Note: This page contains sample records for the topic large aperture laser from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

Advances in optical materials for large aperture lasers  

SciTech Connect

Lawrence Livermore National Laboratory (LLNL) is using large aperture Nd: glass lasers to investigate the feasibility of inertial confinement fusion. In our experiments high power laser light is focussed onto a small (100 to 500 micron) target containing a deuterium-tritium fuel mixture. During the short (1 to 5 ns) laser pulse the fuel is compressed and heated, resulting in fusion reactions. The generation and control of the powerful laser pulses for these experiments is a challenging scientific and engineering task, which requires the development of new optical materials, fabrication techniques, and coatings. LLNL with the considerable cooperation and support from the optical industry, where most of the research and development and almost all the manufacturing is done, has successfully applied several new developments in these areas.

Stokowski, S.E.; Lowdermilk, W.H.; Marchi, F.T.; Swain, J.E.; Wallerstein, E.P.; Wirtenson, G.R.

1981-12-15

2

Large Aperture Multi-Dimensional Laser Radar Testbed.  

National Technical Information Service (NTIS)

A 39 cm aperture multi-dimensional laser radar has been built and made operational. This sensor acquires pixel registered range, Doppler, 3-5 micrometer passive, and visible passive data. Range is digitized at 200 MHz for .75 m range resolution. Doppler i...

D. U. Fluckiger M. P. Boldue L. A. Prior

1988-01-01

3

Large Aperture, High Energy Laser System for Optics and Optical Component Testing.  

National Technical Information Service (NTIS)

A large aperture, kJ-class, multi-wavelength Nd-glass laser system has been constructed at Lawrence Livermore National Lab which has unique capabilities for studying a wide variety of optical phenomena. The master-oscillator, power-amplifier (MOPA) config...

M. C. Nostrand T. L. Weiland R. L. Luthi J. L. Vickers W. D. Sell

2003-01-01

4

System for end-pumping a solid state laser using a large aperture laser diode bar  

NASA Astrophysics Data System (ADS)

An optical system for end-pumping the gain medium of a three-level or a self-terminating solid state laser with the optical output from a wide aperture laser diode bar is disclosed. In a preferred embodiment, the optical system includes: a laser diode bar for emitting from an elongated emissive area thereof a bright light having a lateral divergence and a transverse divergence; and an optical assembly disposed between the laser diode bar and the three-level solid state laser for collecting and focusing the bright light into a relatively small high-intensity spot to end-pump the gain medium of the three-level or self-terminating solid state laser.

Esterowitz, Leon; Stoneman, C.; Lynn, James G.

1993-12-01

5

Large aperture optical switching devices  

SciTech Connect

We have developed a new approach to constructing large aperture optical switches for next generation inertial confinement fusion lasers. A transparent plasma electrode formed in low pressure ionized gas acts as a conductive coating to allow the uniform charging of the optical faces of an electro-optic material. In this manner large electric fields can be applied longitudinally to large aperture, high aspect ratio Pockels cells. We propose a four-electrode geometry to create the necessary high conductivity plasma sheets, and have demonstrated fast (less than 10 nsec) switching in a 5x5 cm aperture KD*P Pockels cell with such a design. Detaid modelling of Pockels cell performance with plasma electrodes has been carried out for 15 and 30 cm aperture designs.

Goldhar, J.; Henesian, M.A.

1983-12-12

6

Performance of large-aperture optical switches for high-energy inertial-confinement fusion lasers  

SciTech Connect

We describe the design and performance of large-aperture ({lt}30 cm {times} 30 cm) optical switches that have demonstrated, for the first time to our knowledge, active switching of a high-energy ({lt}5 kJ) optical pulse in an inertial-confinement fusion laser. These optical switches, which consist of a plasma-electrode Pockels cell (PEPC) and a passive polarizer, permit the design of efficient, multipass laser amplifiers. In a PEPC, plasma discharges on the faces of a thin (1-cm) electro-optic crystal (KDP or KD{bold |}P) act as highly conductive and transparent electrodes. These plasma electrodes facilitate rapid ({lt}100 ns) and uniform charging of the crystal to the half-wave voltage and discharging back to 0 V. We discuss the operating principles, design, optical performance, and technical issues of a 32 cm {times} 32 cm prototype PEPC with both KDP and KD{bold |}P crystals, and a 37 cm {times} 37 cm PEPC with a KDP crystal for the Beamlet laser. This PEPC recently switched a 6-kJ, 3-ns pulse in a four-pass cavity.

Rhodes, M.A.; Woods, B.; DeYoreo, J.J.; Roberts, D.; Atherton, L.J. [University of California, Lawrence Livermore National Laboratory, P.O. Box 808 L-490, Livermore, California 94550 (United States)

1995-08-20

7

Parasitic suppression in large aperture Nd:glass disk laser amplifiers  

Microsoft Academic Search

Threshold conditions for bulk and surface parasitic oscillations, which ; may limit energy storage aperture Nd\\/glass disk lasers, have been developed as a ; function of material parameters. An expression describing the energy storage ; distribution within a disk was used to determine the mode that will be most ; limiting for a particular disk design. Additional modes that may

J. A. Glaze; S. Guch; J. B. Trenholme

1974-01-01

8

Design considerations for large-aperture single-mode oxide-confined vertical-cavity surface-emitting lasers  

NASA Astrophysics Data System (ADS)

The output modal content of the oxide-confined vertical-cavity surface-emitting lasers (VCSELs) crucially depends upon the thickness of the low-index oxide aperture, its position with respect to the standing waves of the transverse-longitudinal modes and the separation from the cavity. Three-dimensional cold-cavity optical modes of typical AlGaAs/GaAs VCSELs at 850 nm were simulated to study these dependencies quantitatively taking into account the field diffraction and the material dispersion. Modification of one or two periods of the distributed Bragg reflector by positioning the thin oxidized aperture layers in the mode nodes allows single-mode regime to extend to the aperture diameters as large as 10 ?m.

Kalosha, V. P.; Ledentsov, N. N.; Bimberg, D.

2012-08-01

9

Developing Magnetorheological Finishing (MRF) Technology for the Manufacture of Large-Aperture Optics in Megajoule Class Laser Systems  

SciTech Connect

Over the last eight years we have been developing advanced MRF tools and techniques to manufacture meter-scale optics for use in Megajoule class laser systems. These systems call for optics having unique characteristics that can complicate their fabrication using conventional polishing methods. First, exposure to the high-power nanosecond and sub-nanosecond pulsed laser environment in the infrared (>27 J/cm{sup 2} at 1053 nm), visible (>18 J/cm{sup 2} at 527 nm), and ultraviolet (>10 J/cm{sup 2} at 351 nm) demands ultra-precise control of optical figure and finish to avoid intensity modulation and scatter that can result in damage to the optics chain or system hardware. Second, the optics must be super-polished and virtually free of surface and subsurface flaws that can limit optic lifetime through laser-induced damage initiation and growth at the flaw sites, particularly at 351 nm. Lastly, ultra-precise optics for beam conditioning are required to control laser beam quality. These optics contain customized surface topographical structures that cannot be made using traditional fabrication processes. In this review, we will present the development and implementation of large-aperture MRF tools and techniques specifically designed to meet the demanding optical performance challenges required in large-aperture high-power laser systems. In particular, we will discuss the advances made by using MRF technology to expose and remove surface and subsurface flaws in optics during final polishing to yield optics with improve laser damage resistance, the novel application of MRF deterministic polishing to imprint complex topographical information and wavefront correction patterns onto optical surfaces, and our efforts to advance the technology to manufacture large-aperture damage resistant optics.

Menapace, J A

2010-10-27

10

MRF Applications: On the Road to Making Large-Aperture Ultraviolet Laser Resistant Continuous Phase Plates for High-Power Lasers  

SciTech Connect

Over the past two years we have developed MRF tools and procedures to manufacture large-aperture (430 X 430 mm) continuous phase plates (CPPs) that are capable of operating in the infrared portion (1053 nm) of high-power laser systems. This is accomplished by polishing prescribed patterns of continuously varying topographical features onto finished plano optics using MRF imprinting techniques. We have been successful in making, testing, and using large-aperture CPPs whose topography possesses spatial periods as low as 4 mm and surface peak-to-valleys as high as 8.6 {micro}m. Combining this application of MRF technology with advanced MRF finishing techniques that focus on ultraviolet laser damage resistance makes it potentially feasible to manufacture large-aperture CPPs that can operate in the ultraviolet (351 nm) without sustaining laser-induced damage. In this paper, we will discuss the CPP manufacturing process and the results of 351-nm/3-nsec equivalent laser performance experiments conducted on large-aperture CPPs manufactured using advanced MRF protocols.

Menapace, J A; Davis, P J; Steele, W A; Hachkowski, M R; Nelson, A; Xin, K

2006-10-26

11

Suppression of parasitic lasing in large-aperture Ti:sapphire laser amplifiers  

SciTech Connect

Transverse, parasitic lasing has been observed in several large Ti:sapphire disk amplifiers. It severely limits the signal gain and the pulse energy that can be extracted from the amplifier. We have developed a technique for suppressing these parasitic lasing modes based on index matching the crystal edges with an absorbing doped polymer thermoplastic. The parasitics are completely suppressed for the range of aperture sizes and pump fluences studied here. A comparison of the amplifier performance before and after edge cladding is presented for several Ti:sapphire crystals. {copyright} {ital 1999} {ital Optical Society of America}

Patterson, F.G.; Bonlie, J.; Price, D.; White, B. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

1999-07-01

12

Suppression of parasitic lasing in large-aperture Ti:sapphire laser amplifiers.  

PubMed

Transverse, parasitic lasing has been observed in several large Ti:sapphire disk amplifiers. It severely limits the signal gain and the pulse energy that can be extracted from the amplifier. We have developed a technique for suppressing these parasitic lasing modes based on index matching the crystal edges with an absorbing doped polymer thermoplastic. The parasitics are completely suppressed for the range of aperture sizes and pump fluences studied here. A comparison of the amplifier performance before and after edge cladding is presented for several Ti:sapphire crystals. PMID:18073910

Patterson, F G; Bonlie, J; Price, D; White, B

1999-07-15

13

Large-aperture CsLiB6O10 frequency doubler for high-energy Nd:glass laser  

NASA Astrophysics Data System (ADS)

We describe the demonstration of the high pulse energy and high efficiency second-harmonic generation (SHG) at 532-nm using large aperture CsLiB6O10 (CLBO) crystals for the first time to our knowledge. A pulsed green energy of 25 J has been generated with 34 J of input 1064-nm Nd:glass laser radiation using a two-stage crystal architecture. High conversion efficiency of 74 % has been attained at fundamental laser intensity of only 370 MW/cm2. This result represents the highest green pulse energy ever reported using the CLBO crystals. We discuss in detail the design and performance of SHG using CLBO crystals.

Kiriyama, Hiromitsu; Inoue, Norihiro; Yamakawa, Koichi

2002-09-01

14

Large aperture diffractive space telescope  

DOEpatents

A large (10's of meters) aperture space telescope including two separate spacecraft--an optical primary objective lens functioning as a magnifying glass and an optical secondary functioning as an eyepiece. The spacecraft are spaced up to several kilometers apart with the eyepiece directly behind the magnifying glass "aiming" at an intended target with their relative orientation determining the optical axis of the telescope and hence the targets being observed. The objective lens includes a very large-aperture, very-thin-membrane, diffractive lens, e.g., a Fresnel lens, which intercepts incoming light over its full aperture and focuses it towards the eyepiece. The eyepiece has a much smaller, meter-scale aperture and is designed to move along the focal surface of the objective lens, gathering up the incoming light and converting it to high quality images. The positions of the two space craft are controlled both to maintain a good optical focus and to point at desired targets which may be either earth bound or celestial.

Hyde, Roderick A. (Livermore, CA)

2001-01-01

15

Large aperture scanning airborne lidar  

NASA Astrophysics Data System (ADS)

A large aperture scanning airborne lidar facility is being developed to provide important new capabilities for airborne lidar sensor systems. The proposed scanning mechanism allows for a large aperture telescope (25 in. diameter) in front of an elliptical flat (25 x 36 in.) turning mirror positioned at a 45 degree angle with respect to the telescope optical axis. The lidar scanning capability will provide opportunities for acquiring new data sets for atmospheric, earth resources, and oceans communities. This completed facility will also make available the opportunity to acquire simulated EOS lidar data on a near global basis. The design and construction of this unique scanning mechanism presents exciting technological challenges of maintaining the turning mirror optical flatness during scanning while exposed to extreme temperatures, ambient pressures, aircraft vibrations, etc.

Smith, J.; Bindschadler, R.; Boers, R.; Bufton, J. L.; Clem, D.; Garvin, J.; Melfi, S. H.

16

Pulsed large aperture E-beam sustained CO2 laser discharge optimization  

SciTech Connect

Results of an experimental program are presented to resolve critical discharge loading and confinement issues for high energy pulsed electron-beam sustained CO2 lasers. The investigations focus on kinetically optimizing the energy loading of a helium-free gas mixture 3:1:0.08 (N2:CO2:H2), and investigating and optimizing configurations for controlling discharge confinement while suppressing plasma streamers and associated arc formation. Factors affecting cavity arcing are isolated and treated in a series of systematic tests, and optimization procedures used to achieve kinetically optimized energy loadings are described. Previous arcing limitations are overcome to permit higher E/N's, energy loadings and projected higher specific laser outputs. At the highest E/N's, a sustainer current oscillation is observed and the discharge plasma exhibits a luminous glow transverse to the applied field.

Cronburg, T.; Hasson, V.; Reilly, D.

1982-06-01

17

Effects of the injection current profile shape on sidelobes in large-aperture semiconductor laser amplifiers  

SciTech Connect

Sharply peaked near-field sidelobes are formed when the input optical field pattern interacts with the edges of the current stripe in a semiconductor laser amplifier. The strength of this interaction is shown theoretically to depend principally on the first and second derivatives of the transverse current profile, and hence one can suppress the sidelobes by smoothing the sharp edges in the current injection.

