Excimer laser processing of backside-illuminated CCDS

NASA Technical Reports Server (NTRS)

Russell, S. D.

1993-01-01

An excimer laser is used to activate previously implanted dopants on the backside of a backside-illuminated CCD. The controlled ion implantation of the backside and subsequent thin layer heating and recrystallization by the short wavelength pulsed excimer laser simultaneously activates the dopant and anneals out implant damage. This improves the dark current response, repairs defective pixels and improves spectral response. This process heats a very thin layer of the material to high temperatures on a nanosecond time scale while the bulk of the delicate CCD substrate remains at low temperature. Excimer laser processing backside-illuminated CCD's enables salvage and utilization of otherwise nonfunctional components by bringing their dark current response to within an acceptable range. This process is particularly useful for solid state imaging detectors used in commercial, scientific and government applications requiring a wide spectral response and low light level detection.

Topographic steep central islands following excimer laser photorefractive keratectomy

NASA Astrophysics Data System (ADS)

Krueger, Ronald R.; McDonnell, Peter J.

1994-06-01

The purpose of this study is to demonstrate that topographic irregularities in the form of central islands of higher refractive power can be seen following excimer laser refractive surgery. We reviewed the computerized corneal topographic maps of 35 patients undergoing excimer laser PRK for compound myopic astigmatism or anisometropia from 8/91 to 8/93 at the USC/Doheny Eye Institute. The topographic maps were generated by the Computed Anatomy Corneal Modeling System, and central islands were defined as topographic areas of steepening of at least 3 diopters and 3 mm in diameter. A grading system was developed based on the presence of central islands during the postoperative period. Visually significant topographic steep central islands may be seen in over 50% of patients at 1 month following excimer laser PRK, and persist at 3 months in up to 24% of patients without nitrogen gas blowing. Loss of best corrected visual acuity or ghosting is associated with island formation, and may prolong visual rehabilitation after excimer laser PRK.

New 223-nm excimer laser surgical system for photorefractive keratectomy

NASA Astrophysics Data System (ADS)

Bagaev, Sergei N.; Razhev, Alexander M.; Zhupikov, Andrey A.

1999-02-01

The using of KrCl (223 nm) excimer laser in ophthalmic devices for Photorefractive Keratectomy (PRK) and phototherapeutic Keratectomy (PTK) is offered. The structure and functions of a new surgical UV ophthalmic laser systems Medilex using ArF (193 nm) or KrCl (223 nm) excimer laser for corneal surgery are presented. The systems Medilex with the new optical delivery system is used for photoablative reprofiling of the cornea to correct refraction errors (myopia, hyperopia and astigmatism) and to treat a corneal pathologies. The use of the 223 nanometer laser is proposed to have advantages over the 193 nanometer laser. The results of application of the ophthalmic excimer laser systems Medilex for treatment of myopia are presented.

Combination treatment with excimer laser and narrowband UVB light in vitiligo patients.

PubMed

Shin, Sungsik; Hann, Seung-Kyung; Oh, Sang Ho

2016-01-01

For the treatment of vitiligo, narrowband UVB (NBUVB) light is considered the most effective for nonsegmental vitiligo, while excimer laser treatment is commonly used for localized vitiligo. However, treatment areas may potentially be missed with excimer laser treatment. We aimed to evaluate the effect of combinational treatment with NBUVB light and excimer laser on vitiligo. All patients were first treated with NBUVB; excimer laser was then applied in conjunction with NBUVB phototherapy due to a slow response or no further improvement with continuous NBUVB treatment alone. To minimize adverse effects, a fixed dose of NBUVB was administered, and the dose of excimer laser was increased based on patient response. Among 80 patients, 54 patients showed responses after combination with excimer laser; however, 26 patients (32.5%) showed no remarkable change after combination therapy. Of the 26 patients who showed no further response, 12 patients (46.1%) presented with vitiligo on the acral areas, which are known to the least responsive sites. Our study suggests that combined treatment of NBUVB and excimer laser in vitiligo may enhance the treatment response without remarkable side effects, therefore might also increase the compliance of the patients to the treatment. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Excimer laser in arthroscopic surgery

NASA Astrophysics Data System (ADS)

Koort, Hans J.

1991-05-01

The development of efficient high-power lasersystems for use in surgery, especially in arthroscopic fields, leads to a new push for all endoscopic techniques. Both techniques, laser and endoscope, complete each other in an ideal way and allow applications which could not be reached with conventional techniques. One of the newer laser types is the excimer laser, which will be a good choice for surface treatment because of its very considerate interaction with tissue. One example is the ablation or smoothing of articular cartilage and meniscal shaving in orthopaedics. On the other hand, the power of this laser system is high enough to cut tissue, for instance in the lateral release, and offers therefore an alternative to the mechanical and electrical instruments. All lasers can only work fine with effective delivery systems. Sometimes there is only a single fiber, which becomes very stiff at diameters of more than 800 micrometers . This fiber often allows only the tangential treatment of tissue, most of the laser power is lost in the background. New fiber systems with many, sometimes hundreds of very thin single fibers, could offer a solution. Special handpieces and fibersystems offer distinct advantages in small joint arthroscopy, especially those for use with excimer lasers will be discussed.

Excimer laser irradiation of metal surfaces

NASA Astrophysics Data System (ADS)

Kinsman, Grant

In this work a new method of enhancing CO2 laser processing by modifying the radiative properties of a metal surface is studied. In this procedure, an excimer laser (XeCl) or KrF) exposes the metal surface to overlapping pulses of high intensity, 10(exp 8) - 10(exp 9) W cm(exp -2), and short pulse duration, 30 nsec FWHM (Full Width Half Maximum), to promote structural and chemical change. The major processing effect at these intensities is the production of a surface plasma which can lead to the formation of a laser supported detonation wave (LSD wave). This shock wave can interact with the thin molten layer on the metal surface influencing to a varying degree surface oxidation and roughness features. The possibility of the expulsion, oxidation and redeposition of molten droplets, leading to the formation of micron thick oxide layers, is related to bulk metal properties and the incident laser intensity. A correlation is found between the expulsion of molten droplets and a Reynolds number, showing the interaction is turbulent. The permanent effects of these interactions on metal surfaces are observed through scanning electron microscopy (SEM), transient calorimetric measurements and Fourier transform infrared (FTIR) spectroscopy. Observed surface textures are related to the scanning procedures used to irradiate the metal surface. Fundamental radiative properties of a metal surface, the total hemispherical emissivity, the near-normal spectral absorptivity, and others are examined in this study as they are affected by excimer laser radiation. It is determined that for heavily exposed Al surface, alpha' (10.6 microns) can be increased to values close to unity. Data relating to material removal rates and chemical surface modification for excimer laser radiation is also discussed. The resultant reduction in the near-normal reflectivity solves the fundamental problem of coupling laser radiation into highly reflective and conductive metals such as copper and aluminum. The

Excimer-laser-induced shock wave and its dependence on atmospheric environment

NASA Astrophysics Data System (ADS)

Krueger, Ronald R.; Krasinski, Jerzy S.; Radzewicz, Czeslaw

1993-06-01

High speed shadow photography is performed on excimer laser ablated porcine corneas and rubber stoppers to capture the excimer laser induced shock waves at various time delays between 40 and 320 nanoseconds. The shock waves in air, nitrogen, and helium are recorded by tangentially illuminating the ablated surface with a tunable dye laser, the XeCl excimer laser pulse. The excimer laser ablates the specimen and excites the dye laser, which is then passed through an optical delay line before illuminating the specimen. The shadow of the shock wave produced during ablation is then cast on a screen and photographed with a CCD video camera. The system is pulsed at 30 times per second to allow a video recording of the shock wave at a fixed time delay. We conclude that high energy acoustic waves and gaseous particles are liberated during excimer laser corneal ablation, and dissipate on a submicrosecond time scale. The velocity of their dissipation is dependent on the atmospheric environment and can be increased two-fold when the ablation is performed in a helium atmosphere. Therefore, local temperature increases due to the liberation of high energy gases may be reduced by using helium during corneal photoablation.

Changing profile of excimer laser coronary angioplasty: refinements in catheters

NASA Astrophysics Data System (ADS)

Bittl, John A.

1994-07-01

During more than five years of investigation with excimer laser angioplasty, several changes have been made in patient selection and laser catheters. It is unclear, however, whether these changes have improved the outcome of excimer laser angioplasty. A total of 2041 patients underwent treatment with excimer laser coronary angioplasty for 2324 lesions with clinical success in 89%, ischemic complications in 7.5%, and vessel perforation in 2.1%. When the entire 5-year period of investigation was divided into four discrete phases, as defined by the successive release of improved laser catheters (prototype, flexible, extremely flexible, and eccentric), clinical success was seen to improve from 86% to 95% (p<0.001) despite the increased incidence of advanced age (pequals0.01) and unstable angina (p<0.001). Multivariable analysis identified improved laser catheters, saphenous vein graft lesions, and unclarified stenoses as predictors of favorable outcome. Operator experience was associated with decreased complications. Reduced catheter size relative to vessel size was associated with decreased risk of vessel perforation. Thus, refinements in patient selection and in laser technique have been associated with enhanced safety and efficacy of excimer laser angioplasty.

Pulsed Laser-Assisted Focused Electron-Beam-Induced Etching of Titanium with XeF 2 : Enhanced Reaction Rate and Precursor Transport

DOE PAGES

Noh, J. H.; Fowlkes, J. D.; Timilsina, R.; ...

2015-01-28

We introduce a laser-assisted focused electron-beam-induced etching (LA-FEBIE) process which is a versatile, direct write nanofabrication method that allows nanoscale patterning and editing; we do this in order to enhance the etch rate of electron-beam-induced etching. The results demonstrate that the titanium electron stimulated etch rate via the XeF2 precursor can be enhanced up to a factor of 6 times with an intermittent pulsed laser assist. Moreover, the evolution of the etching process is correlated to in situ stage current measurements and scanning electron micrographs as a function of time. Finally, the increased etch rate is attributed to photothermally enhancedmore » Ti–F reaction and TiF4 desorption and in some regimes enhanced XeF2 surface diffusion to the reaction zone.« less

Excimer laser debridement of necrotic erosions of skin without collateral damage

NASA Astrophysics Data System (ADS)

Wynne, James J.; Felsenstein, Jerome M.; Trzcinski, Robert; Zupanski-Nielsen, Donna; Connors, Daniel P.

2011-07-01

Pulsed ArF excimer laser radiation at 6.4 eV, at fluence exceeding the ablation threshold, will debride burn eschar and other dry necrotic erosions of the skin. Debridement will cease when sufficiently moist viable tissue is exposed, due to absorption by aqueous chloride ions (Cl-) through the non-thermal process of electron photodetachment, thereby inhibiting collateral damage to the viable tissue. ArF excimer laser radiation debrides/ablates ~1 micron of tissue with each pulse. While this provides great precision in controlling the depth of debridement, the process is relatively time-consuming. In contrast, XeCl excimer laser radiation debrides ~8 microns of tissue with each pulse. However the 4.0 eV photon energy of the XeCl excimer laser is insufficient to photodetach an electron from a Cl- ion, so blood or saline will not inhibit debridement. Consequently, a practical laser debridement system should incorporate both lasers, used in sequence. First, the XeCl excimer laser would be used for accelerated debridement. When the necrotic tissue is thinned to a predetermined thickness, the ArF excimer laser would be used for very precise and well-controlled debridement, removing ultra-thin layers of material with each pulse. Clearly, the use of the ArF laser is very desirable when debriding very close to the interface between necrotic tissue and viable tissue, where the overall speed of debridement need not be so rapid and collateral damage to viable tissue is undesirable. Such tissue will be sterile and ready for further treatment, such as a wound dressing and/or a skin graft.

Excimer laser for the treatment of psoriasis: safety, efficacy, and patient acceptability

PubMed Central

Abrouk, Michael; Levin, Ethan; Brodsky, Merrick; Gandy, Jessica R; Nakamura, Mio; Zhu, Tian Hao; Farahnik, Benjamin; Koo, John; Bhutani, Tina

2016-01-01

Introduction The 308 nm excimer laser is a widely used device throughout the field of dermatology for many diseases including psoriasis. Although the laser has demonstrated clinical efficacy, there is a lack of literature outlining the safety, efficacy, and patient acceptability of the excimer laser. Methods A literature search on PubMed was used with combinations of the terms “excimer”, “excimer laser”, “308 nm”, “psoriasis”, “protocol”, “safety”, “efficacy”, acceptability”, “side effects”, and “dose”. The search results were included if they contained information pertaining to excimer laser and psoriasis treatment and description of the safety, efficacy, and patient acceptability of the treatment. Results The 308 nm excimer laser is generally safe and well tolerated with minimal side effects including erythema, blistering, and pigmentary changes. It has a range of efficacies depending on the protocol used with several different treatment protocols, including the induration protocol, the minimal erythema dose protocol, and the newer minimal blistering dose protocol. Conclusion Although the excimer laser is not a first-line treatment, it remains an excellent treatment option for psoriasis patients and has been demonstrated to be an effective treatment with little to no side effects. PMID:29387603

Advances in 193 nm excimer lasers for mass spectrometry applications

NASA Astrophysics Data System (ADS)

Delmdahl, Ralph; Esser, Hans-Gerd; Bonati, Guido

2016-03-01

Ongoing progress in mass analysis applications such as laser ablation inductively coupled mass spectrometry of solid samples and ultraviolet photoionization mediated sequencing of peptides and proteins is to a large extent driven by ultrashort wavelength excimer lasers at 193 nm. This paper will introduce the latest improvements achieved in the development of compact high repetition rate excimer lasers and elaborate on the impact on mass spectrometry instrumentation. Various performance and lifetime measurements obtained in a long-term endurance test over the course of 18 months will be shown and discussed in view of the laser source requirements of different mass spectrometry tasks. These sampling type applications are served by excimer lasers delivering pulsed 193 nm output of several mJ as well as fast repetition rates which are already approaching one Kilohertz. In order to open up the pathway from the laboratory to broader market industrial use, sufficient component lifetimes and long-term stable performance behavior have to be ensured. The obtained long-term results which will be presented are based on diverse 193 nm excimer laser tube improvements aiming at e.g. optimizing the gas flow dynamics and have extended the operational life the laser tube for the first time over several billion pulses even under high duty-cycle conditions.

Treatment of alopecia areata with the 308-nm xenon chloride excimer laser: case report of two successful treatments with the excimer laser.

PubMed

Gundogan, Cuneyt; Greve, Bärbel; Raulin, Christian

2004-01-01

Alopecia areata is a common disease of unknown etiology; it causes significant cosmetic and psycho-social distress for most of the people it affects. We report on an innovative form of treatment in two patients with typical alopecia areata on the capillitium. We successfully treated two patients whose alopecia areata had worsened progressively for 3 and 14 weeks. The treatment involved the use of a 308 nm xenon chloride excimer laser (dosage 300-2,300 mJ/cm(2) per session). After 11 and 12 sessions within a 9-week and 11-week period, the entire affected focus showed homogenous and thick regrowth. No relapse was observed during the follow-up period of 5 and 18 months. The use of the excimer laser is an effective, elegant, and safe means of treatment and has good tolerability. Analogous to topical treatment of alopecia areata, the immunosuppressive mechanism of the excimer laser can be interpreted as an induction of T-cell apoptosis. This new means of treatment has yet to be discussed in medical literature. Further studies with greater numbers are needed to assess its potential more precisely and evaluate the excimer laser in treating alopecia areata. Copyright 2004 Wiley-Liss, Inc.

Myopic keratomileusis by excimer laser on a lathe.

PubMed

Ganem, S; Aron-Rosa, D; Gross, M; Rosolen, S

1994-01-01

We designed an excimer laser keratomileusis delivery system to increase the regularity of the refractive cut surface and allow greater precision in the level and shape of the ablated zone. A parallel faced corneal disc was produced by microkeratectomy from six human eyes and surgical keratectomy in 12 beagle corneas. A 193-nanometer excimer laser that was used to project an oval beam onto the corneal disc was rotated on a flat surface to ensure overlapping of the ovally ablated areas between pulses. Electron microscopy of eye bank lenticules demonstrated a circular smooth regularly concave ablation zone. Histological examination of nine clear corneas confirmed thinning of the stroma without fibroblastic reaction and no epithelial hypertrophy. Mean preoperative corneal power of 43.15 +/- 2.18 decreased postoperatively to 33.61 +/- 2.34. The new technique of excimer laser keratomileusis has the advantage of a cut surface smoother and the clear zone is devoid of the stepwise concavity and irregularity seen in diaphragm based photoablation delivery systems.

Studies in fiber guided excimer laser surgery for cutting and drilling bone and meniscus.

PubMed

Dressel, M; Jahn, R; Neu, W; Jungbluth, K H

1991-01-01

Our experiments on transmitting high-power excimer laser pulses through optical fibers and our investigations on excimer laser ablation of hard tissue show the feasibility of using the excimer laser as an additional instrument in general and accident surgery involving minimal invasive surgery. By combining XeCl-excimer lasers and tapered fused silica fibers we obtained output fluences up to 32 J/cm2 and ablation rates of 3 microns/pulse of hard tissue. This enables us to cut bone and cartilage in a period of time which is suitable for clinical operations. Various experiments were carried out on cadavers in order to optimize the parameters of the excimer laser and fibers: e.g., wavelength, pulse duration, energy, repetition rate, fiber core diameter. The surfaces of the cut tissue are comparable to cuts with conventional instruments. No carbonisation was observed. The temperature increase is below 40 degrees C in the tissue surrounding the laser spot. The healing rate of an excimer laser cut is not slower than mechanical treatments; the quality is comparable.

Excimer laser coronary angioplasty: relative risk analysis of clinical results

NASA Astrophysics Data System (ADS)

Bittl, John A.

1992-08-01

Reports of successful use of excimer laser coronary angioplasty for complex coronary artery disease abound, yet firm indications for its use have not been defined. We attempted to treat 858 coronary stenoses in 764 consecutive patients (mean age 61 years; range 32 - 91 years; 75% men; 76% with Class III or IV angina) with excimer laser angioplasty at 308 nm. Successful treatment was achieved in 86% of patients, as indicated by excimer laser angioplasty, we used relative risk analysis. This showed that certain angiographic features, such as lesions at a vessel bifurcation (odds ratio, OR equals 0.46; 95% confidence interval 0.23, 0.88; P equals 0.017;) or in a tortuous segment (OR equals 0.54; 95% CI equals 0.34, 0.88; P equals 0.041), have decreased likelihood of clinical success. On the other hand, ostial stenoses (OR equals 1.06; 95% CI equals 0.44, 2.56, P equals 0.903) and saphenous vein graft lesions (OR equals 2.17; 95% CI equals 0.98, 4.82; P equals 0.051) have acceptable success rates. Diffuse disease (> 20 mm), total occlusions and calcified lesions were treated as successfully as all other lesion types. Successful treatment with excimer laser coronary angioplasty was also achieved in almost all patients (15/16) who had a prior unsuccessful attempt at balloon angioplasty in the lesion was crossed with a guidewire yet resists either balloon catheter passage or full dilatation. Follow-up angiography was obtained in 70% of eligible patients. Angiographic restenosis, defined by > 50% stenosis, was seen in 60% of patients. Relative risk analysis showed an increased risk of restenosis when adjunctive balloon angioplasty was not used (OR equals 1.68; 95% CI equals 1.02, 2.28; P equals 0.039). Other variables known to affect the outcome of balloon angioplasty, such as lesion length or stenosis in degenerated saphenous vein bypass graft, did not influence the

Design and performance of a production-worthy excimer-laser-based stepper

NASA Astrophysics Data System (ADS)

Unger, Robert; Sparkes, Christopher; Disessa, Peter A.; Elliott, David J.

1992-06-01

Excimer-laser-based steppers have matured to a production-worthy state. Widefield high-NA lenses have been developed and characterized for imaging down to 0.35 micron and below. Excimer lasers have attained practical levels of performance capability and stability, reliability, safety, and operating cost. Excimer stepper system integration and control issues such as focus, exposure, and overlay stability have been addressed. Enabling support technologies -- resist systems, resist processing, metrology and conventional mask making -- continue to progress and are becoming available. This paper discusses specific excimer stepper design challenges, and presents characterization data from several field installations of XLSTM deep-UV steppers configured with an advanced lens design.

Excimer laser photorefractive keratectomy for myopia: preliminary results at one year

NASA Astrophysics Data System (ADS)

Thompson, Keith P.; Waring, George O., III; Steinert, Roger; Durrie, Daniel S.; Gordon, Michael; Brint, Stephen F.

1992-08-01

Excimer laser photorefractive keratectomy (PRK) is presently under investigation for the correction of myopia. Two companies in the United States, Summit Technology (Waltham, Mass.) and VisX, Inc. (Sunnyvale, Calif.) have developed excimer laser delivery systems and are participating in an FDA study to determine the safety and efficacy of PRK. This is a preliminary report on the refractive and visual results of 51 of 100 eyes treated between October 10, 1990 and March 7, 1991 by the Summit Technology UV200LA excimer laser under the FDA Phase IIB FDA protocol one year after surgery. More detailed information on eight patients treated at Emory University Eye Center (Emory Subgroup) is also reported.

Excimer laser interaction with dentin of the human tooth

NASA Technical Reports Server (NTRS)

Hammond, Ernest C., Jr.; Gilliam, Ruth L.; Baker, George R.

1989-01-01

The use an excimer laser produced many unusual conical structures within the dentin of the inner part of the human tooth. By varying the frequency of the laser one can disperse the energy and cause more bleeding in laser surgery, but not destroy the cells associated with the incision. Therefore, the healing process will virtually be without scarring. Whereas, using the infrared laser the blood loss would be less, but the healing process would tend to be longer because cells are being destroyed due to the cauterization effect of the laser. The question is, are these structures produced as an interaction with the laser or are they an intrinsic part of the structure. The effects of the laser interaction upon dentin was studied, and in using electron microscopy the interaction of the excimer laser upon the tooth dentin and other various biological tissue is more clearly understood.

Treatment of oral lichen planus using 308-nm excimer laser.

PubMed

Liu, Wei-Bing; Sun, Li-Wei; Yang, Hua; Wang, Yan-Fei

2017-09-01

Oral lichen planus (OLP) is a chronic inflammatory disease, has prolonged courses, repeated attacks and resistance to treatment. The traditional narrow spectrum UVB treatment has an established efficacy on skin lichen planus, and high safety. However, most of ultraviolet phototherapy devices have a huge volume, thereby cannot be used in the treatment of OLP. Lymphocytic infiltration is evident in the lesions of lichen planus, and the direct irradiation of 308-nm excimer laser can induce apoptosis of the T lymphocytes in skin lesions, thereby has a unique therapeutic effect on the diseases involving T lymphocytes. This study aims to investigate the efficacy of 308-nm excimer laser in the treatment of OLP. A total of six OLP patients were enrolled into this study, and further pathological diagnosis was conducted, then 308-nm excimer laser was used in the treatment. The efficacy of 308-nm excimer laser in the treatment of OLP was satisfactory. The clinical symptoms of five patients were significantly improved. In two patients, the erosion surface based on congestion and the surrounding white spots completely disappeared, and clinical recovery was achieved. Three patients achieved partial remission, that is, the erosion surface healed, congestion and white spot area shrunk by more than 1/2 of the primary skin lesions. In the remaining one patient, the erosion surface had not completely healed after treatment, and congestion and white spot area shrunk by less than 1/2 of the primary skin lesions. Only one patients had developed mild pain during the treatment, and this symptom alleviated by itself. The 308-nm excimer laser therapy can serve as a safe and effective treatment for OLP. © 2017 Wiley Periodicals, Inc.

Photochemical and Spectroscopic Effects Resulting from Excimer Laser Excitation.

NASA Astrophysics Data System (ADS)

Wang, Xuan Xiao

I. Photochemical production of ozone from pure oxygen using excimer lasers. Production of ozone was observed from experiments when oxygen was under a broadband pulsed KrF laser radiation. The production process was found to be autocatalytic. Mechanisms for the ozone formation were proposed. Experimental results over a range of oxygen pressure and laser pulse energy (irradiance) provided evidences in favor of the proposed mechanisms. Experiments were also numerically modeled. Good agreement between the experimental and the numerical results were observed, which provided further evidence to support the proposed mechanisms. Cross sections for some photochemical processes in the mechanisms were estimated. Production of ozone from pure oxygen under a ArF excimer laser radiation (193 nm) was also studied and numerically modeled. Effects of ambient water vapor on ozone production were investigated. Experimental results showed a fast ozone destruction when water vapor was present in the cell. However, numerical results obtained from the well-known OH and HO _2 chain ozone destruction mechanism predicted a slower ozone destruction. Possible reasons for the discrepancy are discussed. II. Resonance-enhanced multiphoton ionization of N_2 at 193 and 248 nm detected by N_sp{2}{+} fluorescence. Using a broadband excimer laser operating at 193 and 248 nm multiphoton ionization at high pressures in air and pure nitrogen has been detected by fluorescence from N_sp{2}{+} in the B-X firstnegative system. Measurements of the fluorescence intensity as a function of beam irradiance indicate resonance in N_2 at the energy of two 193 nm photons (2 + 1 REMPI) and three 248 nm photons (3 + 1 REMPI). Possible intermediate states are discussed. III. Excimer laser-induced fluorescence from some organic solvents. Fluorescence was observed from vapor phase benzene, toluene, p-xylene, benzyl chloride, methyl benzoate, acetic anhydride, ether, methanol, ethyl acetone, acetone, and 2-butanone using

Forming n/p Junctions With An Excimer Laser

NASA Technical Reports Server (NTRS)

Alexander, Paul, Jr.; Campbell, Robert B.; Wong, David C.; Bottenberg, William L.; Byron, Stanley

1988-01-01

Compact equipment yields high-quality solar cells. Computer controls pulses of excimer laser and movement of silcon wafer. Mirrors direct laser beam to wafer. Lenses focus beam to small spot on surface. Process suitable for silicon made by dendritic-web-growth process.

Excimer laser therapy and narrowband ultraviolet B therapy for exfoliative cheilitis.

PubMed

Bhatia, Bhavnit K; Bahr, Brooks A; Murase, Jenny E

2015-06-01

Exfoliative cheilitis is a condition of unknown etiology characterized by hyperkeratosis and scaling of vermilion epithelium with cyclic desquamation. It remains largely refractory to treatment, including corticosteroid therapy, antibiotics, antifungals, and immunosuppressants. We sought to evaluate the safety and efficacy of excimer laser therapy and narrowband ultraviolet B therapy in female patients with refractory exfoliative cheilitis. We reviewed the medical records of two female patients who had been treated unsuccessfully for exfoliative cheilitis. We implemented excimer laser therapy, followed by hand-held narrowband UVB treatments for maintenance therapy, and followed them for clinical improvement and adverse effects. Both patients experienced significant clinical improvement with minimal adverse effects with excimer laser therapy 600-700 mJ/cm 2 twice weekly for several months. The most common adverse effects were bleeding and burning, which occurred at higher doses. The hand-held narrowband UVB unit was also an effective maintenance tool. Limitations include small sample size and lack of standardization of starting dose and dose increments. Excimer laser therapy is a well-tolerated and effective treatment for refractory exfoliative cheilitis with twice weekly laser treatments of up to 700 mJ/cm 2 . Transitioning to the hand-held narrowband UVB device was also an effective maintenance strategy.

A review of protocols for 308 nm excimer laser phototherapy in psoriasis.

PubMed

Mudigonda, Tejaswi; Dabade, Tushar S; Feldman, Steven R

2012-01-01

308 nm excimer laser phototherapy is efficacious in the treatment of localized psoriasis. Different approaches regarding dose fluency, number of treatments, and maintenance have been utilized, and there is yet to be a consensus on standard protocol. To characterize treatment parameters for 308 nm excimer laser phototherapy. We performed a PubMed search for studies describing excimer laser treatment protocol with particular attention to dosage determination, dose adjustment, dose fluency, number of treatments, and maintenance. Seven prospective studies were found describing the excimer efficacy for psoriasis. All studies determined the initial treatment dose using either the minimal erythema dose (MED) or induration. Fluency ranged from 0.5 MED (low) to 16 MED (high); one study demonstrated that medium to high fluencies yielded better improvement in fewer number of treatments. Fluency adjustments during the course of treatment were important to minimize phototherapy-associated side effects. The use of higher fluencies was reported to result in higher occurrences of blistering. One study implemented a maintenance tapering of dose-frequency phase to better manage psoriasis flare-ups. The 308 nm excimer laser is an effective therapy for psoriasis regardless of the method used to determine initial dosage, dose fluency, or number of treatments. As its usage as a targeted monotherapy increases, future trials should consider evaluating and modifying these parameters to determine the most optimal management of localized psoriasis. Based on our reviewed studies, there is no consensus for a single excimer laser therapy protocol and as a result, patient preferences should continue to be an important consideration for phototherapy regimen planning.

308-nm excimer laser for the treatment of alopecia areata.

PubMed

Al-Mutairi, Nawaf

2007-12-01

Alopecia areata is loss of hair from localized or diffuse areas of hair-bearing area of the skin. Recently there are reports of efficacy of the 308-nm excimer radiation for this condition. To study the effect of the 308-nm excimer laser in the treatment of alopecia areata. Eighteen patients with 42 recalcitrant patches (including 1 adult with alopecia totalis) were enrolled in this study. The lesions were treated with the 308-nm excimer laser twice a week for a period of 12 weeks; one lesion on each patient was left as a control for comparison. There were 7 males and 11 females in this study. Regrowth of hair was observed in 17 (41.5%) patches. Thirteen of the 18 lesions in scalp showed a complete regrowth of hair. The extremity regions failed to show a response. Atopic diatheses had an unfavorable effect on the outcome in our patients. The 308-nm excimer laser is an effective therapeutic option for patchy alopecia areata of the scalp and for some cases with patchy alopecia areata of the beard area. It does not work for patchy alopecia areata of the extremities.

Vacuum barrier for excimer lasers

DOEpatents

Shurter, R.P.

1992-09-15

A barrier for separating the vacuum area of a diode from the pressurized gas area of an excimer laser. The barrier is a composite material comprising layers of a metal such as copper, along with layers of polyimide, and a matrix of graphite fiber yarns impregnated with epoxy. The barrier is stronger than conventional foil barriers, and allows greater electron throughput. 3 figs.

Vacuum barrier for excimer lasers

DOEpatents

Shurter, Roger P.

1992-01-01

A barrier for separating the vacuum area of a diode from the pressurized gas area of an excimer laser. The barrier is a composite material comprising layers of a metal such as copper, along with layers of polyimide, and a matrix of graphite fiber yarns impregnated with epoxy. The barrier is stronger than conventional foil barriers, and allows greater electron throughput.

Comparative study of excimer and erbium:YAG lasers for ablation of structural components of the knee

NASA Astrophysics Data System (ADS)

Vari, Sandor G.; Shi, Wei-Qiang; van der Veen, Maurits J.; Fishbein, Michael C.; Miller, J. M.; Papaioannou, Thanassis; Grundfest, Warren S.

1991-05-01

This study was designed to compare the efficiency and thermal effect of a 135 ns pulsed-stretched XeCl excimer laser (308 nm) and a free-running Erbium:YAG laser (2940 nm) with 200 microsecond(s) pulse duration for ablation of knee joint structures (hyaline and fibrous cartilage, tendon and bone). The radiant exposure used for tissue ablation ranged from 2 to 15 J/cm2 for the XeCl excimer and from 33 to 120 J/cm2 for Er:YAG. The excimer and Er:YAG lasers were operated at 4 and 5 Hz respectively. The ablative laser energy was delivered to tissue through fibers. Ablation rates of soft tissues (hyaline and fibrous cartilage, tendon) varied from 8.5 to 203 micrometers /pulse for excimer and from 8.2 to 273 micrometers /pulse for Er:YAG lasers. Ablation rates of soft tissues are linearly dependent on the radiant exposure. Within the range of parameters tested all the tissues except the bone could be rapidly ablated by both lasers. Bone ablation was much less efficient, requiring 15 J/cm2 and 110 J/cm2 radiant exposure for excimer and Er:YAG lasers to ablate 9.5 and 8.2 micrometers tissue per pulse. However, excimer laser ablation produced less thermal damage in the tissues studied compared to Er:YAG at the same laser parameters. The authors conclude that both lasers are capable of efficient knee joint tissue ablation. XeCl excimer laser requires an order of magnitude less energy than Er:YAG laser for comparable tissue ablation.

Average power scaling of UV excimer lasers drives flat panel display and lidar applications

NASA Astrophysics Data System (ADS)

Herbst, Ludolf; Delmdahl, Ralph F.; Paetzel, Rainer

2012-03-01

Average power scaling of 308nm excimer lasers has followed an evolutionary path over the last two decades driven by diverse industrial UV laser microprocessing markets. Recently, a new dual-oscillator and beam management concept for high-average power upscaling of excimer lasers has been realized, for the first time enabling as much as 1.2kW of stabilized UV-laser average output power at a UV wavelength of 308nm. The new dual-oscillator concept enables low temperature polysilicon (LTPS) fabrication to be extended to generation six glass substrates. This is essential in terms of a more economic high-volume manufacturing of flat panel displays for the soaring smartphone and tablet PC markets. Similarly, the cost-effective production of flexible displays is driven by 308nm excimer laser power scaling. Flexible displays have enormous commercial potential and can largely use the same production equipment as is used for rigid display manufacturing. Moreover, higher average output power of 308nm excimer lasers aids reducing measurement time and improving the signal-to-noise ratio in the worldwide network of high altitude Raman lidar stations. The availability of kW-class 308nm excimer lasers has the potential to take LIDAR backscattering signal strength and achievable altitude to new levels.

Impacts of excimer laser annealing on Ge epilayer on Si

NASA Astrophysics Data System (ADS)

Huang, Zhiwei; Mao, Yichen; Yi, Xiaohui; Lin, Guangyang; Li, Cheng; Chen, Songyan; Huang, Wei; Wang, Jianyuan

2017-02-01

The impacts of excimer laser annealing on the crystallinity of Ge epilayers on Si substrate grown by low- and high-temperature two-step approach in an ultra-high vacuum chemical vapor deposition system were investigated. The samples were treated by excimer laser annealing (ELA) at various laser power densities with the temperature above the melting point of Ge, while below that of Si, resulting in effective reduction of point defects and dislocations in the Ge layer with smooth surface. The full-width at half-maximum (FWHM) of X-ray diffraction patterns of the low-temperature Ge epilayer decreases with the increase in laser power density, indicating the crystalline improvement and negligible effect of Ge-Si intermixing during ELA processes. The short laser pulse time and large cooling rate cause quick melting and recrystallization of Ge epilayer on Si in the non-thermal equilibrium process, rendering tensile strain in Ge epilayer as calculated quantitatively with thermal mismatch between Si and Ge. The FWHM of X-ray diffraction patterns is significantly reduced for the two-step grown samples after treated by a combination of ELA and conventional furnace thermal annealing, indicating that the crystalline of Ge epilayer is improved more effectively with pre- annealing by excimer laser.

Investigation on gas medium parameters for an ArF excimer laser through orthogonal experimental design

NASA Astrophysics Data System (ADS)

Song, Xingliang; Sha, Pengfei; Fan, Yuanyuan; Jiang, R.; Zhao, Jiangshan; Zhou, Yi; Yang, Junhong; Xiong, Guangliang; Wang, Yu

2018-02-01

Due to complex kinetics of formation and loss mechanisms, such as ion-ion recombination reaction, neutral species harpoon reaction, excited state quenching and photon absorption, as well as their interactions, the performance behavior of different laser gas medium parameters for excimer laser varies greatly. Therefore, the effects of gas composition and total gas pressure on excimer laser performance attract continual research studies. In this work, orthogonal experimental design (OED) is used to investigate quantitative and qualitative correlations between output laser energy characteristics and gas medium parameters for an ArF excimer laser with plano-plano optical resonator operation. Optimized output laser energy with good pulse to pulse stability can be obtained effectively by proper selection of the gas medium parameters, which makes the most of the ArF excimer laser device. Simple and efficient method for gas medium optimization is proposed and demonstrated experimentally, which provides a global and systematic solution. By detailed statistical analysis, the significance sequence of relevant parameter factors and the optimized composition for gas medium parameters are obtained. Compared with conventional route of varying single gas parameter factor sequentially, this paper presents a more comprehensive way of considering multivariables simultaneously, which seems promising in striking an appropriate balance among various complicated parameters for power scaling study of an excimer laser.

Ablation algorithms and corneal asphericity in myopic correction with excimer lasers

NASA Astrophysics Data System (ADS)

Iroshnikov, Nikita G.; Larichev, Andrey V.; Yablokov, Michail G.

2007-06-01

The purpose of this work is studying a corneal asphericity change after a myopic refractive correction by mean of excimer lasers. As the ablation profile shape plays a key role in the post-op corneal asphericity, ablation profiles of recent lasers should be studied. The other task of this research was to analyze operation (LASIK) outcomes of one of the lasers with generic spherical ablation profile and to compare an asphericity change with theoretical predictions. The several correction methods, like custom generated aspherical profiles, may be utilized for mitigation of unwanted effects of asphericity change. Here we also present preliminary results of such correction for one of the excimer lasers.

Excimer laser photorefractive surgery of the cornea

NASA Astrophysics Data System (ADS)

Gaster, Ronald N.

1998-09-01

The 193 nm argon fluoride (ArF) excimer laser can effectively be used to change the radius of curvature of the cornea and thus alter the refractive state of the eye. This change allows myopic (nearsighted) patients to see well with less dependence on glasses or contact lenses. The two major techniques of laser refractive surgery currently in effect in the United States are photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). This paper will discuss these refractive cornea surgical techniques.

Excimer laser annealing: A gold process for CZ silicon junction formation

NASA Technical Reports Server (NTRS)

Wong, David C.; Bottenberg, William R.; Byron, Stanley; Alexander, Paul

1987-01-01

A cold process using an excimer laser for junction formation in silicon has been evaluated as a way to avoid problems associated with thermal diffusion. Conventional thermal diffusion can cause bulk precipitation of SiOx and SiC or fail to completely activate the dopant, leaving a degenerate layer at the surface. Experiments were conducted to determine the feasibility of fabricating high quality p-n junctions using a pulsed excimer laser for junction formation at remelt temperature with ion-implanted surfaces. Solar-cell efficiency exceeding 16 percent was obtained using Czochralski single-crystal silicon without benefit of back surface field or surface passivation. Characterization shows that the formation of uniform, shallow junctions (approximately 0.25 micron) by excimer laser scanning preserves the minority carrier lifetime that leads to high current collection. However, the process is sensitive to initial surface conditions and handling parameters that drive the cost up.

Generation of strongly coupled plasmas by high power excimer laser

NASA Astrophysics Data System (ADS)

Zhu, Yongxiang; Liu, Jingru; Zhang, Yongsheng; Hu, Yun; Zhang, Jiyan; Zheng, Zhijian; Ye, Xisheng

2013-05-01

(ultraviolet). To generate strongly coupled plasmas (SCP) by high power excimer laser, an Au-CH-Al-CH target is used to make the Al sample reach the state of SCP, in which the Au layer transforms laser energy to X-ray that heating the sample by volume and the CH layers provides necessary constraints. With aid of the MULTI-1D code, we calculate the state of the Al sample and its relationship with peak intensity, width and wavelength of laser pulses. The calculated results suggest that an excimer laser with peak intensity of the magnitude of 1013W/cm2 and pulse width being 5ns - 10ns is suitable to generate SCP with the temperature being tens of eV and the density of electron being of the order of 1022/cm-3. Lasers with shorter wavelength, such as KrF laser, are preferable.

Effect of a 308-nm excimer laser on atopic dermatitis-like skin lesions in NC/Nga mice.

PubMed

Oh, Chang Taek; Kwon, Tae-Rin; Seok, Joon; Choi, Eun Ja; Kim, Soon Re; Jang, Yu-Jin; Mun, Seog Kyun; Kim, Chan Woong; Lee, Sungeun; Lee, Jongmin; Kim, Myeung Nam; Choi, Sun Young; Kim, Beom Joon

2016-08-01

Atopic dermatitis (AD) is a common inflammatory skin disease that can affect all age groups. It has a relapsing course, which dramatically affects the quality of life of patients. A 308-nm excimer laser has been reported to be a safe and effective treatment for inflammatory skin diseases, although the range of potential application has not been fully explored. The purpose of this study was to evaluate the therapeutic effects of a 308-nm laser on AD-like skin lesions in NC/Nga mice. Dermatophagoides farinae-exposed NC/Nga mice with a clinical score of 12 were treated with either a 308-nm excimer laser or narrowband-UVB (NB-UVB). The effects of the 308-nm excimer laser were evaluated by dermatitis scores, skin histology, skin barrier function, and immunological parameters, including IgE and Th2-mediated cytokines. The 308-nm excimer laser significantly reduced the severity of skin lesions and decreased the total serum levels of IgE and Th2-mediated cytokines. The excimer laser also significantly reduced the inflammatory cellular infiltrate into AD-induced skin lesions. Moreover, treatment with the 308-nm excimer laser led to recovery of skin barrier function in AD-induced skin lesions. The 308-nm excimer laser can be considered a valid and safe therapeutic option for the treatment of localized AD. Lasers Surg. Med. 48:629-637, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

ArF excimer laser debrides burns without destruction of viable tissue: A pilot study.

PubMed

Prasad, Atulya; Sawicka, Katarzyna M; Pablo, Kelly B; Macri, Lauren K; Felsenstein, Jerome; Wynne, James J; Clark, Richard A F

2018-05-01

Recent evidence indicates that early removal of eschar by tangential debridement can promote healing. Laser debridement can be used for debridement of areas that prove challenging for debridement using tangential excision. In particular, irradiation with an ArF excimer laser ablates desiccated eschar and is self-terminating, preserving hydrated or viable tissue. Thermal burns were created on the flanks of two outbred, female Yorkshire pigs using aluminum bars heated to 70°C and applied for different lengths of time. Three days after injury, burns were debrided using an ArF excimer laser (193nm). Tissue was harvested immediately after debridement and 7days after debridement (10days after burn). Data from a pilot study demonstrates that ArF excimer laser irradiation removes burn eschar and promotes healing at 10days after burn. ArF excimer laser debridement is self-terminating and preserves underlying and adjacent perfused tissue. Potentially, this modality would be ideal for the complex curvilinear structures of the body. Copyright © 2017 Elsevier Ltd and ISBI. All rights reserved.

Controlled study of excimer and pulsed dye lasers in the treatment of psoriasis.

PubMed

Taibjee, S M; Cheung, S-T; Laube, S; Lanigan, S W

2005-11-01

The excimer laser delivers high energy monochromatic ultraviolet (UV) B at 308 nm. Advantages over conventional UV sources include targeting of lesional skin, reducing cumulative dose and inducing faster clearance. Studies of the pulsed dye laser (PDL) in psoriasis report between 57% and 82% response rates; remission may extend to 15 months. To our knowledge, this is the first study assessing both excimer and PDL in psoriasis. We conducted a within-patient controlled prospective trial of treatment of localized plaque psoriasis. Twenty-two adult patients, mean Psoriasis Area and Severity Index 7.1, were recruited. Fifteen patients completed the full treatment, of which 13 were followed up to 1 year. Two selected plaques were treated with excimer twice weekly and V Beam PDL, pretreated with salicylic acid (SA), every 4 weeks, respectively. Two additional plaques, treated with SA alone or untreated, served as controls. The primary outcome measures were: (i) changes in plaque-modified Psoriasis Activity and Severity Index (PSI) scores from baseline to end of treatment; (ii) clinical response to treatment (CR(T)), assessed by serial photographs; (iii) percentage of plaques clear at the end of treatment; and (iv) percentage of plaques clear at 1-year follow-up. The secondary outcome measures were: (i) number of laser treatments to clearance; (ii) time to relapse; (iii) frequency of side-effects; and (iv) qualitative observations with SIAscope. The mean improvement in PSI was 4.7 (SD 2.1) with excimer and 2.7 (SD 2.4) with PDL. PSI improvement was significantly greater in excimer than PDL (P = 0.003) or both control plaques (P < 0.001). CR(T) indicated 13 patients responded best with excimer, two patients best with PDL, and in seven patients there was no difference between the two lasers. CR(T) was significantly greater for excimer than PDL (P = 0.003) or both controls (P < 0.001). CR(T) was also significantly greater for PDL than SA alone (P = 0.004) or untreated control

Characterization of absorption and degradation on optical components for high power excimer lasers

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

Mann, K.; Eva, E.; Granitza, B.

1996-12-31

At Laser-Laboratorium Goettingen, the performance of UV optical components for high power excimer lasers is characterized, aiming to employ testing procedures that meet industrial conditions, i.e. very high pulse numbers and repetition rates. Measurements include determination of single and multiple pulse damage thresholds, absorption loss and degradation of optical properties under long-term irradiation. Absorption of excimer laser pulses is investigated by a calorimetric technique which provides greatly enhanced sensitivity compared to transmissive measurements. Thus, it allows determining both single and two photon absorption coefficients at intensities of standard excimer lasers. Results of absorption measurements at 248nm are presented for baremore » substrates (CaF{sub 2}, BaF{sub 2}, z-cut quartz and fused silica). UV calorimetry is also employed to investigate laser induced aging phenomena, e.g. color center formation in fused silica. A separation of transient and cumulative effects as a function of intensity is achieved, giving insight into various loss mechanisms.« less

Pulsed excimer laser processing for cost-effective solar cells

NASA Technical Reports Server (NTRS)

Wong, David C.

1985-01-01

The application of excimer laser in the fabrication of photovoltaic devices was investigated extensively. Processes included junction formation, laser assisted chemical vapor deposition metallization, and laser assisted chemical vapor deposition surface passivation. Results demonstrated that implementation of junction formation by laser annealing in production is feasible because of excellent control in junction depth and quality. Both metallization and surface passivation, however, were found impractical to be considered for manufacturing at this stage.

Collagen crosslinking for ectasia following PRK performed in excimer laser-assisted keratoplasty for keratoconus.

PubMed

Spadea, Leopoldo

2012-01-01

To report the results of corneal collagen crosslinking (CXL) in a patient with corneal ectasia developed after excimer laser-assisted lamellar keratoplasty for keratoconus and a secondary photorefractive keratectomy (PRK) for residual refractive error. A 33-year-old woman, who had originally been treated for keratoconus in the right eye by excimer laser-assisted lamellar keratoplasty, subsequently had her residual ametropia treated by topographically guided, transepithelial excimer laser PRK. Five years after PRK, the patient developed corneal ectasia showing concomitant visual changes of best spectacle-corrected visual acuity (BSCVA) reduced to 20/33 with a refraction of -6.00 +6.00 × 30. The minimum corneal thickness at the ectasia apex was 406 µm. A treatment of riboflavin-UVA-induced corneal CXL was performed on the right eye. Two years after the CXL treatment, the right eye improved to 20/20 BSCVA with a refraction of plano +1.00 × 50 while exhibiting a clear lamellar graft. Corneal CXL provided safe and effective management of ectasia developed after excimer laser-assisted lamellar keratoplasty and PRK.

A design of energy detector for ArF excimer lasers

NASA Astrophysics Data System (ADS)

Feng, Zebin; Han, Xiaoquan; Zhou, Yi; Bai, Lujun

2017-08-01

ArF excimer lasers with short wavelength and high photon energy are widely applied in the field of integrated circuit lithography, material processing, laser medicine, and so on. Excimer laser single pulse energy is a very important parameter in the application. In order to detect the single pulse energy on-line, one energy detector based on photodiode was designed. The signal processing circuit connected to the photodiode was designed so that the signal obtained by the photodiode was amplified and the pulse width was broadened. The amplified signal was acquired by a data acquisition card and stored in the computer for subsequent data processing. The peak of the pulse signal is used to characterize the single pulse energy of ArF excimer laser. In every condition of deferent pulse energy value levels, a series of data about laser pulses energy were acquired synchronously using the Ophir energy meter and the energy detector. A data set about the relationship between laser pulse energy and the peak of the pulse signal was acquired. Then, by using the data acquired, a model characterizing the functional relationship between the energy value and the peak value of the pulse was trained based on an algorithm of machine learning, Support Vector Regression (SVR). By using the model, the energy value can be obtained directly from the energy detector designed in this project. The result shows that the relative error between the energy obtained by the energy detector and by the Ophir energy meter is less than 2%.

Laser-assisted focused He + ion beam induced etching with and without XeF 2 gas assist

DOE PAGES

Stanford, Michael G.; Mahady, Kyle; Lewis, Brett B.; ...

2016-10-04

Focused helium ion (He +) milling has been demonstrated as a high-resolution nanopatterning technique; however, it can be limited by its low sputter yield as well as the introduction of undesired subsurface damage. Here, we introduce pulsed laser- and gas-assisted processes to enhance the material removal rate and patterning fidelity. A pulsed laser-assisted He+ milling process is shown to enable high-resolution milling of titanium while reducing subsurface damage in situ. Gas-assisted focused ion beam induced etching (FIBIE) of Ti is also demonstrated in which the XeF 2 precursor provides a chemical assist for enhanced material removal rate. In conclusion, amore » pulsed laser-assisted and gas-assisted FIBIE process is shown to increase the etch yield by ~9× relative to the pure He+ sputtering process. These He + induced nanopatterning techniques improve material removal rate, in comparison to standard He + sputtering, while simultaneously decreasing subsurface damage, thus extending the applicability of the He + probe as a nanopattering tool.« less

Laser-assisted focused He + ion beam induced etching with and without XeF 2 gas assist

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

Stanford, Michael G.; Mahady, Kyle; Lewis, Brett B.

Focused helium ion (He +) milling has been demonstrated as a high-resolution nanopatterning technique; however, it can be limited by its low sputter yield as well as the introduction of undesired subsurface damage. Here, we introduce pulsed laser- and gas-assisted processes to enhance the material removal rate and patterning fidelity. A pulsed laser-assisted He+ milling process is shown to enable high-resolution milling of titanium while reducing subsurface damage in situ. Gas-assisted focused ion beam induced etching (FIBIE) of Ti is also demonstrated in which the XeF 2 precursor provides a chemical assist for enhanced material removal rate. In conclusion, amore » pulsed laser-assisted and gas-assisted FIBIE process is shown to increase the etch yield by ~9× relative to the pure He+ sputtering process. These He + induced nanopatterning techniques improve material removal rate, in comparison to standard He + sputtering, while simultaneously decreasing subsurface damage, thus extending the applicability of the He + probe as a nanopattering tool.« less

Impulsions laser femtosecondes intenses à contraste élevé dans le bleu-vert par amplification directe dans un milieu gazeux

NASA Astrophysics Data System (ADS)

Uteza, O.; Tcheremiskine, V.; Clady, R.; Coustillier, G.; Sentis, M.; Spiga, Ph.; Mikheev, L. D.

2005-06-01

Cet article présente la conception d'une chaîne laser femtoseconde TW visible, associant (i) un oscillateur solide Ti:Sa opéré à 950 nm, (ii) un amplificateur optique à dérive de fréquence permettant l'amplification du signal à 950 nm au niveau de plusieurs dizaines de mJ, (iii) un système doubleur pour convertir le signal à 475 nm et l'injecter dans le milieu amplificateur XeF (C-A), (iv) un milieu gazeux excimères XeF (C-A) permettant l'amplification directe du signal à 475 nm à plusieurs centaines de mJ et ainsi l'obtention d'impulsions TW visibles à contraste élevé.

Triggering Excimer Lasers by Photoionization from Corona Discharges

NASA Astrophysics Data System (ADS)

Xiong, Zhongmin; Duffey, Thomas; Brown, Daniel; Kushner, Mark

2009-10-01

High repetition rate ArF (192 nm) excimer lasers are used for photolithography sources in microelectronics fabrication. In highly attaching gas mixtures, preionization is critical to obtaining stable, reproducible glow discharges. Photoionization from a separate corona discharge is one technique for preionization which triggers the subsequent electron avalanche between the main electrodes. Photoionization triggering of an ArF excimer laser sustained in multi-atmosphere Ne/Ar/F2/Xe gas mixtures has been investigated using a 2-dimensional plasma hydrodynamics model including radiation transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coincident with the electron temperature with transport coefficients obtained from solutions of Boltzmann's equation. Photoionizing radiation is produced by a surface discharge which propagates along a corona-bar located adjacent to the discharge electrodes. The consequences of pulse power waveform, corona bar location, capacitance and gas mixture on uniformity, symmetry and gain of the avalanche discharge will be discussed.

308-nm excimer laser for the treatment of alopecia areata in children.

PubMed

Al-Mutairi, Nawaf

2009-01-01

Alopecia areata (AA) is a common skin disease which is characterized by nonscarring localized or diffused hair loss. In this study we assessed the efficacy of 308-nm Excimer laser in the treatment of alopecia areata in children. A total of 9 children with 30 recalcitrant patches alopecia areata and two children with alopecia areata totalis were enrolled in this study which included seven male and four female patients, aged between 4 and 14 years and the durations of their disease were between 7 and 25 months. All of these patients had more than one lesion of alopecia areata and at least one of them was left as a control for comparison. The lesions were treated with the 308-nm Excimer laser twice a week for a period of 12 weeks. Regrowth of hair was observed in 18 (60%) alopecia patches in the scalp, while there was no response in the control patches and over the extremities. Only four patients with scalp lesions showed a recurrence of alopecia after 6 months post laser therapy. So, 308-nm Excimer laser is considered an effective safe therapeutic option for patchy alopecia areata in children.

Excimer laser annealing of NiTi shape memory alloy thin film

NASA Astrophysics Data System (ADS)

Xie, Qiong; Huang, Weimin; Hong, Ming Hui; Song, Wendong; Chong, Tow Chong

2003-02-01

NiTi Shape Memory Alloy (SMA) is with great potential for actuation in microsystems. It is particularly suitable for medical applications due to its excellent biocompatibility. In MEMS, local annealing of SMA is required in the process of fabrication. In this paper, local annealing of Ni52Ti48 SMA with excimer laser is proposed for the first time. The Ni52Ti48 thin film in a thickness of 5 μm was deposited on Si (100) wafer by sputtering at room temperature. After that, the thin film was annealed by excimer laser (248nm KrF laser) for the first time. Field-Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) were used to characterize the surface profile of the deposited film after laser annealing. The phase transformation was measured by Differential Scanning Calorimeter (DSC) test. It is concluded that NiTi film sputtering on Si(100) substrate at room temperature possesses phase transformation after local laser annealing but with cracks.

Clinical efficacy of flumetasone/salicylic acid ointment combined with 308-nm excimer laser for treatment of psoriasis vulgaris.

PubMed

Dong, Jie; He, Yanling; Zhang, Xiuying; Wang, Yixuan; Tian, Yongjing; Wang, Jie

2012-06-01

To compare the clinical efficacy and safety of combining flumetasone ointment with 308-nm excimer laser therapy vs. 308-nm excimer laser monotherapy for the treatment of psoriasis vulgaris. Forty patients with psoriasis vulgaris were recruited; 20 were treated with flumetasone ointment plus 308-nm excimer laser therapy, and the other 20 received only excimer laser monotherapy. The flumetasone ointment was applied topically twice a day, and laser treatments were scheduled twice weekly for a total of 10 treatments. Clinical efficacy was evaluated in a blinded manner by two independent physicians using photographs taken before and after treatment. Of the 40 patients who received and completed the entire course of therapy, the psoriasis area and severity index score was improved by 82.51 ± 11.24% and 72.01 ± 20.94% in the combination group and laser group, respectively (P > 0.05), and the average cumulative dose was 5.06 ± 2.20 j/cm(2) in the combination group and 7.75 ± 2.25 j/cm(2) in the laser-only group, respectively (P < 0.05). The clinical data suggest that combination treatment using flumetasone ointment and a 308-nm excimer laser is superior to laser monotherapy for treatment of psoriasis vulgaris. The combination therapy can increase effectiveness and decrease the total laser dose, thus potentially reducing side effects. © 2012 John Wiley & Sons A/S.

Excimer Laser Research.

DTIC Science & Technology

1975-08-01

and sample cylinder were repeatedly allowed to outgas at room temperature (under vacuum but valved off) and then cooled with liquid N_ snd pumped...i i I i | I I I I i I i i i | I I i i i i i l i | I l I I I 320 330 340 350 360 E7470 WAVELENGTH (nm) 2 2 Fig. 9 Densitometer Trace of XeF...2, Xs are within 10%. eFor Arl, Nel, NeBr, NeCl, and the helium halides the inert-gas ionization potential is so large that the Coulomb curve does

Study on the electromagnetic radiation characteristics of discharging excimer laser system

NASA Astrophysics Data System (ADS)

Zhao, Duliang; Liang, Xu; Fang, Xiaodong; Wang, Qingsheng

2016-10-01

Excimer laser in condition of high voltage, large current and fast discharge will produce strong electromagnetic pulse radiation and electromagnetic interference on the around electrical equipment. The research on characteristics and distribution of excimer laser electromagnetic radiation could provide important basis for electromagnetic shielding and suppressing electromagnetic interference, and further improving the electromagnetic compatibility of system. Firstly, electromagnetic radiation source is analyzed according to the working principle of excimer laser. The key test points of the electromagnetic radiation, hydrogen thyratron, main discharge circuit and laser outlet, are determined by the mechanical structure and the theory of electromagnetic radiation. Secondly, characteristics of electromagnetic field were tested using a near field probe on the key positions of the vertical direction at 20, 50, and 80 cm, respectively. The main radiation frequencies and the radiation field characteristics in the near field are obtained. The experimental results show that the main radiation frequencies distribute in 47, 65, and 130 MHz for electric field and the main radiation frequencies distribute in 34, 100, and 165 MHz for magnetic field. The intensity of electromagnetic field decreases rapidly with the increase of test distance. The higher the frequency increases, the faster the amplitude attenuate. Finally, several electromagnetic interference suppression measurement methods are proposed from the perspective of electromagnetic compatibility according to the test results.

