which is measured using a CMOS camera. All the control and monitoring tasks are carried out by a FPGA, taking advantage of its abundance of resources and speed of operation. The robustness of the image processing algorithm is assessed, as well as the control system performance. Laser power is decreased as substrate temperature increases, thus maintaining a constant clad width. This FPGA-based control system is integrated in an adaptive laser cladding system, which also includes an adaptive optical system that will control the laser focus distance on the fly. The whole system will constitute an efficient instrument for part repair with complex geometries and coating selective surfaces. This will be a significant step forward into the total industrial implementation of an automated industrial laser cladding process.

Molecular beam epitaxy growth method for vertical-cavity surface-emitting laser resonators based on substrate thermal emission

NASA Astrophysics Data System (ADS)

Talghader, J. J.; Hadley, M. A.; Smith, J. S.

1995-12-01

A molecular beam epitaxy growth monitoring method is developed for distributed Bragg reflectors and vertical-cavity surface-emitting laser (VCSEL) resonators. The wavelength of the substrate thermal emission that corresponds to the optical cavity resonant wavelength is selected by a monochromator and monitored during growth. This method allows VCSEL cavities of arbitrary design wavelength to be grown with a single control program. This letter also presents a theoretical model for the technique which is based on transmission matrices and simple thermal emission properties. Demonstrated reproducibility of the method is well within 0.1%.

Rapid prototyping of reflectors for vehicle lighting using laser activated remote phosphor

NASA Astrophysics Data System (ADS)

Lachmayer, Roland; Kloppenburg, Gerolf; Wolf, Alexander

2015-03-01

Bright white light sources are of significant importance for automotive front lighting systems. Today's upper class vehicles mainly use HID or LED as light source. As a further step in this development laser diode based systems offer high luminance, efficiency and allow the realization of new styling concepts and new dynamic lighting functions. These white laser diode systems can either be realized by mixing different spectral sources or by combining diodes with specific phosphors. Based on the approach of generating light using a laser and remote phosphor, lighting modules are manufactured. Four blue laser diodes (450 nm) are used to activate a phosphor coating and thus to achieve white light. A segmented paraboloid reflector generates the desired light distribution for an additional car headlamp. We use high speed milling and selective laser melting to build the reflector system for this lighting module. We compare the spectral reflection grade of these materials. Furthermore the generated modules are analyzed regarding their efficiency and light distribution. The use of Rapid Prototyping technologies allows an early validation of the chosen concept and is supposed to reduce cost and time in the product development process significantly. Therefor we discuss costs and times of the applied manufacturing technologies.

Design and manufacture of customized dental implants by using reverse engineering and selective laser melting technology.

PubMed

Chen, Jianyu; Zhang, Zhiguang; Chen, Xianshuai; Zhang, Chunyu; Zhang, Gong; Xu, Zhewu

2014-11-01

Recently a new therapeutic concept of patient-specific implant dentistry has been advanced based on computer-aided design/computer-aided manufacturing technology. However, a comprehensive study of the design and 3-dimensional (3D) printing of the customized implants, their mechanical properties, and their biomechanical behavior is lacking. The purpose of this study was to evaluate the mechanical and biomechanical performance of a novel custom-made dental implant fabricated by the selective laser melting technique with simulation and in vitro experimental studies. Two types of customized implants were designed by using reverse engineering: a root-analog implant and a root-analog threaded implant. The titanium implants were printed layer by layer with the selective laser melting technique. The relative density, surface roughness, tensile properties, bend strength, and dimensional accuracy of the specimens were evaluated. Nonlinear and linear finite element analysis and experimental studies were used to investigate the stress distribution, micromotion, and primary stability of the implants. Selective laser melting 3D printing technology was able to reproduce the customized implant designs and produce high density and strength and adequate dimensional accuracy. Better stress distribution and lower maximum micromotions were observed for the root-analog threaded implant model than for the root-analog implant model. In the experimental tests, the implant stability quotient and pull-out strength of the 2 types of implants indicated that better primary stability can be obtained with a root-analog threaded implant design. Selective laser melting proved to be an efficient means of printing fully dense customized implants with high strength and sufficient dimensional accuracy. Adding the threaded characteristic to the customized root-analog threaded implant design maintained the approximate geometry of the natural root and exhibited better stress distribution and primary stability. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Overview of the laser activities at Rheinmetall Waffe Munition

NASA Astrophysics Data System (ADS)

Ludewigt, Klaus; Riesbeck, Thomas; Schünemann, B.; Graf, A.; Jung, Markus; Schreiber, Th.; Eberhardt, Ramona; Tünnermann, A.

2012-11-01

The paper will give an overview over the laser weapon activities at RWM (Rheinmetall Waffe Munition) over the last years. Starting from the actual scenarios for laser weapon applications as: CRAM (Counter Rocket Artillery Mortar), Air Defence and UXO (unexploded ordnance) clearing. The basic requirements of a future laser weapon as beam diameter, beam quality, tracking capability, adaptive optics were deduced. For the UXO scenario a mobile directed energy laser demonstrator for humanitarian mine and UXO clearing based on fiber lasers is presented. Based on the parameters the system concept including the cooling system, power supply and the integration into the armoured vehicle TM 170 are explained. The contribution show first experiments of UXO and IED clearing. Different technical approaches to achieve laser power in the 100 kW regime combined with very good beam quality are discussed to fulfil the requirements of the CRAM and Air Defence scenario. Spectral coupling and the beam superimposing both are performed by Rheinmetall Waffe Munition. At the spectral coupling the basic technology parameters for the fiber laser and the dielectric grating as the latest results were put into context with the power levels reached at other groups. For the beam super imposing technology the basic experiments regarding the tracking capability and compensation of the atmosphere on the test range at Unterlüß will be explained. A generic 10 kW Laser Weapon Demonstrator based on 2 Laser Weapon Modules (LWM) from RWM each 5 kW fiber Laser with beam forming and tracking integrate by the team of RWM and RAD (Rheinmetall Air Defense) into a Ground based Air Defend system consisting of Skyguard and Millenium turret are presented. The flight path of the UAV within the valley of the life firing range at Ochsenboden Switzerland is shown. Selected results of the successful tests against UAV's are presented. It shows the capability of the generic 10 kW Laser Weapon Demonstrator to track and to destroy the target. From these results the next steps of Rheinmetall Waffe Munition for a 100 kW class laser weapon are explained.

Photothermolysis by laser-induced microbubbles generated around gold nanorod clusters selectively formed in leukemia cells

NASA Astrophysics Data System (ADS)

Lapotko, Dmitri; Lukianova-Hleb, Ekaterina; Zhdanok, Sergei; Rostro, Betty; Simonette, Rebecca; Hafner, Jason; Konopleva, Marina; Andreeff, Michael; Conjusteau, Andre; Oraevsky, Alexander

2008-02-01

In an effort of developing clinical LANTCET (laser-activated nano-thermolysis as cell elimination technology) we achieved selective destruction of individual tumor cells through laser generation of vapor microbubbles around clusters of light absorbing gold nanorods (GNR) selectively formed in target tumor cells. Among all gold nanoparticles, nanorods offer the highest optical absorption in the near-infrared. We applied covalent conjugates of gold nanorods with targeting vectors such as monoclonal antibodies CD33 (specific for Acute Myeloid Leukemia), while GNR conjugates with polyethylene-glycol (PEG) were used as nonspecific targeting control. GNR clusters were formed inside the tumor cells at 37 °C due to endocytosis of large concentration of nanorods accumulated on the surface of tumor cells targeted at 4 °C. Formation of GNR clusters significantly reduces the threshold of tumor cell damage making LANTCET safe for normal cells. Appearance of GNR clusters was verified directly with optical resonance scattering microscopy. LANTCET was performed in vitro with living cells of (1) model myeloid K562 cells (CD33 positive), (2) primary human bone marrow CD33-positive blast cells from patients diagnosed with acute myeloid leukemia. Laser-induced microbubbles were generated and detected with a photothermal microscope equipped with a tunable Ti-Sa pulsed laser. GNT cluster formation caused a 100-fold decrease in the threshold optical fluence for laser microbubble generation in tumor cells compared with that in normal cells under the same targeting and irradiation conditions. Combining imaging based on resonance optical scattering with photothermal imaging of microbubbles, we developed a method for detection, image-guided treatment and monitoring of LANTCET. Pilot experiments were performed in flow mode bringing LANTCET closer to reality of clinical procedure of purging tumor cells from bone marrow grafts.

GaSb-based single-mode distributed feedback lasers for sensing (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gupta, James A.; Bezinger, Andrew; Lapointe, Jean; Poitras, Daniel; Aers, Geof C.

2017-02-01

GaSb-based tunable single-mode diode lasers can enable rapid, highly-selective and highly-sensitive absorption spectroscopy systems for gas sensing. In this work, single-mode distributed feedback (DFB) laser diodes were developed for the detection of various trace gases in the 2-3.3um range, including CO2, CO, HF, H2S, H2O and CH4. The lasers were fabricated using an index-coupled grating process without epitaxial regrowth, making the process significantly less expensive than conventional DFB fabrication. The devices are based on InGaAsSb/AlGaAsSb separate confinement heterostructures grown on GaSb by molecular beam epitaxy. DFB lasers were produced using a two step etch process. Narrow ridge waveguides were first defined by optical lithography and etched into the semiconductor. Lateral gratings were then defined on both sides of the ridge using electron-beam lithography and etched to produce the index-grating. Effective index modeling was used to optimize the ridge width, etch depths and the grating pitch to ensure single-lateral-mode operation and adequate coupling strength. The effective index method was further used to simulate the DFB laser emission spectrum, based on a transfer matrix model for light transmission through the periodic structure. The fabricated lasers exhibit single-mode operation which is tunable through the absorption features of the various target gases by adjustment of the drive current. In addition to the established open-path sensing applications, these devices have great potential for optoelectronic integrated gas sensors, making use of integrated photodetectors and possibly on-chip Si photonics waveguide structures.

Selective ablation of dental calculus with a frequency-doubled Alexandrite laser

NASA Astrophysics Data System (ADS)

Rechmann, Peter; Hennig, Thomas

1996-01-01

The aim of the study was the selective removal of dental calculus by means of pulsed lasers. In a first approach the optical characteristics of subgingival calculus were calculated using fluorescence emission spectroscopy (excitation laser: N2-laser, wavelength 337 nm, pulse duration 4 ns). Subgingival calculus seems to absorb highly in the ultraviolet spectral region up to 420 nm. According to these measurements a frequency doubled Alexandrite-laser (wavelength 377 nm, pulse duration 100 ns, repetition rate 110 Hz) was used to irradiate calculus located on enamel, at the cementum enamel junction and on the root surface (located on dentin or on cementum). Irradiation was performed perpendicular to the root surface with a laser fluence of 1 Jcm-2. During the irradiation procedure an effective water cooling-system was engaged. Histological investigations were done on undecalcified sections. As a result, engaging low fluences allows a fast and strictly selective removal of subgingival calculus. Even more the investigations revealed that supragingival calculus can be removed in a strictly selective manner engaging a frequency doubled Alexandrite-laser. No adverse side effects to the surrounding tissues could be found.

Microprocessing of ITO and a-Si thin films using ns laser sources

NASA Astrophysics Data System (ADS)

Molpeceres, C.; Lauzurica, S.; Ocaña, J. L.; Gandía, J. J.; Urbina, L.; Cárabe, J.

2005-06-01

Selective ablation of thin films for the development of new photovoltaic panels and sensoring devices based on amorphous silicon (a-Si) is an emerging field, in which laser micromachining systems appear as appropriate tools for process development and device fabrication. In particular, a promising application is the development of purely photovoltaic position sensors. Standard p-i-n or Schottky configurations using transparent conductive oxides (TCO), a-Si and metals are especially well suited for these applications, appearing selective laser ablation as an ideal process for controlled material patterning and isolation. In this work a detailed study of laser ablation of a widely used TCO, indium-tin-oxide (ITO), and a-Si thin films of different thicknesses is presented, with special emphasis on the morphological analysis of the generated grooves. Excimer (KrF, λ = 248 nm) and DPSS lasers (λ = 355 and λ = 1064 nm) with nanosecond pulse duration have been used for material patterning. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) techniques have been applied for the characterization of the ablated grooves. Additionally, process parametric windows have been determined in order to assess this technology as potentially competitive to standard photolithographic processes. The encouraging results obtained, with well-defined ablation grooves having thicknesses in the order of 10 µm both in ITO and in a-Si, open up the possibility of developing a high-performance double Schottky photovoltaic matrix position sensor.

Laser activated nanothermolysis of leukemia cells monitored by photothermal microscopy

NASA Astrophysics Data System (ADS)

Lapotko, Dmitri; Lukianova, Ekaterina; Shnip, Alexander; Zheltov, George; Potapnev, Michail; Savitsky, Valeriy; Klimovich, Olga; Oraevsky, Alexander

2005-04-01

We are developing new diagnostic and therapeutic technologies for leukemia based on selective targeting of leukemia cells with gold nanoparticles and thermomechanical destruction of the tumor cells with laser-induced microbubbles. Clusters of spherical gold nanoparticles that have strong optical absorption of laser pulses at 532 nm served as nucleation sites of vapor microbubbles. The nanoparticles were targeted selectively to leukemia cells using leukemia-specific surface receptors and a set of two monoclonal antibodies. Application of a primary myeloid-specific antibody to tumor cells followed by targeting the cells with 30-nm nanoparticles conjugated with a secondary antibody (IgG) resulted in formation of nanoparticulate clusters due to aggregation of IgGs. Formation of clusters resulted in substantial decrease of the damage threshold for target cells. The results encourage development of Laser Activated Nanothermolysis as a Cell Elimination Therapy (LANCET) for leukemia. The proposed technology can be applied separately or in combination with chemotherapy for killing leukemia cells without damage to other blood cells. Potential applications include initial reduction of concentration of leukemia cells in blood prior to chemotherapy and treatment of residual tumor cells after the chemotherapy. Laser-induced bubbles in individual cells and cell damage were monitored by analyzing profile of photothermal response signals over the entire cell after irradiation with a single 10-ns long laser pulse. Photothermal microscopy was utilized for imaging formation of microbubbles around nanoparticulate clusters.

3D nanostructured inkjet printed graphene via UV-pulsed laser irradiation enables paper-based electronics and electrochemical devices.

PubMed

Das, Suprem R; Nian, Qiong; Cargill, Allison A; Hondred, John A; Ding, Shaowei; Saei, Mojib; Cheng, Gary J; Claussen, Jonathan C

2016-09-21

Emerging research on printed and flexible graphene-based electronics is beginning to show tremendous promise for a wide variety of fields including wearable sensors and thin film transistors. However, post-print annealing/reduction processes that are necessary to increase the electrical conductivity of the printed graphene degrade sensitive substrates (e.g., paper) and are whole substrate processes that are unable to selectively anneal/reduce only the printed graphene-leaving sensitive device components exposed to damaging heat or chemicals. Herein a pulsed laser process is introduced that can selectively irradiate inkjet printed reduced graphene oxide (RGO) and subsequently improve the electrical conductivity (Rsheet∼0.7 kΩ□(-1)) of printed graphene above previously published reports. Furthermore, the laser process is capable of developing 3D petal-like graphene nanostructures from 2D planar printed graphene. These visible morphological changes display favorable electrochemical sensing characteristics-ferricyanide cyclic voltammetry with a redox peak separation (ΔEp) ≈ 0.7 V as well as hydrogen peroxide (H2O2) amperometry with a sensitivity of 3.32 μA mM(-1) and a response time of <5 s. Thus this work paves the way for not only paper-based electronics with graphene circuits, it enables the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells, and theranostic devices.

Selective delivery of laser energy to ester bonds of triacylglycerol in lipid droplets of adipocyte using a quantum cascade laser

PubMed Central

Masaki, Noritaka; Okazaki, Shigetoshi

2018-01-01

The recent development of quantum cascade lasers (QCLs) has facilitated the irradiation of a mid-infrared laser beam that is specifically absorbed by a target molecular bond. Aiming for a selective delivery of laser energy to a specific absorption at 1,738 cm−1 by the ester bonds of triacylglycerol (TAG), a QCL beam with a wavenumber of 1,710 cm−1 was irradiated to 3T3–L1 adipocytes and preadipocytes. Neutral red staining, and FITC-labeled annexin V and ethidium homodimer-III assays revealed the occurrence of adipocyte-specific cell death 24 h after QCL irradiation. The selective delivery of laser energy to endogenous molecules can affect biological processes in a living organism. PMID:29760972

Selective delivery of laser energy to ester bonds of triacylglycerol in lipid droplets of adipocyte using a quantum cascade laser.

PubMed

Masaki, Noritaka; Okazaki, Shigetoshi

2018-05-01

The recent development of quantum cascade lasers (QCLs) has facilitated the irradiation of a mid-infrared laser beam that is specifically absorbed by a target molecular bond. Aiming for a selective delivery of laser energy to a specific absorption at 1,738 cm -1 by the ester bonds of triacylglycerol (TAG), a QCL beam with a wavenumber of 1,710 cm -1 was irradiated to 3T3-L1 adipocytes and preadipocytes. Neutral red staining, and FITC-labeled annexin V and ethidium homodimer-III assays revealed the occurrence of adipocyte-specific cell death 24 h after QCL irradiation. The selective delivery of laser energy to endogenous molecules can affect biological processes in a living organism.

Optical design of f-theta lens for dual wavelength selective laser melting

NASA Astrophysics Data System (ADS)

Feng, Lianhua; Cao, Hongzhong; Zhang, Ning; Xu, Xiping; Duan, Xuanming

2016-10-01

F-theta lens is an important unit for selective laser melting (SLM) manufacture. The dual wavelength f-theta lens has not been used in SLM manufacture. Here, we present the design of the f-theta lens which satisfies SLM manufacture with coaxial 532 nm and 1030 nm 1080 nm laser beams. It is composed of three pieces of spherical lenses. The focal spots for 532 nm laser and 1030 nm 1080 nm laser are smaller than 35 μm and 70 μm, respectively. The results meet the demands of high precision SLM. The chromatic aberration could cause separation between two laser focal spots in the scanning plane, so chromatic aberration correction is very important to our design. The lateral color of the designed f-theta lens is less than 11 μm within the scan area of 150 mm x 150 mm, which meet the application requirements of dual wavelength selective laser melting.

Digital selective growth of a ZnO nanowire array by large scale laser decomposition of zinc acetate.

PubMed

Hong, Sukjoon; Yeo, Junyeob; Manorotkul, Wanit; Kang, Hyun Wook; Lee, Jinhwan; Han, Seungyong; Rho, Yoonsoo; Suh, Young Duk; Sung, Hyung Jin; Ko, Seung Hwan

2013-05-07

We develop a digital direct writing method for ZnO NW micro-patterned growth on a large scale by selective laser decomposition of zinc acetate. For ZnO NW growth, by replacing the bulk heating with the scanning focused laser as a fully digital local heat source, zinc acetate crystallites can be selectively activated as a ZnO seed pattern to grow ZnO nanowires locally on a larger area. Together with the selective laser sintering process of metal nanoparticles, more than 10,000 UV sensors have been demonstrated on a 4 cm × 4 cm glass substrate to develop all-solution processible, all-laser mask-less digital fabrication of electronic devices including active layer and metal electrodes without any conventional vacuum deposition, photolithographic process, premade mask, high temperature and vacuum environment.

Laser generation in microdisc resonators with InAs/GaAs quantum dots transferred on a silicon substrate

NASA Astrophysics Data System (ADS)

Nadtochiy, A. M.; Kryzhanovskaya, N. V.; Maximov, M. V.; Zhukov, A. E.; Moiseev, E. I.; Kulagina, M. M.; Vashanova, K. A.; Zadiranov, Yu. M.; Mukhin, I. S.; Arakcheeva, E. M.; Livshits, D.; Lipovskii, A. A.

2013-09-01

Microdisc resonators based on InAs/GaAs quantum dots separated from a GaAs substrate by selective etching and fixed to a silicon substrate by epoxy glue are studied using luminescence spectroscopy. A disc resonator 6 μm in diameter exhibits quasi-single-mode laser generation at a temperature of 78 K with a threshold power of 320 μW and λ/Δλ ˜ 27000.

Resonant-phonon-assisted THz quantum cascade lasers with metal-metal waveguides.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Callebaut, Hans; Kohen, Stephen; Kumar, Sushil

2004-06-01

We report our development of terahertz (THz) quantum-cascade lasers (QCLs) based on two novel features. First, the depopulation of the lower radiative level is achieved through resonant longitudinal optical (LO-)phonon scattering. This depopulation mechanism is robust at high temperatures and high injection levels. In contrast to infrared QCLs that also use LO-phonon scattering for depopulation, in our THz lasers the selectivity of the depopulation scattering is achieved through a combination of resonant tunneling and LO-phonon scattering, hence the term resonant phonon. This resonant-phonon scheme allows a highly selective depopulation of the lower radiative level with a sub-picosecond lifetime, while maintainingmore » a relatively long upper level lifetime (>5 ps) that is due to upper-to-ground-state scattering. The second feature of our lasers is that mode confinement is achieved by using a novel double-sided metal-metal waveguide, which yields an essentially unity mode confinement factor and therefore a low total cavity loss at THz frequencies. Based on these two unique features, we have achieved some record performance, including, but not limited to, the highest pulsed operating temperature of 137 K, the highest continuous-wave operating temperature of 97 K, and the longest wavelength of 141 {micro}m (corresponding to 2.1 THz) without the assistance of a magnetic field.« less

Liquid level and temperature sensing by using dual-wavelength fiber laser based on multimode interferometer and FBG in parallel

NASA Astrophysics Data System (ADS)

Sun, Chunran; Dong, Yue; Wang, Muguang; Jian, Shuisheng

2018-03-01

The detection of liquid level and temperature based on a fiber ring cavity laser sensing configuration is presented and demonstrated experimentally. The sensing head contains a fiber Bragg grating (FBG) and a single-mode-cladding-less-single-mode multimode interferometer, which also functions as wavelength-selective components of the fiber laser. When the liquid level or temperature is applied on the sensing head, the pass-band peaks of both multimode interference (MMI) filter and FBG filter vary and the two output wavelengths of the laser shift correspondingly. In the experiment, the corresponding sensitivities of the liquid level with four different refractive indices (RI) in the deep range from 0 mm to 40 mm are obtained and the sensitivity enhances with the RI of the liquid being measured. The maximum sensitivity of interferometer is 106.3 pm/mm with the RI of 1.391. For the temperature measurement, a sensitivity of 10.3 pm/°C and 13.8 pm/°C are achieved with the temperature ranging from 0 °C to 90 °C corresponding to the two lasing wavelengths selective by the MMI filter and FBG, respectively. In addition, the average RI sensitivity of 155.77 pm/mm/RIU is also obtained in the RI range of 1.333-1.391.

Comparative study of pulsed Nd:YAG laser welding of AISI 304 and AISI 316 stainless steels

NASA Astrophysics Data System (ADS)

Kumar, Nikhil; Mukherjee, Manidipto; Bandyopadhyay, Asish

2017-02-01

Laser welding is a potentially useful technique for joining two pieces of similar or dissimilar materials with high precision. In the present work, comparative studies on laser welding of similar metal of AISI 304SS and AISI 316SS have been conducted forming butt joints. A robotic control 600 W pulsed Nd:YAG laser source has been used for welding purpose. The effects of laser power, scanning speed and pulse width on the ultimate tensile strength and weld width have been investigated using the empirical models developed by RSM. The results of ANOVA indicate that the developed models predict the responses adequately within the limits of input parameters. 3-D response surface and contour plots have been developed to find out the combined effects of input parameters on responses. Furthermore, microstructural analysis as well as hardness and tensile behavior of the selected weld of 304SS and 316SS have been carried out to understand the metallurgical and mechanical behavior of the weld. The selection criteria are based on the maximum and minimum strength achieved by the respective weld. It has been observed that the current pulsation, base metal composition and variation in heat input have significant influence on controlling the microstructural constituents (i.e. phase fraction, grain size etc.). The result suggests that the low energy input pulsation generally produce fine grain structure and improved mechanical properties than the high energy input pulsation irrespective of base material composition. However, among the base materials, 304SS depict better microstructural and mechanical properties than the 316SS for a given parametric condition. Finally, desirability function analysis has been applied for multi-objective optimization for maximization of ultimate tensile strength and minimization of weld width simultaneously. Confirmatory tests have been conducted at optimum parametric conditions to validate the optimization techniques.

Frequency-agile dual-frequency lidar for integrated coherent radar-lidar architectures.

PubMed

Vercesi, Valeria; Onori, Daniel; Laghezza, Francesco; Scotti, Filippo; Bogoni, Antonella; Scaffardi, Mirco

2015-04-01

We propose a novel architecture for implementing a dual-frequency lidar (DFL) exploiting differential Doppler shift measurement. The two frequency tones, needed for target velocity measurements, are selected from the spectrum of a mode-locked laser operating in the C-band. The tones' separation is easily controlled by using a programmable wavelength selective switch, thus allowing for a dynamic trade-off among robustness to atmospheric turbulence and sensitivity. Speed measurements for different tone separations equal to 10, 40, 80, and 160 GHz are demonstrated, proving the system's capability of working in different configurations. Thanks to the acquisition system based on an analog-to-digital converter and digital-signal processing, real-time velocity measurements are demonstrated. The MLL-based proposed architecture enables the integration of the DFL with a photonic-based radar that exploits the same laser for generating and receiving radio-frequency signal with high performance, thus allowing for simultaneous or complementary target observations by exploiting the advantages of both radar and lidar.

Selective material ablation by the TEA CO2 laser

NASA Astrophysics Data System (ADS)

Sumiyoshi, Tetsumi; Shiratori, Akira; Ninomiya, Yutaka; Obara, Minoru

1995-03-01

This paper reports two topics in the material processing using TEA CO2 lasers. We demonstrated selective ablation of hydrogenated amorphous silicon (a-Si:H) thin layer on a quartz substrate by the second harmonic (SH) radiation of TEA CO2 laser generated by AgGaSe2 nonlinear crystal. Si-H bonds contained in a-Si:H strongly absorb the 5 micrometers SH radiation and resulted in the selective ablation of the a-Si:H layer. The successful ablation processing of ethylenetetrafluoroethylene (ETFE) copolymer by the 9.6 micrometers fundamental wavelength TEA CO2 laser is also reported. Only ETFE thin film adhered to an aluminum substrate can be ablated by the TEA CO2 laser.

Optoacoustic temperature determination and automatic coagulation control in rabbits

NASA Astrophysics Data System (ADS)

Schlott, Kerstin; Koinzer, Stefan; Ptaszynski, Lars; Luft, Susanne; Baade, Alex; Bever, Marco; Roider, Johann; Birngruber, Reginald; Brinkmann, Ralf

2011-03-01

Retinal laser photocoagulation is an established treatment method for many retinal diseases like macula edema or diabetic retinopathy. The selection of the laser parameters is so far based on post treatment evaluation of the lesion size and strength. Due to local pigment variations in the fundus and individual transmission the same laser parameters often lead to an overtreatment. Optoacoustic allows a non invasive monitoring of the retinal temperature increase during retinal laser irradiation by measuring the temperature dependent pressure amplitudes, which are induced by short probe laser pulses. A 75 ns/ 523 nm Nd:YLF was used as a probe laser at a repetition rate of 1 kHz, and a cw / 532 nm treatment laser for heating. A contact lens was modified with a ring-shaped ultrasonic transducer to detect the pressure waves at the cornea. Temperatures were collected for irradiations leading to soft or invisible lesions. Based on this data the threshold for denaturation was found. By analyzing the initial temperature increase, the further temperature development during irradiation could be predicted. An algorithm was found to calculate the irradiation time, which is needed for a soft lesion formation, from the temperature curve. By this it was possible to provide a real-time dosimetry by automatically switching off the treatment laser after the calculated irradiation time. Automatically controlled coagulations appear softer and more uniformly.

Investigating the Accuracy of Point Clouds Generated for Rock Surfaces

NASA Astrophysics Data System (ADS)

Seker, D. Z.; Incekara, A. H.

2016-12-01

Point clouds which are produced by means of different techniques are widely used to model the rocks and obtain the properties of rock surfaces like roughness, volume and area. These point clouds can be generated by applying laser scanning and close range photogrammetry techniques. Laser scanning is the most common method to produce point cloud. In this method, laser scanner device produces 3D point cloud at regular intervals. In close range photogrammetry, point cloud can be produced with the help of photographs taken in appropriate conditions depending on developing hardware and software technology. Many photogrammetric software which is open source or not currently provide the generation of point cloud support. Both methods are close to each other in terms of accuracy. Sufficient accuracy in the mm and cm range can be obtained with the help of a qualified digital camera and laser scanner. In both methods, field work is completed in less time than conventional techniques. In close range photogrammetry, any part of rock surfaces can be completely represented owing to overlapping oblique photographs. In contrast to the proximity of the data, these two methods are quite different in terms of cost. In this study, whether or not point cloud produced by photographs can be used instead of point cloud produced by laser scanner device is investigated. In accordance with this purpose, rock surfaces which have complex and irregular shape located in İstanbul Technical University Ayazaga Campus were selected as study object. Selected object is mixture of different rock types and consists of both partly weathered and fresh parts. Study was performed on a part of 30m x 10m rock surface. 2D and 3D analysis were performed for several regions selected from the point clouds of the surface models. 2D analysis is area-based and 3D analysis is volume-based. Analysis conclusions showed that point clouds in both are similar and can be used as alternative to each other. This proved that point cloud produced using photographs which are both economical and enables to produce data in less time can be used in several studies instead of point cloud produced by laser scanner.