White, J.K. [Arizona Center for Mathematical Sciences, University of Arizona, Tucson, Arizona 85721 (United States); McInerney, J.G. [Department of Physics, University College, Cork (Ireland); Moloney, J.V. [Arizona Center for Mathematical Sciences, University of Arizona, Tucson, Arizona 85721 (United States)

1995-03-15

18

Modeling of large aperture third harmonic frequency conversion of high power Nd:glass laser systems  

SciTech Connect

To provide high-energy, high-power beams at short wavelengths for inertial-confinement-fusion experiments, we routinely convert the 1.053-{mu}m output of the Nova, Nd:phosphate-glass, laser system to its third-harmonic wavelength. We describe performance and conversion efficiency modeling of the 3 {times} 3 arrays potassium-dihydrogen-phosphate crystal plates used for type II/type II phase-matched harmonic conversion of Nova 0.74-m diameter beams, and an alternate type I/type II phase-matching configuration that improves the third-harmonic conversion efficiency. These arrays provide energy conversion of up to 65% and intensity conversion to 70%. 19 refs., 11 figs.

Henesian, M.A.; Wegner, P.J.; Speck, D.R.; Bibeau, C.; Ehrlich, R.B.; Laumann, C.W.; Lawson, J.K.; Weiland, T.L.

1991-03-13

19

Suppression of parasitic lasing in large-aperture Ti:sapphire laser amplifiers  

Microsoft Academic Search

Transverse, parasitic lasing has been observed in several large Ti:sapphire disk amplifiers. It severely limits the signal gain and the pulse energy that can be extracted from the amplifier. We have developed a technique for suppressing these parasitic lasing modes based on index matching the crystal edges with an absorbing doped polymer thermoplastic. The parasitics are completely suppressed for the

F. G. Patterson; J. Bonlie; D. Price; B. White

1999-01-01

20

Large aperture Fresnel telescopes/011  

SciTech Connect

At Livermore we`ve spent the last two years examining an alternative approach towards very large aperture (VLA) telescopes, one based upon transmissive Fresnel lenses rather than on mirrors. Fresnel lenses are attractive for VLA telescopes because they are launchable (lightweight, packagable, and deployable) and because they virtually eliminate the traditional, very tight, surface shape requirements faced by reflecting telescopes. Their (potentially severe) optical drawback, a very narrow spectral bandwidth, can be eliminated by use of a second (much smaller) chromatically-correcting Fresnel element. This enables Fresnel VLA telescopes to provide either single band ({Delta}{lambda}/{lambda} {approximately} 0.1), multiple band, or continuous spectral coverage. Building and fielding such large Fresnel lenses will present a significant challenge, but one which appears, with effort, to be solvable.

Hyde, R.A., LLNL

1998-07-16

21

Experimental investigation of the performance of an annular aperture and a circular aperture on the same very-small-aperture laser facet  

NASA Astrophysics Data System (ADS)

A very-small-aperture laser (VSAL) with a circular aperture has a trade-off between the spot size and the output power. A nanometric annular aperture is fabricated to overcome this difficulty. The advantages of the annular aperture are demonstrated by measuring and comparing its near-field intensity distribution with that of a circular aperture. These apertures are fabricated on the same VSAL to ensure that they are under the same illumination conditions. The experimental results indicate that an annular aperture produces a smaller spot size and a higher peak intensity than a circular aperture. The confinement effect and the enhancement effect are attributed to the convergence of the power flow that passes through the annular aperture. The observed enhancement effect decreases when the distance from the VSAL facet is increased, but it does not vanish even when the distance is as large as 3.5 ?m.

Gai, Hongfeng; Wang, Jia; Tian, Qian; Xia, Wei; Xu, Xiangang

2007-09-01

22

Thin-Film-Optics Design and Manufacturing Challenges for Large-Aperture High-Peak-Power, Short-Pulse Lasers  

SciTech Connect

High-peak-power, short-pulse laser systems require specialized thin-film coatings, primarily due to laser damage thresholds and increased spectral bandwidth. The influence of these effects is evident in wavefront performance, coating thickness, and design complexity.

Oliver,J.B.

2004-12-17

23

Large Aperture Electrostatic Dust Detector  

SciTech Connect

Diagnosis and management of dust inventories generated in next-step magnetic fusion devices is necessary for their safe operation. A novel electrostatic dust detector, based on a fine grid of interlocking circuit traces biased to 30 or 50 ? has been developed for the detection of dust particles on remote surfaces in air and vacuum environments. Impinging dust particles create a temporary short circuit and the resulting current pulse is recorded by counting electronics. Up to 90% of the particles are ejected from the grid or vaporized suggesting the device may be useful for controlling dust inventories. We report measurements of the sensitivity of a large area (5x5 cm) detector to microgram quantities of dust particles and review its applications to contemporary tokamaks and ITER.

C.H. Skinner, R. Hensley, and A.L Roquemore

2007-10-09

24

Fast-Operating, Large-Aperture Shutter.  

National Technical Information Service (NTIS)

It is an object of the invention to provide a fast-operating shutter that may be used with large apertures, has a high percent of light transmission when open, complete opacity when closed, and whose operation is not accompanied by a flash. This is accomp...

E. C. Cassidy D. H. Tsai

1966-01-01

25

Laser microdrilling of sheets using aperture system  

NASA Astrophysics Data System (ADS)

In laser drilling of sheet materials, the minimum diameter of the hole processed is determined by the laser machine used. Then, the purpose of this study is to develop a system for minimizing the diameter of the hole and evaluate the performance of the system. A CO2 laser machine, maximum output power of 500 W in single mode, was used in the experiment. This beam includes an area with low power density at the peripheral portion hindering the drilling of a smaller diameter hole. To cope with this problem, an aperture was applied to the system to remove the area described. Metal sheets (0.5 mm thick mild steel and 0.6 mm thick stainless steel) and a ceramic sheet (0.6 mm thick Al2O3) were used as the materials to be processed. The effect of the aperture, together with the effect of pulse conditions such as peak power, frequency and duty, on the diameter and shape of the drilled hole was discussed. Results showed that the diameters of drilled holes are reduced as much as 50%(for mild steel) and 30%(for Al2O3) by the usage of the aperture. It was also found that the drilling of a taper-controlled micro hole is possible by changing the diameter of the aperture used.

Miyazawa, Hajime; Nakayama, Hiroki

2004-09-01

26

Design of large aperture focal plane shutter  

NASA Astrophysics Data System (ADS)

To satisfy the requirement of large telescope, a large aperture focal plane shutter with aperture size of ?200mm was researched and designed to realize, which could be started and stopped in a relative short time with precise position, and also the blades could open and close at the same time at any orientation. Timing-belts and stepper motors were adopted as the drive mechanism. Velocity and position of the stepper motors were controlled by the PWM pulse generated by DSP. Exponential curve is applied to control the velocity of the stepper motors to make the shutter start and stop in a short time. The closing/open time of shutter is 0.2s, which meets the performance requirements of large telescope properly.

Hu, Jia-wen; Ma, Wen-li; Huang, Jin-long

27

Progress toward large-aperture membrane mirrors  

NASA Astrophysics Data System (ADS)

The Air Force Research Laboratory (AFRL) is exploring the feasibility of large-aperture, deployable, space-based membrane telescopes operating in the visible and/or near- infrared spectral regions. One of the near-term goals of this work is to develop an understanding of available and achievable membrane materials, specifically concentrating on practical techniques to form large aperture membranes with the necessary surface quality and economy. When this research began a little more than three years ago, the conceptual design was based upon a totally inflatable structure. An inflatable structure has been used for space solar power collection and radio frequency antennas. This totally inflatable lenticular design is simple and relatively easy to demonstrate, but maintaining inflation during an extended lifetime in near-earth orbit may not be feasible. Recently, a new concept for a membrane telescope has emerged which does not depend on sustained inflation during operation. Thin membranes on the order of 10 to 100 micrometer thick will be packaged and deployed, maintaining their surface figure by means other than inflation. Given the fact that the sub- wavelength level surface tolerances required of imaging telescopes will probably not be practical with a membrane- based telescope, such systems will probably rely on real-time holography or some other wavefront correction or compensation technique. We will discuss the primary experimental work ongoing in the AFRL Membrane Mirror Laboratory, and in doing so, some of the issues relevant to demonstrating a practical, large-aperture membrane mirror system.

Rotge, James R.; Dass, Shiv C.; Marker, Dan K.; Carreras, Richard A.; Lutz, B.; Duneman, Dennis C.

2000-10-01

28

Large-aperture, high-damage-threshold optics for beamlet  

SciTech Connect

Beamlet serves as a test bed for the proposed NIF laser design and components. Therefore, its optics are similar in size and quality to those proposed for the NIF. In general, the optics in the main laser cavity and transport section of Beamlet are larger and have higher damage thresholds than the optics manufactured for any of our previous laser systems. In addition, the quality of the Beamlet optical materials is higher, leading to better wavefront quality, higher optical transmission, and lower-intensity modulation of the output laser beam than, for example, that typically achieved on Nova. In this article, we discuss the properties and characteristics of the large-aperture optics used on Beamlet.

Campbell, J.H.; Atherton, L.J.; DeYoreo, J.J.; Kozlowski, M.R.; Maney, R.T.; Montesanti, R.C.; Sheehan, L.M.; Barker, C.E.

1995-02-23

29

Diffraction from oxide confinement apertures in vertical-cavity lasers  

SciTech Connect

Direct measurement of scattered fields from oxide confinement apertures in vertical-cavity lasers is presented. Diffraction fringes associated with each transverse lasing mode are detected in the far field from devices with varying oxide aperture dimensions and with quantum efficiencies as high as 48{percent}. The diffracted pattern symmetries match the rectangular symmetry of the oxide apertures present in the devices and fringe locations are compared to Fraunhofer theory. The fraction of power diffracted from the lasing mode remains roughly constant as a function of relative pump rate, but is shown to depend on both transverse mode order and oxide aperture size. {copyright} {ital 1999 American Institute of Physics.}

Roos, P.A.; Carlsten, J.L. [Montana State University, Department of Physics, Bozeman, Montana 59717 (United States); Kilper, D.C. [University of North Carolina at Charlotte, Department of Physics, Charlotte, North Carolina 28223 (United States); Lear, K.L. [MicroOptical Devices Inc., 5601C Midway Park Pl. NE, Albuquerque, New Mexico 87109 (United States)

1999-08-01

30

Wide-aperture subnanosecond CO2 laser system  

Microsoft Academic Search

The construction of CO2 laser system generating a train of subnanosecond laser pulses with total train energy up to 5 J is reported. A record level of laser energy was obtained due to utilization of unique 5 X 5 cm2 aperture, 6 atm X- ray preionized CO2 amplifier. The estimations of individual pulses durations in the train are given. The

Victor V. Apollonov; K. K. Kazakov; N. V. Pletnyev; Vladimir R. Sorochenko; Gennady A. Baranov; A. A. Kuchinsky; V. P. Tomashevich

1998-01-01

31

Wide-aperture picosecond CO2 laser system  

Microsoft Academic Search

The construction of CO2 laser system generating a train of subnanosecond laser pulses with total train energy up to 5 J is reported. A record level of laser energy was obtained due to utilization of unique 5 X 5 cm2 aperture, 6 atm X- ray preionized CO2 amplifier. The estimations of individual pulses durations in the train are given. The

Victor V. Apollonov; K. K. Kazakov; N. V. Pletnyev; Vladimir R. Sorochenko; G. A. Baranov; A. A. Kuchinsky; V. P. Tomashevich

1998-01-01

32

Large-aperture compound refractive lenses  

Microsoft Academic Search

We have measured the intensity profile and transmission of x-rays focused by a series of bi-concave parabolic unit lenses fabricated in lithium and beryllium. For specified focal length and photon energy, lithium and beryllium compound refractive lenses (CRL) have a larger transmission, aperture size, and gain compared to aluminum, epoxy, and kapton CRLs. One Li CRL was composed of 335

J. T. Cremer; Melvin A. Piestrup; Charles K. Gary; Richard H. Pantell

2004-01-01

33

Large-aperture broadband sapphire windows for common aperture, target acquisition, tracking, and surveillance systems  

Microsoft Academic Search

State of the art optical sensing systems performing target acquisition\\/tracking and surveillance functions are being designed to incorporate a number of sensors into one package. These include visual and MWIR cameras, FLIRs, and laser range finders. These combined systems are being configured to view through a common aperture window. Typical window diameters are to eleven inches, but some surveillance applications

Joel Askinazi

1997-01-01

34

High power 808 nm vertical cavity surface emitting laser with multi-ring-shaped-aperture structure  

NASA Astrophysics Data System (ADS)

The carrier conglomeration effect has been one of the main problems in developing electrically pumped high power vertical cavity surface emitting laser (VCSEL) with large aperture. We demonstrate a high power 808 nm VCSEL with multi-ring-shaped-aperture (MRSA) to weaken the carrier conglomeration effect. Compared with typical VCSEL with single large aperture (SLA), the 300-?m-diameter VCSEL with MRSA has more uniform near field and far field patterns. Moreover, MRSA laser exhibits maximal CW light output power 0.3 W which is about 3 times that of SLA laser. And the maximal wall-plug efficiency of 17.4% is achieved, higher than that of SLA laser by 10%.

Hao, Y. Q.; Shang, C. Y.; Feng, Y.; Yan, C. L.; Zhao, Y. J.; Wang, Y. X.; Wang, X. H.; Liu, G. J.

2011-02-01

35

Beam combination with a large number of apertures  

NASA Astrophysics Data System (ADS)

The design of a space-based interferometer with a large number of apertures has been a subject of much discussion. In this paper, we argue in favor of using a Michelson beam combiner for the case where a small field of view is acceptable. We address the normal criticism that a Michelson combiner is too complicated by presenting an optical design for a 90-aperture, laboratory prototype. Coupling this device to a large, ground-based telescope with a coherent fiber array forms an imaging system that is a significant improvement over aperture masking.

Mozurkewich, D.