Automatic alignment of double optical paths in excimer laser amplifier

NASA Astrophysics Data System (ADS)

Wang, Dahui; Zhao, Xueqing; Hua, Hengqi; Zhang, Yongsheng; Hu, Yun; Yi, Aiping; Zhao, Jun

2013-05-01

A kind of beam automatic alignment method used for double paths amplification in the electron pumped excimer laser system is demonstrated. In this way, the beams from the amplifiers can be transferred along the designated direction and accordingly irradiate on the target with high stabilization and accuracy. However, owing to nonexistence of natural alignment references in excimer laser amplifiers, two cross-hairs structure is used to align the beams. Here, one crosshair put into the input beam is regarded as the near-field reference while the other put into output beam is regarded as the far-field reference. The two cross-hairs are transmitted onto Charge Coupled Devices (CCD) by image-relaying structures separately. The errors between intersection points of two cross-talk images and centroid coordinates of actual beam are recorded automatically and sent to closed loop feedback control mechanism. Negative feedback keeps running until preset accuracy is reached. On the basis of above-mentioned design, the alignment optical path is built and the software is compiled, whereafter the experiment of double paths automatic alignment in electron pumped excimer laser amplifier is carried through. Meanwhile, the related influencing factors and the alignment precision are analyzed. Experimental results indicate that the alignment system can achieve the aiming direction of automatic aligning beams in short time. The analysis shows that the accuracy of alignment system is 0.63μrad and the beam maximum restoration error is 13.75μm. Furthermore, the bigger distance between the two cross-hairs, the higher precision of the system is. Therefore, the automatic alignment system has been used in angular multiplexing excimer Main Oscillation Power Amplification (MOPA) system and can satisfy the requirement of beam alignment precision on the whole.

Bragg reflector based gate stack architecture for process integration of excimer laser annealing

NASA Astrophysics Data System (ADS)

Fortunato, G.; Mariucci, L.; Cuscunà, M.; Privitera, V.; La Magna, A.; Spinella, C.; Magrı, A.; Camalleri, M.; Salinas, D.; Simon, F.; Svensson, B.; Monakhov, E.

2006-12-01

An advanced gate stack structure, which incorporates a Bragg reflector, has been developed for the integration of excimer laser annealing into the power metal-oxide semiconductor (MOS) transistor fabrication process. This advanced gate structure effectively protects the gate stack from melting, thus solving the problem related to protrusion formation. By using this gate stack configuration, power MOS transistors were fabricated with improved electrical characteristics. The Bragg reflector based gate stack architecture can be applied to other device structures, such as scaled MOS transistors, thus extending the possibilities of process integration of excimer laser annealing.

Comparing laser induced plasmas formed in diode and excimer pumped alkali lasers.

PubMed

Markosyan, Aram H

2018-01-08

Lasing on the D 1 transition (6 2 P 1/2 → 6 2 S 1/2 ) of cesium can be reached in both diode and excimer pumped alkali lasers. The first uses D 2 transition (6 2 S 1/2 → 6 2 P 3/2 ) for pumping, whereas the second is pumped by photoexcitation of ground state Cs-Ar collisional pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (excimers). Despite lasing on the same D 1 transition, differences in pumping schemes enables chemical pathways and characteristic timescales unique for each system. We investigate unavoidable plasma formation during operation of both systems side by side in Ar/C 2 H 6 /Cs.

Electronic-beam analysis of excimer lasers used for photorefractive keratotomy

NASA Astrophysics Data System (ADS)

Roundy, Carlos B.

1998-07-01

Excimer lasers are an excellent instrument for performing photorefractive keratotomy, PRK. The UV light from the laser causes an ablation of the cornea in proportion to the intensity of the light. The primary characteristic essential to successful PRK is the uniformity of the Top Hat, or working portion of the laser beam. In order for this intensity profile to be sufficiently uniform for PRK, it is essential to periodically measure the equality of the laser beam profile. This ensures that the laser continues to operate properly and provide the expected performance.

Excimer laser annealing to fabricate low cost solar cells

NASA Technical Reports Server (NTRS)

1984-01-01

The objective is to show whether or not pulsed excimer laser annealing (PELA) of ion-implanted junctions is a cost effective replacement for diffused junctions in fabricating crystalline silicon solar cells. The preliminary economic analysis completed shows that the use of PELA to fabricate both the front junction and back surface field (BSF) would cost approximately 35 cents per peak watt (Wp), compared to a cost of 15 cents/Wp for diffusion, aluminum BSF and an extra cleaning step in the baseline process. The cost advantage of the PELA process depends on improving the average cell efficiency from 14% to 16%, which would lower the overall cost of the module by about 15 cents/Wp. An optimized PELA process compatible with commercial production is to be developed, and increased cell efficiency with sufficient product for adequate statistical analysis demonstrated. An excimer laser annealing station was set-up and made operational. The first experiment used 248 nm radiation to anneal phosphorus implants in polished and texture-etched silicon.

[Astigmatism correction with Excimer laser].

PubMed

Gauthier, L

2012-03-01

Excimer laser is the best and the more used technique for Astigmatism correction. Lasik is generally preferred to PRK and must be the choice for hyperopic and mix astigmatisms. Myopic astigmatisms are the easier cases to treat: the length of the photoablation is placed on the flat meridian. Hyperopic and mix astigmatisms are more difficult to correct because they are more technically demanding and because the optical zone of the photoablation must be large. Flying spots lasers are the best for these cases. The most important point is to trace the photoablation very precisely on the astigmatism axis. The use of eye trackers with iris recognition or a preoperative marking of the reference axis avoid cyclotorsion or a wrong position of the head. Irregular astigmatism are better corrected with topoguided or wavefront guided photoablations. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

A comparative study of corneal incisions induced by diamond and steel knives and two ultraviolet radiations from an excimer laser.

PubMed Central

Marshall, J; Trokel, S; Rothery, S; Krueger, R R

1986-01-01

This paper reviews the potential role of excimer lasers in corneal surgery. The morphology of incisions induced by two wavelengths of excimer laser radiation, 193 nm and 248 nm, are compared with the morphology of incisions produced by diamond and steel knives. Analysis suggests that ablation induced by excimer laser results from highly localised photochemical reactions and that 193 nm is the optimal wavelength for surgery. The only significant complication of laser surgery is loss of endothelial cells when incisions are within 40 micron of Descemet's membrane. Images PMID:3013283

Composition of the excimer laser-induced plume produced during LASIK refractive surgery

NASA Astrophysics Data System (ADS)

Glickman, Randolph D.; Liu, Yun; Mayo, George L.; Baribeau, Alan D.; Starck, Tomy; Bankhead, Tom

2003-07-01

Because of concerns about potential hazards to surgical personnel of the plume associated with laser refractive surgery, this study was performed to characterize the composition of such plumes. Filter elements were removed from the smoke evacuator of a VISX S3 excimer laser (filter pore size ~0.3 microns) and from a Mastel Clean Room ( filter pore size ~0.2 microns) used with a LADARVISION excimer laser. The filters from both laser systems captured the laser-induced plumes from multiple, routine, LASIK patient procedures. Some filters were processed for scanning electron microscopy, while others were extracted with methanol and chloroform for biochemical analysis. Both the VISX "Final Air" filter and the Mastel "Clean Room" filter captured material that was not observed in filters that had clean operating room air only passed through them. In the VISX system, air flows through the filter unit parallel to the filter matrix. SEM analysis showed these filters captured discrete particles of 0.3 to 3.0 microns in size. In the Mastel Clean Room unit, air flows orthogonally through the filter, and the filter matrix was heavily layered with captured debris so that individual particles were not readily distinguished. Amino acid analysis and gel electrophoresis of extracted material revealed proteinaceous molecules as large as 5000 molecular weight. Such large molecules in the laser plume are not predicted by the existing theory of photochemical ablation. The presence of relatively large biomolecules may constitute a risk of allergenic reactions in personnel exposed to the plume, and also calls into question the precise mechanism of excimer laser photochemical ablation. Supported by the RMG Research Endowment, and Research to Prevent Blindness

Pseudopotential SCF-MO studies of hypervalent compounds. II. XeF+5 and XeF6

NASA Astrophysics Data System (ADS)

Rothman, Michael J.; Bartell, Lawrence S.; Ewig, Carl S.; Van Wazer, John R.

1980-07-01

New evidence bearing upon the anomalous properties of xenon hexafluoride has been obtained via the ab initio molecular orbital approach applied successfully to the di- and tetrafluorides in paper I. Structures of both XeF+5 and XeF6 are governed by a stereochemically active lone pair. In the case of the square-pyramidal cation the Fax-Xe-Feq angle calculated for the bare ion is within 2° of the value observed in the crystalline complex. For the hexafluoride, however, the calculated deformation from Oh symmetry is appreciably greater than that deduced from electron diffraction intensities. Nevertheless, the results of calculations are in sufficient conformity with the Bartell-Gavin, Pitzer-Bernstein interpretation and at variance with the ''electronic-isomers'' interpretation to leave little doubt about the answer. With increasing fluorination in the XeFn series the HOMO-LUMO energy difference decreases and the second-order Jahn-Teller effect is enhanced. Increasing fluorination (and increased positive charge on Xe) also shortens bond lengths; calculated shortenings parallel observed shortenings. The deformation of XeF6 from Oh is along t1u bend and stretch coordinates to a C3v structure with long bonds adjacent to the lone pair, as expected according to the valence-shell-electron-pair-repulsion model. Pure t2g deformations are destabilizing but anharmonic t1u-t2g coupling significantly stabilizes the deformation. Steric aspects of the structure and force field are diagnosed and found to be minor. Values for the force constants f44, f55, f¯4444, f¯444'4', and f¯445 are derived and found to be of the magnitude forecast in the Bartell-Gavin and Pitzer-Bernstein treatments except that the calculations do not reproduce the delicate balances believed to lead to almost free pseudorotation in XeF6.

Effectiveness of 308-nm Excimer Laser Therapy in Treating Alopecia Areata, Determined by Examining the Treated Sides of Selected Alopecic Patches.

PubMed

Byun, Ji Won; Moon, Jong Hyuk; Bang, Chan Yl; Shin, Jeonghyun; Choi, Gwang Seong

2015-01-01

Some studies have reported the use of 308-nm excimer laser therapy for treating alopecia areata (AA); however, the effectiveness of this therapy on a theoretical basis has not yet been comparatively analyzed. To determine the therapeutic effect of excimer laser therapy on AA. One alopecic patch was divided into control and treated sides in 10 patients with AA. Then, 308-nm excimer laser therapy was administered twice a week for 12 weeks. Photograph and phototrichogram analyses were performed. Photographic assessments by both dermatologists and individuals of the general population showed objective improvements after excimer laser therapy. On the treated side, the hair count and hair diameter had statistically increased after treatment. However, only the hair diameter was found to be significantly high in the treated half when it was compared with the control side. The 308-nm excimer laser has a therapeutic effect on AA, which is proven by photograph and phototrichogram analysis by a side-by-side comparison. © 2015 S. Karger AG, Basel.

Comparing laser induced plasmas formed in diode and excimer pumped alkali lasers

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

Markosyan, Aram H.

Here, lasing on the D 1 transition (6 2P 1/2 → 6 2S 1/2) of cesium can be reached in both diode and excimer pumped alkali lasers. The first uses D 2 transition (6 2S 1/2 → 6 2P 3/2) for pumping, whereas the second is pumped by photoexcitation of ground state Cs-Ar collisional pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (excimers). Despite lasing on the same D 1 transition, differences in pumping schemes enables chemical pathways and characteristic timescales unique for each system. We investigate unavoidable plasma formation during operation of both systems side by side inmore » Ar/C 2H 6/Cs.« less

Comparing laser induced plasmas formed in diode and excimer pumped alkali lasers

DOE PAGES

Markosyan, Aram H.

2018-01-05

Here, lasing on the D 1 transition (6 2P 1/2 → 6 2S 1/2) of cesium can be reached in both diode and excimer pumped alkali lasers. The first uses D 2 transition (6 2S 1/2 → 6 2P 3/2) for pumping, whereas the second is pumped by photoexcitation of ground state Cs-Ar collisional pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules (excimers). Despite lasing on the same D 1 transition, differences in pumping schemes enables chemical pathways and characteristic timescales unique for each system. We investigate unavoidable plasma formation during operation of both systems side by side inmore » Ar/C 2H 6/Cs.« less

Excimer-laser-induced surface treatments on metal and ceramic materials: applications to automotive, aerospace, and microelectronic industries

NASA Astrophysics Data System (ADS)

Autric, Michel L.

1999-09-01

Surface treatments by laser irradiation can improve materials properties in terms of mechanical and physico- chemical behaviors, these improvements being related to the topography, the hardness, the microstructure, the chemical composition. Up to now, the use of excimer lasers for industrial applications remained marginal in spite of the interest related to the short wavelength (high photon energy and better energetic coupling with materials and reduced thermal effects in the bulk material). Up to now, the main limitations concerned the beam quality, the beam delivery, the gas handling and the relatively high investment cost. At this time, the cost of laser devices is going down and the ultraviolet radiation can be conducted through optical fibers. These two elements give new interest in using excimer laser for industrial applications. The main objective of this research program which we are involved in, is to underline some materials processing applications for automotive, aerospace or microelectronic industries for which it could be more interesting to use excimer lasers (minimized thermal effects). This paper concerns the modifications of the roughness, porosity, hardness, structure, phase, residual stresses, chemical composition of the surface of materials such as metallic alloys (aluminum, steel, cast iron, titanium, and ceramics (oxide, nitride, carbide,...) irradiated by KrF and XeCl excimer lasers.

X-ray photoelectron spectroscopy study of excimer laser treated alumina films

NASA Astrophysics Data System (ADS)

Georgiev, D. G.; Kolev, K.; Laude, L. D.; Mednikarov, B.; Starbov, N.

1998-01-01

Amorphous alumina layers are deposited on a single crystal Si substrate by a e-gun evaporation technique. These films are then thermally annealed in oxygen to be crystallized and, further, irradiated with an excimer laser beam. At each stage of the film preparation, an x-ray photoelectron spectroscopy analysis is performed at the film surface and in depth, upon ion beam grinding. Results give evidence for the formation of an aluminosilicate upon thermal annealing of the film in oxygen. At the surface itself, this compound is observed to decompose upon excimer laser irradiation at energy densities exceeding 1.75 J/cm2, giving rise to free Si atoms and SiO2, however with complete disappearance of Al atoms. Model photochemical reactions are proposed to explain such transformations.

Effective treatment of etanercept and phototherapy-resistant psoriasis using the excimer laser.

PubMed

Park, Kelly K; Swan, James; Koo, John

2012-03-15

Treatment of moderate-to-severe plaque psoriasis often requires the use of phototherapy or systemic therapy, which includes immunosuppressants, retinoids, and biologic agents. Although biologic use is becoming increasingly popular, it is not uncommon for patients to experience treatment failure. We describe a patient who had a suboptimal response to etanercept monotherapy after twelve weeks of induction dosing (50 mg twice weekly), as well as to a combination of etanercept (50 mg once weekly-maintenance dosing) and narrowband ultraviolet B (NB-UVB) phototherapy three times weekly for an additional twelve weeks. Noticeable improvement was noted after the addition of NB-UVB and the patient's promising response to phototherapy influenced further management. Etanercept and NB-UVB were discontinued and the patient was initiated on excimer laser treatments twice weekly. After 4 weeks, the patient had a 75 percent reduction in Psoriasis Area Severity Index (PASI) score and after 7 weeks had over 95 percent clearance of psoriasis. The unique properties of the excimer laser may account for its clinical efficacy in our patient as well as in other cases of recalcitrant psoriasis. We propose that the excimer laser be considered in cases of biologic or conventional phototherapy failure in addition to being a standard treatment option or adjunct for the treatment of psoriasis.

Spectrally narrowed lasing of a self-injection KrF excimer laser

NASA Astrophysics Data System (ADS)

Shimada, Yasuhiro; Wani, Koichi; Miki, Tadaaki; Kawahara, Hidehito; Mimasu, Mutsumi; Ogata, Yoshiro

1990-08-01

Spectrally nantwed lasing of a KrF excimer laser has teen ahieved by a self-injection technique using abeam splitter for power extraction aixi intravity etalons for spectral-narrowing. The laser cavity is divithi into an amplifying branch aix! a spectralnarrowing branch. The spectral bandwidth was narrowed to <3pm FWHM with air-sed etalons placed in the spectral-narrowing branch. A laser propagation model was intrOdUced for describing the laser intensity traveling in the laser cavity. The calculated intensityincident onthe intracavityetalons wassmaller thanthat in theconventional Fabry-Perotcavity withplane-parallel mirrors.

Endothelial reaction to perforating and non-perforating excimer laser excisions in rabbits

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

Koch, J.W.; Lang, G.K.; Naumann, G.O.

1991-05-01

With an ArF excimer laser (193 nm, 750 mJ/cm2, 20 Hz) and a special slit-mask system, perforating and non-perforating linear keratectomies were performed in 55 rabbit corneas with a follow-up from 1 hour to 6 months. Varying the pulse number according to ablation rate (0.8 micron/pulse) and corneal thickness, four linear radial excisions (3 mm length, 70 microns width) of increasing depth (70%, 80%, 90%, 100% perforation) were produced. The corneas were processed for light microscopy, scanning and transmission electron microscopy, and vital staining of the endothelium. Except for mild cell contact alterations and discrete single cell damage in themore » 90% deep excisions, no endothelial damage could be detected after non-perforating keratectomies. Minute (less than 20 microns) and small (20 to 100 microns maximal diameter) perforations induced cell enlargement, formation of pseudopodia, rosette-like figures, multi-nucleated giant cells, and ultimately uniform reformation of the cell pattern (1 hour to 7 days postoperatively). Larger excimer laser defects of Descemet's membrane (greater than 100 microns) were overgrown by dedifferentiated endothelial cells producing a new PAS-positive basement membrane. Vital staining revealed the complete and stable reorganization of the endothelium over these lesions within 6 months. The authors observations are similar to those reported on the endothelial repair process following other surgical manipulations (knife incisions, direct Nd:YAG-laser trauma) and support the applicability of excimer lasers for corneal trephination in patients.« less

The development and progress of XeCl Excimer laser system

NASA Astrophysics Data System (ADS)

Zhang, Yongsheng; Ma, Lianying; Wang, Dahui; Zhao, Xueqing; Zhu, Yongxiang; Hu, Yun; Qian, Hang; Shao, Bibo; Yi, Aiping; Liu, Jingru

2015-05-01

A large angularly multiplexed XeCl Excimer laser system is under development at the Northwest Institute of Nuclear Technology (NINT). It is designed to explore the technical issues of uniform and controllable target illumination. Short wavelength, uniform and controllable target illumination is the fundamental requirement of high energy density physics research using large laser facility. With broadband, extended light source and multi-beam overlapping techniques, rare gas halide Excimer laser facility will provide uniform target illumination theoretically. Angular multiplexing and image relay techniques are briefly reviewed and some of the limitations are examined to put it more practical. The system consists of a commercial oscillator front end, three gas discharge amplifiers, two electron beam pumped amplifiers and the optics required to relay, encode and decode the laser beam. An 18 lens array targeting optics direct and focus the laser in the vacuum target chamber. The system is operational and currently undergoing tests. The total 18 beams output energy is more than 100J and the pulse width is 7ns (FWHM), the intensities on the target will exceed 1013W/cm2. The aberration of off-axis imaging optics at main amplifier should be minimized to improve the final image quality at the target. Automatic computer controlled alignment of the whole system is vital to efficiency and stability of the laser system, an array of automatic alignment model is under test and will be incorporated in the system soon.

Random noise can help to improve synchronization of excimer laser pulses.

PubMed

Mingesz, Róbert; Barna, Angéla; Gingl, Zoltán; Mellár, János

2016-02-01

Recently, we have reported on a compact microcontroller-based unit developed to accurately synchronize excimer laser pulses (Mingesz et al. 2012 Fluct. Noise Lett. 11, 1240007 (doi:10.1142/S021947751240007X)). We have shown that dithering based on random jitter noise plus pseudorandom numbers can be used in the digital control system to radically reduce the long-term drift of the laser pulse from the trigger and to improve the accuracy of the synchronization. In this update paper, we present our new experimental results obtained by the use of the delay-controller unit to tune the timing of a KrF excimer laser as an addition to our previous numerical simulation results. The hardware was interfaced to the laser using optical signal paths in order to reduce sensitivity to electromagnetic interference and the control algorithm tested by simulations was applied in the experiments. We have found that the system is able to reduce the delay uncertainty very close to the theoretical limit and performs well in real applications. The simple, compact and flexible system is universal enough to also be used in various multidisciplinary applications.

Scattered UV irradiation during VISX excimer laser keratorefractive surgery.

PubMed

Hope, R J; Weber, E D; Bower, K S; Pasternak, J P; Sliney, D H

2008-04-01

To evaluate the potential occupational health hazards associated with scattered ultraviolet (UV) radiation during photorefractive keratectomy (PRK) using the VISX Star S3 excimer laser. The Laser Vision Center, National Naval Medical Center, Bethesda, Maryland, USA. Intraoperative radiometric measurements were made with the Ophir Power/Energy Meter (LaserStar Model PD-10 with silicon detector) during PRK treatments as well as during required calibration procedures at a distance of 20.3 cm from the left cornea. These measurements were evaluated using a worst-case scenario for exposure, and then compared with the American Conference of Governmental Industrial Hygeinists (ACGIH) Threshold Value Limits (TVL) to perform a risk/hazard analysis. During the PRK procedures, the highest measured value was 248.4 nJ/pulse. During the calibration procedures, the highest measured UV scattered radiation level was 149.6 nJ/pulse. The maximum treatment time was 52 seconds. Using a worst-case scenario in which all treatments used the maximum power and time, the total energy per eye treated was 0.132 mJ/cm2 and the total UV radiation at close range (80 cm from the treated eye) was 0.0085 mJ/cm2. With a workload of 20 patients, the total occupational exposure at 80 cm to actinic UV radiation in an 8-hour period would be 0.425 mJ/cm2. The scattered actinic UV laser radiation from the VISX Star S3 excimer laser did not exceed occupational exposure limits during a busy 8-hour workday, provided that operating room personnel were at least 80 cm from the treated eye. While the use of protective eyewear is always prudent, this study demonstrates that the trace amounts of scattered laser emissions produced by this laser do not pose a serious health risk even without the use of protective eyewear.

Excimer laser beam delivery systems for medical applications

NASA Astrophysics Data System (ADS)

Kubo, Uichi; Hashishin, Yuichi; Okada, Kazuyuki; Tanaka, Hiroyuki

1993-05-01

We have been doing the basic experiments of UV laser beams and biotissue interaction with both KrF and XeCl lasers. However, the conventional optical fiber can not be available for power UV beams. So we have been investigating about UV power beam delivery systems. These experiments carry on with the same elements doped quartz fibers and the hollow tube. The doped elements are OH ion, chlorine and fluorine. In our latest work, we have tried ArF excimer laser and biotissue interactions, and the beam delivery experiments. From our experimental results, we found that the ArF laser beam has high incision ability for hard biotissue. For example, in the case of the cow's bone incision, the incision depth by ArF laser was ca.15 times of KrF laser. Therefore, ArF laser would be expected to harden biotissue therapy as non-thermal method. However, its beam delivery is difficult to work in this time. We will develop ArF laser beam delivery systems.

Corneal limbal marking in the treatment of myopic astigmatism with the excimer laser.

PubMed

Bucher, Celine; Zuberbuhler, Bruno; Goggin, Michael; Esterman, Adrian; Schipper, Isaak

2010-07-01

To determine whether preoperative marking of the limbal cornea improves treatment of myopic astigmatism with the excimer laser. Retrospective study on 108 eyes with myopic astigmatism that underwent LASIK or laser epithelial keratomileusis (LASEK) with the Technolas 217 (Bausch & Lomb) excimer laser. Preoperative limbal marking was performed in 47 eyes (marked group). The 12-month results were used for refractive and visual analysis. The achieved cylinder reduction, spherical reduction, and refractive predictability were similar for the marked and unmarked groups in the overall study collective, in the LASIK and LASEK subgroup analysis, and in a higher astigmatism (> 1.25 diopters) subgroup analysis. Limbal marking showed no influence on the refractive results, and vector analysis showed no significant difference in angle of error among groups. Corneal limbal marking failed to improve the refractive outcome in LASIK and LASEK for myopic astigmatism.

Unresolved issues in excimer laser corneal surgery

NASA Astrophysics Data System (ADS)

Trokel, Stephen L.

1991-06-01

More than one hundred fifty clinical excimer laser units designed for corneal surgery have been developed and sold commercially. Manufacturers include Meditec Lasers in Germany, Summit Engineering, Taunton Technologies, and Visx in the United States, and Synthelabo in France. Furthermore a number of prototypes have been built in the USSR and other countries which are being investigated for their clinical use. While in the United States and Canada, substantial regulation of these devices has limited their distribution and use, sales in other parts of the world have been restricted only by market forces. Early clinical successes have created an enthusiasm for this new technology. In spite of this, substantial technical issues remain uncertain and have not been carefully studied. Indeed we have accepted certain parameters for on an almost serendipitous, empirical basis. It is a proper time to pause and consider the bases for these laser techniques.

Theoretical Calculations of XeF Ground State Kinetics.

DTIC Science & Technology

1988-03-01

potential parameters for XeF are taken from Tellinghuisen et al. 3 The values of the Lennard - Jones parameters for HeF...parameters for the Morse potential and the Lennard - Jones potentials are listed in Table 1. These parameters for the Lennard - Jones potentials produce the...relaxation and dissociation. 13 ~ o Table 1. Potential Parameters. Morse Function (XeF)3 De = 3.35 kcal/mol ae=1.726 a.u.-1 re =4.367 a.u. Lennard Jones

[Therapeutic excimer laser treatment of the cornea].

PubMed

Linke, S J; Steinberg, J; Katz, T

2013-06-01

Concomitant with new innovations in the field of refractive surgery, therapeutic excimer laser applications like phototherapeutic keratectomy (PTK) and topography-guided customised ablation treatment are gaining high importance and undergoing rapid evolution. Nowadays, PTK is an effective treatment modality for superficial corneal pathologies. Primary indications are decreased epithelial adherence, superficial opacifications and an irregular corneal surface. For the right indication and successful treatment of corneal pathologies with PTK, a knowledge of the size, depth and nature of the pathology, as well as the refractive status of both eyes is important. Next to slit-lamp examination, objective measuring systems like the topography, confocal microscopy and the anterior segment OCT facilitate presurgical planning. Regarding the treatment procedure the surgeon can choose between a variety of methods. PTK can be combined with manual epithelial debridement or done by only using the excimer laser. In the case of an irregular corneal surface, depending on the pathology, masking fluids or topography-guided custom ablation protocols can increase the visual outcome. To avoid recurrence of the underlying pathology (e.g., corneal dystrophy, haze), the topical application of 0.02% mitomycin C for 20-60 seconds has proved to be a safe and effective procedure. If the surgeon considers all the patient-related factors carefully and manages to combine the available treatment options correctly, PTK embodies an effective and minimally invasive alternative to lamellar or penetrating keratoplasty. Georg Thieme Verlag KG Stuttgart · New York.

Excimer Pumped Pulsed Tunable Dye Laser

NASA Astrophysics Data System (ADS)

Littman, Michael G.

1988-06-01

It has been recently shown and reported for the first time at this meeting, that Excimer pumping of a single-mode, short-cavity, grazing-incidence, longitudinally-pumped pulsed dye laser is feasible. In this paper the key concepts upon which this latest development is based are presented and are in a somewhat unusual form. This manuscript describes five specific dye laser examples. The five examples represent a progression from the simplest type of dye laser to the single-mode version mentioned above. The examples thus serve as a tutorial introduction to potential users of dye lasers. The article is organized into five sections or STEPS, each of which describes a different pulsed dye laser. Since the subtle points about dye lasers are best appreciated only after one actually attempts to build a working model, a PROCEDURES category is included in which details about the construction of the particular form of laser are given. As one reads through this category, think of it as looking over the shoulder of the laser builder. The NOTES category which follows is a brief but essential discussion explaining why various components and procedures are used, as well as how laser performance specifications are obtained. This subsection can he viewed as a discussion with the laser builder concerning the reasons for specific actions and choices made in the assembly of the example laser. The last category contains COMMENTS which provide additional related information pertaining to the example laser that goes beyond the earlier annotated discussion. If you like, these are the narrator's comments. At the end of the article, after the five sequential forms of the laser have been presented, there is a brief summation.

Precision drilling of fused silica with 157-nm excimer laser radiation

NASA Astrophysics Data System (ADS)

Temme, Thorsten; Ostendorf, Andreas; Kulik, Christian; Meyer, Klaus

2003-07-01

μFor drilling fused silica, mechanical techniques like with diamond drills, ultrasonic machining, sand blasting or water jet machining are used. Also chemical techniques like laser assisted wet etching or thermal drilling with CO2-lasers are established. As an extension of these technologies, the drilling of micro-holes in fused silica with VUV laser radiation is presented here. The high absorption of the 157 nm radiation emitted by the F2 excimer laser and the short pulse duration lead to a material ablation with minimised impact on the surrounding material. Contrary to CO2-laser drilling, a molten and solidified phase around the bore can thus be avoided. The high photon energy of 7.9 eV requires either high purity nitrogen flushing or operation in vacuum, which also effects the processing results. Depending on the required precision, the laser can be used for percussion drilling as well as for excimer laser trepanning, by applying rotating masks. Rotating masks are especially used for high aspect ratio drilling with well defined edges and minimised debris. The technology is suitable particularly for holes with a diameter below 200 μm down to some microns in substrates with less than 200 μm thickness, that can not be achieved with mechanical methods. Drilling times in 200 μm fused silica substrates are in the range of ten seconds, which is sufficient to compete with conventional methods while providing similar or even better accuracy.

Wavelength Dependence of Excimer Laser Irradiation Effects on Ethylene-Tetrafluoroethylene Copolymer

NASA Astrophysics Data System (ADS)

Hamada, Yuji; Kawanishi, Shunichi; Nishii, Masanobu; Sugimoto, Shun'ichi; Yamamoto, Tadashi

1994-08-01

Irradiation with an ArF laser at wavelength of 193 nm formed diene in a whole ethylene-tetrafluoroethylene copolymer (ETFE) film and irradiation with a KrF and a XeCl laser at 248 and 308 nm induced the carbonization of ETFE. ArF-laser radiation at 193 nm formed diene in the bulk of ETFE via the process of single-photon absorption, and in case of KrF and XeCl-laser irradiation multiphoton absorption brought about the carbonization of ETFE. The surface analysis by X-ray photoelectron spectroscopy showed that excimer laser-induced elimination of fluorine atoms depended on the laser wavelength.

Excimer laser phototherapeutic keratectomy for shield ulcers and corneal plaques in vernal keratoconjunctivitis.

PubMed

Cameron, J A; Antonios, S R; Badr, I A

1995-01-01

Shield-shaped corneal ulcers and corneal plaques in vernal keratoconjunctivitis are associated with delayed epithelial healing, as well as the risks of infectious keratitis and sterile stromal ulceration. Significant visual impairment due to scarring and irregular astigmatism may result from central corneal lesions. Three eyes with central corneal lesions resulting from vernal keratoconjunctivitis were treated by excimer laser after active vernal keratoconjunctivitis was controlled and inflammatory plaque overlying the shield ulcers was removed. All three eyes showed rapid reepithelialization within 1 week. Spectacle-corrected visual acuity of 20/30 or better was obtained in each eye. In selected patients, excimer laser phototherapeutic keratectomy may be a useful adjunct in the treatment of shield-shaped corneal ulcers and plaques in vernal keratoconjunctivitis.

[The 308 nm Excimer laser for the treatment of psoriasis and inflammatory skin diseases].

PubMed

Fritz, K; Salavastru, C

2018-01-01

Overall, the 308 nm Excimer laser enables not only a more effective and safer UVB therapy than classical UV phototherapy, but also targeted irradiation in higher doses with a lower cumulative load, which results in faster healing of mainly circumscribed skin changes. This also applies to therapy-resistant residual lesions which, despite systemic therapy, did not diminish. Combination therapies usually improve the result and enable the dose of UVB and systemic medication to be reduced. Excimer laser therapy can be used for an increasing number of skin diseases, especially those that respond to phototherapy or photochemotherapy.

Visual and refractive outcomes following myopic laser-assisted subepithelial keratectomy with a flying-spot excimer laser.

PubMed

McAlinden, Colm; Skiadaresi, Eirini; Moore, Jonathan E

2011-05-01

To investigate the visual and refractive outcomes following laser-assisted subepithelial keratectomy (LASEK) surgery with a flying-spot excimer laser. Private practice, Ireland. Case series. In this prospective study, the mean manifest spherical equivalent (SE), sphere, and cylinder were measured preoperatively. All eyes had LASEK surgery with an aberration-free algorithm with the Schwind Amaris excimer laser. Outcomes measured at 1 month, 6 months, and 1 year were uncorrected distance visual acuity (UDVA), manifest refraction, corrected distance visual acuity, contrast sensitivity, aberrometry, and complications. Accuracy, efficacy, and safety were evaluated at 1 year. Preoperatively, the mean SE, sphere, and cylinder in the 80 eyes (48 patients) were -3.58 diopters (D) ± 2.00 (SD), -3.23 ± 1.93 D, and -0.85 ± 0.65 D, respectively. One year postoperatively, the mean SE was -0.00 ± 0.22 D; 57 eyes (71%) were within -0.13 to +0.13 D of the SE, and 71 eyes (98%) were within ±0.50 D. The mean UDVA was -0.06 ± 0.07 logMAR, with an efficacy index of 1.04. The postoperative SE was stable between 1 month, 3 months, and 1 year. One eye (1%) had a change in SE by more than 0.50 D at 6 months and 1 year. There were no statistically significant differences in any aberrations at 1 year. The contrast sensitivity improved from 1.66 ± 0.17 log units preoperatively to 1.72 ± 0.15 log units at 1 month postoperatively (P=.0003), which was unchanged at 6 months and 1 year. This study demonstrated the effectiveness of LASEK for the treatment of myopia with this flying-spot excimer laser. Copyright © 2011 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Physical and optical limitations using ArF-excimer and Er:YAG lasers for PRK

NASA Astrophysics Data System (ADS)

Semchishen, Vladimir A.; Mrochen, Michael; Seiler, Theo

1998-06-01

The Erbium:YAG laser emitting at a wavelength of 2,94 micrometer have been promised as an alternative laser for the ArF-excimer laser (193 nm) in photorefractive keratectomy (PRK). This report discusses the limitations of laser parameters such as wavelength, energy density and pulse duration for the ablation of the cornea. In addition, the melting process during ablation on the corneal surface roughness may play a role.

Oxygen effects on the performance of XeCl excimer lasers

NASA Astrophysics Data System (ADS)

Jeon, S. H.; Soh, B. S.; Kim, Y. P.

2018-03-01

We have investigated the degradation of window transmittance of XeCl excimer laser with oxygen, from which it was analyzed the laser performances such as stability of output energy, pre-ionization voltage, and spatial shift of laser beam. We found that oxygen suppressed the generation of by-products due to the chemical reactions between electrode material and chlorine. The degradation of transmittance ratio of laser window with oxygen improved from 10.4% to 1.4% after 20 million shots compared to without oxygen. Analyzing XPS spectrum for the contaminated window, we have confirmed that W and Cu on window surface were reduced in case of with oxygen, which means oxygen has a role to suppress the contamination on window surface.

Treatment of psoriasis and long-term maintenance using 308 nm excimer laser, clobetasol spray, and calcitriol ointment: a case series.

PubMed

Wong, Jillian W; Nguyen, Tien V; Bhutani, Tina; Koo, John Y M

2012-08-01

Psoriasis is a chronic inflammatory skin disease that is characterized by thickened red plaques covered with silvery scales. Excimer laser therapy is a cutting-edge advancement in UVB phototherapy. In contrast to traditional phototherapy, the 308 nm excimer laser only targets psoriasis plaques, while it spares uninvolved skin. It allows for treatment with a supra-erythmogenic dose of UVB irradiation. Targeted UVB therapy is a possible treatment especially for many who have failed topical treatments, systemic therapy, and traditional phototherapy. For safe and effective psoriasis treatment, a combination of therapies may be used, including a combination of laser treatment with topical medications. We present two cases demonstrating effective treatment with excimer laser in conjunction with clobetasol spray and calcitriol ointment for 12 weeks. Long-term near-clearance of psoriasis was sustained after 6 months and one-year follow up periods without further therapy.

Clinical results of PRK touch-up using Chiron/Technolas Keracor 116 excimer laser

NASA Astrophysics Data System (ADS)

Davidian, Mary E.; Keates, Richard H.; Ren, Qiushi

1995-05-01

Regression of effect as well as undercorrection are well established complications of excimer photorefractive keratectomy for the correction of myopia. In thirteen eyes initially treated with the VISX Taunton excimer laser and then retreated with the Chiron Technolas laser, the minimum follow-up time was six months. The mean postoperative refraction at six months was -0.442 +/- 0.996 D (diopters), significantly different from the pretreatment mean of -1.904 +/- 1.297 D. At six months after retreatment (10/13 eyes) 76.9% had an uncorrected visual acuity greater than or equal to 20/40 and (10/13 eyes) 76.9% were within 1 diopter of emmetropia. Only one eye had a significant increase in postoperative haze. The results of this study indicate that the majority of photorefractive keratectomy regressions and undercorrections can be successfully retreated.

Laser-assisted in situ keratomileusis with optimized, fast-repetition, and cyclotorsion control excimer laser to treat hyperopic astigmatism with high cylinder.

PubMed

Alió Del Barrio, Jorge L; Tiveron, Mauro; Plaza-Puche, Ana B; Amesty, María A; Casanova, Laura; García, María J; Alió, Jorge L

2017-10-18

To evaluate the visual outcomes after femtosecond laser-assisted laser in situ keratomileusis (LASIK) surgery to correct primary compound hyperopic astigmatism with high cylinder using a fast repetition rate excimer laser platform with optimized aspheric profiles and cyclotorsion control. Eyes with primary simple or compound hyperopic astigmatism and a cylinder power ≥3.00 D had uneventful femtosecond laser-assisted LASIK with a fast repetition rate excimer laser ablation, aspheric profiles, and cyclotorsion control. Visual, refractive, and aberrometric results were evaluated at the 3- and 6-month follow-up. The astigmatic outcome was evaluated using the Alpins method and ASSORT software. This study enrolled 80 eyes at 3 months and 50 eyes at 6 months. The significant reduction in refractive sphere and cylinder 3 and 6 months postoperatively (p<0.01) was associated with an improved uncorrected distance visual acuity (p<0.01). A total of 23.75% required retreatment 3 months after surgery. Efficacy and safety indices at 6 months were 0.90 and 1.00, respectively. At 6 months, 80% of eyes had an SE within ±0.50 D and 96% within ±1.00 D. No significant differences were detected between the third and the sixth postoperative months in refractive parameters. A significant increase in the spherical aberration was detected, but not in coma. The correction index was 0.94 at 3 months. Laser in situ keratomileusis for primary compound hyperopic astigmatism with high cylinder (>3.00 D) using the latest excimer platforms with cyclotorsion control, fast repetition rate, and optimized aspheric profiles is safe, moderately effective, and predictable.

Syntheses, Raman spectra, and X-ray crystal structures of [XeF(5)][mu-F(OsO(3)F(2))(2)] and [M][OsO(3)F(3)] (M = XeF(5)(+), Xe(2)F(11)(+)).

PubMed

Hughes, Michael J; Mercier, Hélène P A; Schrobilgen, Gary J

2010-04-05

Stoichiometric amounts of XeF(6) and (OsO(3)F(2))(infinity) react at 25-50 degrees C to form salts of the known XeF(5)(+) and Xe(2)F(11)(+) cations, namely, [XeF(5)][mu-F(OsO(3)F(2))(2)], [XeF(5)][OsO(3)F(3)], and [Xe(2)F(11)][OsO(3)F(3)]. Although XeF(6) is oxophilic toward a number of transition metal and main-group oxides and oxide fluorides, fluoride/oxide metathesis was not observed. The series provides the first examples of noble-gas cations that are stabilized by metal oxide fluoride anions and the first example of a mu-F(OsO(3)F(2))(2)(-) salt. Both [XeF(5)][mu-F(OsO(3)F(2))(2)] and [Xe(2)F(11)][OsO(3)F(3)] are orange solids at room temperature. The [XeF(5)][OsO(3)F(3)] salt is an orange liquid at room temperature that solidifies at 5-0 degrees C. When the salts are heated at 50 degrees C under 1 atm of N(2) for more than 2 h, significant XeF(6) loss occurs. The X-ray crystal structures (-173 degrees C) show that the salts exist as discrete ion pairs and that the osmium coordination spheres in OsO(3)F(3)(-) and mu-F(OsO(3)F(2))(2)(-) are pseudo-octahedral OsO(3)F(3)-units having facial arrangements of oxygen and fluorine atoms. The mu-F(OsO(3)F(2))(2)(-) anion is comprised of two symmetry-related OsO(3)F(2)-groups that are fluorine-bridged to one another. Ion pairing results from secondary bonding interactions between the fluorine/oxygen atoms of the anions and the xenon atom of the cation, with the Xe...F/O contacts occurring opposite the axial fluorine and from beneath the equatorial XeF(4)-planes of the XeF(5)(+) and Xe(2)F(11)(+) cations so as to avoid the free valence electron lone pairs of the xenon atoms. The xenon atoms of [XeF(5)][mu-F(OsO(3)F(2))(2)] and [Xe(2)F(11)][OsO(3)F(3)] are nine-coordinate and the xenon atom of [XeF(5)][OsO(3)F(3)] is eight-coordinate. Quantum-chemical calculations at SVWN and B3LYP levels of theory were used to obtain the gas-phase geometries, vibrational frequencies, and NBO bond orders, valencies, and NPA charges of

LASERS: Excimer XeCl laser excited by microsecond megawatt microwave pulses from a commercial 3.07-GHz microwave oscillator

NASA Astrophysics Data System (ADS)

Vaulin, V. A.; Slinko, V. N.; Sulakshin, S. S.

1990-12-01

An excimer laser (λ approx 308 nm) utilizing an Ne-Xe-HCl mixture was excited by microwave (ν0 = 3.07 GHz) pulses of 2.8-μs duration and ~ 0.9 MW power delivered by a commercial microwave oscillator. A peak laser radiation power of 130 W was obtained in pulses of 280 ns duration. Laser radiation from along the center of a laser tube was recorded in addition to that from the skin layer.

Polycrystalline silicon thin-film transistors with location-controlled crystal grains fabricated by excimer laser crystallization

NASA Astrophysics Data System (ADS)

Tsai, Chun-Chien; Lee, Yao-Jen; Chiang, Ko-Yu; Wang, Jyh-Liang; Lee, I.-Che; Chen, Hsu-Hsin; Wei, Kai-Fang; Chang, Ting-Kuo; Chen, Bo-Ting; Cheng, Huang-Chung

2007-11-01

In this paper, location-controlled silicon crystal grains are fabricated by the excimer laser crystallization method which employs amorphous silicon spacer structure and prepatterned thin films. The amorphous silicon spacer in nanometer-sized width formed using spacer technology is served as seed crystal to artificially control superlateral growth phenomenon during excimer laser irradiation. An array of 1.8-μm-sized disklike silicon grains is formed, and the n-channel thin-film transistors whose channels located inside the artificially-controlled crystal grains exhibit higher performance of field-effect-mobility reaching 308cm2/Vs as compared with the conventional ones. This position-manipulated silicon grains are essential to high-performance and good uniformity devices.

Gaussian broad-beam excimer laser: clinical and experimental results.

PubMed

Schraepen, P; Eskina, E; Gobin, L; Trau, R; Timmermans, J; Tassignon, M J

2005-01-01

To evaluate the mid-term (1-3 years) results of the Gaussian broad-beam excimer laser Delivery System (DS) after single treatment for the correction of myopia. To study the corneal surface with scanning electron microscopy (SEM) after excimer laser ablation using a flying spot delivery system (Bausch & Lomb) and a Gaussian Delivery System (GDS) (InPro). The 1035 consecutive eyes studied were split in four groups with respect to the treated myopia, expressed in spherical equivalent: low myopia up to -3.00 D (183 eyes), moderate myopia from -3.25 D to -6.00 D (540 eyes), high myopia from -6.25 D to -10.00 D (210 eyes) and very high myopia from -10.25 D to -20.00 D (102 eyes). Four post-mortem eyes of two donors were treated using the flying spot DS on one eye and the GDS on the other eye. We achieved postoperative spheriqual equivalent within +/- 1 D of emmetropia in respectively 99.1%, 98.9%, 83% and 21% of the eyes of group 1, 2, 3 and 4. UCVA was 10/10 or better in respectively 65%, 51% and 19% of group 1, 2 and 3. UCVA was 5/10 or better in respectively 86% and 75% of group 3 and 4. The defocus equivalent refraction was 1.0 or less in respectively 98%, 93%, 62%, and 7% of the four groups. On SEM, the corneal surface presented a smooth and polished profile for the GDS. The Gaussian Delivery System gives comparable results to the flying spot laser system for surface laser ablation in myopic eyes up to -10 D. Advantages of this system are: smooth ablation surface, short treatment time, low haze rate, high reliability and easy maintenance of the device due to the optical DS. It is an interesting alternative for the more complex mechanical DS.

Excimer laser delivery system for astigmatic and hyperopic photorefractive surgery

NASA Astrophysics Data System (ADS)

Beck, Rasmus; Foerster, Werner

1994-06-01

Ablation of corneal tissue with excimer laser light is an effective way to correct refractive errors of the eye. For this purpose a beam-stop (iris diaphragm or interchangeable masks) is illuminated by the laser radiation. The beam-stop is imaged onto the cornea, and circular or elliptic ablations are produced. The computer-controlled process varies the diameter of the ablation area in a way that the inner portions of the treatment zone receive more laser energy than the outer portions, thus flattening the curvature of the refractive surface. For the treatment of hyperopia, the outer portions of the ablation area receive more laser energy to steepen the surface profile of the cornea. The beam delivery system employs several sets of circular, elliptic and ring shaped masks which are etched into a stainless-steel tape.

Scythe regulates apoptosis through modulating ubiquitin-mediated proteolysis of the Xenopus elongation factor XEF1AO

PubMed Central

Minami, Ryosuke; Shimada, Masumi; Yokosawa, Hideyoshi; Kawahara, Hiroyuki

2007-01-01

Scythe was originally identified as a novel Reaper-binding anti-apoptotic protein, although the mechanisms of its functions remain largely obscure. Our previous analysis revealed that Scythe can bind to a proteasomal subunit via N-terminal domains and that the domains are required for appropriate development of Xenopus embryos. In the present study, we show evidence that the N-terminus of Scythe interacts with XEF1AO, a maternal form of Xenopus laevis EF1A that was suggested to be a potential inducer of apoptosis in vertebrates, and that the binding enhances the poly-ubiquitin modification and subsequent degradation of XEF1AO. Scythe is required for degradation of XEF1AO, since immunodepletion of Scythe from embryonic extracts stabilized XEF1AO significantly. Furthermore, we show that apoptosis induced by accumulation of XEF1AO can be suppressed by co-expression of the full-length form of Scythe. These observations indicate that the proteolytic regulation of XEF1AO, mediated through Scythe, is essential to prevent inappropriate accumulation of XEF1AO and resulting apoptotic events during the course of Xenopus development. PMID:17428197

Applications of the 308-nm excimer laser in dermatology

NASA Astrophysics Data System (ADS)

Farkas, A.; Kemeny, L.

2006-05-01

Excimer lasers contain a mixture of a noble inert gas and a halogen, which form excited dimers only in the activated state. High-energy current is used to produce these dimers, which have a very short lifetime, and after their fast dissociation they release the excitation energy through ultraviolet photons. The application of these lasers proved to be successful in medicine, including the field of ophthalmology, cardiology, angiology, dentistry, orthopaedics, and, in recent years, dermatology. For medical purposes, the 193-nm argon fluoride, the 248-nm krypton fluoride, the 351-nm xenon fluoride, and the 308-nm xenon chloride lasers are used. Recently, the 308-nm xenon chloride laser has gained much attention as a very effective treatment modality in dermatological disorders. It was successfully utilized in psoriasis; later, it proved to be useful in handling other lightsensitive skin disorders and even in the treatment of allergic rhinitis. This review summarizes the possible applications of this promising tool in dermatology.

XeCl excimer laser with new prism resonator configurations and its performance characteristics

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

Benerji, N. S., E-mail: nsb@rrcat.gov.in, E-mail: bsingh@rrcat.gov.in; Singh, A.; Varshnay, N.

2015-07-15

New resonator cavity configurations, namely, the prism resonator and unstable prism resonator, are demonstrated for the first time in an excimer (XeCl) laser with interesting and novel results. High misalignment tolerance ∼50 mrad is achieved with considerably reduced beam divergence of less than ∼1 mrad without reduction in output power capabilities of the laser. The misalignment tolerance of ∼50 mrad is a dramatic improvement of ∼25 times compared to ∼2 mrad normally observed in standard excimer laser with plane-plane cavity. Increase in depth of focus from 3 mm to 5.5 mm was also achieved in case of prism resonator configurationmore » with an improvement of about 60%. Unstable prism resonator configuration is demonstrated here in this paper with further reduction in beam divergence to about 0.5 mrad using plano-convex lens as output coupler. The misalignment tolerance in case of unstable prism resonator was retained at about 30 mrad which is a high value compared to standard unstable resonators. The output beam spot was completely filled with flat-top profile with prism resonator configurations, which is desired for various material processing applications. Focusing properties and beam divergence in case of prism resonator have been investigated using SEM (scanning electron microscope) images. SEM images of the focused spot size (∼20 μm holes) on metal sheet indicate beam divergence of about 0.05 mrad which is about 1.5 times diffraction limit. Energy contained in this angle is thus sufficient for micro-machining applications. Clean and sharp edges of the micro-holes show high pointing stability with multiple shot exposures. Such characteristics of the excimer laser system will be extremely useful in micro-machining and other field applications.« less

XeCl excimer laser with new prism resonator configurations and its performance characteristics.

PubMed

Benerji, N S; Singh, A; Varshnay, N; Singh, Bijendra

2015-07-01

New resonator cavity configurations, namely, the prism resonator and unstable prism resonator, are demonstrated for the first time in an excimer (XeCl) laser with interesting and novel results. High misalignment tolerance ∼50 mrad is achieved with considerably reduced beam divergence of less than ∼1 mrad without reduction in output power capabilities of the laser. The misalignment tolerance of ∼50 mrad is a dramatic improvement of ∼25 times compared to ∼2 mrad normally observed in standard excimer laser with plane-plane cavity. Increase in depth of focus from 3 mm to 5.5 mm was also achieved in case of prism resonator configuration with an improvement of about 60%. Unstable prism resonator configuration is demonstrated here in this paper with further reduction in beam divergence to about 0.5 mrad using plano-convex lens as output coupler. The misalignment tolerance in case of unstable prism resonator was retained at about 30 mrad which is a high value compared to standard unstable resonators. The output beam spot was completely filled with flat-top profile with prism resonator configurations, which is desired for various material processing applications. Focusing properties and beam divergence in case of prism resonator have been investigated using SEM (scanning electron microscope) images. SEM images of the focused spot size (∼20 μm holes) on metal sheet indicate beam divergence of about 0.05 mrad which is about 1.5 times diffraction limit. Energy contained in this angle is thus sufficient for micro-machining applications. Clean and sharp edges of the micro-holes show high pointing stability with multiple shot exposures. Such characteristics of the excimer laser system will be extremely useful in micro-machining and other field applications.

Features of plasma produced by excimer laser at low intensities

NASA Astrophysics Data System (ADS)

Vergunova, G. A.; Magunov, A. I.; Dyakin, V. M.; Faenov, A. Ya; Pikuz, T. A.; Skobelev, I. Yu; Batani, D.; Bossi, S.; Bernardinello, A.; Flora, F.; di Lazzaro, P.; Bollanti, S.; Lisi, N.; Letardi, T.; Reale, A.; Palladino, L.; Scafati, A.; Reale, L.; Osterheld, A. L.; Goldstein, W. H.

1997-04-01

A plasma, created at interaction of short-wavelength excimer laser radiation with flat targets was investigated (tlas = 12 ns, λlas = 0.308 μm, qlas = 4 - 8 × 1012 W/cm2) with the help of various x-ray spectroscopic methods. The comparison of shapes and intensities of some observable spectral lines of H-, He and Li-like ions of Na, Mg and Al with results of model calculations has allowed to determine space distributions of laser plasma parameters up to distances of 0.4 mm from the target surface. Comparison of obtained results with theoretical models of absorption of short-wavelength radiation in a plasma shows, that the absorption of short-wavelength laser radiation in a plasma (at considered values of laser flux density) is executed due to inverse bremsstrahlung process in the areas with Ne < Ne, crit..

Coordination of XeF2 to calcium and cadmium hexafluorophosphates(V).

PubMed

Bunic, Tina; Tavcar, Gasper; Tramsek, Melita; Zemva, Boris

2006-02-06

[M(XeF2)5](PF6)2 (M = Ca, Cd) complexes were prepared by the reaction of MF2 and XeF2 under pressure of gaseous PF5 in anhydrous HF as solvent. The coordination sphere of the Ca atom consists of nine fluorine atoms: three from two PF6(-) units (one bidentate and one monodentate) and one from each of six XeF2 molecules. The coordination sphere of the Cd atom consists of eight fluorine atoms: one from each of two PF6(-) units and one from each of six XeF2 molecules. Two of the XeF2 ligands about M in each compound are bridging ligands and are each linked to two M, generating infinite (-M-F-Xe-F-M-F-Xe-F-) chains along the b-axis in the Ca salt and along the c-axis in the Cd compound. The Cd2+ cation is smaller and more electronegative than the Ca2+ cation. These differences account for the higher F ligand coordination in the Ca2+ salt and for other structural features that distinguish them. The different stoichiometry of the PF6(-) salts when compared with their AsF6(-) analogues, which have the composition [M(XeF2)4](AsF6)2 (M = Ca, Cd), is in accord with the lower F ligand charge in the AsF6(-) when compared with that in the PF6(-) compound. Indeed, the AsF6(-) ligand charges appear to be similar to those in the XeF2-bridged species.

Excimer Laser Versus Phakic Intraocular Lenses for Myopia and Astigmatism: A Meta-Analysis of Randomized Controlled Trials.

PubMed

Chen, Haiting; Liu, Yu; Niu, Guangzeng; Ma, Jingxue

2018-05-01

Meta-analysis of randomized controlled trials (RCTs) which compared excimer laser refractive surgery and phakic intraocular lenses (PIOLs) for the treatment of myopia and astigmatism. An electronic literature search was performed using the PubMed, EBSCO, CNKI, and Cochrane Library database to identify prospective RCTs which compared excimer laser refractive surgery and PIOL with a follow-up time of at least 12 months. Efficacy, accuracy, safety outcomes, and complications were analyzed by standardized mean difference, risk ratio, and the pooled estimates according to a fixed effect model or random effect model. This review included 5 RCTs with a sum of 405 eyes. The range of myopia was 6.0 to 20.0 D with up to 4.0 D of astigmatism. The PIOL group was more likely to achieve a spherical equivalence within±1.0 D of target refraction at 12 months postoperatively (P=0.009), and was less likely to lose one or more lines of best spectacle corrected visual acuity than the LASER group (P=0.002). On the whole, there is no significant difference in efficacy and complications between the two kinds of surgeries. This meta-analysis indicated that PIOLs were safer and more accurate within 12 months of follow-up compared with excimer laser surgical for refractive errors.

Effect of volatile compounds on excimer laser power delivery.

PubMed

Van Horn, Stewart D; Hovanesian, John A; Maloney, Robert K

2002-01-01

To determine whether vapors from perfume, hairspray, oil-based paint, or water-based paint affect excimer laser beam power delivery at the corneal surface. We measured the power delivery of an Apex Plus laser before, during, and after exposure to vapors from the following volatile compounds: three types of perfume, hair spray, an oil-based paint, and a water-based paint. A digital calorimeter was used to measure the steady-state beam power of the laser during laser discharge at the corneal plane. Multiple trials were run with each compound, and the change in laser energy over time was examined to determine if any of the compounds caused degradation of the laser optics. The presence of a volatile compound in the room caused no change in mean laser energy in comparison to before and after the compound was present. However, perfumes caused a progressive decline in laser beam power throughout the trials. Controlling for this progressive decline, there was no significant difference from perfume to perfume. None of the compounds tested caused a decline in laser beam power while present in the room. However, the presence of any perfume caused a deterioration in beam power over time, suggesting a degradation of the laser optics for all perfumes. Laser centers should consider advising their patients and staff to not wear perfumes in the laser suite.

[Surface modifications of titanium implant material with excimer laser for more effective osseointegration].

PubMed

Pelsoczi, Kovács István; Bereznai, Miklós; Tóth, Zsolt; Turzó, Kinga; Radnai, Márta; Bor, Zsolt; Fazekas, András

2004-12-01

The biointegration of dental and orthopaedic implants depends mainly on the morphology and physical-chemical properties of their surfaces. Accordingly, the development of the desired microstructure is a relevant requirement in the bulk manufacture. Besides the widely used sandblasting plus acid etching and plasma-spray coating techniques, the laser surface modification method offers a plausible alternative. In order to analyze the influence of the laser treatment, the surfaces of titanium samples were exposed to excimer laser irradiation. The aim of this study was to develop surfaces that provide optimal conditions for bone-implant contact, bone growth, formation and maintenance of gingival attachment. For this purpose, holes were ablated on the surface of samples by nanosecond (18 ns, ArF) and also sub-picosecond (0,5 ps, KrF) laser pulses. Using pulses of ns length, due to melt ejection, crown-like protrusions were formed at the border of the holes, which made them sensitive to mechanical effects. To avoid these undesirable crown-like structures ultrashort KrF excimer laser pulses were successfully applied. On the other hand, titanium samples were laser-polished in favour of formation and connection of healthy soft tissues. Irradiation by a series of nanosecond laser pulses resulted in an effective smoothening as detected by atomic force microscopy (AFM). By inhibiting plaque accumulation this favours formation of gingival attachment. X-ray photoelectron spectroscopy (XPS) studies showed that laser treatment, in addition to micro-structural and morphological modification, results in decreasing of surface contamination and thickening of the oxide layer. X-ray diffraction (XRD) analysis revealed that the original alpha-titanium crystalline structure of the laser-polished titanium surface was not altered by the irradiation.