Tunable External Cavity Quantum Cascade Lasers (EC-QCL): an application field for MOEMS based scanning gratings

NASA Astrophysics Data System (ADS)

Grahmann, Jan; Merten, André; Ostendorf, Ralf; Fontenot, Michael; Bleh, Daniela; Schenk, Harald; Wagner, Hans-Joachim

2014-03-01

In situ process information in the chemical, pharmaceutical or food industry as well as emission monitoring, sensitive trace detection and biological sensing applications would increasingly rely on MIR-spectroscopic anal­ysis in the 3 μm - 12 μm wavelength range. However, cost effective, portable, low power consuming and fast spectrometers with a wide tuning range are not available so far. To provide these MIR-spectrometer properties, the combination of quantum cascade lasers with a MOEMS scanning grating as wavelength selective element in the external cavity is addressed to provide a very compact and fast tunable laser source for spectroscopic analysis.

Ultrasensitive detection of target analyte-induced aggregation of gold nanoparticles using laser-induced nanoparticle Rayleigh scattering.

PubMed

Lin, Jia-Hui; Tseng, Wei-Lung

2015-01-01

Detection of salt- and analyte-induced aggregation of gold nanoparticles (AuNPs) mostly relies on costly and bulky analytical instruments. To response this drawback, a portable, miniaturized, sensitive, and cost-effective detection technique is urgently required for rapid field detection and monitoring of target analyte via the use of AuNP-based sensor. This study combined a miniaturized spectrometer with a 532-nm laser to develop a laser-induced Rayleigh scattering technique, allowing the sensitive and selective detection of Rayleigh scattering from the aggregated AuNPs. Three AuNP-based sensing systems, including salt-, thiol- and metal ion-induced aggregation of the AuNPs, were performed to examine the sensitivity of laser-induced Rayleigh scattering technique. Salt-, thiol-, and metal ion-promoted NP aggregation were exemplified by the use of aptamer-adsorbed, fluorosurfactant-stabilized, and gallic acid-capped AuNPs for probing K(+), S-adenosylhomocysteine hydrolase-induced hydrolysis of S-adenosylhomocysteine, and Pb(2+), in sequence. Compared to the reported methods for monitoring the aggregated AuNPs, the proposed system provided distinct advantages of sensitivity. Laser-induced Rayleigh scattering technique was improved to be convenient, cheap, and portable by replacing a diode laser and a miniaturized spectrometer with a laser pointer and a smart-phone. Using this smart-phone-based detection platform, we can determine whether or not the Pb(2+) concentration exceed the maximum allowable level of Pb(2+) in drinking water. Copyright © 2014 Elsevier B.V. All rights reserved.

Laser Technology in Interplanetary Exploration: The Past and the Future

NASA Technical Reports Server (NTRS)

Smith, David E.

2000-01-01

Laser technology has been used in planetary exploration for many years but it has only been in the last decade that laser altimeters and ranging systems have been selected as flight instruments alongside cameras, spectrometers, magnetometers, etc. Today we have an active laser system operating at Mars and another destined for the asteroid Eros. A few years ago a laser ranging system on the Clementine mission changed much of our thinking about the moon and in a few years laser altimeters will be on their way to Mercury, and also to Europa. Along with the increased capabilities and reliability of laser systems has came the realization that precision ranging to the surface of planetary bodies from orbiting spacecraft enables more scientific problems to be addressed, including many associated with planetary rotation, librations, and tides. In addition, new Earth-based laser ranging systems working with similar systems on other planetary bodies in an asynchronous transponder mode will be able to make interplanetary ranging measurements at the few cm level and will advance our understanding of solar system dynamics and relativistic physics.

Laboratory and clinical data on wound healing by low-power laser from the Medical Institute of Vilafortuny, Spain

NASA Astrophysics Data System (ADS)

Trelles, Mario A.; Mayayo, E.; Resa, A. M.; Rigau, Josepa; Calvo, G.

1991-05-01

Low power laser has been claimed, both at laboratory and for clinical treatment to activate wound healing. Chronic ulcers respond very positively to laser treatment when particular rules of irradiation are take into account. The multiple etiology of chronic ulcers is not conductive to treatment selection, including laser treatment, if the associated illness is not taken into consideration. For more than 14 years our clinical experience have been significantly positive using lasers in the treatment of chronic ulcers. Our causistic, based on 242 cases treated from 1975 through 1983, has kept in many cases very close follow-up for an extended time periods of up to six years after healing. By controlling photographically and microscopically a chronic venous ulcer submitted to low density laser irradiation, as well as by studying the process of reparation of experimental ulcers and burns, produce on laboratory animal, the healing effects of laser radiation can be followed. Statistically, it is possible to estimate that low intensity laser irradiation produces faster reparation of damage tissue.

Guidelines of care for vascular lasers and intense pulse light sources from the European Society for Laser Dermatology.

PubMed

Adamič, M; Pavlović, M D; Troilius Rubin, A; Palmetun-Ekbäck, M; Boixeda, P

2015-09-01

Lasers and non-coherent intense pulse light sources (IPLS) are based on the principle of selective photothermolysis and can be used for the treatment of many vascular skin lesions. A variety of lasers has been developed for the treatment of congenital and acquired vascular lesions which incorporate these concepts into their design. Although laser and light sources are very popular due to their non-invasive nature, caution should be considered by practitioners and patients to avoid permanent side-effects. The aim of these guidelines is to give evidence-based recommendations for the use of lasers and IPLS in the treatment of vascular lesions. These guidelines were produced by a Consensus Panel made up of experts in the field of vascular laser surgery under the auspices of the European Society of Laser Dermatology. Recommendations on the use of vascular lasers and IPLS were made based on the quality of evidence for efficacy, safety, tolerability, cosmetic outcome, patient satisfaction/preference and, where appropriate, on the experts' opinion. The recommendations of these guidelines are graded according to the American College of Chest Physicians Task Force recommendations on Grading Strength of Recommendations and Quality of Evidence in Clinical Guidelines. Lasers and IPLS are very useful and sometimes the only available method to treat various vascular lesions. It is of a paramount importance that the type of laser or IPLS and their specific parameters are adapted to the indication but also that the treating physician is familiar with the device to be used. The crucial issue in treating vascular lesions is to recognize the immediate end-point after laser treatment. This is the single most important factor to ensure both the efficacy of the treatment and avoidance of serious side-effects. © 2015 European Academy of Dermatology and Venereology.

The differentiation of oral soft- and hard tissues using laser induced breakdown spectroscopy - a prospect for tissue specific laser surgery.

PubMed

Rohde, Maximilian; Mehari, Fanuel; Klämpfl, Florian; Adler, Werner; Neukam, Friedrich-Wilhelm; Schmidt, Michael; Stelzle, Florian

2017-10-01

Compared to conventional techniques, Laser surgery procedures provide a number of advantages, but may be associated with an increased risk of iatrogenic damage to important anatomical structures. The type of tissue ablated in the focus spot is unknown. Laser-Induced Breakdown-Spectroscopy (LIBS) has the potential to gain information about the type of material that is being ablated by the laser beam. This may form the basis for tissue selective laser surgery. In the present study, 7 different porcine tissues (cortical and cancellous bone, nerve, mucosa, enamel, dentine and pulp) from 6 animals were analyzed for their qualitative and semiquantitative molecular composition using LIBS. The so gathered data was used to first differentiate between the soft- and hard-tissues using a Calcium-Carbon emission based classifier. The tissues were then further classified using emission-ratio based analysis, principal component analysis (PCA) and linear discriminant analysis (LDA). The relatively higher concentration of Calcium in the hard tissues allows for an accurate first differentiation of soft- and hard tissues (100% sensitivity and specificity). The ratio based statistical differentiation approach yields results in the range from 65% (enamel-dentine pair) to 100% (nerve-pulp, cancellous bone-dentine, cancellous bone-enamel pairs) sensitivity and specificity. Experimental LIBS measuring setup. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

High Power Laser Diode Array Qualification and Guidelines for Space Flight Environments

NASA Technical Reports Server (NTRS)

Ott, Melanie N.; Eegholm, Niels; Stephen, Mark; Leidecker, Henning; Plante, Jeannette; Meadows, Byron; Amzajerdian, Farzin; Jamison, Tracee; LaRocca, Frank

2006-01-01

High-power laser diode arrays (LDAs) are used for a variety of space-based remote sensor laser programs as an energy source for diode-pumped solid-state lasers. LDAs have been flown on NASA missions including MOLA, GLAS and MLA and have continued to be viewed as an important part of the laser-based instrument component suite. There are currently no military or NASA-grade, -specified, or - qualified LDAs available for "off-the-shelf" use by NASA programs. There has also been no prior attempt to define a standard screening and qualification test flow for LDAs for space applications. Initial reliability studies have also produced good results from an optical performance and stability standpoint. Usage experience has shown, howeve that the current designs being offered may be susceptible to catastrophic failures due to their physical construction (packaging) combined with the electro-optical operational modes and the environmental factors of space application. design combined with operational mode was at the root of the failures which have greatly reduced the functionality of the GLAS instrument. The continued need for LDAs for laser-based science instruments and past catastrophic failures of this part type demand examination of LDAs in a manner which enables NASA to select, buy, validate and apply them in a manner which poses as little risk to the success of the mission as possible.

Infrared Lasers in Chemistry.

ERIC Educational Resources Information Center

John, Phillip

1982-01-01

Selected infrared laser chemistry topics are discussed including carbon dioxide lasers, infrared quanta and molecules, laser-induced chemistry, structural isomerization (laser purification, sensitized reactions, and dielectric breakdown), and fundamental principles of laser isotope separation, focusing on uranium isotope separation. (JN)

Effect of Fiberoptic Collimation Technique on 808 nm Wavelength Laser Stimulation of Cochlear Neurons.

PubMed

Wang, Jingxuan; Lu, Jianren; Tian, Lan

2016-06-01

The purpose of this study was to evaluate the effects of fiberoptic collimation technique on auditory neural stimulation in the cochlea with 808 nm wavelength lasers. Recently, the pulsed near-infrared lasers in the 800-1000 nm wavelength range have been investigated as an emerging technique to trigger auditory neural response in the cochlea. A laser beam divergence in the optical stimulation pathway exists, which may affect stimulation efficiency and spatial selectivity. The fiberoptic collimation technique was proposed for cochlear neuron stimulation, and the C-lens element was designed as the collimation structure. The spiral ganglion cells in deafened guinea pigs' cochlea were irradiated with collimated and uncollimated near-infrared lasers. Optically evoked auditory brainstem response (OABR) under the two laser output modes were recorded. Laser with the collimation technique evoked an average 58% higher OABR amplitude than the uncollimated laser output. In addition, the collimated laser setup consumed on average 35.2% of laser energy compared with the uncollimated laser when evoking the same OABR amplitude. The fiberoptic collimation technique improved stimulation efficiency and reduced stimulating energy consumption in near-infrared neural stimulation in cochlea. The positive effects of laser collimation technique could benefit further research in optically based cochlear implants.

Characterisation and Modification of Thermally Stable High Explosives for Laser Flyer Applications

NASA Astrophysics Data System (ADS)

Parker, A.; Claridge, R. P.; Proud, W. G.; Johnson, N. A.

2007-12-01

Laser initiation offers improved weapon survivability, versatility and greater Insensitive Munitions (IM) compliance. Detonators based on laser-driven flyers are less vulnerable to electrical initiation and can be based on insensitive secondary explosives. Additionally, this technology will offer advantages in terms of improved flexibility and reliability. Hexanitrostilbene (HNS) and nonanitro-m-terphenyl (NONA) were selected for investigation at QinetiQ as their increased thermal stability over conventional explosives makes them ideal candidates for use in insensitive munition compliant applications. The response of these materials to short duration high-amplitude shock impulses provided by exploding foil initiators (EFI), the electrical equivalent of a laser-driven flyer system, was investigated. Preparation techniques including sonication and the incorporation of additives were used to sensitize the materials to flyer impact, yet maintain their insensitivity to external hazards. Sonication significantly reduced the particle size of both HNS and NONA. The reduced-size explosives exhibited increased sensitivity to EFI impact than the starting materials.

Interferometric Laser Scanner for Direction Determination

PubMed Central

Kaloshin, Gennady; Lukin, Igor

2016-01-01

In this paper, we explore the potential capabilities of new laser scanning-based method for direction determination. The method for fully coherent beams is extended to the case when interference pattern is produced in the turbulent atmosphere by two partially coherent sources. The performed theoretical analysis identified the conditions under which stable pattern may form on extended paths of 0.5–10 km in length. We describe a method for selecting laser scanner parameters, ensuring the necessary operability range in the atmosphere for any possible turbulence characteristics. The method is based on analysis of the mean intensity of interference pattern, formed by two partially coherent sources of optical radiation. Visibility of interference pattern is estimated as a function of propagation pathlength, structure parameter of atmospheric turbulence, and spacing of radiation sources, producing the interference pattern. It is shown that, when atmospheric turbulences are moderately strong, the contrast of interference pattern of laser scanner may ensure its applicability at ranges up to 10 km. PMID:26805841

Interferometric Laser Scanner for Direction Determination.

PubMed

Kaloshin, Gennady; Lukin, Igor

2016-01-21

In this paper, we explore the potential capabilities of new laser scanning-based method for direction determination. The method for fully coherent beams is extended to the case when interference pattern is produced in the turbulent atmosphere by two partially coherent sources. The performed theoretical analysis identified the conditions under which stable pattern may form on extended paths of 0.5-10 km in length. We describe a method for selecting laser scanner parameters, ensuring the necessary operability range in the atmosphere for any possible turbulence characteristics. The method is based on analysis of the mean intensity of interference pattern, formed by two partially coherent sources of optical radiation. Visibility of interference pattern is estimated as a function of propagation pathlength, structure parameter of atmospheric turbulence, and spacing of radiation sources, producing the interference pattern. It is shown that, when atmospheric turbulences are moderately strong, the contrast of interference pattern of laser scanner may ensure its applicability at ranges up to 10 km.

Surface texture and hardness of dental alloys processed by alternative technologies

NASA Astrophysics Data System (ADS)

Porojan, Liliana; Savencu, Cristina E.; Topală, Florin I.; Porojan, Sorin D.

2017-08-01

Technological developments have led to the implementation of novel digitalized manufacturing methods for the production of metallic structures in prosthetic dentistry. These technologies can be classified as based on subtractive manufacturing, assisted by computer-aided design/computer-aided manufacturing (CAD/CAM) systems, or on additive manufacturing (AM), such as the recently developed laser-based methods. The aim of the study was to assess the surface texture and hardness of metallic structures for dental restorations obtained by alternative technologies: conventional casting (CST), computerized milling (MIL), AM power bed fusion methods, respective selective laser melting (SLM) and selective laser sintering (SLS). For the experimental analyses metallic specimens made of Co-Cr dental alloys were prepared as indicated by the manufacturers. The specimen structure at the macro level was observed by an optical microscope and micro-hardness was measured in all substrates. Metallic frameworks obtained by AM are characterized by increased hardness, depending also on the surface processing. The formation of microstructural defects can be better controlled and avoided during SLM and MIL process. Application of power bed fusion techniques, like SLS and SLM, is currently a challenge in dental alloys processing.

Resonance ionization laser ion sources for on-line isotope separators (invited).

PubMed

Marsh, B A

2014-02-01

A Resonance Ionization Laser Ion Source (RILIS) is today considered an essential component of the majority of Isotope Separator On Line (ISOL) facilities; there are seven laser ion sources currently operational at ISOL facilities worldwide and several more are under development. The ionization mechanism is a highly element selective multi-step resonance photo-absorption process that requires a specifically tailored laser configuration for each chemical element. For some isotopes, isomer selective ionization may even be achieved by exploiting the differences in hyperfine structures of an atomic transition for different nuclear spin states. For many radioactive ion beam experiments, laser resonance ionization is the only means of achieving an acceptable level of beam purity without compromising isotope yield. Furthermore, by performing element selection at the location of the ion source, the propagation of unwanted radioactivity downstream of the target assembly is reduced. Whilst advances in laser technology have improved the performance and reliability of laser ion sources and broadened the range of suitable commercially available laser systems, many recent developments have focused rather on the laser/atom interaction region in the quest for increased selectivity and/or improved spectral resolution. Much of the progress in this area has been achieved by decoupling the laser ionization from competing ionization processes through the use of a laser/atom interaction region that is physically separated from the target chamber. A new application of gas catcher laser ion source technology promises to expand the capabilities of projectile fragmentation facilities through the conversion of otherwise discarded reaction fragments into high-purity low-energy ion beams. A summary of recent RILIS developments and the current status of laser ion sources worldwide is presented.

Studies of the augmentation of reaction rates via laser irradiation in the infrared. Final report, 1 Sep 1973--31 Aug 1976. [H/sub 3/BPF/sub 3/ adduct

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauer, S.H.; Lory, E.R.; Chien, K.

1976-10-15

The objective of this research project, to discover a reaction, involving a sizable substrate (more than three atoms) the rate of which is selectively augmented by infrared laser radiation, has been achieved. A preliminary analysis led to criteria for the selection of an optimum reaction type, and for setting the most suitable experimental parameters. The self-scavenging decomposition was studied for a borane adduct: 2 H/sub 3/BPF/sub 3/ yields B/sub 2/H/sub 6/ + 2PF/sub 3/. The relative photolytic efficiencies of the various lines emitted by a CO2 laser were measured as was also the dependence of the rate on laser power,more » gas pressure and reaction cell temperature. Specificity of vibrational excitation was demonstrated in several ways, most directly by the observed isotope fractionation of H/D and /sup 10/B//sup 11/B ratios. The mechanism of the photoactivation process developed is in quantitative agreement with the observed conversion. A dynamic model (based on a normal mode analysis) was proposed for the selective activation. In a parallel study of borane adducts, we evaluated the thermodynamic and kinetic rate parameters for six exchange and abstraction reactions. Rational structures were proposed for the corresponding transition states. (Author)« less

Impact of release dynamics of laser-irradiated polymer micropallets on the viability of selected adherent cells

PubMed Central

Ma, Huan; Mismar, Wael; Wang, Yuli; Small, Donald W.; Ras, Mat; Allbritton, Nancy L.; Sims, Christopher E.; Venugopalan, Vasan

2012-01-01

We use time-resolved interferometry, fluorescence assays and computational fluid dynamics (CFD) simulations to examine the viability of confluent adherent cell monolayers to selection via laser microbeam release of photoresist polymer micropallets. We demonstrate the importance of laser microbeam pulse energy and focal volume position relative to the glass–pallet interface in governing the threshold energies for pallet release as well as the pallet release dynamics. Measurements using time-resolved interferometry show that increases in laser pulse energy result in increasing pallet release velocities that can approach 10 m s−1 through aqueous media. CFD simulations reveal that the pallet motion results in cellular exposure to transient hydrodynamic shear stress amplitudes that can exceed 100 kPa on microsecond timescales, and which produces reduced cell viability. Moreover, CFD simulation results show that the maximum shear stress on the pallet surface varies spatially, with the largest shear stresses occurring on the pallet periphery. Cell viability of confluent cell monolayers on the pallet surface confirms that the use of larger pulse energies results in increased rates of necrosis for those cells situated away from the pallet centre, while cells situated at the pallet centre remain viable. Nevertheless, experiments that examine the viability of these cell monolayers following pallet release show that proper choices for laser microbeam pulse energy and focal volume position lead to the routine achievement of cell viability in excess of 90 per cent. These laser microbeam parameters result in maximum pallet release velocities below 6 m s−1 and cellular exposure of transient hydrodynamic shear stresses below 20 kPa. Collectively, these results provide a mechanistic understanding that relates pallet release dynamics and associated transient shear stresses with subsequent cellular viability. This provides a quantitative, mechanistic basis for determining optimal operating conditions for laser microbeam-based pallet release systems for the isolation and selection of adherent cells. PMID:22158840

Impact of release dynamics of laser-irradiated polymer micropallets on the viability of selected adherent cells.

PubMed

Ma, Huan; Mismar, Wael; Wang, Yuli; Small, Donald W; Ras, Mat; Allbritton, Nancy L; Sims, Christopher E; Venugopalan, Vasan

2012-06-07

We use time-resolved interferometry, fluorescence assays and computational fluid dynamics (CFD) simulations to examine the viability of confluent adherent cell monolayers to selection via laser microbeam release of photoresist polymer micropallets. We demonstrate the importance of laser microbeam pulse energy and focal volume position relative to the glass-pallet interface in governing the threshold energies for pallet release as well as the pallet release dynamics. Measurements using time-resolved interferometry show that increases in laser pulse energy result in increasing pallet release velocities that can approach 10 m s(-1) through aqueous media. CFD simulations reveal that the pallet motion results in cellular exposure to transient hydrodynamic shear stress amplitudes that can exceed 100 kPa on microsecond timescales, and which produces reduced cell viability. Moreover, CFD simulation results show that the maximum shear stress on the pallet surface varies spatially, with the largest shear stresses occurring on the pallet periphery. Cell viability of confluent cell monolayers on the pallet surface confirms that the use of larger pulse energies results in increased rates of necrosis for those cells situated away from the pallet centre, while cells situated at the pallet centre remain viable. Nevertheless, experiments that examine the viability of these cell monolayers following pallet release show that proper choices for laser microbeam pulse energy and focal volume position lead to the routine achievement of cell viability in excess of 90 per cent. These laser microbeam parameters result in maximum pallet release velocities below 6 m s(-1) and cellular exposure of transient hydrodynamic shear stresses below 20 kPa. Collectively, these results provide a mechanistic understanding that relates pallet release dynamics and associated transient shear stresses with subsequent cellular viability. This provides a quantitative, mechanistic basis for determining optimal operating conditions for laser microbeam-based pallet release systems for the isolation and selection of adherent cells.

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber laser based on one polarization-maintaining fiber Bragg grating incorporating saturable absorber

NASA Astrophysics Data System (ADS)

Feng, Suchun; Xu, Ou; Lu, Shaohua; Chen, Ming; Jian, Shuisheng

2009-08-01

Switchable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber laser at room temperature is demonstrated. One fiber Bragg grating (FBG) directly written in a polarization-maintaining and photosensitive erbiumdoped fiber (PMPEDF) as the wavelength-selective component is used in a linear laser cavity. Due to the polarization hole burning (PHB) enhanced by the polarization-maintaining fiber Bragg grating (PMFBG), the laser can be designed to operate in stable dual-wavelength or wavelength-switching modes with a wavelength spacing of 0.202 nm by adjusting a polarization controller (PC). The stable SLM operation is guaranteed by a saturable absorber (SA). The optical signal-tonoise ratio (OSNR) of the laser is over 40 dB. The amplitude variation in nearly one and half an hour is less than 0.5 dB for both wavelengths.

Laser welding of vas deferens in rodents: initial experience with fluid solders.

PubMed

Trickett, R I; Wang, D; Maitz, P; Lanzetta, M; Owen, E R

1998-01-01

This study evaluates the use of sutureless laser welding for vasovasostomy. In 14 rodents, the left vas deferens underwent vasovasostomy using an albumin-based solder applied to the adventitia of the vas deferens. The solder contained the dye, indocyanine green, to allow selective absorption and denaturation by a fiber-coupled 800-nm diode laser. The right vas deferens served as a control, receiving conventional layered microsurgical repair. We used a removable 4/0 nylon stent and microclamps to appose the vas deferens during repair, with no need for stay sutures. The mean time to perform laser solder repair (23.5 min) and conventional repair (23.3 min) were not significantly different (P=0.91). However, examination after 8 weeks showed that granuloma formation (G) and patency (P) rates for the conventional suture technique (G, 14%; P, 93%) were significantly better than observed for the laser solder technique (G, 57%; P, 50%).

a New Approach for Subway Tunnel Deformation Monitoring: High-Resolution Terrestrial Laser Scanning

NASA Astrophysics Data System (ADS)

Li, J.; Wan, Y.; Gao, X.

2012-07-01

With the improvement of the accuracy and efficiency of laser scanning technology, high-resolution terrestrial laser scanning (TLS) technology can obtain high precise points-cloud and density distribution and can be applied to high-precision deformation monitoring of subway tunnels and high-speed railway bridges and other fields. In this paper, a new approach using a points-cloud segmentation method based on vectors of neighbor points and surface fitting method based on moving least squares was proposed and applied to subway tunnel deformation monitoring in Tianjin combined with a new high-resolution terrestrial laser scanner (Riegl VZ-400). There were three main procedures. Firstly, a points-cloud consisted of several scanning was registered by linearized iterative least squares approach to improve the accuracy of registration, and several control points were acquired by total stations (TS) and then adjusted. Secondly, the registered points-cloud was resampled and segmented based on vectors of neighbor points to select suitable points. Thirdly, the selected points were used to fit the subway tunnel surface with moving least squares algorithm. Then a series of parallel sections obtained from temporal series of fitting tunnel surfaces were compared to analysis the deformation. Finally, the results of the approach in z direction were compared with the fiber optical displacement sensor approach and the results in x, y directions were compared with TS respectively, and comparison results showed the accuracy errors of x, y, z directions were respectively about 1.5 mm, 2 mm, 1 mm. Therefore the new approach using high-resolution TLS can meet the demand of subway tunnel deformation monitoring.

Selective laser ionisation of radionuclide 63Ni

NASA Astrophysics Data System (ADS)

Tsvetkov, G. O.; D'yachkov, A. B.; Gorkunov, A. A.; Labozin, A. V.; Mironov, S. M.; Firsov, V. A.; Panchenko, V. Ya.

2017-02-01

We report a search for a scheme of selective laser stepwise ionisation of radionuclide 63Ni by radiation of a dye laser pumped by a copper vapour laser. A three-stage scheme is found with ionisation through an autoionising state (AIS): 3d 84s2 3F4(E = 0) → 3d 94p 1Fo3(31030.99 cm-1) → 3d 94d 2[7/2]4(49322.56 cm-1) → AIS(67707.61 cm-1) which, by employing saturated radiation intensities provides the ionisation selectivity of above 1200 for 63Ni.

Mass-Selective Laser Photoionization.

ERIC Educational Resources Information Center

Smalley, R. E.

1982-01-01

Discusses the nature and applications of mass-selective laser photoionization. The ionization can be done with a single intense laser pulse lasting a few billionths of a second with no molecular fragmentation. Applications focus on: (1) benzene clusters, excimers, and exciplexes; (2) metal clusters; and (3) triplet formation and decay. (Author/JN)

Tunable all-fiber dissipative-soliton laser with a multimode interference filter.

PubMed

Zhang, Lei; Hu, Jinmeng; Wang, Jianhua; Feng, Yan

2012-09-15

We report on a tunable all-fiber dissipative-soliton laser with a multimode interference filter that consists of a multimode fiber spliced between two single-mode fibers. By carefully selecting the fiber parameters, a filter with a central wavelength at 1032 nm and a bandwidth of 7.6 nm is constructed and used for spectral filtering in an all-normal-dispersion mode-locked ytterbium-doped fiber laser based on nonlinear polarization evolution. The laser delivers 31 mW of average output power with positively chirped 7 ps pulses. The repetition rate of the pulses is 15.3 MHz, and pulse energy is 2.1 nJ. Tunable dissipative-soliton over 12 nm is achieved by applying tension to the single-mode-multimode-single-mode filter.

Erbium-doped fiber ring laser based on few-mode-singlemode-few-mode fiber structure for refractive index measurement

NASA Astrophysics Data System (ADS)

Liu, Jingxuan; Wang, Muguang; Liang, Xiao; Dong, Yue; Xiao, Han; Jian, Shuisheng

2017-08-01

A novel Erbium-doped fiber ring cavity laser sensor for refractive index (RI) measurement based on a special designed few-mode-singlemode-few-mode structure is proposed and experimentally demonstrated. The few-mode fiber is a home-made concentric ring core fiber (CRCF) which can only support two scalar modes. Thus a stable mode interference occurs which functions as a sensing head and band-pass filter to select the lasing wavelength simultaneously. A sensitivity of -45.429 nm/RIU is obtained in the range of 1.333-1.363. High optical signal to noise ratio (OSNR) of ∼45 dB and narrow 3-dB bandwidth of ∼0.1 nm indicate that the fiber ring laser sensing system has a high resolution and accuracy RI measurement.

Clock Technology Development for the Laser Cooling and Atomic Physics (LCAP) Program

NASA Technical Reports Server (NTRS)

Klipstein, W. M.; Thompson, R. J.; Seidel, D. J.; Kohel, J.; Maleki, L.

1998-01-01

The Time and Frequency Sciences and Technology Group at Jet Propulsion Laboratory (JPL) has developed a laser cooling capability for flight and has been selected by NASA to support the Laser-Cooling and Atomic Physics (LCAP) program. Current work in the group includes design and development for tee two laser-cooled atomic clock experiments which have been selected for flight on the International Space Station.

Selective laser vaporization of polypropylene sutures and mesh

NASA Astrophysics Data System (ADS)

Burks, David; Rosenbury, Sarah B.; Kennelly, Michael J.; Fried, Nathaniel M.

2012-02-01

Complications from polypropylene mesh after surgery for female stress urinary incontinence (SUI) may require tedious surgical revision and removal of mesh materials with risk of damage to healthy adjacent tissue. This study explores selective laser vaporization of polypropylene suture/mesh materials commonly used in SUI. A compact, 7 Watt, 647-nm, red diode laser was operated with a radiant exposure of 81 J/cm2, pulse duration of 100 ms, and 1.0-mm-diameter laser spot. The 647-nm wavelength was selected because its absorption by water, hemoglobin, and other major tissue chromophores is low, while polypropylene absorption is high. Laser vaporization of ~200-μm-diameter polypropylene suture/mesh strands, in contact with fresh urinary tissue samples, ex vivo, was performed. Non-contact temperature mapping of the suture/mesh samples with a thermal camera was also conducted. Photoselective vaporization of polypropylene suture and mesh using a single laser pulse was achieved with peak temperatures of 180 and 232 °C, respectively. In control (safety) studies, direct laser irradiation of tissue alone resulted in only a 1 °C temperature increase. Selective laser vaporization of polypropylene suture/mesh materials is feasible without significant thermal damage to tissue. This technique may be useful for SUI procedures requiring surgical revision.