2008-07-01

36

Large-aperture discharges in E-beam-sustained CO2 amplifiers  

Microsoft Academic Search

The next generation CO2 laser currently being designed at LASL consists of six electron-beam sustained amplifier modules, each module containing 12 large-aperture laser discharges sustained by (and surrounding) a single, cylindrical cold-cathode electron gun. The large scale and cylindrical geometry combine to generate substantial electric and magnetic field effects which can affect the uniformity of the electron-beam distribution, causing a

W. T. Leland; J. T. Ganley; M. Kircher; G. W. York Jr.

1977-01-01

37

Improving 351-nm damage performance of large-aperture fused silica and DKDP optics  

Microsoft Academic Search

A program to identify and eliminate the causes of UV laser- induced damage and growth in fused silica and DKDP has developed methods to extend optics lifetimes for large- aperture, high-peak-power, UV lasers such as the National Ignition Facility (NIF). Issues included polish-related surface damage initiation and growth on fused silica and DKDP, bulk inclusions in fused silica, pinpoint bulk

Alan K. Burnham; Lloyd A. Hackel; Paul J. Wegner; Thomas G. Parham; Lawrence W. Hrubesh; B. M. Penetrante; P. K. Whitman; Stavros G. Demos; Joseph A. Menapace; Michael Runkel; Michael J. Fluss; Michael D. Feit; Michael H. Key; Thomas A. Biesiada

2002-01-01

38

Wide-aperture subnanosecond CO2 laser system  

NASA Astrophysics Data System (ADS)

The construction of CO2 laser system generating a train of subnanosecond laser pulses with total train energy up to 5 J is reported. A record level of laser energy was obtained due to utilization of unique 5 X 5 cm2 aperture, 6 atm X- ray preionized CO2 amplifier. The estimations of individual pulses durations in the train are given. The prospective of upgrading of present configuration of laser system towards shortening of laser pulses duration and increasing the pressure of working gas mixture of the amplifier and its efficiency are discussed.

Apollonov, Victor V.; Kazakov, K. K.; Pletnyev, N. V.; Sorochenko, Vladimir R.; Baranov, Gennady A.; Kuchinsky, A. A.; Tomashevich, V. P.

1998-12-01

39

Wide-aperture picosecond CO2 laser system  

NASA Astrophysics Data System (ADS)

The construction of CO2 laser system generating a train of subnanosecond laser pulses with total train energy up to 5 J is reported. A record level of laser energy was obtained due to utilization of unique 5 X 5 cm2 aperture, 6 atm X- ray preionized CO2 amplifier. The estimations of individual pulses durations in the train are given. The prospective of upgrading of present configuration of laser system towards shortening of laser pulses duration and increasing the pressure of working gas mixture of the amplifier and its efficiency are discussed.

Apollonov, Victor V.; Kazakov, K. K.; Pletnyev, N. V.; Sorochenko, Vladimir R.; Baranov, G. A.; Kuchinsky, A. A.; Tomashevich, V. P.

1998-09-01

40

Laser microdrilling of sheets using aperture system  

Microsoft Academic Search

In laser drilling of sheet materials, the minimum diameter of the hole processed is determined by the laser machine used. Then, the purpose of this study is to develop a system for minimizing the diameter of the hole and evaluate the performance of the system. A CO2 laser machine, maximum output power of 500 W in single mode, was used

Hajime Miyazawa; Hiroki Nakayama

2004-01-01

41

BLAST: The Balloon-Borne Large Aperture Submillimeter Telescope.  

National Technical Information Service (NTIS)

BLAST is the Balloon-borne Large-Aperture Sub-millimeter Telescope. It will fly from a Long Duration Balloon (LDB) platform from Antarctica. The telescope design incorporates a 2 m primary mirror with large-format bolometer arrays operating at 250, 350 an...

M. Devlin P. Ade J. Bock S. Dicker M. Griffin J. Gunderson M. Halpern P. Hargrave D. Hughes J. Klein

2004-01-01

42

Expected Performance of Adaptive Optics in Large Aperture Solar Telescopes  

NASA Astrophysics Data System (ADS)

Solar adaptive optics has become an indispensable tool for high resolution solar observations. New generation solar telescopes, such as the 4 m aperture Advanced Technology Solar Telescope, introduce a new set of challenges to solar adaptive optics correction. Larger aperture sizes are more susceptible to the effects on AO correction performance of the extended field-of-view of the cross-correlating Shack-Hartmann wavefront sensor. Observations at large zenith angles further enhance these field-of-view effects and can introduce more performance reductions due to atmospheric dispersion. We study the expected correction performance of solar adaptive optics systems in large aperture solar telescopes using an end-to-end adaptive optics simulation package.

Marino, J.; Rimmele, T. R.

2012-12-01

43

CAMERA: a compact, automated, laser adaptive optics system for small aperture telescopes  

Microsoft Academic Search

CAMERA is an autonomous laser guide star adaptive optics system designed for small aperture telescopes. This system is intended to be mounted permanently on such a telescope to provide large amounts of flexibly scheduled observing time, delivering high angular resolution imagery in the visible and near infrared. The design employs a Shack Hartmann wavefront sensor, a 12x12 actuator MEMS device

Matthew Britton; Viswa Velur; Nick Law; Philip Choi; Bryan E. Penprase

2008-01-01

44

Synchronized microscanner array for large aperture receiver optics of LIDAR systems  

NASA Astrophysics Data System (ADS)

Traditional laser scanners for 3D distance measurement involve expensive, heavy, (potentially) slow rotating mirrors for light deflection of the scanning TOF (time of flight) distance measurement, not suitable for compact, robust and highly portable LIDAR system. On the other hand MEMS scanners are limited to small apertures not suitable for a precise TOF measurement. To overcome this problem Fraunhofer IPMS presents a large aperture 1D-MEMS scanner array especially designed for LIDAR applications. It is composed of 2 × 7 silicon mirror elements each having an identical design with comparatively large aperture of 2.51 × 9.51mm2 and +/-30° optical scan range. All mirrors are driven electrostatically resonant with identical frequency close to design frequency of 250 Hz. By driving control all single scanner elements are synchronized to identical phase and amplitude in respect to a master scanner. This results in a large effective scanner aperture of 334 mm2 for the receiver optics and a filling factor of 80 %. To guarantee the synchronized operation the paper discusses in detail the scanner design to enable a sufficiently large frequency bandwidth of all scanner elements to the compensate frequency tolerances caused by fabrication and packaging. In comparison to LIDAR systems with conventional scanner components, the large aperture 1D-MEMS scanner array enables 3D-LIDAR systems to become significantly smaller, more robust and (potentially) less expensive, also higher scan rates can be realized without additional efforts (e.g. no air bearings are needed).

Sandner, Thilo; Grasshoff, Thomas; Wildenhain, Michael; Schenk, Harald

2010-02-01

45

Imaging with Concave Large-Aperture Therapeutic Ultrasound Arrays Using Conventional Synthetic-Aperture Beamforming  

PubMed Central

Several dual-mode ultrasound array (DMUA) systems are being investigated for potential use in image-guided surgery. In therapeutic mode, DMUAs generate pulsed or continuous-wave (CW) high-intensity focused ultrasound (HIFU) beams capable of generating localized therapeutic effects within the focal volume. In imaging mode, pulse-echo data can be collected from the DMUA elements to obtain B-mode images or other forms of feedback on the state of the target tissue before, during, and after the application of the therapeutic HIFU beam. Therapeutic and technological constraints give rise to special characteristics of therapeutic arrays. Specifically, DMUAs have concave apertures with low f-number values and are typically coarsely sampled using directive elements. These characteristics necessitate pre- and post-beamforming signal processing of echo data to improve the spatial and contrast resolution and maximize the image uniformity within the imaging field of view (IxFOV). We have recently developed and experimentally validated beamforming algorithms for concave large-aperture DMUAs with directive elements. Experimental validation was performed using a 1 MHz, 64-element, concave spherical aperture with 100 mm radius of curvature. The aperture was sampled in the lateral direction using elongated elements 1??×33.3? with 1.333??? center-to-center spacing (? is the wavelength). This resulted in f-number values of 0.8 and 2 in the azimuth and elevation directions, respectively. In this paper, we present a new DMUA design approach based on different sampling of the shared concave aperture to improve image quality while maintaining therapeutic performance. A pulse-wave (PW) simulation model using a modified version of the Field II program is used in this study. The model is used in generating pulse-echo data for synthetic-aperture (SA) beamforming for forming images of a variety of targets, e.g., wire arrays and speckle-generating cyst phantoms. To provide validation for the simulation model and illustrate the improvements in image quality, we show SA images of similar targets using pulse-echo data acquired experimentally using our existing 64-element prototype. The PW simulation model is used to investigate the effect of transducer bandwidth as well as finer sampling of the concave DMUA aperture on the image quality. The results show that modest increases in the sampling density and transducer bandwidth result in significant improvement in spatial and contrast resolutions in addition to extending the DMUA IxFOV.

Wan, Yayun; Ebbini, Emad S.

2009-01-01

46

Imaging with concave large-aperture therapeutic ultrasound arrays using conventional synthetic-aperture beamforming.  

PubMed

Several dual-mode ultrasound array (DMUA) systems are being investigated for potential use in image- guided surgery. In therapeutic mode, DMUAs generate pulsed or continuous-wave (CW) high-intensity focused ultrasound (HIFU) beams capable of generating localized therapeutic effects within the focal volume. In imaging mode, pulse-echo data can be collected from the DMUA elements to obtain B-mode images or other forms of feedback on the state of the target tissue before, during, and after the application of the therapeutic HIFU beam. Therapeutic and technological constraints give rise to special characteristics of therapeutic arrays. Specifically, DMUAs have concave apertures with low f-number values and are typically coarsely sampled using directive elements. These characteristics necessitate pre- and post-beamforming signal processing of echo data to improve the spatial and contrast resolution and maximize the image uniformity within the imaging field of view (IxFOV). We have recently developed and experimentally validated beamforming algorithms for concave large-aperture DMUAs with directive elements. Experimental validation was performed using a 1 MHz, 64-element, concave spherical aperture with 100 mm radius of curvature. The aperture was sampled in the lateral direction using elongated elements 1-lambda x 33.3-lambda with 1.333-lambda center-to-center spacing (lambda is the wavelength). This resulted in f-number values of 0.8 and 2 in the azimuth and elevation directions, respectively. In this paper, we present a new DMUA design approach based on different sampling of the shared concave aperture to improve image quality while maintaining therapeutic performance. A pulse-wave (PW) simulation model using a modified version of the Field II program is used in this study. The model is used in generating pulse-echo data for synthetic-aperture (SA) beamforming for forming images of a variety of targets, e.g., wire arrays and speckle-generating cyst phantoms. To provide validation for the simulation model and illustrate the improvements in image quality, we show SA images of similar targets using pulse-echo data acquired experimentally using our existing 64-element prototype. The PW simulation model is used to investigate the effect of transducer bandwidth as well as finer sampling of the concave DMUA aperture on the image quality. The results show that modest increases in the sampling density and transducer bandwidth result in significant improvement in spatial and contrast resolutions in addition to extending the DMUA IxFOV. PMID:18986915

Wan, Yayun; Ebbini, Emad S

2008-08-01

47

Efficient second harmonic conversion of broad-band high-peak-power Nd:glass laser radiation using large-aperture KDP crystals in quadrature  

Microsoft Academic Search

The authors have investigated the second-harmonic conversion efficiency of broadband Nd:glass laser light (??\\/c<30 cm-1 FWHM). Using two KDP crystals in a quadrature arrangement, they obtain energy conversion efficiencies of ≈55% with an initial bandwidth for the fundamental of ??\\/c≈17 cm-1 FWHM. For these conditions, a modest increase (≈70%) was observed in the harmonic bandwidth (FWHM) relative to the fundamental.

MARK S. PRONKO; ROBERT H. LEHMBERG; S. Obenschain; CARL J. PAWLEY; CHARLES K. MANKA; R. Eckardt

1990-01-01

48

Photoreadout statistics analysis during space objects image acquisition in large aperture telescope  

NASA Astrophysics Data System (ADS)

The prospects for image recovery of space objects, observed in the visible range through the turbulent atmosphere by using large aperture telescope, were discussed and evaluated. A "dual" adaptation was introduced: at first - hardware adaptation, using reflected solar radiation from the space object or laser star, then algorithmic. We considered two scenarios for observation. The criterion of image quality was chosen to be potentially full compensation of phase distortion. The characteristics of photoreadout statistics for the various scenarios were analyzed.

Shumilov, Yu. P.; Bakut, P. A.; Vygon, V. G.; Grishin, E. A.; Shargorodskii, V. D.

2013-05-01

49

The LAGO (Large Aperture GRB Observatory) in Peru  

NASA Astrophysics Data System (ADS)

The Large Aperture GRBs Observatory is a continental-wide observatory devised to detect high energy (around 100 GeV) component of Gamma Ray Bursts (GRBs), by using the single particle technique in arrays of Water Cherenkov Detectors (WCDs) at high mountain sites of Argentina, Bolivia, Colombia, Guatemala, Mexico, Venezuela and Peru. Details of the instalation and operation of the detectors in Marcapomacocha in Peru at 4550 m.a.s.l. are given. The detector calibration method will also be shown.

Tueros-Cuadros, E.; Otiniano, L.; Chirinos, J.; Soncco, C.; Guevara-Day, W.

2012-07-01

50

Propagation properties of apertured laser beams with amplitude modulations and phase fluctuations through atmospheric turbulence  

NASA Astrophysics Data System (ADS)

The propagation properties of apertured laser beams with amplitude modulations (AMs) and phase fluctuations (PFs) through atmospheric turbulence are studied in detail both analytically and numerically. The analytical expressions for the average intensity, power in the bucket ( PIB) and Strehl ratio ( S R ) of apertured laser beams with AMs and PFs propagating through atmospheric turbulence are derived. It is found that the worse the phase fluctuation and the higher the amplitude modulation are, the less laser beams are affected by turbulence. Furthermore, apertured Gaussian beams are more sensitive to turbulence than apertured laser beams with AMs and PFs. The average intensity of apertured laser beams with AMs and PFs may be even larger than that of apertured Gaussian beams due to turbulence. In particular, the influence of turbulence on the average maximum intensity of apertured laser beams with PFs and AMs may become serious if an unsuitable truncated parameter is chosen, which should be avoided in practice.