Towards excimer-laser-based stereolithography: a rapid process to fabricate rigid biodegradable photopolymer scaffolds

PubMed Central

Beke, S.; Anjum, F.; Tsushima, H.; Ceseracciu, L.; Chieregatti, E.; Diaspro, A.; Athanassiou, A.; Brandi, F.

2012-01-01

We demonstrate high-resolution photocross-linking of biodegradable poly(propylene fumarate) (PPF) and diethyl fumarate (DEF) using UV excimer laser photocuring at 308 nm. The curing depth can be tuned in a micrometre range by adjusting the total energy dose (total fluence). Young's moduli of the scaffolds are found to be a few gigapascal, high enough to support bone formation. The results presented here demonstrate that the proposed technique is an excellent tool for the fabrication of stiff and biocompatible structures on a micrometre scale with defined patterns of high resolution in all three spatial dimensions. Using UV laser photocuring at 308 nm will significantly improve the speed of rapid prototyping of biocompatible and biodegradable polymer scaffolds and enables its production in a few seconds, providing high lateral and horizontal resolution. This short timescale is indeed a tremendous asset that will enable a more efficient translation of technology to clinical applications. Preliminary cell tests proved that PPF : DEF scaffolds produced by excimer laser photocuring are biocompatible and, therefore, are promising candidates to be applied in tissue engineering and regenerative medicine. PMID:22696484

AlGaAs growth by OMCVD using an excimer laser

NASA Technical Reports Server (NTRS)

Warner, Joseph D.; Wilt, David M.; Pouch, John J.; Aron, Paul R.

1986-01-01

AlGaAs has been grown on GaAs by laser assisted OMCVD using an excimer laser, wavelength 193 nm, and a Cambridge OMCVD reactor. Films were grown at temperatures of 450 and 500 C with the laser beam parallel to the surface and impinging onto the surface at 15 deg from parallel. The samples were heated by RF coils while the laser beam was perpendicular to the gas flow. Typical gas flow parameters are 12 slm of H2, 15 sccm of Ga(CH3)3, 13 sccm of Al(CH3)3, and a pressure of 250 mbar. The initial energy density of the beam at the surface was 40 mJ/sq cm, the pulse rate was 20 pps, and the growth time was 7 min. The films were analyzed by Auger electron spectroscopy for the aluminum concentration and by TEM for the surface morphology.

Improving the ablation efficiency of excimer laser systems with higher repetition rates through enhanced debris removal and optimized spot pattern.

PubMed

Arba-Mosquera, Samuel; Klinner, Thomas

2014-03-01

To evaluate the reasons for the required increased radiant exposure for higher-repetition-rate excimer lasers and determine experimentally possible compensations to achieve equivalent ablation profiles maintaining the same single-pulse energies and radiant exposures for laser repetition rates ranging from 430 to 1000 Hz. Schwind eye-tech-solutions GmbH and Co. KG, Kleinostheim, Germany. Experimental study. Poly(methyl methacrylate) (PMMA) plates were photoablated. The pulse laser energy was maintained during all experiments; the effects of the flow of the debris removal, the shot pattern for the correction, and precooling the PMMA plates were evaluated in terms of achieved ablation versus repetition rate. The mean ablation performance ranged from 88% to 100%; the variability between the profile measurements ranged from 1.4% to 6.2%. Increasing the laser repetition rate from 430 Hz to 1000 Hz reduced the mean ablation performance from 98% to 91% and worsened the variability from 1.9% to 4.3%. Increasing the flow of the debris removal, precooling the PMMA plates to -18°C, and adapting the shot pattern for the thermal response of PMMA to excimer ablation helped stabilize the variability. Only adapting the shot pattern for the thermal response of PMMA to excimer ablation helped stabilize the mean ablation performance. The ablation performance of higher-repetition-rate excimer lasers on PMMA improved with improvements in the debris removal systems and shot pattern. More powerful debris removal systems and smart shot patterns in terms of thermal response improved the performance of these excimer lasers. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Perspectives of using the 223-nm wavelength of the KrCl excimer laser for refractive surgery and for the treatment of some eye diseases

NASA Astrophysics Data System (ADS)

Bagayev, Sergei N.; Chernikh, Valery V.; Razhev, Alexander M.; Zhupikov, Andrey A.

2000-06-01

The new surgical UV ophthalmic laser system Medilex based on the KrCl (223 nm) excimer laser for refractive surgery was created. The comparative analysis of using the UV ophthalmic laser systems Medilex based on the ArF (193 nm) and the KrCl (223 nm) excimer lasers for the correction of refractive errors was performed. The system with the radiation wavelength of 223 nanometer of the KrCl excimer laser for refractive surgery was shown to have several medical and technical advantages over the system with the traditionally used radiation wavelength of 193 nanometer of the ArF excimer laser. In addition the use of the wavelength of 223 nanometer extends functional features of the system, allowing to make not only standard for this type systems surgical and therapeutic procedures but also to treat such ocular diseases as the glaucoma and herpetic keratities. For the UV ophthalmic laser systems Medilex three variations of the beam delivery system including special rotating masks and different beam homogenize systems were developed. All created beam delivery systems are able to make the correction of myopia, hyperopia, astigmatism and myopic or hyperopic astigmatism and may be used for therapeutic procedures. The results of the initial treatments of refractive error corrections using the UV ophthalmic laser systems Medilex for both photorefractive keratectomy (PRK) and LASIK procedures are presented.

Update on laser vision correction using wavefront analysis with the CustomCornea system and LADARVision 193-nm excimer laser

NASA Astrophysics Data System (ADS)

Maguen, Ezra I.; Salz, James J.; McDonald, Marguerite B.; Pettit, George H.; Papaioannou, Thanassis; Grundfest, Warren S.

2002-06-01

A study was undertaken to assess whether results of laser vision correction with the LADARVISION 193-nm excimer laser (Alcon-Autonomous technologies) can be improved with the use of wavefront analysis generated by a proprietary system including a Hartman-Schack sensor and expressed using Zernicke polynomials. A total of 82 eyes underwent LASIK in several centers with an improved algorithm, using the CustomCornea system. A subgroup of 48 eyes of 24 patients was randomized so that one eye undergoes conventional treatment and one eye undergoes treatment based on wavefront analysis. Treatment parameters were equal for each type of refractive error. 83% of all eyes had uncorrected vision of 20/20 or better and 95% were 20/25 or better. In all groups, uncorrected visual acuities did not improve significantly in eyes treated with wavefront analysis compared to conventional treatments. Higher order aberrations were consistently better corrected in eyes undergoing treatment based on wavefront analysis for LASIK at 6 months postop. In addition, the number of eyes with reduced RMS was significantly higher in the subset of eyes treated with a wavefront algorithm (38% vs. 5%). Wavefront technology may improve the outcomes of laser vision correction with the LADARVISION excimer laser. Further refinements of the technology and clinical trials will contribute to this goal.

LASIK for myopia and astigmatism using the SCHWIND AMARIS excimer laser: an international multicenter trial.

PubMed

Arbelaez, Maria Clara; Aslanides, Ioannis M; Barraquer, Carmen; Carones, Francesco; Feuermannova, Alena; Neuhann, Tobias; Rozsival, Pavel

2010-02-01

To assess the efficacy, predictability, and safety of LASIK for the surgical correction of low to moderate myopia with astigmatism using the SCHWIND AMARIS excimer laser. Six international study sites enrolled 358 eyes with a manifest refraction spherical equivalent (MRSE) from -0.50 to -7.38 diopters (D) (mean sphere: -3.13+/-1.58 D) with up to -5.00 D of astigmatism (mean: -0.69+/-0.67 D). All eyes underwent treatment with the nonwavefront-guided aspheric algorithm of the SCHWIND AMARIS excimer laser. All eyes were targeted for emmetropia. Refractive outcomes and corneal higher order aberrations were analyzed pre- and postoperatively. Visual quality was assessed using photopic and mesopic contrast sensitivity. Six-month postoperative outcomes are reported. At 6 months postoperative, the MRSE for all eyes was -0.21+/-0.20 D, and 96% (343/358) of eyes had MRSE within +/-0.50 D. Uncorrected visual acuity was 20/20 or better in 98% (351/358) of eyes, and no eyes lost 2 or more lines of best spectacle-corrected visual acuity. The total corneal higher order aberrations root-mean-square increased by 0.09 microm, spherical aberration increased by 0.08 microm, and coma increased by 0.04 microm postoperatively. Photopic and mesopic contrast sensitivity did not change 6 months postoperatively. Treatment of myopia with astigmatism using the SCHWIND AMARIS excimer laser is safe, efficacious, predictable, and maintains visual quality.

Micro flow-through PCR in a PMMA chip fabricated by KrF excimer laser.

PubMed

Yao, Liying; Liu, Baoan; Chen, Tao; Liu, Shibing; Zuo, Tiechuan

2005-09-01

As the third PCR technology, micro flow-through PCR chip can amplify DNA specifically in an exponential fashion in vitro. Nowadays many academies in the world have successfully amplified DNA using their own-made flow-through PCR chip. In this paper, the ablation principle of PMMA at 248 nm excimer laser was studied, then a PMMA based flow-through PCR chip with 20 cycles was fabricated by excimer laser at 19 kv and 18 mm/min. The chip was bonded together with another cover chip at 105( composite function)C, 160 N and 20 minutes. In the end, it was integrated with electrical thermal thin films and Pt 100 temperature sensors. The temperature controllers was built standard PID digital temperature controller, the temperature control precision was +/- 0.2( composite function)C. The temperature grads between the three temperature zones were 16.5 and 22.2( composite function)C respectively, the gaps between the temperature zones could realize heat insulation.

Effects of XeCl excimer lasers and fluoride application on artificial caries-like lesions

NASA Astrophysics Data System (ADS)

Wilder-Smith, Petra B. B.; Phan, T.; Liaw, Lih-Huei L.; Berns, Michael W.

1994-09-01

In this study the affects of a pulsed excimer laser emitting at 308 nm (XeCl) on enamel susceptibility to artificial caries-like lesions were investigated. Additional effects of fluoride (F) application were also studied and SEC examinations performed. Sixty-four extracted human molar teeth were coated with acid resistant varnish leaving four windows, then sectioned, leaving one window on each tooth quarter. The windows were treated in one of the following ways: untreated (control), or lased, or exposed to 4 min. APF (1.23% F) before lasing, or exposed to 4 min. APF (1.23% F) after lasing. After lasing, microhardness profiles were obtained and SEM was performed. Caries resistance was generally increased at moderate fluences. F application combined with lasing enhanced caries resistance at some parameters. SEM showed effects ranging from minimal to localized effects to extended glazing. Pulsed excimer laser irradiation, especially combined with topical F application can inhibit development of artificial caries-like lesions.

Report on the Study of Radiation Damage in Calcium Fluoride and Magnesium Fluoride Crystals for use in Excimer Laser Applications

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

None, None

1999-10-04

A study was performed to investigate the effects of radiation damage in calcium fluoride and magnesium fluoride crystals caused by gamma rays and UV photons from excimer lasers. The purpose was to study and correlate the damage caused by these two different mechanisms in various types of material used for fabricating optical elements in high power excimer lasers and lens systems of lithography tools. These optical systems are easily damaged by the laser itself, and it is necessary to use only the most radiation resistant materials for certain key elements. It was found that a clear correlation exists between the,more » radiation induced damage caused by high energy gamma rays and that produced by UV photons from the excimer laser. This correlation allows a simple procedure to be developed to select the most radiation resistant material at the ingot level, which would be later used to fabricate various components of the optical system. This avoids incurring the additional cost of fabricating actual optical elements with material that would later be damaged under prolonged use. The result of this screening procedure can result in a considerable savings in the overall cost of the lens and laser system.« less

Excimer laser assisted very fast exfoliation and reduction of graphite oxide at room temperature under air ambient for Supercapacitors electrode

NASA Astrophysics Data System (ADS)

Malek Hosseini, S. M. B.; Baizaee, S. M.; Naderi, Hamid Reza; Dare Kordi, Ali

2018-01-01

Excimer laser was used for reduction and exfoliation of graphite oxide (GO) at room temperature under air ambient. The prepared excimer laser reduced graphite oxide (XLRGO) is characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), nitrogen adsorption/desorption (BET method), X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and UV-vis absorption techniques for surface, structural functional groups and band gap analysis. Electrochemical properties are investigated using cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS) and continues cyclic voltammetry (CCV) in 0.5 M Na2SO4 as electrolyte. Electrochemical investigations revealed that XLRGO electrode has enhanced supercapacitive performance including specific capacitance of 299 F/g at a scan rate of 2 mV/s. Furthermore, CCV measurement showed that XLRGO electrode kept 97.8% of its initial capacitance/capacity after 4000 cycles. The obtained results from electrochemical investigations confirm that the reduction of GO by using an excimer laser produces high-quality graphene for supercapacitor applications without the need for additional operations.

About Losses in Pumping Generators of High-Power Electrodischarge Excimer Lasers

NASA Astrophysics Data System (ADS)

Ivanov, N. G.; Losev, V. F.

2015-04-01

Energy losses in pumping systems of discharge high-power lasers are investigated. To estimate the losses, the discharge circuit operation was modeled, and its calculation was performed using the program PSpice. Results of measurements and calculations demonstrate that the resistance of a rail gap with electric field distortion exceeds several times the resistance of a single-channel gap without field distortion. A difference in the resistances is explained by different mechanisms of discharge burning: in the first case diffusion mechanism and in the second case the spark mechanism. The low efficiency of the high-power excimer lasers (~1%) is explained by high energy losses in the rail gap that reach more than 50% of the initially stored energy.

Calibration of a tunable excimer laser using the optogalvanic effect

NASA Technical Reports Server (NTRS)

Abbitt, John D.

1991-01-01

A device for the calibration of a tunable excimer laser is currently under development. The laser provides UV radiation at three principal wavelengths, 193, 248, and 308 nm and is tunable over a range of 1 nm at each of these wavelengths. The laser is used as a non-intrusive optical probe to excite electronic transitions, and thereby induce fluorescence, of the principle molecules or atoms of interest in supersonic flowfields, both reacting and nonreacting. The fluorescence resulting from the excitation is observed with an intensified camera. Over the range of tunability at the three wavelengths are a number of transitions that can be observed. The intensity of the fluorescence depends in part on the local temperature and density. The nature of this thermodynamic dependence is variable among transitions; thus, identification of the transition under observation is required. The specific transition excited corresponds directly to the wavelength of the radiation. The present technique used for transition identification consists of scanning the laser across the range of tunability and observing the fluorescence resulting from various molecular transitions.

In-vitro ablation of fibrocartilage by XeCl excimer laser

NASA Astrophysics Data System (ADS)

Buchelt, Martin; Papaioannou, Thanassis; Fishbein, Michael C.; Peters, Werner; Beeder, Clain; Grundfest, Warren S.

1991-07-01

A 308 nm excimer laser was employed for ablation of human fibrocartilage. Experiments were conducted in vitro. The tissue response was investigated with respect to dosimetry (ablation rate versus radiant exposure) and thermal effect (thermographic analysis). Irradiation was performed via a 600 um fiber, with radiant exposures ranging between 20mj/mm2 and 80mj/mm2, at 20Hz. The ablation rates were found to range from 3um/pulse to 80um/pulse depending on the radiant exposure and/or the applied pressure on the delivery system. Thermographic analysis, during ablation, revealed maximum average temperatures of about 65 degree(s)C. Similar measurements performed, for the purpose of comparison, with a CW Nd:YAG and a CW CO2 laser showed higher values, of the order of 200 degree(s)C.

Determination of excimer laser ablation rate of the human cornea using in vivo Scheimpflug videography.

PubMed

Huebscher, H J; Genth, U; Seiler, T

1996-01-01

To determine in vivo the amount of human corneal tissue removed by each excimer laser pulse, the so-called ablation rate, during photorefractive keratectomy (PRK). There is confusion in the literature because the experimentally determined ablation rate of 0.4 to 0.5 microns per pulse differs from the nominal ablation rate of 0.23 to 0.3 microns per pulse, which is the value used in clinical procedures. Eleven eyes of 11 patients were treated with PRK for correction of myopia. The corneal curvature was determined by Scheimpflug videography before and immediately after surgery. Starting from this curvature change, the authors calculated the real ablation rate. The real ablation rate is coincident with the nominal ablation rate and differs significantly from the ablation rate derived from deep keratectomy experiments. The outer layers of the cornea show significantly different ablation behavior than the deeper stroma. This information has clinical relevance for the predictability of intrastromal excimer laser procedures.

Controllable Change of Photoluminescence Spectra of Silicone Rubber Modified by 193 nm ArF Excimer Laser

NASA Astrophysics Data System (ADS)

Okoshi, Masayuki; Iyono, Minako; Inoue, Narumi

2009-12-01

Photoluminescence spectra of silicone rubber ([SiO(CH3)2]n) photochemically modified by a 193 nm ArF excimer laser was found to be controllable. Compared with the modification in air, the photoluminescence spectra could be blueshifted by the modification in vacuum or the additional irradiation of ArF excimer laser in vacuum after the modification in air. To redshift, on the other hand, the additional irradiation of a 157 nm F2 laser in air after the modification in air, the modification in oxygen gas, or the postannealing after the modification in oxygen gas was effective. The blue and redshifts of the photoluminescence were essentially due to the acceleration of reduction and oxidation reactions of silicone rubber, respectively, because the photoluminescence derives its origin from oxygen deficiency centers and peroxy centers of the silica structure in the modified silicone rubber. On the basis of the spectra changes, colorful light-guiding sheets made of silicone rubber under illumination of a 375 nm light-emitting diode were successfully fabricated for cellular phone use.

308-nm excimer laser ablation of human cartilage

NASA Astrophysics Data System (ADS)

Prodoehl, John A.; Rhodes, Anthony L.; Meller, Menachem M.; Sherk, Henry H.

1993-07-01

The XeCl excimer laser was investigated as an ablating tool for human fibrocartilage and hyaline cartilage. Quantitative measurements were made of tissue ablation rates as a function of fluence in meniscal fibrocartilage and articular hyaline cartilage. A force of 1.47 Newtons was applied to an 800 micrometers fiber with the laser delivering a range of fluences (40 to 190 mj/mm2) firing at a frequency of 5 Hz. To assess the effect of repetition rate on ablation rate, a set of measurements was made at a constant fluence of 60 mj/mm2, with the repetition rate varying from 10 to 40 Hz. Histologic and morphometric analysis was performed using light microscopy. The results of these studies revealed that the ablation rate was directly proportional to fluence over the range tested. Fibrocartilage was ablated at a rate 2.56 times faster than hyaline cartilage at the maximum fluence tested. Repetition rate had no effect on the penetration per pulse. Adjacent tissue damage was noted to be minimal (10 - 70 micrometers ).

Endobronchial Forceps-Assisted and Excimer Laser-Assisted Inferior Vena Cava Filter Removal: The Data, Where We Are, and How It Is Done.

PubMed

Chen, James X; Montgomery, Jennifer; McLennan, Gordon; Stavropoulos, S William

2018-06-01

The recognition of inferior vena cava filter related complications has motivated increased attentiveness in clinical follow-up of patients with inferior vena cava filters and has led to development of multiple approaches for retrieving filters that are challenging or impossible to remove using conventional techniques. Endobronchial forceps and excimer lasers are tools for designed to aid in complex inferior vena cava filter removals. This article discusses endobronchial forceps-assisted and excimer laser-assisted inferior vena cava filter retrievals. Copyright © 2018 Elsevier Inc. All rights reserved.

Evaluation of corneal ablation by an optical parametric oscillator (OPO) at 2.94 μm and an Er:YAG laser and comparison to ablation by a 193-nm excimer laser

NASA Astrophysics Data System (ADS)

Telfair, William B.; Hoffman, Hanna J.; Nordquist, Robert E.; Eiferman, Richard A.

1998-06-01

Purpose: This study first evaluated the corneal ablation characteristics of (1) an Nd:YAG pumped OPO (Optical Parametric Oscillator) at 2.94 microns and (2) a short pulse Er:YAG laser. Secondly, it compared the histopathology and surface quality of these ablations with (3) a 193 nm excimer laser. Finally, the healing characteristics over 4 months of cat eyes treated with the OPO were evaluated. Methods: Custom designed Nd:YAG/OPO and Er:YAG lasers were integrated with a new scanning delivery system to perform PRK myopic correction procedures. After initial ablation studies to determine ablation thresholds and rates, human cadaver eyes and in-vivo cat eyes were treated with (1) a 6.0 mm Dia, 30 micron deep PTK ablation and (2) a 6.0 mm Dia, -5.0 Diopter PRK ablation. Cadaver eyes were also treated with a 5.0 mm Dia, -5.0 Diopter LASIK ablation. Finally, cats were treated with the OPO in a 4 month healing study. Results: Ablation thresholds below 100 mJ/cm2 and ablation rates comparable to the excimer were demonstrated for both infrared systems. Light Microscopy (LM) showed no thermal damage for low fluence treatments, but noticeable thermal damage at higher fluences. SEM and TEM revealed morphologically similar surfaces for low fluence OPO and excimer samples with a smooth base and no evidence of collagen shrinkage. The Er:YAG and higher fluence OPO treated samples revealed more damage along with visible collagen coagulation and shrinkage in some cases. Healing was remarkably unremarkable. All eyes had a mild healing response with no stromal haze and showed topographic flattening. LM demonstrated nothing except a moderate increase in keratocyte activity in the upper third of the stroma. TEM confirmed this along with irregular basement membranes. Conclusions: A non- thermal ablation process called photospallation is demonstrated for the first time using short pulse infrared lasers yielding damage zones comparable to the excimer and healing which is also comparable to

Application Of The Excimer Laser To Area Recontouring Of The Cornea

NASA Astrophysics Data System (ADS)

Yoder, Paul R.; Telfair, William B.; Warner, John W.; Martin, Clifford A.; L'Esperance, Francis A.

1989-04-01

Excimer lasers operating at 193 nm are being used experimentally in a special type of materials processing wherein the central portion of the anterior surface of the human cornea is selectively ablated so as to change its refractive power and, hopefully, improve impaired vision. Research to date has demonstrated recontouring as a potential means for reducing myopia and hyperopia of cadaver eyes while studies of ablations on the corneas of living monkeys and of blind human volunteers show promise of prompt and successful healing. The procedure has also shown merit in removing superficial scars from the corneal surface. In this paper, we describe the electro-optical system used to deliver the UV laser beam in these experiments and report some preliminary results of the ablation studies.

Investigation of gold and bimetallic gold/silver nanoparticles in soda-lime-silicate glasses formed by means of excimer laser irradiation

NASA Astrophysics Data System (ADS)

Heinz, M.; Dubiel, M.; Meinertz, J.; Ihlemann, J.; Hoell, A.

2017-02-01

In this study, plasmonic Au and Au/Ag nanostructures in soda-lime-silicate glasses have been generated by means of ArF-excimer laser irradiation (193 nm) below the ablation threshold of the glass. For this purpose pure and silver/sodium ion-exchanged float glasses have been coated by gold and then irradiated by the laser. The formation of Au and Au/Ag nanoparticles could be verified by the surface plasmon resonances between 420 and 620 nm, which were obtained by optical spectroscopy. Both, pure Au and Ag particles as well as bimetallic Au/Ag nanoparticles, could be observed by means of small angle X-ray scattering experiments. These results demonstrate that such procedures enable the spaceselected generation of plasmonic nanostructures in glass surfaces by excimer laser irradiation.

Pulse Repetition Frequency Effects In A High Average Power X-Ray Preionised Excimer Laser

NASA Astrophysics Data System (ADS)

Fontaine, Bernard L.; Forestier, Bernard M.; Delaporte, Philippe C.; Canarelli, Patrick

1989-10-01

Experimental study of waves damping in a high repetition rate excimer laser is undertaken. Excitation of laser active medium in a subsonic loop is achieved by means of a classical discharge, through transfer capacitors. The discharge stability is controlled by a wire ion plasma (w.i.p.) X-rays gun. The strong acoustic waves induced by the active medium excitation may lead to a decrease, at high PRF, of the energy per pulse. First results of the influence of a damping of induced density perturbations between two successive pulses are presented.

An alternative method of fabricating sub-micron resolution masks using excimer laser ablation

NASA Astrophysics Data System (ADS)

Hayden, C. J.; Eijkel, J. C. T.; Dalton, C.

2004-06-01

In the work presented here, an excimer laser micromachining system has been used successfully to fabricate high-resolution projection and contact masks. The contact masks were subsequently used to produce chrome-gold circular ac electro-osmotic pump (cACEOP) microelectrode arrays on glass substrates, using a conventional contact photolithography process. The contact masks were produced rapidly (~15 min each) and were found to be accurate to sub-micron resolution, demonstrating an alternative route for mask fabrication. Laser machined masks were also used in a laser-projection system, demonstrating that such fabrication techniques are also suited to projection lithography. The work addresses a need for quick reproduction of high-resolution contact masks, given their rapid degradation when compared to non-contact masks.

Excimer laser correction of hyperopia, hyperopic and mixed astigmatism: past, present, and future.

PubMed

Lukenda, Adrian; Martinović, Zeljka Karaman; Kalauz, Miro

2012-06-01

The broad acceptance of "spot scanning" or "flying spot" excimer lasers in the last decade has enabled the domination of corneal ablative laser surgery over other refractive surgical procedures for the correction of hyperopia, hyperopic and mixed astigmatism. This review outlines the most important reasons why the ablative laser correction of hyperopia, hyperopic and mixed astigmatism for many years lagged behind that of myopia. Most of today's scanning laser systems, used in the LASIK and PRK procedures, can safely and effectively perform low, moderate and high hyperopic and hyperopic astigmatic corrections. The introduction of these laser platforms has also significantly improved the long term refractive stability of hyperopic treatments. In the future, further improvements in femtosecond and nanosecond technology, eye-tracker systems, and the development of new customized algorithms, such as the ray-tracing method, could additionally increase the upper limit for the safe and predictable corneal ablative laser correction ofhyperopia, hyperopic and mixed astigmatism.

Levels of interleukin-6 in tears before and after excimer laser treatment.

PubMed

Resan, Mirko; Stanojević, Ivan; Petković, Aleksandra; Pajić, Bojan; Vojvodić, Danilo

2015-04-01

Immune response and consequent inflammatory process which originate on ocular surface after a trauma are mediated by cytokines. Photoablation of corneal stroma performed by excimer laser causes surgically induced trauma. Interleukin-6 (IL-6) is mostly known as a proinflammatory cytokine. However, it also has regenerative and anti-inflammatory effects. It is supposed that this cytokine is likely to play a significant role in the process of corneal wound healing response after photoablation of stroma carried out by laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) methods. The aim of this study was to determine and compare the levels of IL-6 in tears before and after treatment with LASIK and PRK methods. The study included 68 shortsighted eyes up to -3.0 diopter sphere, i.e. 198 samples of tears (per three samples taken from each of the eyes), divided into two groups according to the kind of excimer laser intervention performed: the group 1--eyes treated by LASIK method (n=31), and the group 2--eyes treated by the PRK method (n=37). The samples of tears were taken from each eye at the following time points: before excimer laser treatment (0 h, the control group), 1 h after the treatment (1 h) and 24 h after the treatment (24 h). The patients did not use anti-inflammatory therapy 24 h after the intervention. Tear samples were collected using microsurgical sponge. Level of IL-6 in tear fluid was determined by the flow cytometry method, applying a commercial test kit which allowed cytokine detection from a small sample volume. Results. The values of IL-6 were detectable in 16% of samples before LASIK treatment and in 30% of samples before PRK treatment. One h after the treatment IL-6 was detectable in 29% of samples for the LASIK group and 43% of samples for the PRK group, and 24 h after the treatment it was detectable in 19% of samples for the LASIK group and in 57% of samples for the PRK group. When we analyzed the dynamics of IL76 production

Photo-triggering and secondary electron produced ionization in electric discharge ArF* excimer lasers

NASA Astrophysics Data System (ADS)

Xiong, Zhongmin; Kushner, Mark J.

2011-10-01

Electric discharge excimer lasers are sustained in multi-atmosphere attaching gas mixtures that are typically preionized to enable a reproducible, uniform glow, which maximizes optical quality and gain. This preionization is often accomplished using UV light produced by a corona discharge within the plasma cavity. To quantify the relationship between corona discharge properties and those of the laser discharge, the triggering of electron avalanche by preionizing UV light in an electric discharge-pumped ArF* excimer laser was numerically investigated using a two-dimensional model. The preionizing UV fluxes were generated by a corona-bar discharge driven by the same voltage pulse as the main discharge sustained in a multi-atmospheric Ne/Ar/Xe/F2 gas mixture. The resulting peak photo-electron density in the inter-electrode spacing is around 108 cm-3, and its distribution is biased toward the UV source. The preionization density increases with increasing dielectric constant and capacitance of the corona bar. The symmetry and uniformity of the discharge are, however, improved significantly once the main avalanche develops. In addition to bulk electron impact ionization, the ionization generated by sheath accelerated secondary electrons was found to be important in sustaining the discharge current at experimentally observed values. At peak current, the magnitude of the ionization by sheath accelerated electrons is comparable to that from bulk electron impact in the vicinity of the cathode.

Update on excimer laser photorefractive keratectomy (PRK) at Cedars-Sinai Medical Center: two-year experience

NASA Astrophysics Data System (ADS)

Maguen, Ezra I.; Salz, James J.; Warren, Cathy; Papaioannou, Thanassis; Nesburn, Anthony B.; Macy, Jonathan I.; Hofbauer, John; Grundfest, Warren S.

1993-06-01

Our two year experience with excimer laser photorefractive keratectomy for the correction of myopia on 160 eyes of 128 patients is described. All eyes were treated with a VISX Twenty- Twenty excimer laser, with the following parameters: radiant exposure 160 mJ/cm2, frequency 5 Hz, ablation zone diameter 5.0 to 5.5 mm, and stromal ablation rate 0.18 to 0.33 (mu) /pulse. A suction fixation ring was used in all cases either with nitrogen flow (79 eyes) or without nitrogen flow (81 eyes) across the cornea. Follow-up ranged from one month (152 eyes) to 24 months (12 eyes). The results are stable between 3 and 24 months with less than 0.25 D change in the mean postoperative spherical equivalents. In eyes with a follow-up of 6 to 24 months, 77% to 100% were 20/40 or better uncorrected, and 84% to 92% were corrected to within +/- 1 D of emmetropia. Further follow-up is needed to assess the long term safety and efficacy of the procedure.

An experimental study on laser drilling and cutting of composite materials for the aerospace industry using excimer and CO2 sources

NASA Astrophysics Data System (ADS)

dell'Erba, M.; Galantucci, L. M.; Miglietta, S.

This paper reports on the results of research which investigated the potential for the application of an excimer laser in the field of composite material drilling and cutting, by comparing this technology with that using CO2 sources. In particular, the scope of the work was to check whether the interaction between excimer lasers and composite materials, whose characteristic feature is the absence of thermal transfer, could yield better results than those obtainable with CO2 sources once heat transfer-induced difficulties had been eliminated. The materials selected for the experiments were multilayer composites having an epoxy resin matrix (65 percent in volume), with aramid fiber (Kevlar), carbon fiber and glass fiber as reinforcing materials, all of considerable interest for the aerospace industry. Optimal operational parameters were identified in relation to each source with a view to obtaining undersize holes or through cuts exhibiting severed areas of good quality. A comparison between the two types of processing carried out show that rims processed by excimer lasers are of better quality - particularly so with Kevlar - whereas the ablation rate is undoubtedly rather low compared with the CO2 technology.

Advanced excimer laser technologies enable green semiconductor manufacturing

NASA Astrophysics Data System (ADS)

Fukuda, Hitomi; Yoo, Youngsun; Minegishi, Yuji; Hisanaga, Naoto; Enami, Tatsuo

2014-03-01

"Green" has fast become an important and pervasive topic throughout many industries worldwide. Many companies, especially in the manufacturing industries, have taken steps to integrate green initiatives into their high-level corporate strategies. Governments have also been active in implementing various initiatives designed to increase corporate responsibility and accountability towards environmental issues. In the semiconductor manufacturing industry, there are growing concerns over future environmental impact as enormous fabs expand and new generation of equipments become larger and more powerful. To address these concerns, Gigaphoton has implemented various green initiatives for many years under the EcoPhoton™ program. The objective of this program is to drive innovations in technology and services that enable manufacturers to significantly reduce both the financial and environmental "green cost" of laser operations in high-volume manufacturing environment (HVM) - primarily focusing on electricity, gas and heat management costs. One example of such innovation is Gigaphoton's Injection-Lock system, which reduces electricity and gas utilization costs of the laser by up to 50%. Furthermore, to support the industry's transition from 300mm to the next generation 450mm wafers, technologies are being developed to create lasers that offer double the output power from 60W to 120W, but reducing electricity and gas consumption by another 50%. This means that the efficiency of lasers can be improve by up to 4 times in 450mm wafer production environments. Other future innovations include the introduction of totally Heliumfree Excimer lasers that utilize Nitrogen gas as its replacement for optical module purging. This paper discusses these and other innovations by Gigaphoton to enable green manufacturing.

Fabrication of self-organized conical microstructures by excimer laser irradiation of cyanoacrylate-carbon nanotube composites

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

Liu Yuming; Liu Liang; Fan Shoushan

2005-02-07

Self-organized conical microstructures are fabricated by 308 nm XeCl excimer laser irradiation of cyanoacrylate-carbon nanotube composites in air. The morphology of the surface on the composite films is studied, varying the total number and fluence of the applied laser pulses. A simple mechanism of the fabrication based on the evaporation of cyanoacrylate and the burning of carbon nanotubes is proposed. The conical peak structures of cyanoacrylate-carbon nanotube composite films show good field-emission properties. Similar structures are also observed on carbon nanotube arrays.

Cracking and Exfoliation of TiO2 Film Irradiated with Excimer Laser

NASA Astrophysics Data System (ADS)

Qian, H. X.; Zhou, W.; Zheng, H. Y.

TiO2 film deposited on glass was irradiated in air with single-shot KrF excimer laser pulse. The surface roughened as the result of the laser ablation. It is further noted that single-pulse irradiation with fluence ranging from 400 to 1200 mJ/cm2 gave rise to protrusion of the irradiated surface above the original surface, which is in contrast to usual expectation that irradiated surface is below the unirradiated surface. The surface protrusion is mainly attributed to the effect of surface tension. At the laser fluence of 1000 mJ/cm2, cracks were formed in the irradiated area and severe film exfoliation was observed at the periphery of the irradiated area due to the release of internal stress. With higher laser fluence above 1000 mJ/cm2, patches of film were observed to peel off within the irradiated areas. Hydrodynamic ablation is proposed to account for film exfoliation. The observed phenomenon is useful for further understanding how TiO2 film reacts to strong UV laser irradiation.

[Histopathological study of wound healing process of rat tongue and femur by excimer laser irradiation--possibility of cutting of vital tissue by laser irradiation].

PubMed

Ochiai, S

1990-12-01

The possibilities of bone and soft tissue ablation without thermal damage by 248 nm KrF excimer laser irradiation were examined. A defect was made on the rat tongue by laser at pulse width: 15 nsec, power density: 12 W/cm2, pulse repetition rate: 20 Hz and irradiated time: 60 seconds. The same size defect was made by stainless steel surgical knife for control. The tongues were examined histopathologically at timed sequence from 1 hour to 7 days after operation. The rat femur was cut by laser at pulse width: 15 nsec, power density: 2.6 kW/cm2, pulse repetition rate: 30 Hz and irradiated time: 3 minutes. The femur was amputated by dental diamond disc for control. The femurs were examined histopathologically at timed sequence from 1 hour to 16 weeks after operation. The rat tongue was easily excised with little thermal injury by laser irradiation, and its healing process is almost the same as that of the control. The laser irradiation had no hemostatic effect. The femur could be amputated by laser irradiation but its wound healing was prolonged. The laser ablation stump showed massive necrosis probably due to the thermal injury and these necrotic bones likely disturbed the wound repair. The degree of the thermal injury by the excimer laser irradiation might depend on the irradiation condition because the condition of bone amputation was stronger than that of tongue excision.

Design Considerations For A Clinical XeC1 Excimer Laser Angioplasty System

NASA Astrophysics Data System (ADS)

Laudenslager, James B.; Goldenberg, Tsvi; Naghieh, Harry R.; Pham, Andrew A.; Narciso, Hugh L.; Tranis, Art; Pacala, Thomas J.

1989-09-01

Laser ablation and removal of intravascular plaque has long been a goal of physicians and physicists as an alternative treatment for coronary and peripheral artery disease. Early application of cw free light beam visible and infrared lasers such as argon ion or Nd:YAG lasers for this application were plagued by thermal side effects of the ablation process. Specifically, imprecise control of the boundary tissue injury produced by the deep penetration depth of the laser beam gave rise to early reclosure of the vessel due to the thermal nature of the ablation process. Pulsed ultraviolet laser free beam ablation of atherosclerotic plaque, however, does not produce thermal effects, cuts tissue precisely leaving a smooth wall and can ablate hard calcific lesions. We have chosen to develop a XeC1 excimer laser-fiberoptic delivery system for the clinical application of laser angioplasty based on achieving the desired therapeutic results for a laser revascularization procedure. Four major engineering design issues must be considered in order to produce a successful clinical laser angioplasty product. These engineering issues are: 1) Functional clinical engineering, 2) Regulatory design issues, 3) Hospital facility and user requirements, and 4) Economic issues for the manufacturer, the hospital and the patient.

Surface morphology and subsurface damaged layer of various glasses machined by 193-nm ArF excimer laser

NASA Astrophysics Data System (ADS)

Liao, Yunn-shiuan; Chen, Ying-Tung; Chao, Choung-Lii; Liu, Yih-Ming

2005-01-01

Owing to the high bonding energy, most of the glasses are removed by photo-thermal rather than photo-chemical effect when they are ablated by the 193 or 248nm excimer lasers. Typically, the machined surface is covered by re-deposited debris and the sub-surface, sometimes surface as well, is scattered with micro-cracks introduced by thermal stress generated during the process. This study aimed to investigate the nature and extent of the surface morphology and sub-surface damaged (SSD) layer induced by the laser ablation. The effects of laser parameters such as fluence, shot number and repetition rate on the morphology and SSD were discussed. An ArF excimer laser (193 nm) was used in the present study to machine glasses such as soda-lime, Zerodur and BK-7. It is found that the melt ejection and debris deposition tend to pile up higher and become denser in structure under a higher energy density, repetition rate and shot number. There are thermal stress induced lateral cracks when the debris covered top layer is etched away. Higher fluence and repetition rate tend to generate more lateral and median cracks which propagate into the substrate. The changes of mechanical properties of the SSD layer were also investigated.

Improved model for the angular dependence of excimer laser ablation rates in polymer materials

NASA Astrophysics Data System (ADS)

Pedder, J. E. A.; Holmes, A. S.; Dyer, P. E.

2009-10-01

Measurements of the angle-dependent ablation rates of polymers that have applications in microdevice fabrication are reported. A simple model based on Beer's law, including plume absorption, is shown to give good agreement with the experimental findings for polycarbonate and SU8, ablated using the 193 and 248 nm excimer lasers, respectively. The modeling forms a useful tool for designing masks needed to fabricate complex surface relief by ablation.

The Improvement of Electrical Characteristics of Pt/Ti Ohmic Contacts to Ga-Doped ZnO by Homogenized KrF Pulsed Excimer Laser Treatment

NASA Astrophysics Data System (ADS)

Oh, Min-Suk

2018-04-01

We investigated the effect of KrF excimer laser surface treatment on Pt/Ti ohmic contacts to Ga-doped n-ZnO ( N d = 4.3 × 1017 cm-3). The treatment of the n-ZnO surfaces by laser irradiation greatly improved the electrical characteristics of the metal contacts. The Pt/Ti ohmic layer on the laser-irradiated n-ZnO showed specific contact resistances of 2.5 × 10-4 ˜ 4.8 × 10-4 Ω cm2 depending on the laser energy density and gas ambient, which were about two orders of magnitude lower than that of the as-grown sample, 8.4 × 10-2 Ω cm2. X-ray photoelectron spectroscopy and photoluminescence measurements showed that the KrF excimer laser treatments increased the electron concentration near the surface region of the Ga-doped n-ZnO due to the preferential evaporation of oxygen atoms from the ZnO surface by the laser-induced dissociation of Zn-O bonds.

Depth-profile investigations of triterpenoid varnishes by KrF excimer laser ablation and laser-induced breakdown spectroscopy

NASA Astrophysics Data System (ADS)

Theodorakopoulos, C.; Zafiropulos, V.

2009-07-01

The ablation properties of aged triterpenoid dammar and mastic films were investigated using a Krypton Fluoride excimer laser (248 nm, 25 ns). Ablation rate variations between surface and bulk layers indicated changes of the ablation mechanisms across the depth profiles of the films. In particular, after removal of the uppermost surface varnish layers there was a reduction of the ablation step in the bulk that was in line with a significant reduction of carbon dimer emission beneath the surface layers as detected by laser-induced breakdown spectroscopy. The results are explicable by the generation of condensation, cross-linking and oxidative gradients across the depth profile of triterpenoid varnish films during the aging degradation process, which were recently quantified and established on the molecular level.

Cleaning of copper traces on circuit boards with excimer laser radiation

NASA Astrophysics Data System (ADS)

Wesner, D. A.; Mertin, M.; Lupp, F.; Kreutz, E. W.

1996-04-01

Cleaning of Cu traces on circuit boards is studied using pulsed excimer laser radiation (pulse width ˜ 20 ns, wavelength 248 nm), with the goal of improving the properties of the Cu surface for soldering and bonding. Traces with well-defined oxide overlayers are cleaned by irradiation in air using ≤ 10 3 laser pulses at fluences per pulse of ≤ 2 J cm -2. After treatment the surface morphology is analyzed using optical microscopy, optical profilometry, and scanning electron microscopy, while the chemical state of the surface is investigated with X-ray photoelectron (XPS) spectroscopy. Ellipsometry is used to determine the oxide overlayer thickness. Prior to cleaning samples exhibit a contamination overlayer about 15-25 nm in thickness containing Cu 2O and C. Cleaning reduces the overlayer thickness to ≤ 10 nm by material removal. The process tends to be self-limiting, since the optical reflectivity of the oxidized Cu surface for laser radiation is smaller than that of the cleaned surface. Additionally, the interaction with the laser radiation results in surface segregation of a minor alloy component out of the bulk (e.g. Zn), which may help to passivate the surface for further chemical reactions.

Analyses of surface coloration on TiO 2 film irradiated with excimer laser

NASA Astrophysics Data System (ADS)

Zheng, H. Y.; Qian, H. X.; Zhou, W.

2008-01-01

TiO 2 film of around 850 nm in thickness was deposited on a soda-lime glass by PVD sputtering and irradiated using one pulse of krypton-fluorine (KrF) excimer laser (wavelength of 248 nm and pulse duration of 25 ns) with varying fluence. The color of the irradiated area became darker with increasing laser fluence. Irradiated surfaces were characterized using optical microscopy, scanning electron microscopy, Raman spectroscopy and atomic force microscopy. Surface undergoes thermal annealing at low laser fluence of 400 and 590 mJ/cm 2. Microcracks at medium laser fluence of 1000 mJ/cm 2 are attributed to surface melting and solidification. Hydrodynamic ablation is proposed to explain the formation of micropores and networks at higher laser fluence of 1100 and 1200 mJ/cm 2. The darkening effect is explained in terms of trapping of light in the surface defects formed rather than anatase to rutile phase transformation as reported by others. Controlled darkening of TiO 2 film might be used for adjustable filters.

Wavefront-optimized laser in situ keratomileusis with the Allegretto Wave Eye-Q excimer laser and the FEMTO LDV Crystal Line femtosecond laser: 6 month visual and refractive results.

PubMed

Ziaei, Mohammed; Mearza, Ali A; Allamby, David

2015-08-01

To present the first reported series of patients undergoing myopic LASIK with the FEMTO LDV Crystal Line femtosecond laser and the WaveLight Allegretto Eye-Q excimer laser. We report the uncorrected and corrected distance visual acuity (UDVA and CDVA), refractive predictability, efficacy and safety of laser in situ keratomileusis (LASIK) performed with the above laser platforms. This prospective interventional case series study evaluated consecutive eyes with low to moderate myopic astigmatism that underwent LASIK with the FEMTO LDV Crystal Line femtosecond laser and the WaveLight Allegretto Eye-Q 400 Hz excimer laser. Visual and refractive changes as well as complications were evaluated after wavefront-optimized laser treatment. Four hundred and forty four patients (887 eyes) reached the 6-month time gate. Mean age at time of procedure was 31 years (range: 20-59). Mean pre-op spherical-equivalent (SE) was -3.44 diopters (D)±1.34D (range: -0.50 to -7.00) whilst the postoperative spherical equivalent decreased to -0.08±0.31D (range -2.25 to 1.00). At 6-month follow up, 96.9% of patients had monocular uncorrected distance visual acuity of 20/20 or better with 95.2% of patients within ±0.5D of intended refractive outcome. All patients achieved 20/20 binocular distance uncorrected visual acuity. No significant intra-operative or postoperative complications were encountered during the 6-month follow-up period. The combination of the above laser platforms provides safe, effective and predictable results in correcting compound myopic astigmatism with excellent visual outcomes. Copyright © 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

Outcomes of LASIK for Myopia or Myopic Astigmatism Correction with the FS200 Femtosecond Laser and EX500 Excimer Laser Platform

PubMed Central

Niparugs, Muanploy; Tananuvat, Napaporn; Chaidaroon, Winai; Tangmonkongvoragul, Chulaluck; Ausayakhun, Somsanguan

2018-01-01

Purpose: To evaluate the efficacy, predictability, stability and safety of laser in situ keratomileusis (LASIK) using the FS200 femtosecond laser and EX500 excimer laser platform. Methods: The outcomes of 254 eyes of 129 consecutive patients with myopia or myopic astigmatism who underwent full correction femtosecond laser-assisted LASIK at CMU LASIK Center were assessed. Pre-operative and post-operative parameters including manifest refraction, Uncorrected Distance Visual Acuity (UDVA), Best Corrected Distance Visual Acuity (BDVA), corneal topography and tomography were analyzed. The results between low to moderate myopia and high myopia were compared up to 12 months. Results: Mean pre-operative Spherical Equivalent (SE) was -5.15±2.41 Diopters (D) (range -0.50 to -11.50 D) and -0.13±0.28 D, -0.13±0.27 D, -0.13±0.28 D and -0.14±0.30 D at 1, 3, 6, and 12 months, post-operatively. At 12 months, the propor¬tion of eyes achieving UDVA ≥ 20/20 was 90.0% and ≥20/40 was 98.8%. The proportion of eyes achieving post-operative mean SE ±0.5 D, and ±1 D was 91.3%, and 98.5%. No eyes lost more than two lines of BDVA. The low to moderate myopic group had a statistically significant better UDVA at one (p=0.017) and three months (p=0.014) but no difference at six (p=0.061) and 12 months (p=0.091). The mean post-operative SE was better in low to moderate myopic group at every follow-up visit (p=0.001, 0.007, <0.001 and <0.001). Conclusion: One-year clinical results of LASIK with the FS200 femtosecond laser and EX500 excimer laser showed high efficacy, predictability, stability and safety. PMID:29872485

Excimer laser decoating of chromium titanium aluminium nitride to facilitate re-use of cutting tools

NASA Astrophysics Data System (ADS)

Sundar, M.; Whitehead, D.; Mativenga, P. T.; Li, L.; Cooke, K. E.

2009-11-01

This work reports on the technical feasibility and establishment of a process window for removing chromium titanium aluminium nitride (CrTiAlN) coating from steel substrates by laser irradiation. CrTiAlN coating has high hardness and oxidation resistance, with applications for use with cutting tools. The motivation for removing such coatings is to facilitate re-use of tooling by enabling regrinding or reshaping of a worn tool and hence promote sustainable material usage. In this work, laser decoating was performed using an excimer laser. The effect of laser fluence, number of pulses, frequency, scanning speed and laser beam overlap on the decoating performance was investigated in detail. The minimum threshold laser fluence for removing the CrTiAlN coating was lower than that of the steel substrate and this factor is beneficial in controlling the decoating process. Successful laser removal of CrTiAlN coating without noticeable damage to the steel substrate was demonstrated.

Safety, efficacy, predictability and stability of laser in situ keratomileusis (LASIK) with a 1000-Hz scanning spot excimer laser.

PubMed

Khoramnia, Ramin; Salgado, Josefina P; Wuellner, Christian; Donitzky, Christof; Lohmann, Chris P; Winkler von Mohrenfels, Christoph

2012-09-01

To evaluate the safety, efficacy, predictability and stability of laser in situ keratomileusis (LASIK) with a 1000-Hz scanning spot excimer laser (Concept System 1000; WaveLight GmbH, Erlangen, Germany). LASIK was performed on twenty eyes with myopia or myopic astigmatism (mean spherical equivalent refraction: -3.97±1.72 dioptres (D); mean cylinder: -0.84±0.77 D) using a microkeratome for flap creation and the Concept System 1000 for photoablation. Patients were examined preoperatively as well as 1, 3 and 6 months after the treatment. Manifest sphere and cylinder, uncorrected (UCDVA) and best corrected (BCDVA) distance visual acuity, corneal topography and pachymetry were analysed. We observed no adverse events that might have been associated with the use of a repetition rate of 1000 Hz. All eyes maintained or had improved BCDVA at 6 months after treatment when compared to preoperative values. Six months after LASIK, UCDVA was 20/20 or better in 85% and 20/25 or better in 100% of the eyes. The spherical equivalent refraction was within ±0.50 D in 95% of the eyes at 6 months after surgery. The refraction stayed stable over time; 95% of the eyes changed<0.5 D postoperatively. LASIK with the prototype 1000-Hz excimer laser was safe, efficient and predictable. The postoperative refraction was stable over time. There were no specific clinical side-effects that might be associated with the use of such a high repetition rate. © 2011 The Authors. Acta Ophthalmologica © 2011 Acta Ophthalmologica Scandinavica Foundation.

CAD/CAM interface design of excimer laser micro-processing system

NASA Astrophysics Data System (ADS)

Jing, Liang; Chen, Tao; Zuo, Tiechuan

2005-12-01

Recently CAD/CAM technology has been gradually used in the field of laser processing. The excimer laser micro-processing system just identified G instruction before CAD/CAM interface was designed. However the course of designing a part with G instruction for users is too hard. The efficiency is low and probability of making errors is high. By secondary development technology of AutoCAD with Visual Basic, an application was developed to pick-up each entity's information in graph and convert them to each entity's processing parameters. Also an additional function was added into former controlling software to identify these processing parameters of each entity and realize continue processing of graphic. Based on the above CAD/CAM interface, Users can design a part in AutoCAD instead of using G instruction. The period of designing a part is sharply shortened. This new way of design greatly guarantees the processing parameters of the part is right and exclusive. The processing of complex novel bio-chip has been realized by this new function.

Calcified lesion modeling for excimer laser ablation

NASA Astrophysics Data System (ADS)

Scott, Holly A.; Archuleta, Andrew; Splinter, Robert

2009-06-01

Objective: Develop a representative calcium target model to evaluate penetration of calcified plaque lesions during atherectomy procedures using 308 nm Excimer laser ablation. Materials and Methods: An in-vitro model representing human calcified plaque was analyzed using Plaster-of-Paris and cement based composite materials as well as a fibrinogen model. The materials were tested for mechanical consistency. The most likely candidate(s) resulting from initial mechanical and chemical screening was submitted for ablation testing. The penetration rate of specific multi-fiber catheter designs and a single fiber probe was obtained and compared to that in human cadaver calcified plaque. The effects of lasing parameters and catheter tip design on penetration speed in a representative calcified model were verified against the results in human cadaver specimens. Results: In Plaster of Paris, the best penetration was obtained using the single fiber tip configuration operating at 100 Fluence, 120 Hz. Calcified human lesions are twice as hard, twice as elastic as and much more complex than Plaster of Paris. Penetration of human calcified specimens was highly inconsistent and varied significantly from specimen to specimen and within individual specimens. Conclusions: Although Plaster of Paris demonstrated predictable increases in penetration with higher energy density and repetition rate, it can not be considered a totally representative laser ablation model for calcified lesions. This is in part due to the more heterogeneous nature and higher density composition of cadaver intravascular human calcified occlusions. Further testing will require a more representative model of human calcified lesions.

Effects of excimer laser illumination on microdrilling into an oblique polymer surface

NASA Astrophysics Data System (ADS)

Wu, Chih-Yang; Shu, Chun-Wei; Yeh, Zhi-Chang

2006-08-01

In this work, we present the experimental results of micromachining into polymethy-methacrylate exposed to oblique KrF excimer laser beams. The results of low-aspect-ratio ablations show that the ablation rate decreases monotonously with the increase of incident angle for various fluences. The ablation rate of high-aspect-ratio drilling with opening center on the focal plane is almost independent of incident angles and is less than that of low-aspect-ratio ablation. The results of high-aspect-ratio ablations show that the openings of the holes at a distance from the focal plane are enlarged and their edges are blurred. Besides, the depth of a hole in the samples oblique to the laser beam at a distance from the focal plane decreases with the increase of the distance from the focal plane. The number of deep holes generated by oblique laser beams through a matrix of apertures decreases with the increase of incident angle. Those phenomena reveal the influence of the local light intensity on microdrilling into an oblique surface.

Treatment of moderate-to-high hyperopia with the WaveLight Allegretto 400 and EX500 excimer laser systems

PubMed Central

Motwani, Manoj; Pei, Ronald

2017-01-01

Purpose To evaluate the efficacy of treating patients with +3.00 diopters (D) to +6.00 D of hyperopia via laser-assisted in situ keratomileusis (LASIK) with the WaveLight Allegretto 400 and EX500 excimer laser systems. Setting Private clinical ophthalmology practice. Patients and methods This was a retrospective study of patients undergoing LASIK treatments of +3.00 to +6.00 D on two different WaveLight laser systems: 163 eyes on the 400 (Hertz) Hz system and 54 eyes on the 500 Hz system. The duration of follow-up was 6 months postoperation. Data were evaluated for uncorrected distance visual acuity, corrected distance visual acuity (CDVA), spherical equivalents (SEQs), and changes in these parameters (eg, loss of vision, regression over time). Results Treatment with both lasers was safe and effective, with loss of one line of CDVA in four of 162 eyes using the 400 Hz laser system, and none of the 54 eyes with the 500 Hz laser system. Overall, regression ≥0.75 D from goal at 6 months was observed in 11.7% (19/163) of eyes in the 400 Hz laser group and 9.26% (5/54) of eyes in the 500 Hz laser group (regression ≥0.50 D =77.9% [127/163] and 77.8% [42/54], respectively). The mean SEQ regressions for all eyes with moderate hyperopia were 0.10 and 0.18 D for those with high hyperopia. Conclusions Both the 400 and 500 Hz excimer laser systems were safe and effective for the LASIK treatment of moderate-to-high hyperopia. The overall rate of regression was low and the amount of regression was relatively small with both systems. PMID:28579751

Determination of etching parameters for pulsed XeF2 etching of silicon using chamber pressure data

NASA Astrophysics Data System (ADS)

Sarkar, Dipta; Baboly, M. G.; Elahi, M. M.; Abbas, K.; Butner, J.; Piñon, D.; Ward, T. L.; Hieber, Tyler; Schuberth, Austin; Leseman, Z. C.

2018-04-01

A technique is presented for determination of the depletion of the etchant, etched depth, and instantaneous etch rate for Si etching with XeF2 in a pulsed etching system in real time. The only experimental data required is the pressure data collected temporally. Coupling the pressure data with the knowledge of the chemical reactions allows for the determination of the etching parameters of interest. Using this technique, it is revealed that pulsed etching processes are nonlinear, with the initial etch rate being the highest and monotonically decreasing as the etchant is depleted. With the pulsed etching system introduced in this paper, the highest instantaneous etch rate of silicon was recorded to be 19.5 µm min-1 for an initial pressure of 1.2 Torr for XeF2. Additionally, the same data is used to determine the rate constant for the reaction of XeF2 with Si; the reaction is determined to be second order in nature. The effect of varying the exposed surface area of Si as well as the effect that pressure has on the instantaneous etch rate as a function of time is shown applying the same technique. As a proof of concept, an AlN resonator is released using XeF2 pulses to remove a sacrificial poly-Si layer.

Irradiation planning for automated treatment of psoriasis with a high-power excimer laser

NASA Astrophysics Data System (ADS)

Klämpfl, Florian; Schmidt, Michael; Hagenah, Hinnerk; Görtler, Andreas; Wolfsgruber, Frank; Lampalzer, Ralf; Kaudewitz, Peter

2006-02-01

American and European statistics have shown that 1-2 per cent of the human population is affected by the skin disease psoriasis. Recent research reports promising treatment results when irradiating skin areas affected by psoriasis with high powered excimer lasers with a wavelength of 308 nm. In order to apply the necessary high energy dose without hurting healthy parts of the skin new approaches regarding the system technology must be considered. The aim of the current research project is the development of a sensor-based, automated laser treatment system for psoriasis. In this paper we present the algorithms used to cope with the diffculties of irradiating irregularly shaped areas on curved surfaces with a predefined energy level using a pulsed laser. Patients prefer the treatment to take as little time as possible. This also helps to reduce costs. Thus the distribution of laser pulses on the surface to achieve the given energy level on every point of the surface has to be calculated within a limited time frame. The remainder of the paper will describe in detail an efficient method to plan and optimize the laser pulse distribution. Towards the end, some first results will be presented.

A retrospective comparison of efficacy and safety of 680 consecutive lasik treatments for high myopia performed with two generations of flying-spot excimer lasers.