Numerical study on the selective excitation of Helmholtz-Gauss beams in end-pumped solid-state digital lasers with the control of the laser gain transverse position provided by off-axis end pumping

NASA Astrophysics Data System (ADS)

Tsai, Ko-Fan; Chu, Shu-Chun

2018-03-01

This study proposes a complete and unified method for selective excitation of any specified nearly nondiffracting Helmholtz-Gauss (HzG) beam in end-pumped solid-state digital lasers. Four types of the HzG beams: cosine-Gauss beams, Bessel-Gauss beams, Mathieu-Gauss beams, and, in particular, parabolic-Gauss beams are successfully demonstrated to be generated with the proposed methods. To the best of the authors’ knowledge, parabolic-Gauss beams have not yet been directly generated from any kind of laser system. The numerical results of this study show that one can successfully achieve any lasing HzG beams directly from the solid-state digital lasers with only added control of the laser gain transverse position provided by off-axis end pumping. This study also presents a practical digital laser set-up for easily manipulating off-axis pumping in order to achieve the control of the laser gain transverse gain position in digital lasers. The reported results in this study provide advancement of digital lasers in dynamically generating nondiffracting beams. The control of the digital laser cavity gain position creates the possibility of achieving real-time selection of more laser modes in digital lasers, and it is worth further investigation in the future.

Numerical simulation of residual stress in laser based additive manufacturing process

NASA Astrophysics Data System (ADS)

Kalyan Panda, Bibhu; Sahoo, Seshadev

2018-03-01

Minimizing the residual stress build-up in metal-based additive manufacturing plays a pivotal role in selecting a particular material and technique for making an industrial part. In beam-based additive manufacturing, although a great deal of effort has been made to minimize the residual stresses, it is still elusive how to do so by simply optimizing the processing parameters, such as beam size, beam power, and scan speed. Amid different types of additive manufacturing processes, Direct Metal Laser Sintering (DMLS) process uses a high-power laser to melt and sinter layers of metal powder. The rapid solidification and heat transfer on powder bed endows a high cooling rate which leads to the build-up of residual stresses, that will affect the mechanical properties of the build parts. In the present work, the authors develop a numerical thermo-mechanical model for the measurement of residual stress in the AlSi10Mg build samples by using finite element method. Transient temperature distribution in the powder bed was assessed using the coupled thermal to structural model. Subsequently, the residual stresses were estimated with varying laser power. From the simulation result, it found that the melt pool dimensions increase with increasing the laser power and the magnitude of residual stresses in the built part increases.

Directed dewetting of amorphous silicon film by a donut-shaped laser pulse.

PubMed

Yoo, Jae-Hyuck; In, Jung Bin; Zheng, Cheng; Sakellari, Ioanna; Raman, Rajesh N; Matthews, Manyalibo J; Elhadj, Selim; Grigoropoulos, Costas P

2015-04-24

Irradiation of a thin film with a beam-shaped laser is proposed to achieve site-selectively controlled dewetting of the film into nanoscale structures. As a proof of concept, the laser-directed dewetting of an amorphous silicon thin film on a glass substrate is demonstrated using a donut-shaped laser beam. Upon irradiation of a single laser pulse, the silicon film melts and dewets on the substrate surface. The irradiation with the donut beam induces an unconventional lateral temperature profile in the film, leading to thermocapillary-induced transport of the molten silicon to the center of the beam spot. Upon solidification, the ultrathin amorphous silicon film is transformed to a crystalline silicon nanodome of increased height. This morphological change enables further dimensional reduction of the nanodome as well as removal of the surrounding film material by isotropic silicon etching. These results suggest that laser-based dewetting of thin films can be an effective way for scalable manufacturing of patterned nanostructures.

Laser modification of macroscopic properties of metal surface layer

NASA Astrophysics Data System (ADS)

Kostrubiec, Franciszek

1995-03-01

Surface laser treatment of metals comprises a number of diversified technological operations out of which the following can be considered the most common: oxidation and rendering surfaces amorphous, surface hardening of steel, modification of selected physical properties of metal surface layers. In the paper basic results of laser treatment of a group of metals used as base materials for electric contacts have been presented. The aim of the study was to test the usability of laser treatment from the viewpoint of requirements imposed on materials for electric contacts. The results presented in the paper refer to two different surface treatment technologies: (1) modification of infusible metal surface layer: tungsten and molybdenum through laser fusing of their surface layer and its crystallization, and (2) modification of surface layer properties of other metals through laser doping of their surface layer with foreign elements. In the paper a number of results of experimental investigations obtained by the team under the author's supervision are presented.

Laser Encapsulation of Organic Electronics with Adapted Diode Lasers in Flexible Production Processes

NASA Astrophysics Data System (ADS)

Brosda, Maximilian; Olowinsky, Alexander; Pelzer, Alexander

Flexible organic electronics such as OLPV and OLED modules are highly sensitive against water and oxygen. To protect them against the environment and to ensure a long lifetime visual transparent ultra high barrier films are used for the encapsulation process. These multilayer films usually consist of a polymer substrate on which, depending on the requirements, various functional layers are applied. The organic device is then fully packed in this films. Instead of conventional joining these film with adhesive, a flexible laser based process can be an interesting alternative especially for roll2roll applications. According to a precise spectral analysis and a consideration of the interaction between the laser radiation and the individual layers of the film a suitable laser beam source is selected. With this laser beam source the weldability of the films is investigated. For analysis of the weldseam and the melted volume cross sections and scanning-electron-microscopy-images are prepared. The strength of the weld is determined by T-Peel tensile tests.

Improved GaSb-based quantum well laser performance through metamorphic growth on GaAs substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richardson, Christopher J. K., E-mail: richardson@lps.umd.edu; He, Lei; Apiratikul, Paveen

The promise of the metamorphic growth paradigm is to enable design freedom of the substrate selection criteria beyond current choices that are limited by lattice matching requirements. A demonstration of this emerging degree of freedom is reported here by directly comparing identical laser structures grown both pseudomorphically on a GaSb substrate and metamorphically on a GaAs substrate. Improved thermal performance of the metamorphic laser material enables a higher output power before thermal roll-over begins. These performance gains are demonstrated in minimally processed gain-guided broad-area type-I lasers emitting close to 2-μm wavelengths and mounted p-side up. Continuous wave measurements at roommore » temperature yield a T{sub 0} of 145 K and peak output power of 192 mW from metamorphic lasers, compared to a T{sub 0} of 96 K and peak output power of 164 mW from identical lasers grown pseudomorphically on GaSb.« less

Autonomous Selection of a Rover Laser Target on Mars

NASA Image and Video Library

2016-07-21

NASA's Curiosity Mars rover autonomously selects some of the targets for the laser and telescopic camera of the rover's Chemistry and Camera (ChemCam) instrument. For example, on-board software analyzed the image on the left, chose the target highlighted with the yellow dot, and pointed ChemCam to acquire laser analysis and the image on the right. Most ChemCam targets are still selected by scientists discussing rocks or soil seen in images the rover has sent to Earth, but the autonomous targeting provides an added capability. It can offer a head start on acquiring composition information at a location just reached by a drive. The software for target selection and instrument pointing is called AEGIS, for Autonomous Exploration for Gathering Increased Science. The image on the left was taken by the left eye of Curiosity's stereo Navigation Camera (Navcam) a few minutes after the rover completed a drive of about 43 feet (13 meters) on July 14, 2016, during the 1,400th Martian day, or sol, of the rover's work on Mars. Using AEGIS for target selection and pointing based on the Navcam imagery, Curiosity's ChemCam zapped a grid of nine points on a rock chosen for meeting criteria set by the science team. In this run, parameters were set to find bright-toned outcrop rock rather than darker rocks, which in this area tend to be loose on the surface. Within less than 30 minutes after the Navcam image was taken, ChemCam had used its laser on all nine points and had taken before-and-after images of the target area with its remote micro-imager (RMI) camera. The image at right combines those two RMI exposures. The nine laser targets are marked in red at the center. On the Navcam image at left, the yellow dot identifies the selected target area, which is about 2.2 inches (5.6 centimeters) in diameter. An unannotated version of this Sol 1400 Navcam image is available. ChemCam records spectra of glowing plasma generated when the laser hits a target point. These spectra provide information about the chemical elements present in the target. The light-toned patch of bedrock identified by AEGIS on Sol 1400 appears, geochemically, to belong to the "Stimson" sandstone unit of lower Mount Sharp. In mid-2016, Curiosity typically uses AEGIS for selecting a ChemCam target more than once per week. http://photojournal.jpl.nasa.gov/catalog/PIA20762

Parameters in selective laser melting for processing metallic powders

NASA Astrophysics Data System (ADS)

Kurzynowski, Tomasz; Chlebus, Edward; Kuźnicka, Bogumiła; Reiner, Jacek

2012-03-01

The paper presents results of studies on Selective Laser Melting. SLM is an additive manufacturing technology which may be used to process almost all metallic materials in the form of powder. Types of energy emission sources, mainly fiber lasers and/or Nd:YAG laser with similar characteristics and the wavelength of 1,06 - 1,08 microns, are provided primarily for processing metallic powder materials with high absorption of laser radiation. The paper presents results of selected variable parameters (laser power, scanning time, scanning strategy) and fixed parameters such as the protective atmosphere (argon, nitrogen, helium), temperature, type and shape of the powder material. The thematic scope is very broad, so the work was focused on optimizing the process of selective laser micrometallurgy for producing fully dense parts. The density is closely linked with other two conditions: discontinuity of the microstructure (microcracks) and stability (repeatability) of the process. Materials used for the research were stainless steel 316L (AISI), tool steel H13 (AISI), and titanium alloy Ti6Al7Nb (ISO 5832-11). Studies were performed with a scanning electron microscope, a light microscopes, a confocal microscope and a μCT scanner.

Selective Photophysical Modification on Light-Emitting Polymer Films for Micro- and Nano-Patterning

PubMed Central

Zhang, Xinping; Liu, Feifei; Li, Hongwei

2016-01-01

Laser-induced cross-linking in polymeric semiconductors was utilized to achieve micro- and nano-structuring in thin films. Single- and two-photon cross-linking processes led to the reduction in both the refractive index and thickness of the polymer films. The resultant photonic structures combine the features of both relief- and phase-gratings. Selective cross-linking in polymer blend films based on different optical response of different molecular phases enabled “solidification” of the phase-separation scheme, providing a stable template for further photonic structuring. Dielectric and metallic structures are demonstrated for the fabrication methods using cross-linking in polymer films. Selective cross-linking enables direct patterning into polymer films without introducing additional fabrication procedures or additional materials. The diffraction processes of the emission of the patterned polymeric semiconductors may provide enhanced output coupling for light-emitting diodes or distributed feedback for lasers. PMID:28773248

Linearly polarized pumped passively Q-switched Nd:YVO4 microchip laser for Ince-Gaussian laser modes with controllable orientations

NASA Astrophysics Data System (ADS)

He, Hong-Sen; Zhang, Ming-Ming; Dong, Jun; Ueda, Ken-Ichi

2016-12-01

A tilted, linearly polarized laser diode end-pumped Cr4+:YAG passively Q-switched a-cut Nd:YVO4 microchip laser for generating numerous Ince-Gaussian (IG) laser modes with controllable orientations has been demonstrated by selecting the crystalline orientation of an a-cut Nd:YVO4 crystal. The same IG laser mode with different orientations has been achieved with the same absorbed pump power in a passively Q-switched Nd:YVO4 microchip laser under linearly polarized pumping when the incident pump power and the crystalline orientation of an a-cut Nd:YVO4 crystal are both properly selected. The significant improvement of pulsed laser performance of controllable IG modes has been achieved by selecting the crystalline orientation of an a-cut Nd:YVO4 crystal. The maximum pulse energy is obtained along the a-axis of an a-cut Nd:YVO4 crystal and the highest peak power is achieved along the c-axis of an a-cut Nd:YVO4 crystal, respectively, which has potential applications on quantum computation and optical manipulation. The generation of controllable IG laser modes in microchip lasers under linearly polarized pumping provides a convenient and universal way to control IG laser mode numbers with anisotropic crystal as a gain medium.

Effectiveness of CO2 laser with subcision in patients with acne scars.

PubMed

Anupama, Y G; Wahab, Afthab Jameela

2016-11-01

Post-acne facial scarring has always been a challenge to treat. It requires multiple therapeutic modalities as single modality is not hundred percent effective. Therefore, we have combined CO 2 laser resurfacing with subcision in patients with acne scars for better results. The aim is to study the effectiveness and side effects of CO 2 laser with subcision in patients with atrophic acne scars. Fifty patients were selected for the study. Baseline grading was done with Goodman and Baron grading system. Twenty-five patients were randomly selected for subcision followed by CO 2 laser and the remaining patients were selected for CO 2 laser alone. The treatment was done for four sessions at 4-week interval. Clinical photographs were obtained for evaluation. CO 2 laser with subcision showed excellent response in grade-2 and -3 acne scars. Statistically there is a significant difference between CO 2 laser following subcision and CO 2 laser alone at 5% level (p < 0.05). Both procedures were well tolerated with minimal side effects. The highly versatile CO 2 laser is useful for treating acne scars. Subcision prior to the CO 2 laser procedure showed better improvement when compared to CO 2 laser alone. Thus, in acne scars, multiple therapeutic modalities achieve better results.

Selective laser sintering of single-phase powder Cr-V tool steel

NASA Astrophysics Data System (ADS)

Kovalev, A. I.; Mishina, V. P.; Wainstein, D. L.; Titov, V. I.; Moiseev, V. F.; Tolochko, N. K.

2002-10-01

Presented is positive experience from selective laser sintering (SLS) of cylindrical steel specimens (3.0% C, 3.0% Cr, 1.0% Si, 12.0% V, Fe balance) 30 mm long and 5 mm in diameter by rapid prototyping. It was demonstrated that monolithic steel material could be successfully fabricated by this technology. Differential thermal analysis (DTA), scanning electron microscopy (SEM), and x-ray diffractometry (XRD) were used to study the microstructure, phase, and chemical composition of the source material and obtained specimens. Low-melting cementite-based eutectic was found to provide the liquid phase sintering of powder tool steel. The porosity of the green sintered specimens did not exceed 5%. The mean hardness value of sintered specimens was 825 HV.

An auto-locked diode laser system for precision metrology

NASA Astrophysics Data System (ADS)

Beica, H. C.; Carew, A.; Vorozcovs, A.; Dowling, P.; Pouliot, A.; Barron, B.; Kumarakrishnan, A.

2017-05-01

We present a unique external cavity diode laser system that can be auto-locked with reference to atomic and molecular spectra. The vacuum-sealed laser head design uses an interchangeable base-plate comprised of a laser diode and optical elements that can be selected for desired wavelength ranges. The feedback light to the laser diode is provided by a narrow-band interference filter, which can be tuned from outside the laser cavity to fineadjust the output wavelength in vacuum. To stabilize the laser frequency, the digital laser controller relies either on a pattern-matching algorithm stored in memory, or on first or third derivative feedback. We have used the laser systems to perform spectroscopic studies in rubidium at 780 nm, and in iodine at 633 nm. The linewidth of the 780-nm laser system was measured to be ˜500 kHz, and we present Allan deviation measurements of the beat note and the lock stability. Furthermore, we show that the laser system can be the basis for a new class of lidar transmitters in which a temperature-stabilized fiber-Bragg grating is used to generate frequency references for on-line points of the transmitter. We show that the fiber-Bragg grating spectra can be calibrated with reference to atomic transitions.

High brilliance negative ion and neutral beam source

DOEpatents

Compton, Robert N.

1991-01-01

A high brilliance mass selected (Z-selected) negative ion and neutral beam source having good energy resolution. The source is based upon laser resonance ionization of atoms or molecules in a small gaseous medium followed by charge exchange through an alkali oven. The source is capable of producing microampere beams of an extremely wide variety of negative ions, and milliampere beams when operated in the pulsed mode.

Quasi-periodic photonic crystal Fabry–Perot optical filter based on Si/SiO2 for visible-laser spectral selectivity

NASA Astrophysics Data System (ADS)

Qi, Dong; Wang, Xian; Cheng, Yongzhi; Chen, Fu; Liu, Lei; Gong, Rongzhou

2018-06-01

We report on a 1D quasi-periodic photonic crystal Fabry–Perot optical filter Cs(Si/SiO2)3(SiO2/Si)3 for spectral selectivity of visible light and 1.55 µm laser. A material transparency interval of 1.03–2.06 µm makes Si a unique choice of high refractive index material. Owing to the CIE 1931 standard and equal inclination interference, the designed structure can be successfully fabricated with a certain color (brown, khaki, or blue) corresponding to the different Cs physical thickness d and response R(λ). In addition, the peak transmittance T max of the proposed structure can reach as high as 92.56% (Cs  =  20 nm), 90.83% (Cs  =  40 nm), and 88.85% (Cs  =  60 nm) with a relatively narrow full width at half maximum of 4.4, 4.6, and 4.8 nm at 1.55 µm. The as-prepared structure indicates that it is feasible for a photonic crystal Fabry–Perot optical filter to achieve visible-laser (1.55 µm) spectral selectivity.

Deployable wavelength optimizer for multi-laser sensing and communication undersea

NASA Astrophysics Data System (ADS)

Neuner, Burton; Hening, Alexandru; Pascoguin, B. Melvin; Dick, Brian; Miller, Martin; Tran, Nghia; Pfetsch, Michael

2017-05-01

This effort develops and tests algorithms and a user-portable optical system designed to autonomously optimize the laser communication wavelength in open and coastal oceans. In situ optical meteorology and oceanography (METOC) data gathered and analyzed as part of the auto-selection process can be stored and forwarded. The system performs closedloop optimization of three visible-band lasers within one minute by probing the water column via passive retroreflector and polarization optics, selecting the ideal wavelength, and enabling high-speed communication. Backscattered and stray light is selectively blocked by employing polarizers and wave plates, thus increasing the signal-to-noise ratio. As an advancement in instrumentation, we present autonomy software and portable hardware, and demonstrate this new system in two environments: ocean bay seawater and outdoor test pool freshwater. The next generation design is also presented. Once fully miniaturized, the optical payload and software will be ready for deployment on manned and unmanned platforms such as buoys and vehicles. Gathering timely and accurate ocean sensing data in situ will dramatically increase the knowledge base and capabilities for environmental sensing, defense, and industrial applications. Furthermore, communicating on the optimal channel increases transfer rates, propagation range, and mission length, all while reducing power consumption in undersea platforms.

Adaptation and micro-structure of Co-Cr alloy maxillary complete denture base plates fabricated by selective laser melting technique.

PubMed

Ye, Ye; Jiao, Ting; Zhu, Jiarui; Sun, Jian

2018-01-24

The purpose of the study was to evaluate the adaptation and micro-structure of Co-Cr alloy maxillary complete denture base plates fabricated by the selective laser melting (SLM) technique. Twenty pairs of edentulous casts were randomly and evenly divided into two groups, and manufacturing of the Co-Cr alloy maxillary complete denture base was conducted either by the SLM technique or by the conventional method. The base-cast sets were transversally sectioned into three sections at the distal canines, mesial of the first molars and the posterior palatal zone. The gap between the metal base and cast was measured in these three sections with a stereoscopic microscope, and the data were analysed using t tests. A total of five specimens of 5 mm diameter were fabricated with the Co-Cr alloy by SLM and the traditional casting technology. A scanning electron microscope (SEM) was used to evaluate the differences in microstructure between these specimens. There was no statistical difference between the three sections in all four groups (P > 0.05). At the region of the canines, the clearance value for the SLM Co-Cr alloy group was larger than that of the conventional method group (P < 0.05). At the mesial of the first molar region and the posterior palatal zone, there was no statistical difference between the gaps observed in the two groups (P > 0.05). The SLM Co-Cr alloy has a denser microstructure behaviour and less casting defect than the cast Co-Cr alloy. The SLM technique showed initial feasibility for the manufacture of dental bases of complete dentures, but large sample studies are needed to prove its reliability in clinical applications. The mechanical properties and microstructure of the denture frameworks prepared by selective laser melting indicate that these dentures are appropriate for clinical use.

Layerwise Monitoring of the Selective Laser Melting Process by Thermography

NASA Astrophysics Data System (ADS)

Krauss, Harald; Zeugner, Thomas; Zaeh, Michael F.

Selective Laser Melting is utilized to build parts directly from CAD data. In this study layerwise monitoring of the temperature distribution is used to gather information about the process stability and the resulting part quality. The heat distribution varies with different kinds of parameters including scan vector length, laser power, layer thickness and inter-part distance in the job layout. By integration of an off-axis mounted uncooled thermal detector, the solidification as well as the layer deposition are monitored and evaluated. This enables the identification of hot spots in an early stage during the solidification process and helps to avoid process interrupts. Potential quality indicators are derived from spatially resolved measurement data and are correlated to the resulting part properties. A model of heat dissipation is presented based on the measurement of the material response for varying heat input. Current results show the feasibility of process surveillance by thermography for a limited section of the building platform in a commercial system.

Photo-ionization of aluminum in a hot cavity for the selective production of exotic species project

NASA Astrophysics Data System (ADS)

Scarpa, D.; Makhathini, L.; Tomaselli, A.; Grassi, D.; Corradetti, S.; Manzolaro, M.; Vasquez, J.; Calderolla, M.; Rossignoli, M.; Monetti, A.; Andrighetto, A.; Prete, G.

2014-02-01

SPES (Selective Production of Exotic Species) is an Isotope Separation On-Line (ISOL) based accelerator facility that will be built in the Legnaro-Istituto Nazionale di Fisica Nucleare (INFN) Laboratory (Italy), intended to provide intense neutron-rich radioactive ion beams obtained by proton-induced fission of a uranium carbide (UCx) target. Besides this main target material, silicon carbide (SiC) will be the first to be used to deliver p-rich beams. This target will also validate the functionality of the SPES facility with aluminum beam as result of impinging SiC target with proton beam. In the past, off line studies on laser photoionization of aluminum have been performed in Pavia Spectroscopy Laboratory and in Laboratori Nazionali di Legnaro; a XeCl excimer laser was installed in order to test the laser ionization in the SPES hot cavity. With the new Wien filter installed a better characterization of the ionization process in terms of efficiency was performed and results are discussed.

Strategies for laser-induced fluorescence detection of nitric oxide in high-pressure flames. III. Comparison of A-X excitation schemes

NASA Astrophysics Data System (ADS)

Bessler, Wolfgang G.; Schulz, Christof; Lee, Tonghun; Jeffries, Jay B.; Hanson, Ronald K.

2003-08-01

Laser-induced fluorescence (LIF) has proven a reliable technique for nitric oxide (NO) diagnostics in practical combustion systems. However, a wide variety of different excitation and detection strategies are proposed in the literature without giving clear guidelines of which strategies to use for a particular diagnostic situation. We give a brief review of the high-pressure NO LIF diagnostics literature and compare strategies for exciting selected transitions in the A-X(0, 0), (0, 1), and (0, 2) bands using a different detection bandpass. The strategies are compared in terms of NO LIF signal strength, attenuation of laser and signal light in the hot combustion gases, signal selectivity against LIF interference from O2 and CO2, and temperature and pressure sensitivity of the LIF signal. The discussion is based on spectroscopic measurements in laminar premixed methane-air flames at pressures between 1 and 60 bars and on NO and O2 LIF spectral simulations.

Near-infrared tunable laser diode spectroscopy: an easy way for gas sensing

NASA Astrophysics Data System (ADS)

Larive, Marc; Henriot, V.

1997-05-01

A gas sensor using optical spectrometry and dedicated to a specific gas is studied. It should be able to operate out of laboratories with a very long life and a low maintenance requirement. It is based on TLDS (tunable laser diode spectroscopy) and uses a standard Perot-Fabry laser diode already developed for telecommunications. The mode selection is realized by a passband filter and the wavelength tuning is performed via the diode temperature or its injection current. A PIN photodiode is used for detection, however a rough photoacoustic solution is intended for the future. Absorptions as low as 3.10-3 are detected with this rough system and a limit detection of 10-3 is available with a signal to noise ratio of unity. Experiments have shown that this system is strongly selective for the specified gas (currently the methane). A simulation has been performed which very well fits the experiment and allows us to extrapolate the performances of the system for other gases.

Plasma block acceleration based upon the interaction between double targets and an ultra-intense linearly polarized laser pulse

NASA Astrophysics Data System (ADS)

Xu, Yanxia; Wang, Jiaxiang; Hora, Heinrich; Qi, Xin; Xing, Yifan; Yang, Lei; Zhu, Wenjun

2018-04-01

A new scheme of plasma block acceleration based upon the interaction between double targets and an ultra-intense linearly polarized laser pulse with intensity I ˜ 1022 W/cm2 is investigated via two-dimensional particle-in-cell simulations. The targets are composed of a pre-target of low-density aluminium plasma and an overdense main-target of hydrogen plasma. Through intensive parameter optimization, we have observed highly efficient plasma block accelerations with a monochromatic proton beam peaked at GeVs. The underlying mechanism is attributed to the enhancement of the charge separation field due to the properly selected pre-target.

Comparing Laser Welding Technologies with Friction Stir Welding for Production of Aluminum Tailor-Welded Blanks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hovanski, Yuri; Carsley, John; Carlson, Blair

2014-01-15

A comparison of welding techniques was performed to determine the most effective method for producing aluminum tailor-welded blanks for high volume automotive applications. Aluminum sheet was joined with an emphasis on post weld formability, surface quality and weld speed. Comparative results from several laser based welding techniques along with friction stir welding are presented. The results of this study demonstrate a quantitative comparison of weld methodologies in preparing tailor-welded aluminum stampings for high volume production in the automotive industry. Evaluation of nearly a dozen welding variations ultimately led to down selecting a single process based on post-weld quality and performance.

Assessment of laser ablation techniques in a-si technologies for position-sensor development

NASA Astrophysics Data System (ADS)

Molpeceres, C.; Lauzurica, S.; Ocana, J. L.; Gandia, J. J.; Urbina, L.; Carabe, J.

2005-07-01

Laser micromachining of semiconductor and Transparent Conductive Oxides (TCO) materials is very important for the practical applications in photovoltaic industry. In particular, a problem of controlled ablation of those materials with minimum of debris and small heat affected zone is one of the most vital for the successful implementation of laser micromachining. In particular, selective ablation of thin films for the development of new photovoltaic panels and sensoring devices based on amorphous silicon (a-Si) is an emerging field, in which laser micromachining systems appear as appropriate tools for process development and device fabrication. In particular, a promising application is the development of purely photovoltaic position sensors. Standard p-i-n or Schottky configurations using Transparent Conductive Oxides (TCO), a-Si and metals are especially well suited for these applications, appearing selective laser ablation as an ideal process for controlled material patterning and isolation. In this work a detailed study of laser ablation of a widely used TCO, Indium-tin-oxide (ITO), and a-Si thin films of different thicknesses is presented, with special emphasis on the morphological analysis of the generated grooves. The profiles of ablated grooves have been studied in order to determine the best processing conditions, i.e. laser pulse energy and wavelength, and to asses this technology as potentially competitive to standard photolithographic processes. The encouraging results obtained, with well defined ablation grooves having thicknesses in the order of 10 μm both in ITO and a-Si, open up the possibility of developing a high-performance double Schottky photovoltaic matrix position sensor.

Selective ex-vivo photothermal ablation of human pancreatic cancer with albumin functionalized multiwalled carbon nanotubes.

PubMed

Mocan, Lucian; Tabaran, Flaviu A; Mocan, Teodora; Bele, Constantin; Orza, Anamaria Ioana; Lucan, Ciprian; Stiufiuc, Rares; Manaila, Ioana; Iulia, Ferencz; Dana, Iancu; Zaharie, Florin; Osian, Gelu; Vlad, Liviu; Iancu, Cornel

2011-01-01

The process of laser-mediated ablation of cancer cells marked with biofunctionalized carbon nanotubes is frequently called "nanophotothermolysis". We herein present a method of selective nanophotothermolisys of pancreatic cancer (PC) using multiwalled carbon nanotubes (MWCNTs) functionalized with human serum albumin (HSA). With the purpose of testing the therapeutic value of these nanobioconjugates, we have developed an ex-vivo experimental platform. Surgically resected specimens from patients with PC were preserved in a cold medium and kept alive via intra-arterial perfusion. Additionally, the HSA-MWCNTs have been intra-arterially administered in the greater pancreatic artery under ultrasound guidance. Confocal and transmission electron microscopy combined with immunohistochemical staining have confirmed the selective accumulation of HSA-MWCNTs inside the human PC tissue. The external laser irradiation of the specimen has significantly produced extensive necrosis of the malign tissue after the intra-arterial administration of HSA-MWCNTs, without any harmful effects on the surrounding healthy parenchyma. We have obtained a selective photothermal ablation of the malign tissue based on the selective internalization of MWCNTs with HSA cargo inside the pancreatic adenocarcinoma after the ex-vivo intra-arterial perfusion.

Influence of metal substrates on the detection of explosive residues with laser-induced breakdown spectroscopy.

PubMed

Gottfried, Jennifer L

2013-02-01

Laser-induced breakdown spectroscopy is a promising approach for explosive residue detection, but several limitations to its widespread use remain. One issue is that the emission spectra of the residues are dependent on the substrate composition because some of the substrate is usually entrained in the laser-induced plasma and the laser-material interaction can be significantly affected by the substrate type. Here, we have demonstrated that despite the strong spectral variation in cyclotrimethylenetrinitramine (RDX) residues applied to various metal substrates, classification of the RDX residue independent of substrate type is feasible. Several approaches to improving the chemometric models based on partial least squares discriminant analysis (PLS-DA) have been described: classifying the RDX residue spectra together in one class independent of substrate, using selected emission intensities and ratios to increase the true positive rate (TPR) and decrease the false positive rate (FPR), and fusing the results from two PLS-DA models generated using the full broadband spectra and selected intensities and ratios. The combination of these approaches resulted in a TPR of 97.5% and a FPR of 1.0% for RDX classification on metal substrates.