Ji, X.; Li, X.

2011-07-01

51

Pulse power requirements for large aperture optical switches based on plasma electrode Pockels cells  

SciTech Connect

We discuss very large-aperture optical switches (greater than 30 [times] 30 cm) as an enabling technology for inertial confinement fusion drivers based on multipass laser amplifiers. Large-scale laser fusion drivers such as the Nova laser have been based on single-pass amplifier designs in part because of the unavailability of a suitable large-aperture switch. We are developing an optical switch based on a Pockels cell employing plasma-electrodes. A plasma-electrode Pockels cell (PEPC) is a longitudinal-mode Pockels cell in which a plasma discharge is formed on each side of an electro-optic crystal (typically KDP or deuterated KDP, often designated KD*P). The plasmas formed on either side of the crystal act as transparent electrodes for a switching-pulse and are intended to allow uniform charging of the entire crystal. The switching-pulse is a nominally rectangular high-voltage pulse equal to the half-wave voltage V[sub x] ( 8 kV for KD*P or 17 kV for KDP) and is applied across the crystal via the plasma-electrodes. When the crystal is charged to V[sub x], the polarization of an incoming, linearly polarized, laser beam is rotated by 90[degree]. When used in conjunction with an appropriate, passive polarizer, an optical switch is thus realized. A switch with a clear aperture of 37 [times] 37 cm is now in construction for the Beamlet laser which will serve as a test bed for this switch as well as other technologies required for an advanced NOVA laser design. In this paper, we discuss the unique power electronics requirements of PEPC optical switches.

Rhodes, M.A.; Taylor, J.

1992-06-01

52

Pulse power requirements for large aperture optical switches based on plasma electrode Pockels cells  

SciTech Connect

We discuss very large-aperture optical switches (greater than 30 {times} 30 cm) as an enabling technology for inertial confinement fusion drivers based on multipass laser amplifiers. Large-scale laser fusion drivers such as the Nova laser have been based on single-pass amplifier designs in part because of the unavailability of a suitable large-aperture switch. We are developing an optical switch based on a Pockels cell employing plasma-electrodes. A plasma-electrode Pockels cell (PEPC) is a longitudinal-mode Pockels cell in which a plasma discharge is formed on each side of an electro-optic crystal (typically KDP or deuterated KDP, often designated KD*P). The plasmas formed on either side of the crystal act as transparent electrodes for a switching-pulse and are intended to allow uniform charging of the entire crystal. The switching-pulse is a nominally rectangular high-voltage pulse equal to the half-wave voltage V{sub x} ( 8 kV for KD*P or 17 kV for KDP) and is applied across the crystal via the plasma-electrodes. When the crystal is charged to V{sub x}, the polarization of an incoming, linearly polarized, laser beam is rotated by 90{degree}. When used in conjunction with an appropriate, passive polarizer, an optical switch is thus realized. A switch with a clear aperture of 37 {times} 37 cm is now in construction for the Beamlet laser which will serve as a test bed for this switch as well as other technologies required for an advanced NOVA laser design. In this paper, we discuss the unique power electronics requirements of PEPC optical switches.

Rhodes, M.A.; Taylor, J.

1992-06-01

53

Pulse power requirements for large aperture optical switches based on plasma electrode Pockels cells  

NASA Astrophysics Data System (ADS)

We discuss very large-aperture optical switches (greater than 30 x 30 cm) as an enabling technology for inertial confinement fusion drivers based on multipass laser amplifiers. Large-scale laser fusion drivers such as the Nova laser have been based on single-pass amplifier designs in part because of the unavailability of a suitable large-aperture switch. We are developing an optical switch based on a Pockels cell employing plasma-electrodes. A plasma-electrode Pockels cell (PEPC) is a longitudinal-mode Pockels cell in which a plasma discharge is formed on each side of an electro-optic crystal (typically KDP or deuterated KDP, often designated KD*P). The plasmas formed on either side of the crystal act as transparent electrodes for a switching-pulse and are intended to allow uniform charging of the entire crystal. The switching-pulse is a nominally rectangular high-voltage pulse equal to the half-wave voltage V(sub x) (8 kV for KD*P or 17 kV for KDP) and is applied across the crystal via the plasma-electrodes. When the crystal is charged to V(sub x), the polarization of an incoming, linearly polarized, laser beam is rotated by 90 degree. When used in conjunction with an appropriate, passive polarizer, an optical switch is thus realized. A switch with a clear aperture of 37 x 37 cm is now in construction for the Beamlet laser which will serve as a test bed for this switch as well as other technologies required for an advanced NOVA laser design. In this paper, we discuss the unique power electronics requirements of PEPC optical switches.

Rhodes, M. A.; Taylor, J.

1992-06-01

54

Performance Impacts for Actuator Misalignments and Failures in Large-Aperture Adaptive-Optic Telescopes.  

National Technical Information Service (NTIS)

Large-aperture telescopes require adaptive optics in order to compensate for atmospheric turbulence which would otherwise negate the resolution advantages of using large apertures. This investigation analyzes the impacts of misalignments and failures, in ...

T. D. Hogan

1993-01-01

55

Autofocus algorithm for synthetic aperture radar imaging with large curvilinear apertures  

NASA Astrophysics Data System (ADS)

An approach to autofocusing for large curved synthetic aperture radar (SAR) apertures is presented. Its essential feature is that phase corrections are being extracted not directly from SAR images, but rather from reconstructed SAR phase-history data representing windowed patches of the scene, of sizes sufficiently small to allow the linearization of the forward- and back-projection formulae. The algorithm processes data associated with each patch independently and in two steps. The first step employs a phase-gradient-type method in which phase correction compensating (possibly rapid) trajectory perturbations are estimated from the reconstructed phase history for the dominant scattering point on the patch. The second step uses phase-gradient-corrected data and extracts the absolute phase value, removing in this way phase ambiguities and reducing possible imperfections of the first stage, and providing the distances between the sensor and the scattering point with accuracy comparable to the wavelength. The features of the proposed autofocusing method are illustrated in its applications to intentionally corrupted small-scene 2006 Gotcha data. The examples include the extraction of absolute phases (ranges) for selected prominent point targets. They are then used to focus the scene and determine relative target-target distances.

Bleszynski, E.; Bleszynski, M.; Jaroszewicz, T.

2013-05-01

56

Laser aperture diagnostics system for gain and wavefront measurements on NIF/LMJ amplifiers  

SciTech Connect

We are in the midst of constructing an amplifier laboratory (Arnplab) that will be the physics and engineering proving ground for fill sized segmented glass amplifiers of designs that will outfit the National Ignition Facility (NIF) and Laser Megajoule (LMJ) projects. Amplab will demonstrate the cornerstone mechanical, electrical and optical concepts that support the NW and LMJ amplifier schemes. Here we address the optical diagnostics that will be used to characterize optical performance of the amplifiers. We describe, the apparatus that will be used in pulsed measurements of gain distribution and wave-front distortions. The large aperture diagnostic system or LADS, is now being built through a collaborative effort between CEL-V and LLNL. The LADS will provide measurements of gain and wave front distortions over the fill extracting aperture of the NIF and LMJ prototype amplifiers. The LADS will be able to address each of eight apertures via motorized stages and following semi-automated alignment, take data on the aperture of interest. The LADS should be operational in mid-1997 at LLNL and will be used to characterize the optical performance of the very first fill scale prototype 4 x 2 NIF and LMJ amplifiers. It will be transported to Bordeaux, France to make similar measurements during activation of the first 8-aperture LMJ-like facility (LIL) that is planned to start in the near future.

Zapata, L. E., LLNL

1996-12-17

57

Design of large aperture, low mass vacuum windows  

SciTech Connect

Large vacuum vessels are employed downstream of fixed targets in High Energy Physics experiments to provide a long path for particles to traverse without interacting with air molecules. These vessels generally have a large aperture opening known as a vacuum window which employs a thin membrane to preserve the vacuum environment yet allows the particles to pass through with a minimal effect on them. Several large windows have been built using a composite of Kevlar/Mylar including circular windows to a diameter of 96.5 cm and rectangular windows up to 193 cm x 86 cm. This paper describes the design, fabrication, testing and operating experience with these windows and relates the actual performance to theoretical predictions.

Leonhardt, W.J.; Mapes, M.

1993-01-01

58

Design of large aperture, low mass vacuum windows  

SciTech Connect

Large aperture, low mass, thin vacuum windows are required to minimize beam loss in the beam lines of particle accelerators as the products of nuclear collisions move from upstream targets to downstream detectors. This article describes the design, fabrication, testing, and operating experience of a large rectangular vacuum window, 122 cm[times]61 cm, and two circular windows of 91.4 and 96.5 cm diam. These window designs utilize a composite Kevlar 29 fabric and Mylar laminate as a window material with a typical combined thickness of 0.35 mm. Data for several material thicknesses are also presented. The windows are usually designed to withstand a pressure differential of two to three atmospheres to achieve the required factor of safety. These windows are typically used in the medium vacuum range of 10[sup [minus]4] Torr. The equations used to predict the behavior of the window material will also be discussed.

Mapes, M.; Leonhardt, W.J. (Brookhaven National Laboratory, Upton, New York 11973 (United States))

1993-07-01

59

Optical aligning and measuring methods for large aperture optical system  

NASA Astrophysics Data System (ADS)

How to implement high accuracy measurement of large-aperture coaxial optical system is crucial to the optical alignment and optical property evaluation. The methods of image quality measurement including interferometer-collimating testing, wave front testing by using Hartmann, image processing and analysis of out-of-focus image were introduced. Both the advantages and disadvantages of the three methods were compared, which showed that the alignment method based on interferometer-collimating testing is the one with the highest accuracy. The method of computer-aided alignment (CAA) based on interferometer-collimating was discussed in detail. By using a ZYGO interferometer, interferograms with different field of views and a series of Zernike coefficients were obtained to express the disalignment of the system, and then these incorrect parameters were calculated by CAA algorithms. An alignment experiment of coaxial three-mirror system with 4m focal length and 500mm aperture was carried out. The RMS value of the system is lower than 0.07? after iterations, which is close to the optical diffraction limit, proving the effectiveness of CAA method in alignment guidance.

Zhang, Xue-min; Wei, Ru-yi; Duan, Jia-you; Yang, Jian-feng; Li, Hua; Hou, Xiaohua

2012-10-01

60

Development of an efficient large-aperture high damage-threshold sol-gel diffraction grating.  

SciTech Connect

In order to develop the next generation of high peak intensity lasers, new grating technology providing higher damage thresholds and large apertures is required. The current assumption is that this technical innovation will be multilayer dielectric gratings, wherein the uppermost layer of a thin film mirror is etched to create the desired binary phase grating. A variant of this is explored with the upper grating layer being a lower density gelatin-based volume phase grating in either sol-gel or dichromated gelatin. One key benefit is the elimination of the etching step.

Ashley, Carol S.; Rambo, Patrick K.; Schwarz, Jens; Dunphy, Darren Robert; Branson, Eric D.; Smith, Ian Craig; Johnson, William Arthur; Reed, Scott T.; Cook, Adam W.

2005-03-01

61

A large aperture magnification lens for velocity map imaging  

NASA Astrophysics Data System (ADS)

We have designed and implemented a large aperture electrostatic Einzel lens that magnifies the images of low energy ions or electrons in a standard velocity map imaging apparatus by up to a factor of 5 while allowing the normal use of the apparatus (without blocking any part of the detector). The field strength in the interaction region remains reasonably constant with or without magnification, and the lens can be used in the normal ``crush'' mode or with any of the different variants of the ``slicing'' mode. We have characterized the performance of the lens by imaging ion recoil due to two-photon resonant three-photon ionization [(2+1) REMPI] of O(3P2) atoms and by imaging slow NO molecules from the near-threshold photodissociation of the NO-Ar van der Waals complex.

Zhang, Yongwei; Yang, Chung-Hsin; Wu, Shiou-Min; van Roij, Andre; van der Zande, Wim J.; Parker, David H.; Yang, Xueming

2011-01-01

62

Development of a large aperture Nb3Sn racetrack quadrupolemagnet  

SciTech Connect

The U.S. LHC Accelerator Research Program (LARP), a collaboration between BNL, FNAL, LBNL, and SLAC, has among its major objectives the development of advanced magnet technology for an LHC luminosity upgrade. The LBNL Superconducting Magnet Group supports this program with a broad effort involving design studies, Nb{sub 3}Sn conductor development, mechanical models, and basic prototypes. This paper describes the development of a large aperture Nb{sub 3}Sn racetrack quadrupole magnet using four racetrack coils from the LBNL Subscale Magnet (SM) Program. The magnet provides a gradient of 95 T/m in a 110 mm bore, with a peak field in the conductor of 11.2 T. The coils are prestressed by a mechanical structure based on a pre-tensioned aluminum shell, and axially supported with aluminum rods. The mechanical behavior has been monitored with strain gauges and the magnetic field has been measured. Results of the test are reported and analyzed.

Ferracin, Paolo; Bartlett, Scott E.; Caspi, Shlomo; Dietderich,Daniel R.; Gourlay, Steven A.; Hannaford, Charles R.; Hafalia, AurelioR.; Lietzke, Alan F.; Mattafirri, Sara; McInturff, Alfred D.; Nyman,Mark; Sabbi, Gianluca

2005-04-14

63

A large aperture blackbody bath for calibration of thermal imagers  

NASA Astrophysics Data System (ADS)

Thermal imagers are becoming widely used instruments for noncontact absolute temperature measurements as opposed to previous practice when they were mostly used to measure temperature differences. To assure accurate and reliable absolute temperature measurements, a calibration procedure including evaluation of the thermal imager entire field of view (FOV) is needed. The challenge was to construct a large aperture blackbody, covering the complete FOV of the thermal imager and having better stability and non-uniformity than the thermal sensitivity of the imager. The blackbody calibration bath was designed on hypothesis analogous to the multi zone furnace, where the role of electrical heaters was superseded by electrically controlled valves. The experimental work showed that the designed system enables traceable calibration of thermal imagers in the temperature range from 10 to 70 °C with the expanded uncertainty of 0.2 °C, while further investigations are needed to cover ranges beyond that.