PubMed

Gazieva, Lola; Beer, Mette Hjuler; Nielsen, Kim; Hjortdal, Jesper

2011-12-01

To compare the visual refractive outcome and complication of laser in situ keratomileusis (LASIK) carried out with a Carl Zeiss-Meditec MEL-70 Excimer laser and a MEL-80 laser for treatment of high myopia. Journal records of 680 consecutive eyes that underwent LASIK with a Schwind Supratome microkeratome and a MEL-70 Excimer laser (Group A), or a Moria M2 microkeratome and a MEL-80 Excimer laser (Group B) were reviewed. Manifest refraction, uncorrected and best spectacle-corrected visual acuity (BSCVA), corneal topography and central corneal thickness (CCT) were recorded before and 3 months after treatment. Pre- and postoperative complications, visual and refractive outcome and frequency of retreatments were registered. Mean preoperative spherical equivalent refraction was -8.52 dioptres (-5.50- -18 dioptres), and the mean attempted laser correction was -8.02 dioptres (-5.50- -11 dioptres). Three months after LASIK, the average treatment error (difference between achieved and attempted correction) was 1.20 (SD=1.19) dioptres of under correction in Group A and 0.52 (SD=1.00) dioptres in Group B. Four eyes lost more than two lines of BSCVA (0.6%). In 110 eyes (16%), a re-LASIK procedure was performed to reduce remaining myopia after the primary procedure. Laser in situ keratomileusis treatment for high myopia can effectively reduce high degrees of myopia. Under correction was observed in both treatment groups but Group B has a slightly better predictability. Significant loss of BSCVA occurs infrequently after LASIK for even considerable grades of myopia (0.6% in each group). © 2010 The Authors. Journal compilation © 2010 Acta Ophthalmol.

Negative charge emission due to excimer laser bombardment of sodium trisilicate glass

NASA Astrophysics Data System (ADS)

Langford, S. C.; Jensen, L. C.; Dickinson, J. T.; Pederson, L. R.

1990-10-01

We describe measurements of negative charge emission accompanying irradiation of sodium trisilicate glass (Na2Oṡ3SiO2) with 248-nm excimer laser light at fluences on the order of 2 J/cm2 per pulse, i.e., at the threshold for ablative etching of the glass surface. The negative charge emission consists of a very prompt photoelectron burst coincident with the laser pulse, followed by a much slower plume of electrons and negative ions traveling with a high density cloud of positive ions, previously identified as primarily Na+. Using combinations of E and B fields in conjunction with time-of-flight methods, the negative ions were successfully separated from the plume and tentatively identified as O-, Si-, NaO-, and perhaps NaSi-. These negative species are probably formed by gas phase collisions in the near-surface region which result in electron attachment.

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.

Influence of the ablation plume on the removal process during ArF-excimer laser photoablation

NASA Astrophysics Data System (ADS)

Doerbecker, Christina; Lubatschowski, Holger; Lohmann, Stefan; Ruff, Christine; Kermani, Omid; Ertmer, Wolfgang

1996-01-01

Correction of myopia with the ArF-excimer laser (PRK) sometimes leads to a so called 'central island' formation on the anterior corneal surface. The attenuation of the laser beam by the ablation plume might be one reason for this phenomenon. The attenuation properties of the ablation plume were investigated by a probe beam parallel to the surface of the tissue probe. By varying the laser parameters (fluence, repetition rate, spot size) and the target tissue (cornea, PMMA) the attenuation of the probe beam was measured time and spatial resolved. As a result of this study, a significant influence of the removal process due to scattering and absorption within the ablation plume can be assumed as a function of repetition rate, spot size and air flow on the tissue surface.

Performance characteristics of an excimer laser (XeCl) with single-stage magnetic pulse compression

NASA Astrophysics Data System (ADS)

Varshnay, N. K.; Singh, A.; Benerji, N. S.

2017-02-01

Performance characteristics of an excimer laser (XeCl) with single-stage magnetic pulse compression suitable for material processing applications are presented here. The laser incorporates in-built compact gas circulation and gas cooling to ensure fresh gas mixture between the electrodes for repetitive operation. A magnetically coupled tangential blower is used for gas circulation inside the laser chamber for repetitive operation. The exciter consists of C-C energy transfer circuit and thyratron is used as a high-voltage main switch with single-stage magnetic pulse compression (MPC) between thyratron and the laser electrodes. Low inductance of the laser head and uniform and intense pre-ionization are the main features of the electric circuit used in the laser. A 250 ns rise time voltage pulse was compressed to 100 ns duration with a single-stage magnetic pulse compressor using Ni-Zn ferrite cores. The laser can generate about 150 mJ at ˜100 Hz rep-rate reliably from a discharge volume of 100 cm 3. 2D spatial laser beam profile generated is presented here. The profile shows that the laser beam is completely filled with flat-top which is suitable for material processing applications. The SEM image of the microhole generated on copper target is presented here.

Preliminary results of VISX excimer laser myopic photorefractive keratectomy at Cedars-Sinai Medical Center

NASA Astrophysics Data System (ADS)

Maguen, Ezra I.; Berlin, Michael S.; Hofbauer, John; Macy, Jonathan I.; Nesburn, Anthony B.; Papaioannou, Thanassis; Salz, James J.

1992-08-01

Sixty-two eyes underwent excimer laser photorefractive keratectomy (PRK) for the correction of myopia at Cedars-Sinai-Medical-Center. The first group of 12 patients are presented with follow up data of ten months postoperatively. The second group of 50 patients are presented with follow up data of three months postoperatively. An in-depth comparison of pre and postoperative refractive data is presented. Comparisons between pre and postoperative corrected and uncorrected Snellen visual acuities are provided in order to asses the functional visual result of the procedure.

Topography-guided treatment of irregular astigmatism with the wavelight excimer laser.

PubMed

Jankov, Mirko R; Panagopoulou, Sophia I; Tsiklis, Nikolaos S; Hajitanasis, Georgos C; Aslanides, loannis M; Pallikaris, loannis G

2006-04-01

To evaluate the feasibility, safety, and predictability of correcting high irregular astigmatism in symptomatic eyes with the use of topography-guided photoablation. In a prospective, non-comparative case series, 16 consecutive symptomatic eyes of 11 patients with small hyperopic and myopic excimer laser optical zones, decentered and irregular ablation after corneal graft, and corneal scars were operated. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest and cycloplegic refraction, and corneal topography, with asphericity and regularity, were analyzed. LASIK (n = 10) and photorefractive keratectomy (n = 6) were performed using the ALLEGRETTO WAVE excimer laser and T-CAT software (Topography-guided Customized Ablation Treatment; WaveLight Laser Technologie AG, Erlangen, Germany). In the LASIK group, UCVA improved from 0.81 +/- 0.68 IogMAR (20/130) (range: 0.2 to 2.0) to 0.29 +/- 0.21 logMAR (20/39) (range: 0.1 to 0.7) at 6 months. In the PRK group, mean UCVA improved from 0.89 +/- 0.87 IogMAR (20/157) (range: 0.1 to 2.0) to 0.42 +/- 0.35 logMAR (20/53) (range: 0.1 to 1.0) at 6 months. Best spectacle-corrected visual acuity did not change significantly in either group. One PRK patient lost one line of BSCVA. Refractive cylinder for the LASIK group improved from -2.53 +/- 1.71 diopters (D) (range: -0.75 to -5.75 D) to -1.28 +/- 0.99 D (range: 0 to -2.50 D) at 6 months. Refractive cylinder in the PRK group improved from -2.21 +/- 2.11 D (range: -0.25 to -5.50 D) to -1.10 +/- 0.42 D (range: -0.50 to -1.50 D). Index of surface irregularity showed a decrease from 60 +/- 12 (range: 46 to 89) to 50 +/- 9 (range: 32 to 63) at 6 months in the LASIK group whereas no significant change was noted in the PRK group. Subjective symptoms, such as glare, halos, ghost images, starbursts, and monocular diplopia, were not present postoperatively. Topography-guided LASIK and PRK resulted in a significant reduction of refractive cylinder and

Comparison of 2 wavefront-guided excimer lasers for myopic laser in situ keratomileusis: one-year results.

PubMed

Yu, Charles Q; Manche, Edward E

2014-03-01

To compare laser in situ keratomileusis (LASIK) outcomes between 2 wavefront-guided excimer laser systems in the treatment of myopia. University eye clinic, Palo Alto, California, USA. Prospective comparative case series. One eye of patients was treated with the Allegretto Wave Eye-Q system (small-spot scanning laser) and the fellow eye with the Visx Star Customvue S4 IR system (variable-spot scanning laser). Evaluations included measurement of uncorrected visual acuity, corrected visual acuity, and wavefront aberrometry. One hundred eyes (50 patients) were treated. The mean preoperative spherical equivalent (SE) refraction was -3.89 diopters (D) ± 1.67 (SD) and -4.18 ± 1.73 D in the small-spot scanning laser group and variable-spot scanning laser group, respectively. There were no significant differences in preoperative higher-order aberrations (HOAs) between the groups. Twelve months postoperatively, all eyes in the small-spot scanning laser group and 92% in the variable-spot scanning laser group were within ±0.50 D of the intended correction (P = .04). At that time, the small-spot scanning laser group had significantly less spherical aberration (0.12 versus 0.15) (P = .04) and significantly less mean total higher-order root mean square (0.33 μm versus 0.40 μm) (P = .01). Subjectively, patients reported that the clarity of night and day vision was significantly better in the eye treated with the small-spot scanning laser. The predictability and self-reported clarity of vision of wavefront-guided LASIK were better with the small-spot scanning laser. Eyes treated with the small-spot scanning laser had significantly fewer HOAs. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

UV excimer laser and low temperature plasma treatments of polyamide materials

NASA Astrophysics Data System (ADS)

Yip, Yiu Wan Joanne

Polyamides have found widespread application in various industrial sectors, for example, they are used in apparel, home furnishings and similar uses. However, the requirements for high quality performance products are continually increasing and these promote a variety of surface treatments for polymer modification. UV excimer laser and low temperature plasma treatments are ideally suited for polyamide modification because they can change the physical and chemical properties of the material without affecting its bulk features. This project aimed to study the modification of polyamides by UV excimer laser irradiation and low temperature plasma treatment. The morphological changes in the resulting samples were analysed by scanning electron microscopy (SEM) and tapping mode atomic force microscopy (TM-AFM). The chemical modifications were studied by x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and chemical force microscopy (CFM). Change in degree of crystallinity was examined by differential scanning calorimetry (DSC). After high-fluence laser irradiation, topographical results showed that ripples of micrometer size form on the fibre surface. By contrast, sub-micrometer size structures form on the polyamide surface when the applied laser energy is well below its ablation threshold. After high-fluence laser irradiation, chemical studies showed that the surface oxygen content of polyamide is reduced. A reverse result is obtained with low-fluence treatment. The DSC result showed no significant change in degree of crystallinity in either high-fluence or low-fluence treated samples. The same modifications in polyamide surfaces were studied after low temperature plasma treatment with oxygen, argon or tetrafluoromethane gas. The most significant result was that the surface oxygen content of polyamide increased after oxygen and argon plasma treatments. Both treatments induced many hydroxyl (-OH) and carboxylic acid (-COOH

An airborne compatible photofragmentation two-photon laser-induced fluorescence instrument for measuring background tropospheric levels of NO, NO(x), and NO2

NASA Technical Reports Server (NTRS)

Sandholm, S. T.; Bradshaw, J. D.; Dorris, K. S.; Rodgers, M. O.; Davis, D. D.

1990-01-01

The operating principle, design, and performance of a two-photon LIF (TP-LIF) sensor for simultaneous measurements of NO, NO(x) (NO + NO2), and NO2 are described. In this instrument, NO is first measured by direct spectroscopic TP-LIF detection; NO2 is converted to NO by photofragmentation using an XeF excimer laser operating at 353 nm; and the resulting NO is then detected quantitatively by TP-LIF. The detection limits of the instrument are found to be 3.5 parts per trillion by volume (pptv) of NO and 10 pptv for NO2, with integration times of 2 and 6 min, respectively. The in-flight performance of the instrument was evaluated during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 program in summer 1986, as reported by Gregory et al. (1990).

Diamagnetic to ferromagnetic switching in VO2 epitaxial thin films by nanosecond excimer laser treatment

NASA Astrophysics Data System (ADS)

Molaei, R.; Bayati, R.; Nori, S.; Kumar, D.; Prater, J. T.; Narayan, J.

2013-12-01

VO2(010)/NiO(111) epitaxial heterostructures were integrated with Si(100) substrates using a cubic yttria-stabilized zirconia (c-YSZ) buffer. The epitaxial alignment across the interfaces was determined to be VO2(010)‖NiO(111)‖c-YSZ(001)‖Si(001) and VO2[100]‖NiO⟨110⟩‖c-YSZ⟨100⟩‖Si⟨100⟩. The samples were subsequently treated by a single shot of a nanosecond KrF excimer laser. Pristine as-deposited film showed diamagnetic behavior, while laser annealed sample exhibited ferromagnetic behavior. The population of majority charge carriers (e-) and electrical conductivity increased by about two orders of magnitude following laser annealing. These observations are attributed to the introduction of oxygen vacancies into the VO2 thin films and the formation of V3+ defects.

Results of excimer laser photorefractive keratectomy for the correction of myopia at Cedars-Sinai Medical Center: 1993

NASA Astrophysics Data System (ADS)

Maguen, Ezra I.; Salz, James J.; Nesburn, Anthony B.; Warren, Cathy; Macy, Jonathan I.; Papaioannou, Thanassis; Hofbauer, John; Berlin, Michael S.

1994-06-01

This report summarizes the authors' 3-year experience with excimer laser photorefractive keratectomy (PRK) on 240 eyes of 161 patients. With constant laser emission parameters, nitrogen (N2) flow across the cornea was used on 79 eyes while 161 eyes had no N2 flow. 74 eyes were operated on without fixation with a suction ring. Postoperative pain management included patching and oral analgesics in 77 eyes and the use of topical Diclofenac or Ketorolac, and a therapeutic soft contact lens in 163 eyes. Follow up ranged from 1 month (206 eyes) to 36 months (10 eyes).

Temperature monitoring by infrared radiation measurements during ArF excimer laser ablation with cornea

NASA Astrophysics Data System (ADS)

Ishihara, Miya; Arai, Tsunenori; Sato, Shunichi; Nakano, Hironori; Obara, Minoru; Kikuchi, Makoto

1999-06-01

We measured infrared thermal radiation from porcine cornea during various fluences ArF excimer laser ablations with 1 microsecond(s) rise time. To obtain absolute temperature by means of Stefan-Boltzman law of radiation, we carried out a collection efficiency and detective sensitivity by a pre-experiment using panel heater. We measured the time course of the thermal radiation intensity with various laser fluences. We studied the relation between the peak cornea temperature during the ablation and irradiation fluences. We found the ablation situations, i.e., sub-ablation threshold, normal thermal ablation, and over-heated ablation, may be judged by both of the measured temperature transient waveforms and peak temperature. The boundary fluences corresponding to normal thermal ablation were 90 and 160 mJ/cm2. Our fast remote temperature monitoring during cornea ablation might be useful to control ablation quality/quantity of the cornea ArF laser ablation, that is PRK.

Interaction of 308-nm excimer laser light with temporomandibular joint related structures

NASA Astrophysics Data System (ADS)

Liesenhoff, Tim; Funk, Armin

1994-02-01

Arthroscopy of TMJ has become a clinically important and more and more accepted method for diagnosis and treatment of TMJ alteration. This minimal invasive method is clearly limited by the anatomical dimensions of the TMJ. A 308 nm excimer laserlight has already found clinical applications in angioplasty, ophthalmology, and dentistry. The aim of the presented study was to find out if it is possible to ablate TMJ related structures under arthroscopic conditions. It also aims to evaluate the energy-threshold for ablation and the maximal possible rate of ablation. Contrary to other laser systems it offers a unique combination of minimal tissue alteration, precise tissue ablation guidability through optical fibers, and a good transmission through water.

Picosecond excimer laser-plasma x-ray source for microscopy, biochemistry, and lithography

NASA Astrophysics Data System (ADS)

Turcu, I. C. Edmond; Ross, Ian N.; Trenda, P.; Wharton, C. W.; Meldrum, R. A.; Daido, Hiroyuki; Schulz, M. S.; Fluck, P.; Michette, Alan G.; Juna, A. P.; Maldonado, Juan R.; Shields, Harry; Tallents, Gregory J.; Dwivedi, L.; Krishnan, J.; Stevens, D. L.; Jenner, T.; Batani, Dimitri; Goodson, H.

1994-02-01

At Rutherford Appleton Laboratory we developed a high repetition rate, picosecond, excimer laser system which generates a high temperature and density plasma source emitting approximately 200 mW (78 mW/sr) x ray average power at h(nu) approximately 1.2 KeV or 0.28 KeV < h(nu) < 0.53 KeV (the `water window'). At 3.37 nm wavelength the spectral brightness of the source is approximately 9 X 1011 photons/s/mm2/mrad2/0.1% bandwidth. The x-ray source serves a large user community for applications such as: scanning and holographic microscopy, the study of the biochemistry of DNA damage and repair, microlithography and spectroscopy.

The influence of ArF excimer laser micromachining on physicochemical properties of bioresorbable poly(L-lactide)

NASA Astrophysics Data System (ADS)

Stepak, Bogusz D.; Antończak, Arkadiusz J.; Szustakiewicz, Konrad; Pezowicz, Celina; Abramski, Krzysztof M.

2016-03-01

The main advantage of laser processing is a non-contact character of material removal and high precision attainable thanks to low laser beam dimensions. This technique enables forming a complex, submillimeter geometrical shapes such as vascular stents which cannot be manufactured using traditional techniques e.g. injection moulding or mechanical treatment. In the domain of nanosecond laser sources, an ArF excimer laser appears as a good candidate for laser micromachining of bioresorbable polymers such as poly(L-lactide). Due to long pulse duration, however, there is a risk of heat diffusion and accumulation in the material. In addition, due to short wavelength (193 nm) photochemical process can modify the chemical composition of ablated surfaces. The motivation for this research was to evaluate the influence of laser micromachining on physicochemical properties of poly(L-lactide). We performed calorimetric analysis of laser machined samples by using differential scanning calorimetry (DSC). It allowed us to find the optimal process parameters for heat affected zone (HAZ) reduction. The chemical composition of the ablated surface was investigated by FTIR in attenuated total reflectance (ATR) mode.

Latest result of PRK with excimer laser

NASA Astrophysics Data System (ADS)

Okamoto, Shinseiro; Okamoto, Michika

1996-05-01

We have in the last two years, performed PRK operation on over 300 human myopic eyes using ArF excimer laser with a Summit 'Omnimed' machine. For the initial 53 myopic eyes we treated, results were very good for those with correction less than minus 6 diopters. However, as previously reported, we also witnessed some regression for those eyes exceeding correction of more than minus 6 diopters. To counter such ill results of PRK we devised and suggested many new procedures for PRK with very good results. One such invention is the 'Okamoto-type' cooling machine for the cornea which reduces and stabilizes cornea temperature at 0 degrees Celsius while simultaneously bathing the cornea with special cooling fluid. After the operation, EGF, fibronectin and hexapeptide were administered using eyedrops. Soft contact lenses were used to protect the cornea, improve delivery of medication to the operated area, prevent infection and inflammation and also promote uniform and faster ephiterium regrowth. We were able to document very good post-operative results using this method, thereby giving us strong assurance that we have reached a significant milestone in PRK operation. Our report today covers post operative results of the 52 eyes we operated on and tracked for more than one year.

Stretchable multilayer self-aligned interconnects fabricated using excimer laser photoablation and in situ masking

NASA Astrophysics Data System (ADS)

Lin, Kevin L.; Jain, Kanti

2009-02-01

Stretchable interconnects are essential to large-area flexible circuits and large-area sensor array systems, and they play an important role towards the realization of the realm of systems which include wearable electronics, sensor arrays for structural health monitoring, and sensor skins for tactile feedback. These interconnects must be reliable and robust for viability, and must be flexible, stretchable, and conformable to non-planar surfaces. This research describes the design, modeling, fabrication, and testing of stretchable interconnects on polymer substrates using metal patterns both as functional interconnect layers and as in-situ masks for excimer laser photoablation. Excimer laser photoablation is often used for patterning of polymers and thin-film metals. The fluences for photoablation of polymers are generally much lower than the threshold fluence for removal or damage of high-thermallyconductive metals; thus, metal thin films can be used as in-situ masks for polymers if the proper fluence is used. Selfaligned single-layer and multi-layer interconnects of various designs (rectilinear and 'meandering') have been fabricated, and certain 'meandering' interconnect designs can be stretched up to 50% uniaxially while maintaining good electrical conductivity and structural integrity. These results are compared with Finite Element Analysis (FEA) models and are observed to be in good accordance with them. This fabrication approach eliminates masks and microfabrication processing steps as compared to traditional fabrication approaches; furthermore, this technology is scalable for large-area sensor arrays and electronic circuits, adaptable for a variety of materials and interconnects designs, and compatible with MEMS-based capacitive sensor technology.

Excimer laser deinsulation of Parylene-C on iridium for use in an activated iridium oxide film-coated Utah electrode array

PubMed Central

Yoo, Je-Min; Negi, Sandeep; Tathireddy, Prashant; Solzbacher, Florian; Song, Jong-In; Rieth, Loren W.

2013-01-01

Implantable microelectrodes provide a measure to electrically stimulate neurons in the brain and spinal cord and record their electrophysiological activity. A material with a high charge capacity such as activated or sputter-deposited iridium oxide film (AIROF or SIROF) is used as an interface. The Utah electrode array (UEA) uses SIROF for its interface material with neural tissue and oxygen plasma etching (OPE) with an aluminium foil mask to expose the active area, where the interface between the electrode and neural tissue is formed. However, deinsulation of Parylene-C using OPE has limitations, including the lack of uniformity in the exposed area and reproducibility. While the deinsulation of Parylene-C using an excimer laser is proven to be an alternative for overcoming the limitations, the iridium oxide (IrOx) suffers from fracture when high laser fluence (>1000 mJ/cm2) is used. Iridium (Ir), which has a much higher fracture resistance than IrOx, can be deposited before excimer laser deinsulation and then the exposed Ir film area can be activated by electrochemical treatment to acquire the AIROF. Characterisation of the laser-ablated Ir film and AIROF by surface analysis (X-ray photoelectron spectroscopy, scanning electron microscope, and atomic force microscope) and electrochemical analysis (electrochemical impedance spectroscopy, and cyclic voltammetry) shows that the damage on the Ir film induced by laser irradiation is significantly less than that on SIROF, and the AIROF has a high charge storage capacity. The results show the potential of the laser deinsulation technique for use in high performance AIROF-coated UEA fabrication. PMID:23458659

X-Ray Radiation Measurements With Photodiodes In Plasmas Generated By 1017 W/Cm2 Intensity Krf Excimer Laser Pulses

NASA Astrophysics Data System (ADS)

Rácz, E.; Földes, I. B.; Ryć, L.

2006-01-01

Experiments were carried out using a prepulse-free hybrid KrF excimer-dye laser system (700fs pulse duration, 248nm wavelength, 15mJ pulse energy). The intensity of the p-polarized, focused laser beam was 1.5ṡ1017 W/cm2. Vacuum ultraviolet (VUV) and x-rays from solid state laser plasmas were generated in the laser-plasma interaction of subpicosecond laser pulses of nonrelativistic laser intensities. An x-ray sensitive FLM photodiode (ITE, Warsaw) was used to detect x-rays between 1-19 keV in front of the targets. The diode was filtered by a 4μm Al foil. The dependence of the x-ray flux on laser intensity and the angular distribution of x-rays for aluminum and copper targets in the half space of the front side of the targets were investigated.

Excimer laser induced surface chemical modification of polytetrafluoroethylene

NASA Astrophysics Data System (ADS)

Révész, K.; Hopp, B.; Bor, Z.

1997-02-01

Polytetrafluoroethylene has a notoriously non adhesive and non reactive character. Its successful surface photochemical modification was performed by irradiating the polytetrafluoroethylene/liquid triethylamine interface with an ArF excimer laser (λ=193 nm). Due to the photochemical treatment the polytetrafluoroethylene surface became more hydrophilic. The water receding contact angle decreased from 94° to 43°. The reaction cross section was determined from the decrease of the contact angles. It was found to be as high as 6.4×10-18 cm2. XPS measurements evidenced the removal of fluorine from the polytetrafluoroethylene, incorporation of alkyl carbon and nitrogen. Photochemical dissociation path of the triethylamine makes probable that it bonded to the fluoropolymer backbone via the α-carbon atom of an ethyl group. A radical, or a photoinduced electron transfer mechanism was suggested to describe this reaction. A selective area electroless plating of silver was performed after pretreating the sample with patterned photomodification. The increased adhesion of the sample was proved by gluing with epoxy resin. As a result of the surface modification the tensile strength of gluing increased by 210× and reached 24% of the value characteristic for the bulk material.

H and Au diffusion in high mobility a-InGaZnO thin-film transistors via low temperature KrF excimer laser annealing

NASA Astrophysics Data System (ADS)

Bermundo, Juan Paolo S.; Ishikawa, Yasuaki; Fujii, Mami N.; Ikenoue, Hiroshi; Uraoka, Yukiharu

2017-03-01

We report the fabrication of high mobility amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) irradiated by a single shot of a 248 nm KrF excimer laser. Very high mobilities (μ) of up to 43.5 cm2/V s were obtained after the low temperature excimer laser annealing (ELA) process. ELA induces high temperatures primarily in the upper layers and maintains very low temperatures of less than 50 °C in the substrate region. Scanning Transmission Electron micrographs show no laser induced damage and clear interfaces after the laser irradiation. In addition, several characterization studies were performed to determine the μ improvement mechanism. The analysis of Secondary Ion Mass Spectrometry and X-ray Photoelectron Spectroscopy suggests incorporation of H mainly from the hybrid passivation layer into the channel. Moreover, Energy-dispersive X-ray Spectroscopy results show that Au diffused into the channel after ELA. Both KrF ELA-induced H and Au diffusion contributed to the higher μ. These results demonstrate that ELA can greatly enhance the electrical properties of a-IGZO TFTs for promising applications in large area, transparent, and flexible electronics.

80 A/cm2 electron beams from metal targets irradiated by KrCl and XeCl excimer lasers

NASA Astrophysics Data System (ADS)

Beloglazov, A.; Martino, M.; Nassisi, V.

1996-05-01

Due to the growing demand for high-current and long-duration electron-beam devices, laser electron sources were investigated in our laboratory. Experiments on electron-beam generation and propagation from aluminium and copper targets illuminated by XeCl (308 nm) and KrCl (222 nm) excimer lasers, were carried out under plasma ignition due to laser irradiation. This plasma supplied a spontaneous accelerating electric field of about 370 kV/m without an external accelerating voltage. By applying the modified one-dimensional Poisson equation, we computed the expected current and we also estimated the plasma concentration during the accelerating process. At 40 kV of accelerating voltage, an output current pulse of about 80 A/cm2 was detected from an Al target irradiated by the shorter wavelength laser.

Management of central venous gradient using excimer laser lead extraction of chronic indwelling pacemaker leads in the setting of ipsilateral arteriovenous fistula.

PubMed

Ramirez, Alexies; Gentlesk, Philip J; Peele, Mark E; Eckart, Robert E

2012-07-01

Device therapy is becoming common in those patients with renal insufficiency. Coexisting need for arteriovenous (AV) fistula placement is often contemplated relative to device placement. We describe the excimer laser lead extraction of a malfunctioning chronic atrial pacemaker lead ipsilateral to an AV fistula.

Dynamics of excimer laser ablation of thin tungsten films studied by fast photography

NASA Astrophysics Data System (ADS)

Toth, Zsolt; Hopp, Bela; Kantor, Zoltan; Ignacz, Ferenc; Szoerenyi, Tamas; Bor, Zsolt

1994-09-01

The time evolution of ablation and material transport during ArF excimer laser induced blow off of tungsten films from glass substrates is studied by fast photography using delayed dye laser pulses. The analysis of experimental results combined with heat flow calculations provides evidence that tungsten removal in the solid phase is the dominant mechanism in the 40 - 200 mJ/cm2 fluence domain, while partially inhomogeneous melting is observed between 200 and 800 mJ/cm2. In this fluence range, solid fragments and a halo consisting of molten droplets are observed indicating spatial separation of the two phases. The molten phase advances faster, forming a protective mist in front of the solid piece(s). At yet higher fluences (800 - 1000 mJ/cm2), a well separated solid phase could be recorded under the halo although model calculations suggest full vaporization of the layer. This unexpected phenomenon is explained by the optical shielding effect of the halo.

Negative charge emission due to excimer laser bombardment of sodium trisilicate glass

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

Langford, S.C.; Jensen, L.C.; Dickinson, J.T.

We describe measurements of negative charge emission accompanying irradiation of sodium trisilicate glass (Na{sub 2}O{center dot}3SiO{sub 2}) with 248-nm excimer laser light at fluences on the order of 2 J/cm{sup 2} per pulse, i.e., at the threshold for ablative etching of the glass surface. The negative charge emission consists of a very prompt photoelectron burst coincident with the laser pulse, followed by a much slower plume of electrons and negative ions traveling with a high density cloud of positive ions, previously identified as primarily Na{sup +}. Using combinations of {bold E} and {bold B} fields in conjunction with time-of-flight methods,more » the negative ions were successfully separated from the plume and tentatively identified as O{sup {minus}}, Si{sup {minus}}, NaO{sup {minus}}, and perhaps NaSi{sup {minus}}. These negative species are probably formed by gas phase collisions in the near-surface region which result in electron attachment.« less

Efficacy of the 308-nm excimer laser for treatment of psoriasis: results of a multicenter study.

PubMed

Feldman, Steven R; Mellen, Beverly G; Housman, Tamara Salam; Fitzpatrick, Richard E; Geronemus, Roy G; Friedman, Paul M; Vasily, David B; Morison, Warwick L

2002-06-01

Our purpose was to demonstrate the efficacy of the 308-nm excimer laser for treatment of psoriasis. This study was a multicenter open trial from 5 dermatology practices (one university-based and 4 private practices). Up to 30 patients per center with stable mild to moderate plaque-type psoriasis constituted the study population. Patients received 308-nm ultraviolet B doses to affected areas. The initial dose was based on multiples of a predetermined minimal erythema dose. Subsequent doses were based on the response to treatment. Treatments were scheduled twice weekly for a total of 10 treatments. The main outcome measure was 75% clearing of the target plaque. Time to clearing was analyzed by Kaplan-Meier methods, accounting for truncated observations. One hundred twenty-four patients were enrolled in the study, and 80 completed the entire protocol. The most common reason for exiting from the study was noncompliance. Of the patients who met the protocol requirements of 10 treatments or clearing, 72% (66/92) achieved at least 75% clearing in an average of 6.2 treatments. Eighty-four percent of patients (95% confidence interval [CI], 79%-87%) reached improvement of 75% or better after 10 or fewer treatments. Fifty percent of patients (95% CI, 35%-61%) reached improvement of 90% or better after 10 or fewer treatments. Common side effects included erythema, blisters, hyperpigmentation, and erosions, but they were well tolerated. Monochromatic 308-nm excimer laser treatment appears to be effective and safe for psoriasis. It requires fewer patient visits than conventional phototherapy, and, unlike those treatments, the laser targets only the affected areas of the skin, sparing the surrounding uninvolved skin.

Photoinitiator-free 3D scaffolds fabricated by excimer laser photocuring.

PubMed

Farkas, Balázs; Dante, Silvia; Brandi, Fernando

2017-01-20

Photoinitiator-free fabrication of poly(ethylene glycol) diacrylate (PEGDA) scaffolds is achieved using a novel three-dimensional (3D) printing method called mask projected excimer laser stereolithography (MPExSL). The spatial resolution of photoinitiator-free curing is suitable for 3D layer-by-layer fabrication with a single layer thickness well controllable at tens to hundreds of microns using 248 nm wavelength for the irradiation. The photoinitiator-free scaffolds are superior compared to their counterparts fabricated by using photoinitiator molecules, showing a higher level of biocompatibility. A release of toxic chemicals from the photoinitiator containing scaffolds is proven by cell proliferation tests. In contrast, no toxic release is found from the photoinitiator-free scaffolds, resulting in the very same level of cell proliferation as the control sample. The demonstration of photoinitiator-free PEGDA scaffolds enables the fabrication of 3D scaffolds with the highest level of biocompatibility for both in vitro and in vivo applications.

[Excimer laser therapy of alopecia areata--side-by-side evaluation of a representative area].

PubMed

Raulin, Christian; Gündogan, Cüneyt; Greve, Bärbel; Gebert, Susanne

2005-07-01

We report for the first time on hair regrowth in alopecia areata of the scalp achieved with the 308-nm xenon-chloride excimer laser in a prospective side-by-side trial. The alopecia areata had shown progression over a period of three years, and various treatments had not been effective. Out of a number of affected areas, one representative lesion was chosen; one half of it was treated, the other half remained untreated. After 27 sessions (200 - 4000 mJ/cm2, cumulative dose 52.6 J/cm2) over 3 months, only the treated area showed hair growth; which suggests that this was most probably not a spontaneous remission.

One-kilohertz eye tracker and active intraoperative torsion detection in the NIDEK CXIII and Quest excimer lasers.

PubMed

Waring, George O

2009-10-01

To describe recent technological additions to the NIDEK CXIII and Quest excimer lasers. A summary article with data from previous published studies outlining the benefits of newer technology. The addition of a 1-kHz infrared eye tracker decreased the spread of laser spot placement from a mean of 228.79 microm without a tracker to 38.47 microm with the eye tracker. The addition of real-time torsion error correction produced a statistically significantly lower cylinder dispersion, mean manifest refractive cylinder, and error of angle postoperatively in eyes that underwent LASIK. The incorporation of an ultrahigh speed eye tracker and active cyclotorsion correction surpasses the minimal technology criteria required for accurate wavefront-based ablations. Copyright 2009, SLACK Incorporated.

Impact of Angioscopic Evaluation for Femoropopliteal In-Stent Restenosis Before and After Excimer Laser Atherectomy.

PubMed

Idemoto, Akiko; Okamoto, Naotaka; Tanaka, Akihiro; Mori, Naoki; Nakamura, Daisuke; Yano, Masamichi; Makino, Nobuhiko; Egami, Yasuyuki; Shutta, Ryu; Tanouchi, Jun; Nishino, Masami

2017-07-01

In-stent restenosis (ISR) is a prevalent problem following stenting of femoropopliteal lesions. A potential novel treatment modality for ISR including excimer laser atherectomy (ELA) has become available. We performed ELA for in-stent chronic total occlusion (CTO) of femoropopliteal lesions and evaluated lesion morphology before and after ELA by angioscopy in 2 patients. The angioscopic findings clearly showed removal of in-stent thrombi after ELA. Thus, ELA may be effective for in-stent CTO of femoropopliteal lesions. This is the first report describing the direct visualization of ELA effect for vaporization of thrombi in femoropopliteal in-stent lesions by angioscopy.

Bubble formation during pulsed laser ablation: mechanism and implications

NASA Astrophysics Data System (ADS)

van Leeuwen, Ton G. J. M.; Jansen, E. Duco; Motamedi, Massoud; Welch, Ashley J.; Borst, Cornelius

1993-07-01

Holmium ((lambda) equals 2.09 micrometers ) and excimer ((lambda) equals 308 nm) lasers are used for ablation of tissue. In a previous study it was demonstrated that both excimer and holmium laser pulses produce fast expanding and collapsing vapor bubbles. To investigate whether the excimer induced bubble is caused by vaporization of water, the threshold fluence for bubble formation at a bare fiber tip in water was compared between the excimer laser (pulse length 115 ns) and the Q-switched and free-running holmium lasers (pulse length 1 microsecond(s) to 250 microsecond(s) , respectively). To induce bubble formation by excimer laser light in water, the absorber oxybuprocaine-hydrochloride (OBP-HCl) was added to the water. Fast flash photography was used to measure the threshold fluence as a function of the water temperature (6 - 90 degree(s)C) at environmental pressure. The ultraviolet excimer laser light is strongly absorbed by blood. Therefore, to document the implications of bubble formation at fluences above the tissue ablation threshold, excimer laser pulses were delivered in vitro in hemoglobin solution and in vivo in the femoral artery of the rabbit. We conclude that the principal content of the fast bubble induced by a 308 nm excimer laser pulse is water vapor. Therefore, delivery of excimer laser pulses in a water or blood environment will cause fast expanding water vapor bubbles, which may induce mechanical damage to adjacent tissue.

Visualization of corona discharge induced by UV (248 nm) pulses of a KrF excimer laser

NASA Astrophysics Data System (ADS)

Mizeraczyk, Jerzy; Ohkubo, Toshikazu; Kanazawa, Seiji; Nomoto, Yukiharu; Kawasaki, Toshiyuki; Kocik, Marek

2000-11-01

A KrF excimer laser (248 nm) was used to induce DC corona discharge streamers in air between the electrodes of a needle-to-plane geometry. The UV laser beam pulses were transformed into the form of a laser sheet (1.5 mm thick and 20 mm-wide) that was positioned along the axis directed from the needle electrode to the plane electrode. The laser pulses were time-synchronized with the exposure of an ICCD camera that record images of the corona streamers induced by the laser sheet. The laser pulse energy flux (75 MW/cm2) crossing the gap was high enough to induce corona streamers with a reliability of 100% even at relatively low operating voltages (e.g., 15 kV) at which self-sustained streamers could not occur. Due to the full synchronization of the corona streamer onset, induced by the laser pulse and the exposure of the ICCD camera, 2-D visualization of the corona streamer evolution with a time resolution of 10 ns was possible. The recorded images made possible determining such features of the corona discharge streamer as its velocity (2.5 105 m/s) and the diameters of the leader channel (200 micrometers ) and the leader streamers (100 micrometers ).

Analysis of excimer laser radiant exposure effect toward corneal ablation volume at LASIK procedure

NASA Astrophysics Data System (ADS)

Adiati, Rima Fitria; Rini Rizki, Artha Bona; Kusumawardhani, Apriani; Setijono, Heru; Rahmadiansah, Andi

2016-11-01

LASIK (Laser Asissted In Situ Interlamelar Keratomilieusis) is a technique for correcting refractive disorders of the eye such as myopia and astigmatism using an excimer laser. This procedure use photoablation technique to decompose corneal tissues. Although preferred due to its efficiency, permanency, and accuracy, the inappropriate amount radiant exposure often cause side effects like under-over correction, irregular astigmatism and problems on surrounding tissues. In this study, the radiant exposure effect toward corneal ablation volume has been modelled through several processes. Data collecting results is laser data specifications with 193 nm wavelength, beam diameter of 0.065 - 0.65 cm, and fluence of 160 mJ/cm2. For the medical data, the myopia-astigmatism value, cornea size, corneal ablation thickness, and flap data are taken. The first modelling step is determining the laser diameter between 0.065 - 0.65 cm with 0.45 cm increment. The energy, power, and intensity of laser determined from laser beam area. Number of pulse and total energy is calculated before the radiant exposure of laser is obtained. Next is to determine the parameters influence the ablation volume. Regression method used to create the equation, and then the spot size is substituted to the model. The validation used is statistic correlation method to both experimental data and theory. By the model created, it is expected that any potential complications can be prevented during LASIK procedures. The recommendations can give the users clearer picture to determine the appropriate amount of radiant exposure with the corneal ablation volume necessary.

0.35-μm excimer DUV photolithography process

NASA Astrophysics Data System (ADS)

Arugu, Donald O.; Green, Kent G.; Nunan, Peter D.; Terbeek, Marcel; Crank, Sue E.; Ta, Lam; Capsuto, Elliott S.; Sethi, Satyendra S.

1993-08-01

It is becoming increasingly clear that DUV excimer laser based imaging will be one of the technologies for printing sub-half micron devices. This paper reports the investigation of 0.35 micrometers photolithography process using chemically amplified DUV resists on organic anti- reflective coating (ARC). Production data from the GCA XLS excimer DUV tools with nominal gate width of 0.35 micrometers lines, 0.45 micrometers spaces was studied to demonstrate device production worthiness. This data included electrical yield information for device characterization. Exposure overlay was done by mixing and matching DUV and I-line GCA steppers for critical and non critical levels respectively. Working isolated transistors down to 0.2 micrometers have been demonstrated.

The early results of excimer laser photorefractive keratectomy for compound myopic astigmatism.

PubMed

Horgan, S E; Pearson, R V

1996-01-01

An excimer laser (VISX Twenty/Twenty Excimer Refractive System) was used to treat 51 eyes for myopia and astigmatism. Uncorrected pretreatment visual acuity was between 6/18 and 6/60 (log unit +0.45 to +1.0) in 59% and worse than 6/60 in 29%. The mean pretreatment spherical refractive error was -4.05 dioptre (range 1.25 to 13.25), and the mean pretreatment cylindrical error was -0.97 dioptre (range 0.25 to 4.00). Uncorrected visual acuity measured 6/6 or better (log unit 0.0 or less) in 80% at three months, and averaged 6/6 for all eyes at six months post-treatment, with 75% eyes obtaining 6/6 or better. The mean post-treatment spherical error decayed according to pre-treatment values, with a mean sphere of -0.20 dioptre for eyes initially less than -2.00 dioptre, -0.40 dioptre (for those between -2.25 and -3.00), -0.71 dioptre (for those between -4.25 and -5.00), and -1.15 dioptre for eyes initially above -6.25 dioptre. Vectored cylindrical correction exhibited response proportional to initial refraction, with a mean post-treatment cylinder of -1.83 dioptre for eyes formerly averaging -3.08 dioptre, -0.55 dioptre (eyes initially averaging -1.63 dioptre), and -0.51 dioptre (eyes initially averaging -0.67 dioptre). Vector analysis of post-treatment astigmatism showed 58% eyes exhibiting 51 or more degrees of axis shift, although 34% eyes remained within 20 degrees of their pretreatment axis. An effective reduction in spherocylindrical error was achieved with all eyes, although axis misalignment was a common event.

High-tensile strength sticking induced by ArF excimer laser surface treatment of poly(tetrafluoroethylene)

NASA Astrophysics Data System (ADS)

Hopp, Bela; Revesz, K.; Bor, Zsolt

1998-07-01

A successful enhancement of sticking of PTFE is demonstrated using ArF excimer laser irradiation in the presence of novel photoreagents. The applied laser fluence was very low at the sample - photoreagent liquid interface compared to the energy density applied in earlier investigations. After the treatment the PTFE films were glued by epoxy resin. It was found that at low doses the tensile strength of the sticking increased rapidly with the UV pulse number and the reached a saturation value, which was 6.66 MPa for triethylamine, 5.56 MPa in the case of 1,2-diaminoethane and 4.64 MPa for triethylene-tetramine. These are around two hundred times higher than the value of the untreated surface. It was found that this procedure makes the metallization and painting of PTFE surface also possible. A photoinduced electron transfer mechanism was suggested to describe the photoreaction, which is responsible for the increase of adhesion features on PTFE surface.

Modulation of corneal wound healing after excimer laser keratomileusis using topical mitomycin C and steroids

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

Talamo, J.H.; Gollamudi, S.; Green, W.R.

1991-08-01

A 193-nm excimer laser system was used to create deep stromal ablations in seven New Zealand white rabbits and shallow ablations in three. Eyes were randomized for treatment with topical mitomycin C, steroids, and erythromycin; topical steroids and erythromycin; or topical erythromycin only. All treatment regimens were instituted twice daily for 14 days. All eyes reepithelialized normally within 3 to 5 days. During 10 weeks of follow-up, all eyes developed moderate reticular subepithelial haze without significant differences among treatment groups. Results of light, fluorescence, and electron microscopic examination showed anterior stromal scarring and markedly reduced new subepithelial collagen formation inmore » the group treated with mitomycin C, corticosteroids, and erythromycin. Focal abnormalities of Descemet's membrane and endothelial abnormalities were present in all treatment groups. Combination therapy with topical steroids, mitomycin C, and erythromycin to control the corneal wound healing response after refractive laser surgery appears promising and warrants further study.« less

Analysis of the change in peak corneal temperature during excimer laser ablation in porcine eyes

NASA Astrophysics Data System (ADS)

Mosquera, Samuel Arba; Verma, Shwetabh

2015-07-01

The objective is to characterize the impact of different ablation parameters on the thermal load during corneal refractive surgery by means of excimer laser ablation on porcine eyes. One hundred eleven ablations were performed in 105 porcine eyes. Each ablation was recorded using infrared thermography and analyzed mainly based on the two tested local frequencies (40 Hz, clinical local frequency; 1000 Hz, no local frequency). The change in peak corneal temperature was analyzed with respect to varying ablation parameters [local frequency, system repetition rate, pulse energy, optical zone (OZ) size, and refractive correction]. Transepithelial ablations were also compared to intrastromal ablations. The average of the baseline temperature across all eyes was 20.5°C±1.1 (17.7°C to 22.2°C). Average of the change in peak corneal temperature for all clinical local frequency ablations was 5.8°C±0.8 (p=3.3E-53 to baseline), whereas the average was 9.0°C±1.5 for all no local frequency ablations (p=1.8E-35 to baseline, 1.6E-16 to clinical local frequency ablations). A logarithmic relationship was observed between the changes in peak corneal temperature with increasing local frequency. For clinical local frequency, change in peak corneal temperature was comparatively flat (r2=0.68 with a range of 1.5°C) with increasing system repetition rate and increased linearly with increasing OZ size (r2=0.95 with a range of 2.4°C). Local frequency controls help maintain safe corneal temperature increase during excimer laser ablations. Transepithelial ablations induce higher thermal load compared to intrastromal ablations, indicating a need for stronger thermal controls in transepithelial refractive procedures.

Laser assisted deposition

NASA Technical Reports Server (NTRS)

Dutta, S.

1983-01-01

Applications of laser-based processing techniques to solar cell metallization are discussed. Laser-assisted thermal or photolytic maskless deposition from organometallic vapors or solutions may provide a viable alternative to photovoltaic metallization systems currently in use. High power, defocused excimer lasers may be used in conjunction with masks as an alternative to direct laser writing to provide higher throughput. Repeated pulsing with excimer lasers may eliminate the need for secondary plating techniques for metal film buildup. A comparison between the thermal and photochemical deposition processes is made.

Raman scattering measurements in flames using a tunable KrF excimer laser

NASA Technical Reports Server (NTRS)

Wehrmeyer, Joseph A.; Cheng, Tsarng-Sheng; Pitz, Robert W.

1992-01-01

A narrow-band tunable KrF excimer laser is used as a spontaneous vibrational Raman scattering source to demonstrate that single-pulse concentration and temperature measurements, with only minimal fluorescence interference, are possible for all major species (O2, N2, H2O, and H2) at all stoichiometries (fuel-lean to fuel rich) of H2-air flames. Photon-statistics-limited precisions in these instantaneous and spatially resolved single-pulse measurements are typically 5 percent, which are based on the relative standard deviations of single-pulse probability distributions. In addition to the single-pulse N2 Stokes/anti-Stokes ratio temperature measurement technique, a time-averaged temperature measurement technique is presented that matches the N2 Stokes Raman spectrum to theoretical spectra by using a single intermediate state frequency to account for near-resonance enhancement. Raman flame spectra in CH4-air flames are presented that have good signal-to-noise characteristics and show promise for single-pulse UV Raman measurements in hydrocarbon flames.

Enabling laser applications in microelectronics manufacturing

NASA Astrophysics Data System (ADS)

Delmdahl, Ralph; Brune, Jan; Fechner, Burkhard; Senczuk, Rolf

2016-02-01

In this experimental study, we report on high-pulse-energy excimer laser drilling into high-performance build-up films which are pivotal in microelectronics manufacturing. Build-up materials ABF-GX13 from Ajinomoto as well as ZS-100 from Zeon Corporation are evaluated with respect to their viability for economic excimer laser-based micro-via formation. Excimer laser mask imaging projection at laser wavelengths of 193, 248 and 308 nm is employed to generate matrices of smaller micro-vias with different diameters and via pitches. High drilling quality is achievable for all excimer laser wavelengths with the fastest ablation rates measured in the case of 248 and 308 nm wavelengths. The presence of glass fillers in build-up films as in the ABF-GX13 material poses some limitations to the minimum achievable via diameter. However, surprisingly good drilling results are obtainable as long as the filler dimensions are well below the diameter of the micro-vias. Sidewall angles of vias are controllable by adjusting the laser energy density and pulse number. In this work, the structuring capabilities of excimer lasers in build-up films as to taper angle variations, attainable via diameters, edge-stop behavior and ablation rates will be elucidated.

Acute effects of pulsed-laser irradiation on the arterial wall

NASA Astrophysics Data System (ADS)

Nakamura, Fumitaka; Kvasnicka, Jan; Lu, Hanjiang; Geschwind, Herbert J.; Levame, Micheline; Bousbaa, Hassan; Lange, Francoise

1992-08-01

Pulsed laser coronary angioplasty with an excimer or a holmium-yttrium-aluminum-garnet (Ho:YAG) laser may become an alternative treatment for patients with coronary artery disease. However, little is known about its acute consequences on the normal arterial wall. This study was designed to examine the acute histologic consequences of these two pulsed lasers on the arterial wall of normal iliac arteries in rabbits. Irradiation with each laser was performed in 15 normal iliac sites on eight male New Zealand white rabbits. The excimer laser was operated at 308 nm, 25 Hz, 50 mJ/mm2/pulse, and 135 nsec/pulse and the Ho:YAG laser was operated at 2.1 micrometers , 3/5 Hz, 400 mJ/pulse, and 250 microsecond(s) ec/pulse. The excimer and Ho:YAG laser were coupled into a multifiber wire-guided catheter of 1.4 and 1.5 mm diameter, respectively. The sites irradiated with excimer or Ho:YAG laser had the same kinds of histologic features, consisting of exfoliation of the endothelium, disorganization of internal elastic lamina, localized necrosis of vascular smooth muscle cells, and fissures in the medial layer. However, the sites irradiated with excimer laser had lower grading scores than those irradiated with Ho:YAG laser (p < 0.05). Laser irradiation with excimer or Ho:YAG laser of normal arteries results in localized mechanical vascular injury.

Energy-density and repetition-rate dependences of the KrF-excimer-laser-induced 1.9-eV emission band in type-III fused silicas

NASA Astrophysics Data System (ADS)

Kuzuu, Nobu; Komatsu, Yoshikazu; Murahara, Masataka

1993-02-01

The energy-density and repetition-rate dependences of the intensity of KrF-excimer-laser (5.0 eV) -induced 1.9-eV emission band in type-III fused silicas synthesized under different conditions were investigated. The intensity of the 1.9-eV band is proportional to the 1.7-th power of the energy density and the 0.6-th power of the repetition rate of the laser pulse. The origin of these dependencies was discussed based on the trapped-oxygen-molecule model proposed by Awazu and Kawazoe; by irradiating with the excimer laser, ozone molecules are formed from dissolved oxygen molecules and 1.9-eV photons are emitted in the course of the photodecomposition of the ozone molecules. Therefore, a two-step photon-absorption process is needed to emit the 1.9-eV photon. To form the ozone molecule, diffusion of the oxygen atoms produced by the photodecomposition of the trapped oxygen molecules are needed. This model suggests that the intensity of the 1.9-eV band is proportional to the square of the energy density and the square root of the repetition rate; this dependency is nearly the same as that of our experimental result.

Excimer laser-induced hydrohynamical effects and surface modifications on silicon carbide

NASA Astrophysics Data System (ADS)

Nicolas, Gines; Autric, Michel

1996-04-01

The use of lasers in many applications requires an understanding and control of the fundamental processes involved during the laser radiation-material interaction. The importance and the duration of the phenomena involved (optical, thermal, mechanical, electromagnetic, radiative) depend on parameters such as the power density of the laser radiation, the nature and the surface morphology of the material, the surrounding gas and the wavelength of the radiation. A part of the incident energy is reflected by the surface, while the remaining quantity of this energy is absorbed by the material. This incident energy contributes to heating, melting, vaporization and plasma formation if the laser intensity is sufficiently high. The present study is devoted to the ceramic material irradiation in air by an excimer laser at a wavelength of 248 nm and a pulse duration of 20 ns. The objective is to understand the different phenomena induced by radiation and to improve mechanical properties of the surface. Presented results concern the dynamics of plasmas and shock waves, plus surface modifications (porosity, roughness, composition changes) on silicon carbide samples (SiC). A part of the study has resulted in the characterization of the flow created in front of the sample revealing different hydrodynamical regimes. Visualizations of the luminous plasma front and shock waves have been obtained using a fast electronic camera IMACON 790 and a ICCD camera. These optical devices have permitted us to observe simultaneously the formation and expansion of different fronts (plasma and shock waves) propagating into the surrounding gas. The results have been compared to the theory. Complex structures inside the plume have been observed inducing a turbulence phenomena some milliseconds after the irradiation. On the other hand, the surface morphology has been characterized by observations with a scanning electron microscope (SEM) showing important modifications of the morphology according to

Cost-effective SU-8 micro-structures by DUV excimer laser lithography for label-free biosensing

NASA Astrophysics Data System (ADS)

Sanza, F. J.; Laguna, M. F.; Casquel, R.; Holgado, M.; Barrios, C. A.; Ortega, F. J.; López-Romero, D.; García-Ballesteros, J. J.; Bañuls, M. J.; Maquieira, A.; Puchades, R.

2011-04-01

Cost-effective SU-8 micro-structures on a silicon substrate were developed using 248 nm excimer laser KrF projection, studying the influence of the different variables on the final pattern geometry, finding out that the most critical are exposure dose and post-bake condition. Also a novel and cost effective type of photomask based on commercial polyimide Kapton produced by 355 nm DPSS laser microprocessing was developed, studying the influence of the cutting conditions on the photomask. Finally, as a likely application the biosensing capability with a standard BSA/antiBSA immunoassay over a 10 × 10 micro-plates square lattice of around 10 μm in diameter, 15 μm of spacing and 400 nm in height was demonstrated, finding a limit of detection (LOD) of 33.4 ng/ml which is in the order of magnitude of bioapplications such as detection of cortisol hormone or insulin-like growth factor. Low cost fabrication and vertical interrogation characterization techniques lead to a promising future in the biosensing technology field.

Excimer PRK testing in the clinic

NASA Astrophysics Data System (ADS)

Forrest, Gary T.

1994-06-01

Testing of the excimer lasers used in PRK requires special considerations in terms of ease of use, day-to-day reliability, and high resolution to see details of beam interference effects. SensorPhysics employs a patented photochromic material on a polyester substrate to record permanent, instant records of the laser and laser system output. Since each SensorCard is used only once concerns about detection device deterioration are not an issue. The SensorCards have a demonstrated resolving power on the order of 0.1 micrometers . A small, portable reading device is used to convert the SensorCard optical density to a mJ/cm2 value. Special software also measures beam uniformity to +/- 1% to provide both qualitative and quantitative analysis. Results of use in clinic environments will be presented. In particular detection of exposure `islands' will be demonstrated. The techniques employed are similar to those we developed for UV laser micromachining and lithography four years ago.

Evaluation of some technical factors affecting surgical outcome in photorefractive keratectomy with the VISX 2020 excimer laser

NASA Astrophysics Data System (ADS)

Maguen, Ezra I.; Salz, James J.; Papaioannou, Thanassis; Nesburn, Anthony B.

1995-05-01

Some technical factors relating to the use of the VISX model 20/20 excimer laser for photorefractive keratectomy will be discussed and the way they affect the final optical correction will be demonstrated, as follows: (1) Discontinuation of nitrogen flow: improved corneal haze but induced a mean undercorrection of 0.8 D, 18 months postoperatively. (2) Discontinuation of the use of the fixation ring did not affect centration in a statistically significant fashion. (3) Enlargement of the optical from 5.0 mm to 6.0 mm zone did not affect the refractive outcome. Visual acuity was improved in eyes which had PRK done with a 6.0 mm optical zone.

Research on radiation induced laser plasmas

NASA Technical Reports Server (NTRS)

Schneider, R. T.; Rowe, M. J.; Carter, B. D.; Walters, R. A.; Cox, J. D.; Liang, R.; Roxey, T.; Zapata, L.

1979-01-01

The development of high power nuclear pumped lasers is discussed. The excitation mechanism of continuous wave (CW) HeNe nuclear pumped lasers is studied and a CO2 nuclear pumped laser is used to demonstrate the CW output in the order of watts. The assumption that high power densities are only achievable by volume fission fragment sources is used to identify laser gases which are compatible with UF6 by excited states lifetime measurements. The examination of Xe2, XeF, and KrF under nuclear irradiation to determine if they are good candidates for nuclear-pumped lasers is described.

Randomized controlled study of excimer laser atherectomy for treatment of femoropopliteal in-stent restenosis: initial results from the EXCITE ISR trial (EXCImer Laser Randomized Controlled Study for Treatment of FemoropopliTEal In-Stent Restenosis).

PubMed

Dippel, Eric J; Makam, Prakash; Kovach, Richard; George, Jon C; Patlola, Raghotham; Metzger, D Christopher; Mena-Hurtado, Carlos; Beasley, Robert; Soukas, Peter; Colon-Hernandez, Pedro J; Stark, Matthew A; Walker, Craig

2015-01-01

The purpose of this study was to evaluate the safety and efficacy of excimer laser atherectomy (ELA) with adjunctive percutaneous transluminal angioplasty (PTA) versus PTA alone for treating patients with chronic peripheral artery disease with femoropopliteal bare nitinol in-stent restenosis (ISR). Femoropopliteal stenting has shown superiority to PTA for lifestyle-limiting claudication and critical limb ischemia, although treating post-stenting artery reobstruction, or ISR, remains challenging. The multicenter, prospective, randomized, controlled EXCITE ISR (EXCImer Laser Randomized Controlled Study for Treatment of FemoropopliTEal In-Stent Restenosis) trial was conducted across 40 U.S. centers. Patients with Rutherford Class 1 to 4 and lesions of target lesion length ≥4 cm, vessel diameter 5 to 7 mm were enrolled and randomly divided into ELA + PTA and PTA groups by a 2:1 ratio. The primary efficacy endpoint was target lesion revascularization (TLR) at 6-month follow up. The primary safety endpoint was major adverse event (death, amputation, or TLR) at 30 days post-procedure. Study enrollment was stopped at 250 patients due to early efficacy demonstrated at a prospectively-specified interim analysis. A total of 169 ELA + PTA subjects (62.7% male; mean age 68.5 ± 9.8 years) and 81 PTA patients (61.7% male; mean age 67.8 ± 10.3 years) were enrolled. Mean lesion length was 19.6 ± 12.0 cm versus 19.3 ± 11.9 cm, and 30.5% versus 36.8% of patients exhibited total occlusion. ELA + PTA subjects demonstrated superior procedural success (93.5% vs. 82.7%; p = 0.01) with significantly fewer procedural complications. ELA + PTA and PTA subject 6-month freedom from TLR was 73.5% versus 51.8% (p < 0.005), and 30-day major adverse event rates were 5.8% versus 20.5% (p < 0.001), respectively. ELA + PTA was associated with a 52% reduction in TLR (hazard ratio: 0.48; 95% confidence interval: 0.31 to 0.74). The EXCITE ISR trial is the first large, prospective, randomized study

Coronary Intervention with the Excimer Laser: Review of the Technology and Outcome Data

PubMed Central

Rawlins, John; Din, Jehangir N; Talwar, Suneel

2016-01-01

Excimer laser coronary atherectomy (ELCA) is a long-established adjunctive therapy that can be applied during percutaneous coronary intervention (PCI). Technical aspects have evolved and there is an established safety and efficacy record across a number of clinical indications in contemporary interventional practice where complex lesions are routinely encountered. The role of ELCA during PCI for thrombus, non-crossable or non-expandable lesions, chronic occlusions and stent under-expansion are discussed in this review. The key advantage of ELCA over alternative atherectomy interventions is delivery on a standard 0.014-inch guidewire. Additionally, the technique can be mastered by any operator after a short period of training. The major limitation is presence of heavy calcification although when rotational atherectomy (RA) is required but cannot be applied due to inability to deliver the dedicated RotaWireTM (Boston Scientific), ELCA can create an upstream channel to permit RotaWire passage and complete the case with RA – the RASER technique. PMID:29588701

Excimer Laser Surgery: Biometrical Iris Eye Recognition with Cyclorotational Control Eye Tracker System.