Evaluation of uranium transitions for isotopically-selective laser induced fluorescence with diode lasers (technical report for ST064)

NASA Astrophysics Data System (ADS)

Cannon, B. D.

1993-10-01

Isotopically-selective excitation of uranium atoms by diode lasers can be the basis for a portable instrument to perform uranium isotopic assays in the field. Such an instrument would improve the ability of on-site inspections to detect and deter nuclear proliferation. Published and unpublished spectroscopic data on atomic uranium were examined to identify candidate transitions for isotopically-selective laser excitation with diode lasers. Eleven candidate transitions were identified and evaluated for their potential usefulness for a portable uranium assay instrument. Eight of these transitions are suitable for laser induced fluorescence using different excitation and detection wavelengths, which will improve sensitivity and elemental selectivity. Data sheets on the 25 uranium transitions in the wavelength range 629 nm to 1,000 nm that originate in the ground or first excited states of neutral atomic uranium are included. Each data sheet provides the wavelength, upper and lower energy levels, angular momentum quantum numbers, U-235 isotope shift (relative to U-238, and high-resolution spectra of weapons-grade uranium (93% U-235 and 7% U-238).

Reconfiguration of the multiwavelength operation of optical fiber ring lasers by the modifiable intra-cavity induced losses of an in-fiber tip probe modal Michelson interferometer

NASA Astrophysics Data System (ADS)

Salceda-Delgado, G.; Martinez-Rios, A.; Sierra-Hernandez, J. M.; Rodríguez-Carreón, V. C.; Toral-Acosta, D.; Selvas-Aguilar, R.; Álvarez-Tamayo, R. I.; Castillo-Guzman, A. A.; Rojas-Laguna, R.

2018-03-01

A straightforward and versatile method for switching from single to different multiwavelength laser emission in ring cavity fiber lasers is proposed and demonstrated experimentally. The method is based on using the changeable interference pattern from an optical fiber modal Michelson interferometer as a wavelength selective filter into the ring cavity laser. The interferometer is constructed using a bi-conical tapered fiber and a single-mode fiber segment, with these being spliced together to form an optical fiber tip probe. When the length of the single-mode fiber piece is modified, the phase difference between the interfering modes of the interferometer causes a change in the interferometer free spectral range. As a consequence, the laser intra-cavity losses lead to gain competition, which allows us to adjust the number of simultaneously generated laser lines. A multiwavelength reconfiguration of the laser from one up to a maximum of eight emission lines was obtained, with a maximum SNR of around 47 dBm.

Time of Flight based diagnostics for high energy laser driven ion beams

NASA Astrophysics Data System (ADS)

Scuderi, V.; Milluzzo, G.; Alejo, A.; Amico, A. G.; Booth, N.; Cirrone, G. A. P.; Doria, D.; Green, J.; Kar, S.; Larosa, G.; Leanza, R.; Margarone, D.; McKenna, P.; Padda, H.; Petringa, G.; Pipek, J.; Romagnani, L.; Romano, F.; Schillaci, F.; Borghesi, M.; Cuttone, G.; Korn, G.

2017-03-01

Nowadays the innovative high power laser-based ion acceleration technique is one of the most interesting challenges in particle acceleration field, showing attractive characteristics for future multidisciplinary applications, including medical ones. Nevertheless, peculiarities of optically accelerated ion beams make mandatory the development of proper transport, selection and diagnostics devices in order to deliver stable and controlled ion beams for multidisciplinary applications. This is the main purpose of the ELIMAIA (ELI Multidisciplinary Applications of laser-Ion Acceleration) beamline that will be realized and installed within 2018 at the ELI-Beamlines research center in the Czech Republic, where laser driven high energy ions, up to 60 MeV/n, will be available for users. In particular, a crucial role will be played by the on-line diagnostics system, recently developed in collaboration with INFN-LNS (Italy), consisting of TOF detectors, placed along the beamline (at different detection distances) to provide online monitoring of key characteristics of delivered beams, such as energy, fluence and ion species. In this contribution an overview on the ELIMAIA available ion diagnostics will be briefly given along with the preliminary results obtained during a test performed with high energy laser-driven proton beams accelerated at the VULCAN PW-laser available at RAL facility (U.K.).

Study of Nonlinear Propagation of Ultrashort Laser Pulses and Its Application to Harmonic Generation

NASA Astrophysics Data System (ADS)

Weerawarne, Darshana L.

Laser filamentation, which is one of the exotic nonlinear optical phenomena, is self-guidance of high-power laser beams due to the dynamic balance between the optical Kerr effect (self-focusing) and other nonlinear effects such as plasma defocusing. It has many applications including supercontinuum generation (SCG), high-order harmonic generation (HHG), lightning guiding, stand-off sensing, and rain making. The main focus of this work is on studying odd-order harmonic generation (HG) (i.e., 3o, 5o, 7o, etc., where o is the angular frequency) in centrosymmetric media while a high-power, ultrashort harmonic-driving pulse undergoes nonlinear propagation such as laser filamentation. The investigation of highly-controversial nonlinear indices of refraction by measuring low-order HG in air is carried out. Furthermore, time-resolved (i.e., pump-probe) experiments and significant harmonic enhancements are presented and a novel HG mechanism based on higher-order nonlinearities is proposed to explain the experimental results. C/C++ numerical simulations are used to solve the nonlinear Schrodinger equation (NLSE) which supports the experimental findings. Another project which I have performed is selective sintering using lasers. Short-pulse lasers provide a fascinating tool for material processing, especially when the conventional oven-based techniques fail to process flexible materials for smart energy/electronics applications. I present experimental and theoretical studies on laser processing of nanoparticle-coated flexible materials, aiming to fabricate flexible electronic devices.

Risks and injuries in laser and high-frequency applications

NASA Astrophysics Data System (ADS)

Giering, K.; Philipp, Carsten M.; Berlien, Hans-Peter

1995-01-01

An analysis of injuries and risks using high frequency (HF) and lasers in medicine based on a literature search with MEDLINE was performed. The cases reported in the literature were classified according to the following criteria: (1) Avoidable in an optimal operational procedure. These kind of injuries are caused by a chain of unfortunate incidents. They are in principle avoidable by the 'right action at the right time' which presupposes an appropriate training of the operating team, selection of the optimal parameters for procedure and consideration of all safety instructions. (2) Avoidable, caused by malfunction of the equipment and/or accessories. The injuries classified into this group are avoidable if all safety regulations were fulfilled. This includes a pre-operational check-up and the use of medical lasers and high frequency devices only which meet the international safety standards. (3) Avoidable, caused by misuse/mistake. Injuries of this group were caused by an inappropriate selection of the procedure, wrong medical indication or mistakes during application. (4) Unavoidable, fateful. These injuries can be caused by risks inherent to the type of energy used, malfunction of the equipment and/or accessories though a pre-operational check-up was done. Some risks and complications are common to high frequency and laser application. But whereas these risks can be excluded easily in laser surgery there is often a great expenditure necessary or they are not avoidable if high frequency if used. No unavoidable risks due to laser energy occur.

Laser ion source for multi-nucleon transfer reaction products

NASA Astrophysics Data System (ADS)

Hirayama, Y.; Watanabe, Y. X.; Imai, N.; Ishiyama, H.; Jeong, S. C.; Miyatake, H.; Oyaizu, M.; Kimura, S.; Mukai, M.; Kim, Y. H.; Sonoda, T.; Wada, M.; Huyse, M.; Kudryavtsev, Yu.; Van Duppen, P.

2015-06-01

We have developed a laser ion source for the target-like fragments (TLFs) produced in multi-nucleon transfer (MNT) reactions. The operation principle of the source is based on the in-gas laser ionization and spectroscopy (IGLIS) approach. In the source TLFs are thermalized and neutralized in high pressure and high purity argon gas, and are extracted after being selectively re-ionized in a multi-step laser resonance ionization process. The laser ion source has been implemented at the KEK Isotope Separation System (KISS) for β-decay spectroscopy of neutron-rich isotopes with N = 126 of nuclear astrophysical interest. The simulations of gas flow and ion-beam optics have been performed to optimize the gas cell for efficient thermalization and fast transporting the TLFs, and the mass-separator for efficient transport with high mass-resolving power, respectively. To confirm the performances expected at the design stage, off-line experiments have been performed by using 56Fe atoms evaporated from a filament in the gas cell. The gas-transport time of 230 ms in the argon cell and the measured KISS mass-resolving power of 900 are consistent with the designed values. The high purity of the gas-cell system, which is extremely important for efficient and highly-selective production of laser ions, was achieved and confirmed from the mass distribution of the extracted ions. After the off-line tests, on-line experiments were conducted by directly injecting energetic 56Fe beam into the gas cell. After thermalization of the injected 56Fe beam, laser-produced singly-charged 56Fe+ ions were extracted. The extraction efficiency and selectivity of the gas cell in the presence of plasma induced by 56Fe beam injection as well as the time profile of the extracted ions were investigated; extraction efficiency of 0.25%, a beam purity of >99% and an extraction time of 270 ms. It has been confirmed that the performance of the KISS laser ion source is satisfactory to start the measurements of lifetimes of the β-decayed nuclei with N = 126 .

Selective Laser Melting Produced Ti-6Al-4V: Post-Process Heat Treatments to Achieve Superior Tensile Properties

PubMed Central

Becker, Thorsten H.

2018-01-01

Current post-process heat treatments applied to selective laser melting produced Ti-6Al-4V do not achieve the same microstructure and therefore superior tensile behaviour of thermomechanical processed wrought Ti-6Al-4V. Due to the growing demand for selective laser melting produced parts in industry, research and development towards improved mechanical properties is ongoing. This study is aimed at developing post-process annealing strategies to improve tensile behaviour of selective laser melting produced Ti-6Al-4V parts. Optical and electron microscopy was used to study α grain morphology as a function of annealing temperature, hold time and cooling rate. Quasi-static uniaxial tensile tests were used to measure tensile behaviour of different annealed parts. It was found that elongated α’/α grains can be fragmented into equiaxial grains through applying a high temperature annealing strategy. It is shown that bi-modal microstructures achieve a superior tensile ductility to current heat treated selective laser melting produced Ti-6Al-4V samples. PMID:29342079

Selective laser spectroscopy of molecules and ions in solids: a history, fundamentals and applications

NASA Astrophysics Data System (ADS)

Sapozhnikov, Michael

2018-03-01

A history of the development of selective laser spectroscopy is presented, beginning with a pioneering work by Yu. V. Denisov and V. A. Kizel in 1967, who were the first to demonstrate the possibility of removing the inhomogeneous broadening of luminescence spectra of impurity ions in glasses upon monochromatic resonance excitation. Selective excitation of optical centers can be achieved due to existence of zero-phonon transitions corresponding to narrow homogeneous zero-phonon lines in the spectra of impurity centers in solids, which are hidden in broad inhomogeneous optical bands upon usual nonselective excitation. The fundamentals of zero-phonon transition spectroscopy are considered and the mechanism of removing the inhomogeneous broadening of optical spectra of ions and molecules in crystals and amorphous solids under selective laser excitation of luminescence and persistent hole burning in absorption spectra is presented in detail. Various applications of selective laser spectroscopy for fundamental and applied studies are discussed.

Switchable multi-wavelength fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer with photonic crystal fiber

NASA Astrophysics Data System (ADS)

Chen, W. G.; Lou, S. Q.; Feng, S. C.; Wang, L. W.; Li, H. L.; Guo, T. Y.; Jian, S. S.

2009-11-01

Switchable multi-wavelength fiber ring laser with an in-fiber Mach-Zehnder interferometer incorporated into the ring cavity serving as wavelength-selective filter at room temperature is demonstrated. The filter is formed by splicing a section of few-mode photonic crystal fiber (PCF) and two segments of single mode fiber (SMF) with the air-holes on the both sides of PCF intentionally collapsed in the vicinity of the splices. By adjusting the states of the polarization controller (PC) appropriately, the laser can be switched among the stable single-, dual- and triple-wavelength lasing operations by exploiting polarization hole burning (PHB) effect.

Stabilized and tunable single-longitudinal-mode erbium fiber laser employing ytterbium-doped fiber based interference filter

NASA Astrophysics Data System (ADS)

Yeh, Chien-Hung; Tsai, Ning; Zhuang, Yuan-Hong; Chow, Chi-Wai; Chen, Jing-Heng

2017-02-01

In this demonstration, to achieve stabilized and wavelength-selectable single-longitudinal-mode (SLM) erbium-doped fiber (EDF) laser, a short length of ytterbium-doped fiber (YDF) is utilized to serve as a spatial multi-mode interference (MMI) inside a fiber cavity for suppressing multi-longitudinal-mode (MLM) significantly. In the measurement, the output powers and optical signal to noise ratios (OSNRs) of proposed EDF ring laser are measured between -9.85 and -5.71 dBm; and 38.03 and 47.95 dB, respectively, in the tuning range of 1530.0-1560.0 nm. In addition, the output SLM and stability performance are also analyzed and discussed experimentally.

Quantum Cascade Laser-Based Photoacoustic Sensor for Trace Detection of Formaldehyde Gas

PubMed Central

Elia, Angela; Di Franco, Cinzia; Spagnolo, Vincenzo; Lugarà, Pietro Mario; Scamarcio, Gaetano

2009-01-01

We report on the development of a photoacoustic sensor for the detection of formaldehyde (CH2O) using a thermoelectrically cooled distributed-feedback quantum cascade laser operating in pulsed mode at 5.6 μm. A resonant photoacoustic cell, equipped with four electret microphones, is excited in its first longitudinal mode at 1,380 Hz. The absorption line at 1,778.9 cm−1 is selected for CH2O detection. A detection limit of 150 parts per billion in volume in nitrogen is achieved using a 10 seconds time constant and 4 mW laser power. Measurements in ambient air will require water vapour filters. PMID:22574040

Recent trends in precision measurements of atomic and nuclear properties with lasers and ion traps

NASA Astrophysics Data System (ADS)

Block, Michael

2017-11-01

The X. international workshop on "Application of Lasers and Storage Devices in Atomic Nuclei Research" took place in Poznan in May 2016. It addressed the latest experimental and theoretical achievements in laser and ion trap-based investigations of radionuclides, highly charged ions and antiprotons. The precise determination of atomic and nuclear properties provides a stringent benchmark for theoretical models and eventually leads to a better understanding of the underlying fundamental interactions and symmetries. This article addresses some general trends in this field and highlights select recent achievements presented at the workshop. Many of these are covered in more detail within the individual contributions to this special issue of Hyperfine Interactions.

The impact of dispersion on selective laser melting of titanium and niobium fine powders mixture

NASA Astrophysics Data System (ADS)

Razin, A.; Ovchinnikov, V.; Akhmetshin, R.; Krinitcyn, M.; Fedorov, V.; Akhmetshina, V.

2016-11-01

This paper is dedicated to the study of selective laser melting process of metal powders. Experiments were performed in the Research Center Modern Manufacturing Technologies of TPU with the fine powders of titanium and niobium. The research was carried out on 3D laser printer designed at TPU. In the framework of experiments aimed at determining possibilities of obtaining niobium-titanium alloy by SLS (selective laser sintering) there were studied the basic processes of laser melting and their effect on the quality of final samples and products. We determined operation modes of 3D printers which allow obtaining high quality of printed sample surface. The research results show that rigid requirements related to powder dispersiveness and proportions are needed to achieve better quality of products.

Application of scanning laser Doppler vibrometry for delamination detection in composite structures

NASA Astrophysics Data System (ADS)

Kudela, Pawel; Wandowski, Tomasz; Malinowski, Pawel; Ostachowicz, Wieslaw

2017-12-01

In this paper application of scanning laser Doppler vibrometry for delamination detection in composite structures was presented. Delamination detection was based on a guided wave propagation method. In this papers results from numerical and experimental research were presented. In the case of numerical research, the Spectral Element Method (SEM) was utilized, in which a mesh was composed of 3D spectral elements. SEM model included also a piezoelectric transducer. In the experimental research guided waves were excited using the piezoelectric transducer whereas the sensing process was conducted using scanning laser Doppler vibrometer (SLDV). Analysis of guided wave propagation and its interaction with delamination was based on a full wavefield approach. Attention was focused on interactions of guided waves with delamination manifested by A0 mode reflection, A0 mode entrapment, and S0/A0 mode conversion. Delamination was simulated by a teflon insert located between plies of composite material. Results of interaction with symmetrically and nonsymmetrical placed delamination (in respect to the composite sample thickness) were presented. Moreover, the authors investigated different size of delaminations. Damage detection was based on a new signal processing algorithm proposed by the authors. In this approach the weighted RMS was utilized selectively. It means that the summation in RMS formula was performed only for a specially selected time instances. Results for simple composite panels, panel with honeycomb core, and real stiffened composite panel from the aircraft were presented.

Fiber-coupled 2.7 µm laser absorption sensor for CO2 in harsh combustion environments

NASA Astrophysics Data System (ADS)

Spearrin, R. M.; Goldenstein, C. S.; Jeffries, J. B.; Hanson, R. K.

2013-05-01

A tunable diode laser absorption sensor near 2.7 µm, based on 1f-normalized wavelength-modulation spectroscopy with second-harmonic detection (WMS-2f), was developed to measure CO2 concentration in harsh combustion flows. Wavelength selection at 3733.48 cm-1 exploited the overlap of two CO2 transitions in the ν1 + ν3 vibrational band at 3733.468 cm-1 and 3733.498 cm-1. Primary factors influencing wavelength selection were isolation and strength of the CO2 absorption lines relative to infrared water absorption at elevated pressures and temperatures. The HITEMP 2010 database was used to model the combined CO2 and H2O absorption spectra, and key line-strength and line-broadening spectroscopic parameters were verified by high-temperature static cell measurements. To validate the accuracy and precision of the WMS-based sensor, measurements of CO2 concentration were carried out in non-reactive shock-tube experiments (P ˜ 3-12 atm, T ˜ 1000-2600 K). The laser was then free-space fiber-coupled with a zirconium fluoride single-mode fiber for remote light delivery to harsh combustion environments, and demonstrated on an ethylene/air pulse detonation combustor at pressures up to 10 atm and temperatures up to 2500 K. To our knowledge, this work represents the first time-resolved in-stream measurements of CO2 concentration in a detonation-based engine.

Characteristics of products generated by selective sintering and stereolithography rapid prototyping processes

NASA Technical Reports Server (NTRS)

Cariapa, Vikram

1993-01-01

The trend in the modern global economy towards free market policies has motivated companies to use rapid prototyping technologies to not only reduce product development cycle time but also to maintain their competitive edge. A rapid prototyping technology is one which combines computer aided design with computer controlled tracking of focussed high energy source (eg. lasers, heat) on modern ceramic powders, metallic powders, plastics or photosensitive liquid resins in order to produce prototypes or models. At present, except for the process of shape melting, most rapid prototyping processes generate products that are only dimensionally similar to those of the desired end product. There is an urgent need, therefore, to enhance the understanding of the characteristics of these processes in order to realize their potential for production. Currently, the commercial market is dominated by four rapid prototyping processes, namely selective laser sintering, stereolithography, fused deposition modelling and laminated object manufacturing. This phase of the research has focussed on the selective laser sintering and stereolithography rapid prototyping processes. A theoretical model for these processes is under development. Different rapid prototyping sites supplied test specimens (based on ASTM 638-84, Type I) that have been measured and tested to provide a data base on surface finish, dimensional variation and ultimate tensile strength. Further plans call for developing and verifying the theoretical models by carefully designed experiments. This will be a joint effort between NASA and other prototyping centers to generate a larger database, thus encouraging more widespread usage by product designers.

Selective Removal of Demineralization Using Near Infrared Cross Polarization Reflectance and a Carbon Dioxide Laser.

PubMed

Chan, Kenneth H; Fried, Daniel

2012-02-09

Lasers can ablate/remove tissue in a non-contact mode of operation and a pulsed laser beam does not interfere with the ability to image the tooth surface, therefore lasers are ideally suited for integration with imaging devices for image-guided ablation. Laser energy can be rapidly and efficiently delivered to tooth surfaces using a digitally controlled laser beam scanning system for precise and selective laser ablation with minimal loss of healthy tissues. Under the appropriate irradiation conditions such laser energy can induce beneficial chemical and morphological changes in the walls of the drilled cavity that can increase resistance to further dental decay and produce surfaces with enhanced adhesive properties to restorative materials. Previous studies have shown that images acquired using near-IR transillumination, optical coherence tomography and fluorescence can be used to guide the laser for selective removal of demineralized enamel. Recent studies have shown that NIR reflectance measurements at 1470-nm can be used to obtain images of enamel demineralization with very high contrast. The purpose of this study was to demonstrate that image guided ablation of occlusal lesions can be successfully carried out using a NIR reflectance imaging system coupled with a carbon dioxide laser operating at 9.3-μm with high pulse repetition rates.

Automatic irradiation control by an optical feedback technique for selective retina treatment (SRT) in a rabbit model

NASA Astrophysics Data System (ADS)

Seifert, Eric; Roh, Young-Jung; Fritz, Andreas; Park, Young Gun; Kang, Seungbum; Theisen-Kunde, Dirk; Brinkmann, Ralf

2013-06-01

Selective Retina Therapy (SRT) targets the Retinal Pigment Epithelium (RPE) without effecting neighboring layers as the photoreceptors or the choroid. SRT related RPE defects are ophthalmoscopically invisible. Owing to this invisibility and the variation of the threshold radiant exposure for RPE damage the treating physician does not know whether the treatment was successful or not. Thus measurement techniques enabling a correct dosing are a demanded element in SRT devices. The acquired signal can be used for monitoring or automatic irradiation control. Existing monitoring techniques are based on the detection of micro-bubbles. These bubbles are the origin of RPE cell damage for pulse durations in the ns and μs time regime 5μs. The detection can be performed by optical or acoustical approaches. Monitoring based on an acoustical approach has already been used to study the beneficial effects of SRT on diabetic macula edema and central serous retinopathy. We have developed a first real time feedback technique able to detect micro-bubble induced characteristics in the backscattered laser light fast enough to cease the laser irradiation within a burst. Therefore the laser energy within a burst of at most 30 pulses is increased linearly with every pulse. The laser irradiation is ceased as soon as micro-bubbles are detected. With this automatic approach it was possible to observe invisible lesions, an intact photoreceptor layer and a reconstruction of the RPE within one week.

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Refractive indices of superlattices made of III-V semiconductor compounds and their solid solutions and semiconductor waveguide laser structures

NASA Astrophysics Data System (ADS)

Unger, K.

1988-11-01

An analysis is made of the theoretical problems encountered in precision calculations of refractive indices of semiconductor materials arising in connection with the use of superlattices as active layers in double-heterostructure lasers and in connection with the use of the impurity-induced disordering effect, i.e., the ability to transform selectively a superlattice into a corresponding solid solution. This can be done by diffusion or ion implantation. A review is given of calculations of refractive indices based on the knowledge of the energy band structure and the role of disorder is considered particularly. An anomaly observed in the (InAl)As system is considered. It is shown that the local field effects and exciton transitions are important. A reasonable approach is clearly a direct calculation of the difference between the refractive indices of superlattices based on compounds and of those based on their solid solutions.

Shaping propagation invariant laser beams

NASA Astrophysics Data System (ADS)

Soskind, Michael; Soskind, Rose; Soskind, Yakov

2015-11-01

Propagation-invariant structured laser beams possess several unique properties and play an important role in various photonics applications. The majority of propagation invariant beams are produced in the form of laser modes emanating from stable laser cavities. Therefore, their spatial structure is limited by the intracavity mode formation. We show that several types of anamorphic optical systems (AOSs) can be effectively employed to shape laser beams into a variety of propagation invariant structured fields with different shapes and phase distributions. We present a propagation matrix approach for designing AOSs and defining mode-matching conditions required for preserving propagation invariance of the output shaped fields. The propagation matrix approach was selected, as it provides a more straightforward approach in designing AOSs for shaping propagation-invariant laser beams than the alternative technique based on the Gouy phase evolution, especially in the case of multielement AOSs. Several practical configurations of optical systems that are suitable for shaping input laser beams into a diverse variety of structured propagation invariant laser beams are also presented. The laser beam shaping approach was applied by modeling propagation characteristics of several input laser beam types, including Hermite-Gaussian, Laguerre-Gaussian, and Ince-Gaussian structured field distributions. The influence of the Ince-Gaussian beam semifocal separation parameter and the azimuthal orientation between the input laser beams and the AOSs onto the resulting shape of the propagation invariant laser beams is presented as well.

Vortex Laser based on III-V semiconductor metasurface: direct generation of coherent Laguerre-Gauss modes carrying controlled orbital angular momentum

PubMed Central

Seghilani, Mohamed S.; Myara, Mikhael; Sellahi, Mohamed; Legratiet, Luc; Sagnes, Isabelle; Beaudoin, Grégoire; Lalanne, Philippe; Garnache, Arnaud

2016-01-01

The generation of a coherent state, supporting a large photon number, with controlled orbital-angular-momentum L = ħl (of charge l per photon) presents both fundamental and technological challenges: we demonstrate a surface-emitting laser, based on III-V semiconductor technology with an integrated metasurface, generating vortex-like coherent state in the Laguerre-Gauss basis. We use a first order phase perturbation to lift orbital degeneracy of wavefunctions, by introducing a weak anisotropy called here “orbital birefringence”, based on a dielectric metasurface. The azimuthal symmetry breakdown and non-linear laser dynamics create “orbital gain dichroism” allowing selecting vortex handedness. This coherent photonic device was characterized and studied, experimentally and theoretically. It exhibits a low divergence (<1°) diffraction limited beam, emitting 49 mW output power in the near-IR at λ ≃ 1 μm, a charge l = ±1, … ±4 (>50 dB vortex purity), and single frequency operation in a stable low noise regime (0.1% rms). Such high performance laser opens the path to widespread new photonic applications. PMID:27917885

Nanoparticle assisted laser desorption/ionization mass spectrometry for small molecule analytes.

PubMed

Abdelhamid, Hani Nasser

2018-03-01

Nanoparticle assisted laser desorption/ionization mass spectrometry (NPs-ALDI-MS) shows remarkable characteristics and has a promising future in terms of real sample analysis. The incorporation of NPs can advance several methods including surface assisted LDI-MS, and surface enhanced LDI-MS. These methods have advanced the detection of many thermally labile and nonvolatile biomolecules. Nanoparticles circumvent the drawbacks of conventional organic matrices for the analysis of small molecules. In most cases, NPs offer a clear background without interfering peaks, absence of fragmentation of thermally labile molecules, and allow the ionization of species with weak noncovalent interactions. Furthermore, an enhancement in sensitivity and selectivity can be achieved. NPs enable straightforward analysis of target species in a complex sample. This review (with 239 refs.) covers the progress made in laser-based mass spectrometry in combination with the use of metallic NPs (such as AuNPs, AgNPs, PtNPs, and PdNPs), NPs consisting of oxides and chalcogenides, silicon-based NPs, carbon-based nanomaterials, quantum dots, and metal-organic frameworks. Graphical abstract An overview is given on nanomaterials for use in surface-assisted laser desorption/ionization mass spectrometry of small molecules.

A New Femtosecond Laser-Based Three-Dimensional Tomography Technique

NASA Astrophysics Data System (ADS)

Echlin, McLean P.

2011-12-01

Tomographic imaging has dramatically changed science, most notably in the fields of medicine and biology, by producing 3D views of structures which are too complex to understand in any other way. Current tomographic techniques require extensive time both for post-processing and data collection. Femtosecond laser based tomographic techniques have been developed in both standard atmosphere (femtosecond laser-based serial sectioning technique - FSLSS) and in vacuum (Tri-Beam System) for the fast collection (10 5mum3/s) of mm3 sized 3D datasets. Both techniques use femtosecond laser pulses to selectively remove layer-by-layer areas of material with low collateral damage and a negligible heat affected zone. To the authors knowledge, femtosecond lasers have never been used to serial section and these techniques have been entirely and uniquely developed by the author and his collaborators at the University of Michigan and University of California Santa Barbara. The FSLSS was applied to measure the 3D distribution of TiN particles in a 4330 steel. Single pulse ablation morphologies and rates were measured and collected from literature. Simultaneous two-phase ablation of TiN and steel matrix was shown to occur at fluences of 0.9-2 J/cm2. Laser scanning protocols were developed minimizing surface roughness to 0.1-0.4 mum for laser-based sectioning. The FSLSS technique was used to section and 3D reconstruct titanium nitride (TiN) containing 4330 steel. Statistical analysis of 3D TiN particle sizes, distribution parameters, and particle density were measured. A methodology was developed to use the 3D datasets to produce statistical volume elements (SVEs) for toughness modeling. Six FSLSS TiN datasets were sub-sampled into 48 SVEs for statistical analysis and toughness modeling using the Rice-Tracey and Garrison-Moody models. A two-parameter Weibull analysis was performed and variability in the toughness data agreed well with Ruggieri et al. bulk toughness measurements. The Tri-Beam system combines the benefits of laser based material removal (speed, low-damage, automated) with detectors that collect chemical, structural, and topological information. Multi-modal sectioning information was collected after many laser scanning passes demonstrating the capability of the Tri-Beam system.