Miklavec, A.; Pušnik, I.; Batagelj, V.; Drnovšek, J.

2013-02-01

64

Radial support analysis for large-aperture rotating wedge prism  

NASA Astrophysics Data System (ADS)

The different radial support ways for a rotation prism are presented to evaluate the strains and stresses induced by the gravity action and the thermal effects. Due to the large-aperture, non-uniform quality distribution and especially rotation from 0° to 360°, neither the multi-point support way nor the full surface-contact support can well meet the assembly requirements. The paper proposes a novel project of an adjustable partial surface-contact support way to solve this support problem. The maximum strain and stress under this support way both are less than the tolerance limit of the strength assurance regardless of the prism rotating to any position. Meanwhile, the thermally-induced structural analysis is performed to predict some specific work cases, which is much valuable for the improvement of the assembly design.

Li, Anhu; Jiang, Xuchun; Sun, Jianfeng; Bian, Yongming; Wang, Lijuan; Liu, Liren

2012-09-01

65

Design considerations for a large aperture high field superconducting dipole  

SciTech Connect

The final phase of the Fermilab upgrade proposal calls for a new ring of superconducting magnets to be placed in the existing Main Accelerator tunnel. The goal of this design study is to specify a high field dipole (HFD) that is capable of supporting fixed target operation (ramping, resonant extraction) at a field of 6.6T (1.5 Tev) and colliding beam physics at 8.0T (1.8 Tev). The magnetic field quality at high field is set by the large amplitude orbits associated with resonant extraction. The field quality must therefore be at least as good as the existing Tevatron magnets which fulfill these criteria. The high fields and large aperture of this magnet result in large forces on the coil and collar assemblies. Therefore, the cold mass design must be able to sustain these forces while providing sufficient cooling to the coils during 4.2 K fixed target operation, and a minimum heat load during 1.8 K collider operation. The design work is still in progress but a cosine-theta, cold-iron dipole with a 70mm inner diameter coil has been tentatively adopted. This report presents details on the conductor and cable parameters, coil cross-section, projected manufacturing tolerances, iron yoke design, and cold mass assembly. 4 refs., 5 figs., 1 tab.

Harfoush, F.; Ankenbrandt, C.; Harrison, M.; Kerby, J.; Koepke, K.; Mantsch, P.; Nicol, T.; Riddiford, A.; Theilacker, J.

1989-03-01

66

Low mass large aperture vacuum window development at CEBAF  

SciTech Connect

Large aperture low mass vacuum windows are being developed for the HMS (High Momentum Spectrometer) and SOS (Short Orbit Spectrometer) spectrometers in Hall C at CEBAF. Because multiple scattering degrades the performance of a spectrometer it is important that the volume be evacuated and that the entrance and exit windows be as low mass as possible. The material used for such windows must be thin and light enough so as to have minimum effect of the beam, and at the same time, be thick and strong enough to operate reliably and safely. To achieve these goals, composite vacuum windows have been constructed of a thin sheet of Mylar with a reinforcing fabric. Reinforcing fabrics such as Kevlar and Spectra are available with tensile strengths significantly greater than that of Mylar. A thin layer of Myler remains necessary since the fabrics cannot achieve any sort of vacuum seal. The design, fabrication, testing, and operating experience with such composite windows for the Hall C spectrometers will be discussed.

Keppel, C.

1995-04-01

67

The Balloon-borne Large Aperture Submillimeter Telescope: BLAST  

NASA Astrophysics Data System (ADS)

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a suborbital surveying experiment designed to study the evolutionary history and processes of star formation in local galaxies (including the Milky Way) and galaxies at cosmological distances. The BLAST continuum camera, which consists of 270 detectors distributed between three arrays, observes simultaneously in broadband (30%) spectral windows at 250, 350, and 500 ?m. The optical design is based on a 2 m diameter telescope, providing a diffraction-limited resolution of 30" at 250 ?m. The gondola pointing system enables raster mapping of arbitrary geometry, with a repeatable positional accuracy of ~30" postflight pointing reconstruction to <~5" rms is achieved. The onboard telescope control software permits autonomous execution of a preselected set of maps, with the option of manual override. In this paper we describe the primary characteristics and measured in-flight performance of BLAST. BLAST performed a test flight in 2003 and has since made two scientifically productive long-duration balloon flights: a 100 hr flight from ESRANGE (Kiruna), Sweden to Victoria Island, northern Canada in 2005 June; and a 250 hr, circumpolar flight from McMurdo Station, Antarctica, in 2006 December.

Pascale, E.; Ade, P. A. R.; Bock, J. J.; Chapin, E. L.; Chung, J.; Devlin, M. J.; Dicker, S.; Griffin, M.; Gundersen, J. O.; Halpern, M.; Hargrave, P. C.; Hughes, D. H.; Klein, J.; MacTavish, C. J.; Marsden, G.; Martin, P. G.; Martin, T. G.; Mauskopf, P.; Netterfield, C. B.; Olmi, L.; Patanchon, G.; Rex, M.; Scott, D.; Semisch, C.; Thomas, N.; Truch, M. D. P.; Tucker, C.; Tucker, G. S.; Viero, M. P.; Wiebe, D. V.

2008-07-01

68

X-ray prism lenses with large apertures  

Microsoft Academic Search

Existing refractive X-ray lenses are characterized by either small apertures due to high absorption in the border areas. They can only be used with synchrotron sources, offering high brilliance. By increasing transparency and aperture the range of applications will expand, common X-ray tubes might turn out to be reasonable X-ray sources in an application with X-ray lenses. A basic concept

M. Simon; E. Reznikova; V. Nazmov; A. Last; W. Jark

2008-01-01

69

Large- and Small-Aperture Fixed-Point Cells of Cu, Pt C, and Re C  

NASA Astrophysics Data System (ADS)

Extending the application of metal (carbide) carbon eutectic fixed-point cells to radiometry, e.g., for measurements in irradiance mode, requires fixed-point cells with large apertures. In order to make large-aperture cells more readily usable in furnace systems with smaller furnace tubes commonly used for small-aperture fixed-point cells, a novel cell design was developed. For each of Cu, Pt C, and Re C fixed points, two types of fixed-point cells were manufactured, the small- and large-aperture cell. For Pt C and Re C, the large-aperture cells were filled with a hyper-eutectic metal carbon mixture; for the small cells, a hypo-eutectic mixture was used for filling. For each material, the small and large cells were compared with respect to radiometric differences. Whereas plateau shape and melting temperature are in good agreement for the small- and large-aperture Cu cells, a larger difference was observed between small- and large-aperture cells of Pt C and Re C, respectively. The origin of these observations, attributed to the temperature distribution inside the furnace, ingot contamination during manufacture, and non-uniform ingot formation for the larger cells, is discussed. The comparison of measurements by a radiation thermometer and filter radiometer of the Re C and Pt C large-aperture cells showed large differences that could be explained only by a strong radiance distribution across the cavity bottom. Further investigations are envisaged to clarify the cause.

Anhalt, Klaus; Wang, Yunfen; Yamada, Yoshiro; Hartmann, Jürgen

2008-06-01

70

Multidimensional maximum-likelihood processing of a large aperture seismic array  

Microsoft Academic Search

The experimental Large Aperture Seismic Array (LASA) represents an attempt to improve the capability to monitor underground nuclear weapons tests and small earthquakes by making a large extrapolation in the existing art of building arrays of spaced and interconnected seismic transducers. The LASA is roughly equivalent to 21 separate subarrays, each consisting of 25 sensors, spread over an aperture of

J. Capon; R. J. Greenfield; R. J. Kolker

1967-01-01

71

Performance impacts for actuator misalignments and failures in large-aperture adaptive-optic telescopes  

Microsoft Academic Search

Large-aperture telescopes require adaptive optics in order to compensate for atmospheric turbulence which would otherwise negate the resolution advantages of using large apertures. This investigation analyzes the impacts of misalignments and failures, in the deformable mirror actuators, upon the performance of such systems. A numerical simulation of a standard adaptive optics system is used to generate characteristic optical transfer function

Timothy D. Hogan

1993-01-01

72

A study of very small aperture lasers (VSAL) for near field optical recording  

NASA Astrophysics Data System (ADS)

A practical approach for producing very small aperture lasers (VSAL) from low-cost, commercial index guided edge-emitting diode lasers was developed. Detailed fabrication procedures are provided and rationales behind the design choices were explained. For the trickiest issue in the fabrication processes, three solutions were provided to locate the active layer for aperturing. Between 100200 units of VSALs were successfully fabricated and used for a number of studies. Focused Ion Beam (FIB) operating parameters for best nano-structure etching resolution are discussed. In practice, apertures as small as 30nm in size were achieved. Size dependent etching rate for nano-apertures was observed experimentally and re-deposition was hypothesized as the explanation. A VSAL far-field power measurement method was established. It was used as a calibration tool for VSAL power throughput optimization. Using this system, three fabrication parameters were studied: the metal layer thickness, dielectric layer thickness and the aperture size. It was found that the ideal Al thickness is 50nm˜60nm and that the aperture power decays in proportion to the sixth power of aperture size when it is below 150nm. This is consistent with the near-field theory. Aperture shape and geometry were also investigated. The most important result was to apply the waveguide theory to the VSAL aperture. By using overlap integral approximation and a lossy waveguide model, the throughput of rectangular apertures with a linearly polarized incident field was simulated. By comparing experimental and simulation results, it was proved that near-field nano-apertures behave like waveguides in cutoff. High throughput geometries were fabricated and higher powers were obtained. A cutoff waveguide approach was also applied to obtain the minimum aperture size limit for recording and explain near-field scanning optical microscopy (NSOM) probe's low throughput. On the device level, the threshold current changes during the fabrication processes were observed, explained and quantified. The tiny increase of threshold current due to aperturing could have great significance for phase change media readback or aperture near-field power estimation. The polarization property of the aperture emission was compared with that of the original laser. An improved polarization ratio of the aperture emission indicates polarization selective nature of nano-aperture, which further strengthens the waveguide argument. The angular distribution of the aperture power was measured. (Abstract shortened by UMI.)

Chen, Fang

73

New optimization criteria for slit-apertured and gain-apertured KLM all-solid-state lasers  

Microsoft Academic Search

The aim of this paper is to discuss the limitations of the conventional mode-locking parameter ?, and to introduce new Kerr-lens mode-locking (KLM) criteria that we believe to be more reliable indicators of the preference for mode-locked operation in real-world diode-pumped lasers. The new criteria take into account both the losses at an intra-cavity slit and the gain-aperturing by the

E. J Grace; A Ritsataki; P. M. W French; G. H. C New

2000-01-01

74

New optimization criteria for slit-apertured and gain-apertured KLM all-solid-state lasers  

Microsoft Academic Search

The aim of this paper is to discuss the limitations of the conventional mode-locking parameter \\/delta, and to introduce new Kerr-lens mode-locking (KLM) criteria that we believe to be more reliable indicators of the preference for mode-locked operation in real-world diode-pumped lasers. The new criteria take into account both the losses at an intra-cavity slit and the gain-aperturing by the

E. J. Grace; A. Ritsataki; P. M. W. French; G. H. C. New

2000-01-01

75

Improved design of support for large aperture space lightweight mirror  

NASA Astrophysics Data System (ADS)

In order to design a kind of rational large aperture space mirror which can adapt to the space gravity and thermal environment, by taking the choice of material, the lightweight of the mirror and the design of support into account in detail, a double-deck structure with traditional flexible hinge was designed, then the analytical mathematical model of the mirror system was established. The design adopts six supports on back. in order to avoid the constraints, mirror is connected to three middle transition pieces through six flexible hinges, and then the three transition pieces are connected to support plate through another three flexible hinges. However, the initial structure is unable to reach the expected design target and needs to be made further adjustments. By improving and optimizing the original structure, a new type of flexible hinge in the shape of the letter A is designed finally. Compared with the traditional flexible hinge structure, the new structure is simpler and has less influence on the surface figure accuracy of mirror. By using the finite element analysis method, the static and dynamic characteristics as well as the thermal characteristics of the mirror system are analyzed. Analysis results show that the maximum PV value is 37 nm and the maximum RMS value is 10.4 nm when gravity load is applied. Furthermore, the maximum PV value is 46 nm and the maximum RMS value is 10.5 nm under the load case of gravity coupled with 4? uniform temperature rise. The results satisfy the index of optical design. The first order natural frequency of the mirror component is 130 Hz according to the conclusion obtained by modal analytical solution, so the mirror structure has high enough fundamental frequency. And, the structural strength can meet the demand under the overload and the random vibration environment respectively. It indicates that the mirror component structure has enough dynamic, static stiffness and thermal stability, meeting the design requirements.

Wang, Chao; Ruan, Ping; Liu, Qimin

2013-08-01

76

The Balloon-borne Large Aperture Submillimeter Telescope: BLAST  

NASA Astrophysics Data System (ADS)

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a suborbital surveying experiment designed to study the evolutionary history and processes of star formation in local galaxies (including the Milky Way) and galaxies at cosmological distances. The BLAST continuum camera, which consists of 270 detectors distributed between three arrays, observes simultaneously in broadband (30%) spectral windows at 250, 350, and 500 microns. The optical design is based on a 2 m diameter telescope, providing a diffraction-limited resolution of 30" at 250 microns. The gondola pointing system enables raster mapping of arbitrary geometry, with a repeatable positional accuracy of 30"; postflight pointing reconstruction to <5" rms is achieved. The onboard telescope control software permits autonomous execution of a preselected set of maps, with the option of manual override. On this poster, we describe the primary characteristics and measured in-flight performance of BLAST. BLAST performed a test flight in 2003 and has since made two scientifically productive long-duration balloon flights: a 100 hour flight from ESRANGE (Kiruna), Sweden to Victoria Island, northern Canada in 2005 June; and a 250 hour, circumpolar flight from McMurdo Station, Antarctica in 2006 December. The BLAST collaboration acknowledges the support of NASA through grants NAG5-12785, NAG5-13301, and NNGO-6GI11G, the Canadian Space Agency (CSA), the Science and Technology Facilities Council (STFC), Canada's Natural Sciences and Engineering Research Council (NSERC), the Canada Foundation for Innovation, the Ontario Innovation Trust, the Puerto Rico Space Grant Consortium, the Fondo Institucional para la Investigacion of the University of Puerto Rico, and the National Science Foundation Office of Polar Programs.