PubMed

Pajic, Bojan; Cvejic, Zeljka; Mijatovic, Zoran; Indjin, Dragan; Mueller, Joerg

2017-05-25

A prospective comparative study assessing the importance of the intra-operative dynamic rotational tracking-especially in the treatment of astigmatisms in corneal refractive Excimer laser correction-concerning clinical outcomes is presented. The cyclotorsion from upright to supine position was measured using iris image comparison. The Group 1 of patients was additionally treated with cyclorotational control and Group 2 only with X-Y control. Significant differences were observed between the groups regarding the mean postoperative cylinder refraction ( p < 0.05). The mean cyclotorsion can be calculated to 3.75° with a standard deviation of 3.1°. The total range of torsion was from -14.9° to +12.6°. Re-treatment rate was 2.2% in Group 1 and 8.2% in Group 2, which is highly significant ( p < 0.01). The investigation confirms that the dynamic rotational tracking system used for LASIK results in highly predictable refraction quality with significantly less postoperative re-treatments.

Excimer Laser Surgery: Biometrical Iris Eye Recognition with Cyclorotational Control Eye Tracker System

PubMed Central

Pajic, Bojan; Cvejic, Zeljka; Mijatovic, Zoran; Indjin, Dragan; Mueller, Joerg

2017-01-01

A prospective comparative study assessing the importance of the intra-operative dynamic rotational tracking—especially in the treatment of astigmatisms in corneal refractive Excimer laser correction—concerning clinical outcomes is presented. The cyclotorsion from upright to supine position was measured using iris image comparison. The Group 1 of patients was additionally treated with cyclorotational control and Group 2 only with X-Y control. Significant differences were observed between the groups regarding the mean postoperative cylinder refraction (p < 0.05). The mean cyclotorsion can be calculated to 3.75° with a standard deviation of 3.1°. The total range of torsion was from −14.9° to +12.6°. Re-treatment rate was 2.2% in Group 1 and 8.2% in Group 2, which is highly significant (p < 0.01). The investigation confirms that the dynamic rotational tracking system used for LASIK results in highly predictable refraction quality with significantly less postoperative re-treatments. PMID:28587100

Comparison of two techniques of marking the horizontal axis during excimer laser keratorefractive surgery for myopic astigmatism.

PubMed

Burka, Jenna M; Bower, Kraig S; Cute, David L; Stutzman, Richard D; Subramanian, Prem S; Rabin, Jeff C

2005-04-01

To compare two methods of limbal marking used during laser refractive surgery for myopic astigmatism. Retrospective chart review. Forty-two eyes of 42 patients who underwent photorefractive keratectomy (PRK) or laser-assisted in-situ keratomileusis (LASIK) for myopic astigmatism were marked preoperatively to identify the horizontal axis. In 18 eyes, marks were placed at the slit lamp (SL) with the slit beam set at 180 degrees as a reference. In 24 eyes, marks were placed in the laser room (LR) immediately before reclining under the laser. All treatments were performed with the Alcon LADARVision excimer laser system. Vector analysis of postoperative cylinder and reduction in cylinder and uncorrected and best-corrected visual acuity were evaluated for both groups. The mean postoperative magnitude of error was -0.19 +/- 0.44 diopters for the LR group and -0.09 +/- 0.42 diopters for the SL group (P = .439, NS). Both groups had a mean angle of error indicating an overall counterclockwise rotation of axis with an angle of error of 6.3 +/- 8.7 degrees for the LR group and 8.0 +/- 10.2 degrees for the SL group (P = .562, NS). We found no significant difference in outcomes with an overall trend toward undercorrection of cylinder in both groups, leaving room for improvement after refractive surgery for myopic astigmatism.

Consistent comparison of angle Kappa adjustment between Oculyzer and Topolyzer Vario topography guided LASIK for myopia by EX500 excimer laser.

PubMed

Sun, Ming-Shen; Zhang, Li; Guo, Ning; Song, Yan-Zheng; Zhang, Feng-Ju

2018-01-01

To evaluate and compare the uniformity of angle Kappa adjustment between Oculyzer and Topolyzer Vario topography guided ablation of laser in situ keratomileusis (LASIK) by EX500 excimer laser for myopia. Totally 145 cases (290 consecutive eyes )with myopia received LASIK with a target of emmetropia. The ablation for 86 cases (172 eyes) was guided manually based on Oculyzer topography (study group), while the ablation for 59 cases (118 eyes) was guided automatically by Topolyzer Vario topography (control group). Measurement of adjustment values included data respectively in horizontal and vertical direction of cornea. Horizontally, synclastic adjustment between manually actual values (dx manu ) and Oculyzer topography guided data (dx ocu ) accounts 35.5% in study group, with mean dx manu /dx ocu of 0.78±0.48; while in control group, synclastic adjustment between automatically actual values (dx auto ) and Oculyzer topography data (dx ocu ) accounts 54.2%, with mean dx auto /dx ocu of 0.79±0.66. Vertically, synclastic adjustment between dy manu and dy ocu accounts 55.2% in study group, with mean dy manu /dy ocu of 0.61±0.42; while in control group, synclastic adjustment between dy auto and dy ocu accounts 66.1%, with mean dy auto /dy ocu of 0.66±0.65. There was no statistically significant difference in ratio of actual values/Oculyzer topography guided data in horizontal and vertical direction between two groups ( P =0.951, 0.621). There is high consistency in angle Kappa adjustment guided manually by Oculyzer and guided automatically by Topolyzer Vario topography during corneal refractive surgery by WaveLight EX500 excimer laser.

Does imiquimod pretreatment optimize 308-nm excimer laser (UVB) therapy in psoriasis patients?

PubMed

Tacastacas, Joselin D; Oyetakin-White, Patricia; Soler, David C; Young, Andrew; Groft, Sarah; Honda, Kord; Cooper, Kevin D; McCormick, Thomas S

2017-07-01

Psoriasis continues to be a debilitating skin disease affecting 1-3% of the United States population. Although the effectiveness of several current biologic therapies have described this pathology as a IL-23, TNF-a and Th17-mediated disease, less invasive approaches are still in use and in need of refinement. One of these is the usage of narrow band-UVB (NB-UVB) therapy to deplete specifically intra-epidermal CD3+, CD4+ and CD8+ cells to clear psoriatic plaques. In order to improve NB-UVB therapy, we sought to determine whether skin pre-treatment with the TLR7 agonist imiquimod (IMQ) would help increase the efficiency of the former at resolving psoriatic plaques. Eucerin ® Original Moisturizing Lotion (topical vehicle) or Aldara ® (imiquimod 5% topical cream) were applied for 5 days once daily to a maximum contiguous area of 25 cm 2 (5 cm × 5 cm area). Patients were provided with sachets containing 12.5 mg of imiquimod each and were instructed to apply imiquimod (I) to two psoriasis plaques (5 sachets of imiquimod allotted to each plaque). A PHAROS excimer Laser EX-308 (Ra Medical Systems, Inc. Carlsbad, CA, USA) with an output of monochromatic 308-nm light and pulse width of 20-50 ns was used for all patients. Punch biopsies of psoriatic lesions (6 mm) were taken at 4 and 48 h after final application of topical treatment with or without excimer laser treatment. Real-time quantitative RT-PCR was performed according to manufacturer's instructions and Inmunohistochemistry was used as described before. Our results suggests that although IMQ seemed to activate the type I interferon pathway as previously described, its concomitant usage with NB-UVB for clearing psoriatic skin was ineffective. Although upregulation of genes MxA, GRAMD1A and DMXL2 suggested that IMQ treatment did induce skin changes in psoriasis patients, more optimal dosing of IMQ and NB-UVB might be necessary to achieve desired treatment responses. The observation that psoriasis involvement was not

Laser ablation of human atherosclerotic plaque without adjacent tissue injury

NASA Technical Reports Server (NTRS)

Grundfest, W. S.; Litvack, F.; Forrester, J. S.; Goldenberg, T.; Swan, H. J. C.

1985-01-01

Seventy samples of human cadaver atherosclerotic aorta were irradiated in vitro using a 308 nm xenon chloride excimer laser. Energy per pulse, pulse duration and frequency were varied. For comparison, 60 segments were also irradiated with an argon ion and an Nd:YAG laser operated in the continuous mode. Tissue was fixed in formalin, sectioned and examined microscopically. The Nd:YAG and argon ion-irradiated tissue exhibited a central crater with irregular edges and concentric zones of thermal and blast injury. In contrast, the excimer laser-irradiated tissue had narrow deep incisions with minimal or no thermal injury. These preliminary experiments indicate that the excimer laser vaporizes tissue in a manner different from that of the continuous wave Nd:YAG or argon ion laser. The sharp incision margins and minimal damage to adjacent normal tissue suggest that the excimer laser is more desirable for general surgical and intravascular uses than are the conventionally used medical lasers.

Periodic structure with a periodicity of 2-3.5 μm on crystalline TiO2 induced by unpolarized KrF excimer lasers

NASA Astrophysics Data System (ADS)

He, Rong; Ma, Hongliang; Zheng, Jiahui; Han, Yongmei; Lu, Yuming; Cai, Chuanbing

2016-08-01

Laser-induced periodic surface structures (LIPSS) were processed on the TiO2 bulk surface under the irradiation of 248 nm unpolarized KrF excimer laser pulses in air. Spatial LIPSS periods ranging from 2 to 3.5 μm are ascribed to the capillary wave. These microstructures were analyzed at different laser pulse numbers with the laser energy from 192 to 164 mJ. The scanning electron microscopy results indicated eventually stripes that have been disrupted as the increase in the laser pulse numbers, which is reasonably explained by the energy accumulating effect. In addition, investigations were concentrated on the surface modifications at pre-focal plane, focal plane and post-focal plane in the same defocusing amount. Compared with condition at pre-focal plane, in addition to the plasma produced at target, the air was also breakdown for the situation of post-focal plane. So it was reasonable that stripes appeared at pre-focal plane but not at post-focal plane.

Some optical and electron microscope comparative studies of excimer laser-assisted and nonassisted molecular-beam epitaxically grown thin GaAs films on Si

NASA Technical Reports Server (NTRS)

Lao, Pudong; Tang, Wade C.; Rajkumar, K. C.; Guha, S.; Madhukar, A.; Liu, J. K.; Grunthaner, F. J.

1990-01-01

The quality of GaAs thin films grown via MBE under pulsed excimer laser irradiation on Si substrates is examined in both laser-irradiated and nonirradiated areas using Raman scattering, Rayleigh scattering, and by photoluminescence (PL), as a function of temperature, and by TEM. The temperature dependence of the PL and Raman peak positions indicates the presence of compressive stress in the thin GaAs films in both laser-irradiated and nonirradiated areas. This indicates incomplete homogeneous strain relaxation by dislocations at the growth temperature. The residual compressive strain at the growth temperature is large enough such that even with the introduction of tensile strain arising from the difference in thermal expansion coefficients of GaAs and Si, a compressive strain is still present at room temperature for these thin GaAs/Si films.

Inner-shell photoionization and core-hole decay of Xe and XeF2.

PubMed

Southworth, Stephen H; Wehlitz, Ralf; Picón, Antonio; Lehmann, C Stefan; Cheng, Lan; Stanton, John F

2015-06-14

Photoionization cross sections and partial ion yields of Xe and XeF2 from Xe 3d(5/2), Xe 3d(3/2), and F 1s subshells in the 660-740 eV range are compared to explore effects of the F ligands. The Xe 3d-ϵf continuum shape resonances dominate the photoionization cross sections of both the atom and molecule, but prominent resonances appear in the XeF2 cross section due to nominal excitation of Xe 3d and F 1s electrons to the lowest unoccupied molecular orbital (LUMO), a delocalized anti-bonding MO. Comparisons of the ion products from the atom and molecule following Xe 3d photoionization show that the charge-state distribution of Xe ions is shifted to lower charge states in the molecule along with production of energetic F(+) and F(2+) ions. This suggests that, in decay of a Xe 3d core hole, charge is redistributed to the F ligands and the system dissociates due to Coulomb repulsion. The ion products from excitation of the F 1s-LUMO resonance are different and show strong increases in the yields of Xe(+) and F(+) ions. The subshell ionization thresholds, the LUMO resonance energies, and their oscillator strengths are calculated by relativistic coupled-cluster methods and agree well with measurements.

Inner-shell photoionization and core-hole decay of Xe and XeF 2

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

Southworth, Stephen H.; Wehlitz, Ralf; Picón, Antonio

2015-06-14

Photoionization cross sections and partial ion yields of Xe and XeF2 from Xe 3d5/2, Xe 3d3/2, and F 1s subshells in the 660–740 eV range are compared to explore effects of the F ligands. The Xe 3d-ϵf continuum shape resonances dominate the photoionization cross sections of both the atom and molecule, but prominent resonances appear in the XeF2 cross section due to nominal excitation of Xe 3d and F 1s electrons to the lowest unoccupied molecular orbital (LUMO), a delocalized anti-bonding MO. Comparisons of the ion products from the atom and molecule following Xe 3d photoionization show that the charge-statemore » distribution of Xe ions is shifted to lower charge states in the molecule along with production of energetic F+ and F2+ ions. This suggests that, in decay of a Xe 3d core hole, charge is redistributed to the F ligands and the system dissociates due to Coulomb repulsion. The ion products from excitation of the F 1s-LUMO resonance are different and show strong increases in the yields of Xe+ and F+ ions. The subshell ionization thresholds, the LUMO resonance energies, and their oscillator strengths are calculated by relativistic coupled-cluster methods and agree well with measurements.« less

Laser- and Particle-Beam Chemical Processes on Surfaces. Volume 129

DTIC Science & Technology

1989-12-26

explosive decomposition of organometallic compounds with single pulse laser irradiation . This new... ultrashort , meaning ultra high intensity , excimer laser pulses , two-photon absorption becomes important and limits the penetration depth of the laser ...requires a higher photon load before suffering damage to its chemical structure. With extremely high light intensities , ultrashort excimer laser pulses

Factors affecting the outcome of excimer laser photorefractive keratectomy: a preliminary multivariable regression analysis

NASA Astrophysics Data System (ADS)

Maguen, Ezra I.; Papaioannou, Thanassis; Nesburn, Anthony B.; Salz, James J.; Warren, Cathy; Grundfest, Warren S.

1996-05-01

Multivariable regression analysis was used to evaluate the combined effects of some preoperative and operative variables on the change of refraction following excimer laser photorefractive keratectomy for myopia (PRK). This analysis was performed on 152 eyes (at 6 months postoperatively) and 156 eyes (at 12 months postoperatively). The following variables were considered: intended refractive correction, patient age, treatment zone, central corneal thickness, average corneal curvature, and intraocular pressure. At 6 months after surgery, the cumulative R2 was 0.43 with 0.38 attributed to the intended correction and 0.06 attributed to the preoperative corneal curvature. At 12 months, the cumulative R2 was 0.37 where 0.33 was attributed to the intended correction, 0.02 to the preoperative corneal curvature, and 0.01 to both preoperative corneal thickness and to the patient age. Further model augmentation is necessary to account for the remaining variability and the behavior of the residuals.

Post-growth annealing of germanium-tin alloys using pulsed excimer laser

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

Wang, Lanxiang; Wang, Wei; Zhou, Qian

2015-07-14

We investigate the impact of pulsed excimer laser anneal on fully strained germanium-tin alloys (Ge{sub 1−x}Sn{sub x}) epitaxially grown on Ge substrate by molecular beam epitaxy. Using atomic force microscopy, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, the morphological and compositional evolution of Ge{sub 1−x}Sn{sub x} with Sn content up to 17% after annealing using various conditions is studied. Ge{sub 0.83}Sn{sub 0.17} samples annealed at 80 mJ/cm{sup 2} or 150 mJ/cm{sup 2} have no observable changes with respect to the as-grown sample. However, Ge{sub 0.83}Sn{sub 0.17} samples annealed at 250 mJ/cm{sup 2} or 300 mJ/cm{sup 2} have Sn-richmore » islands on the surface, which is due to Sn segregation in the compressively strained epitaxial film. For Ge{sub 0.89}Sn{sub 0.11}, significant Sn redistribution occurs only when annealed at 300 mJ/cm{sup 2}, indicating that it has better thermal stability than Ge{sub 0.83}Sn{sub 0.17}. A mechanism is proposed to explain the formation of Sn-rich islands and Sn-depleted regions.« less

Dual Laser-Assisted Lamellar Anterior Keratoplasty with Tophat Graft: A Laboratory Study

PubMed Central

Cleary, Catherine; Song, Jonathan C.; Tang, Maolong; Li, Yan; Liu, Ying; Yiu, Samuel; Huang, David

2011-01-01

Objectives To develop a dual laser-assisted lamellar anterior keratoplasty (LALAK) technique, using excimer and femtosecond lasers to perform surgery on eye-bank eyes. Methods First we compared corneal stromal surfaces produced by (1) deep excimer ablation, (2) femtosecond lamellar cuts, and (3) manual dissection, and evaluated the effect of excimer laser smoothing with fluid masking on each surface. Masked observers graded scanning electron microscopy (SEM) images on a 5-point roughness scale. Then we performed a 6-mm diameter excimer laser phototherapeutic keratectomy (PTK) ablation to a residual bed thickness of 200μm, followed by laser smoothing. We used the femtosecond laser to cut donors in a modified top-hat design with a thin tapered brim, which fitted into a manually dissected circumferential pocket at the base of the recipient bed. Fourier-domain optical coherence tomography (OCT) was used to measure corneal pachymetry and evaluate graft fit. Results Deep excimer ablation with smoothing (n=4) produced a significantly (p<0.05) smoother surface (grade=3.5) than deep excimer alone (n=4, grade=3.8) or manual dissection with (n=1, grade=3.8) and without smoothing (n=1, grade=4.8). Deep femtosecond cuts (n=2) produced macroscopic concentric ridges on the stromal surface. Experimental LALAK was performed on 4 recipients prepared by deep excimer ablation and 4 donors cut with the femtosecond laser. After suturing good peripheral graft-host match was observed on FD-OCT imaging. Conclusion These preliminary studies show that the LALAK technique permits improved interface smoothness and graft edge matching. Clinical trials are needed to determine whether these improvements can translate to better vision. PMID:22378114

Thermodynamic measurements in a high pressure hydrogen-oxygen flame using Raman scattering from a broadband excimer laser

NASA Technical Reports Server (NTRS)

Hartfield, Roy, Jr.

1996-01-01

Raman scattering is an inelastic molecular scattering process in which incident radiation is reemitted at a fixed change in frequency. Raman spectroscopy can be used to measure the number density and temperature of the irradiated species. The strength of the Raman signal is inversely proportional to the wavelength raised to the fourth power. Consequently, high signal to noise ratios are obtained by using ultraviolet (UV) excitation sources. Using UV sources for Raman Spectroscopy in flames is complicated by the fact that some of the primary constituents in hydrogen-oxygen combustion absorb and reemit light in the UV and these fluorescence processes interfere with the Raman signals. This problem has been handled in atmospheric pressure flames in some instances by using a narrowband tunable excimer laser as a source. This allows for detuning from absorption transitions and the elimination of interfering fluorescence signals at the Raman wavelengths. This approach works well in the atmospheric pressure flame; however, it has two important disadvantages. First, injection-locked narrowband tunable excimer lasers are very expensive. More importantly, however, is the fact that at the high pressures characteristic of rocket engine combustion chambers, the absorption transitions are broadened making it difficult to tune to a spectral location at which substantial absorption would not occur. The approach taken in this work is to separate the Raman signal from the fluorescence background by taking advantage of the fact that Raman signal has nonisotropic polarization characteristics while the fluorescence signals are unpolarized. Specifically, for scattering at right angles to the excitation beam path, the Raman signal is completely polarized. The Raman signal is separated from the fluorescence background by collecting both horizontally and vertically polarized signals separately. One of the polarizations has both the Raman signal and the fluorescence background while the

Pulsed Gas Lasers Pumped by a Runaway Electron Initiated Discharge

NASA Astrophysics Data System (ADS)

Panchenko, A. N.; Tarasenko, V. F.; Panchenko, N. A.

2017-12-01

The generation parameters are investigated in a runaway electron preionized diffuse discharge (REP DD). Laser generation is produced in different spectral bands from the IR to VUV range. New modes of the nitrogen laser operation are obtained. Ultimate efficiencies of N2- and nonchain HF(DF)-lasers are achieved. A possibility of increasing the pulse durations of XeF-, KrF-, ArF- and VUV F2- lasers (157 nm) in an oscillating REP DD is shown. The efficiencies of VUV- and UV-generation comparable with that of a laser pumped by a self-sustained volume discharge with preionization are gained.

Comparison of Wavelight Allegretto Eye-Q and Schwind Amaris 750S excimer laser in treatment of high astigmatism.

PubMed

Bohac, Maja; Biscevic, Alma; Koncarevic, Mateja; Anticic, Marija; Gabric, Nikica; Patel, Sudi

2014-10-01

To compare functional outcomes of Wavelight Allegretto Eye-Q 400Hz and Schwind Amaris 750S excimer laser for astigmatism between 2 and 7 diopters(D). Prospective comparative non-randomized case series of 480 eyes assigned in two laser groups and further divided into myopic and mixed astigmatism subgroups. All treatments were centered on corneal vertex. One-year results were compared between the groups. Statistical analysis was performed using z-test. Both Allegretto and Amaris postoperative uncorrected distance visual acuity (UDVA) improved in comparison to preoperative corrected distance visual acuity (CDVA). The difference was significant in the Allegretto group for myopic astigmatism (p = 0.017). There was no difference in postoperative UDVA between lasers. Average sphere decreased in all groups for both lasers (p < 0.001) without difference in effectiveness of spherical correction between lasers for both groups. In Allegretto, average cylinder decreased from -3.30D to -0.55D in myopic astigmatism (p < 0.001) and from -3.84D to -0.85D in mixed astigmatism (p < 0.001). In Amaris average cylinder decreased from -3.21D to -0.43D in myopic astigmatism (p < 0.001) and from -3.66D to -0.58D in mixed astigmatism (p < 0.001). Amaris group had less residual astigmatism (myopic astigmatism p = 0.023, mixed astigmatism p < 0.001). Mean spherical aberration shifted from positive to negative in mixed astigmatism for both lasers. Both lasers are effective in terms of UDVA, CDVA, spherical correction, and preservation of high-order aberrations. However, Amaris was more effective in cylinder correction.

Rapid fabrication of rigid biodegradable scaffolds by excimer laser mask projection technique: a comparison between 248 and 308 nm

NASA Astrophysics Data System (ADS)

Beke, S.; Anjum, F.; Ceseracciu, L.; Romano, I.; Athanassiou, A.; Diaspro, A.; Brandi, F.

2013-03-01

High-resolution photocrosslinking of the biodegradable poly(propylene fumarate) (PPF) and diethyl fumarate (DEF), using pulsed laser light at 248 and 308 nm is presented. The curing depth can be modulated between a few hundreds of nm and a few μm when using 248 nm and ten to a hundred μm when using 308 nm. By adjusting the total fluence (pulse numbers×laser fluence) dose and the weight ratios of PPF, DEF, and the photoinitiator in the photocrosslinkable mixtures, the height of polymerized structures can be precisely tuned. The lateral resolution is evaluated by projecting a pattern of a grid with a specified line width and line spacing. Young’s modulus of the cured parts is measured and found to be several GPa for both wavelengths, high enough to support bone formation. Several 2D and 2.5D microstructures, as well as porous 3D scaffolds fabricated by a layer-by-layer method, are presented. The results demonstrate that excimer laser-based photocuring is suitable for the fabrication of stiff and biocompatible structures with defined patterns of micrometer resolution in all three spatial dimensions.

Laser interaction with tissue

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

Berns, M.W.

These proceedings collect papers on laser biomedicine. Topics include: light distributions on tissue; chemical byproducts of laser/tissue interactions; laser applications in ophthalmology; phododynamic therapy; diode pumped solid state lasers at two and three micrometers; and applications of excimer lasers to peripheral nerve repair.

On the importance of electron impact processes in excimer-pumped alkali laser-induced plasmas

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

Markosyan, Aram H.

We present that the excimer-pumped alkali laser (XPAL) system has recently been demonstrated in several different mixtures of alkali vapor and rare gas. Without special preventive measures, plasma formation during operation of XPAL is unavoidable. Some recent advancements in the availability of reliable data for electron impact collisions with atoms and molecules have enabled development of a complete reaction mechanism to investigate XPAL-induced plasmas. Here, we report on pathways leading to plasma formation in an Ar/C 2H 6/CsAr/C2H6/Cs XPAL sustained at different cell temperatures. We find that depending on the operating conditions, the contribution of electron impact processes can bemore » as little as bringing the excitation of Cs(P 2) states to higher level Cs** states, and can be as high as bringing Cs(P 2) excited states to a full ionization. Increasing the input pumping power or cell temperature, or decreasing the C 2H 6 mole fraction leads to electron impact processes dominating in plasma formation over the energy pooling mechanisms previously reported in literature.« less

On the importance of electron impact processes in excimer-pumped alkali laser-induced plasmas

DOE PAGES

Markosyan, Aram H.

2017-10-18

We present that the excimer-pumped alkali laser (XPAL) system has recently been demonstrated in several different mixtures of alkali vapor and rare gas. Without special preventive measures, plasma formation during operation of XPAL is unavoidable. Some recent advancements in the availability of reliable data for electron impact collisions with atoms and molecules have enabled development of a complete reaction mechanism to investigate XPAL-induced plasmas. Here, we report on pathways leading to plasma formation in an Ar/C 2H 6/CsAr/C2H6/Cs XPAL sustained at different cell temperatures. We find that depending on the operating conditions, the contribution of electron impact processes can bemore » as little as bringing the excitation of Cs(P 2) states to higher level Cs** states, and can be as high as bringing Cs(P 2) excited states to a full ionization. Increasing the input pumping power or cell temperature, or decreasing the C 2H 6 mole fraction leads to electron impact processes dominating in plasma formation over the energy pooling mechanisms previously reported in literature.« less

Plasma ignition thresholds in UV laser ablation plumes

NASA Astrophysics Data System (ADS)

Clarke, P.; Dyer, P. E.; Key, P. H.; Snelling, H. V.

Ultraviolet (UV) laser thresholds for plasma ignition on solid targets predicted from electron-neutral collisional heating are generally much higher than those observed experimentally. This inconsistency was reconciled by Rosen, et al. [2], who showed that excited-state photoionization played a key role in long-pulse UV laser breakdown. Here we develop a related model but with emphasis on pulses of 10 ns duration. Experimental results are also reported for titanium, copper, silicon, and ferulic acid targets in vacuum, irradiated with combinations of the XeF, KrF, and ArF lasers for comparison with predictions.

Visual and refractive outcomes of LASIK with the SCHWIND ESIRIS and WaveLight ALLEGRETTO WAVE Eye-q excimer lasers: a prospective, contralateral study.

PubMed

Mearza, Ali A; Muhtaseb, Mohammed; Aslanides, Ioannis M

2008-11-01

To compare the safety, efficacy, and predictability of LASIK with the SCHWIND ESIRIS and WaveLight ALLEGRETTO WAVE Eye-Q excimer laser platforms. This prospective study comprised 44 eyes of 22 consecutive patients who were treated with LASIK using the Moria M2 microkeratome. One eye was treated with the SCHWIND ESIRIS laser and the fellow eye treated with the WaveLight ALLEGRETTO WAVE Eye-Q laser. All eyes operated with the SCHWIND ESIRIS were treated with standard aspheric ablation, whereas the eyes operated with the WaveLight ALLEGRETTO WAVE Eye-Q received treatment with three different ablation types according to the common practice at our clinic. Outcome measures were uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and proximity to target refraction at 6-month follow-up. At 6 months postoperative, mean decimal UCVA was 0.96+/-0.22 (range: 0.3 to 1.2) for ESIRIS eyes and 0.98+/-0.17 (range: 0.6 to 1.2) for ALLEGRETTO eyes (P=.57). Mean postoperative spherical equivalent refraction was -0.02+/-0.28 diopters (D) (range: -0.75 to +0.75 D) for ESIRIS eyes and 0.11+/-0.91 D (range: -1.00 to +3.88 D) for ALLEGRETTO eyes (P=.49). Of the ESIRIS eyes, 20/22 (91%) were within +/-1.00 D of target refraction and 20/22 (91%) were within +/-0.50 D of target refraction. Of the ALLEGRETTO eyes, 20/22 (91%) and 19/22 (86%) were within +/-1.00 D and +/-0.50 D, respectively, of target refraction. No patient lost > or =2 lines of BSCVA in either group. No differences were seen in safety and efficacy outcome parameters between the SCHWIND ESIRIS and WaveLight ALLEGRETTO WAVE Eye-Q excimer lasers when used according to a previously established treatment algorithm at our clinic in the treatment of refractive error.

Deep Laser-Assisted Lamellar Anterior Keratoplasty with Microkeratome-Cut Grafts

PubMed Central

Yokogawa, Hideaki; Tang, Maolong; Li, Yan; Liu, Liang; Chamberlain, Winston; Huang, David

2016-01-01

Background The goals of this laboratory study were to evaluate the interface quality in laser-assisted lamellar anterior keratoplasty (LALAK) with microkeratome-cut grafts, and to achieve good graft–host apposition. Methods Simulated LALAK surgeries were performed on six pairs of eye bank corneoscleral discs. Anterior lamellar grafts were precut with microkeratomes. Deep femtosecond (FS) laser cuts were performed on host corneas followed by excimer laser smoothing. Different parameters of FS laser cuts and excimer laser smoothing were tested. OCT was used to measure corneal pachymetry and evaluate graft-host apposition. The interface quality was quantified in a masked fashion using a 5-point scale based on scanning electron microscopy images. Results Deep FS laser cuts at 226–380 μm resulted in visible ridges on the host bed. Excimer laser smoothing with central ablation depth of 29 μm and saline as a smoothing agent did not adequately reduce ridges (score = 4.0). Deeper excimer laser ablation of 58 μm and Optisol-GS as a smoothing agent smoothed ridges to an acceptable level (score = 2.1). Same sizing of the graft and host cut diameters with an approximately 50 μm deeper host side-cut relative to the central graft thickness provided the best graft–host fit. Conclusions Deep excimer laser ablation with a viscous smoothing agent was needed to remove ridges after deep FS lamellar cuts. The host side cut should be deep enough to accommodate thicker graft peripheral thickness compared to the center. This LALAK design provides smooth lamellar interfaces, moderately thick grafts, and good graft-host fits. PMID:26890667

In vitro analysis of laser meniscectomy.

PubMed

Vangsness, C T; Akl, Y; Nelson, S J; Liaw, L H; Smith, C F; Marshall, G J

1995-01-01

Partial meniscectomies were performed on 32 fresh human meniscal autopsy specimens. The following laser systems were tested: carbon dioxide (CO2), neodymium:yttrium aluminum garnet (Nd:YAG), potassium titanyl phosphate (KTP), holmium:YAG (Ho:YAG), and excimer. Meniscectomies with these lasers were compared with scalpel, mechanical, and electrocautery meniscectomies. Lasers were applied to specimens in and out of normal saline. Routine hematoxylin and eosin and sirius red sections were prepared for each specimen, and the depths of thermal changes were analyzed. Scanning electron microscopy was used to visualize the meniscectomy interface. Among these specimens, the scalpel and mechanical meniscectomies showed the least extension of cellular changes (range, 10-15 nm). The excimer laser caused the least tissue changes of the lasers tested. Tissue changes were less extensive with the pulsed CO2 laser than with the holmium:YAG, neodymium:YAG, and KTP lasers. Scanning electron microscopy showed that use of the scalpel meniscectomy resulted in the smoothest meniscectomy edge, followed by use of the excimer, CO2, holmium:YAG, neodymium:YAG, and KTP lasers. The most surface disruption occurred with electrocautery. Meniscectomies under saline required more energy and took longer in each case, with the holmium:YAG, neodymium:YAG, and CO2 laser cutting the best. Saline meniscectomies showed less thermal change. The CO2 and KTP lasers cut best in air.

Microgroove fabrication with excimer laser ablation techniques for optical fiber array alignment purposes

NASA Astrophysics Data System (ADS)

Naessens, Kris; Van Hove, An; Coosemans, Thierry; Verstuyft, Steven; Vanwassenhove, Luc; Van Daele, Peter; Baets, Roel G.

2000-11-01

Currently, an ever increasing need for bandwidth, compactness and efficiency characterizes the world of interconnect and data communication. This tendency has already led to serial links being gradually replaced by parallel optical interconnect solutions. However, as the maximum capacity for the latter will be reached in the near future, new approaches are required to meet demand. One possible option is to switch to 2D parallel implementations of fiber arrays. In this paper we present the fabrication of a 2D connector for coupling a 4x8 array of plastic optical fibers to RCLED or VCSEL arrays. The connector consists primarily of dedicated PMMA plates in which arrays of 8 precisely dimensioned grooves at a pitch of 250 micrometers are introduced. The trenches are each 127 micrometers deep and their width is optimized to allow fixation of plastic optical fibers. We used excimer laser ablation for prototype fabrication of these alignment microstructures. In a later stage, the plates can be replicated using standard molding techniques. The laser ablation technique is extremely well suited for rapid prototyping and proves to be a versatile process yielding high accuracy dimensioning and repeatability of features in a wide diversity of materials. The dependency of the performance in terms of quality of the trenches (bottom roughness) and wall angle on various parameters (wavelength, energy density, pulse frequency and substrate material) is discussed. The fabricated polymer sheets with grooves are used to hold optical fibers by means of a UV-curable adhesive. In a final phase, the plates are stacked and glued in order to realize the 2D-connector of plastic optical fibers for short distance optical interconnects.

Critical review on refractive surgical lasers

NASA Astrophysics Data System (ADS)

Lin, J. T.

1995-03-01

The current status of refractive surgical lasers (including excimer and nonexcimer lasers) is reviewed with an emphasis on photorefractive keratectomy (PRK). The correlation of engineering parameters and the clinical requirements with optimal conditions are presented. The fundamentals of corneal reshaping with formulas for ablation profiles and the advantages of the multizone method are discussed. Updated information on the Mini-Excimer PRK laser system, with an emphasis on the scanning delivery device, is presented. PMMA ablation profiles performed by standard diaphragm and scanning modes are compared for surface ablation quality. Scanning mode ablation patterns for myopia, hyperopia, and regular and irregular astigmatism are presented.

Laser micromachining of optical devices

NASA Astrophysics Data System (ADS)

Kopitkovas, Giedrius; Lippert, Thomas; David, Christian; Sulcas, Rokas; Hobley, Jonathan; Wokaun, Alexander J.; Gobrecht, Jens

2004-10-01

The combination of a gray tone phase mask with a laser assisted wet etching process was applied to fabricate complex microstructures in UV transparent dielectric materials. This one-step method allows the generation of arrays of plano-convex and Fresnel micro-lenses using a conventional XeCl excimer laser and an absorbing liquid, which is in contact with the UV transparent material. An array of plano-convex micro-lenses was tested as beam homogenizer for a high power XeCl excimer and ps Nd:YAG laser. The roughness of the etched features varies from several μm to 10 nm, depending on the laser fluence and concentration of the dye in the organic liquid. The etching process can be divided into several etching mechanisms which vary with laser fluence.

Ruthenium Grubbs' catalyst nanostructures grown by UV-excimer-laser ablation for self-healing applications

NASA Astrophysics Data System (ADS)

Aïssa, B.; Nechache, R.; Haddad, E.; Jamroz, W.; Merle, P. G.; Rosei, F.

2012-10-01

A self healing composite material consisting of 5-Ethylidene-2-Norbornene (5E2N) monomer reacted with Ruthenium Grubbs' Catalyst (RGC) was prepared. First, the kinetics of the 5E2N ring opening metathesis polymerization (ROMP) reaction RGC was studied as a function of temperature. We show that the polymerization reaction is still effective in a large temperature range (-15 to 45 °C), occurring at short time scales (less than 1 min at 40 °C). Second, the amount of RGC required for ROMP reaction significantly decreased through its nanostructuration by means of a UV-excimer laser ablation process. RGC nanostructures of few nanometers in size where successfully obtained directly on silicon substrates. The X-ray photoelectron spectroscopy data strongly suggest that the RGC still keep its original stoichiometry after nanostructuration. More importantly, the associated ROMP reaction was successfully achieved at an extreme low RGC concentration equivalent to (11.16 ± 1.28) × 10-4 Vol.%, occurring at very short time reaction. This approach opens new prospects for using healing agent nanocomposite materials for self-repair functionality, thereby obtaining a higher catalytic efficiency per unit mass.

The safety and efficacy of the 308-nm excimer laser for pigment correction of hypopigmented scars and striae alba.

PubMed

Alexiades-Armenakas, Macrene R; Bernstein, Leonard J; Friedman, Paul M; Geronemus, Roy G

2004-08-01

To assess the safety and efficacy of the 308-nm excimer laser in pigment correction of hypopigmented scars and striae alba. Institutional review board-approved randomized controlled trial. Private research center. Volunteer sample of 31 adult subjects with hypopigmented scars or striae alba distributed on the face, torso, or extremities. Lesions were randomized to receive treatment or not, with site-matched normal control areas. Treatments were initiated with a minimal erythema dose minus 50 mJ/cm(2) to affected areas. Subsequent treatments were performed biweekly until 50% to 75% pigment correction, then every 2 weeks thereafter until a maximum of 10 treatments, 75% increase in colorimetric measurements, or 100% visual pigment correction. Pigment correction by visual and colorimetric assessments compared with untreated control lesions and site-matched normal skin before each treatment and at 1-, 2-, 4-, and 6-month follow-up intervals. Occurrence of erythema, blistering, dyspigmentation, or other adverse effects was monitored. The percentage pigment correction by both assessments increased in direct proportion to the number of treatments. The mean percentage pigment correction by visual assessment relative to control of 61% (95% confidence interval [CI], 55%-67%) for scars and 68% (95% CI, 62%-74%) for striae was achieved after 9 treatments. The mean percentage pigmentation by colorimetric measurements relative to control of 101% (95% CI, 99%-103%) for scars and 102% (95% CI, 99%-104%) for striae was achieved after 9 treatments. Both sets of values gradually declined toward baseline levels during the 6-month follow-up. No blistering or dyspigmentation occurred. Therapy with the 308-nm excimer laser is safe and effective in pigment correction of hypopigmented scars and striae alba. Mean final pigment correction rates relative to control sites of approximately 60% to 70% by visual assessment and 100% by colorimetric analysis were observed after 9 treatments

Location-Control of Large Si Grains by Dual-Beam Excimer-Laser and Thick Oxide Portion

NASA Astrophysics Data System (ADS)

Ishihara, Ryoichi; Burtsev, Artyom; Alkemade, Paul F. A.

2000-07-01

An array of large Si grains was placed at a predetermined position by dual excimer-laser irradiation of a multi-layer structure of silicon (Si), silicon dioxide (SiO2) with an array of bumps and metal on a glass substrate. We have investigated the effects of irradiating energy density and the topology of the structure on the grain size and crystallographic structure by scanning electron microscopy (SEM) and electron back-scattering pattern (EBSP) analysis. In the low-energy-density regime, numerous small grains and petal shaped grains formed on top of the SiO2 bumps. The number of small grains on the bumps decreased with increasing irradiating energy density. At sufficiently high energy densities, one single Si grain as large as 3.5 μm was positioned at the center of the bumps. Although most of the area of the large Si grain has a single crystallographic orientation, twins and low-angle grain boundaries are often formed at the periphery of the grain. There was no preferred crystallographic orientation in the center of the location-controlled Si grain. Numerical analysis of the temperature profile showed that a temperature drop occurs at the center of the bump, during and immediately after laser irradiation. The diameter of the location-controlled Si grain increased with total thickness of the intermediate SiO2 layer, and took the maximum value of 6.2 μm.

Excimer laser ablation of the cornea

NASA Astrophysics Data System (ADS)

Pettit, George H.; Ediger, Marwood N.; Weiblinger, Richard P.

1995-03-01

Pulsed ultraviolet laser ablation is being extensively investigated clinically to reshape the optical surface of the eye and correct vision defects. Current knowledge of the laser/tissue interaction and the present state of the clinical evaluation are reviewed. In addition, the principal findings of internal Food and Drug Administration research are described in some detail, including a risk assessment of the laser-induced-fluorescence and measurement of the nonlinear optical properties of cornea during the intense UV irradiation. Finally, a survey is presented of the alternative laser technologies being explored for this ophthalmic application.

Laser Refractive Surgery

NASA Astrophysics Data System (ADS)

Wynne, James

Refractive surgery has its roots in corneal transplant surgery, first performed in 1905, where the damaged or diseased cornea of a living individual is replaced by donated corneal tissue taken from a recently deceased individual. Since the cornea has no blood supply, there is no danger of organ rejection. Recognizing the exceptional healing power of corneal tissue, ophthalmologists began to explore methods of reshaping the cornea to improve the visual acuity of patients suffering from myopia, hyperopia, and astigmatism. In 1964, a procedure known as keratomileusis was introduced. In 1974, radial keratotomy (RK) was introduced. In 1981, excimer laser surgery was discovered by the speaker and his IBM Research colleagues. In 1983, the excimer laser was used to create clean, precise incisions in the cornea of enucleated calf eyes, derived from slaughter, launching the era of laser refractive surgery, with more precise and safer techniques to correct myopia, hyperopia, and stigmatism. This talk will describe the widely practiced surgical procedures known as photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK), which have improved the visual acuity of more than 35 million people. Most patients undergoing PRK or LASIK end up with uncorrected vision better than 20/20. In 2007, development commenced on a new procedure known as small incision lenticule extraction (SMILE), employing a femtosecond laser and no excimer laser. SMILE is promoted as minimally invasive and combining the advantages of PRK and LASIK. However, long term stability of visual acuity following SMILE surgery is yet to be determined.

Clinical results of excimer laser photorefractive keratectomy: a multicenter study of 265 eyes.

PubMed

Aron-Rosa, D S; Colin, J; Aron, B; Burin, N; Cochener, B; Febraro, J L; Gallinaro, C; Ganem, S; Valdes, R

1995-11-01

Efficacy, predictability, and safety of excimer laser photorefractive keratectomy were evaluated at centers in Paris and Brest, France. Photoablation was performed with the VISX laser on 265 eyes (151 at the Paris center and 114 at the Brest center). The eyes were clinically and statistically evaluated over a six month follow-up. Initial myopia ranged from -0.7 to -19.4 diopters (D) (mean spherical equivalent [SE] -5.9 D) in the Paris center and from -0.9 to -14.5 D (SE -4.5 D) in the Brest center. At both centers, the mean uncorrected visual acuity was worse than 20/200; over 90% of cases in each center had a best uncorrected visual acuity of 20/100 or worse. Results are reported globally and for subgroups of myopia: Group A, SE better than or equal to -3.0 D; Group B, SE worse than -3.0 D and better than or equal to -7.0 D; Group C, SE worse than -7.0 D. Uncorrected visual acuity was significantly improved in the patients followed for six months; 64% of Paris cases and 62% of Brest cases obtained an uncorrected visual acuity of 20/40 or better. Predictability of the treatment was good; 67% of Paris eyes and 74% of Brest eyes were less than 1.0 D from the intended correction after six months. The data suggest that the initial myopia affected the efficacy and predictability of the treatment; results in the mild to moderate myopia eyes were significantly better than results in the severe myopia eyes. One case of visual acuity regression (less than one line) was observed in the two groups. This was associated with corneal haze of moderate intensity.

Application of LIF technique for the space- and time-resolved monitoring of pollutant gas decomposition in nonthermal plasma reactors

NASA Astrophysics Data System (ADS)

Mizeraczyk, Jerzy; Ohkubo, Toshikazu; Kanazawa, Seiji; Kocik, Marek

2003-10-01

Laser-induced fluorescence (LIF) technique aided by intensified CCD light signal detection and fast digital image processing is demonstrated to be a useful diagnostic method for in-situ observation of the discharge-induced plasma-chemistry processes responsible for NOx(NO + NO2) decomposition occurring in non-thermal plasma reactors. In this paper a method and results of the LIF measurement of two-dimensional distribution of the ground-state NO molecule density inside a DC positive streamer corona reactor during NO removal from a flue gas simulator [air/NO(up to 300 ppm)] are presented. Either a needle-to-plate or nozzle-to-plate electrode system, having an electrode gap of 30-50 mm was used for generating the corona discharge in the reactor. The LIF monitoring of NO molecules was carried out under the steady-state DC corona discharge condition. The laser-induced fluorescence on the transition NO X2Π(v"=0)<--A2Σ+(v'=0) at λ=226nm was chosen for monitoring ground-state NO molecules in the reactor. This transition was induced by irradiation of the NO molecules with UV laser pulses generated by a laser system consisted of a XeF excimer laser, dye laser and BBO crystal. The laser pulses from the XeF excimer laser (Lambda Physik, Complex 150, λ=351 nm) pumped the dye laser (Lambda Physik, Scanmate) with Coumarin 47 as a dye, which generated the laser beam of a wavelength turned around λ=450 nm. Then, the tuned dye laser beam pumped the BBO crystal in which the second harmonic radiation of a wavelength correspondingly tuned around λ=226 nm was generated. The 226-nm UV laser pulses of energy of 0.8-2 mJ and duration of about 20 ns were transformed into the form of the so-called laser sheet (width of 1 mm, height of 30-50 mm) which passed between the electrodes through the operating gas. The obtained results, presented in the form of images, which illustrated the two-dimensional distributions of NO molecule concentration in the non-thermal reactor, showed that the

Endothermic singlet fission is hindered by excimer formation

NASA Astrophysics Data System (ADS)

Dover, Cameron B.; Gallaher, Joseph K.; Frazer, Laszlo; Tapping, Patrick C.; Petty, Anthony J.; Crossley, Maxwell J.; Anthony, John E.; Kee, Tak W.; Schmidt, Timothy W.

2018-03-01

Singlet fission is a process whereby two triplet excitons can be produced from one photon, potentially increasing the efficiency of photovoltaic devices. Endothermic singlet fission is desired for a maximum energy-conversion efficiency, and such systems have been considered to form an excimer-like state with multiexcitonic character prior to the appearance of triplets. However, the role of the excimer as an intermediate has, until now, been unclear. Here we show, using 5,12-bis((triisopropylsilyl)ethynyl)tetracene in solution as a prototypical example, that, rather than acting as an intermediate, the excimer serves to trap excited states to the detriment of singlet-fission yield. We clearly demonstrate that singlet fission and its conjugate process, triplet-triplet annihilation, occur at a longer intermolecular distance than an excimer intermediate would impute. These results establish that an endothermic singlet-fission material must be designed to avoid excimer formation, thus allowing singlet fission to reach its full potential in enhancing photovoltaic energy conversion.

Endothermic singlet fission is hindered by excimer formation.

PubMed

Dover, Cameron B; Gallaher, Joseph K; Frazer, Laszlo; Tapping, Patrick C; Petty, Anthony J; Crossley, Maxwell J; Anthony, John E; Kee, Tak W; Schmidt, Timothy W

2018-03-01

Singlet fission is a process whereby two triplet excitons can be produced from one photon, potentially increasing the efficiency of photovoltaic devices. Endothermic singlet fission is desired for a maximum energy-conversion efficiency, and such systems have been considered to form an excimer-like state with multiexcitonic character prior to the appearance of triplets. However, the role of the excimer as an intermediate has, until now, been unclear. Here we show, using 5,12-bis((triisopropylsilyl)ethynyl)tetracene in solution as a prototypical example, that, rather than acting as an intermediate, the excimer serves to trap excited states to the detriment of singlet-fission yield. We clearly demonstrate that singlet fission and its conjugate process, triplet-triplet annihilation, occur at a longer intermolecular distance than an excimer intermediate would impute. These results establish that an endothermic singlet-fission material must be designed to avoid excimer formation, thus allowing singlet fission to reach its full potential in enhancing photovoltaic energy conversion.

Hydroxyapatite and bioactive glass surfaces for fiber reinforced composite implants via surface ablation by Excimer laser.

PubMed

Kulkova, Julia; Moritz, Niko; Huhtinen, Hannu; Mattila, Riina; Donati, Ivan; Marsich, Eleonora; Paoletti, Sergio; Vallittu, Pekka K

2017-11-01

In skeletal reconstructions, composites, such as bisphenol-A-glycidyldimethacrylate resin reinforced with glass fibers, are potentially useful alternatives to metallic implants. Recently, we reported a novel method to prepare bioactive surfaces for these composites. Surface etching by Excimer laser was used to expose bioactive glass granules embedded in the resin. The purpose of this study was to analyze two types of bioactive surfaces created by this technique. The surfaces contained bioactive glass and hydroxyapatite granules. The selected processing parameters were adequate for the creation of the surfaces. However, the use of porous hydroxyapatite prevented the complete exposure the granules. In cell culture, for bioactive glass coatings, the pattern of proliferation of MG63 cells was comparable to that in the positive control group (Ti6Al4V) while inferior cell proliferation was observed on the surfaces containing hydroxyapatite granules. Scanning electron microscopy revealed osteointegration of implants with both types of surfaces. The technique is suitable for the exposure of solid bioactive glass granules. However, the long-term performance of the surfaces needs further assessment. Copyright © 2017 Elsevier Ltd. All rights reserved.

Long-Term Clinical Outcomes of Myopic Patients Having Thin Residual Corneal Thickness after Excimer Laser Surface Ablation.

PubMed

Kocamış, Sücattin İlker; Çakmak, Hasan Basri; Gerçeker, Sıdıka; Çağıl, Nurullah

2017-01-01

To investigate and compare the long-term safety, efficacy, and accuracy of PRK (photorefractive keratectomy) and LASEK (laser epithelial keratomileusis) in myopic corneas having residual corneal thickness less than 400 micron meters (µm). The medical reports of the patients who had undergone excimer laser surface ablation between 2007-2011 and had a residual corneal thickness less than 400 µm were retrospectively reviewed. Forty-two eyes of 42 patients with a mean age of 28.79±7.76 years were enrolled into the study. Twenty-two PRK and 20 LASEK procedures were performed. The mean follow-up time was 45.00±11.80 months. At the end of follow-up, no ectasia was detected. Nineteen percent of eyes had trace haze. No eyes lost any lines in corrected distance visual acuity. Eighty-one percent of the patients had an uncorrected distance visual acuity better than 20/40. The regression rate was 16.7%. Sixty-two percent of eyes were within ±1.00 D. The safety and efficacy indexes were 1.19±0.42 and 1.00±0.40, respectively. There was not any difference between LASEK and PRK regarding achieved spherical equivalent refraction, haze ratio, visual acuity, safety, efficacy, and regression. Both PRK and LASEK are safe and effective in myopic corneas having thin residual thickness.

Raman Shifting a Tunable ArF Excimer Laser to Wavelengths of 190 to 240 nm With a Forced Convection Raman Cell

NASA Technical Reports Server (NTRS)

Balla, R. Jeffrey; Herring, G. C.

2000-01-01

Tunable radiation, at ultraviolet wavelengths, is produced by Raman shifting a modified 285-mJ ArF excimer laser. Multiple Stokes outputs are observed in H2, CH4, D2, N2, SF6, and CF4 (20, 22, 53, 21, 2.1, and 0.35 percent, respectively). Numbers in parentheses are the first Stokes energy conversion efficiencies. We can access 70 percent of the frequency range 42000-52000 cm (exp -1) (190-240 nm) with Stokes energies that vary from 0.2 microJoule to 58 mJ inside the Raman cell. By using 110 mJ of pump energy and D 2 , the tunable first Stokes energy varies over the 29-58 mJ range as the wavelength is tuned over the 204-206 nm range. Dependence on input energy, gas pressure, He mixture fraction, and circulation of the gas in the forced convection Raman cell is discussed; Stokes conversion is also discussed for laser repetition rates from 1 to 100 Hz. An empirical equation is given to determine whether forced convection can improve outputs for a given repetition rate.

Biomodulation of light on cells in laser surgery

NASA Astrophysics Data System (ADS)

Liu, Timon C.; Li, Yan; Duan, Rui; Cai, Xiongwei

2002-04-01

In laser surgery, it has been observed pulsed 532-nm laser can avoid postoperative purpura, but pulsed 585-nm, 595-nm or 600-nm lasers nonetheless cause purpura when they were used to treat port-wine stains; the XeCl excimer laser (308 nm) can safely and effectively clear psoriasis; both XeCl excimer laser and Ho:YAG laser were used in coronary interventions, but only former was approved by the FDA; open channels after ultraviolet (UV) laser treatment and closed channels with infrared (IR) lasers for transmyocardial laser revascularization; and so on. In this paper, the biological information model of low intensity laser (BIML) is extended to include UVA biomodulation and is used to understand these phenomena. Although the central intensity of the laser beam is so intense that it destroys the tissue, the edge intensity is so low that it can induce biomodulation. Our investigation showed that biomodulation of light on cells might play an important role in the long-term effects of laser surgery.

Applications of lasers and electro-optics

NASA Astrophysics Data System (ADS)

Tan, B. C.; Low, K. S.; Chen, Y. H.; Ahmad, Harith; Tou, T. Y.

Supported by the IRPA Programme on Laser Technology and Applications, many types of lasers have been designed, constructed and applied in various areas of science, medicine and industries. Amongst these lasers constructed were high power carbon dioxide lasers, rare gas halide excimer lasers, solid state Neodymium-YAG lasers, nitrogen lasers, flashlamp pumped dye lasers and nitrogen and excimer laser pumped dye lasers. These lasers and the associated electro-optics system, some with computer controlled, are designed and developed for the following areas of applications: (1) industrial applications of high power carbon dioxide lasers for making of i.c. components and other materials processing purposes -- prototype operational systems have been developed; (2) Medical applications of lasers for cancer treatment using the technique of photodynamic therapy -- a new and more effective treatment protocol has been proposed; (3) agricultural applications of lasers in palm oil and palm fruit-fluorescence diagnostic studies -- fruit ripeness signature has been developed and palm oil oxidation level were investigated; (4) development of atmospheric pollution monitoring systems using laser lidar techniques -- laboratory scale systems were developed; and (5) other applications of lasers including laser holographic and interferometric methods for the non destructive testing of materials.

Neutron detection by scintillation of noble-gas excimers

NASA Astrophysics Data System (ADS)

McComb, Jacob Collin

Neutron detection is a technique essential to homeland security, nuclear reactor instrumentation, neutron diffraction science, oil-well logging, particle physics and radiation safety. The current shortage of helium-3, the neutron absorber used in most gas-filled proportional counters, has created a strong incentive to develop alternate methods of neutron detection. Excimer-based neutron detection (END) provides an alternative with many attractive properties. Like proportional counters, END relies on the conversion of a neutron into energetic charged particles, through an exothermic capture reaction with a neutron absorbing nucleus (10B, 6Li, 3He). As charged particles from these reactions lose energy in a surrounding gas, they cause electron excitation and ionization. Whereas most gas-filled detectors collect ionized charge to form a signal, END depends on the formation of diatomic noble-gas excimers (Ar*2, Kr*2,Xe* 2) . Upon decaying, excimers emit far-ultraviolet (FUV) photons, which may be collected by a photomultiplier tube or other photon detector. This phenomenon provides a means of neutron detection with a number of advantages over traditional methods. This thesis investigates excimer scintillation yield from the heavy noble gases following the boron-neutron capture reaction in 10B thin-film targets. Additionally, the thesis examines noble-gas excimer lifetimes with relationship to gas type and gas pressure. Experimental data were collected both at the National Institute of Standards and Technology (NIST) Center for Neutron Research, and on a newly developed neutron beamline at the Maryland University Training Reactor. The components of the experiment were calibrated at NIST and the University of Maryland, using FUV synchrotron radiation, neutron imaging, and foil activation techniques, among others. Computer modeling was employed to simulate charged-particle transport and excimer photon emission within the experimental apparatus. The observed excimer

Influence of spatial and temporal spot distribution on the ocular surface quality and maximum ablation depth after photoablation with a 1050 Hz excimer laser system.

PubMed

Mrochen, Michael; Schelling, Urs; Wuellner, Christian; Donitzky, Christof

2009-02-01

To investigate the effect of temporal and spatial distributions of laser spots (scan sequences) on the corneal surface quality after ablation and the maximum ablation of a given refractive correction after photoablation with a high-repetition-rate scanning-spot laser. IROC AG, Zurich, Switzerland, and WaveLight AG, Erlangen, Germany. Bovine corneas and poly(methyl methacrylate) (PMMA) plates were photoablated using a 1050 Hz excimer laser prototype for corneal laser surgery. Four temporal and spatial spot distributions (scan sequences) with different temporal overlapping factors were created for 3 myopic, 3 hyperopic, and 3 phototherapeutic keratectomy ablation profiles. Surface quality and maximum ablation depth were measured using a surface profiling system. The surface quality factor increased (rough surfaces) as the amount of temporal overlapping in the scan sequence and the amount of correction increased. The rise in surface quality factor was less for bovine corneas than for PMMA. The scan sequence might cause systematic substructures at the surface of the ablated material depending on the overlapping factor. The maximum ablation varied within the scan sequence. The temporal and spatial distribution of the laser spots (scan sequence) during a corneal laser procedure affected the surface quality and maximum ablation depth of the ablation profile. Corneal laser surgery could theoretically benefit from smaller spot sizes and higher repetition rates. The temporal and spatial spot distributions are relevant to achieving these aims.