Breath Analysis Using Laser Spectroscopic Techniques: Breath Biomarkers, Spectral Fingerprints, and Detection Limits

PubMed Central

Wang, Chuji; Sahay, Peeyush

2009-01-01

Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in laser spectroscopic techniques and laser sources have driven breath analysis to new heights, moving from laboratory research to commercial reality. Laser spectroscopic detection techniques not only have high-sensitivity and high-selectivity, as equivalently offered by the MS-based techniques, but also have the advantageous features of near real-time response, low instrument costs, and POC function. Of the approximately 35 established breath biomarkers, such as acetone, ammonia, carbon dioxide, ethane, methane, and nitric oxide, 14 species in exhaled human breath have been analyzed by high-sensitivity laser spectroscopic techniques, namely, tunable diode laser absorption spectroscopy (TDLAS), cavity ringdown spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), cavity enhanced absorption spectroscopy (CEAS), cavity leak-out spectroscopy (CALOS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb cavity-enhanced absorption spectroscopy (OFC-CEAS). Spectral fingerprints of the measured biomarkers span from the UV to the mid-IR spectral regions and the detection limits achieved by the laser techniques range from parts per million to parts per billion levels. Sensors using the laser spectroscopic techniques for a few breath biomarkers, e.g., carbon dioxide, nitric oxide, etc. are commercially available. This review presents an update on the latest developments in laser-based breath analysis. PMID:22408503

Effects of momentum transfer on sizing of current collectors for lithium-ion batteries during laser cutting

NASA Astrophysics Data System (ADS)

Lee, Dongkyoung; Mazumder, Jyotirmoy

2018-02-01

One of the challenges of the lithium-ion battery manufacturing process is the sizing of electrodes with good cut surface quality. Poor cut surface quality results in internal short circuits in the cells and significant heat generation. One of the solutions that may improve the cut quality with a high cutting speed is laser cutting due to its high energy concentration, fast processing time, high precision, small heat affected zone, flexible range of laser power and contact free process. In order to utilize the advantages of laser electrode cutting, understanding the physical phenomena for each material is crucial. Thus, this study focuses on the laser cutting of current collectors, such as pure copper and aluminum. A 3D self-consistent mathematical model for the laser cutting, including fluid flow, heat transfer, recoil pressure, multiple reflections, capillary and thermo-capillary forces, and phase changes, is presented and solved numerically. Simulation results for the laser cutting are analyzed in terms of penetration time, depth, width, and absorptivity, based on these selected laser parameters. In addition, melt pool flow, melt pool geometry and temperature distribution are investigated.

Reduction of Surface Roughness by Means of Laser Processing over Additive Manufacturing Metal Parts.

PubMed

Alfieri, Vittorio; Argenio, Paolo; Caiazzo, Fabrizia; Sergi, Vincenzo

2016-12-31

Optimization of processing parameters and exposure strategies is usually performed in additive manufacturing to set up the process; nevertheless, standards for roughness may not be evenly matched on a single complex part, since surface features depend on the building direction of the part. This paper aims to evaluate post processing treating via laser surface modification by means of scanning optics and beam wobbling to process metal parts resulting from selective laser melting of stainless steel in order to improve surface topography. The results are discussed in terms of roughness, geometry of the fusion zone in the cross-section, microstructural modification, and microhardness so as to assess the effects of laser post processing. The benefits of beam wobbling over linear scanning processing are shown, as heat effects in the base metal are proven to be lower.

Contemporary review of the 532 nm laser for treatment of benign prostatic hyperplasia.

PubMed

Chughtai, Bilal; Laor, Leanna; Dunphy, Claire; Te, Alexis

2015-04-01

Benign prostatic hyperplasia (BPH) is a condition that occurs increasingly with age. The established gold standard treatment for BPH has been the electrocautery-based transurethral resection of the prostate (TURP). TURP, however, is associated with several complications and side effects. Therefore, there is an increasing interest in a number of emerging minimally invasive therapies as alterative treatment options. Laser therapy using the Greenlight laser is a promising alternative to the traditional TURP. Selective absorption by hemoglobin allows rapid, hemostatic vaporization of prostate tissue. Additional advantages include avoidance or minimization of complications such as intraoperative fluid absorption, and bleeding, retrograde ejaculation, impotence, and incontinence, as well as its use in treating high volume BPH. We review the use of the Greenlight laser in the treatment of BPH, when comparing complications and advantages in relation to TURP.

Reduction of Surface Roughness by Means of Laser Processing over Additive Manufacturing Metal Parts

PubMed Central

Alfieri, Vittorio; Argenio, Paolo; Caiazzo, Fabrizia; Sergi, Vincenzo

2016-01-01

Optimization of processing parameters and exposure strategies is usually performed in additive manufacturing to set up the process; nevertheless, standards for roughness may not be evenly matched on a single complex part, since surface features depend on the building direction of the part. This paper aims to evaluate post processing treating via laser surface modification by means of scanning optics and beam wobbling to process metal parts resulting from selective laser melting of stainless steel in order to improve surface topography. The results are discussed in terms of roughness, geometry of the fusion zone in the cross-section, microstructural modification, and microhardness so as to assess the effects of laser post processing. The benefits of beam wobbling over linear scanning processing are shown, as heat effects in the base metal are proven to be lower. PMID:28772380

Histological effects of He-Ne laser on the healing of experimental colon anastomoses in the rat

NASA Astrophysics Data System (ADS)

Asencio-Arana, Francisco; Torres-Gil, Vicente; Martinez-Soriano, Francisco; Perez-Sarrio, R.

1990-06-01

Despite technical advances, the incidence of anastomotic leaks in elective colorectal surgery remains around 14%, Recent studies suggest that the use of low energy lasers may enhance wound healing in different tissues in a selective, nondestructive manner. Based on these findings we have attempted to provide experimental background on the histological effects of He-Ne laser during the early stages of healing in 70 colonic anastornoses performed on rats, The irradiation of the anastomoses by two doses of 3.6 J/cm produces an increase in the populations of round cells and fibroblasts of the scar tissue, an increase in new vessel formation and a significant improvement in epithelialization. This suggests that the irradiation of colonic wounds with He-Ne lasers can result in an enhancement of healing.

Commissioning of a compact laser-based proton beam line for high intensity bunches around 10Â MeV

NASA Astrophysics Data System (ADS)

Busold, S.; Schumacher, D.; Deppert, O.; Brabetz, C.; Kroll, F.; Blažević, A.; Bagnoud, V.; Roth, M.

2014-03-01

We report on the first results of experiments with a new laser-based proton beam line at the GSI accelerator facility in Darmstadt. It delivers high current bunches at proton energies around 9.6 MeV, containing more than 109 particles in less than 10 ns and with tunable energy spread down to 2.7% (ΔE/E0 at FWHM). A target normal sheath acceleration stage serves as a proton source and a pulsed solenoid provides for beam collimation and energy selection. Finally a synchronous radio frequency (rf) field is applied via a rf cavity for energy compression at a synchronous phase of -90 deg. The proton bunch is characterized at the end of the very compact beam line, only 3 m behind the laser matter interaction point, which defines the particle source.

Stable and wavelength-tunable silicon-micro-ring-resonator based erbium-doped fiber laser.

PubMed

Yang, L G; Yeh, C H; Wong, C Y; Chow, C W; Tseng, F G; Tsang, H K

2013-02-11

In this work, we propose and demonstrate a stable and wavelength-tunable erbium-doped fiber (EDF) ring laser. Here, a silicon-on-insulator (SOI)-based silicon-micro-ring-resonator (SMRR) is used as the wavelength selective element inside the fiber ring cavity. A uniform period grating coupler (GC) is used to couple between the SMRR and single mode fiber (SMF) and serves also as a polarization dependent element in the cavity. The output lasing wavelength of the proposed fiber laser can be tuned at a tuning step of 2 nm (defined by the free spectral range (FSR) of the SMRR) in a bandwidth of 35.2 nm (1532.00 to 1567.20 nm), which is defined by the gain of the EDF. The optical-signal-to-noise-ratio (OSNR) of each lasing wavelength is larger than 42.0 dB. In addition, the output stabilities of power and wavelength are also discussed.

Consensus recommendations from the American acne & rosacea society on the management of rosacea, part 4: a status report on physical modalities and devices.

PubMed

Tanghetti, Emil; Del Rosso, James Q; Thiboutot, Diane; Gallo, Richard; Webster, Guy; Eichenfield, Lawrence F; Stein-Gold, Linda; Berson, Diane; Zaenglein, Andrea

2014-02-01

The fourth article in this 5-part series reviews physical modalities and devices used to treat cutaneous rosacea based on consensus recommendations from the American Acne & Rosacea Society (AARS) on the management of the common presentations of cutaneous rosacea. The major therapeutic uses of physical modalities and devices, especially laser and light-based systems, are for treatment of telangiectases and persistent facial erythema (background erythema). Phymas, especially rhinophyma, also are treated with physical modalities such as ablative lasers or surgical devices (eg, electrosurgical loop). Appropriately selected and properly used lasers and intense pulsed light (IPL) devices can successfully address specific clinical manifestations of rosacea that exhibit limited or no response to available medical therapies, such as telangiectases and background centrofacial erythema. Rosacea-associated symptoms also may improve. In most cases, treatment will need to be repeated intermittently to sustain improvement.

Part-per-trillion level SF6 detection using a quartz enhanced photoacoustic spectroscopy-based sensor with single-mode fiber-coupled quantum cascade laser excitation.

PubMed

Spagnolo, Vincenzo; Patimisco, Pietro; Borri, Simone; Scamarcio, Gaetano; Bernacki, Bruce E; Kriesel, Jason

2012-11-01

A sensitive spectroscopic sensor based on a hollow-core fiber-coupled quantum cascade laser (QCL) emitting at 10.54 μm and quartz enhanced photoacoustic spectroscopy (QEPAS) technique is reported. The design and realization of mid-IR fiber and coupler optics has ensured single-mode QCL beam delivery to the QEPAS sensor. The collimation optics was designed to produce a laser beam of significantly reduced beam size and waist so as to prevent illumination of the quartz tuning fork and microresonator tubes. SF(6) was selected as the target gas. A minimum detection sensitivity of 50 parts per trillion in 1 s was achieved with a QCL power of 18 mW, corresponding to a normalized noise-equivalent absorption of 2.7×10(-10) W·cm(-1)/Hz(1/2).

Part-Per-Trillion Level SF6 Detection Using a Quartz Enhanced Photoacoustic Spectroscopy-Based Sensor with Single-Mode Fiber-Coupled Quantum Cascade Laser Excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spagnolo, V.; Patimisco, P.; Borri, Simone

2012-10-23

A sensitive spectroscopic sensor based on a hollow-core fiber-coupled quantum cascade laser (QCL) emitting at 10.54 µm and quartz enhanced photoacoustic spectroscopy (QEPAS) technique is reported. The design and realization of mid-infrared fiber and coupler optics has ensured single-mode QCL beam delivery to the QEPAS sensor . The collimation optics was designed to produce a laser beam of significantly reduced beam size and waist so as to prevent illumination of the quartz tuning fork and micro-resonator tubes. SF6 was selected as the target gas. A minimum detection sensitivity of 50 parts per trillion in 1 s was achieved with amore » QCL power of 18 mW, corresponding to a normalized noise-equivalent absorption of 2.7x10-10 W•cm-1/Hz1/2.« less

Selective treatment of carious dentin using a mid-infrared tunable pulsed laser at 6 μm wavelength range

NASA Astrophysics Data System (ADS)

Saiki, Masayuki; Ishii, Katsunori; Yoshikawa, Kazushi; Yasuo, Kenzo; Yamamoto, Kazuyo; Awazu, Kunio

2011-03-01

Optical technologies have good potential for caries detection, prevention, excavation, and the realization of minimal intervention dentistry. This study aimed to develop a selective excavation technique of carious tissue using the specific absorption in 6 μm wavelength range. Bovine dentin demineralized with lactic acid solution was used as a carious dentin model. A mid-infrared tunable pulsed laser was obtained by difference-frequency generation technique. The wavelength was tuned to 6.02 and 6.42 μm which correspond to absorption bands called amide I and amide II, respectively. The laser delivers 5 ns pulse width at a repetition rate of 10 Hz. The morphological change after irradiation was observed with a scanning electron microscope, and the measurement of ablation depth was performed with a confocal laser microscope. At λ = 6.02 μm and the average power density of 15 W/cm2, demineralized dentin was removed selectively with less-invasive effect on sound dentin. The wavelength of 6.42 μm also showed the possibility of selective removal. High ablation efficiency and low thermal side effect were observed using the nanosecond pulsed laser with λ = 6.02 μm. In the near future, development of compact laser device will open the minimal invasive laser treatment to the dental clinic.

Single mode pulsed dye laser oscillator

DOEpatents

Hackel, Richard P.

1992-01-01

A single mode pulsed dye laser oscillator is disclosed. The dye laser oscillator provides for improved power efficiency by reducing the physical dimensions of the overall laser cavity, which improves frequency selection capability.

In vitro and in vivo targeting of hollow gold nanoshells directed at epidermal growth factor receptors for photothermal ablation therapy

PubMed Central

Melancon, Marites P.; Lu, Wei; Yang, Zhi; Zhang, Rui; Cheng, Zhi; Elliot, Andrew M.; Stafford, Jason; Olson, Tammy; Zhang, Jin Z.; Li, Chun

2009-01-01

Laser-induced phototherapy is a new therapeutic use of electromagnetic radiation for cancer treatment. The use of targeted plasmonic gold nanoparticles can reduce the laser energy necessary for selective tumor cell destruction. However, the ability for targeted delivery of the currently used gold nanoparticles to tumor cells is limited. Here, we describe a new class of molecular specific photothermal coupling agents based on hollow gold nanoshells (HAuNS, average diameter ~30 nm) covalently attached to monoclonal antibody directed at epidermal growth factor receptor (EGFR). The resulting anti-EGFR-HAuNS exhibited excellent colloidal stability and efficient photothermal effect in the near-infrared region. EGFR-mediated, selective uptake of anti-EGFR-HAuNS in EGFR-positive A431 tumor cells but not IgG-HAuNS control was demonstrated in vitro by imaging scattered light from the nanoshells. Irradiation of A431 cells treated with anti-EGFR-HAuNS with near-infrared laser resulted in selective destruction of these cells. In contrast, cells treated with anti-EGFR-HAuNS alone, laser alone, or IgG-HAuNS plus laser did not show observable effect on cell viability. Using 111In-labeled HAuNS, we showed that anti-EGFR-HAuNS could be delivered to EGFR-positive tumors at 6.8% of injected dose per gram of tissue, and the microscopic image of excised tumor with scattering signal from nanoshells confirmed preferential delivery to A431 tumor of anti-EGFR-HAuNS compared with IgG-HAuNS. The absence of silica core, the relatively small particle size and high tumor uptake, and the absence of cytotoxic surfactant required to stabilize other gold nanoparticles suggest that immuno-hollow gold nanoshells have the potential to extend to in vivo molecular therapy. PMID:18566244

Analysis of enamel surface damage after selective laser ablation of composite from tooth surfaces.

PubMed

Chan, Kenneth H; Hirasuna, Krista; Fried, Daniel

2014-02-01

Resin-based composites are used for many applications in dentistry. They are difficult to remove without damage to the underlying enamel since they adhere strongly and are color matched to the tooth. The objective of this study was to determine if an automated laser scanning system with spectral feedback could be used for selective removal of residual orthodontic composite from tooth surfaces with minimal damage to the underlying enamel. A CO 2 laser operating at a wavelength of 9.3 μm with a pulse duration of 10-15 μs and a pulse repetition rate of ~200 Hz was used to selectively remove composite from the buccal surfaces of extracted teeth. A spectral feedback system utilizing a miniature spectrometer was used to control the laser scanning system. Pulpal temperature measurements were performed during composite removal to determine if there was excessive heat accumulation. Conventional and digital microscopes were used to assess the amount of enamel lost during removal. The amount of enamel lost averaged between 20 and 25 μm for irradiation intensities from 3.8 to 4.2 J/cm 2 , respectively. An average maximum temperature rise of 1.9±1.5°C was recorded, with no teeth approaching the critical value of 5.5°C. The average time for composite removal from an area of 5 mm 2 was 19.3±4.1 s, fast enough for clinical feasibility. Residual composite can be rapidly removed from tooth surfaces using a CO 2 laser with spectral feedback, with minimal temperature rise within the pulp and with minimal loss of sound enamel.

Synchronization of pulses from mode-locked lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harvey, G.T.

A study of the synchronization of mode-locked lasers is presented. In particular, we investigate the timing of the laser output pulses with respect to the radio frequency (RF) signal driving the mode-locking elements in the laser cavity. Two types of mode-locked lasers are considered: a cw loss-modulated mode-locked argon ion laser; and a q-switched active-passive mode-locked Nd:YAG laser. We develop theoretical models for the treatment of laser pulse synchronization in both types of lasers. Experimental results are presented on a combined laser system that synchronizes pulses from both an argon ion and a Nd:YAG laser by using a common RFmore » signal to drive independent mode-lockers in both laser cavities. Shot to shot jitter as low as 18 ps (RMS) was measured between the output pulses from the two lasers. The theory of pulse synchronization for the cw loss-modulated mode-locked argon ion laser is based on the relationship between the timing of the mode-locked laser pulse (with respect to the peak of the RF signal) and the length of the laser cavity. Experiments on the argon laser include the measurement of the phase shift of the mode-locked pulse as a function of cavity length and intracavity intensity. The theory of synchronization of the active-passive mode-locked Nd:YAG laser is an extension of the pulse selection model of the active-passive laser. Experiments on the active-passive Nd:YAG laser include: measurement of the early noise fluctuations; measurement of the duration of the linear build-up stage (time between laser threshold and saturation of the absorber); measurement of jitter as a function of the mode-locker modulation depth; and measurement of the output pulse phase shift as a function of cavity length.« less

Single mode pulsed dye laser oscillator

DOEpatents

Hackel, R.P.

1992-11-24

A single mode pulsed dye laser oscillator is disclosed. The dye laser oscillator provides for improved power efficiency by reducing the physical dimensions of the overall laser cavity, which improves frequency selection capability. 6 figs.

Ambient methods and apparatus for rapid laser trace constituent analysis

DOEpatents

Snyder, Stuart C.; Partin, Judy K.; Grandy, Jon D.; Jeffery, Charles L.

2002-01-01

A method and apparatus are disclosed for measuring trace amounts of constituents in samples by using laser induced breakdown spectroscopy and laser induced fluorescence under ambient conditions. The laser induced fluorescence is performed at a selected wavelength corresponding to an absorption state of a selected trace constituent. The intensity value of the emission decay signal which is generated by the trace constituent is compared to calibrated emission intensity decay values to determine the amount of trace constituent present.

Lateral electrochemical etching of III-nitride materials for microfabrication

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Jung

Conductivity-selective lateral etching of III-nitride materials is described. Methods and structures for making vertical cavity surface emitting lasers with distributed Bragg reflectors via electrochemical etching are described. Layer-selective, lateral electrochemical etching of multi-layer stacks is employed to form semiconductor/air DBR structures adjacent active multiple quantum well regions of the lasers. The electrochemical etching techniques are suitable for high-volume production of lasers and other III-nitride devices, such as lasers, HEMT transistors, power transistors, MEMs structures, and LEDs.

Development of Processing Parameters for Organic Binders Using Selective Laser Sintering

NASA Technical Reports Server (NTRS)

Mobasher, Amir A.

2003-01-01

This document describes rapid prototyping, its relation to Computer Aided Design (CAD), and the application of these techniques to choosing parameters for Selective Laser Sintering (SLS). The document reviews the parameters selected by its author for his project, the SLS machine used, and its software.

Quantitative elemental imaging of heterogeneous catalysts using laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Trichard, F.; Sorbier, L.; Moncayo, S.; Blouët, Y.; Lienemann, C.-P.; Motto-Ros, V.

2017-07-01

Currently, the use of catalysis is widespread in almost all industrial processes; its use improves productivity, synthesis yields and waste treatment as well as decreases energy costs. The increasingly stringent requirements, in terms of reaction selectivity and environmental standards, impose progressively increasing accuracy and control of operations. Meanwhile, the development of characterization techniques has been challenging, and the techniques often require equipment with high complexity. In this paper, we demonstrate a novel elemental approach for performing quantitative space-resolved analysis with ppm-scale quantification limits and μm-scale resolution. This approach, based on laser-induced breakdown spectroscopy (LIBS), is distinguished by its simplicity, all-optical design, and speed of operation. This work analyzes palladium-based porous alumina catalysts, which are commonly used in the selective hydrogenation process, using the LIBS method. We report an exhaustive study of the quantification capability of LIBS and its ability to perform imaging measurements over a large dynamic range, typically from a few ppm to wt%. These results offer new insight into the use of LIBS-based imaging in the industry and paves the way for innumerable applications.

Laser fabrication of porous silicon-based platforms for cell culturing.

PubMed

Peláez, Ramón-J; Afonso, Carmen-N; Vega, Fidel; Recio-Sánchez, Gonzalo; Torres-Costa, Vicente; Manso-Silván, Miguel; García-Ruiz, Josefa-P; Martín-Palma, Raúl-J

2013-11-01

In this study, we explore the selective culturing of human mesenchymal stem cells (hMSCs) on Si-based diffractive platforms. We demonstrate a single-step and flexible method for producing platforms on nanostructured porous silicon (nanoPS) based on the use of single pulses of an excimer laser to expose phase masks. The resulting patterns are typically 1D patterns formed by fringes or 2D patterns formed by circles. They are formed by alternate regions of almost unmodified nanoPS and regions where the nanoPS surface has melted and transformed into Si nanoparticles. The patterns are produced in relatively large areas (a few square millimeters) and can have a wide range of periodicities and aspect ratios. Direct binding, that is, with no previous functionalization of the pattern, alignment, and active polarization of hMSCs are explored. The results show the preferential direct binding of the hMSCs along the transformed regions whenever their width compares with the dimensions of the cells and they escape from patterns for smaller widths suggesting that the selectivity can be tailored through the pattern period. Copyright © 2013 Wiley Periodicals, Inc.

Optical Characterization and 2,525 micron Lasing of Cr(2+):Cd(0.85)Mn(0.15)Te

NASA Technical Reports Server (NTRS)

Davis, V. R.; Wu, X.; Hoemmerich, U.; Trivedi, S. B.; Grasza, K.; Yu, Z.

1997-01-01

Transition metal doped solids are of significant current interest for the development of tunable solid-state lasers for the near and mid-infrared (1-4 pm) spectral region. Applications of these lasers include basic research in atomic, molecular, and solid-state physics, optical communication, medicine, and environmental studies of the atmosphere. In transition metal based laser materials, absorption and emission of light arises from electronic transitions between crystal field split energy levels of 3d transition metal ions. The optical spectra generally exhibit broad bands due to the strong interaction between dopant and host (electron-phonon coupling). Broad emission bands offer the prospect of tunable laser activity over a wide wavelength range, e.g. the tuning range of Ti:Sapphire extends from 700-1100 run. The only current transition metal laser operating in the mid-infrared wavelength region (1.8-2.4 micro-m) is CO(2+):MgF2, but its performance is severely limited due to strong nonradiative decay at room temperature. Based on lifetime data, the quantum efficiency is estimated to be less than 3 deg/0 11,21. In general, the probability for non-radiative decay via multi-phonon relaxation increases with decreasing energy gap between ground and excited state. Therefore, efficient transition metal lasers beyond -1.6 micro-m are rare. Recently, tunable laser activity around 2.3 micro-m was observed from Cr doped ZnS and ZnSe. The new lasing center in these materials was identified as Cr(2+) occupying the tetrahedral Zn site. Tetrahedrally coordinated optical centers are rather unusual among transition metal lasers. Their potential usefulness, however, has been demonstrated by the recent development of near infrared laser materials such as Cr:forsterite and Cr:YAG, which are based on tetrahedrally coordinated Cr(4+) ions. According to the Laporte selection rule, electric-dipole transition within the optically active 3d-electron shells are parity forbidden. However, a static acentric electric crystal field or the coupling of asymmetric phonons can force electric-dipole transitions by the admixture of wave functions with opposite parity. Tetrahedral sites lack inversion symmetry which provides the odd-parity field necessary to relax the parity selection rule. Therefore, high absorption and emission cross sections are observed. An enhanced radiative emission rate is also expected to reduce the detrimental effect of non-radiative decay. Motivated by the initial results on Cr doped ZnS and ZnSe, we have started a comprehensive effort to study Cr(2+) doped II-VI semiconductors for solid-state laser applications. In this paper we present the optical properties and the demonstration of mid-infrared lasing from Cr doped Cd(0.85)Mn(0.15)Te.

Pancreatic tumor detection using hypericin-based fluorescence spectroscopy and cytology

NASA Astrophysics Data System (ADS)

Lavu, Harish; Geary, Kevin; Fetterman, Harold R.; Saxton, Romaine E.

2005-04-01

Hypericin is a novel, highly fluorescent photosensitizer that exhibits selective tumor cell uptake properties and is particularly resistant to photobleaching. In this study, we have characterized hypericin uptake in human pancreatic tumor cells with relation to incubation time, cell number, and drug concentration. Ex vivo hypericin based fluorescence spectroscopy was performed to detect the presence of MIA PaCa-2 pancreatic tumor cells in the peritoneal cavity of BALB/c nude mice, as well as to quantify gross tumor burden. Hypericin based cytology of peritoneal lavage samples, using both one and two photon laser confocal microscopy, demonstrated more than a two-fold increase in fluorescence emission of pancreatic tumor cells as compared to control samples. In vitro treatment of pancreatic cancer cells with hypericin based photodynamic therapy showed tumor cell cytotoxicity in a drug dose, incident laser power, and time dependent manner. For these experiments, a continuous wavelength solid-state laser source (532 nm) was operated at power levels in the range of 100-400 mW. Potential applications of hypericin in tumor diagnosis, staging, and therapy will be presented.

Design of Wear-Resistant Austenitic Steels for Selective Laser Melting

NASA Astrophysics Data System (ADS)

Lemke, J. N.; Casati, R.; Lecis, N.; Andrianopoli, C.; Varone, A.; Montanari, R.; Vedani, M.

2018-03-01

Type 316L stainless steel feedstock powder was modified by alloying with powders containing carbide/boride-forming elements to create improved wear-resistant austenitic alloys that can be readily processed by Selective Laser Melting. Fe-based alloys with high C, B, V, and Nb contents were thus produced, resulting in a microstructure that consisted of austenitic grains and a significant amount of hard carbides and borides. Heat treatments were performed to modify the carbide distribution and morphology. Optimal hard-phase spheroidization was achieved by annealing the proposed alloys at 1150 °C for 1 hour followed by water quenching. The total increase in hardness of samples containing 20 pct of C/B-rich alloy powder was of 82.7 pct while the wear resistance could be increased by a factor of 6.

Holmium laser use in the treatment of selected dry eye syndrome complications

NASA Astrophysics Data System (ADS)

Kecik, Dariusz; Kecik, Tadeusz; Kasprzak, Jan; Kecik, Mariusz

1996-03-01

The authors present initial results of treatment selected complications of dry eye syndrome with holmium laser. The lacrimal puncta obliteration and coagulation of the corneal ulcer surface were done.

Sensitive, selective, disposable electrochemical dopamine sensor based on PEDOT-modified laser scribed graphene.

PubMed

Xu, Guangyuan; Jarjes, Zahraa A; Desprez, Valentin; Kilmartin, Paul A; Travas-Sejdic, Jadranka

2018-06-01

The fabrication of a novel, and highly selective electrochemical sensor based on a poly(3,4-ethylenedioxythiophene) (PEDOT) modified laser scribed graphene (LSG), and detection of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA) is described. LSG electrodes were produced with a 3-dimensional macro-porous network and large electrochemically-active surface area via direct laser writing on polyimide sheets. PEDOT was electrodeposited on the LSG electrode, and the physical properties of the obtained films were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray diffraction microanalysis (EDAX). The modified electrodes were applied for the determination of DA in the presence of AA and UA using cyclic voltammetry (CV), and differential pulse voltammetry (DPV) techniques. The linear range for dopamine detection was found to be 1-150 µM with a sensitivity of 0.220 ± 0.011 µA μM -1 and a detection limit of 0.33 µM; superior values to those obtained without PEDOT. For the first time, PEDOT-modified LSG have been fabricated and assessed for high-performance dopamine sensing using cost-effective, disposable electrodes, with potential for development in further sensing applications. Copyright © 2018 Elsevier B.V. All rights reserved.

System and method of infrared matrix-assisted laser desorption/ionization mass spectrometry in polyacrylamide gels

DOEpatents

Haglund, Jr., Richard F.; Ermer, David R.; Baltz-Knorr, Michelle Lee

2004-11-30

A system and method for desorption and ionization of analytes in an ablation medium. In one embodiment, the method includes the steps of preparing a sample having analytes in a medium including at least one component, freezing the sample at a sufficiently low temperature so that at least part of the sample has a phase transition, and irradiating the frozen sample with short-pulse radiation to cause medium ablation and desorption and ionization of the analytes. The method further includes the steps of selecting a resonant vibrational mode of at least one component of the medium and selecting an energy source tuned to emit radiation substantially at the wavelength of the selected resonant vibrational mode. The medium is an electrophoresis medium having polyacrylamide. In one embodiment, the energy source is a laser, where the laser can be a free electron laser tunable to generate short-pulse radiation. Alternatively, the laser can be a solid state laser tunable to generate short-pulse radiation. The laser can emit light at various ranges of wavelength.

In vitro laser nerve repair: protein solder strip irradiation or irradiation alone?

PubMed

Trickett, I; Dawes, J M; Knowles, D S; Lanzetta, M; Owen, E R

1997-01-01

This study investigated the potential of sutureless nerve repair using two promising laser fusion methods: direct 2 microns irradiation of the epineurium, and protein solder assisted epineurial fusion using a 800 nm laser. Laser anastomosis of the rat sciatic nerve was performed in vitro without stay sutures in two groups of six animals. In the first group, direct laser fusion used a pulsed Cr, Tm: YAG laser. In the second group an albumin-based fluid solder containing the dye indocyanine green was applied to the epineurium, then irradiated with a diode laser. These two techniques were compared with regards to coaptation success and axonal damage. Direct laser welding produced weak bonds despite microscopic investigation of the irradiated nerves showing fusion of the epineurium. The unsatisfactory bonding can be attributed to poor tissue overlap and insufficient protein in the thin epineurium denaturation of underlying axons was also observed. In contrast, the laser solder method produced successful welds with greatly reduced axonal damage, and significantly improved the tensile strength. This study confirmed the technical possibilities of sutureless nerve anastomosis. Laser activated solders enable stronger bonds, by the addition of protein to the anastomosis site, and less thermal damage to underlying tissue through selective absorption of laser energy by dye in the solder. Further in vivo studies are required before drawing final conclusions.