Truch, Matthew D. P.; Ade, P. A. R.; Bock, J. J.; Chapin, E. L.; Chung, J.; Devlin, M. J.; Dicker, S.; Griffin, M.; Gundersen, J. O.; Halpern, M.; Hargrave, P. C.; Hughes, D. H.; Klein, J.; MacTavish, C. J.; Marsden, G.; Martin, P. G.; Martin, T. G.; Mauskopf, P.; Netterfield, C. B.; Olmi, L.; Pascale, E.; Patanchon, G.; Rex, M.; Scott, D.; Semisch, C.; Thomas, N. E.; Tucker, C.; Tucker, G. S.; Viero, M. P.; Wiebe, D. V.

2009-01-01

77

A low-cost large-aperture optical receiver for remote sensing and imaging applications  

NASA Astrophysics Data System (ADS)

An inexpensive large aperture (10 m class) receiver for optical wavelength imaging and remote sensing applications is discussed. The design was developed for active (laser illumination) imaging of remote objects using pupil plane measurement techniques, where relatively low optical quality collecting elements can be used. The approach is also well suited for conventional imaging at lower resolutions when light collection capability is of primary importance. The approach relies on a large aperture heliostat consisting of an array of flat mirror segments, like those used in solar collector systems, to collect light from the region of interest. The heliostat segments are tilted in a manner to concentrate the light, by making the light from all segments overlap at a common point, resulting in a region of higher intensity about the size of a segment at the heliostat "focus". A smaller secondary collector, consisting of a concave mirror located at the overlap point, further concentrates the light and forms a pupil image of the heliostat. Additional optics near the pupil image collimate the light for efficient transmission though a narrow band interference filter used to reduce sky background, and focus the light onto a PMT, or other sensor, for detection. Several design approaches for the collimating optics are discussed as well as system performance and limitations.

Hanes, Stephen A.

2003-03-01

78

Annular polishing of large-aperture Nd-doped metaphosphate glasses  

NASA Astrophysics Data System (ADS)

Large-aperture Nd-doped metaphosphate glasses are used in high-power/high-energy laser facilities. High transmission wave front accuracy of Nd-doped metaphosphate glasses is required to decrease beam distortion, which affects the focus ability and damages optical components. Elliptical shape astigmatism of the transmission wave front easily occurs when Nd-doped metaphosphate glasses are detected and utilized at Brewster incident angle compared with zero angle. The astigmatism is difficult to decrease for precision annular polishing because the surface profile adjustment of the polishing pitch plane has low accuracy. Non-uniform removal at different velocity rates between the pitch plane and Nd-doped metaphosphate glasses can be used to eliminate horizontal elliptical-shaped astigmatism. The improved process contributes to the production of high-efficiency Nd-doped metaphosphate glasses.

Shan, Haiyang; Xu, Xueke; He, Hongbo; Wu, Fulin; Yi, Kui; Shao, Jianda

2013-07-01

79

In-situ monitoring of surface post-processing in large aperture fused silica optics with Optical Coherence Tomography  

SciTech Connect

Optical Coherence Tomography is explored as a method to image laser-damage sites located on the surface of large aperture fused silica optics during post-processing via CO{sub 2} laser ablation. The signal analysis for image acquisition was adapted to meet the sensitivity requirements for this application. A long-working distance geometry was employed to allow imaging through the opposite surface of the 5-cm thick optic. The experimental results demonstrate the potential of OCT for remote monitoring of transparent material processing applications.

Guss, G M; Bass, I l; Hackel, R P; Mailhiot, C; Demos, S G

2008-02-08

80

Ablation of silicon by focusing a femtosecond laser through a subwavelength annular aperture structure  

Microsoft Academic Search

We experimentally examined the effect of laser energy fluence on the ablation of a silicon wafer using a Ti:sapphire femtosecond laser system. A femtosecond laser was focused through an oxide-metal-oxide (Al2O3\\/Al\\/Al2O3) film engraved with a subwavelength annular aperture (SAA) structure, i.e., a Bessel beam composed of a femtosecond laser created using a SAA. The optical performance, such as depth-of-focus (DOF)

Y. Y. Yu; C. K. Chang; M. W. Lai; L. S. Huang; C. K. Lee

2010-01-01

81

Aberrations and focusability in large solid-state-laser systems  

SciTech Connect

Solid state lasers for fusion experiments must reliably deliver maximum power to small (approximately .5 mm) targets from stand-off focal distances of 1 m or more. This requirement places stringent limits upon the optical quality of the several major components - amplifiers, Faraday isolators, spatial filters - in each amplifier train. Residual static aberrations in optical components are transferred to the beam as it traverses the optical amplifier chain. Although individual components are typically less than lambda/20 for components less than 10 cm clear aperture; and less than lambda/10 for components less than 20 cm clear aperture; the large number of such components in optical series results in a wavefront error that may exceed one wave for modern solid state lasers. For pulse operation, the focal spot is additionally broadened by intensity dependent nonlinearities. Specific examples of the performance of large aperture components will be presented within the context of the Argus and Shiva laser systems, which are presently operational at Lawrence Livermore National Laboratory. Design requirements upon the larger aperture Nova laser components, up to 74 cm in clear aperture, will also be discussed; these pose a significant challenge to the optical industry.

Simmons, W.W.

1981-01-01

82

Time dependence of Fresnel diffraction of ultrashort laser pulses by a circular aperture.  

PubMed

We report on the time dependences of the Fresnel diffraction of ultrashort laser pulses by a circular aperture. The diffraction leads to a pulse delay, time shape change, pulse broadening, and peak power decrease. These effects may have to be taken into account whenever critical thresholds are encountered as, for example, in nonlinear optics or laser fusion. PMID:18259222

Jiang, Z; Jacquemin, R; Eberhardt, W

1997-07-01

83

ULTIMA free-flying large-aperture space telescope  

NASA Astrophysics Data System (ADS)

Project ULTIMA is an investigation into the feasibility of building ultralarge aperture visible/mid-LR space telescopes. A promising concept found by the study is a freely flying spherical primary mirror, 20 m or more in diameter, located at the L1 or L2 Earth-sun libration point. The primary would be passively cooled to 45 K. There would be no metering structure. Instead, using a combination of alignment and steering mirrors, reaction wheels, and microthrusters, the aspherical secondary mirror, active tertiary mirror, and focal plane instruments would be precisely stationed in the correct position above the primary. The primary advanced composition would be either a membrane or ultralight segmented technology. Preliminary findings show that a 20-30-m telescope may be feasible for imaging in the 1-20-micron regime.

Campbell, Jonathan W.; Taylor, Charles R.

1997-01-01

84

Large-aperture, tapered fiber-coupled, 10-kHz particle-image velocimetry.  

PubMed

We demonstrate the design and implementation of a fiber-optic beam-delivery system using a large-aperture, tapered step-index fiber for high-speed particle-image velocimetry (PIV) in turbulent combustion flows. The tapered fiber in conjunction with a diffractive-optical-element (DOE) fiber-optic coupler significantly increases the damage threshold of the fiber, enabling fiber-optic beam delivery of sufficient nanosecond, 532-nm, laser pulse energy for high-speed PIV measurements. The fiber successfully transmits 1-kHz and 10-kHz laser pulses with energies of 5.3 mJ and 2 mJ, respectively, for more than 25 min without any indication of damage. It is experimentally demonstrated that the tapered fiber possesses the high coupling efficiency (~80%) and moderate beam quality for PIV. Additionally, the nearly uniform output-beam profile exiting the fiber is ideal for PIV applications. Comparative PIV measurements are made using a conventionally (bulk-optic) delivered light sheet, and a similar order of measurement accuracy is obtained with and without fiber coupling. Effective use of fiber-coupled, 10-kHz PIV is demonstrated for instantaneous 2D velocity-field measurements in turbulent reacting flows. Proof-of-concept measurements show significant promise for the performance of fiber-coupled, high-speed PIV using a tapered optical fiber in harsh laser-diagnostic environments such as those encountered in gas-turbine test beds and the cylinder of a combustion engine. PMID:23481818

Hsu, Paul S; Roy, Sukesh; Jiang, Naibo; Gord, James R

2013-02-11

85

34 GB Multilevel-Enabled Rewritable System Using Blue Laser and High-Numeric Aperture Optics  

NASA Astrophysics Data System (ADS)

Multilevel (ML) technology increases storage capacity and data transfer rates of an optical data storage system. ML is shown to be a strong candidate for use with a high numeric aperture (NA) and blue-laser system by demonstrating good margin performance.

Hieslmair, Henry; Stinebaugh, Jason; Wong, Terrence; O'Neill, Michael; Kuijper, Maarten; Langereis, Geert

2003-02-01

86

Large-aperture focusing of x rays with micropore optics using dry etching of silicon wafers.  

PubMed

Large-aperture focusing of Al K(?) 1.49 keV x-ray photons using micropore optics made from a dry-etched 4 in. (100 mm) silicon wafer is demonstrated. Sidewalls of the micropores are smoothed with high-temperature annealing to work as x-ray mirrors. The wafer is bent to a spherical shape to collect parallel x rays into a focus. Our result supports that this new type of optics allows for the manufacturing of ultralight-weight and high-performance x-ray imaging optics with large apertures at low cost. PMID:22378391

Ezoe, Yuichiro; Moriyama, Teppei; Ogawa, Tomohiro; Kakiuchi, Takuya; Mitsuishi, Ikuyuki; Mitsuda, Kazuhisa; Aoki, Tatsuhiko; Morishita, Kohei; Nakajima, Kazuo

2012-03-01

87

Adaptive optics technique to overcome the turbulence in a large-aperture collimator.  

PubMed

A collimator with a long focal length and large aperture is a very important apparatus for testing large-aperture optical systems. But it suffers from internal air turbulence, which may limit its performance and reduce the testing accuracy. To overcome this problem, an adaptive optics system is introduced to compensate for the turbulence. This system includes a liquid crystal on silicon device as a wavefront corrector and a Shack-Hartmann wavefront sensor. After correction, we can get a plane wavefront with rms of about 0.017 lambda (lambda=0.6328 microm) emitted out of a larger than 500 mm diameter aperture. The whole system reaches diffraction-limited resolution. PMID:18709077

Mu, Quanquan; Cao, Zhaoliang; Li, Dayu; Hu, Lifa; Xuan, Li

2008-03-20

88

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Influence of the aperture angle on the efficiency of the melting of steel by millisecond laser pulses  

NASA Astrophysics Data System (ADS)

The influence of the divergence and aperture of millisecond laser pulses on the efficiency, the dynamic characteristics, and the depth of the molten zone in steel under conditions ensuring the rapid growth of a vapour — gas channel was investigated experimentally. It was established that the dependence of the efficiency on the aperture angle passes through a maximum, the efficiency and depth-of-melting maxima being attained for an aperture angle of 75 — 80 mrad. The highest rate of growth of the vapour — gas channel is also achieved for these aperture angles. It is pointed out that this aperture angle is optimal and that it should be aimed at in the design of pulsed industrial laser systems.

Kayukov, S. V.; Gusev, A. A.

2000-04-01

89

Field and structural analysis of 56 mm aperture dipole model magnets for the Large Hadron Collider  

Microsoft Academic Search

A new dipole model magnet design has been made with an aperture of 56 mm according to re-optimization of the accelerator design for the Large Hadron Collider (LHC) to be built at CERN, A feature of “symmetric\\/separate collar configuration” in the new design proposed by KEK has been evaluated in terms of field quality and mechanical stability according to the

Naihao Song; Akira Yamamoto; Takakazu Shintomi; Hiromi Hirabayashi; Hiroshi Yamaoka; A. Terashima

1996-01-01

90

Passive sonar limits upon nulling multiple moving ships with large aperture arrays  

Microsoft Academic Search

Large aperture sonar arrays have small resolution cells which (i) limit the number of “snapshots” available for accumulating sample covariance matrices and (ii) resolve the multipath propagation between each source and the array. Moving ships with high bearing rates transit resolution cells quickly setting limits upon short term stationarity assumptions. Usually, this leads to “snapshot deficient” processing which must be

Arthur B. Baggeroer; Henry Cox

1999-01-01

91

Performance characteristics of large aperture, ten-cell, atmospheric pressure isobutane Cherenkov counters  

SciTech Connect

Two large aperture, 10 cell atmospheric-pressure isobutane Cherenkov counters were designed and constructed for a SLAC streamer chamber experiment. The rejection efficiencies for a 9 GeV/c ..pi../sup -/ were measured to be 99.838 +- .006% and 99.717 +- 008% for the two counters. The design details and performance characteristics are discussed.

Hylen, J.; Ma, Z.M.; Jawahery, A.; Maruyama, T.; Milburn, R.; Thornton, R.

1980-05-24

92

A hybridization technique for MLFMM for a large class of cavity backed aperture scattering problems  

Microsoft Academic Search

An efficient technique for the analysis of electromagnetic problems involving large metallic bodies with arbitrary complex interior and a number of apertures is presented. Typical applications for this technique are the computation of EMC related transfer-functions of the electromagnetic field, describing the coupling of energy into complex systems as well as the computation of the RCS of complex cavities in

Arthur Enneking; Jan Ritter; Rainer Bunger

2003-01-01

93

Evapotranspiration fluxes over mixed vegetation areas measured from large aperture scintillometer  

Microsoft Academic Search

Routine measurement of spatially averaged surface fluxes of sensible heat (H) in river basins is now feasible. These fluxes, when combined with net radiation estimates, can be used to derive areally averaged actual evapotranspiration (ET). The scintillation method is shown to be promising method for estimating areally averaged sensible heat fluxes. The large aperture scintillometer (LAS) is an optical device

H. M. Hemakumara; Lalith Chandrapala; Arnold F. Moene

2003-01-01

94

A new method for fabricating high density and large aperture ratio liquid microlens array.  