193nm high power lasers for the wide bandgap material processing

NASA Astrophysics Data System (ADS)

Fujimoto, Junichi; Kobayashi, Masakazu; Kakizaki, Koji; Oizumi, Hiroaki; Mimura, Toshio; Matsunaga, Takashi; Mizoguchi, Hakaru

2017-02-01

Recently infrared laser has faced resolution limit of finer micromachining requirement on especially semiconductor packaging like Fan-Out Wafer Level Package (FO-WLP) and Through Glass Via hole (TGV) which are hard to process with less defect. In this study, we investigated ablation rate with deep ultra violet excimer laser to explore its possibilities of micromachining on organic and glass interposers. These results were observed with a laser microscopy and Scanning Electron Microscope (SEM). As the ablation rates of both materials were quite affordable value, excimer laser is expected to be put in practical use for mass production.

Laser Angioplasty

NASA Technical Reports Server (NTRS)

1990-01-01

The principal method of dealing with coronary artery blockage is bypass surgery. A non-surgical alternative available to some patients is balloon angioplasty. For several years, medical researchers have been exploring another alternative that would help a wider circle of patients than the balloon treatment and entail less risk than bypass surgery. A research group is on the verge of an exciting development: laser angioplasty with a 'cool' type of laser, called an excimer laser, that does not damage blood vessel walls and offers non-surgical cleansing of clogged arteries with extraordinary precision. The system is the Dymer 200+ Excimer Laser Angioplasty System, developed by Advanced Intraventional Systems. Used in human clinical tests since 1987, the system is the first fully integrated 'cool' laser capable of generating the requisite laser energy and delivering the energy to target arteries. Thirteen research hospitals in the U.S. have purchased Dymer 200+ systems and used them in clinical trials in 121 peripheral and 555 coronary artery cases. The success rate in opening blocked coronary arteries is 85 percent, with fewer complications than in balloon angioplasty. Food and Drug Administration approval for the system is hoped for in the latter part of 1990. * Advanced Intraventional Systems became Spectranetics in 1994 and discontinued the product.

Laser-driven hydrothermal process studied with excimer laser pulses

NASA Astrophysics Data System (ADS)

Mariella, Raymond; Rubenchik, Alexander; Fong, Erika; Norton, Mary; Hollingsworth, William; Clarkson, James; Johnsen, Howard; Osborn, David L.

2017-08-01

Previously, we discovered [Mariella et al., J. Appl. Phys. 114, 014904 (2013)] that modest-fluence/modest-intensity 351-nm laser pulses, with insufficient fluence/intensity to ablate rock, mineral, or concrete samples via surface vaporization, still removed the surface material from water-submerged target samples with confinement of the removed material, and then dispersed at least some of the removed material into the water as a long-lived suspension of nanoparticles. We called this new process, which appears to include the generation of larger colorless particles, "laser-driven hydrothermal processing" (LDHP) [Mariella et al., J. Appl. Phys. 114, 014904 (2013)]. We, now, report that we have studied this process using 248-nm and 193-nm laser light on submerged concrete, quartzite, and obsidian, and, even though light at these wavelengths is more strongly absorbed than at 351 nm, we found that the overall efficiency of LDHP, in terms of the mass of the target removed per Joule of laser-pulse energy, is lower with 248-nm and 193-nm laser pulses than with 351-nm laser pulses. Given that stronger absorption creates higher peak surface temperatures for comparable laser fluence and intensity, it was surprising to observe reduced efficiencies for material removal. We also measured the nascent particle-size distributions that LDHP creates in the submerging water and found that they do not display the long tail towards larger particle sizes that we had observed when there had been a multi-week delay between experiments and the date of measuring the size distributions. This is consistent with transient dissolution of the solid surface, followed by diffusion-limited kinetics of nucleation and growth of particles from the resulting thin layer of supersaturated solution at the sample surface.

Evaluation of the performance of small diode pumped UV solid state (DPSS) Nd:YAG lasers as new radiation sources for atmospheric pressure laser ionization mass spectrometry (APLI-MS).

PubMed

Kersten, Hendrik; Lorenz, Matthias; Brockmann, Klaus J; Benter, Thorsten

2011-06-01

The performance of a KrF* bench top excimer laser and a compact diode pumped UV solid state (DPSS) Nd:YAG laser as photo-ionizing source in LC-APLI MS is compared. The commonly applied bench-top excimer laser, operating at 248 nm, provides power densities of the order of low MW/cm(2) on an illuminated area of 0.5 cm(2) (8 mJ/pulse, 5 ns pulse duration, beam waist area 0.5 cm(2), 3 MW/cm(2)). The DPSS laser, operating at 266 nm, provides higher power densities, however, on a two orders of magnitude smaller illuminated area (60 μJ/pulse, 1 ns pulse duration, beam waist area 2 × 10(-3) cm(2), 30 MW/cm(2)). In a common LC-APLI MS setup with direct infusion of a 10 nM pyrene solution, the DPSS laser yields a significantly smaller ion signal (0.9%) and signal to noise ratio (1.4%) compared with the excimer laser. With respect to the determined low detection limits (LODs) for PAHs of 0.1 fmol using an excimer laser, LODs in DPSS laser LC-APLI MS in the low pmol regime are expected. The advantages of the DPSS laser with respect to applicability (size, cost, simplicity) may render this light source the preferred one for APLI applications not focusing on ultimately high sensitivities. Furthermore, the impact of adjustable ion source parameters on the performance of both laser systems is discussed in terms of the spatial sensitivity distribution described by the distribution of ion acceptance (DIA) measurements. Perspectives concerning the impact on future APLI-MS applications are given.

Laser assisted processing; Proceedings of the Meeting, Hamburg, Federal Republic of Germany, Sept. 19, 20, 1988

NASA Astrophysics Data System (ADS)

Laude, Lucien D.; Rauscher, Gerhard

The use of lasers in industrial material processing is discussed in reviews and reports. Sections are devoted to high-precision laser machining, deposition methods, ablation and polymers, and synthesis and oxidation. Particular attention is given to laser cutting of steel sheets, laser micromachining of material surfaces, process control in laser soldering, laser-induced CVD of doped Si stripes on SOS and their characterization by piezoresistivity measurements, laser CVD of Pt spots on glass, laser deposition of GaAs, UV-laser photoablation of polymers, ArF excimer-laser ablation of HgCdTe semiconductor, pulsed laser synthesis of Ti silicides and nitrides, the kinetics of laser-assisted oxidation of metallic films, and excimer-laser-assisted etching of solids for microelectronics.

Advances in solid state laser technology for space and medical applications

NASA Technical Reports Server (NTRS)

Byvik, C. E.; Buoncristiani, A. M.

1988-01-01

Recent developments in laser technology and their potential for medical applications are discussed. Gas discharge lasers, dye lasers, excimer lasers, Nd:YAG lasers, HF and DF lasers, and other commonly used lasers are briefly addressed. Emerging laser technology is examined, including diode-pumped lasers and other solid state lasers.

Lasers '92; Proceedings of the International Conference on Lasers and Applications, 15th, Houston, TX, Dec. 7-10, 1992

NASA Technical Reports Server (NTRS)

Wang, Charles P. (Editor)

1993-01-01

Papers from the conference are presented, and the topics covered include the following: x-ray lasers, excimer lasers, chemical lasers, high power lasers, blue-green lasers, dye lasers, solid state lasers, semiconductor lasers, gas and discharge lasers, carbon dioxide lasers, ultrafast phenomena, nonlinear optics, quantum optics, dynamic gratings and wave mixing, laser radar, lasers in medicine, optical filters and laser communication, optical techniques and instruments, laser material interaction, and industrial and manufacturing applications.

Laser effect on the 248 nm KrF transition using heavy ion beam pumping

NASA Astrophysics Data System (ADS)

Adonin, A.; Jacoby, J.; Turtikov, V.; Fertman, A.; Golubev, A.; Hoffmann, D. H. H.; Ulrich, A.; Varentsov, D.; Wieser, J.

2007-07-01

In December 2005 the first successful operation of a UV excimer laser pumped with a heavy ion beam was demonstrated at GSI. It was the first experiment in which the specific power deposition was sufficient to overcome laser threshold for a UV excimer scheme. The well known KrF* excimer laser line at λ=248 nm has been chosen for this experiment, because the wavelength is short, but still in the range of usual optical diagnostic tools and the emitted light can propagate in air without attenuation. A bunch compressed U+73238 beam with a particle energy of 250 MeV/u and about 110 ns pulse duration (FWHM) was used for this experiment. Single pulses of a beam intensity up to 2.5×109 particles per bunch were focused into the laser cell along the cavity axis. Compact spectrometers, high speed UV-photodiodes and gated CCD-cameras were used for diagnostics of the spontaneous and stimulated emission. As a main result of the experiment laser effect on the 248 nm KrF* excimer laser line has been obtained and verified by temporal and spectral narrowing of the laser line as well as the threshold behaviour and exponential growth of intensity with increasing pumping power. In summary it could be shown that the pumping power of the heavy ion beam at GSI is now sufficient to pump short wavelength lasers. It is planned to extend laser experiments in near future to the VUV range of the spectrum (λ<200 nm).

Effect of excimer laser annealing on a-InGaZnO thin-film transistors passivated by solution-processed hybrid passivation layers

NASA Astrophysics Data System (ADS)

Bermundo, Juan Paolo; Ishikawa, Yasuaki; Fujii, Mami N.; Nonaka, Toshiaki; Ishihara, Ryoichi; Ikenoue, Hiroshi; Uraoka, Yukiharu

2016-01-01

We demonstrate the use of excimer laser annealing (ELA) as a low temperature annealing alternative to anneal amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) passivated by a solution-processed hybrid passivation layer. Usually, a-IGZO is annealed using thermal annealing at high temperatures of up to 400 °C. As an alternative to high temperature thermal annealing, two types of ELA, XeCl (308 nm) and KrF (248 nm) ELA, are introduced. Both ELA types enhanced the electrical characteristics of a-IGZO TFTs leading to a mobility improvement of ~13 cm2 V-1 s-1 and small threshold voltage which varied from ~0-3 V. Furthermore, two-dimensional heat simulation using COMSOL Multiphysics was used to identify possible degradation sites, analyse laser heat localization, and confirm that the substrate temperature is below 50 °C. The two-dimensional heat simulation showed that the substrate temperature remained at very low temperatures, less than 30 °C, during ELA. This implies that any flexible material can be used as the substrate. These results demonstrate the large potential of ELA as a low temperature annealing alternative for already-passivated a-IGZO TFTs.

Velocity measurement in rocket exhaust and general aerodynamic flows by photolysis of H2O and laser induced fluorescence of OH

NASA Technical Reports Server (NTRS)

Boedeker, Laurence R.

1992-01-01

A 'tagging' approach in which the photolysis of H2O by an excimer laser creates a zone of enhanced OH concentration, while a second, pulsed-UV laser detects tagged-zone convection via time-delayed excitation of OH fluorescence, depends on the photodissociation process and the kinetics of OH decay (relative to velocity). For application to the fuel-rich, high supersonic Mach number exhaust flow of the SSME, the detection of OH is being accomplished with either a pulsed narrowband UV dye laser or a tunable XeCl excimer laser for excitation of an OH 0-0 band transition, while the two-photon photolysis of H2O is conducted by focusing an injection-locked KrF excimer laser into the flow.

Large eccentric laser angioplasty catheter

NASA Astrophysics Data System (ADS)

Taylor, Kevin D.; Reiser, Christopher

1997-05-01

In response to recent demand for increased debulking of large diameter coronary vascular segments, a large eccentric catheter for excimer laser coronary angioplasty has been developed. The outer tip diameter is 2.0 mm and incorporates approximately 300 fibers of 50 micron diameter in a monorail- type percutaneous catheter. The basic function of the device is to ablate a coronary atherosclerotic lesion with 308 nm excimer laser pulses, while passing the tip of the catheter through the lesion. By employing multiple passes through the lesion, rotating the catheter 90 degrees after each pass, we expect to create luminal diameters close to 3 mm with this device. Design characteristics, in-vitro testing, and initial clinical experience is presented.

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)

Atomic force microscopy analysis of human cornea surface after UV (λ=266 nm) laser irradiation

NASA Astrophysics Data System (ADS)

Spyratou, E.; Makropoulou, M.; Moutsouris, K.; Bacharis, C.; Serafetinides, A. A.

2009-07-01

Efficient cornea reshaping by laser irradiation for correcting refractive errors is still a major issue of interest and study. Although the excimer laser wavelength of 193 nm is generally recognized as successful in ablating corneal tissue for myopia correction, complications in excimer refractive surgery leads to alternative laser sources and methods for efficient cornea treatment. In this work, ablation experiments of human donor cornea flaps were conducted with the 4th harmonic of an Nd:YAG laser, with different laser pulses. AFM analysis was performed for examination of the ablated cornea flap morphology and surface roughness.

Tunable, rare earth-doped solid state lasers

DOEpatents

Emmett, John L.; Jacobs, Ralph R.; Krupke, William F.; Weber, Marvin J.

1980-01-01

Laser apparatus comprising combinations of an excimer pump laser and a rare earth-doped solid matrix, utilizing the 5d-4f radiative transition in a rare earth ion to produce visible and ultra-violet laser radiation with high overall efficiency in selected cases and relatively long radiative lifetimes.

EFFECTS OF LASER RADIATION ON MATTER. LASER PLASMA: Selective metallisation of diamonds with the aid of laser radiation

NASA Astrophysics Data System (ADS)

Shafeev, Georgii A.; Pimenov, S. M.; Lubnin, Evgenii N.; Smolin, A. A.; Konov, Vitalii I.; Laptev, V. A.

1995-02-01

An experimental investigation was made of laser activation of diamond surfaces (single crystals and polycrystalline diamond films) prior to electroless before catalytic deposition of metals from solutions. The activation was carried out by a copper vapour laser or a KrF excimer laser in two ways: decomposition of a thin film of palladium acetylacetonate and local laser stimulated modification of the diamond surface by laser evaporation. An ohmic contact (Cu or Ni) with an adhesive strength of 3 N mm-2 was formed and the spatial resolution achieved was 10 μm.

Enhanced electrical and optical properties of room temperature deposited Aluminium doped Zinc Oxide (AZO) thin films by excimer laser annealing

NASA Astrophysics Data System (ADS)

El hamali, S. O.; Cranton, W. M.; Kalfagiannis, N.; Hou, X.; Ranson, R.; Koutsogeorgis, D. C.

2016-05-01

High quality transparent conductive oxides (TCOs) often require a high thermal budget fabrication process. In this study, Excimer Laser Annealing (ELA) at a wavelength of 248 nm has been explored as a processing mechanism to facilitate low thermal budget fabrication of high quality aluminium doped zinc oxide (AZO) thin films. 180 nm thick AZO films were prepared by radio frequency magnetron sputtering at room temperature on fused silica substrates. The effects of the applied RF power and the sputtering pressure on the outcome of ELA at different laser energy densities and number of pulses have been investigated. AZO films deposited with no intentional heating at 180 W, and at 2 mTorr of 0.2% oxygen in argon were selected as the optimum as-deposited films in this work, with a resistivity of 1×10-3 Ω.cm, and an average visible transmission of 85%. ELA was found to result in noticeably reduced resistivity of 5×10-4 Ω.cm, and enhancing the average visible transmission to 90% when AZO is processed with 5 pulses at 125 mJ/cm2. Therefore, the combination of RF magnetron sputtering and ELA, both low thermal budget and scalable techniques, can provide a viable fabrication route of high quality AZO films for use as transparent electrodes.

Lasers '81

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

Collins, C.B.

1982-01-01

Progress in lasers is discussed. The subjects addressed include: excimer lasers, surface spectroscopy, modern laser spectroscopy, free electron lasers, cavities and propagation, lasers in medicine, X-ray and gamma ray lasers, laser spectroscopy of small molecules and clusters, optical bistability, excitons, nonlinear optics in the X-ray and gamma ray regions, collective atomic phenomena, tunable IR lasers, far IR/submillimeter lasers, and laser-assisted collisions. Also treated are: special applications, multiphoton processes in atoms and small molecules, nuclear pumped lasers, material processing and applications, polarization, high energy lasers, laser chemistry, IR molecular lasers, laser applications of collision and dissociation phenomena, solid state laser materials,more » phase conjugation, advances in laser technology for fusion, metal vapor lasers, picosecond phenomena, laser ranging and geodesy, and laser photochemistry of complex molecules.« less

New Class of Excimer-Pumped Atomic Lasers (XPALS)

DTIC Science & Technology

2017-01-27

quantum efficiency greater thnn one, has been demonstrated. We believe this laser to represent a breakthrough in laser technology because the system...navy.mil Prepared by J. G. Eden and A. E. Mironov Laboratory For Optical Physics and Engineering Department of Electrical and Computer Engineering...viability of an atomic laser having a quantum efficiency greater than one. We believe this laser to represent a breakthrough in laser technology

Potential use of lasers for penetrating keratoplasty.

PubMed

Thompson, K P; Barraquer, E; Parel, J M; Loertscher, H; Pflugfelder, S; Roussel, T; Holland, S; Hanna, K

1989-07-01

Experimental corneal trephination has been achieved with the 193 nm argon fluoride excimer and 2.9 microns hydrogen fluoride and Er:YAG laser systems. Compared with metal blades and other lasers, the 193 nm excimer laser creates the best quality corneal excision, but has a relatively slow etch rate through the stroma, and its use requires toxic gas. The mid-infrared laser systems trephine the cornea in less than 10 seconds, but cause a 10 microns to 15 microns zone of adjacent stromal damage and create wounds that are approximately 2.5 times larger than wounds made by metal scalpels. The wavelength and laser pulse duration influence the cutting characteristics of the laser. Optical delivery systems using an axicon lens, a rotating slit, and a computer controlled scanning optical system have been developed for penetrating keratoplasty. Selection of the optimal laser system for penetrating keratoplasty must await further experimental studies. Refinements of the laser cavity and delivery system are necessary before clinical studies can begin. A carefully controlled randomized clinical trial comparing laser trephination with conventional mechanical trephines will be necessary to determine the safety and efficacy of a laser trephination system.

Pulsed UV laser technologies for ophthalmic surgery

NASA Astrophysics Data System (ADS)

Razhev, A. M.; Chernykh, V. V.; Bagayev, S. N.; Churkin, D. S.; Kargapol'tsev, E. S.; Iskakov, I. A.; Ermakova, O. V.

2017-01-01

The paper provides an overview of the results of multiyear joint researches of team of collaborators of Institute of Laser Physics SB RAS together with NF IRTC “Eye Microsurgery” for the period from 1988 to the present, in which were first proposed and experimentally realized laser medical technologies for correction of refractive errors of known today as LASIK, the treatment of ophthalmic herpes and open-angle glaucoma. It is proposed to carry out operations for the correction of refractive errors the use of UV excimer KrCl laser with a wavelength of 222 nm. The same laser emission is the most suitable for the treatment of ophthalmic herpes, because it has a high clinical effect, combined with many years of absence of recrudescence. A minimally invasive technique of glaucoma operations using excimer XeCl laser (λ=308 nm) is developed. Its wavelength allows perform all stages of glaucoma operations, while the laser head itself has high stability and lifetime, will significantly reduce operating costs, compared with other types of lasers.

Advanced Raman water vapor lidar

NASA Technical Reports Server (NTRS)

Whiteman, David N.; Melfi, S. Harvey; Ferrare, Richard A.; Evans, Keith A.; Ramos-Izquierdo, Luis; Staley, O. Glenn; Disilvestre, Raymond W.; Gorin, Inna; Kirks, Kenneth R.; Mamakos, William A.

1992-01-01

Water vapor and aerosols are important atmospheric constituents. Knowledge of the structure of water vapor is important in understanding convective development, atmospheric stability, the interaction of the atmosphere with the surface, and energy feedback mechanisms and how they relate to global warming calculations. The Raman Lidar group at the NASA Goddard Space Flight Center (GSFC) developed an advanced Raman Lidar for use in measuring water vapor and aerosols in the earth's atmosphere. Drawing on the experience gained through the development and use of our previous Nd:YAG based system, we have developed a completely new lidar system which uses a XeF excimer laser and a large scanning mirror. The additional power of the excimer and the considerably improved optical throughput of the system have resulted in approximately a factor of 25 improvement in system performance for nighttime measurements. Every component of the current system has new design concepts incorporated. The lidar system consists of two mobile trailers; the first (13m x 2.4m) houses the lidar instrument, the other (9.75m x 2.4m) is for system control, realtime data display, and analysis. The laser transmitter is a Lambda Physik LPX 240 iCC operating at 400 Hz with a XeF gas mixture (351 nm). The telescope is a .75m horizontally mounted Dall-Kirkham system which is bore sited with a .8m x 1.1m elliptical flat which has a full 180 degree scan capability - horizon to horizon within a plane perpendicular to the long axis of the trailer. The telescope and scan mirror assembly are mounted on a 3.65m x .9m optical table which deploys out the rear of the trailer through the use of a motor driven slide rail system. The Raman returns from water vapor (403 nm), nitrogen (383 nm) and oxygen (372 nm) are measured in addition to the direct Rayleigh/Mie backscatter (351). The signal from each of these is split at about a 5/95 ratio between two photomultiplier detectors. The 5 percent detector is used for

Stripping by laser

NASA Astrophysics Data System (ADS)

Malavallon, Olivier

1995-04-01

Laser beam stripping can be achieved using several active materials: YAG, CO2 Tea, or Excimer. The YAG laser appears to be the most efficient laser assessed in this report. However, the results obtained for productivity, quality, and type of stripping were very poor. Also, for stripping and on account of its specifications, the laser beam can only be used in an automated manner. In spite of these results, it seems that certain companies in Europe have recently developed technical solutions allowing better results to be obtained.

Quality of vision after excimer laser phototherapeutic keratectomy with intraoperative mitomycin-C for Salzmann nodular degeneration.

PubMed

Reddy, Jagadesh C; Rapuano, Christopher J; Felipe, Anthony F; Nagra, Parveen K; Hammersmith, Kristin M

2014-07-01

To assess the effect of excimer laser phototherapeutic keratectomy (PTK) with intraoperative mitomycin-C (MMC) on the quality of vision in patients with Salzmann nodular degeneration (SND). Thirteen eyes of 12 patients were enrolled in the study between December 2010 and March 2012. Uncorrected and best-corrected Snellen distance visual acuities were measured at every visit. Contrast sensitivity and manifest refraction were measured preoperatively, at 1 month and at 3 months. Corneal topography, Galilei dual Scheimpflug imaging, VISX WaveScan, and ultrasound central corneal pachymetry were measured preoperatively and at 3 months after PTK procedure. Contrast sensitivity was statistically significantly better both at 1 month (P<0.01) and 3 months (P<0.01). Postoperatively, there was 46% increase in eyes with measurable corneal topography, 69% increase in Galilei dual Scheimpflug imaging, and a 77% increase in WaveScan measurements. The third-order (P<0.01) and total corneal higher-order aberrations (HOAs) (P=0.01) were significantly lower postoperatively compared with the preoperative corneal aberrations measured on Galilei dual Scheimpflug imaging. Significant improvement in contrast sensitivity and corneal HOAs was seen after PTK for SND. Phototherapeutic keratectomy with MMC can be considered as an effective procedure in the improvement of the quality of vision in patients with SND.

Treatment of alopecia areata with 308-nm excimer lamp.

PubMed

Ohtsuki, Akiko; Hasegawa, Toshio; Ikeda, Shigaku

2010-12-01

Alopecia areata is considered to be a T-cell mediated autoimmune disorder. The 308-nm excimer lamp is thought to be capable of inducing T-cell apoptosis in vitro, suggesting that the lamp might be effective for the treatment of alopecia areata. We examined the effectiveness of the 308-nm excimer lamp for the treatment of alopecia areata. We recruited three patients with single alopecia areata lesions that were resistant to conventional treatment. The lesions were exposed to a 308-nm excimer lamp at 2-weekly intervals. Hair regrowth was observed in all three patients after approximately 10 treatment sessions. Our study showed that exposure to the 308-nm excimer lamp effectively induced hair regrowth in solitary alopecia areata lesions. Apart from erythema, there were no significant adverse effects. Therefore, we suggest that it may be considered as a treatment modality for recalcitrant alopecia areata. © 2010 Japanese Dermatological Association.

[Analysis of AC/A ratio after myopic excimer laser in situ keratomileusis].

PubMed

Wu, Xiao-ying; Liu, Shuang-zhen

2003-03-01

To study the changes of AC/A ratio of myopia after excimer laser in situ keratomileusis (LASIK). 135 myopia patients were treated by LASIK, their AC/A ratios were measured with synoptohore before surgery and 3 months after surgery. The average AC/A ratios of naked eyes or eyes wearing glasses before surgery and the naked after surgery were (0.724 +/- 0.587) (Delta)/D, (2.754 +/- 1.565) (Delta)/D, (1.618 +/- 1.027) (Delta)/D in turn. There were significant difference among those groups (P < 0.001). That also appeared in different degree of myopia naked before surgery (P < 0.01). We found no significant difference between the groups wearing glasses before surgery and naked after surgery (P > 0.05). A positive correlation was built up between postoperative AC/A ratio and AC/A ratio of wearing glasses or refractive diopter before surgery (r = 0.550, P < 0.001; r = 0.185, P < 0.005). And the postoperative AC/A ratios had a negative correlation to age or length of ocular axis (r = -0.340, P < 0.001; r = -0.192, P < 0.002). The regression equation for postoperative AC/A ratios was figured out as Y((Delta)/D) = 4.080 0 - 0.031 8X(1) - 0.097 1X(2) + 0.325 0X(3) (P < 0.001). X(1) = age (year), X(2) = length of ocular axis (mm), X(3) = preoperative AC/A ratio with weaning glasses ((Delta)/D). The naked AC/A ratios are higher than the preoperative's after LASIK, but lower than the wearing glasses's before surgery. It is influenced by the factors, such as: the preoperative AC/A ratio of wearing glasses, the length of ocular axis and the age.

[Reduction of decentration after LASIK using a modified eye tracker ring for the MEL-70 excimer laser].

PubMed

Schulze, S; Nietgen, G; Sekundo, W

2004-07-01

The aim of this study was to determine and compare the rate of eccentric laser ablation after LASIK depending on the eye tracker ring used. All LASIK treatments were carried out using the MEL-70 flying spot excimer laser (Zeiss-Meditec, Jena). The flap was produced using a Corneal Shaper trade mark or Hansatome trade mark Microkeratome (B and L Surgical, Heidelberg). Initially we used an 11 mm eye tracker ring without hinge protector. At the end of February 2001 this ring was replaced by a 10 mm and a 9.5 mm ring with built-in hinge protector. An additional modification was introduced by us: at 1 mm separations little teeth-like spikes were engraved into the eyeward side of the ring, thus stabilising the position of the ring on the globe and allowing free liquid to flow through the spaces between each spike. The built-in calibration system of the corneal topography (TMS 3, Tomey, Erlangen) from patients with a follow-up of one month or longer was used to determine the distance between the centre of the ablation zone from the fixation point. In group I patients (old ring) 42 eyes were treated. In 4 eyes ablation was perfect, in 21 eyes the ablation centre was located 0.1 to 0.49 mm from the fixation point, in 11 eyes 0.51 to 0.99 mm and in 5 eyes 1.1 to 1.49 mm whereas one eye showed a decentred ablation of 1.53 mm. In group II (new ring) 42 eyes were investigated also. In 11 eyes ablation was perfect, in 20 eyes the ablation centre was located 0.1 to 0.49 mm from the fixation point, in 10 eyes 0.5 to 0.99 mm and one eye had an eccentric ablation of 1.28 mm from the fixation point. The further development of our eye tracker ring for the MEL-70 laser considerably reduced the rate of decentred ablations. An enhanced grip of the ring onto the globe reduces a slow slide during the laser procedure.

Four-year to seven-year outcomes of advanced surface ablation with excimer laser for high myopia.

PubMed

Hansen, Rasmus Søgaard; Lyhne, Niels; Grauslund, Jakob; Grønbech, Keea Treu; Vestergaard, Anders Højslet

2015-07-01

We aimed to evaluate and compare outcomes after photorefractive keratectomy with cooling (cPRK) and laser-assisted subepithelial keratectomy (LASEK) for high myopia. This was a retrospective, single-masked follow-up study of patients treated for myopia between 2007 and 2009 with cPRK or LASEK, using a high-frequency flying-spot excimer laser with eye-tracker (MEL80; Carl Zeiss, Jena, Germany). One eye of each patient was randomly chosen for analysis. Re-treated eyes were excluded. Forty-six cPRK patients and 35 LASEK patients were included. Spherical equivalent averaged -7.69 ± 1.47 diopters (D) in cPRK eyes and -7.98 ± 2.06 D in LASEK eyes (p = 0.31) before surgery. The average follow-up time was 4.6 years in cPRK patients and 6.0 years in LASEK patients (p < 0.05). At final follow-up, no cPRK eyes and one LASEK eye (p = 0.46) had lost two lines of corrected distance visual acuity (CDVA). No eyes had significant haze at final follow-up, although trace haze was found in four cPRK eyes and six LASEK eyes (p = 0.44). However, at 6 weeks after surgery, zero cPRK eyes and nine LASEK eyes (p < 0.05) had significant haze. At final follow-up, 63 % of cPRK eyes and 35 % of LASEK eyes (p = 0.17) were within ±1.0 D of intended refraction. Finally, 100 % of cPRK patients and 92 % of LASEK patients (p = 0.87) were satisfied or very satisfied with the surgery at final follow-up. cPRK and LASEK seemed safe and with high patient satisfaction 4 to 7 years after surgery for high myopia. However, cPRK was more effective than LASEK in reducing initial significant corneal haze.

Surface 3D Micro Free Forms: Multifunctional Microstructured Mesoporous α-Alumina by in Situ Slip Casting Using Excimer Laser Ablated Polycarbonate Molds.

PubMed

Rowthu, Sriharitha; Böhlen, Karl; Bowen, Paul; Hoffmann, Patrik

2015-11-11

Ceramic surface microstructuring is a rapidly growing field with a variety of applications in tribology, wetting, biology, and so on. However, there are limitations to large-area microstructuring and fabrication of three-dimensional (3D) micro free forms. Here, we present a route to obtain intricate surface structures through in situ slip casting using polydimethylsiloxane (PDMS) negative molds which are replicated from excimer laser ablated polycarbonate (PC) master molds. PC sheets are ablated with a nanosecond KrF (λ = 248 nm) excimer laser mask projection system to obtain micron-scale 3D surface features over a large area of up to 3 m(2). Complex surface structures that include 3D free forms such as 3D topography of Switzerland, shallow structures such as diffractive optical elements (60 nm step) and conical micropillars have been obtained. The samples are defect-free produced with thicknesses of up to 10 mm and 120 mm diameter. The drying process of the slip cast alumina slurry takes place as a one-dimensional process, through surface evaporation and water permeation through the PDMS membrane. This allows homogeneous one-dimensional shrinkage during the drying process, independent of the sample's lateral dimensions. A linear mass diffusion model has been proposed to predict and explain the drying process of these ceramic colloidal suspensions. The calculated drying time is linearly proportional to the height of the slurry and the thickness of the negatively structured PDMS and is validated by the experimental results. An experimentally observed optimum Sylgard PDMS thickness range of ∼400 μm to 1 mm has achieved the best quality microstructured green compacts. Further, the model predicts that the drying time is independent of the microstructured areas and was validated using experimental observations carried out with microstructured areas of 300 mm(2), 1200 mm(2), and 120 cm(2). Therefore, in principle, the structures can be further replicated in areas up

Laser technologies in ophthalmic surgery

NASA Astrophysics Data System (ADS)

Atezhev, V. V.; Barchunov, B. V.; Vartapetov, S. K.; Zav'yalov, A. S.; Lapshin, K. E.; Movshev, V. G.; Shcherbakov, I. A.

2016-08-01

Excimer and femtosecond lasers are widely used in ophthalmology to correct refraction. Laser systems for vision correction are based on versatile technical solutions and include multiple hard- and software components. Laser characteristics, properties of laser beam delivery system, algorithms for cornea treatment, and methods of pre-surgical diagnostics determine the surgical outcome. Here we describe the scientific and technological basis for laser systems for refractive surgery developed at the Physics Instrumentation Center (PIC) at the Prokhorov General Physics Institute (GPI), Russian Academy of Sciences.

Deposition of silicon carbide thin films by pulsed excimer laser ablation technique in the 25-700°C deposition temperature range

NASA Astrophysics Data System (ADS)

El Khakani, My A.; Gat, E.; Beaudoin, Yves; Chaker, Mohamed; Monteil, C.; Guay, Daniel; Letourneau, G.; Pepin, Henri

1995-04-01

Laser ablation deposition technique was used to deposit silicon carbide thin films on both Si(100) and quartz substrates. The deposition was accomplished by ablating SiC sintered ceramic targets, using a KrF (248 nm) excimer laser. At a laser intensity of about 1 X 109 W/cm2, substrate temperatures in the (25-700) degree(s)C range were investigated. When the deposition temperature is varied from 27 to 650 degree(s)C, (i) the density of a-SiC films increases from 2.6 to 3.0 g cm-3, while their mean roughness value (for a film thickness of about 1 micrometers ) slightly changes from 0.44 to 0.5 nm; (ii) the optical transmission of a-SiC films is significantly improved (the absorption coefficient at 632.8 nm wavelength was reduced by a factor of about 5); and (iii) their Si-C bond density, as determined by FTIR spectroscopy, increases from (13.1 +/- 1.3) to (23.4 +/- 2.4) 1022 bond cm-3. The increased number of Si-C bonds is correlated to the increase of the optical transmission. Over all the investigated deposition temperature range, the a-SiC films were found to be under high compressive stress around a mean value of about 1.26 GPa. The control of the stress of a-SiC films was achieved by means of post- thermal annealings and the annealed a-SiC films were successfully used to fabricate x-ray membranes.

Surface-pattern geometry, topography, and chemical modifications during KrF excimer laser micro-drilling of p-type Si (111) wafers in ambient environment of HCl fumes in air

NASA Astrophysics Data System (ADS)

Zakria Butt, Muhammad; Saher, Sobia; Waqas Khaliq, Muhammad; Siraj, Khurram

2016-11-01

Eight mirror-like polished p-type Si (111) wafers were irradiated with 100, 200, 300, 400, 800, 1200, 1600, and 2000 KrF excimer laser pulses in ambient environment of HCl fumes in air. The laser parameters were: wavelength = 248 nm, pulse width = 20 ns, pulse energy = 20 mJ, and repetition rate = 20 Hz. For each set of laser pulses, characterization of the rectangular etched patterns formed on target surface was done by optical/scanning electron microscopy, XRD, and EDX techniques. The average etched depth increased with the increase in number of laser pulses from 100 to 2000 in accord with Sigmoidal (Boltzmann) function, whereas the average etch rate followed an exponential decay with the increase in number of laser pulses. However, the etched area, maximum etched depth, and maximum etch rate were found to increase linearly with the number of laser pulses, but the rate of increase was faster for 100-400 laser pulses (region I) than that for 800-2000 laser pulses (region II). The elemental composition for each etched-pattern determined by EDX shows that both O and Cl contents increase progressively with the increase in the number of laser shots in region I. However, in region II both O and Cl contents attain saturation values of about 39.33 wt.% and 0.14 wt.%, respectively. Perforation of Si wafers was achieved on irradiation with 1200-2000 laser pulses. XRD analysis confirmed the formation of SiO2, SiCl2 and SiCl4 phases in Si (111) wafers due to chemical reaction of silicon with both HCl fumes and oxygen in air.

Application of erbium: YAG laser in ocular ablation.

PubMed

Tsubota, K

1990-01-01

Recent developments in lasers have provided us the possibility of laser ocular surgery. The xenon, argon, neodymium:YAG and dye lasers have been successfully used in out-patient clinics. The excimer laser has been attracting researchers' interest in the new application of laser to cornea and lens. The erbium:YAG laser emits a 2.94-microns beam that can ablate the transparent ocular tissues such as lenses and corneas. The author has applied this laser to the cornea, lens, vitreous and other ocular tissues. The erbium:YAG laser beam was directed through a 1.5-meter-long, 200-microns-diameter fiberoptic guide. The radiant energy measured about 50 mJ at the end of the probe. The laser was emitted as a 400-microsecond pulse. Freshly enucleated rabbit eyes were used in this study. Laser burns were applied to the tissue surface at various energy settings. At minimal power, the tissues were coagulated by the erbium:YAG laser application. At a power of more than 636-954 mJ/mm2, tissue began to evaporate; the tissue loss was observed under a surgical light microscope. Corneal photoablation, lens ablation, iridotomy, trabeculotomy, cutting of the vitreous and retinal ablation were easily performed. Like the excimer laser, the erbium:YAG laser is a potential tool for ocular surgery.

Laser etching of polymer masked leadframes

NASA Astrophysics Data System (ADS)

Ho, C. K.; Man, H. C.; Yue, T. M.; Yuen, C. W.

1997-02-01

A typical electroplating production line for the deposition of silver pattern on copper leadframes in the semiconductor industry involves twenty to twenty five steps of cleaning, pickling, plating, stripping etc. This complex production process occupies large floor space and has also a number of problems such as difficulty in the production of rubber masks and alignment, generation of toxic fumes, high cost of water consumption and sometimes uncertainty on the cleanliness of the surfaces to be plated. A novel laser patterning process is proposed in this paper which can replace many steps in the existing electroplating line. The proposed process involves the application of high speed laser etching techniques on leadframes which were protected with polymer coating. The desired pattern for silver electroplating is produced by laser ablation of the polymer coating. Excimer laser was found to be most effective for this process as it can expose a pattern of clean copper substrate which can be silver plated successfully. Previous working of Nd:YAG laser ablation showed that 1.06 μm radiation was not suitable for this etching process because a thin organic and transparent film remained on the laser etched region. The effect of excimer pulse frequency and energy density upon the removal rate of the polymer coating was studied.

Variable laser attenuator

DOEpatents

Foltyn, Stephen R.

1988-01-01

The disclosure relates to low loss, high power variable attenuators comprng one or more transmissive and/or reflective multilayer dielectric filters. The attenuator is particularly suitable to use with unpolarized lasers such as excimer lasers. Beam attenuation is a function of beam polarization and the angle of incidence between the beam and the filter and is controlled by adjusting the angle of incidence the beam makes to the filter or filters. Filters are selected in accordance with beam wavelength.

Experimental investigation of the laser ablation process on wood surfaces

NASA Astrophysics Data System (ADS)

Panzner, M.; Wiedemann, G.; Henneberg, K.; Fischer, R.; Wittke, Th.; Dietsch, R.

1998-05-01

Processing of wood by conventional mechanical tools like saws or planes leaves behind a layer of squeezed wood only slightly adhering to the solid wood surface. Laser ablation of this layer could improve the durability of coatings and glued joints. For technical applications, thorough knowledge about the laser ablation process is necessary. Results of ablation experiments by excimer lasers, Nd:YAG lasers, and TEA-CO 2 lasers on surfaces of different wood types and cut orientations are shown. The process of ablation was observed by a high-speed camera system and optical spectroscopy. The influence of the experimental parameters are demonstrated by SEM images and measurement of the ablation rate depending on energy density. Thermal effects like melting and also carbonizing of cellulose were found for IR- and also UV-laser wavelengths. Damage of the wood surface after laser ablation was weaker for excimer lasers and CO 2-TEA lasers. This can be explained by the high absorption of wood in the ultraviolet and middle infrared spectral range. As an additional result, this technique provides an easy way for preparing wood surfaces with excellently conserved cellular structure.

Skin graft take and healing following 193-nm excimer, continuous-wave carbon dioxide (CO2), pulsed CO2, or pulsed holmium: YAG laser ablation of the graft bed.

PubMed

Green, H A; Burd, E E; Nishioka, N S; Compton, C C

1993-08-01

Ablative lasers have been used for cutaneous surgery for greater than two decades since they can remove skin and skin lesions bloodlessly and efficiently. Because full-thickness skin wounds created after thermal laser ablation may require skin grafting in order to heal, we have examined the effect of the residual laser-induced thermal damage in the wound bed on subsequent skin graft take and healing. In a pig model, four different pulsed and continuous-wave lasers with varying wavelengths and radiant energy exposures were used to create uniform fascial graft bed thermal damage of approximately 25, 160, 470, and 1100 microns. Meshed split-thickness skin graft take and healing on the thermally damaged fascial graft beds were examined on a gross and microscopic level on days 3 and 7, and then weekly up to 42 days. Laser-induced thermal damage on the graft bed measuring greater than 160 +/- 60 microns in depth significantly decreased skin graft take. Other deleterious effects included delayed graft revascularization, increased inflammatory cell infiltrate at the graft-wound bed interface, and accelerated formation of hypertrophied fibrous tissue within the graft bed and underlying muscle. Ablative lasers developed for cutaneous surgery should create less than 160 +/- 60 microns of residual thermal damage to permit optimal skin graft take and healing. Pulsed carbon dioxide and 193-nm excimer lasers may be valuable instruments for the removal of full-thickness skin, skin lesions, and necrotic tissue, since they create wound beds with minimal thermal damage permitting graft take comparable to that achieved with standard surgical techniques.

How predictable are the results of excimer laser photorefractive keratectomy? A review.

PubMed

Grosvenor, T

1995-10-01

At the close of 1994, the AOA News reported that at least 14 companies were preparing to market equipment for excimer laser photorefractive keratectomy (PRK). More than a dozen PRK centers had been formed for the purpose of recruiting optometrists to co-manage PRK patients. Because the surgery is a "no-touch" computer-driven procedure whose duration is measured in seconds, the preoperative and postoperative care of PRK patients will assume major importance. Optometrists who will be asked to take part in the management of PRK patients must be able to counsel patients on matters such as the predictability of the procedure in terms of postoperative refractive error and visual acuity, as well as the possibility of unintended consequences such as difficulty in night driving. Information currently available, mainly as a result of studies conducted in other countries, shows that the results of PRK are highly predictable for preoperative myopia up to about -3.00 D and somewhat less predictable for myopia between -3.00 and -6.00 D, whereas for myopia greater than -6.00 D the probability of achieving a full correction decreases rapidly with increasing amounts of myopia. As compared to radial keratotomy (RK) in which the postoperative refractive error drifts relentlessly in the hyperopic direction, PRK brings about an initial hyperopic shift followed by regression leading to increasing myopia. Researchers disagree on the cause of the postoperative hyperopic shift and regression, and on the value of various methods of controlling regression including the use of wider and deeper ablation profiles and the postoperative use of corticosteroids and nonsteroid anti-inflammatory drugs. It is too early to determine whether the myopic creep in PRK will be as persistent as the hyperopic creep in RK, but it is likely that whereas presbyopic post-RK patients may have adequate distance vision but require corrective lenses for reading, presbyopic post-PRK patients may be sufficiently myopic

Effects of excimer laser irradiation on the expression of Th17, Treg, TGF-beta1, and IL-6 in patients with psoriasis vulgaris

NASA Astrophysics Data System (ADS)

Xiong, Guo-Xin; Li, Xin-Zhong

2017-11-01

The effects of laser irradiation on the expression of T helper 17 (Th17) and regulatory T (Treg) cells and their related cytokines, transforming growth factor beta 1 (TGF-β1) and interleukin-6 (IL-6), respectively, in the peripheral blood of patients with psoriasis vulgaris were investigated. 38 patients with psoriasis vulgaris in the stable state were selected as the treatment group that was treated twice a week for eight weeks. Another 38 healthy persons were chosen as the control group. Before and after treatment, the percentages of Th17 cells and Treg cells in the patients’ peripheral blood were detected using flow cytometry, the content of TGF-β1 and IL-6 in the patients’ sera were detected using enzyme-linked immunosorbent assay, and the extent and severity of lesions were determined by weighing the psoriasis area and severity index (PASI). After laser treatment, the percentage of Th17 cells, the Th17/Treg cell ratio and the level of IL-6 in the peripheral blood of patients with psoriasis in the treatment group were significantly lower than those of the same patients before the treatment (P  <  0.01), while the percentage of Treg and the content of TGF-β1 in the patients’ sera were significantly higher than before the treatment (P  <  0.01). The effective rate for laser irradiation of psoriasis vulgaris was 84.21%, and the PASI score was significantly lower (P  <  0.01). Excimer laser irradiation can positively affect the Th17/Treg cell ratio and the expression of related cytokines in the peripheral blood of patients with psoriasis vulgaris.

Corneal reshaping using a pulsed UV solid-state laser

NASA Astrophysics Data System (ADS)

Ren, Qiushi; Simon, Gabriel; Parel, Jean-Marie A.; Shen, Jin-Hui; Takesue, Yoshiko

1993-06-01

Replacing the gas ArF (193 nm) excimer laser with a solid state laser source in the far-UV spectrum region would eliminate the hazards of a gas laser and would reduce its size which is desirable for photo-refractive keratectomy (PRK). In this study, we investigated corneal reshaping using a frequency-quintupled (213 nm) pulsed (10 ns) Nd:YAG laser coupled to a computer-controlled optical scanning delivery system. Corneal topographic measurements showed myopic corrections ranging from 2.3 to 6.1 diopters. Post-operative examination with the slit-lamp and operating microscope demonstrated a smoothly ablated surface without corneal haze. Histological results showed a smoothly sloping surface without recognizable steps. The surface quality and cellular effects were similar to that of previously described excimer PRK. Our study demonstrated that a UV solid state laser coupled to an optical scanning delivery system is capable of reshaping the corneal surface with the advantage of producing customized, aspheric corrections without corneal haze which may improve the quality of vision following PRK.

Pulsed lasers in dentistry: sense or nonsense?

NASA Astrophysics Data System (ADS)

Koort, Hans J.; Frentzen, Matthias

1991-05-01

The great interest in the field of laser applications in dentistry provokes the question, if all these new techniques may really fulfill advantages, which are expected after initial in-vitro studies. Whereas laser surgery of soft oral tissues has been developed to a standard method, laser treatment of dental hard tissues and the bone are attended with many unsolved problems. Different laser types, especially pulsed lasers in a wide spectrum of wavelengths have been proofed for dental use. Today neither the excimer lasers, emitting in the far uv-range from 193 to 351 nm, nor the mid-infrared lasers like Nd:YAG (1,064 μm), Ho:YAG (2,1 μm) and Er:YAG (2,96 μm) or the C02-laser (10,6 μm) show mechanism of interaction more carefully and faster than a preparation of teeth with diamond drillers. The laser type with the most precise and considerate treatment effects in the moment is the short pulsed (15 ns) ArF-excimer laser with a wavelength of 193 nm. However this laser type has not yet the effectivity of mechanical instruments and it needs a mirror system to deliver the radiation. Histological results point out, that this laser shows no significant pathological alterations in the adjacent tissues. Another interesting excimer laser, filled with XeCI and emitting at a wavelength of 308 nm has the advantage to be good to deliver through quartz fibers. A little more thermal influence is to be seen according to the longer wavelength. Yet the energy density, necessary to cut dental hard tissues will not be reached with the laser systems available now. Both the pulsed Er:YAG- (2,94 μm, pulse duration 250 s) and the Ho:YAG -laser (2,1 μm, pulse duration 250 μs) have an effective coupling of the laser energy to hydrogeneous tissues, but they do not work sufficient on healthy enamel and dentine. The influence to adjacent healthy tissue is not tolerable, especially in regard of the thermal damage dentine and pulp tissues. Moreover, like the 193 nm ArF-excimer laser

Excimer Formation Dynamics of Dipyrenyldecane in Structurally Different Ionic Liquids.

PubMed

Yadav, Anita; Pandey, Siddharth

2017-12-07

Ionic liquids, being composed of ions alone, may offer alternative pathways for molecular aggregation. These pathways could be controlled by the chemical structure of the cation and the anion of the ionic liquids. Intramolecular excimer formation dynamics of a bifluorophoric probe, 1,3-bis(1-pyrenyl)decane [1Py(10)1Py], where the fluorophoric pyrene moieties are separated by a long decyl chain, is investigated in seven different ionic liquids in 10-90 °C temperature range. The long alkyl separator allows for ample interaction with the solubilizing milieu prior to the formation of the excimer. The ionic liquids are composed of two sets, one having four ionic liquids of 1-butyl-3-methylimidazolium cation ([bmim + ]) with different anions and the other having four ionic liquids of bis(trifluoromethylsulfonyl)imide anion ([Tf 2 N - ]) with different cations. The excimer-to-monomer emission intensity ratio (I E /I M ) is found to increase with increasing temperature in sigmoidal fashion. Chemical structure of the ionic liquid controls the excimer formation efficiency, as I E /I M values within ionic liquids with the same viscosities are found to be significantly different. The excited-state intensity decay kinetics of 1Py(10)1Py in ionic liquids do not adhere to a simplistic Birk's scheme, where only one excimer conformer forms after excitation. The apparent rate constants of excimer formation (k a ) in highly viscous ionic liquids are an order of magnitude lower than those reported in organic solvents. In general, the higher the viscosity of the ionic liquid, the more sensitive is the k a to the temperature with higher activation energy, E a . The trend in E a is found to be similar to that for activation energy of the viscous flow (E a,η ). Stokes-Einstein relationship is not followed in [bmim + ] ionic liquids; however, with the exception of [choline][Tf 2 N], it is found to be followed in [Tf 2 N - ] ionic liquids suggesting the cyclization dynamics of 1Py(10)1Py

Variable laser attenuator

DOEpatents

Foltyn, S.R.

1987-05-29

The disclosure relates to low loss, high power variable attenuators comprising one or more transmissive and/or reflective multilayer dielectric filters. The attenuator is particularly suitable to use with unpolarized lasers such as excimer lasers. Beam attenuation is a function of beam polarization and the angle of incidence between the beam and the filter and is controlled by adjusting the angle of incidence the beam makes to the filter or filters. Filters are selected in accordance with beam wavelength. 9 figs.

APPLICATIONS OF LASERS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Laser system based on a commercial microwave oscillator with time compression of a microwave pump pulse

NASA Astrophysics Data System (ADS)

Arteev, M. S.; Vaulin, V. A.; Slinko, V. N.; Chumerin, P. Yu; Yushkov, Yu G.

1992-06-01

An analysis is made of the possibility of using a commercial microsecond microwave oscillator, supplemented by a device for time compression of microwave pulses, in pumping of industrial lasers with a high efficiency of conversion of the pump source energy into laser radiation. The results are reported of preliminary experiments on the commissioning of an excimer XeCl laser.

High resolution imaging studies into the formation of laser-induced periodic surface structures.

PubMed

Kerr, N C; Clark, S E; Emmony, D C

1989-09-01

We report the results of an investigation into the formation mechanism of laser-induced ripple structures based on obtaining direct images of a surface while the transient heating induced by a KrF excimer laser is still present. These images reveal transient but well-defined periodic heating patterns which, if enough subsequent excimer pulses are incident on the surface, become permanently induced ripple structures. It is evident from these transient images that the surface heating is confined to the induced structures, thus strongly supporting the idea that at low fluences the ripples are formed by localizing surface melting.

Excimer laser phototherapy for the dissolution of abnormal growth

DOEpatents

Gruen, Dieter M.; Young, Charles E.; Pellin, Michael J.

1987-01-01

Removal of abnormal human tissue with reduced thermal damage is achieved by selecting a laser having a wavelength in the order of 290-400 nm, orienting a laser-transmitting glass member toward the abnormal tissue and directing the laser through the glass member at power densities, pulse rates, and times sufficient to cause multiphoton absorption and bond breaking by Coulomb repulsion rather than thermal destruction. The glass member may include a laser beam concentrator provided by a lens or cone at the tissue-treatment end to increase the beam energy per unit area and reduce the treatment area.

Excimer laser phototherapy for the dissolution of abnormal growth

DOEpatents

Gruen, D.M.; Young, C.E.; Pellin, M.J.

1985-02-19

Removal of abnormal human tissue with reduced thermal damage is achieved by selecting a laser having a wavelength in the order of 290 to 400 nm, orienting a laser-transmitting glass member toward the abnormal tissue and directing the laser through the glass member at power densities, pulse rates, and times sufficient to cause multiphoton absorption and bond breaking by Coulomb repulsion rather than thermal destruction. The glass member may include a laser beam concentrator provided by a lens or cone at the tissue-treatment end to increase the beam energy per unit area and reduce the treatment area. 6 figs.

Excimer laser phototherapy for the dissolution of vascular obstruction

DOEpatents

Gruen, D.M.; Young, C.E.; Pellin, M.J.

1984-01-09

Removal of abnormal human tissue with reduced thermal damage is achieved by selecting a laser having a wavelength in the order of 290 to 400 nm, orienting a laser-transmitting glass member toward the abnormal tissue and directing the laser through the glass member at power densities, pulse rates, and times sufficient to cause multiphoton absorption and bond breaking by Coulomb repulsion rather than thermal destruction. 2 figures.

Laser micro machining of medical devices.

PubMed

Rausch, Y

2009-01-01

Excimer and increasingly ultra-short-pulsed lasers are important tools in the creation of microstructures and nanostructures. Capabilities of the latest systems are described, which include drilling 30-microm diameter holes in 50 to 100 microm thick metal foils and subsurface engraving of transparent materials.

Preliminary results of tracked photorefractive keratectomy (T-PRK) for mild to moderate myopia with the autonomous technologies excimer laser at Cedars-Sinai Medical Center

NASA Astrophysics Data System (ADS)

Maguen, Ezra I.; Salz, James J.; Nesburn, Anthony B.

1997-05-01

Preliminary results of the correction of myopia up to -7.00 D by tracked photorefractive keratectomy (T-PRK) with a scanning and tracking excimer laser by Autonomous Technologies are discussed. 41 eyes participated (20 males). 28 eyes were evaluated one month postop. At epithelization day mean uncorrected vision was 20/45.3. At one month postop, 92.8 of eyes were 20/40 and 46.4% were 20/20. No eye was worse than 20/50. 75% of eyes were within +/- 0.5 D of emmetropia and 82% were within +/- 1.00 D of emmetropia. Eyes corrected for monovision were included. One eye lost 3 lines of best corrected vision, and had more than 1.00 D induced astigmatism due to a central corneal ulcer. Additional complications included symptomatic recurrent corneal erosions which were controlled with topical hypertonic saline. T-PRK appears to allow effective correction of low to moderate myopia. Further study will establish safety and efficacy of the procedure.

Cleaning of optical surfaces by excimer laser radiation

NASA Astrophysics Data System (ADS)

Mann, K.; Wolff-Rottke, B.; Müller, F.

1996-04-01

The effect of particle removal from Al mirror surfaces by the influence of pulsed UV laser radiation has been studied. The investigations are closely related to the demands of astronomers, who are looking for a more effective way to clean future very large telescope (VLT) mirrors [1]. A systematic parameter study has been performed in order to determine the irradiation conditions which yield the highest dust removal efficiency (i.e. reflectivity increase) on contaminated samples. The particle removal rate increases with increasing laser fluence, being limited however by the damage threshold of the coating. Data indicate that on Al coated BK7 and Zerodur samples KrF laser radiation yields the optimum result, with cleaning efficiencies comparable to polymer film stripping. The initial reflectivity of the clean coating can nearly be restored, in particular when an additional solvent film on the sample surface is applied.

Laser Assisted CVD Growth of A1N and GaN

DTIC Science & Technology

1990-08-31

additional cost sharing. RESEARCH FACILITIES The york is being performed in the Howard University Laser Laboratory. This is a free-standing buildinq...would be used to optimize computer models of the laser induced CVD reactor. FACILITIES AND EQUIPMENT - ADDITIONAL COST SHARING This year Howard ... University has provided $45,000 for the purchase of an excimer laser to be shared by Dr. Crye for the diode laser probe experiments and another Assistant

Direct Observation of Excimer-Mediated Intramolecular Electron Transfer in a Cofacially-Stacked Perylene Bisimide Pair.

PubMed

Sung, Jooyoung; Nowak-Król, Agnieszka; Schlosser, Felix; Fimmel, Benjamin; Kim, Woojae; Kim, Dongho; Würthner, Frank

2016-07-27

We have elucidated excimer-mediated intramolecular electron transfer in cofacially stacked PBIs tethered by two phenylene-butadiynylene loops. The electron transfer between energetically equivalent PBIs is revealed by the simultaneous observation of the PBI radical anion and cation bands in the transient absorption spectra. The fluorescence decay time of the excimer states is in good agreement with the rise time of PBI radical bands in transient absorption spectra suggesting that the electron transfer dynamics proceed via the excimer state. We can conclude that the excimer state effectuates the efficient charge transfer in the cofacially stacked PBI dimer.

[Results of residual ametropia correction using CIRCLE technology after femtosecond laser SMILE surgery].

PubMed

Kostin, O A; Rebrikov, S V; Ovchinnikov, A I; Stepanov, A A; Takhchidi, Kh P

to evaluate functional results of reoperation performed according to the CIRCLE technology and using the VisuMax femtosecond laser and MEL-80 excimer laser in cases of regression of the refractive effect after SMILE surgery. We studied a group of post-SMILE patients. In those, who showed regression of the refractive effect at 1 year, reoperation was performed according to the CIRCLE technology and using the VisuMax femtosecond laser. The corneal flap was separated from the stromal bed and turned aside. Excimer laser ablation of the stromal bed was performed with the MEL 80 machine. The corneal flap was then placed back and rinsed from both sides. Uncorrected (UCVA) and corrected (BCVA) visual acuity as well as spherical equivalent (SE) were estimated before reoperation, on day 1, and at 1 month. After reoperation, BCVA and UCVA improved. Patient refraction became close to emmetropia. Specifically, UCVA was 0.23±0.18 at baseline (i.e. 1 year after SMILE) and 0.93±0.11 after the CIRCLE procedure (p<0.05). The absolute value of SE was 1.86±1.15 D and 0±0 D before and after CIRCLE, respectively (p<0.05). BCVA change was not statistically significant - from 0.95±0.1 to 0.93±0.11 (p>0.05). Reoperation performed according to the CIRCLE technology and using the VisuMax femtosecond laser and MEL-80 excimer laser provides an increase in visual acuity in case of post-SMILE regression of the refractive effect.