Mid-infrared laser-absorption diagnostic for vapor-phase measurements in an evaporating n-decane aerosol

NASA Astrophysics Data System (ADS)

Porter, J. M.; Jeffries, J. B.; Hanson, R. K.

2009-09-01

A novel three-wavelength mid-infrared laser-based absorption/extinction diagnostic has been developed for simultaneous measurement of temperature and vapor-phase mole fraction in an evaporating hydrocarbon fuel aerosol (vapor and liquid droplets). The measurement technique was demonstrated for an n-decane aerosol with D 50˜3 μ m in steady and shock-heated flows with a measurement bandwidth of 125 kHz. Laser wavelengths were selected from FTIR measurements of the C-H stretching band of vapor and liquid n-decane near 3.4 μm (3000 cm -1), and from modeled light scattering from droplets. Measurements were made for vapor mole fractions below 2.3 percent with errors less than 10 percent, and simultaneous temperature measurements over the range 300 K< T<900 K were made with errors less than 3 percent. The measurement technique is designed to provide accurate values of temperature and vapor mole fraction in evaporating polydispersed aerosols with small mean diameters ( D 50<10 μ m), where near-infrared laser-based scattering corrections are prone to error.

Space-based laser-powered orbital transfer vehicle (Project SLICK)

NASA Technical Reports Server (NTRS)

1988-01-01

The project SLICK (Space Laser Interorbital Cargo Kite) involves conceptual designs of reusable space-based laser-powered orbital transfer vehicle (LOTV) for ferrying 16,000 kg cargo primarily between low Earth orbit (LEO) and geosynchronous earth orbit (GEO). The power of LOTV is beamed by a single 32-MW solar-pumped iodide laser orbiting the Earth at an altitude of one Earth radius. The laser engine selected for the LOTV is based on a continuous-wave, steady-state propulsion scheme and uses an array of seven discrete plasmas in a flow of hydrogen propellant. Both all-propulsive and aerobraked LOTV configurations were analyzed and developed. The all-propulsive vehicle uses a rigid 11.5-m aperture primary mirror and its engine produces a thrust of 2000 N at a specific impulse of 1500 sec. For the LEO-to-GEO trip, the payload ratio, m(sub payload/m(sub propellant)+m(sub dry vehicle) = 1.19 and the trip time is about 6 days. The aerobraked version uses a lightweight, retractable wrapped-rib primary mirror which is folded for aerobraking and a 20-m-diameter inflatable-ballute aeroshield which is jettisoned after aeromaneuver. Lifecycle cost analysis shows that the aerobraked configuration may have an economic advantage over the all-propulsive configuration as long as the cost of launching the propellant to LEO is higher than about $500/kg in current dollars.

Laser-induced selective metallization of polypropylene doped with multiwall carbon nanotubes

NASA Astrophysics Data System (ADS)

Ratautas, Karolis; Gedvilas, Mindaugas; Stankevičiene, Ina; Jagminienė, Aldona; Norkus, Eugenijus; Pira, Nello Li; Sinopoli, Stefano; Račiukaitis, Gediminas

2017-08-01

Moulded interconnect devices (MID) offer the material, weight and cost saving by integration electronic circuits directly into polymeric components used in automotive and other consumer products. Lasers are used to write circuits directly by modifying the surface of polymers followed by an electroless metal plating. A new composite material - the polypropylene doped with multiwall carbon nanotubes was developed for the laser-induced selective metallization. Mechanism of surface activation by laser irradiation was investigated in details utilising pico- and nanoseconds lasers. Deposition of copper was performed in the autocatalytic electroless plating bath. The laser-activated polymer surfaces have been studied using the Raman spectroscopy and scanning electron microscope (SEM). Microscopic images revealed that surface becomes active only after its melting by a laser. Alterations in the Raman spectra of the D and G bands indicated the clustering of carbon additives in the composite material. Optimal laser parameters for the surface activation were found by measuring a sheet resistance of the finally metal-plated samples. A spatially selective copper plating was achieved with the smallest conductor line width of 22 μm at the laser scanning speed of 3 m/s and the pulse repetition rate of 100 kHz. Finally, the technique was validated by making functional electronic circuits by this MID approach.

Research on the optoacoustic communication system for speech transmission by variable laser-pulse repetition rates

NASA Astrophysics Data System (ADS)

Jiang, Hongyan; Qiu, Hongbing; He, Ning; Liao, Xin

2018-06-01

For the optoacoustic communication from in-air platforms to submerged apparatus, a method based on speech recognition and variable laser-pulse repetition rates is proposed, which realizes character encoding and transmission for speech. Firstly, the theories and spectrum characteristics of the laser-generated underwater sound are analyzed; and moreover character conversion and encoding for speech as well as the pattern of codes for laser modulation is studied; lastly experiments to verify the system design are carried out. Results show that the optoacoustic system, where laser modulation is controlled by speech-to-character baseband codes, is beneficial to improve flexibility in receiving location for underwater targets as well as real-time performance in information transmission. In the overwater transmitter, a pulse laser is controlled to radiate by speech signals with several repetition rates randomly selected in the range of one to fifty Hz, and then in the underwater receiver laser pulse repetition rate and data can be acquired by the preamble and information codes of the corresponding laser-generated sound. When the energy of the laser pulse is appropriate, real-time transmission for speaker-independent speech can be realized in that way, which solves the problem of underwater bandwidth resource and provides a technical approach for the air-sea communication.

Esophageal-guided biopsy with volumetric laser endomicroscopy and laser cautery marking: a pilot clinical study.

PubMed

Suter, Melissa J; Gora, Michalina J; Lauwers, Gregory Y; Arnason, Thomas; Sauk, Jenny; Gallagher, Kevin A; Kava, Lauren; Tan, Khay M; Soomro, Amna R; Gallagher, Timothy P; Gardecki, Joseph A; Bouma, Brett E; Rosenberg, Mireille; Nishioka, Norman S; Tearney, Guillermo J

2014-06-01

Biopsy surveillance protocols for the assessment of Barrett's esophagus can be subject to sampling errors, resulting in diagnostic uncertainty. Optical coherence tomography is a cross-sectional imaging technique that can be used to conduct volumetric laser endomicroscopy (VLE) of the entire distal esophagus. We have developed a biopsy guidance platform that places endoscopically visible marks at VLE-determined biopsy sites. The objective of this study was to demonstrate in human participants the safety and feasibility of VLE-guided biopsy in vivo. A pilot feasibility study. Massachusetts General Hospital. A total of 22 participants were enrolled from January 2011 to June 2012 with a prior diagnosis of Barrett's esophagus. Twelve participants were used to optimize the laser marking parameters and the system platform. A total of 30 target sites were selected and marked in real-time by using the VLE-guided biopsy platform in the remaining 10 participants. Volumetric laser endomicroscopy. Endoscopic and VLE visibility, and accuracy of VLE diagnosis of the tissue between the laser cautery marks. There were no adverse events of VLE and laser marking. The optimal laser marking parameters were determined to be 2 seconds at 410 mW, with a mark separation of 6 mm. All marks made with these parameters were visible on endoscopy and VLE. The accuracies for diagnosing tissue in between the laser cautery marks by independent blinded readers for endoscopy were 67% (95% confidence interval [CI], 47%-83%), for VLE intent-to-biopsy images 93% (95% CI, 78%-99%), and for corrected VLE post-marking images 100% when compared with histopathology interpretations. This is a single-center feasibility study with a limited number of patients. Our results demonstrate that VLE-guided biopsy of the esophagus is safe and can be used to guide biopsy site selection based on the acquired volumetric optical coherence tomography imaging data. ( NCT01439633.). Copyright © 2014 American Society for Gastrointestinal Endoscopy. Published by Mosby, Inc. All rights reserved.

Esophageal-guided biopsy with volumetric laser endomicroscopy and laser cautery marking: a pilot clinical study

PubMed Central

Suter, Melissa J.; Gora, Michalina J.; Lauwers, Gregory Y.; Arnason, Thomas; Sauk, Jenny; Gallagher, Kevin A.; Kava, Lauren; Tan, Khay M.; Soomro, Amna R.; Gallagher, Timothy P.; Gardecki, Joseph A.; Bouma, Brett E.; Rosenberg, Mireille; Nishioka, Norman S.; Tearney, Guillermo J.

2018-01-01

Background Biopsy surveillance protocols for the assessment of Barrett’s esophagus can be subject to sampling errors, resulting in diagnostic uncertainty. Optical coherence tomography is a cross-sectional imaging technique that can be used to conduct volumetric laser endomicroscopy (VLE) of the entire distal esophagus. We have developed a biopsy guidance platform that places endoscopically visible marks at VLE-determined biopsy sites. Objective The objective of this study was to demonstrate in human participants the safety and feasibility of VLE-guided biopsy in vivo. Design A pilot feasibility study. Setting Massachusetts General Hospital. Patients A total of 22 participants were enrolled from January 2011 to June 2012 with a prior diagnosis of Barrett’s esophagus. Twelve participants were used to optimize the laser marking parameters and the system platform. A total of 30 target sites were selected and marked in real-time by using the VLE-guided biopsy platform in the remaining 10 participants. Intervention Volumetric laser endomicroscopy. Main Outcome Measurements Endoscopic and VLE visibility, and accuracy of VLE diagnosis of the tissue between the laser cautery marks. Results There were no adverse events of VLE and laser marking. The optimal laser marking parameters were determined to be 2 seconds at 410 mW, with a mark separation of 6 mm. All marks made with these parameters were visible on endoscopy and VLE. The accuracies for diagnosing tissue in between the laser cautery marks by independent blinded readers for endoscopy were 67% (95% confidence interval [CI], 47%–83%), for VLE intent-to-biopsy images 93% (95% CI, 78%–99%), and for corrected VLE post-marking images 100% when compared with histopathology interpretations. Limitations This is a single-center feasibility study with a limited number of patients. Conclusion Our results demonstrate that VLE-guided biopsy of the esophagus is safe and can be used to guide biopsy site selection based on the acquired volumetric optical coherence tomography imaging data. (Clinical trial registration number: NCT01439633.) PMID:24462171

Off-axis holographic laser speckle contrast imaging of blood vessels in tissues

NASA Astrophysics Data System (ADS)

Abdurashitov, Arkady; Bragina, Olga; Sindeeva, Olga; Sergey, Sindeev; Semyachkina-Glushkovskaya, Oxana V.; Tuchin, Valery V.

2017-09-01

Laser speckle contrast imaging (LSCI) has become one of the most common tools for functional imaging in tissues. Incomplete theoretical description and sophisticated interpretation of measurement results are completely sidelined by a low-cost and simple hardware, fastness, consistent results, and repeatability. In addition to the relatively low measuring volume with around 700 μm of the probing depth for the visible spectral range of illumination, there is no depth selectivity in conventional LSCI configuration; furthermore, in a case of high NA objective, the actual penetration depth of light in tissues is greater than depth of field (DOF) of an imaging system. Thus, the information about these out-of-focus regions persists in the recorded frames but cannot be retrieved due to intensity-based registration method. We propose a simple modification of LSCI system based on the off-axis holography to introduce after-registration refocusing ability to overcome both depth-selectivity and DOF problems as well as to get the potential possibility of producing a cross-section view of the specimen.

Site-selective nitrogen isotopic ratio measurement of nitrous oxide using a TE-cooled CW-RT-QCL based spectrometer.

PubMed

Li, Jingsong; Zhang, Lizhu; Yu, Benli

2014-12-10

The feasibility of laser spectroscopic isotopic composition measurements of atmospheric N2O was demonstrated, although making them useful will require further improvements. The system relies on a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser source emitting wavelength of around 4.6μm, where strong fundamental absorption bands occur for the considered specie and its isotopomers. The analysis technique is based on wavelength modulation spectroscopy with second-harmonic detection and the combination of long-path absorption cell. Primary laboratory tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of (15)N/(14)N and (18)O/(16)O isotope ratios. The experiment results showed that the site-selective (15)N/(14)N ratio can be measured with a precision of 3‰ with 90s averaging time using natural-abundance N2O sample of 12.7ppm. Copyright © 2014 Elsevier B.V. All rights reserved.

Narrow-band double-pass superluminescent diodes emitting at 1060 nm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lobintsov, A A; Perevozchikov, M V; Shramenko, M V

2009-09-30

Experimental data are presented which show that double-pass superluminescent diodes (SLDs) with fibre Bragg grating (FBG) based spectrally selective external reflectors offer emission linewidths in the range 0.1-1.0 nm, i.e., one to two orders of magnitude narrower in comparison with conventional SLDs and considerably broader in comparison with single-frequency semiconductor lasers. Their optical power at the single-mode fibre output reaches 5.0-8.0 mW, and can be raised to 50 mW using a semiconductor optical amplifier. (lasers)

Free-space wavelength-multiplexed optical scanner.

PubMed

Yaqoob, Z; Rizvi, A A; Riza, N A

2001-12-10

A wavelength-multiplexed optical scanning scheme is proposed for deflecting a free-space optical beam by selection of the wavelength of the light incident on a wavelength-dispersive optical element. With fast tunable lasers or optical filters, this scanner features microsecond domain scan setting speeds and large- diameter apertures of several centimeters or more for subdegree angular scans. Analysis performed indicates an optimum scan range for a given diffraction order and grating period. Limitations include beam-spreading effects based on the varying scanner aperture sizes and the instantaneous information bandwidth of the data-carrying laser beam.

Stable L-band multi-wavelength SOA fiber laser based on polarization rotation.

PubMed

Liu, Tonghui; Jia, Dongfang; Yang, Tianxin; Wang, Zhaoying; Liu, Ying

2017-04-01

We propose and experimentally demonstrate a stable multi-wavelength fiber ring laser operating in the L-band with wavelength spacing of 25 GHz. The mechanism is induced by a polarization rotation intensity equalizer consisting of a semiconductor optical amplifier and polarization devices. A Fabry-Perot filter is inserted into the cavity to serve as a multi-wavelength selection device. Stable L-band multi-wavelength lasing with 3 dB uniformity of 21.2 nm, and simultaneous oscillation of 101 lines with wavelength spacing of 25 GHz, is obtained.

Advanced laser stratospheric monitoring systems analyses

NASA Technical Reports Server (NTRS)

Larsen, J. C.

1984-01-01

This report describes the software support supplied by Systems and Applied Sciences Corporation for the study of Advanced Laser Stratospheric Monitoring Systems Analyses under contract No. NAS1-15806. This report discusses improvements to the Langley spectroscopic data base, development of LHS instrument control software and data analyses and validation software. The effect of diurnal variations on the retrieved concentrations of NO, NO2 and C L O from a space and balloon borne measurement platform are discussed along with the selection of optimum IF channels for sensing stratospheric species from space.

A Novel Nanoparticle Mediated Selective Inner Retinal Photocoagulation for Diseases of the Inner Retina.

PubMed

Singh, Rupesh; Rajaraman, Srinivas; Balasubramanian, Madhusudhanan

2017-10-01

A novel nanoparticle mediated methodology for laser photocoagulation of the inner retina to achieve tissue selective treatment is presented. Transport of 527, 577, and 810 nm laser, heat deposition, and eventual thermal damage in vitreous, retina, RPE, choroid, and sclera were modeled using Bouguer-Beer-Lambert law of absorption and solved numerically using the finite volume method. Nanoparticles were designed using Mie theory of scattering. Performance of the new photocoagulation strategy using gold nanospheres and gold-silica nanoshells was compared with that of conventional methods without nanoparticles. For experimental validation, vitreous cavity of ex vivo porcine eyes was infused with gold nanospheres. After ~6 h of nanoparticle diffusion, the porcine retina was irradiated with a green laser and imaged simultaneously using a spectral domain optical coherence tomography (Spectralis SD-OCT, Heidelberg Engineering). Our computational model predicted a significant spatial shift in the peak temperature from RPE to the inner retinal region when infused with nanoparticles. Arrhenius thermal damage in the mid-retinal location was achieved in ~14 ms for 527 nm laser thereby reducing the irradiation duration by ~30 ms compared with the treatment without nanoparticles. In ex vivo porcine eyes infused with gold nanospheres, SD-OCT retinal images revealed a lower thermal damage and expansion at RPE due to laser photocoagulation. Nanoparticle infused laser photocoagulation strategy provided a selective inner retinal thermal damage with significant decrease in laser power and laser exposure time. The proposed treatment strategy shows possibilities for an efficient and highly selective inner retinal laser treatment.

Monolithically integrated mid-infrared sensor using narrow mode operation and temperature feedback

NASA Astrophysics Data System (ADS)

Ristanic, Daniela; Schwarz, Benedikt; Reininger, Peter; Detz, Hermann; Zederbauer, Tobias; Andrews, Aaron Maxwell; Schrenk, Werner; Strasser, Gottfried

2015-01-01

A method to improve the sensitivity and selectivity of a monolithically integrated mid-infrared sensor using a distributed feedback laser (DFB) is presented in this paper. The sensor is based on a quantum cascade laser/detector system built from the same epitaxial structure and with the same fabrication approach. The devices are connected via a dielectric-loaded surface plasmon polariton waveguide with a twofold function: it provides high light coupling efficiency and a strong interaction of the light with the environment (e.g., a surrounding fluid). The weakly coupled DFB quantum cascade laser emits narrow mode light with a FWHM of 2 cm-1 at 1586 cm-1. The room temperature laser threshold current density is 3 kA/cm2 and a pulsed output power of around 200 mW was measured. With the superior laser noise performance, due to narrow mode emission and the compensation of thermal fluctuations, the lower limit of detection was expanded by one order of magnitude to the 10 ppm range.

CO{sub 2} Laser Ablation Propulsion Area Scaling With Polyoxymethylene Propellant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sinko, John E.; Ichihashi, Katsuhiro; Ogita, Naoya

The topic of area scaling is of great importance in the laser propulsion field, including applications to removal of space debris and to selection of size ranges for laser propulsion craft in air or vacuum conditions. To address this issue experimentally, a CO{sub 2} laser operating at up to 10 J was used to irradiate targets. Experiments were conducted in air and vacuum conditions over a range of areas from about 0.05-5 cm{sup 2} to ablate flat polyoxymethylene targets at several fluences. Theoretical effects affecting area scaling, such as rarefaction waves, thermal diffusion, and diffraction, are discussed in terms ofmore » the experimental results. Surface profilometry was used to characterize the ablation samples. A CFD model is used to facilitate analysis, and key results are compared between experimental and model considerations. The dependence of key laser propulsion parameters, including the momentum coupling coefficient and specific impulse, are calculated based on experimental data, and results are compared to existing literature data.« less

Switchable dual-wavelength SLM narrow linewidth fiber laser based on nonlinear amplifying loop mirror

NASA Astrophysics Data System (ADS)

Fu, Pan; Feng, Xiao-qiang; Lu, Baole; Qi, Xin-yuan; Chen, Haowei; Sun, Bo; Jiang, Man; Wang, Kaile; Bai, Jintao

2018-01-01

We demonstrate a stable switchable dual-wavelength single longitudinal mode (SLM) narrow linewidth ytterbium-doped fiber (YDF) laser using a nonlinear amplifying fiber loop mirror (NALM) at 1064 nm. The NALM of intensity-dependent transmission acts as a saturable absorber filter and an amplitude equalizer to suppress mode competition and the fiber Bragg grating (FBG) pair is used as one wavelength selection component. By properly adjusting the polarization controllers (PCs), the switchable dual-wavelength SLM fiber laser can be operated steadily at room temperature. The optical signal-to-noise ratio (OSNR) is better than 50 dB for both lasing wavelengths. Meanwhile, the linewidth of the fiber laser for each wavelength is approximate 17.07 kHz and 18.64 kHz with a 20 dB linewidth, which means the laser linewidth is approximate 853 Hz and 932 Hz FWHM. Correspondingly, the measured relative intensity noise (RIN) is less than -120 dB/Hz at frequencies over 5.0 MHz.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandula, Gábor, E-mail: mandula.gabor@wigner.mta.hu; Kis, Zsolt; Lengyel, Krisztián

We report on a method for real-time dynamic calibration of a tunable external cavity diode laser by using a partially mode-matched plano-concave Fabry-Pérot interferometer in reflection geometry. Wide range laser frequency scanning is carried out by piezo-driven tilting of a diffractive grating playing the role of a frequency selective mirror in the laser cavity. The grating tilting system has a considerable mechanical inertness, so static laser frequency calibration leads to false results. The proposed real-time dynamic calibration based on the identification of primary- and Gouy-effect type secondary interference peaks with known frequency and temporal history can be used for amore » wide scanning range (from 0.2 GHz to more than 1 GHz). A concave spherical mirror with a radius of R = 100 cm and a plain 1% transmitting mirror was used as a Fabry-Pérot interferometer with various resonator lengths to investigate and demonstrate real-time calibration procedures for two kinds of laser frequency scanning functions.« less

Nuclear Science and Applications with the Next Generation of High-Power Lasers and Brilliant Low-Energy Gamma Beams at ELI-NP

NASA Astrophysics Data System (ADS)

Gales, S.; ELI-NP Team

2015-10-01

The development of high power lasers and the combination of such novel devices with accelerator technology has enlarged the science reach of many research fields, in particular High Energy, Nuclear and Astrophysics as well as societal applications in Material Science, Nuclear Energy and Medicine. The European Strategic Forum for Research Infrastructures (ESFRI) has selected a proposal based on these new premises called "ELI" for Extreme Light Infrastructure. ELI will be built as a network of three complementary pillars at the frontier of laser technologies. The ELI-NP pillar (NP for Nuclear Physics) is under construction near Bucharest (Romania) and will develop a scientific program using two 10 PW class lasers and a Back Compton Scattering High Brilliance and Intense Low Energy Gamma Beam, a marriage of Laser and Accelerator technology at the frontier of knowledge. In the present paper, the technical and scientific status of the project as well as the applications of the gamma source will be discussed.

Ultrasensitive and selective gold film-based detection of mercury (II) in tap water using a laser scanning confocal imaging-surface plasmon resonance system in real time.

PubMed

Zhang, Hongyan; Yang, Liquan; Zhou, Bingjiang; Liu, Weimin; Ge, Jiechao; Wu, Jiasheng; Wang, Ying; Wang, Pengfei

2013-09-15

An ultrasensitive and selective detection of mercury (II) was investigated using a laser scanning confocal imaging-surface plasmon resonance system (LSCI-SPR). The detection limit was as low as 0.01ng/ml for Hg(2+) ions in ultrapure and tap water based on a T-rich, single-stranded DNA (ssDNA)-modified gold film, which can be individually manipulated using specific T-Hg(2+)-T complex formation. The quenching intensity of the fluorescence images for rhodamine-labeled ssDNA fitted well with the changes in SPR. The changes varied with the Hg(2+) ion concentration, which is unaffected by the presence of other metal ions. The coefficients obtained for ultrapure and tap water were 0.99902 and 0.99512, respectively, for the linear part over a range of 0.01-100ng/ml. The results show that the double-effect sensor has potential for practical applications with ultra sensitivity and selectivity, especially in online or real-time monitoring of Hg(2+) ions pollution in tap water with the further improvement of portable LSCI-SPR instrument. Copyright © 2013 Elsevier B.V. All rights reserved.

Method and apparatus for chemical and topographical microanalysis

NASA Technical Reports Server (NTRS)

Kossakovski, Dmitri A. (Inventor); Baldeschwieler, John D. (Inventor); Beauchamp, Jesse L. (Inventor)

2002-01-01

A scanning probe microscope is combined with a laser induced breakdown spectrometer to provide spatially resolved chemical analysis of the surface correlated with the surface topography. Topographical analysis is achieved by scanning a sharp probe across the sample at constant distance from the surface. Chemical analysis is achieved by the means of laser induced breakdown spectroscopy by delivering pulsed laser radiation to the sample surface through the same sharp probe, and consequent collection and analysis of emission spectra from plasma generated on the sample by the laser radiation. The method comprises performing microtopographical analysis of the sample with a scanning probe, selecting a scanned topological site on the sample, generating a plasma plume at the selected scanned topological site, and measuring a spectrum of optical emission from the plasma at the selected scanned topological site. The apparatus comprises a scanning probe, a pulsed laser optically coupled to the probe, an optical spectrometer, and a controller coupled to the scanner, laser and spectrometer for controlling the operation of the scanner, laser and spectrometer. The probe and scanner are used for topographical profiling the sample. The probe is also used for laser radiation delivery to the sample for generating a plasma plume from the sample. Optical emission from the plasma plume is collected and delivered to the optical spectrometer so that analysis of emission spectrum by the optical spectrometer allows for identification of chemical composition of the sample at user selected sites.

Selective enzymatic cleavage and labeling for sensitive capillary electrophoresis laser-induced fluorescence analysis of oxidized DNA bases.

PubMed

Li, Cuiping; Wang, Hailin

2015-08-07

Oxidatively generated DNA damage is considered to be a significant contributing factor to cancer, aging, and age-related human diseases. It is important to detect oxidatively generated DNA damage to understand and clinically diagnosis diseases caused by oxidative damage. In this study, using selective enzymatic cleavage and quantum dot (QD) labeling, we developed a novel capillary electrophoresis-laser induced fluorescence method for the sensitive detection of oxidized DNA bases. First, oxidized DNA bases are recognized and removed by one DNA base excision repair glycosylase, leaving apurinic and apyrimidinic sites (AP sites) at the oxidized positions. The AP sites are further excised by the AP nicking activity of the chosen glycosylase, generating a nucleotide gap with 5'- and 3'- phosphate groups. After dephosphorylation with one alkaline phosphatase, a biotinylated ddNTP is introduced into the nucleotide space within the DNA strand by DNA polymerase I. The biotin-tagged DNA is further labeled with a QD-streptavidin conjugate via non-covalent interactions. The DNA-bound QD is well-separated from excess DNA-unbound QD by highly efficient capillary electrophoresis and is sensitively detected by online coupled laser-induced fluorescence analysis. Using this method, we can assess the trace levels of oxidized DNA bases induced by the Fenton reaction and UV irradiation. Interestingly, the use of the formamidopyrimidine glycosylase (FPG) protein and endonuclease VIII enables the detection of oxidized purine and pyrimidine bases, respectively. Using the synthesized standard DNA, the approach has low limits of detection of 1.1×10(-19)mol in mass and 2.9pM in concentration. Copyright © 2015 Elsevier B.V. All rights reserved.

Direct laser writing of microstructures on optically opaque and reflective surfaces

NASA Astrophysics Data System (ADS)

Rekštytė, S.; Jonavičius, T.; Malinauskas, M.

2014-02-01

Direct laser writing (DLW) based on ultra-localized polymerization is an efficient way to produce three-dimensional (3D) micro/nano-structures for diverse applications in science and industry. It is attractive for its flexibility to materialize CAD models out of wide spectrum of materials on the desired substrates. In case of direct laser lithography, photo-crosslinking can be achieved by tightly focusing ultrashort laser pulses to a photo- or thermo-polymers. Selectively exposing material to laser radiation allows creating fully 3D structures with submicrometer spatial resolution. In this paper we present DLW results of hybrid organic-inorganic material SZ2080 on optically opaque and reflective surfaces, such as silicon and various metals (Cr, Ti, Au). Our studies prove that one can precisely fabricate 2D and 3D structures with lower than 1 μm spatial resolution even on glossy or rough surfaces (surface roughness rms 0.068-0.670 μm) using sample translation velocities of up to 1 mm/s. Using femtosecond high pulse repetition rate laser, sample translation velocity can reach over 1 mm/s ensuring repeatable submicrometer structuring resolution.

Laser driven nuclear science and applications: The need of high efficiency, high power and high repetition rate Laser beams

NASA Astrophysics Data System (ADS)

Gales, S.

2015-10-01

Extreme Light Infrastructure (ELI) is a pan European research initiative selected on the European Strategy Forum on Research Infrastructures Roadmap that aims to close the gap between the existing laboratory-based laser driven research and international facility-grade research centre. The ELI-NP facility, one of the three ELI pillars under construction, placed in Romania and to be operational in 2018, has as core elements a couple of new generation 10 PW laser systems and a narrow bandwidth Compton backscattering gamma source with photon energies up to 19 MeV. ELI-NP will address nuclear photonics, nuclear astrophysics and quantum electrodynamics involving extreme photon fields. Prospective applications of high power laser in nuclear astrophysics, accelerator physics, in particular towards future Accelerator Driven System, as well as in nuclear photonics, for detection and characterization of nuclear material, and for nuclear medicine, will be discussed. Key issues in these research areas will be at reach with significant increase of the repetition rates and of the efficiency at the plug of the high power laser systems as proposed by the ICAN collaboration.

Bactericidal effect of Nd:YAG laser irradiation in endodontics

NASA Astrophysics Data System (ADS)

Aun, Carlos E.; Barberini, Alexandre F.; Camargo, Selma C. C.; Silva Kfouri, Luciana; Lorenzetti Simionato, Maria R.

1999-05-01

The success of endodontic therapy is based on the elimination of bacterial colonization from the endodontic system and periapical tissues. Recent studies have been showing the bactericidal effect of laser in root canal treatment. The propose of the study is to evaluate the effect of Nd:YAG laser irradiation in contaminated root canal treatment. The propose of the study is to evaluate the effect of Nd:YAG laser irradiation in contaminated root canals from upper central incisor. For the experiment 12 teeth were selected, respect at the apical third, sterilized, and 10 μm Streptococcus sanguis liquid culture were inoculated in the root canals. The laser test groups were irradiated with Nd:YAG laser at standard setting of 15Hz, 100mj and 1,5 W for 10, 20 and 30 seconds each in slow helicoidal movements from the apex to the top using a 300 micrometers fiber. After the procedure the specimens were placed in Tryptic Soy Agar, the number of colony forming units was evaluated. The experiment showed a significant reduction on viability of Streptococcus sanguis at the respective time of 20 and 30 seconds.