PubMed

Conventional liquid microlens arrays are facing bottlenecks in controlling droplet size and shape, and limited aperture ratio. We report a new liquid/solvent approach to overcome these obstacles for making uniform droplet array and achieving approximately 90% aperture ratio. The droplets are very stable due to the pinning effect of the polymer walls and substrate surfaces. Using the fabricated droplet array, we demonstrate a tunable-focus microlens array based on dielectrophoretic effect. The microlens array exhibits a large dynamic range and fast response time (tens of milliseconds). Besides liquid microlens arrays, this fabrication method also opens a new door for making other tunable photonic devices. PMID:20052129

Ren, Hongwen; Ren, Daqiu; Wu, Shin-Tson

2009-12-21

95

Experimental Observations of Dual-Polarization Oscillations in Laser-Diode-Pumped Wide-Aperture Thin-Slice Nd:GdVO4 Lasers  

NASA Astrophysics Data System (ADS)

Dual-polarization oscillations (DPO) on different transitions have been observed for the first time in a mirror-coated thin-slice Nd:GdVO4 laser possessing a large fluorescence anisotropy with laser-diode (LD) pumping. Oscillation spectra, input-output characteristics, pump-dependent pattern formations and noise power spectra are studied experimentally. Simultaneous oscillations of orthogonally-polarized different (higher-order) transverse modes and the resultant violation of inherent antiphase dynamics in multimode lasers have been demonstrated. The experimental results have been explained in terms of the reduced three-dimensional cross-saturation of population inversions among orthogonally-polarized modes peculiar to LD-pumped wide-aperture anisotropic lasers, in which a pumped area is larger than a lasing beam diameter.

Ko, Jing-Yuan; Lin, Chi-Ching; Otsuka, Kenju; Miyasaka, Yoshihiko; Kamikariya, Koji; Nemoto, Kana; Ho, Ming-Chung; Jiang, I.-Min

2007-02-01

96

An automatic method for assembling a large synthetic aperture digital hologram.  

PubMed

A major issue so far for digital holography is the low spatial resolution generally achieved. The numerical aperture is limited by the area of currently available detectors, such as CCD sensors, which is significantly lower than that of a holographic plate. This is an even more severe constraint when IR sensors such as microbolometers are taken into account. In order to increase the numerical aperture of such systems, we developed an automatic technique which is capable of recording several holograms and of stitching them together, obtaining a digital hologram with a synthetic but larger numerical aperture. In this way we show that more detail can be resolved and a wider parallax angle can be achieved. The method is demonstrated for visible as well IR digital holography, recording and displaying large size objects. PMID:22418289

Pelagotti, A; Paturzo, M; Locatelli, M; Geltrude, A; Meucci, R; Finizio, A; Ferraro, P

2012-02-27

97

WIDE APERTURE PICOSECOND CO2 LASER SYSTEM: NEW APPLICATIONS  

Microsoft Academic Search

Analysis of possible approaches for powerful CO2 laser system utilization in experiments on difference frequency ge n- eration shows that it is possible to obtain submillimetric radiation of the 1 MW power range. Also approaches to submillimetric half-cycle radiation pulse generation are su ggested.

V. V. Apollonov; K. Kh; A. Shakir; V. R. Sorochenko

98

A highly efficient broadband picosecond pump high-gain OPCPA system for Ti-sapphire seed pulses; an ideal seed for high-contrast, large-energy/aperture CPA laser system: Vulcan  

NASA Astrophysics Data System (ADS)

The achievement of high contrast, high efficiency OPCPA systems has been a long established goal. We achieve close to ~20% conversion in a picosecond OPCPA system. This is now the standard seed for our petawatt pre-amplifier laser system which had a conventional 108 nanosecond gain. We thereby eliminate the need to the first nanosecond gain stage. We achieve a contrast at the 10-8 level when using the petawatt system in this configuration. We have also demonstrated a second stage of picosecond amplification with an extra gain of >2, maintaining the bandwidth and transform limited nature of the pulses, providing the potential for further improvements.

Shaikh, W.; Musgrave, I. O.; Galimberti, M.; Boyle, A.

2012-02-01

99

Analysis of the effect of numerical aperture on Pr:ZBLAN upconversion fiber lasers.  

PubMed

Theoretical analyses show that the use of high-numerical-aperture (NA) fibers can significantly increase the conversion efficiency of a blue Pr(3+) -doped fluoride fiber upconversion laser and reduce the pump-power threshold. A record high efficiency of ~14% and a low 1017-nm threshold of ~30 mW were achieved experimentally with a fiber with a NA of ~0.39. PMID:18084516

Zhao, Y; Fleming, S

1998-03-01

100

Design of large aperture solar optical telescope for the SOLAR-C mission  

NASA Astrophysics Data System (ADS)

A large aperture optical telescope is planned for the next Japanese solar mission SOLAR-C as one of major three observing instruments. The optical telescope is designed to provide high-angular-resolution investigation of lower atmosphere from the photosphere to the uppermost chromosphere with enhanced spectroscopic and spectro-polarimetric capability covering a wide wavelength region from 280 nm to 1100 nm. The opto-mechanical and -thermal performance of the telescope is crucial to attain high-quality solar observations and we present a study of optical and structural design of the large aperture space solar telescope, together with conceptual design of its accompanying focal plane instruments: wide-band and narrow-band filtergraphs and a spectro-polarimeter for high spatial and temporal observations in the solar photospheric and chromospheric lines useful for sounding physical condition of dynamical phenomena.

Suematsu, Y.; Katsukawa, Y.; Hara, H.; Shimizu, T.; Ichimoto, K.

2012-09-01

101

Image degradation of large-aperture R-C optical system induced by micro-vibration  

NASA Astrophysics Data System (ADS)

As part of the spacecraft optical loads, space camera will be subject to all working components in aircraft and space environment disturbance on-orbit, which have great influence on image resolution and image contrast, especially for large-aperture Ritchey-Chretien (R-C) optical system. This article puts forward a new method about estimating image quality degradation induced by micro-vibration. With the space coordinate transformation, the amount of optical elements jitter expressed by six variables are acquired, then the data can be imported to optical design software Code V, image motion and the root mean square(RMS) diameter will be quickly attained, then the image quality could be judged. The simulation and analysis are of significance for studying the influence of satellite micro-vibration on imaging system. For high resolution large-aperture R-C imaging system, this study provides important reference for system control and isolation.

Wang, Hongjuan; Wang, Wei; Liu, QiMin; Li, Gang

2013-01-01

102

Development of twin aperture dipole magnets for the Large Hadron Collider  

Microsoft Academic Search

A twin aperture dipole magnet has been developed with a feature of symmetric, separate coil\\/collar design in a R&D cooperation between CERN and KEK towards the LHC (Large Hadron Collider) project. The magnet reached 8.1 T at 4.2 K and 9.6 T at 1.8 K in the training test. Development of the magnet and test results are discussed. Design study

Akira Yamamoto; Takakazu Shintomi; Nono Higashi; Hiromi Hirabayashi; Hiroshi Kawamata; Naihao Song; Akio Terashima; Hiroshi Yamaoka; Shuma Kawabata; G. Brianti; J. Buckley; D. Leroy; R. Perin; A. Siemko; L. Walckiers; M. Hirano; T. Origasa; K. Makishima; I. Inoue; M. Ikeda; S. Meguro; M. Kondo

1995-01-01

103

Construction and Characterization of a Large Aperture Blackbody for Infrared Radiometer Calibration  

Microsoft Academic Search

A large aperture blackbody (LABB) with a diameter of 1 m has been successfully constructed for calibrating radiation thermometers\\u000a and infrared radiometers with a wide field of view in the temperature range between 10 °C and 90 °C. The blackbody is a 1 m\\u000a long cylindro-conical cavity with a diameter of 1.1 m. Its conical bottom has an apex angle of 120°. To achieve good

Chul-Woung Park; Yong Shim Yoo; Bong-Hak Kim; Sejong Chun; Seung-Nam Park

2011-01-01

104

Dynamic aperture optical arrays based on polymeric MEMS actuators for large scale coding elements with application in visible to MWIR  

Microsoft Academic Search

Extension of coded apertures to the MWIR introduces the effects of diffraction and other distortions not observed in shorter wavelength systems. A new approach is being developed under the DARPA\\/SPO funded LACOSTE (Large Area Coverage Optical search-while Track and Engage) program, that addresses the effects of diffraction while gaining the benefits of coded apertures, thus providing flexibility to vary resolution,

S. Goodwin; J. Carlson; S. Rogers; J. Kim; C. Kim; D. Brady; B. R. Stoner

2007-01-01

105

Fabrication of Efficient, Large Aperture Transmission Diffraction Gratings by Ion-Beam Etching  

SciTech Connect

The utilization of high-power short pulse laser employing chirped-pulse amplification (CPA) for material processing and inertial confinement research is widely increasing. The performance of these high-power CPA laser system continues to be limited by the ability of the pulse compression gratings to hold up to the high-average-power or high-peak-power of the laser. Pulse compression gratings used in transmission and fabricated out of bulk fused silica have intrinsically the highest laser damage threshold when compared with metal or multilayer dielectric gratings that work in reflection. LLNL has developed processing capability to produce high efficiency fused silica transmission gratings at sizes useful to future Petawatt-class systems, and has demonstrated high efficiency at smaller aperture. This report shows that fused silica diffraction exhibiting >95% efficiency into the -1 diffraction order in transmission (90{sup o} deflection of the incident light, at an incidence angle of 45{sup o} to the grating face). The microstructure of this grating consisted of grooves ion-beam etched to a depth of 1.6 microns with a pitch of 0.75 microns, using a holographically produced photoresist mask that was subsequently stripped away in significance to the fabrication of the small scale high efficiency grating was the development of the processing technology and infrastructure for production of such gratings at up to 65 cm diameter. LLNL is the currently the only location in the world with the ability to coat, interferometrically expose, and ion etch diffractive optics at this aperture. Below, we describe the design, fabrication, performance and, the scaleup process for a producing a high-efficiency transmission grating on a 65 cm fused silica substrate.

Nguyen, H T; Bryan, S R; Britten, J A; Perry, M D

2000-09-14

106

ATLAST-9.2m: a large-aperture deployable space telescope  

NASA Astrophysics Data System (ADS)

We present results of a study of a deployable version of the Advanced Technology Large-Aperture Space Telescope (ATLAST), designed to operate in a Sun-Earth L2 orbit. The primary mirror of the segmented 9.2-meter aperture has 36 hexagonal 1.315 m (flat-to-flat) glass mirrors. The architecture and folding of the telescope is similar to JWST, allowing it to fit into the 6.5 m fairing of a modest upgrade to the Delta-IV Heavy version of the Evolved Expendable Launch Vehicle (EELV). We discuss the overall observatory design, optical design, instruments, stray light, wavefront sensing and control, pointing and thermal control, and in-space servicing options.

Oegerle, William R.; Feinberg, Lee D.; Purves, Lloyd R.; Hyde, T. Tupper; Thronson, Harley A.; Townsend, Jacqueline A.; Postman, Marc; Bolcar, Matthew R.; Budinoff, Jason G.; Dean, Bruce H.; Clampin, Mark C.; Ebbets, Dennis C.; Gong, Qian; Gull, Theodore R.; Howard, Joseph M.; Jones, Andrew L.; Lyon, Richard G.; Pasquale, Bert A.; Perrygo, Charles; Smith, Jeffrey S.; Thompson, Patrick L.; Woodgate, Bruce E.

2010-07-01

107

The use of a large-aperture radio system for meteor studies  

NASA Astrophysics Data System (ADS)

A large sampled-aperture antenna array has been used to investigate the structure of the radio wave field scattered by meteor trails. The experiment measured the phase and amplitude of the radio waves in the frequency range 20 to 30 MHz at 58 points distributed over an aperture of almost 1.2 km. The temporal changes in the structure of the scattered radiation clearly show the influence of distortion of the meteor trails by atmospheric winds, but are incompatible with the widely accepted model which attributes fading and anomalous decay times to the distortion of a single trail. The observations seem to imply the simultaneous existence of two or more trails but whether these trails are due to fragmentation of the meteoroid in the atmosphere or to simultaneous entry of independent meteoroids is not clear.

Herring, R. W.; Forsyth, P. A.

1980-06-01

108

A new polishing process for large-aperture and high-precision aspheric surface  

NASA Astrophysics Data System (ADS)

The high-precision aspheric surface is hard to be achieved due to the mid-spatial frequency error in the finishing step. The influence of mid-spatial frequency error is studied through the simulations and experiments. In this paper, a new polishing process based on magnetorheological finishing (MRF), smooth polishing (SP) and ion beam figuring (IBF) is proposed. A 400mm aperture parabolic surface is polished with this new process. The smooth polishing (SP) is applied after rough machining to control the MSF error. In the middle finishing step, most of low-spatial frequency error is removed by MRF rapidly, then the mid-spatial frequency error is restricted by SP, finally ion beam figuring is used to finish the surface. The surface accuracy is improved from the initial 37.691nm (rms, 95% aperture) to the final 4.195nm. The results show that the new polishing process is effective to manufacture large-aperture and high-precision aspheric surface.