EMERGING TECHNOLOGY PROJECT BULLETIN: LASER INDUCED PHOTOCHEMICAL OXIDATIVE DESTRUCTION

EPA Science Inventory

The process developed by Energy and Environmental Engineering, Incorporated, is designed to photochemically oxidize organic compounds in wastewater by applying ultraviolet radiation using an Excimer laser. The photochemical reactor can destroy low to moderate concentrations...

Laser-assisted solar cell metallization processing

NASA Technical Reports Server (NTRS)

Dutta, S.

1984-01-01

Laser-assisted processing techniques utilized to produce the fine line, thin metal grid structures that are required to fabricate high efficiency solar cells are examined. Two basic techniques for metal deposition are investigated; (1) photochemical decomposition of liquid or gas phase organometallic compounds utilizing either a focused, CW ultraviolet laser (System 1) or a mask and ultraviolet flood illumination, such as that provided by a repetitively pulsed, defocused excimer laser (System 2), for pattern definition, and (2) thermal deposition of metals from organometallic solutions or vapors utilizing a focused, CW laser beam as a local heat source to draw the metallization pattern.

Diode-pumped UV refractive surgery laser

NASA Astrophysics Data System (ADS)

Lin, Jui T.; Hwang, Ming-Yi; Huang, C. H.

1993-07-01

Ophthalmic applications of medical lasers have been extensively explored recently because of their market potential. Refractive surgical lasers represent one of the major development efforts due to the large population of eye disorders: about 160 million people in the USA and more than 2 billion worldwide. The first refractive laser developed was the ArF excimer laser at 193 nm in 1987 - 88 for a procedure called photorefractive keratectomy (PRK). More recently, solid state refractive lasers have also been explored for preliminary clinical trials. These lasers include Nd:YLF (picosecond at 1054 nm), doubled-Nd:YAG (nanosecond at 532 nm), Ho:YAG (microsecond at 2100 nm) and ultraviolet (UV) lasers generated from the harmonic of Ti:sapphire-laser (205 - 220 nm) and Nd:YAG (at 213 nm).

Melting in Superheated Silicon Films Under Pulsed-Laser Irradiation

NASA Astrophysics Data System (ADS)

Wang, Jin Jimmy

This thesis examines melting in superheated silicon films in contact with SiO2 under pulsed laser irradiation. An excimer-laser pulse was employed to induce heating of the film by irradiating the film through the transparent fused-quartz substrate such that most of the beam energy was deposited near the bottom Si-SiO2 interface. Melting dynamics were probed via in situ transient reflectance measurements. The temperature profile was estimated computationally by incorporating temperature- and phase-dependent physical parameters and the time-dependent intensity profile of the incident excimer-laser beam obtained from the experiments. The results indicate that a significant degree of superheating occurred in the subsurface region of the film. Surface-initiated melting was observed in spite of the internal heating scheme, which resulted in the film being substantially hotter at and near the bottom Si-SiO2 interface. By considering that the surface melts at the equilibrium melting point, the solid-phase-only heat-flow analysis estimates that the bottom Si-SiO2 interface can be superheated by at least 220 K during excimer-laser irradiation. It was found that at higher laser fluences (i.e., at higher temperatures), melting can be triggered internally. At heating rates of 1010 K/s, melting was observed to initiate at or near the (100)-oriented Si-SiO2 interface at temperatures estimated to be over 300 K above the equilibrium melting point. Based on theoretical considerations, it was deduced that melting in the superheated solid initiated via a nucleation and growth process. Nucleation rates were estimated from the experimental data using Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Interpretation of the results using classical nucleation theory suggests that nucleation of the liquid phase occurred via the heterogeneous mechanism along the Si-SiO2 interface.

Gas Lasers

NASA Astrophysics Data System (ADS)

Dixit, S. K.

The field of gas lasers, started with the invention of He-Ne laser in 1961, has witnessed tremendous growth in terms of technology development, research into gaseous gain medium, resonator physics and application in widely diverse arenas. This was possible due to high versatility of gas lasers in terms of operating wavelengths, power, beam quality and mode of operation. In recent years, there is a definite trend to replace the gas lasers, wherever possible, by more efficient and compact solid-state lasers. However, for many industrial, medical and military applications, the gas lasers still rule the roost due to their high-power capabilities with good beam quality at specific wavelengths. This chapter presents a short review covering the operating principle, important technical details and application potential of all the important gas lasers such as He-Ne, CO2, argon ion, copper vapour, excimer and chemical lasers. These neutral atoms, ions and molecule gas lasers are discussed as per applicable electrical, chemical and optical excitation schemes. The optically pumped gas lasers, recently experiencing resurgence, are discussed in the context of far infrared THz molecular lasers, diode-pumped alkali lasers and optically pumped gas-filled hollow-core fibre lasers.

F 2 excimer laser (157 nm) radiation modification and surface ablation of PHEMA hydrogels and the effects on bioactivity: Surface attachment and proliferation of human corneal epithelial cells

NASA Astrophysics Data System (ADS)

Zainuddin; Chirila, Traian V.; Barnard, Zeke; Watson, Gregory S.; Toh, Chiong; Blakey, Idriss; Whittaker, Andrew K.; Hill, David J. T.

2011-02-01

Physical and chemical changes at the surface of poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels modified by ablation with an F 2 excimer laser were investigated experimentally. An important observation was that only the outer exposed surface layers of the hydrogel were affected by the exposure to 157 nm radiation. The effect of the surface changes on the tendency of cells to adhere to the PHEMA was also investigated. A 0.5 cm 2 area of the hydrogel surfaces was exposed to laser irradiation at 157 nm to fluences of 0.8 and 4 J cm -2. The changes in surface topography were analysed by light microscopy and atomic force microscopy, while the surface chemistry was characterized by attenuated total reflection infrared and X-ray photoelectron spectroscopies. Cell-interfacial interactions were examined based on the proliferation of human corneal limbal epithelial (HLE) cells cultured on the laser-modified hydrogels, and on the unexposed hydrogels and tissue culture plastic for comparison. It was observed that the surface topography of laser-exposed hydrogels showed rippled patterns with a surface roughness increasing at the higher exposure dose. The changes in surface chemistry were affected not only by an indirect effect of hydrogen and hydroxyl radicals, formed by water photolysis, on the PHEMA, but also by the direct action of laser radiation on PHEMA if the surface layers of the gel become depleted of water. The laser treatment led to a change in the surface characteristics, with a lower concentration of ester side-chains and the formation of new oxygenated species at the surface. The surface also became more hydrophobic. Most importantly, the surface chemistry and the newly created surface topographical features were able to improve the attachment, spreading and growth of HLE cells.

Raman Lidar Measurements of Pinatubo Aerosols over Southeastern Kansas During November-december 1991

NASA Technical Reports Server (NTRS)

Ferrare, R. A.; Melfi, S. H.; Whiteman, D. N.; Evans, K. D.

1992-01-01

The eruptions of the Philippine volcano Pinatubo during June 1991 produced large amounts of stratospheric aerosols that could significantly affect earth's climate as well as trigger stratospheric ozone depletion through heterogeneous chemical reactions. Information regarding the physical and optical properties of these aerosols is required to quantify those effects. By measuring both the elastically backscattered signal and the inelastic signal produced by Raman scattering from nitrogen molecules, Raman lidar can provide some of this information. In this presentation we discuss Raman lidar measurements of the scattering ratio, backscattering, extinction, extinction/backscattering ratio, and optical thickness of the Pinatubo aerosols over southeastern Kansas made on 10 nights during November and December, 1991. The Raman lidar developed at GSFC is a trailer-based system which uses an XeF excimer laser to transmit light at 351 nm. The light backscattered by molecules and aerosols at this wavelength is detected as well as Raman scattered light from water vapor, nitrogen, and oxygen molecules. Since background skylights interfere with the detection of the Raman signals the data discussed in this paper were acquired only at night.

Laser wound: (two) mixed-beam (cw Nd:YAG-PW XeCl) lasing results in mixed injuries

NASA Astrophysics Data System (ADS)

Kull, Mart M.; Kruuv, H.; Zeltzer, Gregory L.; Nevorotin, Alexey J.

1992-08-01

The POLYCON system has been developed for simultaneous passage of different laser beams to a target. In this study, CW Nd:YAG (9 W/cm2) and XeCl excimer (30 mJ/pulse, 80 nsec, 10 Hz) laser beams were directed via individual fibers to a cone-shaped optical mixer continuously connected at the site of its outlet aperture with a common flexible cable destined for surgery. Contact mode cuts were made on rat liver and biopsy samples taken for electron microscopy. Injuries of mixed type have been found within the same cells, e.g., mitochondrial ballooning detected recently after Nd:YAG and vesiculation of the endoplasmic reticulum which is a feature characteristic of XeCl excimer laser. Taking into consideration satisfactory cutting properties, good hemostatic effect and favorable prognosis for recovery as evidenced by active phagocytosis along with proteolytic digestibility of debris in the wound, mixed beam lasing with the parameters tested can be approved as a perspective kind of surgery. In one study, a low potential for healing after CW mode Nd:YAG lasing has been revealed by specially devised tests. Contrary to that, the PW mode XeCl laser has been shown to provide better conditions for local recovery not incompatible with the impression of other workers. The excimers are also believed to be good cutters but they are mainly utilized in the experiments on tissues with low blood supply, due presumably to inherent poor hemostatic capacity of these tools. The lasers of that kind would undoubtedly be tried for tissues with high levels of blood supply provided hemostasis could be secured at the site of surgery by some means. In this paper, such a means is offered, and it is a mixed beam system in which XeCl excimer laser is used in the capacity of a cutter while Nd:YAG one is operating to stop bleeding with minimal side effects on healing in the post-operation period.

Excimer-monomer switch: a reaction-based approach for selective detection of fluoride.

PubMed

Song, Qiao; Bamesberger, Angela; Yang, Lingyun; Houtwed, Haley; Cao, Haishi

2014-07-21

A N-aryl-1,8-naphthalimide based sensor (ES-1) bearing a trimethylsilyl ether has been synthesized by a two-step reaction for quantitative detection of fluoride (F(-)). ES-1 exhibited monomer/excimer emissions at 410 and 524 nm respectively in CH2Cl2. In the presence of F(-), the desilylation of trimethylsilyl ether caused decay of the excimer emission as well as enhancement of the monomer emission to give a ratiometric signal. The fluoride-triggered desilylation showed a high reaction rate and high affinity to F(-) over nine other interfering anions. ES-1 provided a novel fluorescence assay based on excimer-monomer switch of N-aryl-1,8-naphthalimide to quantitatively measure F(-) with a detection limit of 0.133 ppm.

Controlled reshaping of the front surface of the cornea through its full-area ablation outside of the optical zone with a Gaussian ArF excimer laser beam

NASA Astrophysics Data System (ADS)

Semchishen, A. V.; Semchishen, V. A.

2014-01-01

We studied in vitro the response of the topography of the cornea to its full-area laser ablation (the laser beam spot diameter is commensurable with the size of the interface) outside of the central zone with an excimer laser having a Gaussian fluence distribution across the beam. Subject to investigation were the topographically controlled surface changes of the anterior cornea in 60 porcine eyes with a 5 ± 1.25-diopter artificially induced astigmatism, the changes being caused by laser ablation of the stromal collagen in two 3.5-mm-dia. circular areas along the weaker astigmatism axis. Experimental relationships are presented between the actual astigmatism correction and the expected correction for the intact optical zones 1, 2, 3, and 4 mm in diameter. The data for each zone were approximated by the least-squares method with the function d = a + bx. The coefficient b is given with the root-mean-square error. The statistical processing of the data yielded the following results: d = (0.14 ± 0.037)x for the 1-mm-dia. optical zone, (1.10 ± 0.036)x for the 2-mm-dia. optical zone, (1.04 ± 0.020)x for the 3-mm-dia. optical zone, and (0.55 ± 0.04)x for the 4-mm-dia. optical zone. Full astigmatism correction was achieved with ablation effected outside of the 3-mm-dia. optical zone. The surface changes of the cornea are shown to be due not only to the removal of the corneal tissue, but also to the biomechanical topographic response of the cornea to its strain caused by the formation of a dense pseudomembrane in the ablation area.

Choice of the laser wavelength for a herpetic keratitis treatment

NASA Astrophysics Data System (ADS)

Razhev, Alexander M.; Bagayev, Sergei N.; Chernikh, Valery V.; Kargapoltsev, Evgeny S.; Trunov, Alexander; Zhupikov, Andrey A.

2002-06-01

For the first time the effect of the UV laser radiation to human eye cornea with herpetic keratitis was experimentally investigated. In experiments the UV radiation of ArF (193 nm), KrCl (223 nm), KrF (248 nm) excimer lasers were used. Optimal laser radiation parameters for the treatment of the herpetic keratitis were determined. The immuno-biochemical investigations were carried out and the results of clinical trials are presented. The maximum ablation rate was obtained for the 248 nm radiation wavelength. The process of healing was successful but in some cases the haze on the surface of the cornea was observed. When used the 193 nm radiation wavelength the corneal surface was clear without any hazes but the epithelization process was slower than for 248 nm wavelength and in some cases the relapse was occurred. The best results for herpetic keratitis treatment have been achieved by utilizing the 223 nm radiation wavelength of the KrCl excimer laser. The use of the 223 nm radiation wavelength allows treating the herpetic keratitis with low traumatic process of ablation and provides high quality of corneal surface.

All-femtosecond laser-assisted in situ keratomileusis

NASA Astrophysics Data System (ADS)

Gabryte, Egle; Danieliene, Egle; Vaiceliunaite, Agne; Ruksenas, Osvaldas; Vengris, Mikas; Danielius, Romualdas

2013-03-01

We present a femtosecond solid-state Yb:KGW laser system capable of performing the complete laser-assisted in situ keratomileusis (LASIK) ophthalmic procedure. The fundamental infrared radiation (IR) is used to create the corneal flap, and subsequently the corneal stromal ablation is performed using the ultraviolet (UV) pulses of the fifth harmonic. The heating of cornea, ablated surface quality, and healing outcomes of the surgeries performed using the femtosecond laser system are investigated by both ex vivo and in vivo experiments and compared to the results of conventional clinical ArF excimer laser application. The results of this research indicate the feasibility of clinical application of femtosecond UV lasers for LASIK procedure.

Comparison of outcomes of conventional WaveLight® Allegretto Wave® and Technolas® excimer lasers in myopic laser in situ keratomileusis

PubMed Central

Han, Daphne CY; Chen, Jean; Htoon, Hla Myint; Tan, Donald TH; Mehta, Jodhbir S

2012-01-01

Objective To compare the results of laser in situ keratomileusis for myopia using WaveLight® Allegretto Wave® Eye-Q® and Technolas® 217z excimer lasers. Method A retrospective, comparative case series of 442 eyes matched for age and myopia: half each were treated with Allegretto’s wavefront-optimized algorithm and Technolas PlanoScan. Outcome measures were postoperative mean logarithm of the minimum angle of resolution (logMAR) uncorrected visual acuity (UCVA), manifest refraction spherical equivalent (MRSE), cylinder, safety and efficacy indices, refractive predictability, and optical zone size selection. Refractive predictability of a subgroup treated for −2.50 to −4.0 diopter (D) was analyzed separately. Results At mean follow-up of 80.5 days, mean logMAR UCVA, mean MRSE and mean postoperative cylinder were 0.02 ± 0.07 (range −0.12 to 0.30), 0.27 ± 0.36 D (range −1.25 to 1.50 D) and −0.33 ± 0.30 D (range 0.00 to −1.50 D) for Allegretto versus 0.02 ± 0.08 (range −0.12 to 0.40), 0.095 ± 0.47 D (range −1.25 to 1.13 D) and −0.44 ± 0.5 2 D (range 0.00 to −2.25 D) for Technolas (P = 0.98, 0.80 and 0.006). Mean safety and efficacy indices were 1.05 ± 0.13 (0.75–1.33) and 0.97 ± 0.13 (0.50–1.33) for Allegretto and 1.07 ± 0.14 (0.75–1.49) and 0.97 ± 0.17 (0.40–1.49) for Technolas (P = 0.23 and 0.69). Proportions of eyes achieving postoperative MRSE within ±1.0 D, ±0.5 D, and ±0.25 D were 98.2%, 91.9% and 75.6% for Allegretto and 99.1%, 97.8% and 72.4% for Technolas (P = 0.68, 0.20 and 0.51). Mean optical zone size selected was 6.48 ± 0.10 mm (range 6.0–6.5 mm) for Allegretto and 6.38 ± 0.19 mm (range 5.6–6.6 mm) for Technolas (P < 0.001). Of the subgroup with treatment between −2.5 and −4.0 D, 86.8% and 58.5% of eyes treated with Allegretto achieved postoperative MRSE within ±0.50 D and ±0.25 D versus 70.4% and 44.4% for Technolas (P = 0.006 and 0.057). Conclusion No differences were seen in postoperative mean

Influence of laser wavelength on two-dimensional carbon nanosheet formation from laser-induced exfoliation of naphthalene

NASA Astrophysics Data System (ADS)

Qian, Min; Niu, Yue Ping; Gong, Shang Qing

2018-01-01

Pulsed Nd:YAG (532 nm) and Excimer (248 nm) lasers were employed to produce freestanding, two-dimensional (2D), carbon nanosheets (CNSs) from naphthalene, through laser-induced exfoliation. The polymer-to-carbon transition was investigated in terms of laser wavelengths, fluences, as well as target preparations. Continuous and porous CNSs of several nanometers in thickness and micrometers in size were obtained from 532 and 248 nm pulsed laser exfoliation of spin-coated naphthalene films, respectively. The porous morphology is ascribed to the photon-induced dissociation of chemical bonds dominated in 248 nm laser interaction with ablated naphthalene. With the increase of laser fluences from 1 to 5 J cm-2, amorphous carbon and ultrathin CNS structures were obtained in sequence. This work revealed a general mechanism of producing 2D structured carbon materials from pulsed laser exfoliation.

KrF laser pumping by electron beam discharge

NASA Astrophysics Data System (ADS)

Bonnet, J.; Fournier, G.; Pigache, D.

1981-09-01

The pumping of excimer lasers used in nuclear fusion and isotope separation is considered. Homogeneous ionization with an electron beam permitted discharge pumping of a KrF laser with a discharge-energy/beam-energy ratio 5. This high value is obtained to the detriment of an energy density and an efficiency which are about half the best values obtained under other conditions. This result does not modify a recent conclusion indicating that an electron beam controlled discharge has no significant advantage over a pure electron beam as regards pumping high energy KrF lasers at high repetition rate.

Experimental investigation of a pulsed Rb-Ar excimer-pumped alkali laser

NASA Astrophysics Data System (ADS)

Cheng, Hongling; Wang, Zhimin; Zhang, Fengfeng; Wang, Mingqiang; Tian, Zhaoshuo; Peng, Qinjun; Cui, Dafu; Xu, Zuyan

2017-03-01

We present experimental results of an exciplex-pumped alkali laser (XPAL) at 780 nm based on the 52P3/2 → 52S1/2 transition of the Rb atom in mixtures of Rb vapor and Ar. A laboratory-built Ti:sapphire laser with a pulse repetition rate of 3 kHz and a pulse width of 100 ns is used as the pump source. The maximum laser pulse energy of 0.26 µJ at 780 nm is obtained under an absorbed pump pulse energy of 42 µJ at 755 nm in mixtures of Rb vapor and Ar at a temperature of 423 K, corresponding to an optical conversion efficiency of 0.62%. Further experiments show that the output laser at 780 nm can always be detected for pump wavelengths ranging from 754 to 759 nm, indicating that Rb-Ar mixtures can be effectively pumped by commercial laser diodes (LDs) with a bandwidth of 5 nm.

Nano-crystallization in ZnO-doped In2O3 thin films via excimer laser annealing for thin-film transistors

NASA Astrophysics Data System (ADS)

Fujii, Mami N.; Ishikawa, Yasuaki; Ishihara, Ryoichi; van der Cingel, Johan; Mofrad, Mohammad R. T.; Bermundo, Juan Paolo Soria; Kawashima, Emi; Tomai, Shigekazu; Yano, Koki; Uraoka, Yukiharu

2016-06-01

In a previous work, we reported the high field effect mobility of ZnO-doped In2O3 (IZO) thin film transistors (TFTs) irradiated by excimer laser annealing (ELA) [M. Fujii et al., Appl. Phys. Lett. 102, 122107 (2013)]. However, a deeper understanding of the effect of ELA on the IZO film characteristics based on crystallinity, carrier concentrations, and optical properties is needed to control localized carrier concentrations for fabricating self-aligned structures in the same oxide film and to adequately explain the physical characteristics. In the case of as-deposited IZO film used as the channel, a high carrier concentration due to a high density of oxygen vacancies was observed; such a film does not show the required TFT characteristics but can act as a conductive film. We achieved a decrease in the carrier concentration of IZO films by crystallization using ELA. This means that ELA can form localized conductive or semi-conductive areas on the IZO film. We confirmed that the reason for the carrier concentration decrease was the decrease of oxygen-deficient regions and film crystallization. The annealed IZO films showed nano-crystalline phase, and the temperature at the substrate was substantially less than the temperature limit for flexible films such as plastic, which is 50°C. This paves the way for the formation of self-aligned structures and separately formed conductive and semi-conductive regions in the same oxide film.

Clinical results of the laser-assisted in situ keratomileusis (LASIK) for myopia

NASA Astrophysics Data System (ADS)

Guo, Hai-ke; Yao, Da-qing; Gui, Lu-ping

1998-11-01

To observe and analyze the refractive and complications of the LASIK for corrections of myopia. With the microlamellar keratoplasty and the excimer laser, LASIK was performed on 194 cases. According to the preoperative spherical equivalent refraction, divide the patients into three groups.

Thermal characterization of poly(ethylene glycol)-poly(D,L-lactide) block copolymer micelles based on pyrene excimer formation.

PubMed

Jule, Eduardo; Yamamoto, Yuji; Thouvenin, Muriel; Nagasaki, Yukio; Kataoka, Kazunori

2004-07-07

Poly(ethylene glycol)--poly(D,L-lactide) (PEG-PDLLA) block copolymers were prepared by anionic ring-opening polymerization, resulting in block sizes effectively controlled by initial monomer/initiator ratios and low molecular weight distributions (<1.12). A pyrene derivative (1-pyrenyl carbonyl cyanide--Py) was conjugated to the end of the hydrophobic block (PDLLA) in a quantitative manner, with coupling efficiencies >95%. The so-obtained PEG-PDLLA-Py copolymers displayed fluorescent properties that were associated with the pyrene monomers, when placed in good solvents for both the hydrophilic and hydrophobic blocks. When placed in selective solvents, these copolymers self-assembled into micelles in the 30-nm range, also with low particle size distributions (<0.09), within which Py could be readily entrapped in the hydrophobic PDLLA core. Py entrapment resulted in the formation of excimers, as evident from fluorescence measurements. Observation of excimer formation/dissociation further conveyed information on the physicochemical properties of the core. Thermal characterization of these systems showed that an increase in the temperature resulted in changes in the properties of excimer fluorescence, an occurrence attributed to a higher mobility of the otherwise glassy PDLLA. This, in turn, greatly affected the inter-molecular distance between pyrene molecules, a crucial factor for excimer formation. The glass transition of the PDLLA block, approximately 38 degrees C, defined the onset for increasing chain mobility and whence excimer dissociation. Excimer fluorescence appeared to be time-dependent. Based on these observations, chain exchange processes were clearly evidenced through the time-dependent dissociation of excimers into unimers, a process that was influenced by changes in temperature.

Lasers in endodontics: an overview

NASA Astrophysics Data System (ADS)

Frentzen, Matthias; Braun, Andreas; Koort, Hans J.

2002-06-01

The interest in endodontic use of dental laser systems is increasing. Developing laser technology and a better understanding of laser effects widened the spectrum of possible endodontic indications. Various laser systems including excimer-, argon+-, diode-, Nd:YAG-, Er:YAG- and CO2-lasers are used in pulp diagnosis, treatment of hypersensitivity, pulp capping, sterilization of root canals, root canal shaping and obturation or apicoectomy. With the development of new delivery systems - thin and flexible fibers - for many different wavelengths laser applications in endodontics may increase. Since laser devices are still relatively costly, access to them is limited. Most of the clinical applications are laser assisted procedures such as the removing of pulp remnants and debris or disinfection of infected root canals. The essential question is whether a laser can provide improved treatment over conventional care. To perform laser therapy in endodontics today different laser types with adopted wavelengths and pulse widths are needed, each specific to a particular application. Looking into the future we will need endodontic laser equipment providing optimal laser parameters for different treatment modalities. Nevertheless, the quantity of research reports from the last decade promises a genuine future for lasers in endodontics.

Excimer-based peptide beacons: a convenient experimental approach for monitoring polypeptide-protein and polypeptide-oligonucleotide interactions.

PubMed

Oh, Kenneth J; Cash, Kevin J; Plaxco, Kevin W

2006-11-01

While protein-polypeptide and nucleic acid-polypeptide interactions are of significant experimental interest, quantitative methods for the characterization of such interactions are often cumbersome. Here we described a relatively simple means of optically monitoring such interactions using excimer-based peptide beacons (PBs). The design of PBs is based on the observation that, whereas short peptides are almost invariably unfolded and highly dynamic, they become rigid when complexed with macromolecular targets. Using this binding-induced folding to segregate two pyrene moieties and therefore inhibit excimer formation, we have produced PBs directed against both anti-HIV antibodies and the retroviral transactive response (TAR) RNA hairpin. For both polypeptides, target recognition is accompanied by a roughly 2-fold decrease in excimer emission, thus allowing the detection of their respective targets at concentrations of a few nanomolar. Because excimer emission requires the formation of a tight, precisely oriented pyrene dimer, even relatively trivial binding-induced segregation reduces fluorescence significantly. This suggests that the PB approach will be suitable for monitoring a wide range of peptide-macromolecule recognition events. Moreover, the synthesis of excimer-based PBs utilizes commercially available modified pyrenes in a simple and well-established protocol, making the approach well suited for routine laboratory applications.

The advances and characteristics of high-power diode laser materials processing

NASA Astrophysics Data System (ADS)

Li, Lin

2000-10-01

This paper presents a review of the direct applications of high-power diode lasers for materials processing including soldering, surface modification (hardening, cladding, glazing and wetting modifications), welding, scribing, sheet metal bending, marking, engraving, paint stripping, powder sintering, synthesis, brazing and machining. The specific advantages and disadvantages of diode laser materials processing are compared with CO 2, Nd:YAG and excimer lasers. An effort is made to identify the fundamental differences in their beam/material interaction characteristics and materials behaviour. Also an appraisal of the future prospects of the high-power diode lasers for materials processing is given.

Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation

NASA Technical Reports Server (NTRS)

Harris, S. E.; Siegman, A. E.; Kuizenga, D. J.; Kung, A. H.; Young, J. F.; Bekkers, G. W.; Bloom, D. M.; Newton, J. H.; Phillion, D. W.

1975-01-01

The generation of tunable visible, infrared, and ultraviolet light is examined, along with the control of this light by means of novel mode-locking and modulation techniques. Transient mode-locking of the Nd:YAG laser and generation of short tunable pulses in the visible and the alkali metal inert gas excimer laser systems were investigated. Techniques for frequency conversion of high power and high energy laser radiation are discussed, along with high average power blue and UV laser light sources.

Periodic structure formation and surface morphology evolution of glassy carbon surfaces applying 35-fs-200-ps laser pulses

NASA Astrophysics Data System (ADS)

Csontos, J.; Toth, Z.; Pápa, Z.; Budai, J.; Kiss, B.; Börzsönyi, A.; Füle, M.

2016-06-01

In this work laser-induced periodic structures with lateral dimensions smaller than the central wavelength of the laser were studied on glassy carbon as a function of laser pulse duration. To generate diverse pulse durations titanium-sapphire (Ti:S) laser (center wavelength 800 nm, pulse durations: 35 fs-200 ps) and a dye-KrF excimer laser system (248 nm, pulse durations: 280 fs, 2.1 ps) were used. In the case of Ti:S laser treatment comparing the central part of the laser-treated areas a striking difference is observed between the femtoseconds and picoseconds treatments. Ripple structure generated with short pulse durations can be characterized with periodic length significantly smaller than the laser wavelength (between 120 and 165 nm). At higher pulse durations the structure has a higher periodic length (between 780 and 800 nm), which is comparable to the wavelength. In case of the excimer laser treatment the different pulse durations produced similar surface structures with different periodic length and different orientation. One of the structures was parallel with the polarization of the laser light and has a higher periodic length (~335 nm), and the other was perpendicular with smaller periodic length (~78-80 nm). The possible mechanisms of structure formation will be outlined and discussed in the frame of our experimental results.

PRK by Er:YAG laser: in-vitro studies and first in-vivo experiences

NASA Astrophysics Data System (ADS)

Steiner, Rudolf W.; Leiacker, Richard; Russ, Detlef; Seiler, Theo

1996-01-01

Photorefractive keratectomy (PRK) is usually performed by an excimer laser at 193 nm wavelength. Ablatio of corneal tissue is, however, not only possible in the UV region of the optical spectrum but also in the IR where water is an excellent absorber. Therefore, an Er:YAG laser was used at 2.94 micrometer wavelength as an alternative laser light source to perform in vitro studies of corneal ablation and also first clinical experiments to correct myopia of patients with blind eyes.

Simple Model of Macroscopic Instability in XeCl Discharge Pumped Lasers

NASA Astrophysics Data System (ADS)

Ahmed, Belasri; Zoheir, Harrache

2003-10-01

The aim of this work is to study the development of the macroscopic non uniformity of the electron density of high pressure discharge for excimer lasers and eventually its propagation because of the medium kinetics phenomena. This study is executed using a transverse mono-dimensional model, in which the plasma is represented by a set of resistance's in parallel. This model was employed using a numerical code including three strongly coupled parts: electric circuit equations, electron Boltzmann equation, and kinetics equations (chemical kinetics model). The time variations of the electron density in each plasma element are obtained by solving a set of ordinary differential equations describing the plasma kinetics and external circuit. The use of the present model allows a good comprehension of the halogen depletion phenomena, which is the principal cause of laser ending and allows a simple study of a large-scale non uniformity in preionization density and its effects on electrical and chemical plasma properties. The obtained results indicate clearly that about 50consumed at the end of the pulse. KEY WORDS Excimer laser, XeCl, Modeling, Cold plasma, Kinetic, Halogen depletion, Macroscopic instability.

Bound-bound transitions in the emission spectra of Ba+-He excimer

NASA Astrophysics Data System (ADS)

Moroshkin, P.; Kono, K.

2016-05-01

We present an experimental and theoretical study of the emission and absorption spectra of the Ba+ ions and Ba+*He excimer quasimolecules in the cryogenic Ba-He plasma. We observe several spectral features in the emission spectrum, which we assign to the electronic transitions between bound states of the excimer correlating to the 6 2P3 /2 and 5 2D3 /2 ,5 /2 states of Ba+. The resulting Ba+(5 2DJ) He is a metastable electronically excited complex with orbital angular momentum L =2 , thus expanding the family of known metal-helium quasimolecules. It might be suitable for high-resolution spectroscopic studies and for the search for new polyatomic exciplex structures.

SITE - EMERGING TECHNOLOGIES: LASER INDUCED PHOTO- CHEMICAL OXIDATIVE DESTRUCTION OF TOXIC ORGANICS IN LEACHATES AND GROUNDWATERS

EPA Science Inventory

The technology described in this report has been developed under the Emerging Technology Program of the Superfund Innovative Technology Evaluation (SITE) Program to photochemically oxidize organic compounds in wastewater by applying ultraviolet radiation using an excimer laser. T...

High-energy krypton fluoride lasers for inertial fusion.

PubMed

Obenschain, Stephen; Lehmberg, Robert; Kehne, David; Hegeler, Frank; Wolford, Matthew; Sethian, John; Weaver, James; Karasik, Max

2015-11-01

Laser fusion researchers have realized since the 1970s that the deep UV light from excimer lasers would be an advantage as a driver for robust high-performance capsule implosions for inertial confinement fusion (ICF). Most of this research has centered on the krypton-fluoride (KrF) laser. In this article we review the advantages of the KrF laser for direct-drive ICF, the history of high-energy KrF laser development, and the present state of the art and describe a development path to the performance needed for laser fusion and its energy application. We include descriptions of the architecture and performance of the multi-kilojoule Nike KrF laser-target facility and the 700 J Electra high-repetition-rate KrF laser that were developed at the U.S. Naval Research Laboratory. Nike and Electra are the most advanced KrF lasers for inertial fusion research and energy applications.

Evaluation of OH laser-induced fluorescence techniques for supersonic combustion diagnostics

NASA Technical Reports Server (NTRS)

Quagliaroli, T. M.; Laufer, G.; Krauss, R. H.; Mcdaniel, J. C., Jr.

1992-01-01

The limitations on application of dye laser and narrowband tunable KrF excimer laser systems to planar OH fluorescence measurements in supersonic combustion test facilities are examined. Included in the analysis are effects of collisional quenching, beam absorption, fluorescence trapping, and signal strengths on achievable measurement accuracy using several excitation and detection options for either of the two laser systems. Dye-based laser systems are found to be the method of choice for imaging OH concentrations less than 10 exp 15 per cu cm, while the KrF based systems provide significant reduction in measurement ambiguity for concentrations in excess of 10 exp 15 per cu cm.

Laser in situ keratomileusis using optimized aspheric profiles and cyclotorsion control to treat compound myopic astigmatism with high cylinder.

PubMed

Alió, Jorge L; Plaza-Puche, Ana B; Martinez, Lorena M; Torky, Magda; Brenner, Luis F

2013-01-01

To evaluate the visual outcomes after laser in situ keratomileusis (LASIK) surgery to correct primary compound myopic astigmatism with high cylinder performed using a fast-repetition-rate excimer laser platform with optimized aspheric profiles and cyclotorsion control. Vissum Corporation and Division of Ophthalmology, Universidad Miguel Hernández, Alicante, Spain. Retrospective consecutive observational nonrandomized noncomparative case series. Eyes with primary compound myopic astigmatism and a cylinder power over 3.00 diopters (D) had uneventful LASIK with femtosecond flap creation and fast-repetition-rate excimer laser ablation with aspheric profiles and cyclotorsion control. Visual, refractive, and aberrometric outcomes were evaluated at the 6-month follow-up. The astigmatic correction was evaluated using the Alpins method and Assort software. The study enrolled 37 eyes (29 patients; age range 19 to 55 years). The significant reduction in refractive sphere and cylinder 3 months and 6 months postoperatively (P<.01) was associated with improved uncorrected distance visual acuity (P<.01). Eighty-seven percent of eyes had a spherical equivalent within ±0.50 D; 7.5% of eyes were retreated. There was no significant induction of higher-order aberrations (HOAs). The targeted and surgically induced astigmatism magnitudes were 3.23 D and 2.96 D, respectively, and the correction index was 0.91. The safety and efficacy indices were 1.05 and 0.95, respectively. Laser in situ keratomileusis for primary compound myopic astigmatism with high cylinder (>3.00 D) performed using a fast-repetition-rate excimer laser with optimized aspheric profiles and cyclotorsion control was safe, effective, and predictable and did not cause significant induction of HOAs. Copyright © 2012 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Pulsed laser-induced formation of silica nanogrids

PubMed Central

2014-01-01

Silica grids with micron to sub-micron mesh sizes and wire diameters of 50 nm are fabricated on fused silica substrates. They are formed by single-pulse structured excimer laser irradiation of a UV-absorbing silicon suboxide (SiO x ) coating through the transparent substrate. A polydimethylsiloxane (PDMS) superstrate (cover layer) coated on top of the SiO x film prior to laser exposure serves as confinement for controlled laser-induced structure formation. At sufficiently high laser fluence, this process leads to grids consisting of a periodic loop network connected to the substrate at regular positions. By an additional high-temperature annealing, the residual SiO x is oxidized, and a pure SiO2 grid is obtained. PACS 81.07.-b; 81.07.Gf; 81.65.Cf PMID:24581305

Laser micromachining of biofactory-on-a-chip devices

NASA Astrophysics Data System (ADS)

Burt, Julian P.; Goater, Andrew D.; Hayden, Christopher J.; Tame, John A.

2002-06-01

Excimer laser micromachining provides a flexible means for the manufacture and rapid prototyping of miniaturized systems such as Biofactory-on-a-Chip devices. Biofactories are miniaturized diagnostic devices capable of characterizing, manipulating, separating and sorting suspension of particles such as biological cells. Such systems operate by exploiting the electrical properties of microparticles and controlling particle movement in AC non- uniform stationary and moving electric fields. Applications of Biofactory devices are diverse and include, among others, the healthcare, pharmaceutical, chemical processing, environmental monitoring and food diagnostic markets. To achieve such characterization and separation, Biofactory devices employ laboratory-on-a-chip type components such as complex multilayer microelectrode arrays, microfluidic channels, manifold systems and on-chip detection systems. Here we discuss the manufacturing requirements of Biofactory devices and describe the use of different excimer laser micromachined methods both in stand-alone processes and also in conjunction with conventional fabrication processes such as photolithography and thermal molding. Particular attention is given to the production of large area multilayer microelectrode arrays and the manufacture of complex cross-section microfluidic channel systems for use in simple distribution and device interfacing.

Evaluation of a Novel Laser-assisted Coronary Anastomotic Connector - the Trinity Clip - in a Porcine Off-pump Bypass Model

PubMed Central

Stecher, David; Bronkers, Glenn; Noest, Jappe O.T.; Tulleken, Cornelis A.F.; Hoefer, Imo E.; van Herwerden, Lex A.; Pasterkamp, Gerard; Buijsrogge, Marc P.

2014-01-01

To simplify and facilitate beating heart (i.e., off-pump), minimally invasive coronary artery bypass surgery, a new coronary anastomotic connector, the Trinity Clip, is developed based on the excimer laser-assisted nonocclusive anastomosis technique. The Trinity Clip connector enables simplified, sutureless, and nonocclusive connection of the graft to the coronary artery, and an excimer laser catheter laser-punches the opening of the anastomosis. Consequently, owing to the complete nonocclusive anastomosis construction, coronary conditioning (i.e., occluding or shunting) is not necessary, in contrast to the conventional anastomotic technique, hence simplifying the off-pump bypass procedure. Prior to clinical application in coronary artery bypass grafting, the safety and quality of this novel connector will be evaluated in a long-term experimental porcine off-pump coronary artery bypass (OPCAB) study. In this paper, we describe how to evaluate the coronary anastomosis in the porcine OPCAB model using various techniques to assess its quality. Representative results are summarized and visually demonstrated. PMID:25490000

Nanosecond laser-induced ablation and laser-induced shockwave structuring of polymer foils down to sub-μm patterns

NASA Astrophysics Data System (ADS)

Lorenz, P.; Bayer, L.; Ehrhardt, M.; Zimmer, K.; Engisch, L.

2015-03-01

Micro- and nanostructures exhibit a growing commercial interest where a fast, cost-effective, and large-area production is attainable. Laser methods have a great potential for the easy fabrication of surface structures into flexible polymer foils like polyimide (PI). In this study two different concepts for the structuring of polymer foils using a KrF excimer laser were tested and compared: the laser-induced ablation and the laser-induced shock wave structuring. The direct front side laser irradiation of these polymers allows the fabrication of different surface structures. For example: The low laser fluence treatment of PI results in nano-sized cone structures where the cone density can be controlled by the laser parameters. This allows inter alia the laser fabrication of microscopic QR code and high-resolution grey-tone images. Furthermore, the laser treatment of the front side of the polymer foil allows the rear side structuring due to a laserinduced shock wave. The resultant surface structures were analysed by optical and scanning electron microscopy (SEM) as well as white light interferometry (WLI).

Cool excimer laser-assisted angioplasty (CELA) and tibial balloon angioplasty (TBA) in management of infragenicular arterial occlusion in critical lower limb ischemia (CLI).

PubMed

Sultan, Sherif; Tawfick, Wael; Hynes, Niamh

2013-04-01

We aim to compare cool excimer laser-assisted angioplasty (CELA) versus tibial balloon angioplasty (TBA) in patients with critical limb ischemia (CLI) with tibial artery occlusive disease. The primary end point is sustained clinical improvement (SCI) and amputation-free survival (AFS). The secondary end points are binary restenosis, target extremity revascularization (TER), and cost-effectiveness. From June 2005 to October 2010, 1506 patients were referred with peripheral vascular disease and 572 with CLI. A total of 80 patients underwent 89 endovascular revascularizations (EVRs) for tibial occlusions, 47 using TBA and 42 using CELA. All patients were Rutherford category 4 to 6. Three-year SCI was enhanced with CELA (81%) compared to TBA (63.8%; P = .013). Three-year AFS significantly improved with CELA (95.2%) versus TBA (89.4%; P = .0165). Three-year freedom from TER was significantly improved with CELA (92.9%) versus 78.7% TBA (P = .026). Three-year freedom from MACE was comparable in both the groups (P = .455). Patients with CELA had significantly improved quality time without symptoms of disease or toxicity of treatment (Q-TWiST) at 3 years (10.5 months; P = .048) with incremental cost of €2073.19 per quality-adjusted life year gained. Tibial EVR provides exceptional outcome in CLI. The CELA has superior SCI, AFS, and freedom from TER, with improved Q-TWiST and cost-effectiveness.

Excimer UV lamp irradiation induced grafting on synthetic polymers

NASA Astrophysics Data System (ADS)

Praschak, D.; Bahners, T.; Schollmeyer, E.

Surface modifications on polyethyleneterephthalate (PET) films following excimer UV lamp irradiation induced grafting were studied. Characteristics of the modifications depending on the conditions during the irradiation were analysed using contact-angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). Depending on the conditions during the irradiation different surface modifications were obtained, which can generally be classified regarding the hydrophilic or hydrophobic characteristics of the resulting surface. It is shown that not every substance that meets the general demands will be grafted on synthetic polymers using excimer UV radiation. Examples of agents that can simply be grafted onto polymer surfaces and those that undergo further crosslinking, building up thin films are listed. Agents used for grafting on polymers are 1,5-hexadiene, perfluoro-4-methyl-pent-2-ene, polyethyleneglycol 200, monosilane and polyethylene. The transferability of the effects achieved to substrates such as polyparaphenylene terephthalamide or polymetaphenylene isophthalamide is shown.

Mitomycin-C in corneal surface excimer laser ablation techniques: a report by the American Academy of Ophthalmology.

PubMed

Majmudar, Parag A; Schallhorn, Steven C; Cason, John B; Donaldson, Kendall E; Kymionis, George D; Shtein, Roni M; Verity, Steven M; Farjo, Ayad A

2015-06-01

To review the published literature assessing the efficacy and safety of mitomycin-C (MMC) as an adjunctive treatment in corneal surface excimer laser ablation procedures. Literature searches of the PubMed and Cochrane Library databases were last conducted on August 19, 2014, without language or date limitations. The searches retrieved a total of 239 references. Of these, members of the Ophthalmic Technology Assessment Committee Refractive Management/Intervention Panel selected 26 articles that were considered to be of high or medium clinical relevance, and the panel methodologist rated each article according to the strength of evidence. Ten studies were rated as level I evidence, 5 studies were rated as level II evidence, and the remaining 11 studies were rated as level III evidence. The majority of the articles surveyed in this report support the role of MMC as an adjunctive treatment in surface ablation procedures. When MMC is applied in the appropriate concentration and confined to the central cornea, the incidence of post-surface ablation haze is decreased. Although a minority of studies that evaluated endothelial cell density (ECD) reported an MMC-related decrease in ECD, no clinical adverse outcomes were reported. Over the past 15 years, the use of MMC during surgery in surface ablation has become widespread. There is good evidence of the effectiveness of MMC when used intraoperatively as prophylaxis against haze in higher myopic ablations. Although there are reports of decreased endothelial counts after the administration of MMC during surgery, the clinical significance of this finding remains uncertain, because no adverse outcomes were reported with as much as 5 years of follow-up. Optimal dosage, effectiveness as prophylaxis in lower myopic and hyperopic ablations, and long-term safety, particularly in eyes with reduced corneal endothelial cell counts from prior intraocular surgery, have yet to be established. Copyright © 2015 American Academy of

Differences in optical coherence tomographic findings and clinical outcomes between excimer laser and cutting balloon angioplasty for focal in-stent restenosis lesions.

PubMed

Nishino, Masami; Lee, Yasuharu; Nakamura, Daisuke; Yoshimura, Takahiro; Taniike, Masayuki; Makino, Nobuhiko; Kato, Hiroyasu; Egami, Yasuyuki; Shutta, Ryu; Tanouchi, Jun; Yamada, Yoshio

2012-10-01

In-stent restenosis (ISR), especially focal ISR, after percutaneous coronary intervention (PCI) remains one of the major clinical problems in the drug-eluting stent (DES) era. Several reports have revealed that excimer laser coronary angioplasty (ELCA) is useful for ISR; however, detailed findings after ELCA are unknown. Therefore, we investigated the condition of the neointima after ELCA for ISR with optical coherence tomography (OCT) and compared the OCT findings and clinical outcome between ELCA and cutting-balloon angioplasty (CBA). Twenty-one consecutive patients with focal ISR who underwent ELCA or CBA were enrolled. All patients underwent 12- to 15-month follow-up coronary angiography. OCT was performed immediately after successful PCI to evaluate the neointimal condition in the ISR lesion. We compared the following OCT parameters between ELCA and CBA groups: maximal thickness of remaining in-stent neointima (MTN), number of tears, minimum lumen dimension (MLD), and minimum lumen area (MLA). We also evaluated clinical outcomes, including target vessel revascularization, acute myocardial infarction, death, and stent thrombosis. MLA in the ELCA group (n = 10) was significantly larger than in the CBA group, and number of tears in the ELCA group was significantly lower than in the CBA group. A trend was shown toward lower TLR with ELCA versus CBA (10.0% vs 45.5%). OCT immediately after ELCA for ISR lesions revealed larger lumen area and smaller number of tears compared with CBA, which may support favorable effects of ELCA for focal ISR.

Laser applications in advanced chip packaging

NASA Astrophysics Data System (ADS)

Müller, Dirk; Held, Andrew; Pätzel, Rainer; Clark, Dave; van Nunen, Joris

2016-03-01

While applications such as drilling μ-vias and laser direct imaging have been well established in the electronics industry, the mobile device industry's push for miniaturization is generating new demands for packaging technologies that allow for further reduction in feature size while reducing manufacturing cost. CO lasers have recently become available and their shorter wavelength allows for a smaller focus and drilling hole diameters down to 25μm whilst keeping the cost similar to CO2 lasers. Similarly, nanosecond UV lasers have gained significantly in power, become more reliable and lower in cost. On a separate front, the cost of ownership reduction for Excimer lasers has made this class of lasers attractive for structuring redistribution layers of IC substrates with feature sizes down to 2μm. Improvements in reliability and lower up-front cost for picosecond lasers is enabling applications that previously were only cost effective with mechanical means or long-pulsed lasers. We can now span the gamut from 100μm to 2μm for via drilling and can cost effectively structure redistribution layers with lasers instead of UV lamps or singulate packages with picosecond lasers.

Laser synthesis and spectroscopy of acetonitrile/silver nanoparticles

NASA Astrophysics Data System (ADS)

Akin, S. T.; Liu, X.; Duncan, M. A.

2015-11-01

Silver nanoparticles with acetonitrile ligands are produced in a laser ablation flow reactor. Excimer laser ablation produces gas phase metal clusters which are thermalized with helium or argon collisions in the flowtube, and reactions with acetonitrile vapor coordinate this ligand to the particle surface. The gaseous mixture is captured in a cryogenic trap; warming produces a solution of excess ligand and coated particles. TEM images reveal particle sizes of 10-30 nm diameter. UV-vis absorption and fluorescence spectra are compared to those of standard silver nanoparticles with surfactant coatings. Deep-UV ligand absorption is strongly enhanced by nanoparticle adsorption.

Removal of dust particles from metal-mirror surfaces by excimer-laser radiation

NASA Astrophysics Data System (ADS)

Mann, Klaus R.; Wolff-Rottke, B.; Mueller, F.

1995-07-01

The effect of particle desorption from Al mirror surfaces by the influence of pulsed UV laser radiation has been studied. The investigations are closely related to the demands of astronomers, who are looking for a more effective way of cleaning the Al coatings of future very large telescope mirrors. A systematic parameter study has been performed in order to determine the irradiation conditions which yield the highest dust removal efficiency (i.e. reflectivity increase) on contaminated samples, taking particularly into account laser-induced damage and degradation effects of coating and substrate. The particle removal rate increases with increasing laser fluence, being limited however by the damage threshold of the coating. Therefore, parameters influencing the damage threshold of metal coatings like wavelength, pulse width, and number of pulses have been studied in detail. Data indicate that on Al coated BK7 and Zerodur samples KrF laser radiation yields the optimum result, with cleaning efficiencies comparable to polymer film stripping. The initial reflectivity of the clean coating can nearly be reinstalled, in particular when an additional solvent film on the sample surface is applied. Hence, laser desorption seems to be a viable method of cleaning large Al mirrors for telescopes.

Keratorefractive procedures

NASA Astrophysics Data System (ADS)

Seiler, Theo

1991-11-01

Two laser types are going to find a place in refractive surgery of the cornea: the excimer laser (193 nm) and mid-infrared YAG lasers, such as Ho:YAG (2.1 micrometers ) and Er:YAG (2.94 micrometers ). Whereas the excimer laser used for photorefractive keratectomy (PRK) and phototherapeutic keratectomy (PTK) is currently studied in clinical trials, Ho:YAG and Er:YAG lasers are still in the state of preclinical evaluation. For myopic corrections excimer laser PRK has shown to be safe and effective in the range up to -7.0 D. The results compare favorably with conventional procedures such as radial keratotomy. Complications are rare. Hyperopic and astigmatic corrections using the Ho:YAG laser (HOT) are effective, but safety and stability has yet to be proven. Er:YAG laser photoablation yields a healing response in animal eyes similar to the excimer laser.

Removal of dust particles from metal mirror surfaces by excimer laser radiation

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

Mann, K.; Wolff-Rottke, B.; Mueller, F.

1995-12-31

The effect of particle desorption from Al mirror surfaces by the influence of pulsed UV laser radiation has been studied. The investigations are closely related to the demands of astronomers, who are looking for a more effective way of cleaning the Al coatings of future very large telescope (VLT) mirrors. A systematic parameter study has been performed in order to determine the irradiation conditions which yield the highest dust removal efficiency (i.e. reflectivity increase) on contaminated samples, taking particularly into account laser induced damage and degradation effects of coating and substrate. The particle removal rate increases with increasing laser fluence,more » being limited however by the damage threshold of the coating. Therefore, parameters influencing the damage threshold of metal coatings like wavelength, pulse width and number of pulses have been studied in detail. Data indicate that on Al coated BK7 and Zerodur samples KrF laser radiation yields the optimum result, with cleaning efficiencies comparable to polymer film stripping. The initial reflectivity of the clean coating can nearly be reinstalled, in particular when an additional solvent film on the sample surface is applied. Hence, laser desorption seems to be a viable method of cleaning large Al mirrors for telescopes.« less

Laser plasma interaction at an early stage of laser ablation

NASA Astrophysics Data System (ADS)

Lu, Y. F.; Hong, M. H.; Low, T. S.

1999-03-01

Laser scattering and its interaction with plasma during KrF excimer laser ablation of silicon are investigated by ultrafast phototube detection. There are two peaks in an optical signal with the first peak attributed to laser scattering and the second one to plasma generation. For laser fluence above 5.8 J/cm2, the second peak rises earlier to overlap with the first one. The optical signal is fitted by a pulse distribution for the scattered laser light and a drifted Maxwell-Boltzmann distribution with a center-of-mass velocity for the plasma. Peak amplitude and its arrival time, full width at half maximum (FWHM), starting time, and termination time of the profiles are studied for different laser fluences and detection angles. Laser pulse is scattered from both the substrate and the plasma with the latter part as a dominant factor during the laser ablation. Peak amplitude of the scattered laser signal increases but its FWHM decreases with the laser fluence. Angular distribution of the peak amplitude can be fitted with cosn θ(n=4) while the detection angle has no obvious influence on the FWHM. In addition, FWHM and peak amplitude of plasma signal increase with the laser fluence. However, starting time and peak arrival time of plasma signal reduce with the laser fluence. The time interval between plasma starting and scattered laser pulse termination is proposed as a quantitative parameter to characterize laser plasma interaction. Threshold fluence for the interaction is estimated to be 3.5 J/cm2. For laser fluence above 12.6 J/cm2, the plasma and scattered laser pulse distributions tend to saturate.

Pulsed Excimer Laser Processing for Cost-Effective Solar Cells

NASA Technical Reports Server (NTRS)

Wong, D.

1985-01-01

Residual lattice damage by 5 keV ion implantation and surface flaws induced by wafer cleaning are proven to affect the V sub oc more adversely for laser annealed cells than conventional thermal diffusion. However, an alternative, molecular implantation of molecular species holds potential. The first experimental results are encouraging. The lack of a commercially available mass analyzed implantation with low energy, high fluence ions is constraining.

Modeling topology formation during laser ablation

NASA Astrophysics Data System (ADS)

Hodapp, T. W.; Fleming, P. R.

1998-07-01

Micromachining high aspect-ratio structures can be accomplished through ablation of surfaces with high-powered lasers. Industrial manufacturers now use these methods to form complex and regular surfaces at the 10-1000 μm feature size range. Despite its increasingly wide acceptance on the manufacturing floor, the underlying photochemistry of the ablation mechanism, and hence the dynamics of the machining process, is still a question of considerable debate. We have constructed a computer model to investigate and predict the topological formation of ablated structures. Qualitative as well as quantitative agreement with excimer-laser machined polyimide substrates has been demonstrated. This model provides insights into the drilling process for high-aspect-ratio holes.

The excimer lamp induces cutaneous nerve degeneration and reduces scratching in a dry-skin mouse model.

PubMed

Kamo, Atsuko; Tominaga, Mitsutoshi; Kamata, Yayoi; Kaneda, Kazuyuki; Ko, Kyi C; Matsuda, Hironori; Kimura, Utako; Ogawa, Hideoki; Takamori, Kenji

2014-12-01

Epidermal hyperinnervation, which is thought to underlie intractable pruritus, has been observed in patients with atopic dermatitis (AD). The epidermal expression of axonal guidance molecules has been reported to regulate epidermal hyperinnervation. Previously, we showed that the excimer lamp has antihyperinnervative effects in nonpruritic dry-skin model mice, although epidermal expression of axonal guidance molecules was unchanged. Therefore, we investigated the antipruritic effects of excimer lamp irradiation and its mechanism of action. A single irradiation of AD model mice significantly inhibited itch-related behavior 1 day later, following improvement in the dermatitis score. In addition, irradiation of nerve fibers formed by cultured dorsal root ganglion neurons increased bleb formation and decreased nerve fiber expression of nicotinamide mononucleotide adenylyl transferase 2, suggesting degenerative changes in these fibers. We also analyzed whether attaching a cutoff excimer filter (COF) to the lamp, thus decreasing cytotoxic wavelengths, altered hyperinnervation and the production of cyclobutane pyrimidine dimer (CPD), a DNA damage marker, in dry-skin model mice. Irradiation with COF decreased CPD production in keratinocytes, as well as having an antihyperinnervative effect, indicating that the antipruritic effects of excimer lamp irradiation with COF are due to induction of epidermal nerve degeneration and reduced DNA damage.

Boron nitride microfibers grown by plasma-assisted laser chemical vapor deposition without a metal catalyst

NASA Astrophysics Data System (ADS)

Komatsu, Shojiro; Kazami, Daisuke; Tanaka, Hironori; Shimizu, Yoshiki; Moriyoshi, Yusuke; Shiratani, Masaharu; Okada, Katsuyuki

2006-04-01

Boron nitride fibers were found to grow on polycrystalline nickel and Si (100) substrates by plasma-assisted laser chemical vapor deposition from B2H6+NH3 using an excimer laser at 193nm. Their diameter was typically a few hundreds of nanometers, while the length was a few tens of micrometers. They were stoichiometric or boron-rich BN in chemical composition. When the substrate was rotated during deposition, spiral fibers were found to grow. We conclude that they grew with the help of laser light by other than the vapor - liquid - solid mechanism.

IV INTERNATIONAL CONFERENCE ON ATOM AND MOLECULAR PULSED LASERS (AMPL'99): Surface oxide removal by a XeCl laser for decontamination

NASA Astrophysics Data System (ADS)

Sentis, M. L.; Delaporte, Ph; Marine, W.; Uteza, O.

2000-06-01

The laser ablation performed with an automated excimer XeCl laser unit is used for large surface cleaning. The study focuses on metal surfaces that are oxidised and are representative of contaminated surfaces with radionuclides in a context of nuclear power plant maintenance. The unit contains an XeCl laser, the beam delivery system, the particle collection cell, and the system for real-time control of cleaning processes. The interaction of laser radiation with a surface is considered, in particular, the surface damage caused by cleaning radiation. The beam delivery system consists of an optical fibre bundle of 5 m long and allows delivering 150 W at 308 nm for laser surface cleaning. The cleaning process is controlled by analysing in real time the plasma electric field evolution. The system permits the cleaning of 2 to 6 m2 h-1 of oxides with only slight substrate modifications.

Femtosecond laser refractive surgery: small-incision lenticule extraction vs. femtosecond laser-assisted LASIK.

PubMed

Lee, Jimmy K; Chuck, Roy S; Park, Choul Yong

2015-07-01

Small-incision lenticule extraction (SMILE) is a novel technique devised to correct refractive errors. SMILE circumvents excimer laser photoablation of cornea, as the stromal lenticule cut by femtosecond laser is removed manually. Smaller incisions and preservation of anterior corneal biomechanical strength have been suggested as some of the advantages of SMILE over femtosecond laser-assisted LASIK (FS-LASIK). In this review, we compared previous published results of SMILE and FS-LASIK. The advantage, efficacy and safety of SMILE are compared with FS-LASIK. SMILE achieved similar efficacy, predictability and safety as FS-LASIK. Greater preservations of corneal biomechanical strength and corneal nerves were observed in SMILE when compared with LASIK or PRK. Additionally, the incidence of postoperative dry eye syndrome was found to be less problematic in SMILE than in FS-LASIK. SMILE is a promising new surgery for refractive error correction. Prospective and retrospective studies of SMILE have shown that results of SMILE are similar to FS-LASIK. With advances in femtosecond laser technology, SMILE may gain greater acceptance in the future.