Transparent silicon strip sensors for the optical alignment of particle detector systems

NASA Astrophysics Data System (ADS)

Blum, W.; Kroha, H.; Widmann, P.

1996-02-01

Modern large-area precision tracking detectors require increasing accuracy for the alignment of their components. A novel multi-point laser alignment system has been developed for such applications. The position of detector components with respect to reference laser beams is monitored by semi-transparent optical position sensors which work on the principle of silicon strip photodiodes. Two types of custom designed transparent strip sensors, based on crystalline and on amorphous silicon as active material, have been studied. The sensors are optimized for the typical diameters of collimated laser beams of 3-5 mm over distances of 10-20 m. They provide very high position resolution, on the order of 1 μm, uniformly over a wide measurement range of several centimeters. The preparation of the sensor surfaces requires special attention in order to achieve high light transmittance and minimum distortion of the traversing laser beams. At selected wavelengths, produced by laser diodes, transmission rates above 90% have been achieved. This allows to position more than 30 sensors along one laser beam. The sensors will be equipped with custom designed integrated readout electronics.

Mass Spectrometric Imaging Using Laser Ablation and Solvent Capture by Aspiration (LASCA)

NASA Astrophysics Data System (ADS)

Brauer, Jonathan I.; Beech, Iwona B.; Sunner, Jan

2015-09-01

A novel interface for ambient, laser ablation-based mass spectrometric imaging (MSI) referred to as laser ablation and solvent capture by aspiration (LASCA) is presented and its performance demonstrated using selected, unaltered biological materials. LASCA employs a pulsed 2.94 μm laser beam for specimen ablation. Ablated materials in the laser plumes are collected on a hanging solvent droplet with electric field-enhanced trapping, followed by aspiration of droplets and remaining plume material in the form of a coarse aerosol into a collection capillary. The gas and liquid phases are subsequently separated in a 10 μL-volume separatory funnel, and the solution is analyzed with electrospray ionization in a high mass resolution Q-ToF mass spectrometer. The LASCA system separates the sampling and ionization steps in MSI and combines high efficiencies of laser plume sampling and of electrospray ionization (ESI) with high mass resolution MS. Up to 2000 different compounds are detected from a single ablation spot (pixel). Using the LASCA platform, rapid (6 s per pixel), high sensitivity, high mass-resolution ambient imaging of "as-received" biological material is achieved routinely and reproducibly.

Construction and Characterization of External Cavity Diode Lasers for Atomic Physics

PubMed Central

Hardman, Kyle S.; Bennetts, Shayne; Debs, John E.; Kuhn, Carlos C. N.; McDonald, Gordon D.; Robins, Nick

2014-01-01

Since their development in the late 1980s, cheap, reliable external cavity diode lasers (ECDLs) have replaced complex and expensive traditional dye and Titanium Sapphire lasers as the workhorse laser of atomic physics labs1,2. Their versatility and prolific use throughout atomic physics in applications such as absorption spectroscopy and laser cooling1,2 makes it imperative for incoming students to gain a firm practical understanding of these lasers. This publication builds upon the seminal work by Wieman3, updating components, and providing a video tutorial. The setup, frequency locking and performance characterization of an ECDL will be described. Discussion of component selection and proper mounting of both diodes and gratings, the factors affecting mode selection within the cavity, proper alignment for optimal external feedback, optics setup for coarse and fine frequency sensitive measurements, a brief overview of laser locking techniques, and laser linewidth measurements are included. PMID:24796259

Construction and characterization of external cavity diode lasers for atomic physics.

PubMed

Hardman, Kyle S; Bennetts, Shayne; Debs, John E; Kuhn, Carlos C N; McDonald, Gordon D; Robins, Nick

2014-04-24

Since their development in the late 1980s, cheap, reliable external cavity diode lasers (ECDLs) have replaced complex and expensive traditional dye and Titanium Sapphire lasers as the workhorse laser of atomic physics labs. Their versatility and prolific use throughout atomic physics in applications such as absorption spectroscopy and laser cooling makes it imperative for incoming students to gain a firm practical understanding of these lasers. This publication builds upon the seminal work by Wieman, updating components, and providing a video tutorial. The setup, frequency locking and performance characterization of an ECDL will be described. Discussion of component selection and proper mounting of both diodes and gratings, the factors affecting mode selection within the cavity, proper alignment for optimal external feedback, optics setup for coarse and fine frequency sensitive measurements, a brief overview of laser locking techniques, and laser linewidth measurements are included.

Single diode laser sensor for wide-range H2O temperature measurements.

PubMed

Gharavi, Mohammadreza; Buckley, Steven G

2004-04-01

A single diode laser absorption sensor (near 1477 nm) useful for simultaneous temperature and H2O concentration measurements is developed. The diode laser tunes approximately 1.2 cm(-1) over three H2O absorption transitions in each measurement. The line strengths of the transitions are measured over a temperature range from 468 to 977 K, based on high-resolution absorption measurements in a heated static cell. The results indicate that the selected transitions are suitable for sensitive temperature measurements in atmospheric pressure combustion systems using absorption line ratios. Comparing the results with HITRAN 96 data, it appears that these transitions will be sensitive over a wide range of temperatures (450-2000 K), suggesting applicability for combustion measurements.

Neutron Production from In-situ Heavy Ice Coated Targets at Vulcan

NASA Astrophysics Data System (ADS)

Morrison, John; Krygier, A. G.; Kar, S.; Ahmed, H.; Alejo, A.; Clarke, R.; Fuchs, J.; Green, A.; Jung, D.; Kleinschmidt, A.; Najmudin, Z.; Nakamura, H.; Norreys, P.; Notley, M.; Oliver, M.; Roth, M.; Vassura, L.; Zepf, M.; Borghesi, M.; Freeman, R. R.

2015-05-01

Laser based neutron production experiments have been performed utilizing ultra-high intensity laser accelerated ions impinging upon a secondary target. The neutron yield from such experiments may be improved if the accelerated ions were primarily deuterons taking advantage of the d-d cross section. Recent experiments have demonstrated that selective deuteron acceleration from in-situ heavy ice coating of targets can produce ion spectra where deuterons comprise > 99 % of the measured ions. Results will be presented from integrated neutron production experiments from heavy ice targets coated in-situ recently performed on the Vulcan laser at Rutherford Appleton Laboratory. We are grateful for the Staff at RAL and acknowledge funding from the US DoE. AFOSR, European Social Fund, and the Czech Republic.

Four-dimensional optoacoustic temperature mapping in laser-induced thermotherapy

NASA Astrophysics Data System (ADS)

Oyaga Landa, Francisco Javier; Deán-Ben, Xosé Luís.; Sroka, Ronald; Razansky, Daniel

2018-02-01

Photoablative laser therapy is in common use for selective destruction of malignant masses, vascular and brain abnormalities. Tissue ablation and coagulation are irreversible processes occurring shortly after crossing a certain thermal exposure threshold. As a result, accurate mapping of the temperature field is essential for optimizing the outcome of these clinical interventions. Here we demonstrate four-dimensional optoacoustic temperature mapping of the entire photoablated region. Accuracy of the method is investigated in tissue-mimicking phantom experiments. Deviations of the volumetric optoacoustic temperature readings provided at 40ms intervals remained below 10% for temperature elevations above 3°C, as validated by simultaneous thermocouple measurements. The excellent spatio-temporal resolution of the new temperature monitoring approach aims at improving safety and efficacy of laser-based photothermal procedures.

Terahertz lasers and amplifiers based on resonant optical phonon scattering to achieve population inversion

NASA Technical Reports Server (NTRS)

Hu, Qing (Inventor); Williams, Benjamin S. (Inventor)

2007-01-01

The present invention provides quantum cascade lasers and amplifier that operate in a frequency range of about 1 Terahertz to about 10 Terahertz. In one aspect, a quantum cascade laser of the invention includes a semiconductor heterostructure that provides a plurality of lasing modules connected in series. Each lasing module includes a plurality of quantum well structure that collectively generate at least an upper lasing state, a lower lasing state, and a relaxation state such that the upper and the lower lasing states are separated by an energy corresponding to an optical frequency in a range of about 1 to about 10 Terahertz. The lower lasing state is selectively depopulated via resonant LO-phonon scattering of electrons into the relaxation state.

Terahertz lasers and amplifiers based on resonant optical phonon scattering to achieve population inversion

NASA Technical Reports Server (NTRS)

Williams, Benjamin S. (Inventor); Hu, Qing (Inventor)

2009-01-01

The present invention provides quantum cascade lasers and amplifier that operate in a frequency range of about 1 Terahertz to about 10 Terahertz. In one aspect, a quantum cascade laser of the invention includes a semiconductor heterostructure that provides a plurality of lasing modules connected in series. Each lasing module includes a plurality of quantum well structure that collectively generate at least an upper lasing state, a lower lasing state, and a relaxation state such that the upper and the lower lasing states are separated by an energy corresponding to an optical frequency in a range of about 1 to about 10 Terahertz. The lower lasing state is selectively depopulated via resonant LO-phonon scattering of electrons into the relaxation state.

A novel process for production of spherical PBT powders and their processing behavior during laser beam melting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Jochen, E-mail: jochen.schmidt@fau.de; Sachs, Marius; Fanselow, Stephanie

2016-03-09

Additive manufacturing processes like laser beam melting of polymers are established for production of prototypes and individualized parts. The transfer to other areas of application and to serial production is currently hindered by the limited availability of polymer powders with good processability. Within this contribution a novel process route for the production of spherical polymer micron-sized particles of good flowability has been established and applied to produce polybutylene terephthalate (PBT) powders. Moreover, the applicability of the PBT powders in selective laser beam melting and the dependencies of process parameters on device properties will be outlined. First, polymer micro particles aremore » produced by a novel wet grinding method. To improve the flowability the produced particles the particle shape is optimized by rounding in a heated downer reactor. A further improvement of flowability of the cohesive spherical PBT particles is realized by dry coating. An improvement of flowability by a factor of about 5 is achieved by subsequent rounding of the comminution product and dry-coating as proven by tensile strength measurements of the powders. The produced PBT powders were characterized with respect to their processability. Therefore thermal, rheological, optical and bulk properties were analyzed. Based on these investigations a range of processing parameters was derived. Parameter studies on thin layers, produced in a selective laser melting system, were conducted. Hence appropriate parameters for processing the PBT powders by laser beam melting, like building chamber temperature, scan speed and laser power have been identified.« less

Laser treatment of port-wine stains

PubMed Central

Brightman, Lori A; Geronemus, Roy G; Reddy, Kavitha K

2015-01-01

Port-wine stains are a type of capillary malformation affecting 0.3% to 0.5% of the population. Port-wine stains present at birth as pink to erythematous patches on the skin and/or mucosa. Without treatment, the patches typically darken with age and may eventually develop nodular thickening or associated pyogenic granuloma. Laser and light treatments provide improvement through selective destruction of vasculature. A variety of vascular-selective lasers may be employed, with the pulsed dye laser being the most common and well studied. Early treatment produces more optimal results. Advances in imaging and laser treatment technologies demonstrate potential to further improve clinical outcomes. PMID:25624768

Laser furnace and method for zone refining of semiconductor wafers

NASA Technical Reports Server (NTRS)

Griner, Donald B. (Inventor); zur Burg, Frederick W. (Inventor); Penn, Wayne M. (Inventor)

1988-01-01

A method of zone refining a crystal wafer (116 FIG. 1) comprising the steps of focusing a laser beam to a small spot (120) of selectable size on the surface of the crystal wafer (116) to melt a spot on the crystal wafer, scanning the small laser beam spot back and forth across the surface of the crystal wafer (116) at a constant velocity, and moving the scanning laser beam across a predetermined zone of the surface of the crystal wafer (116) in a direction normal to the laser beam scanning direction and at a selectible velocity to melt and refine the entire crystal wafer (116).

NASA selects scientific investigations for Earth dynamics studies

NASA Technical Reports Server (NTRS)

1981-01-01

Forty two domestic investigators affiliated with U.S. universities, governmental agencies, or private concerns and 14 investigators from France, West Germany, the Netherlands, Switzerland, Spain, Sweden, Australia, New Zealand, Venezuela, and Canada were selected to use precise geodetic data obtained by laser ranging and very long base interferometry in a study of the Earth's tectonic plate movement, crustal deformation, and rotational dynamics. The studies to be made and the principal investigators for each are listed.

Spin selective filtering of polariton condensate flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, T.; Department of Materials Science and Technology, University of Crete, 71003 Heraklion, Crete; Antón, C.

2015-07-06

Spin-selective spatial filtering of propagating polariton condensates, using a controllable spin-dependent gating barrier, in a one-dimensional semiconductor microcavity ridge waveguide is reported. A nonresonant laser beam provides the source of propagating polaritons, while a second circularly polarized weak beam imprints a spin dependent potential barrier, which gates the polariton flow and generates polariton spin currents. A complete spin-based control over the blocked and transmitted polaritons is obtained by varying the gate polarization.

Clinical-scale laser-based scanning and processing of live cells: selective photothermal killing of fluorescent tumor targets for autologous stem cell transplantation

NASA Astrophysics Data System (ADS)

Koller, Manfred R.; Hanania, Elie G.; Eisfeld, Timothy; O'Neal, Robert A.; Khovananth, Kevin M.; Palsson, Bernhard O.

2001-04-01

High-dose chemotherapy, followed by autologous hematopoietic stem cell (HSC) transplantation, is widely used for the treatment of cancer. However, contaminating tumor cells within HSC harvests continue to be of major concern since re-infused tumor cells have proven to contribute to disease relapse. Many tumor purging methods have been evaluated, but all leave detectable tumor cells in the transplant and result in significant loss of HSCs. These shortcomings cause engraftment delays and compromise the therapeutic value of purging. A novel approach integrating automated scanning cytometry, image analysis, and selective laser-induced killing of labeled cells within a cell mixture is described here. Non-Hodgkin's lymphoma (NHL) cells were spiked into cell mixtures, and fluorochrome-conjugated antibodies were used to label tumor cells within the mixture. Cells were then allowed to settle on a surface, and as the surface was scanned with a fluorescence excitation source, a laser pulse was fired at every detected tumor cell using high-speed beam steering mirrors. Tumor cells were selectively killed with little effect on adjacent non-target cells, demonstrating the feasibility of this automated cell processing approach. This technology has many potential research and clinical applications, one example of which is tumor cell purging for autologous HSC transplantation.

The Effect of Photobiomodulation on the Depth of Anesthesia During Endodontic Treatment of Teeth With Symptomatic Irreversible Pulpitis (Double Blind Randomized Clinical Trial)

PubMed Central

Ghabraei, Sholeh; Chiniforush, Nasim; Bolhari, Behnam; Aminsobhani, Mohsen; Khosarvi, Abbas

2018-01-01

Introduction: Achieving appropriate anesthesia in patients with symptomatic irreversible pulpitis in mandibular molars during endodontic treatment is always one of the most challenging aspects. Photobiomodulation (PBM) has been used in dentistry due to its anti-inflammatory properties and regenerative effects. This study evaluates the effects of PBM in the depth of anesthesia in inferior alveolar nerve block. Methods: In this randomized clinical trial, 44 patients requiring endodontic treatment in lower molar, left or right were selected, half of them were randomly treated with PBM therapy. Laser irradiation by 980 nm diode laser with a single dose (15 J/cm2, for 20 seconds) before anesthesia was performed at the buccal aspect. Inferior alveolar nerve block was performed once. Success was defined as no or mild pain (no need for any supplemental injection), based on the visual analogue scale during access cavity preparation. Results were evaluated using SPSS software. Results: The results of this study showed that the necessity for supplemental injection was lower in the group receiving laser than in the group without laser (P = 0.033). The mean pain intensity during dentin cutting was lower in the group receiving laser than in the group without laser (P = 0.031). Also, the mean pain intensity during pulp dropping was lower in the group receiving laser, than the group without laser (P = 0.021). Conclusion: Based on the results of this study, it seems that the application of PBM before anesthesia is effective on increasing depth of anesthesia. PMID:29399304

Parameter optimization for selective laser melting of TiAl6V4 alloy by CO2 laser

NASA Astrophysics Data System (ADS)

Baitimerov, R. M.; Lykov, P. A.; Radionova, L. V.; Safonov, E. V.

2017-10-01

TiAl6V4 alloy is one of the widely used materials in powder bed fusion additive manufacturing technologies. In recent years selective laser melting (SLM) of TiAl6V4 alloy by fiber laser has been well studied, but SLM by CO2-lasers has not. SLM of TiAl6V4 powder by CO2-laser was studied in this paper. Nine 10×10×10 mm cubic specimens were fabricated using different SLM process parameters. All of the fabricated specimens have a good dense structure and a good surface finish quality without dimensional distortion. The lowest porosity that was achieved was about 0.5%.

Laser ablation of dental calculus at 400 nm using a Ti:sapphire laser

NASA Astrophysics Data System (ADS)

Schoenly, Joshua E.; Seka, Wolf; Rechmann, Peter

2009-02-01

A Nd:YAG laser-pumped, frequency-doubled Ti:sapphire laser is used for selective ablation of calculus. The laser provides <=25 mJ at 400 nm (60-ns pulse width, 10-Hz repetition rate). The laser is coupled into an optical multimode fiber coiled around a 4-in.-diam drum to generate a top-hat output intensity profile. With coaxial water cooling, this is ideal for efficient, selective calculus removal. This is in stark contrast with tightly focused Gaussian beams that are energetically inefficient and lead to irreproducible results. Calculus is well ablated at high fluences >=2J/cm2 stalling occurs below this fluence because of photobleaching. Healthy hard tissue is not removed at fluences <=3 J/cm2.

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

PubMed Central

Liu, Neng; Moumanis, Khalid; Dubowski, Jan J.

2015-01-01

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75°. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15°, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer’s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103°. The XPS results indicate ArF laser induced formation of Si–(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals. PMID:26575362

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment.

PubMed

Liu, Neng; Moumanis, Khalid; Dubowski, Jan J

2015-11-09

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75°. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm(2), respectively, has decreased the CA to near 15°, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer's surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm(2) and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103°. The XPS results indicate ArF laser induced formation of Si-(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

Two Dimensional Host-Guest Metal-Organic Framework Sensor with High Selectivity and Sensitivity to Picric Acid.

PubMed

Bagheri, Minoo; Masoomi, Mohammad Yaser; Morsali, Ali; Schoedel, Alexander

2016-08-24

A dye-sensitized metal-organic framework, TMU-5S, was synthesized based on introducing the laser dye Rhodamine B into the porous framework TMU-5. TMU-5S was investigated as a ratiometric fluorescent sensor for the detection of explosive nitro aromatic compounds and showed four times greater selectivity to picric acid than any state-of-the-art luminescent-based sensor. Moreover, it can selectively discriminate picric acid concentrations in the presence of other nitro aromatics and volatile organic compounds. Our findings indicate that using this sensor in two dimensions leads to a greatly reduced environmental interference response and thus creates exceptional sensitivity toward explosive molecules with a fast response.

LASER BIOLOGY AND MEDICINE: Optoacoustic laser monitoring of cooling and freezing of tissues

NASA Astrophysics Data System (ADS)

Larin, Kirill V.; Larina, I. V.; Motamedi, M.; Esenaliev, R. O.

2002-11-01

Real-time monitoring of cooling and freezing of tissues, cells, and other biological objects with a high spatial and time resolution, which is necessary for selective destruction of cancer and benign tumours during cryotherapy, as well as for preventing any damage to the structure and functioning of biological objects in cryobiology, is considered. The optoacoustic method, based on the measurement and analysis of acoustic waves induced by short laser pulses, is proposed for monitoring the cooling and freezing of the tissue. The effect of cooling and freezing on the amplitude and time profile of acoustic signals generated in real tissues and in a model object is studied. The experimental results indicate that the optoacoustic laser technique can be used for real-time monitoring of cooling and freezing of biological objects with a submillimeter spatial resolution and a high contrast.

The Effect of Multiple Surface Treatments on Biological Properties of Ti-6Al-4V Alloy

NASA Astrophysics Data System (ADS)

Parsikia, Farhang; Amini, Pupak; Asgari, Sirous

2014-09-01

In this research, the effect of various surface treatments including laser processing, grit blasting and anodizing on chemical structure, surface topography, and bioactivity of Ti-6Al-4V was investigated. Six groups of samples were prepared by a combination of two alternative laser processes, grit blasting and anodizing. Selected samples were first evaluated using microanalysis techniques and contact roughness testing and were then exposed to in vitro environment. Scanning electron microscopy was used to characterize the corresponding final surface morphologies. Weight measurement and atomic absorption tests were employed for determination of bioactivity limits of different surface conditions. Based on the data obtained in this study, low-energy laser processing generally yields a better biological response. The maximum bioactivity was attained in those samples exposed to a three step treatment including low-energy laser treatment followed by grit blasting and anodizing.

Possibilities of the treatment of certain diseases in stomatology with the help of noninvasive laser therapy

NASA Astrophysics Data System (ADS)

Navratil, Leos; Navratilova, Blanka

2000-06-01

Non-invasive laser therapy is currently frequently used in stomatological practice thanks to its analgesic, anti- inflammatory and biostimulating effects. Suitable indications and methodic procedures of treatment should be established to provide the relevant efficacy of the method. The work characteristics the efficacy of the treatment in selected indications with checking suitable physical parameters of laser radiation. The study was carried out on total of 382 patients divided into three groups depending on the method of the treatment. The treatment result were evaluated based on the above-mentioned effects expressed with the help of relevant coefficients. The result demonstrated the contribution of therapeutic laser to the treatment of herpetic affections, aphthae, erosions, decubiti on the mucous membrane, conditions after difficult extractions, papilitits, wounds after teeth resection, linqua geographica, scar and treatment aimed at reducing the dentin sensitivity.

Mid-IR super-continuum generation

NASA Astrophysics Data System (ADS)

Islam, Mohammed N.; Xia, Chenan; Freeman, Mike J.; Mauricio, Jeremiah; Zakel, Andy; Ke, Kevin; Xu, Zhao; Terry, Fred L., Jr.

2009-02-01

A Mid-InfraRed FIber Laser (MIRFIL) has been developed that generates super-continuum covering the spectral range from 0.8 to 4.5 microns with a time-averaged power as high as 10.5W. The MIRFIL is an all-fiber integrated laser with no moving parts and no mode-locked lasers that uses commercial off-the-shelf parts and leverages the mature telecom/fiber optics platform. The MIRFIL power can be easily scaled by changing the repetition rate and modifying the erbium-doped fiber amplifier. Some of the applications using the super-continuum laser will be described in defense, homeland security and healthcare. For example, the MIRFIL is being applied to a catheter-based medical diagnostic system to detect vulnerable plaque, which is responsible for most heart attacks resulting from hardening-of-the-arteries or atherosclerosis. More generally, the MIRFIL can be a platform for selective ablation of lipids without damaging normal protein or smooth muscle tissue.

Acousto-ultrasonic nondestructive evaluation of materials using laser beam generation and detection. M.S. Thesis

NASA Technical Reports Server (NTRS)

Huber, Robert D.; Green, Robert E., Jr.

1990-01-01

The acousto-ultrasonic method has proven to be a most interesting technique for nondestructive evaluation of the mechanical properties of a variety of materials. Use of the technique or a modification thereof, has led to correlation of the associated stress wave factor with mechanical properties of both metals and composite materials. The method is applied to the nondestructive evaluation of selected fiber reinforced structural composites. For the first time, conventional piezoelectric transducers were replaced with laser beam ultrasonic generators and detectors. This modification permitted true non-contact acousto-ultrasonic measurements to be made, which yielded new information about the basic mechanisms involved as well as proved the feasibility of making such non-contact measurements on terrestrial and space structures and heat engine components. A state-of-the-art laser based acousto-ultrasonic system, incorporating a compact pulsed laser and a fiber-optic heterodyne interferometer, was delivered to the NASA Lewis Research Center.

Generation of laser-induced periodic surface structures on transparent material-fused silica

NASA Astrophysics Data System (ADS)

Schwarz, Simon; Rung, Stefan; Hellmann, Ralf

2016-05-01

We report on a comparison between simulated and experimental results for the generation of laser-induced periodic surface structures with low spatial frequency on dielectrics. Using the established efficacy factor theory extended by a Drude model, we determine the required carrier density for the generation of low spatial frequency LIPSS (LSFL) and forecast their periodicity and orientation. In a subsequent calculative step, we determine the fluence of ultrashort laser pulses necessary to excite this required carrier density in due consideration of the pulse number dependent ablation threshold. The later calculation is based on a rate equation including photo- and avalanche ionization and derives appropriate process parameters for a selective generation of LSFL. Exemplarily, we apply this approach to the generation of LSFL on fused silica using a 1030 nm femtosecond laser. The experimental results for the orientation and spatial periodicity of LSFL reveal excellent agreement with the simulation.

Generation of laser-induced periodic surface structures on transparent material-fused silica

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwarz, Simon; Rung, Stefan; Hellmann, Ralf

2016-05-02

We report on a comparison between simulated and experimental results for the generation of laser-induced periodic surface structures with low spatial frequency on dielectrics. Using the established efficacy factor theory extended by a Drude model, we determine the required carrier density for the generation of low spatial frequency LIPSS (LSFL) and forecast their periodicity and orientation. In a subsequent calculative step, we determine the fluence of ultrashort laser pulses necessary to excite this required carrier density in due consideration of the pulse number dependent ablation threshold. The later calculation is based on a rate equation including photo- and avalanche ionizationmore » and derives appropriate process parameters for a selective generation of LSFL. Exemplarily, we apply this approach to the generation of LSFL on fused silica using a 1030 nm femtosecond laser. The experimental results for the orientation and spatial periodicity of LSFL reveal excellent agreement with the simulation.« less

Coherent detection of position errors in inter-satellite laser communications

NASA Astrophysics Data System (ADS)

Xu, Nan; Liu, Liren; Liu, De'an; Sun, Jianfeng; Luan, Zhu

2007-09-01

Due to the improved receiver sensitivity and wavelength selectivity, coherent detection became an attractive alternative to direct detection in inter-satellite laser communications. A novel method to coherent detection of position errors information is proposed. Coherent communication system generally consists of receive telescope, local oscillator, optical hybrid, photoelectric detector and optical phase lock loop (OPLL). Based on the system composing, this method adds CCD and computer as position error detector. CCD captures interference pattern while detection of transmission data from the transmitter laser. After processed and analyzed by computer, target position information is obtained from characteristic parameter of the interference pattern. The position errors as the control signal of PAT subsystem drive the receiver telescope to keep tracking to the target. Theoretical deviation and analysis is presented. The application extends to coherent laser rang finder, in which object distance and position information can be obtained simultaneously.

Review of selective laser melting: Materials and applications

NASA Astrophysics Data System (ADS)

Yap, C. Y.; Chua, C. K.; Dong, Z. L.; Liu, Z. H.; Zhang, D. Q.; Loh, L. E.; Sing, S. L.

2015-12-01

Selective Laser Melting (SLM) is a particular rapid prototyping, 3D printing, or Additive Manufacturing (AM) technique designed to use high power-density laser to melt and fuse metallic powders. A component is built by selectively melting and fusing powders within and between layers. The SLM technique is also commonly known as direct selective laser sintering, LaserCusing, and direct metal laser sintering, and this technique has been proven to produce near net-shape parts up to 99.9% relative density. This enables the process to build near full density functional parts and has viable economic benefits. Recent developments of fibre optics and high-power laser have also enabled SLM to process different metallic materials, such as copper, aluminium, and tungsten. Similarly, this has also opened up research opportunities in SLM of ceramic and composite materials. The review presents the SLM process and some of the common physical phenomena associated with this AM technology. It then focuses on the following areas: (a) applications of SLM materials and (b) mechanical properties of SLM parts achieved in research publications. The review is not meant to put a ceiling on the capabilities of the SLM process but to enable readers to have an overview on the material properties achieved by the SLM process so far. Trends in research of SLM are also elaborated in the last section.

Vibration-based photoacoustic tomography

NASA Astrophysics Data System (ADS)

Li, Rui; Rajian, Justin R.; Wang, Pu; Slipchenko, Mikhail N.; Cheng, Ji-Xin

2013-03-01

Photoacoustic imaging employing molecular overtone vibration as contrast mechanism opens a new avenue for deep tissue imaging with chemical bond selectivity. Here, we demonstrate vibration-based photoacoustic tomography with an imaging depth on the centimeter scale. To provide sufficient pulse energy at the overtone transition wavelengths, we constructed a compact, barium nitrite crystal-based Raman laser for excitation of 2nd overtone of C-H bond. Using a 5-ns Nd:YAG laser as pumping source, up to 105 mJ pulse energy at 1197 nm was generated. Vibrational photoacoutic spectroscopy and tomography of phantom (polyethylene tube) immersed in whole milk was performed. With a pulse energy of 47 mJ on the milk surface, up to 2.5 cm penetration depth was reached with a signal-to-noise ratio of 12.

Development and performance of a laser heterodyne spectrometer using tunable semiconductor lasers as local oscillators

NASA Technical Reports Server (NTRS)

Glenar, D.; Kostiuk, T.; Jennings, D. E.; Mumma, M. J.

1980-01-01

A diode laser based IR heterodyne spectrometer for laboratory and field use was developed for high efficiency operation between 7.5 and 8.5 microns. The local oscillator is a PbSSe tunable diode laser kept continuously at operating temperatures of 12-60 K using a closed cycle cooler. The laser output frequency is controlled and stabilized using a high precision diode current supply, constant temperature controller, and a shock isolator mounted between the refrigerator cold tip and the diode mount. Single laser modes are selected by a grating placed in the local oscillator beam. The system employs reflecting optics throughout to minimize losses from internal reflection and absorption, and to eliminate chromatic effects. Spectral analysis of the diode laser output between 0 and 1 GHz reveals excess noise at many diode current settings, which limits the infrared spectral regions over which useful heterodyne operation can be achieved. System performance has been studied by making heterodyne measurements of etalon fringes and several Freon 13 (CF3Cl) absorption lines against a laboratory blackbody source. Preliminary field tests have also been performed using the Sun as a source.

Fractionated laser skin resurfacing treatment complications: a review.

PubMed

Metelitsa, Andrei I; Alster, Tina S

2010-03-01

Fractional photothermolysis represents a new modality of laser skin resurfacing that was developed to provide a successful clinical response while minimizing postoperative recovery and limiting treatment complications. To review all of the reported complications that develop as a result of fractional ablative and nonablative laser skin resurfacing. A literature review was based on a MEDLINE search (1998-2009) for English-language articles related to laser treatment complications and fractional skin resurfacing. Articles presenting the highest level of evidence and the most recent reports were preferentially selected. Complications with fractional laser skin resurfacing represent a full spectrum of severity and can be longlasting. In general, a greater likelihood of developing post-treatment complications is seen in sensitive cutaneous areas and in patients with intrinsically darker skin phototypes or predisposing medical risk factors. Although the overall rate of complications associated with fractional laser skin resurfacing is much lower than with traditional ablative techniques, recent reports suggest that serious complications can develop. An appreciation of all of the complications associated with fractional laser skin resurfacing is important, especially given that many of them can be potentially prevented. The authors have indicated no significant interest with commercial supporters.

Comparative microstructural analysis of bone osteotomies after cutting by computer-assisted robot-guided laser osteotome and piezoelectric osteotome: an in vivo animal study.

PubMed

Augello, Marcello; Deibel, Waldemar; Nuss, Katja; Cattin, Philippe; Jürgens, Philipp

2018-04-13

Most industrial laser applications utilize computer and robot assistance, for guidance, safety, repeatability, and precision. In contrast, medical applications using laser systems are mostly conducted manually. The advantages can be effective only when the system is coupled to a robotic guidance, as operating by hand does not reach the required accuracy. We currently developed the first laser osteotome which offers preoperative planning based on CT data, robot guidance, and a precise execution of the laser cuts. In an animal trial, our system was used to create a grid pattern of the same depth on the inner layer of parietal bone in 12 adult sheep. The same bone cuts were done with piezoelectric osteotome on the contralateral side. The micro-CT and histological analysis showed more new mineralized bone in the laser group compared to the piezoelectric group. As well, a cutting pattern with especially a constant osteotomy depth in the laser group was demonstrated. The here presented autonomous osteotomy tool shows not only an advantage in early bone healing stage but additionally sharp bone cuts with a very high accuracy and freely selectable design cuts.

Pulse Width Dependence Of Pigment Cell Damage At 694 nm In Guinea Pig Skin

NASA Astrophysics Data System (ADS)

Dover, Jeffrey S.; Polla, Luigi L.; Margolis, Randall J.; Whitaker, Diana; Watanabe, Schinichi; Murphy, George F.; Parrish, John A.; Anderson, R. R.

1987-03-01

351 nm, 20-nsec XeF excimer laser irradiation has previously been shown to selectively target and damage melanosomes in human skin. In the following studies selective targeting with melanosomal photodisruption has been demonstrated in pigmented guinea pig skin with a Q-switched 40-nsec ruby laser, and a 750-nsec pulsed dye laser but not with a 400-usec pulsed dye laser. The pulse width dependence of melanosomal disruption, occurring only at pulsewidths shorter than the thermal relaxation time of the melanosome (0.5 - 1.0 usec), is in accordance with the theory of selective photothermolysis. Possible mechanisms of melanosomal photodisruption include development of sudden thermal gradients leading to cavitation or shock wave production.

Gaseous phase ion detection method based on laser-induced fluorescence for ion mobility spectrometer

NASA Astrophysics Data System (ADS)

Guo, Kaitai; Ni, Kai; Ou, Guangli; Zhang, Xiaoguo; Yu, Quan; Qian, Xiang; Wang, Xiaohao

2015-08-01

Ion mobility spectrometry (IMS) is widely used in the field of chemical composition analysis. Faraday cup is the most classical method to detect ions for IMS in the atmospheric pressure. However, the performance of Faraday plate was limited by many kinds of factors, including interfering electromagnetic waves, thermal(Johnson) noise, induced current , gain bandwidth product, etc. There is a theoretical limit in detection of ions at ambient condition which is approximately 106 ions per second. In this paper, we introduced a novel way using laser-induced fluorescence (LIF) to bypass the limitation of Faraday plate. Fluorescent ions which were selected by IMS get excited when they fly through the laser excitation area. The fluorescence emitted by the excited ions was captured exponentially and amplified through proper optoelectronic system. Rhodamine 6G (R6G) was selected as the fluorochrome for the reason that excitation wavelength, emission wavelength, and fluorescence quantum yield were more appropriate than others. An orthometric light path is designed to eliminate the adverse impact which was caused by induced laser. The experiment result shows that a fluorescence signal from the sample ions of the IMS could be observed. Compared with Faraday plate, the LIF-IMS may find a potential application in more system at the atmosphere condition.

Modeling of high efficiency solar cells under laser pulse for power beaming applications

NASA Technical Reports Server (NTRS)

Jain, Raj K.; Landis, Geoffrey A.

1994-01-01

Solar cells have been used to convert sunlight to electrical energy for many years and also offer great potential for non-solar energy conversion applications. Their greatly improved performance under monochromatic light compared to sunlight, makes them suitable as photovoltaic (PV) receivers in laser power beaming applications. Laser beamed power to a PV array receiver could provide power to satellites, an orbital transfer vehicle, or a lunar base. Gallium arsenide (GaAs) and indium phosphide (InP) solar cells have calculated efficiencies of more than 50 percent under continuous illumination at the optimum wavelength. Currently high power free-electron lasers are being developed which operate in pulsed conditions. Understanding cell behavior under a laser pulse is important in the selection of the solar cell material and the laser. An experiment by NAsA lewis and JPL at the AVLIS laser facility in Livermore, CA presented experimental data on cell performance under pulsed laser illumination. Reference 5 contains an overview of technical issues concerning the use of solar cells for laser power conversion, written before the experiments were performed. As the experimental results showed, the actual effects of pulsed operation are more complicated. Reference 6 discusses simulations of the output of GaAs concentrator solar cells under pulsed laser illumination. The present paper continues this work, and compares the output of Si and GaAs solar cells.

Advanced Laser Architecture for Two-Step Laser Tandem Mass Spectrometer

NASA Technical Reports Server (NTRS)

Fahey, Molly E.; Li, Steven X.; Yu, Anthony W.; Getty, Stephanie A.

2016-01-01

Future astrobiology missions will focus on planets with significant astrochemical or potential astrobiological features, such as small, primitive bodies and the icy moons of the outer planets that may host diverse organic compounds. These missions require advanced instrument techniques to fully and unambiguously characterize the composition of surface and dust materials. Laser desorptionionization mass spectrometry (LDMS) is an emerging instrument technology for in situ mass analysis of non-volatile sample composition. A recent Goddard LDMS advancement is the two-step laser tandem mass spectrometer (L2MS) instrument to address the need for future flight instrumentation to deconvolve complex organic signatures. The L2MS prototype uses a resonance enhanced multi-photon laser ionization mechanism to selectively detect aromatic species from a more complex sample. By neglecting the aliphatic and inorganic mineral signatures in the two-step mass spectrum, the L2MS approach can provide both mass assignments and clues to structural information for an in situ investigation of non-volatile sample composition. In this paper we will describe our development effort on a new laser architecture that is based on the previously flown Lunar Orbiter Laser Altimeter (LOLA) laser transmitter for the L2MS instrument. The laser provides two discrete midinfrared wavelengths (2.8 m and 3.4 m) using monolithic optical parametric oscillators and ultraviolet (UV) wavelength (266 nm) on a single laser bench with a straightforward development path toward flight readiness.

Physics in Europe--A Data File of Selected Research.

DTIC Science & Technology

1984-06-18

Negev Sapir Proc. 16th Euro. Conf. on Laser Interac. with Matter, London 26-30 Sept. 1983 1025 CPBICF laser plasma soft x-ray refractometry France...CPBICF laser plasma Schlieren diagnostic France 623 CPBICF laser plasma self focusing numerics UK 1025 CPBICF laser plasma soft x-ray refractometry

Selective ex-vivo photothermal ablation of human pancreatic cancer with albumin functionalized multiwalled carbon nanotubes

PubMed Central

Mocan, Lucian; Tabaran, Flaviu A; Mocan, Teodora; Bele, Constantin; Orza, Anamaria Ioana; Lucan, Ciprian; Stiufiuc, Rares; Manaila, Ioana; Iulia, Ferencz; Dana, Iancu; Zaharie, Florin; Osian, Gelu; Vlad, Liviu; Iancu, Cornel

2011-01-01

The process of laser-mediated ablation of cancer cells marked with biofunctionalized carbon nanotubes is frequently called “nanophotothermolysis”. We herein present a method of selective nanophotothermolisys of pancreatic cancer (PC) using multiwalled carbon nanotubes (MWCNTs) functionalized with human serum albumin (HSA). With the purpose of testing the therapeutic value of these nanobioconjugates, we have developed an ex-vivo experimental platform. Surgically resected specimens from patients with PC were preserved in a cold medium and kept alive via intra-arterial perfusion. Additionally, the HSA-MWCNTs have been intra-arterially administered in the greater pancreatic artery under ultrasound guidance. Confocal and transmission electron microscopy combined with immunohistochemical staining have confirmed the selective accumulation of HSA-MWCNTs inside the human PC tissue. The external laser irradiation of the specimen has significantly produced extensive necrosis of the malign tissue after the intra-arterial administration of HSA-MWCNTs, without any harmful effects on the surrounding healthy parenchyma. We have obtained a selective photothermal ablation of the malign tissue based on the selective internalization of MWCNTs with HSA cargo inside the pancreatic adenocarcinoma after the ex-vivo intra-arterial perfusion. PMID:21720504

Transverse mode selection in vertical-cavity surface-emitting lasers via deep impurity-induced disordering

NASA Astrophysics Data System (ADS)

O'Brien, Thomas R.; Kesler, Benjamin; Dallesasse, John M.

2017-02-01

Top emission 850-nm vertical-cavity surface-emitting lasers (VCSELs) demonstrating transverse mode selection via impurity-induced disordering (IID) are presented. The IID apertures are fabricated via closed ampoule zinc diffusion. A simple 1-D plane wave model based on the intermixing of Group III atoms during IID is presented to optimize the mirror loss of higher-order modes as a function of IID strength and depth. In addition, the impact of impurity diffusion into the cap layer of the lasers is shown to improve contact resistance. Further investigation of the mode-dependent characteristics of the device imply an increase in the thermal impedance associated with the fraction of IID contained within the oxide aperture. The optimization of the ratio of the IID aperture to oxide aperture is experimentally determined. Single fundamental mode output of 1.6 mW with 30 dBm side mode suppression ratio is achieved by a 3.0 μm oxide-confined device with an IID aperture of 1.3 μm indicating an optimal IID aperture size of 43% of the oxide aperture.

What Is New with Sexual Side Effects After Transurethral Male Lower Urinary Tract Symptom Surgery?

PubMed

Rieken, Malte; Antunes-Lopes, Tiago; Geavlete, Bogdan; Marcelissen, Tom

2018-01-01

Transurethral resection of the prostate as well as laser prostatectomy (by either holmium laser enucleation of the prostate or Greenlight laser vaporization) is associated with risks of sexual dysfunction such as antegrade ejaculation and occasionally erectile dysfunction. While ejaculation-sparing variations of these techniques show promising results, larger multicenter studies are needed to confirm promising data. Prostatic urethral lift maintains erectile and ejaculatory function at 5-yr follow-up. The same is true for the 3-yr data on the Rezum system. Recently, Aquablation has shown promising results; however, these 6-mo data need to be confirmed during longer follow-up. An individualized, shared decision-making process based on clinical parameters and patient preference is warranted to select the ideal treatment option for each patient. Sexual dysfunction such as loss of ejaculation and, less frequently, erectile dysfunction can occur after transurethral prostate surgery. Ejaculation-sparing modifications as well as minimally invasive alternatives show promising results. An individualized approach is warranted to select the ideal technique for each patient. Copyright © 2018 European Association of Urology. Published by Elsevier B.V. All rights reserved.

Design and development of short- and long-wavelength MQW infrared vertical cavity surface emitting lasers

NASA Astrophysics Data System (ADS)

Iliadis, Agisilaos A.; Christou, Aristos

2003-07-01

The design, fabrication and performance of low threshold selectively oxidized infrared vertical cavity surface emitting lasers (VCSELs) for operation at 0.89μm and 1.55μm wavelengths using optimized graded Bragg mirrors, is reported. The devices are based on III-V ternary (AlGaAs/GaAs) and quaternary (AlInGaAs/GaInAsP/InP) graded semiconductor alloys and quantum wells and are grown by Molecular Beam Epitaxy. The VCSEL arrays are processed using inductively coupled plasma (ICP) etching with BCl3 gas mixtures to achieve vertical walls and small geometries, and the fabrication of the devices proceeds by using conventional Ohmic contacts (Ti-Pt-Au and Ni-Au-Ge-Ni) and indium tin oxide (ITO) transparent contacts. The theoretical investigation of the optical properties of the quaternary compound semiconductor alloys allows us to select the optimum materials for highly reflective Bragg mirrors with less periods. The simulation of the designed VCSEL performance has been carried out by evaluation of the important laser characteristics such as threshold gain, threshold current density and external quantum efficiency.

Corrosion resistance characteristics of a Ti-6Al-4V alloy scaffold that is fabricated by electron beam melting and selective laser melting for implantation in vivo.

PubMed

Zhao, Bingjing; Wang, Hong; Qiao, Ning; Wang, Chao; Hu, Min

2017-01-01

The purpose of this study is to determine the corrosion resistance of Ti-6Al-4V alloy fabricated with electron beam melting and selective laser melting for implantation in vivo. Ti-6Al-4V alloy specimens were fabricated with electron beam melting (EBM) and selective laser melting (SLM). A wrought form of Ti-6Al-4V alloy was used as a control. Surface morphology observation, component analysis, corrosion resistance experimental results, electrochemical impedance spectroscopy, crevice corrosion resistance experimental results, immersion test and metal ions precipitation analysis were processed, respectively. The thermal stability of EBM specimen was the worst, based on the result of open circuit potential (OCP) result. The result of electrochemical impedance spectroscopy indicated that the corrosion resistance of the SLM specimen was the best under the low electric potential. The result of potentiodynamic polarization suggested that the corrosion resistance of the SLM specimen was the best under the low electric potential (<1.5V) and EBM specimen was the best under the high electric potential (>1.5V).The crevice corrosion resistance of the EBM specimen was the best. The corrosion resistance of SLM specimen was the best, based on the result of immersion test. The content of Ti, Al and V ions of EBM, SLM and wrought specimens was very low. In general, the scaffolds that were fabricated with EBM and SLM had good corrosion resistance, and were suitable for implantation in vivo. Copyright © 2016 Elsevier B.V. All rights reserved.

A method for selective excitation of Ince-Gaussian modes in an end-pumped solid-state laser

NASA Astrophysics Data System (ADS)

Lei, J.; Hu, A.; Wang, Y.; Chen, P.

2014-12-01

A method for selective excitation of Ince-Gaussian modes is presented. The method is based on the spatial distributions of Ince-Gaussian modes as well as the transverse mode selection theory. Significant diffraction loss is introduced in a resonator by using opaque lines at zero-intensity positions, and this loss allows to excite a specific mode; we call this method "loss control." We study the method by means of numerical simulation of a half-symmetric laser resonator. The simulated field is represented by angular spectrum of the plane waves representation, and its changes are calculated by the two-dimensional fast Fourier transform algorithm when it passes through the optical elements and propagates back and forth in the resonator. The output lasing modes of our method have an overlap of over 90 % with the target Ince-Gaussian modes. The method will be beneficial to the further study of properties and potential applications of Ince-Gaussian modes.

Effect of Laser Power and Scan Speed on Melt Pool Characteristics of Commercially Pure Titanium (CP-Ti)

NASA Astrophysics Data System (ADS)

Kusuma, Chandrakanth; Ahmed, Sazzad H.; Mian, Ahsan; Srinivasan, Raghavan

2017-07-01

Selective laser melting (SLM) is an additive manufacturing technique that creates complex parts by selectively melting metal powder layer-by-layer using a laser. In SLM, the process parameters decide the quality of the fabricated component. In this study, single beads of commercially pure titanium (CP-Ti) were melted on a substrate of the same material using an in-house built SLM machine. Multiple combinations of laser power and scan speed were used for single bead fabrication, while the laser beam diameter and powder layer thickness were kept constant. This experimental study investigated the influence of laser power, scan speed, and laser energy density on the melt pool formation, surface morphology, geometry (width and height), and hardness of solidified beads. In addition, the observed unfavorable effect such as inconsistency in melt pool width formation is discussed. The results show that the quality, geometry, and hardness of solidified melt pool are significantly affected by laser power, scanning speed, and laser energy density.

Effects of 532 nm pulsed-KTP laser parameters on vessel ablation in the avian chorioallantoic membrane: implications for vocal fold mucosa.

PubMed

Broadhurst, Matthew S; Akst, Lee M; Burns, James A; Kobler, James B; Heaton, James T; Anderson, R Rox; Zeitels, Steven M

2007-02-01

Selective vascular ablation (photoangiolysis) using pulsed lasers that target hemoglobin is an effective treatment strategy for many vocal fold lesions. However, vessel rupture with extravasation of blood reduces selectivity for vessels, which is frequently observed with the 0.45-ms, 585-nm pulsed dye laser. Previous studies have shown that vessel rupture is the result of vaporization of blood, an event that varies with laser pulse width and pulse fluence (energy per unit area). Clinical observations using a 532-nm wavelength pulsed potassium-titanyl-phosphate (KTP) laser revealed less laser-induced hemorrhage than the pulsed dye laser. This study investigated settings for the pulsed KTP laser to achieve selective vessel destruction without rupture using the avian chorioallantoic membrane under conditions similar to flexible laryngoscopic delivery of the laser in clinical practice. The chick chorioallantoic membrane offers convenient access to many small blood vessels similar in size to those targeted in human vocal fold. Using a 532-nm pulsed KTP laser, pulse width, pulse energy, and working distance from the optical delivery fiber were varied to assess influence on the ability to achieve vessel coagulation without vessel wall rupture. Third-order vessels (n = 135) were irradiated: Energy (471-550 mJ), pulse width (10, 15, 30 ms), and fiber-to-tissue distance (1 mm, 3 mm) were varied systematically. Selective vessel destruction without vessel wall rupture was more often achieved by increasing pulse width, increasing the fiber-to-tissue distance, and decreasing energy. Vessel destruction without rupture was consistently achieved using 15- or 30-ms pulses with a fiber-to-tissue distance of 3 mm (pulse fluence of 13-16 J/cm). This study substantiates our clinical observation that a 532-nm pulsed KTP laser was effective for ablating microcirculation while minimizing vessel wall rupture and hemorrhage.

Photothermal and photoacoustic processes of laser activated nano-thermolysis of cells

NASA Astrophysics Data System (ADS)

Lapotko, Dmitri; Lukianova, Ekaterina; Mitskevich, Pavel; Smolnikova, Victoria; Potapnev, Michail; Konopleva, Marina; Andreeff, Michael; Oraevsky, Alexander

2007-02-01

Laser Activated Nano-Thermolysis was recently proposed for selective damage of individual target (cancer) cells by pulsed laser induced microbubbles around superheated clusters of optically absorbing nanoparticles (NP). One of the clinical applications of this technology is the elimination of residual tumor cells from human blood and bone marrow. Clinical standards for the safety and efficacy of such procedure require the development and verification of highly selective and controllable mechanisms of cell killing. Our previous experiments showed that laser-induced microbubble is the main damaging factor in the case cell irradiation by short laser pulses above the threshold. Our current aim was to study the cell damage mechanisms and analyze selectivity and efficacy of cell damage as a function of NP parameters, NP-cell interaction conditions, and conditions of bubble generation around NP and NP clusters in cells. Generation of laser-induced bubbles around gold NP with diameters 10-250 nm was studied in Acute Myeloblast Leukemia (AML) cultures, normal stem and model K562 human cells. Short laser pulses (10 ns, 532 nm) were applied to those cells in vitro and the processes in cells were investigated with photothermal, fluorescent and atomic force microscopies and also with fluorescence flow cytometry. We have found that the best selectivity of cell damage is achieved by (1) forming large clusters of optically absorbing NP in target cells and (2) irradiating the cells with single laser pulses with the lowest fluence that can generate microbubble only around large clusters but not around single NP. Laser microbubbles with the lifetime from 20 ns to 2000 ns generated in individual cells caused damage and lysis of the cellular membrane and consequently cell death. Laser microbubbles did not damage normal cells around the damaged target (tumor) cell. Laser irradiation with equal fluence did not cause any damage of cells without accumulated NP clusters.

Wavelength-switchable and stable-ring-cavity, erbium-doped fiber laser based on Mach-Zehnder interferometer and tunable filter

NASA Astrophysics Data System (ADS)

He, Wei; Zhu, Lianqing; Dong, Mingli; Lou, Xiaoping; Luo, Fei

2018-04-01

This paper proposes and tests a ring cavity-based, erbium-doped fiber laser that incorporates a Mach-Zehnder interferometer and tunable filter. A four-m-long erbium-doped fiber was selected as the gain medium. The all-fiber Mach-Zehnder interferometer was composed of two 2  ×  2 optical couplers, and the tunable filter was used as wavelength reflector. A lasing threshold of 103 mW was used in the experiment, and the tunable laser with stable single and dual wavelengths was implemented by adjusting the tunable filter. The channel spacing was 0.6 nm within the range 1539.4-1561.6 nm, where the power difference between the lines was less than 0.4 dB. The side-mode suppression ratio was higher than 36 dB and the 3 dB linewidth was 0.02 nm. When a single-wavelength laser was implemented at 1557.4 nm, the power fluctuations were lower than 0.34 dB within 20 min of scan time. When lasers at wavelengths of 1558.6 nm and 1559.2 nm were simultaneously applied, the power shifts were lower than 0.29 dB and 0.43 dB, respectively, at room temperature.

Analysis and design of a high power laser adaptive phased array transmitter

NASA Technical Reports Server (NTRS)

Mevers, G. E.; Soohoo, J. F.; Winocur, J.; Massie, N. A.; Southwell, W. H.; Brandewie, R. A.; Hayes, C. L.

1977-01-01

The feasibility of delivering substantial quantities of optical power to a satellite in low earth orbit from a ground based high energy laser (HEL) coupled to an adaptive antenna was investigated. Diffraction effects, atmospheric transmission efficiency, adaptive compensation for atmospheric turbulence effects, including the servo bandwidth requirements for this correction, and the adaptive compensation for thermal blooming were examined. To evaluate possible HEL sources, atmospheric investigations were performed for the CO2, (C-12)(O-18)2 isotope, CO and DF wavelengths using output antenna locations of both sea level and mountain top. Results indicate that both excellent atmospheric and adaption efficiency can be obtained for mountain top operation with a micron isotope laser operating at 9.1 um, or a CO laser operating single line (P10) at about 5.0 (C-12)(O-18)2um, which was a close second in the evaluation. Four adaptive power transmitter system concepts were generated and evaluated, based on overall system efficiency, reliability, size and weight, advanced technology requirements and potential cost. A multiple source phased array was selected for detailed conceptual design. The system uses a unique adaption technique of phase locking independent laser oscillators which allows it to be both relatively inexpensive and most reliable with a predicted overall power transfer efficiency of 53%.

Diode-Laser-Based Spectrometer for Sensing Gases

NASA Technical Reports Server (NTRS)

Silver, Joel A.

2005-01-01

A diode-laser-based spectrometer has been developed for measuring concentrations of gases and is intended particularly for use in analyzing and monitoring combustion processes under microgravitational conditions in a drop tower or a spacecraft. This instrument is also well suited for use on Earth in combustion experiments and for such related purposes as fire-safety monitoring and monitoring toxic and flammable gases in industrial settings. Of the gas-sensing spectrometers available prior to the development of this instrument, those that were sensitive enough for measuring the combustion gases of interest were too large, required critical optical alignments, used far too much electrical power, and were insufficiently rugged for use under the severe conditions of spacecraft launch and space flight. In contrast, the present instrument is compact, consumes relatively little power, and is rugged enough to withstand launch vibrations and space flight. In addition, this instrument is characterized by long-term stability, accuracy, and reliability. The diode laser in this spectrometer is operated in a wavelength-modulation mode. Different gases to be measured can be selected by changing modular laser units. The operation of the laser is controlled by customized, low-power electronic circuitry built around a digital signal-processor board. This customized circuitry also performs acquisition and analysis of data, controls communications, and manages errors.

Highly sensitive SnO2 sensor via reactive laser-induced transfer

PubMed Central

Palla Papavlu, Alexandra; Mattle, Thomas; Temmel, Sandra; Lehmann, Ulrike; Hintennach, Andreas; Grisel, Alain; Wokaun, Alexander; Lippert, Thomas

2016-01-01

Gas sensors based on tin oxide (SnO2) and palladium doped SnO2 (Pd:SnO2) active materials are fabricated by a laser printing method, i.e. reactive laser-induced forward transfer (rLIFT). Thin films from tin based metal-complex precursors are prepared by spin coating and then laser transferred with high resolution onto sensor structures. The devices fabricated by rLIFT exhibit low ppm sensitivity towards ethanol and methane as well as good stability with respect to air, moisture, and time. Promising results are obtained by applying rLIFT to transfer metal-complex precursors onto uncoated commercial gas sensors. We could show that rLIFT onto commercial sensors is possible if the sensor structures are reinforced prior to printing. The rLIFT fabricated sensors show up to 4 times higher sensitivities then the commercial sensors (with inkjet printed SnO2). In addition, the selectivity towards CH4 of the Pd:SnO2 sensors is significantly enhanced compared to the pure SnO2 sensors. Our results indicate that the reactive laser transfer technique applied here represents an important technical step for the realization of improved gas detection systems with wide-ranging applications in environmental and health monitoring control. PMID:27118531

Hot working behavior of selective laser melted and laser metal deposited Inconel 718

NASA Astrophysics Data System (ADS)

Bambach, Markus; Sizova, Irina

2018-05-01

The production of Nickel-based high-temperature components is of great importance for the transport and energy sector. Forging of high-temperature alloys often requires expensive dies, multiple forming steps and leads to forged parts with tolerances that require machining to create the final shape and a large amount of scrap. Additive manufacturing offers the possibility to print the desired shapes directly as net-shape components, requiring only little additional effort in machining. Especially for high-temperature alloys carrying a large amount of energy per unit mass, additive manufacturing could be more energy-efficient than forging if the energy contained in the machining scrap exceeds the energy needed for powder production and laser processing. However, the microstructure and performance of 3d-printed parts will not reach the level of forged material unless further expensive processes such as hot-isostatic pressing are used. Using the design freedom and possibilities to locally engineer material, additive manufacturing could be combined with forging operations to novel process chains, offering the possibility to reduce the number of forging steps and to create near-net shape forgings with desired local properties. Some innovative process chains combining additive manufacturing and forging have been patented recently, but almost no scientific knowledge on the workability of 3D printed preforms exists. The present study investigates the flow stress and microstructure evolution during hot working of pre-forms produced by laser powder deposition and selective laser melting (Figure 1) and puts forward a model for the flow stress.

Manufacturing and Characterization of Ti6Al4V Lattice Components Manufactured by Selective Laser Melting

PubMed Central

Campanelli, Sabina L.; Contuzzi, Nicola; Ludovico, Antonio D.; Caiazzo, Fabrizia; Cardaropoli, Francesco; Sergi, Vincenzo

2014-01-01

The paper investigates the fabrication of Selective Laser Melting (SLM) titanium alloy Ti6Al4V micro-lattice structures for the production of lightweight components. Specifically, the pillar textile unit cell is used as base lattice structure and alternative lattice topologies including reinforcing vertical bars are also considered. Detailed characterizations of dimensional accuracy, surface roughness, and micro-hardness are performed. In addition, compression tests are carried out in order to evaluate the mechanical strength and the energy absorbed per unit mass of the lattice truss specimens made by SLM. The built structures have a relative density ranging between 0.2234 and 0.5822. An optimization procedure is implemented via the method of Taguchi to identify the optimal geometric configuration which maximizes peak strength and energy absorbed per unit mass. PMID:28788707

Application of time-division-multiplexed lasers for measurements of gas temperature and CH4 and H2O concentrations at 30 kHz in a high-pressure combustor.

PubMed

Caswell, Andrew W; Kraetschmer, Thilo; Rein, Keith; Sanders, Scott T; Roy, Sukesh; Shouse, Dale T; Gord, James R

2010-09-10

Two time-division-multiplexed (TDM) sources based on fiber Bragg gratings were applied to monitor gas temperature, H(2)O mole fraction, and CH(4) mole fraction using line-of-sight absorption spectroscopy in a practical high-pressure gas turbine combustor test article. Collectively, the two sources cycle through 14 wavelengths in the 1329-1667 nm range every 33 μs. Although it is based on absorption spectroscopy, this sensing technology is fundamentally different from typical diode-laser-based absorption sensors and has many advantages. Specifically, the TDM lasers allow efficient, flexible acquisition of discrete-wavelength information over a wide spectral range at very high speeds (typically 30 kHz) and thereby provide a multiplicity of precise data at high speeds. For the present gas turbine application, the TDM source wavelengths were chosen using simulated temperature-difference spectra. This approach is used to select TDM wavelengths that are near the optimum values for precise temperature and species-concentration measurements. The application of TDM lasers for other measurements in high-pressure, turbulent reacting flows and for two-dimensional tomographic reconstruction of the temperature and species-concentration fields is also forecast.