Crystallization to polycrystalline silicon thin film and simultaneous inactivation of electrical defects by underwater laser annealing

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

Machida, Emi; Research Fellowships of the Japan Society for the Promotion of Science, Japan Society for the Promotion of Science, 1-8 Chiyoda, Tokyo 102-8472; Horita, Masahiro

2012-12-17

We propose a low-temperature laser annealing method of a underwater laser annealing (WLA) for polycrystalline silicon (poly-Si) films. We performed crystallization to poly-Si films by laser irradiation in flowing deionized-water where KrF excimer laser was used for annealing. We demonstrated that the maximum value of maximum grain size of WLA samples was 1.5 {mu}m, and that of the average grain size was 2.8 times larger than that of conventional laser annealing in air (LA) samples. Moreover, WLA forms poly-Si films which show lower conductivity and larger carrier life time attributed to fewer electrical defects as compared to LA poly-Si films.

Laser-induced tissue autofluorescence versus exogenous chemical probe induced fluorescence as an arterial layer detection method: a comparative study

NASA Astrophysics Data System (ADS)

Papazoglou, Theodore G.; Arakawa, Koh; Grundfest, Warren S.; Papaioannou, Thanassis; Fishbein, Michael C.; Litvack, Frank

1990-07-01

The goal ofihis sludy was o develop a reliable laser inducedfluorescence specira analysis system using the 308nm Excimer Laser as an ablaiion andfluorescence inducing source. During our analysis we also aflempled lo determine whether exogenous chloroeiracycline hydrocloride (CTC) increased the discrimination capacity of the LIFS system. We then assessed the ability of CTC to improve the detection of the boundary between atheroma and normal media.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: On the possibility of pumping Xe2* lasers and VUV lamps in the afterglow of a background-electron multiplication wave

NASA Astrophysics Data System (ADS)

Boichenko, Aleksandr M.; Yakovlenko, Sergei I.

2006-12-01

It was shown earlier that the ionisation propagation in a gas at about the atmospheric pressure may proceed due to the multiplication of the existing electrons with a low background density rather than the transfer of electrons or photons. We consider the feasibility of using the plasma produced in the afterglow of this background-electron multiplication wave for pumping plasma lasers (in particular, Xe2* xenon excimer lasers) as well as excilamps. Simulations show that it is possible to achieve the laser effect at λapprox172 nm as well as to substantially improve the peak specific power of the spontaneous radiation of xenon lamps.

Studies of discharge mechanisms in high pressure gases-applications to high efficiency high power lasers. Ph.D. Thesis. Semiannual Progress Report

NASA Technical Reports Server (NTRS)

Cherrington, B. E.; Verdeyen, J. T.; Eden, J. G.; Leslie, S. G.

1975-01-01

By measuring the absorption and emission cantinua of various states in the cesium/xenon molecule, the collisional rates critical in populating the alkali/rare gas excimer levels have been estimated. Cs atomic states that are weakly optically connected to ground have been shown to form excimer levels that are attractive as potential dissociation lasers. In particular, the (Cs/7 2S/Xe) excited molecule appears promising as a source of high energy laser radiation due to its large dissociation energy, stimulated emission cross section, and small population inversion densities. Monitoring of the optically pumped Cs2 molecular absorption profile in the presence of xenon shows a drastic change with increasing xenon pressure for the Cs2C band. Dominant absorption at large xenon densities is centered around approximately 6380 A as opposed to 6300 A for lower perturber pressure.

Singlet Fission via an Excimer-Like Intermediate in 3,6-Bis(thiophen-2-yl)diketopyrrolopyrrole Derivatives.

PubMed

Mauck, Catherine M; Hartnett, Patrick E; Margulies, Eric A; Ma, Lin; Miller, Claire E; Schatz, George C; Marks, Tobin J; Wasielewski, Michael R

2016-09-14

Singlet fission (SF) in polycrystalline thin films of four 3,6-bis(thiophen-2-yl)diketopyrrolopyrrole (TDPP) chromophores with methyl (Me), n-hexyl (C6), triethylene glycol (TEG), and 2-ethylhexyl (EH) substituents at the 2,5-positions is found to involve an intermediate excimer-like state. The four different substituents yield four distinct intermolecular packing geometries, resulting in variable intermolecular charge transfer (CT) interactions in the solid. SF from the excimer state of Me, C6, TEG, and EH takes place in τSF = 22, 336, 195, and 1200 ps, respectively, to give triplet yields of 200%, 110%, 110%, and 70%, respectively. The transient spectra of the excimer-like state and its energetic proximity to the lowest excited singlet state in these derivatives suggests that this state may be the multiexciton (1)(T1T1) state that precedes formation of the uncorrelated triplet excitons. The excimer decay rates correlate well with the SF efficiencies and the degree of intermolecular donor-acceptor interactions resulting from π-stacking of the thiophene donor of one molecule with the DPP core acceptor in another molecule as observed in the crystal structures. Such interactions are found to also increase with the SF coupling energies, as calculated for each derivative. These structural and spectroscopic studies afford a better understanding of the electronic interactions that enhance SF in chromophores having strong intra- and intermolecular CT character.

Prospects for Practical Applications of a Discharge Chemical HF Laser as a Coherent Source for IR Holography

NASA Astrophysics Data System (ADS)

Fedotov, O. G.; Fomin, V. M.

2018-02-01

Preliminary experimental results on recording of phase and amplitude holograms using the radiation of electric-discharge HF lasers are presented, and prospects for applications of such lasers in diagnostics of various objects are discussed. It is shown that lasers with homogeneous working medium may generate coherent radiation with a coherence length of greater than 6 m in the absence of mode selection. Methods for control of spatial distribution of electron concentration in excimer and discharge chemical HF (DF) lasers and distributions of the main combustible components are considered. Deposition of holographic identification marks on artworks is studied.

Crystallographic texture in pulsed laser deposited hydroxyapatite bioceramic coatings

PubMed Central

Kim, Hyunbin; Camata, Renato P.; Lee, Sukbin; Rohrer, Gregory S.; Rollett, Anthony D.; Vohra, Yogesh K.

2008-01-01

The orientation texture of pulsed laser deposited hydroxyapatite coatings was studied by X-ray diffraction techniques. Increasing the laser energy density of the KrF excimer laser used in the deposition process from 5 to 7 J/cm2 increases the tendency for the c-axes of the hydroxyapatite grains to be aligned perpendicular to the substrate. This preferred orientation is most pronounced when the incidence direction of the plume is normal to the substrate. Orientation texture of the hydroxyapatite grains in the coatings is associated with the highly directional and energetic nature of the ablation plume. Anisotropic stresses, transport of hydroxyl groups and dehydroxylation effects during deposition all seem to play important roles in the texture development. PMID:18563207

Distinguished Lectureship Award on the Applications of Physics: Illuminating My Career - From Flash Gordon to Laser Surgery

NASA Astrophysics Data System (ADS)

Wynne, James

2015-03-01

As a child, I was fascinated by television programs about Flash Gordon. His partner in conquering the universe was Dr. Alexis Zarkov, a physicist, who had invented, among other things, a death ray gun. My personal ``death ray'' was a magnifying glass, focusing sunlight on unsuspecting insects, like crawling ants. I also practiced sneaking up on resting, flying, stinging insects and burning their wings before they could take off and attack me. So I understood something about the power of sunlight. In my senior year of high school, I had a fabulous physics teacher, Lewis E. Love, and I knew after one week that I wanted to be a physicist, not a medical doctor, which is the career my parents wanted me to pursue. It turns out that the first laser functioned on May 16, 1960, just one month before I graduated from high school, and it was inevitable that I would pursue a career working with lasers. My first job as a physicist, during the summer of 1963, was working with lasers at TRG, Inc. a small company whose guru was Gordon Gould, now recognized as the inventor of the laser. After three summers at TRG, I spent three years working on nonlinear optics for my PhD thesis, under the guidance of Prof. Nicolaas Bloembergen, who later won the Nobel Prize in Physics for codifying nonlinear optics. Following completion of my PhD research in 1969, I joined IBM Research, where I have worked ever since. Upon joining the Quantum Electronics group in the Physical Sciences Dept. of the T.J. Watson Research Center, my management told me to ``do something great'' with lasers. After working on atomic spectroscopy with dye lasers through the 1970s, I had the inspiration to acquire an excimer laser for the Laser Physics and Chemistry group. Using this laser, my colleagues and I discovered excimer laser surgery, capable of removing human and animal tissue with great precision, while leaving the underlying and adjacent tissue free of collateral damage. This discovery laid the foundation for

High-temperature-resistant distributed Bragg reflector fiber laser written in Er/Yb co-doped fiber.

PubMed

Guan, Bai-Ou; Zhang, Yang; Wang, Hong-Jun; Chen, Da; Tam, Hwa-Yaw

2008-03-03

We present a high-temperature-resistant distributed Bragg reflector fiber laser photowritten in Er/Yb codoped phosphosilicate fiber that is capable of long-term operation at 500 degrees C. Highly saturated Bragg gratings are directly inscribed into the Er/Yb fiber without hydrogen loading by using a 193 nm excimer laser and phase mask method. After annealing at elevated temperature, the remained gratings are strong enough for laser oscillation. The laser operates in robust single mode with output power more than 1 dBm and signal-to-noise ratio better than 70 dB over the entire temperature range from room temperature to 500 degrees C.

Comparison of retina damage thresholds simulating the femtosecond-laser in situ keratomileusis (fs-LASIK) process with two laser systems in the CW- and fs-regime

NASA Astrophysics Data System (ADS)

Sander, M.; Minet, O.; Zabarylo, U.; Müller, M.; Tetz, M. R.

2012-04-01

The femtosecond-laser in situ keratomileusis procedure affords the opportunity to correct ametropia by cutting transparent corneal tissue with ultra-short laser pulses. Thereby the tissue cut is generated by a laser-induced optical breakdown in the cornea with ultra-short laser pulses in the near-infrared range. Compared to standard procedures such as photorefractive keratectomy and laser in-situ keratomileusis with the excimer laser, where the risk potential for the eye is low due to the complete absorption of ultraviolet irradiation from corneal tissue, only a certain amount of the pulse energy is deposited in the cornea during the fs-LASIK process. The remaining energy propagates through the eye and interacts with the retina and the strong absorbing tissue layers behind. The objective of the presented study was to determine and compare the retina damage thresholds during the fs-LASIK process simulated with two various laser systems in the CW- and fs-regime.

Laser-induced surface-plasmon desorption of dye molecules from aluminum films

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

Lee, I.; Callcott, T.A.; Arakawa, E.T.

1992-03-01

Rhodamine 8 molecules were desorbed without fragmentation from the surface of an Al film by surface-plasmon-induced desorption. Surface plasmons were excited In the Al film by the second harmonic of a Nd:YAG laser in an attenuated-to-tal-reflection (ATR) geometry. The desorbed neutrals were Ionized by a XeCl excimer laser and detected by a time-of-flight mass spectrometer. The desorption yields of both Al and rhodamine B showed a dependence with incidence angle which peaked at the plasmon resonance angle. The thresholds for desorption of Al and rhodamine B occur at the same laser fluence. Two models are proposed to explain these observations.more » 31 refs., 4 figs.« less

Morphological studies of laser-induced photoacoustic damage

NASA Astrophysics Data System (ADS)

Flotte, Thomas J.; Yashima, Yutaka; Watanabe, Shinichi; McAuliffe, Daniel J., Sr.; Jacques, Steven L.

1990-06-01

Argon-fluoride excimer laser ablation of stratum comeum causes deeper tissue damage than expected for thermal or photochemical mechanisms, suggesting thatphotoacoustic waves have arole in tissue damage. Laserirradiation (193 nm, 14 ns pulses, 1-2 Hz) attworadiantexposures, 60 and 160 mJ/cm2perpulse was usedto ablate the stratumcomeumofskin. Light and electron microscopy ofimmediate biopsies demonstrated damage to fibroblasts as deep as 88 and 220 jun, respectively, below the ablation site. Ablation throughwaterwas usedtoinertially confine the ablation zone. Partial ablationofs.c. through airproducedno damage, whereas partial ablation through water damaged skin to amean depth of 1 14.5 8.8( Full thickness ablation of s.c. through air and water produced damage zones measuring 192.2 16.2 and 293.0 71.6 rim, respectively (p <0.05). The increased depth ofdamage in the presence ofinertial confinementprovided by the layer of water strongly supports a photoacoustic mechanism ofdamage. The depths ofdamage for thelarge spot, line, and small spots were 43 1 164 urn, 269 96xni, andno damage. The spot size dependence ofthedepthofdamage is consistentwiththe geometric attenuation one would expect to be present from a pressure wave related phenomena. Sequential biopsies were taken over a 7 day period for light and transmission electron microscopy. At 24 hours, there was necrosis of the epidermis and papillary dermis subjacent to the ablation site, with neutrophils surrounding and demarcating the affected area. The necrotic zone sloughedby48 hours. Thereepithelializationwas completeby7 days. The sequenceofrepairis similartoknife wound healing which we have previously studied, and is analogous to other wound healing processes. We have used an experimental model of ArF excimer laser ablation of stratum corneum to investigate laser-induced photoacoustic damage. The evidence for the injury being due to pressure transients is indirectbutcompelling. Whether these pressuretransients are

Tunable Solid State Lasers Based on Molecular Ions

DTIC Science & Technology

1992-01-01

02215 July 15, 1988 to September 30, 1991. N’ o ~...... 1 C~~ I -- ,t,’**, "> I : tt : o0.’. * On leave from Institute of Physics, Copernicus ...Physics, N. Copernicus University, ments provided the ratio (Jo- 81)/10, where l0 is the 87-100 Toruo, Poland. probe beam intensity after passing through...luminescence, following t 30 ns long excitation pulse (308 nm On leave from Institute of Physics, N. Copernicus University, line, excimer laser

High-speed photography of plasma during excimer laser-tissue interaction.

PubMed

Murray, Andrea K; Dickinson, Mark R

2004-08-07

During high fluence laser-tissue interaction, ablation of tissue occurs, debris is removed from the ablation site and is then ejected at high velocity. This debris may be observed as a combination of luminous plasma and non-luminous plume, both of which have the potential to shield the ablation site. This study examined the role of ablation debris in shielding the tissue and determined its effects on the ablation rate over a range of laser pulse energies, pulse repetition rates and pulse numbers for dentine; the velocity differences between hard and soft tissues were also examined. High-speed photography was carried out at up to 1 x 10(8) frames per second. A maximum velocity of 2.58 +/- 0.52 x 10(4) m s(-1) was recorded for dentine debris within the first 10 ns following ejection. The maximum duration of tissue shielding due to a single pulse, determined by attenuation of a probe beam, was found to be approximately 7 ms, approximately 80 micros of which was due to luminous plasma and the remainder due to the non-luminous plume.

Polyfluorophore Excimers and Exciplexes as FRET Donors in DNA

PubMed Central

Teo, Yin Nah; Kool, Eric T.

2009-01-01

We describe studies aimed at testing whether oligomeric exciplex- and excimer fluorophores conjugated to DNA have the potential to act as donors for energy transfer by the Förster mechanism. Oligodeoxyfluorosides (ODFs) are composed of stacked, electronically interacting fluorophores replacing the bases on a DNA scaffold. The monomer chromophores in the twenty tetramer-length ODFs studied here include pyrene (Y), benzopyrene (B), perylene (E), dimethylaminostilbene (D), and a nonfluorescent spacer (S); these are conjugated in varied combinations at the 3’ end of a 14mer DNA probe sequence. In the absence of an acceptor chromophore, many of the ODF-DNAs show broad, unstructured long-wavelength emission peaks characteristic of excimer and exciplex excited states, similar to what has been observed for unconjugated ODFs. Although such delocalized excited states have been widely studied, we know of no prior report of their use in FRET. We tested the ability of the twenty ODFs to donate energy to Cy5 and TAMRA dyes conjugated to a complementary strand of DNA, with these acceptors oriented either at the near or far end of the ODF-conjugated probes. Results showed that a number of the ODF fluorophores exhibited relatively efficient energy transfer characteristic of the Förster mechanism, as judged by drops in donor emission quantum yield and fluorescence lifetime, accompanied by increases in intensity of acceptor emission bands. Excimer/exciplex bands in the donors were selectively quenched while shorter-wavelength monomer emission stayed relatively constant, consistent with the notion that the delocalized excited states, rather than individual fluorophores, are the donors. Interestingly, only specific sequences of ODFs were able to act as donors, while others did not, even though their emission wavelengths were similar. The new FRET donors possess large Stokes shifts, which can be beneficial for multiple applications. In addition, all ODFs can be excited at a single

Laser-induced fluorescence detection strategies for sodium atoms and compounds in high-pressure combustors

NASA Technical Reports Server (NTRS)

Weiland, Karen J. R.; Wise, Michael L.; Smith, Gregory P.

1993-01-01

A variety of laser-induced fluorescence schemes were examined experimentally in atmospheric pressure flames to determine their use for sodium atom and salt detection in high-pressure, optically thick environments. Collisional energy transfer plays a large role in fluorescence detection. Optimum sensitivity, at the parts in 10 exp 9 level for a single laser pulse, was obtained with the excitation of the 4p-3s transition at 330 nm and the detection of the 3d-3p fluorescence at 818 nm. Fluorescence loss processes, such as ionization and amplified spontaneous emission, were examined. A new laser-induced atomization/laser-induced fluorescence detection technique was demonstrated for NaOH and NaCl. A 248-nm excimer laser photodissociates the salt molecules present in the seeded flames prior to atom detection by laser-induced fluorescence.

An experimental evaluation of precision laser cutting of dental hard tissues and materials.

PubMed

Cox, C J; Patel, B C; Pearson, G J

1993-06-01

This paper examines the use of excimer laser radiation in the controlled removal of tooth tissue and three plastic restorative materials. Freshly extracted human third molar teeth were filled with three restorative materials and sectioned longitudinally through the restoratives. The cut surfaces of the materials and surrounding enamel and dentine were exposed to three laser energy densities and the dimensions and topographical details of the irradiated sites assessed using optical and scanning electron microscopy. The results showed that the radiation produced lesions of uniformly reproducible size and shape.

Laser synthesized super-hydrophobic conducting carbon with broccoli-type morphology as a counter-electrode for dye sensitized solar cells

NASA Astrophysics Data System (ADS)

Gokhale, Rohan; Agarkar, Shruti; Debgupta, Joyashish; Shinde, Deodatta; Lefez, Benoit; Banerjee, Abhik; Jog, Jyoti; More, Mahendra; Hannoyer, Beatrice; Ogale, Satishchandra

2012-10-01

A laser photochemical process is introduced to realize superhydrophobic conducting carbon coatings with broccoli-type hierarchical morphology for use as a metal-free counter electrode in a dye sensitized solar cell. The process involves pulsed excimer laser irradiation of a thin layer of liquid haloaromatic organic solvent o-dichlorobenzene (DCB). The coating reflects a carbon nanoparticle-self assembled and process-controlled morphology that yields solar to electric power conversion efficiency of 5.1% as opposed to 6.2% obtained with the conventional Pt-based electrode.A laser photochemical process is introduced to realize superhydrophobic conducting carbon coatings with broccoli-type hierarchical morphology for use as a metal-free counter electrode in a dye sensitized solar cell. The process involves pulsed excimer laser irradiation of a thin layer of liquid haloaromatic organic solvent o-dichlorobenzene (DCB). The coating reflects a carbon nanoparticle-self assembled and process-controlled morphology that yields solar to electric power conversion efficiency of 5.1% as opposed to 6.2% obtained with the conventional Pt-based electrode. Electronic supplementary information (ESI) available: Materials and equipment details, solar cell fabrication protocol, electrolyte spreading time measurement details, XPS spectra, electronic study, film adhesion test detailed analysis and field emission results. See DOI: 10.1039/c2nr32082g

[Advantages and disadvantages of femtosecond laser assisted LASIK and SMILE].

PubMed

Zhang, F J; Sun, M S

2018-01-11

With the development of excimer laser and femtosecond laser equipment, application of diversified and customized surgical decision in modern corneal refractive surgery has been an inevitable trend. However, how to make a personalized decision with an accurate surgical design to achieve better visual quality becomes the main focus in clinical applications. Small-incision lenticule extraction (SMILE) and femtosecond assisted laser in situ keratomileusis (FS-LASIK) have been commonly acknowledged as the mainstream of corneal refractive surgery for ametropia correction nowadays. Both methods have been verified by clinical practice for many years. This article compares and elaborates the different characteristics with advantages and disadvantages of the two methods so as to provide some reasonable treatment options for refractive surgery. (Chin J Ophthalmol, 2018, 54: 7-10) .

Carbazole-based BODIPYs with ethynyl substituents at the boron center: solid-state excimer fluorescence in the VIS/NIR region.

PubMed

Maeda, Chihiro; Nagahata, Keiji; Ema, Tadashi

2017-09-26

Carbazole-based BODIPYs 1-6 with several different substituents at the boron atom site were synthesized. These dyes fluoresced in the solid state, and 3a with phenylethynyl groups exhibited a red-shifted and broad fluorescence spectrum, which suggested an excimer emission. Its derivatives 3b-n were synthesized, and the relationship between the solid-state emission and crystal packing was investigated. The X-ray crystal structures revealed cofacial dimers that might form excimers. From the structural optimization results, we found that the introduction of mesityl groups hindered intermolecular access and led to reduced interactions between the dimers. In addition, the red-shifted excimer fluorescence suppressed self-absorption, and dyes with ethynyl groups showed solid-state fluorescence in the vis/NIR region.

Modeling of solid-state and excimer laser processes for 3D micromachining

NASA Astrophysics Data System (ADS)

Holmes, Andrew S.; Onischenko, Alexander I.; George, David S.; Pedder, James E.

2005-04-01

An efficient simulation method has recently been developed for multi-pulse ablation processes. This is based on pulse-by-pulse propagation of the machined surface according to one of several phenomenological models for the laser-material interaction. The technique allows quantitative predictions to be made about the surface shapes of complex machined parts, given only a minimal set of input data for parameter calibration. In the case of direct-write machining of polymers or glasses with ns-duration pulses, this data set can typically be limited to the surface profiles of a small number of standard test patterns. The use of phenomenological models for the laser-material interaction, calibrated by experimental feedback, allows fast simulation, and can achieve a high degree of accuracy for certain combinations of material, laser and geometry. In this paper, the capabilities and limitations of the approach are discussed, and recent results are presented for structures machined in SU8 photoresist.

A Review of Luminescent Anionic Nano System: d10 Metallocyanide Excimers and Exciplexes in Alkali Halide Hosts

PubMed Central

Li, Xiaobo; Patterson, Howard H.

2013-01-01

Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in solution and in doped hosts. A series of spectroscopic methods (luminescence, UV-reflectance, IR, and Raman) as well as theoretical calculations have confirmed the existence of excimers and exciplexes. This leads to the tunability of these nano systems over a wide wavelength interval. The population of these nanoclusters varies with temperature and external laser irradiation, which explains the thermochromism and optical memory. DFT calculations indicate an MLCT transition for each nanocluster and the emission energy decreases with increasing cluster size. This is in agreement with the relatively long life-time for the emission peaks and the multiple emission peaks dependence upon cluster concentration. PMID:28811397

Selective removal of cholesterol ester in atherosclerotic plaque using nanosecond pulsed laser at 5.75 μm

NASA Astrophysics Data System (ADS)

Ishii, K.; Tsukimoto, H.; Hazama, H.; Awazu, K.

2008-02-01

Laser angioplasty, for example XeCl excimer laser angioplasty, has gained more attention in addition to conventional methods of surgical and interventional treatment of atherosclerotic diseases such as bypass operation and balloon dilatation. Low degrees of thermal damage after ablation of atherosclerotic lesions have been achieved by XeCl excimer laser at 308 nm. However, in most cases, laser ablation is not selective and normal arterial wall is also damaged. To avoid complications such as severe dissections or perforation of the arterial wall in an angioplasty, a laser light source with high ablation efficiency but low arterial wall injury is desirable. At atherosclerotic lesions, cholesterol accumulates on the tunica intima by establishing an ester bond with fatty acids such as oleic acid, and thus cholesterol ester is the main component of atherosclerotic plaques. Mid-infrared pulsed laser at 5.75 μm is selectively well absorbed in C=O stretching vibration mode of ester bonds. The purpose of this study is to determine the effectiveness of nanosecond pulsed laser at 5.75 μm irradiation of cholesterol ester in atherosclerotic plaques. In this study, we used a mid-infrared tunable solid-state laser which is operated by difference frequency generation method, with a wavelength of 5.75 μm, a pulse width of 5 nsec and a pulse duration of 10 Hz. It was confirmed that non-invasive interaction to normal thoracic aortas could be induce by the parameters, the wavelength of 5.75 μm, the average power densities of 35 W/cm2 and the irradiation time under 10 sec. This study shows that nanosecond pulsed laser irradiations at 5.75 μm provide an alternative laser light source as an effectively cutting, less traumatic tool for removal of atherosclerotic plaque.

[Indomethacin (indocollyre) versus diclofenac (voltarene) for the control of pain following excimer photoablation].

PubMed

Cochener, B; Kling, F; Savary-Le Floch, G; Colin, J

2000-06-01

To compare effect of two topical non steroidal anti-inflammatory (NSAI) drugs: Indomethacin (Indocollyre)0.1 %, Chauvin Inc.) and Diclofenac (Voltaren 0.1%, Cibavision) on postoperative pain and epithelial regrowth following surface excimer photoablation. Eighty-six excimer operated patients, were divided in two similar groups depending on the NSAI instilled postoperatively and for 3 days (4 drops daily). No patient was informed of any other available drug. Pain intensity was quantified between 1 and 10 according to an analog scale (reported from 1 to 10 hours, then 4 times a day during 7 days). Complementary medications and functional symptoms were also notified. Biomicroscopic evaluation using fluorescein test was performed to assess reepithelialization. In term of pain, no significative difference was observed between the two groups concerning intensity, associated medications, or numbers of days of discomfort. Controversially, retreated eyes might induce more pain than initial treatments. No delay in epithelial regrowth was noted and the difference between the two groups in functional complaints was no statistically significant. Pain appears to be not related to ablation depth. DISCUSSION- CONCLUSION: Our results are correlated to literature reported data. Introduction of NSAI constitutes a real advent in the care of excimer postoperative pain. Effect of indomethacin seems comparable to diclofenac effect, but might be of interest because of no anesthetic property that might guarantee of no delay in wound healing response.

Cluster formation in laser-induced ablation and evaporation of solids observed by laser ionization time-of-flight mass spectrometry and scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Tench, R. J.; Balooch, M.; Bernardez, L.; Allen, Mike J.; Siekhaus, W. J.; Olander, D. R.; Wang, W.

1990-04-01

Laser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency-quadrupled Nd-YAG laser (266 nm) focused onto spots of 4 to 100 microns diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO 2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material. Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10(exp -5) Torr by 1 to 3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10(exp -8) Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with angstrom resolution. Clusters up to 30 A in diameter were observed.

Laser-Ablation (U-Th)/He Geochronology

NASA Astrophysics Data System (ADS)

Hodges, K.; Boyce, J.

2003-12-01

Over the past decade, ultraviolet laser microprobes have revolutionized the field of 40Ar/39Ar geochronology. They provide unprecedented information about Ar isotopic zoning in natural crystals, permit high-resolution characterization of Ar diffusion profiles produced during laboratory experiments, and enable targeted dating of multiple generations of minerals in thin section. We have modified the analytical protocols used for 40Ar/39Ar laser microanalysis for use in (U-Th)/He geochronologic studies. Part of the success of the 40Ar/39Ar laser microprobe stems from fact that measurements of Ar isotopic ratios alone are sufficient for the calculation of a date. In contrast, the (U-Th)/He method requires separate analysis of U+Th and 4He. Our method employs two separate laser microprobes for this process. A target mineral grain is placed in an ultrahigh vacuum chamber fitted with a window of appropriate composition to transmit ultraviolet radiation. A focused ArF (193 nm) excimer laser is used to ablate tapered cylindrical pits on the surface of the target. The liberated material is scrubbed with a series of getters in a fashion similar to that used for 40Ar/39Ar geochronology, and the 4He abundance is determined using a quadrupole mass spectrometer with well-calibrated sensitivity. A key requirement for calculation of the 4He abundance in the target is a precise knowledge of the volume of the ablation pit. This is the principal reason why we employ the ArF excimer for 4He analysis rather than a less-expensive frequency-multiplied Nd-YAG laser; the excimer creates tapered cylindrical pits with extremely reproducible and easily characterized geometry. After 4He analysis, U and Th are measured on the same sample surface using the more familiar technique of laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Our early experiments have been done using a frequency-quintupled Nd-YAG microprobe (213nm), While the need to analyze U+Th and He in separate

Hydroxyapatite thin films grown by pulsed laser deposition and matrix assisted pulsed laser evaporation: Comparative study

NASA Astrophysics Data System (ADS)

Popescu-Pelin, G.; Sima, F.; Sima, L. E.; Mihailescu, C. N.; Luculescu, C.; Iordache, I.; Socol, M.; Socol, G.; Mihailescu, I. N.

2017-10-01

Pulsed Laser Deposition (PLD) and Matrix Assisted Pulsed Laser Evaporation (MAPLE) techniques were applied for growing hydroxyapatite (HA) thin films on titanium substrates. All experiments were conducted in a reaction chamber using a KrF* excimer laser source (λ = 248 nm, τFWHM ≈ 25 ns). Half of the samples were post-deposition thermally treated at 500 °C in a flux of water vapours in order to restore crystallinity and improve adherence. Coating surface morphologies and topographies specific to the deposition method were evidenced by scanning electron, atomic force microscopy investigations and profilometry. They were shown to depend on deposition technique and also on the post-deposition treatment. Crystalline structure of the coatings evaluated by X-ray diffraction was improved after thermal treatment. Biocompatibility of coatings, cellular adhesion, proliferation and differentiation tests were conducted using human mesenchymal stem cells (MSCs). Results showed that annealed MAPLE deposited HA coatings were supporting MSCs proliferation, while annealed PLD obtained films were stimulating osteogenic differentiation.

Holmium:YAG laser coronary angioplasty: quantitative angiography and clinical results in a large experience of a single medical center

NASA Astrophysics Data System (ADS)

Topaz, On; Luxenberg, Michael; Schumacher, Audrey

1994-07-01

Clinical experience with the mid IR holmium:YAG laser in a single medical center (St. Paul Ramsey Medical Center, University of Minnesota Medical School, St. Paul, MN) includes 112 patients who underwent holmium laser coronary angioplasty. Utilizing a unique lasing technique; `pulse and retreat,' we applied this laser to thrombotic and nonthrombotic lesions in patients presenting with unstable angina, stable angina, and acute myocardial infarction. A very high clinical success and very low complication rates were achieved. Holmium:YAG laser is effective and safe therapy for patients with symptomatic coronary artery disease. Unlike excimer lasers, the clinical success, efficacy and safety of holmium laser angioplasty is not compromised when thrombus is present.

Bulk damage and absorption in fused silica due to high-power laser applications

NASA Astrophysics Data System (ADS)

Nürnberg, F.; Kühn, B.; Langner, A.; Altwein, M.; Schötz, G.; Takke, R.; Thomas, S.; Vydra, J.

2015-11-01

Laser fusion projects are heading for IR optics with high broadband transmission, high shock and temperature resistance, long laser durability, and best purity. For this application, fused silica is an excellent choice. The energy density threshold on IR laser optics is mainly influenced by the purity and homogeneity of the fused silica. The absorption behavior regarding the hydroxyl content was studied for various synthetic fused silica grades. The main absorption influenced by OH vibrational excitation leads to different IR attenuations for OH-rich and low-OH fused silica. Industrial laser systems aim for the maximum energy extraction possible. Heraeus Quarzglas developed an Yb-doped fused silica fiber to support this growing market. But the performance of laser welding and cutting systems is fundamentally limited by beam quality and stability of focus. Since absorption in the optical components of optical systems has a detrimental effect on the laser focus shift, the beam energy loss and the resulting heating has to be minimized both in the bulk materials and at the coated surfaces. In collaboration with a laser research institute, an optical finisher and end users, photo thermal absorption measurements on coated samples of different fused silica grades were performed to investigate the influence of basic material properties on the absorption level. High purity, synthetic fused silica is as well the material of choice for optical components designed for DUV applications (wavelength range 160 nm - 260 nm). For higher light intensities, e.g. provided by Excimer lasers, UV photons may generate defect centers that effect the optical properties during usage, resulting in an aging of the optical components (UV radiation damage). Powerful Excimer lasers require optical materials that can withstand photon energy close to the band gap and the high intensity of the short pulse length. The UV transmission loss is restricted to the DUV wavelength range below 300 nm and

Photoablation of the cornea with a Q-switched Er:YAG laser

NASA Astrophysics Data System (ADS)

Lubatschowski, Holger; Hetzel, U.; Kermani, Omid; Ziolek, Carsten; Drommer, Wolfgang; Ertmer, Wolfgang

1997-12-01

In this study the ablation characteristics and the wound healing process of rabbit cornea irradiated with a Q- switched Er:YAG laser was evaluated. The laser, emitting at 2.94 micrometers wavelength, has a pulse width of 100 ns. The spot size on the corneal surface was 1 mm in diameter at a fluence of 750 mJ/cm2. The laser beam was applied by a `flying spot' mode, performing refractive ablations of -7 to -8 dpt. As a biological model, the corneas of 9 rabbits were irradiated. The post-treatment follow-up was as long as 39 days. The treated corneas were investigated by light and electron microscopy. The wound healing on rabbit cornea of the Q-switched Er:YAG laser radiation in corneal tissue processing resembles to what is known from ArF- excimer laser application. To shorten the pulse width by means of Q-switching is one major key to the successful application of the Er:YAG laser for PRK.

Surface nanotexturing of tantalum by laser ablation in water

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

Barmina, E V; Simakin, Aleksandr V; Shafeev, Georgii A

2009-01-31

Surface nanotexturing of tantalum by ablation with short laser pulses in water has been studied experimentally using three ablation sources: a neodymium laser with a pulse duration of 350 ps, an excimer laser (248 nm) with a pulse duration of 5 ps and a Ti:sapphire laser with a pulse duration of 180 fs. The morphology of the nanotextured surfaces has been examined using a nanoprofilometer and field emission scanning electron microscope. The results demonstrate that the average size of the hillocks produced on the target surface depends on the laser energy density and is {approx}200 nm at an energy densitymore » approaching the laser-melting threshold of tantalum and a pulse duration of 350 ps. Their surface density reaches 10{sup 6} cm{sup -2}. At a pulse duration of 5 ps, the average hillock size is 60-70 nm. Nanotexturing is accompanied by changes in the absorption spectrum of the tantalum surface in the UV and visible spectral regions. The possible mechanisms of surface nanotexturing and potential applications of this effect are discussed. (nanostructures)« less

Excimer Potential Curves

DTIC Science & Technology

1980-01-01

lasers see A. V. Phelps, JILA Report 110, "Tunable Gas Lasers Using Ground State Dissociation," (1972) and references therein. 2. This requires highly...possibility of using GaXe as a laser if the Ga can be obtained from dissociation of Gal 3 . Consequently the GaKr curves should also be of intrinsic interest... laser transitions The interest in the group IIIB-rare gas systems arises from the possibility of their use as visible laser systems. In order to judge

Experience With Laser Safety In The USA--A Review

NASA Astrophysics Data System (ADS)

Sliney, David H.

1986-10-01

Following several research programs in the 1960's aimed at studying the adverse biological effects of lasers and other optical radiation sources, laser occupational exposure limits were set and general safety standards were developed. Today, the experience from laser accidents and the development of new lasers and new applications have altered the format of the exposure limits and the safety procedures. It is critically important to distinguish between different biological injury mechanisms. The biological effects of ultraviolet radiation upon the skin and eye are additive over a period of at least one workday, and require different safety procedures. The scattered UV irradiance from excimer lasers may be quite hazardous, depending upon wavelength and action spectra. Since laser technology is young, the exposure of an individual in natural sunlight must be studied to evaluate the potential for chronic effects. The safety measures necessary in the use of lasers depend upon a hazard evaluation. The appropriate control measures and alternate means of enclosure, baffling, and operational control measures are presented. Present laser safety standards are explained briefly. Eye protective techniques and eyewear are considered for a variety of sources. The optical properties of enclosure materials are also discussed.

Lasers for the treatment of psoriasis

NASA Astrophysics Data System (ADS)

Piruzian, A.; Korsunskaya, I.; Goldenkova, I.; Hertsen, A.; Sarkisova, M.; Egorenkova, L.

2005-08-01

Psoriasis is a chronic, genetically-determined disease, characterized by an immuno-mediated pathogenesis. Treatment of psoriasis is often complicated and remains a challenge. Along with the many new immunomodulatory approaches, various laser systems have been employed for chronic plaque psoriasis treatment. Recently, it has been demonstrated that the light produced by xenon-chloride excimers (generated by sophisticated devices with peak emission of 308 nm) is effective in the treatment of several psoriasis forms. We treated patients, ranging in age from 35 to 55 years, affected by plaque-type psoriasis vulgaris with monochromatic excimer light (MEL). We used MEL in a complex with basic treatment. Therapy was administered three times a week. At the end of the 3th week of treatment all patients showed an improvement, as evidenced by flattening of plaques, decreased scaling and erythema, and decreased vesicle and pustule formation. Unwanted side effects such as pain, blistering was not observed. Minimal erythema and a hyperpigmentation were noted in some patients. It was concluded that the MEL therapy may be a valuable option for treatment of plaque-type psoriasis vulgaris in shorter time compare with traditional NB UVB, with exposure to lower cumulative doses

Bandgap engineering of InGaAsP/InP laser structure by photo-absorption-induced point defects

NASA Astrophysics Data System (ADS)

Kaleem, Mohammad; Nazir, Sajid; Saqib, Nazar Abbas

2016-03-01

Integration of photonic components on the same photonic wafer permits future optical communication systems to be dense and advanced performance. This enables very fast information handling between photonic active components interconnected through passive optical low loss channels. We demonstrate the UV-Laser based Quantum Well Intermixing (QWI) procedure to engineer the band-gap of compressively strained InGaAsP/InP Quantum Well (QW) laser material. We achieved around 135nm of blue-shift by simply applying excimer laser (λ= 248nm). The under observation laser processed material also exhibits higher photoluminescence (PL) intensity. Encouraging experimental results indicate that this simple technique has the potential to produce photonic integrated devices and circuits.

Soft X-Ray Optics by Pulsed Laser Deposition

NASA Technical Reports Server (NTRS)

Fernandez, Felix E.

1996-01-01

Mo/Si and C/Co multilayers for soft x-ray optics were designed for spectral regions of interest in possible applications. Fabrication was effected by Pulsed Laser Deposition using Nd:YAG (355 nm) or excimer (248 nm) lasers in order to evaluate the suitability of this technique. Results for Mo/Si structures were not considered satisfactory due mainly to problems with particulate production and target surface modification during Si ablation. These problems may be alleviated by a two-wavelength approach, using separate lasers for each target. Results for C/Co multilayers are much more encouraging, since indication of good layering was observed for extremely thin layers. We expect to continue investigating this possibility. In order to compete with traditional PVD techniques, it is necessary to achieve film coverage uniformity over large enough areas. It was shown that this is feasible, and novel means of achieving it were devised.

Lasers in Materials Processing

NASA Astrophysics Data System (ADS)

Kukreja, L. M.; Paul, C. P.; Kumar, Atul; Kaul, R.; Ganesh, P.; Rao, B. T.

Laser is undoubtedly one of the most important inventions of the twentieth century. Today, it is widely deployed for a cornucopia of applications including materials processing. Different lasers such as CO2, Nd:YAG, excimer, copper vapor, diode, fiber lasers, etc., are being used extensively for various materials processing applications like cutting, welding, brazing, surface treatment, peening, and rapid manufacturing by adopting conventional and unconventional routes with unprecedented precision. In view of its potential for providing solution to the emerging problems of the industrial materials processing and manufacturing technologies, a comprehensive program on laser materials processing and allied technologies was initiated at our laboratory. A novel feature-based design and additive manufacturing technologies facilitated the laser rapid manufacturing of complex engineering components with superior performance. This technology is being extended for the fabrication of anatomically shaped prosthetics with internal heterogeneous architectures. Laser peening of spring steels brought significant improvement in its fatigue life. Laser surface treatments resulted in enhanced intergranular corrosion resistance of AISI 316(N) and 304 stainless steel. Parametric dependence of laser welding of dissimilar materials, AISI 316M stainless steel with alloy D9, was established for avoiding cracks under optimum processing conditions. In the domain of laser cutting and piercing, the development of a power ramped pulsed mode with high pulse repetition frequency and low duty cycle scheme could produce highly circular, narrow holes with minimum spattered pierced holes. A review of these experimental and some theoretical studies is presented and discussed in this chapter. These studies have provided deeper insight of fascinating laser-based materials processing application for industrial manufacturing technologies.

Raman shifting of KrF laser radiation for tropospheric ozone measurements

NASA Technical Reports Server (NTRS)

Grant, William B.; Browell, Edward V.; Higdon, Noah S.; Ismail, Syed

1991-01-01

The differential absorption lidar (DIAL) measurement of tropospheric ozone requires use of high average power UV lasers operating at two appropriate DIAL wavelengths. Laboratory experiments have demonstrated that a KrF excimer laser can be used to generate several wavelengths with good energy conversion efficiencies by stimulated Raman shifting using hydrogen (H2) and deuterium (D2). Computer simulations for an airborne lidar have shown that these laser emissions can be used for the less than 5 percent random error, high resolution measuremment of ozone across the troposphere using the DIAL technique. In the region of strong ozone absorption, laser wavelengths of 277.0 and 291.7 nm were generated using H2 and D2, respectively. In addition, a laser wavelength at 302.0 nm was generated using two cells in series, with the first containing D2 and the second containing H2. The energy conversion efficiency for each wavelength was between 14 and 27 percent.

Endothelial cell density after photorefractive keratectomy for moderate myopia using a 213 nm solid-state laser system.

PubMed

Tsiklis, Nikolaos S; Kymionis, George D; Pallikaris, Aristofanis I; Diakonis, Vasilios F; Ginis, Harilaos S; Kounis, George A; Panagopoulou, Sophia I; Pallikaris, Ioannis G

2007-11-01

To evaluate whether photorefractive keratectomy (PRK) for moderate myopia using a solid-state laser with a wavelength of 213 nm alters the corneal endothelial cell density. University refractive surgery center. The corneal endothelium was analyzed preoperatively and 1, 6, and 12 months postoperatively using corneal confocal microscopy (modified HRT II with a Rostock Cornea Module, Heidelberg Engineering) in 60 eyes (30 patients). Patients were randomized to have myopic PRK using a 213 nm wavelength solid-state laser (study group) or a conventional 193 nm wavelength excimer laser (control group). Three endothelial images were acquired in each of 30 preoperative normal eyes to evaluate the repeatability of endothelial cell density measurements. Repeated-measures analysis of variance was used to compare the variations in endothelial cell density between the 2 lasers and the changes in endothelial cell density over time. There were no statistically significant differences in sex, age, corneal pachymetry, attempted correction, preoperative endothelial cell density, or postoperative refractive outcomes (uncorrected visual acuity, best spectacle-corrected visual acuity, and spherical equivalent refraction) between the 2 groups (P>.05). The coefficient of repeatability of endothelial cell density was 131 cells/mm(2). The measured endothelial cell count per 1.0 mm(2) did not significantly change up to 1 year postoperatively in either group (both P>.05). No statistically significant difference was found between the 2 groups in any postoperative interval (P>.05). Photorefractive keratectomy for moderate myopia using a 213 nm wavelength solid-state laser or a conventional 193 nm wavelength excimer laser did not significantly affect corneal endothelial density during the 1-year postoperative period.

Fluorescence diagnosis and photochemical treatment of diseased tissue using lasers: Part I.

PubMed

Andersson-Engels, S; Johansson, J; Svanberg, S; Svanberg, K

1989-12-15

Lasers are useful in many applications in medicine and biology. Historically, most laser use has involved heat generated in the interaction of the laser beam with the tissue. Today, however, the spectroscopic aspects of this laser use are playing a more dominant role in a number of applications. In this two-part series, Sune Svanberg and co-workers present illustrations of emerging clinical applications from cooperative work performed by the Lund Institute of Technology and the Lund University Hospital. Part I includes a survey of laser techniques for atomic and molecular analyses of samples of medical interest, spectroscopic analysis of the laser-induced plasma obtained when a high-power pulsed laser beam interacts with tissue, and the use of tumor-seeking agents in combination with laser radiation to provide new possibilities for malignant tumor detection and treatment. Part II, which will appear in the January 1, 1990, issue, describes the use of laser-induced fluorescence for tumor and plaque diagnostics. Different lasers have been used, and research efforts increasingly are being focused on excimer lasers and lasers in the IR region for the ablation of atherosclerotic plaques, cell layer by cell layer.

Keratin film ablation for the fabrication of brick and mortar skin structure using femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Haq, Bibi Safia; Khan, Hidayat Ullah; Dou, Yuehua; Alam, Khan; Attaullah, Shehnaz; Zari, Islam

2015-09-01

The patterning of thin keratin films has been explored to manufacture model skin surfaces based on the "bricks and mortar" view of the relationship between keratin and lipids. It has been demonstrated that laser light is capable of preparing keratin-based "bricks and mortar" wall structure as in epidermis, the outermost layer of the human skin. "Bricks and mortar" pattern in keratin films has been fabricated using an ArF excimer laser (193 nm wavelength) and femtosecond laser (800 and 400 nm wavelength). Due to the very low ablation threshold of keratin, femtosecond laser systems are practical for laser processing of proteins. These model skin structures are fabricated for the first time that will help to produce potentially effective moisturizing products for the protection of skin from dryness, diseases and wrinkles.

Imaging of acoustic waves induced by excimer laser ablation of the cornea

NASA Astrophysics Data System (ADS)

Rossi, Francesca; Pini, Roberto; Siano, Salvatore; Salimbeni, Renzo

1996-12-01

In this present study a pump-and-probe imaging set up was arranged to image and analyze the evolution of pressure waves induced by ArF ablation of the cornea, during their propagation into the eyeball. In vitro experiments simulating the effects of clinical PRK have been performed by using an artificial model of the human eyeball, composed of a cell filled with hyaluronic acid gel with a sample of freshly excised bovine cornea placed on the gel surface. LAser irradiation was provided at a fluence of 180 mJ/cm2. Irradiation spot diameters were varied in the range 2.0-5.0 mm. Images of the traveling acoustic waves evidenced diffraction effects, related to the diameter of laser spots on the corneal surface.

A review of monochromatic light devices for the treatment of alopecia areata.

PubMed

Darwin, Evan; Arora, Harleen; Hirt, Penelope A; Wikramanayake, Tongyu Cao; Jimenez, Joaquin J

2018-02-01

There are many laser technologies that are being tested that claim to support hair regrowth for patients with alopecia areata (AA). In this paper, we will determine whether the body of evidence supports the use of devices using monochromatic light sources to treat AA. Articles were gathered from PubMed, Embase, and the Cochrane database using these keywords: lasers, excimer laser, low-level laser therapy (LLLT), low-level light therapy, alopecia, alopecia areata, and hair loss with a category modifier of English. Ten clinical trials and seven case reports/abstracts were assessed. Eight clinical trials and two case reports demonstrated hair regrowth with the 308-nm excimer laser/light in men, women, and children. One case report demonstrated hair regrowth with the ALBA 355® laser. One clinical trial and two case reports demonstrated hair regrowth with LLLT. While two case reports demonstrated hair regrowth with fractional laser therapy, one clinical trial showed no improvement. The 308-nm excimer laser is a safe and effective treatment for men, women, and children with refractory AA of the scalp and beard. Larger, double-blinded clinical trials should be conducted to compare excimer laser therapy to standard treatments. More data is needed to determine the efficacy of LLLT and fractional laser therapy in the treatment of AA.

Escape of carbon element in surface ablation of cobalt cemented tungsten carbide with pulsed UV laser

NASA Astrophysics Data System (ADS)

Li, Tiejun; Lou, Qihong; Dong, Jingxing; Wei, Yunrong; Liu, Jingru

2001-03-01

Surface ablation of cobalt cemented tungsten carbide hardmetal has been carried out in this work using a 308 nm, 30 ns XeCl excimer laser. The surface phase transformation on different pulse number of laser shots has been investigated by means of XRD and microphotography as well as AES at laser fluence of 2.5 J/cm 2. The experimental results showed that the phase structure of irradiated area has partly transformed from original WC to β-WC 1- x, then to α-W 2C and CW 3, and finally to W crystal. It is suggested that the formation of non-stoichiometric tungsten carbide should result from the escaping of carbon element due to accumulated heating of surface by pulsed laser irradiation.

Compact erbium lasers in the IR photorefractive keratectomy (PRK)

NASA Astrophysics Data System (ADS)

Liu, Baining; Eichler, Hans J.; Sperlich, O.; Holschbach, A.; Kayser, M.

1996-09-01

Erbium lasers deliver laser radiation near 3 micrometers and are a promising alternative to excimer laser photorefractive keratectomy (UV-PRK). In addition to easier handling due to all solid state technology, especially when operated in the fundamental mode, IR-PRK eliminates the potential of mutagenic side effects associated with UV-PRK. However, a successful IR-PRK for the clinic treatment in the near future demands both technological development of erbium lasers in different operation modes and clinical investigation of interaction between 3 micrometers radiation and human corneas. The excellent cooperation between university, company and hospital makes this possible. Uncoated thin plates made from infrared materials were found to be effective etalon reflectors with high damage threshold as high as 1 GW/cm2 for erbium lasers. Four kinds of such reflectors were successfully tested in Q-switched Er:YAG-laser at 2.94 micrometers and Er:Cr:YSGG-laser at 2.80 micrometers. Very stable operation of our erbium lasers with high output energy both in free-running and Q-switched modes is realized. First infrared photorefractive keratectomy (IR-PRK) for myopic correction in human corneas by a free-running erbium laser based on our new construction concepts was achieved.

Efficacy of fractional lasers in treating alopecia: a literature review.

PubMed

Perper, Marina; Aldahan, Adam S; Fayne, Rachel A; Emerson, Christopher P; Nouri, Keyvan

2017-11-01

Hair loss stemming from different types of alopecia, such as androgenic alopecia and alopecia areata, negatively affects over half the population and, in many circumstances, causes serious psychosocial distress. Current treatment options for alopecia, such as minoxidil, anthralin, and intralesional corticosteroids, vary efficacy and side effect profiles. It is known that low-level laser/light therapies (LLLT), or photobiomodulations, such as the US FDA-cleared HairMax Lasercomb®, He-Ne laser, and excimer laser, are relatively affordable, user-friendly, safe, and effective forms of treatment for hair loss. While less is known about the effectiveness of fractional lasers for combating hair loss, research suggests that by creating microscopic thermal injury zones, fractional lasers may cause an increase in hair growth from a wound healing process, making them potential therapeutic options for alopecia. A literature review was performed to evaluate the effectiveness of fractional lasers on hair regrowth. The specific fractional laser therapies include the 1550-nm nonablative fractional erbium-glass laser, the ablative fractional 2940-nm erbium:YAG laser, and the ablative fractional CO 2 fractional laser. Additional randomized controlled trials are necessary to further evaluate the effectiveness of the lasers, as well as to establish appropriate parameters and treatment intervals.

Rayleigh rejection filters for 193-nm ArF laser Raman spectroscopy

NASA Technical Reports Server (NTRS)

Mckenzie, Robert L.

1993-01-01

Selected organic absorbers and their solvents are evaluated as spectral filters for the rejection of 193-nm Rayleigh light associated with the use of an ArF excimer laser for Raman spectroscopy. A simply constructed filter cell filled with 0.5 percent acetone in water and an optical path of 7 mm is shown effectively to eliminate stray Rayleigh light underlying the Raman spectrum from air while transmitting 60 percent of the Raman light scattered by O2.

Halos--a problem for all myopes? A comparison between spectacles, contact lenses, and photorefractive keratectomy.

PubMed

Lohmann, C P; Fitzke, F W; O'Brart, D; Muir, M K; Marshall, J

1993-01-01

After photorefractive keratectomy (PRK) using excimer lasers (193 nm) many patients report the presence of halos around light sources at night. However, halos are not unique to PRK patients, as they are a common observation in myopic contact lens wearers. We present an objective measurement of the halos using a computerized technique. The patient fixated on a red cross within a white circle in the center of a video monitor which served as the halo source. The screen surrounding the circle was not illuminated. The operator controlled the movement of the white spot and moved the spot toward the halo source until the subject indicated when the cursor was at the outer parameter of the halo. Measurements were made at 30 degree intervals around the halo source and expressed as square degrees. The study found that spectacles, soft contact lenses, and excimer laser surgery were superior to hard contact lenses in terms of the size of the halo. A mean value of 2.51 square degrees was obtained for spectacles wearers compared with 3.18 square degrees for soft contact lenses, 3.14 square degrees for excimer laser patients with 4-millimeter ablation zone, 2.76 square degrees for excimer laser patients with a 5-millimeter ablation zone, and 89.5 square degrees for hard contact lenses. It appears that this device is very useful for measuring the halo size after excimer laser PRK. We concluded that halos were not a problem for our patients after excimer laser photorefractive keratectomy.

Intense laser beams; Proceedings of the Meeting, Los Angeles, CA, Jan. 23, 24, 1992

NASA Technical Reports Server (NTRS)

Wade, Richard C. (Editor); Ulrich, Peter B. (Editor)

1992-01-01

Various papers on intense laser beams are presented. Individual topics addressed include: novel methods of copper vapor laser excitation, UCLA IR FEL, lasing characteristics of a large-bore copper vapor laser (CVL), copper density measurement of a large-bore CVL, high-power XeCl excimer laser, solid state direct-drive circuit for pumping gas lasers, united energy model for FELs, intensity and frequency instabilities in double-mode CO2 lasers, comparison of output power stabilities of CO and CO2 lasers, increasing efficiency of sealed-off CO lasers, thermal effects in singlet delta oxygen generation, optical extraction from the chemical oxygen-iodine laser medium, generation and laser diagnostic analysis of bismuth fluoride. Also discussed are: high-Q resonator design for an HF overtone chemical lasers, improved coatings for HF overtone lasers, scaled atmospheric blooming experiment, simulation on producing conjugate field using deformable mirrors, paraxial theory of amplitude correction, potential capabilities of adaptive optical systems in the atmosphere, power beaming research at NASA, system evaluations of laser power beaming options, performance projections for laser beam power to space, independent assessment of laser power beaming options, removal of atmospheric CFCs by lasers, efficiency of vaporization cutting by CVL.

Measurement of temperature and density fluctuations in turbulence using an ultraviolet laser

NASA Technical Reports Server (NTRS)

Massey, G. A.

1984-01-01

Noninvasive measurement of density and temperature fluctuations in turbulent air flow was examined. The approach used fluorescence of oxygen molecules which are selectively excited by a tunable vacuum ultraviolet laser beam. The strength of the fluorescence signal and its dependence on laser wavelength vary with the density and temperature of the air in the laser beam. Because fluorescence can be detected at 90 degrees from the beam propagation direction, spatial resolution in three dimensions, rather than path-integrated measurements can be achieved. With spatial resolutions of the order of a millimeter and at supersonic air velocities it is necessary to perform each measurement in a time of the order of a microsecond; this is possible by by using laser pulses of ten nanosecond duration. In this method atmospheric O2 is excited by the emission of a tunable ArF excimer laser, and the fluorescence, which spans the 210 to 420 range, is detected by an ultraviolet phototube.

Femtosecond all-solid-state laser for refractive surgery

NASA Astrophysics Data System (ADS)

Zickler, Leander; Han, Meng; Giese, G.'nter; Loesel, Frieder H.; Bille, Josef F.

2003-06-01

Refractive surgery in the pursuit of perfect vision (e.g. 20/10) requires firstly an exact measurement of abberations induced by the eye and then a sophisticated surgical approach. A recent extension of wavefront measurement techniques and adaptive optics to ophthalmology has quantitatively characterized the quality of the human eye. The next milestone towards perfect vision is developing a more efficient and precise laser scalpel and evaluating minimal-invasive laser surgery strategies. Femtosecond all-solid-state MOPA lasers based on passive modelocking and chirped pulse amplification are excellent candidates for eye surgery due to their stability, ultra-high intensity and compact tabletop size. Furthermore, taking into account the peak emission in the near IR and diffraction limited focusing abilities, surgical laser systems performing precise intrastromal incisions for corneal flap resection and intrastromal corneal reshaping promise significant improvement over today's Photorefractive Keratectomy (PRK) and Laser Assisted In Situ Keratomileusis (LASIK) techniques which utilize UV excimer lasers. Through dispersion control and optimized regenerative amplification, a compact femtosecond all-solid-state laser with pulsed energy well above LIOB threshold and kHz repetition rate is constructed. After applying a pulse sequence to the eye, the modified corneal morphology is investigated by high resolution microscopy (Multi Photon/SHG Confocal Microscope).

Laser synthesized super-hydrophobic conducting carbon with broccoli-type morphology as a counter-electrode for dye sensitized solar cells.

PubMed

Gokhale, Rohan; Agarkar, Shruti; Debgupta, Joyashish; Shinde, Deodatta; Lefez, Benoit; Banerjee, Abhik; Jog, Jyoti; More, Mahendra; Hannoyer, Beatrice; Ogale, Satishchandra

2012-11-07

A laser photochemical process is introduced to realize superhydrophobic conducting carbon coatings with broccoli-type hierarchical morphology for use as a metal-free counter electrode in a dye sensitized solar cell. The process involves pulsed excimer laser irradiation of a thin layer of liquid haloaromatic organic solvent o-dichlorobenzene (DCB). The coating reflects a carbon nanoparticle-self assembled and process-controlled morphology that yields solar to electric power conversion efficiency of 5.1% as opposed to 6.2% obtained with the conventional Pt-based electrode.