Nie, Xuqing; Li, Shengyi; Dai, Yifan; Song, Ci

2013-07-01

109

Differential Synthetic Aperture Radar Interferometry in monitoring large landslide (La Frasse, Switzerland)  

NASA Astrophysics Data System (ADS)

Spaceborne Differential Interferometric Synthetic Aperture Radar (DInSAR) is able to detect quasi vertical movements covering very large areas in a continuous way; it can be considered as an efficient tool to detect and monitor slope instabilities. The La Frasse landslide is located in the Canton of Vaud (Switzerland). It has a length of 2 km, a width of 500 m and its sliding surface is located at a depth of 60 to 100 m. With high velocities (presently at 40 cm/y in the active lower part), La Frasse landslide is in highly hazardous area according to the Swiss legislation. According to Varnes classification, it is a complex slide composed of tertiary flysch material and flowing over on flysch and limestone bedrock. The landscape is occupied by forests, pastures, some habitations and two main roads to touristic areas. The foot of the landslide is continuously eroded by the river "Grande-Eau". First of all, two interferometric pairs are constructed with data provided by the satellite Alos. The big wavelength (24 cm) of ALOS' PALSAR sensor gives good results in the foot of the landslide, where the movements are highest. Afterwards, fifty-three interferometric pairs are constructed with twenty-two images acquired with the European satellite Envisat. With the shorter wavelength (5.6 cm) of the Envisat's ASAR sensor, but the higher number of interferograms, the analysis provides the mean velocities of landslide's scaterrers by using the Small Baseline Subset (SBAS) methodology. The DInSAR results were compared to ground displacements measured every 2h by an optical total station (Robovec™ System). The results of this study are coherent with the amplitude of the deformations monitored by Robovec™. Moreover, the computation of the mean velocities shows that today, total displacements are measured in the active lower part of the landslide; the data complete Robovec™ results. But the accuracy of the measured displacements and the number of scatterers could be improved by synthetizing the topographic phase from an aerial laser scanning DEM instead of the STRM DEM. The number of scatterers can also be increased by installing corner reflectors in the fastest-moving area of the landslide. At present, a draining gallery is being constructed under the active part of the landslide. As soon as the construction is finished, it would be interesting to measure displacements by SBAS to control the efficiency of the gallery.

Michoud, C.; Rune Lauknes, T.; Pedrazzini, A.; Jaboyedoff, M.; Tapia, R.; Steinmann, G.

2009-04-01

110

Large coded aperture mask for spaceflight hard x-ray images  

NASA Astrophysics Data System (ADS)

The 2.6 square meter coded aperture mask is a vital part of the Burst Alert Telescope on the Swift mission. A random, but known pattern of more than 50,000 lead tiles, each 5 mm square, was bonded to a large honeycomb panel which projects a shadow on the detector array during a gamma ray burst. A two-year development process was necessary to explore ideas, apply techniques, and finalize procedures to meet the strict requirements for the coded aperture mask. Challenges included finding a honeycomb substrate with minimal gamma ray attenuation, selecting an adhesive with adequate bond strength to hold the tiles in place but flexible enough to allow the tiles to expand and contract without distorting the panel under large temperature gradients, and eliminating excess adhesive from all untiled areas. Finding an efficient way to bond the > 50,000 lead tiles to the panel while maintaining positional tolerances within +0.1 mm was no small task. In order to generate the desired bondline, adhesive was applied and allowed to cure to each tile. The 'pre-cured' tiles were located in a tool to maintain positional accuracy, wet adhesive was applied to the panel, and the wetted substrate was lowered to the tile surface with synchronized actuators. Using this procedure, the entire tile pattern was transferred to the large honeycomb panel in a single bond. The pressure for the bond was achieved by enclosing the entire system in a vacuum bag. Thermal vacuum and acoustic tests validated this approach. This paper discusses the methods, materials, and techniques used to fabricate this very large and unique coded aperture mask for the Swift mission.

Vigneau, Danielle; Robinson, David W.

2003-03-01

111

Temporally focused femtosecond laser pulses for low numerical aperture micromachining through optically transparent materials  

PubMed Central

Temporal focusing of spatially chirped femtosecond laser pulses overcomes previous limitations for ablating high aspect ratio features with low numerical aperture (NA) beams. Simultaneous spatial and temporal focusing reduces nonlinear interactions, such as self-focusing, prior to the focal plane so that deep (~1 mm) features with parallel sidewalls are ablated at high material removal rates (25 µm3 per 80 µJ pulse) at 0.04-0.05 NA. This technique is applied to the fabrication of microfluidic devices by ablation through the back surface of thick (6 mm) fused silica substrates. It is also used to ablate bone under aqueous immersion to produce craniotomies.

Vitek, Dawn N.; Adams, Daniel E.; Johnson, Adrea; Tsai, Philbert S.; Backus, Sterling; Durfee, Charles G.; Kleinfeld, David; Squier, Jeffrey A.

2010-01-01

112

Large aperture transducer designed for MR-HIFU treatment of breast tumors  

NASA Astrophysics Data System (ADS)

A novel large aperture transducer design is proposed for MR-HIFU treatment of breast tumors. The phased array is composed of 384 elements placed on a circular structure with a lateral beam direction. This beam path orientation considerably reduces the risk of damaging nearby vital organs. In addition, this transducer shape induces a well delineated sharp focal point with low energy density in the near and far field for safe, accurate and efficient treatment. The performance of the transducer is demonstrated with acoustic field measurements and temperature maps of a phantom sonication.

Mougenot, C.; Köhler, M.; Tillander, M.; Moonen, C.; Bartels, L. W.; Ehnholm, G.

2012-10-01

113

Spacecraft conceptual design for the 8-meter Advanced Technology Large Aperture Space Telescope (ATLAST)  

NASA Astrophysics Data System (ADS)

The Advanced Concepts Office at Marshall Space Flight Center completed a brief spacecraft design study for the 8- meter monolithic Advanced Technology Large Aperture Space Telescope (ATLAST-8m). This spacecraft concept provides all power, communication, telemetry, avionics, guidance and control, and thermal control for the observatory, and inserts the observatory into a halo orbit about the second Sun-Earth Lagrange point. The multidisciplinary design team created a simple spacecraft design that enables component and science instrument servicing, employs articulating solar panels for help with momentum management, and provides precise pointing control while at the same time fast slewing for the observatory.

Hopkins, Randall C.; Capizzo, Peter; Fincher, Sharon; Hornsby, Linda S.; Jones, David; Mosier, Gary; Stahl, H. Philip; Thomas, Dan; Thompson, Kevin S.

2010-07-01

114

Intense terahertz generation at low frequencies using an interdigitated ZnSe large aperture photoconductive antenna  

NASA Astrophysics Data System (ADS)

We demonstrate the generation of intense THz pulses at low frequencies, and THz pulse shaping, using a ZnSe interdigitated large aperture photoconductive antenna. We have experimentally measured a THz pulse energy of 3.6 +/-0.8 ?J, corresponding to a calculated peak THz electric field of 143 +/- 17 kV/cm. We also used a binary phase mask instead of a traditional shadow mask with our interdigitated photoconductive antenna, which allows us to generate THz field profiles that range from a symmetric single-cycle THz pulse to an asymmetric half-cycle THz pulse.

Ropagnol, X.; Blanchard, F.; Ozaki, T.; Reid, M.

2013-10-01

115

Point-spread function reconstruction in high aperture lenses focusing ultra-short laser pulses  

NASA Astrophysics Data System (ADS)

In this paper we discuss the measurement of the amplitude point-spread function (PSF) of high aperture lenses focusing ultrashort laser pulses. In the experimental set-up a Twyman-Green interferometer and an autocorrelator are combined to function as a phase-shifting interferometer which is then used to measure the phase distribution in the pupil plane of the lens. Numerical reconstruction of the interferograms permits us to calculate the spatial distribution of the amplitude and phase of the point-spread function. Our work is relevant for cases when ultra-short laser pulses are focused for applications such as two- and three-photon fluorescence, second- and third-harmonic generation microscopy, optical coherence tomography and microscopy, and optical data storage.

Török, Peter; Kao, Fu-Jen

2002-11-01

116

Spatial mode dynamics in wide-aperture quantum-dot lasers  

SciTech Connect

We present a systematic theoretical study of spatial mode dynamics in wide-aperture semiconductor quantum-dot lasers within the Maxwell-Bloch formalism. Our opto-electro-thermal model self-consistently captures the essential dynamical coupling between field, polarization, and carrier density in both thermal and nonthermal regimes, providing detailed description of the complex spatiotemporal modal intensity structure and spectra in these novel devices and broad area edge-emitting lasers in general. Using linear stability analysis and high resolution adaptive-grid finite element numerical simulation, we show that in the nonthermal regime, the presence of inhomogeneous broadening in quantum-dot active media leads to suppressed filamentation and enhanced spatial coherence compared to conventional quantum well devices with comparable phase-amplitude coupling (alpha parameter). Increasing the degree of inhomogeneous broadening in the active medium leads to further improvement in spatial coherence. In the thermal regime, there is further suppression of filamentation in the inhomogeneously broadened quantum-dot active medium; however, the spatial coherence aided by inhomogeneous broadening is partly lost due to the effect of temperature on cavity detuning. We propose that device designs based on optimized inhomogeneous broadening of quantum-dot gain medium could ultimately lead to diffraction-limited outputs in the quasi-cw regime which are still very difficult to achieve in conventional wide-aperture designs.

Mukherjee, Jayanta; McInerney, John G. [Department of Physics and Tyndall National Institute, Optoelectronics Group, National University of Ireland, University College, Cork (Ireland)

2009-05-15

117

Surface profile measurement techniques for large aperture optical thin film membrane structures  

NASA Astrophysics Data System (ADS)

Large aperture thin film optics typically have substantial shape errors which are difficult to quantify with conventional measurement methods, such as interferometry. The interferograms are normally too complex and contain too much information to discern relevant shape information pertinent to (for example) solar energy collection. This has led to the development of the laboratory-oriented, less expensive and less complex measurement procedure presented here. The method is based on well-defined geometric relationships and provides a novel approach to measuring the shape of large optics that are known to have substantial surface distortion. Once the local reflection (surface tilt) angles are determined, the overall shape can be reconstructed and further analyzed using ray tracing software to obtain aberration coefficients if desired. This technique lends itself to being easily scalable to very large membrane structures and the measurement precision is only limited by the equipment chosen.

Spradley, Kevin D.; Gregory, Don A.; John Outerbridge, G.

2013-10-01

118

Third harmonic generation of high-energy large-aperture one microlaser and its spatial beam property investigation  

NASA Astrophysics Data System (ADS)

In this paper we report on the design and performance of the large KDP crystal plates that were constructed to convert 1.054 micrometer laser beam to its third harmonic. The KDP crystals were AR-coated by sol-gel films. Type II/type II phase-matching configurations for cascade frequency doubling and tripling have been implemented at 250 mm aperture. High conversion efficiencies approaching to 70% were achieved. Focusing properties of harmonic beam are also investigated in the paper. Based on the transfer of electric-field amplitude and phase ripple in frequency tripling, simple formulas are derived for the harmonic laser beam-quality factor, M3(omega )2, with an arbitrary fundamental beam incident to ideal nonlinear crystals. Harmonic beam-quality is generally degraded, while the beam divergence is similar to that of the fundamental after a nonlinear frequency-conversion process. For practical crystals with periodic surface ripples due to their machining, a multi-order diffractive model is presented to study the focusing properties of harmonic beam. Predictions of the theories are shown to be in excellent agreement with full numerical simulations of tripling.

Zhu, Baoqiang; Zhan, Tingyu; Gu, Zhen; Wang, Tao; Qian, Liejia

2001-05-01

119

Large aperture asymmetric Fabry Perot modulator based on asymmetric tandem quantum well for low voltage operation.  

PubMed

Large aperture image modulators used as demodulator in receiver path are an important component for the use in three dimensional (3D) image sensing. For practical applications, low voltage operation and high modulation performance are the key requirements for modulators. Here, we propose an asymmetric Fabry-Perot modulator (AFPM) with asymmetric tandem quantum wells (ATQWs) for 3D image sensing. By using ATQWs for the AFPM design, the device operated at -4.25V, and the operating voltage was significantly lower by about 23% compared to -5.5V of a conventional AFPM with 8nm thick multiple QW with a single QW thickness (SQWs), while achieving high reflectivity modulation in excess of 50%. The performance of the fabricated devices is in good agreement with theoretical calculations. The pixelated device shows a high modulation speed of 21.8 MHz over a large aperture and good uniformity. These results show that AFPM with ATQWs is a good candidate as an optical image modulator for 3D image sensing applications. PMID:22418477

Na, Byung Hoon; Ju, Gun Wu; Choi, Hee Ju; Cho, Yong Chul; Park, Yong Hwa; Lee, Yong Tak

2012-03-12

120

Electromechanical simulation of a large-aperture MOEMS Fabry-Perot tunable filter  

NASA Astrophysics Data System (ADS)

We are developing as micro-machined electrostatically actuated Fabry-Perot tunable filter with a large clear aperture for application in high through-put wide-field imaging spectroscopy and lidar systems. In the first phase of this effort, we are developing key components based on coupled electro-mechanical simulations. In particular, the movable etalon plate design leverages high coating stress to yield a flat surface in drum- head tension over a large diameter. In this approach, the cylindrical silicon movable plate is back etched, resulting in an optically coated membrane that is suspended from a thick silicon support ring. Underestimating the interaction between the support ring, suspended membrane, and coating is critical to developing surfaces that are flat to within stringent etalon requirements. In this work, we present the simulations used to develop the movable plate, spring suspension system, and electrostatic actuation mechanism. We also present results form test of fabricated proof of concept components.

Kuhn, Jonathan L.; Barclay, Richard B.; Greenhouse, Matthew A.; Mott, David B.; Satyapal, Shobita

2000-08-01

121

Diffractive imaging analysis of large-aperture segmented telescope based on partial Fourier transform  

NASA Astrophysics Data System (ADS)

Large-aperture segmented primary mirror will be widely used in next-generation space-based and ground-based telescopes. The effects of intersegment gaps, obstructions, position and figure errors of segments, which are all involved in the pupil plane, on the image quality metric should be analyzed using diffractive imaging theory. Traditional Fast Fourier Transform (FFT) method is very time-consuming and costs a lot of memory especially in dealing with large pupil-sampling matrix. A Partial Fourier Transform (PFT) method is first proposed to substantially speed up the computation and reduce memory usage for diffractive imaging analysis. Diffraction effects of a 6-meter segmented mirror including 18 hexagonal segments are simulated and analyzed using PFT method. The influence of intersegment gaps and position errors of segments on Strehl ratio is quantitatively analyzed by computing the Point Spread Function (PSF). By comparing simulation results with theoretical results, the correctness and feasibility of PFT method is confirmed.

Dong, Bing; Qin, Shun; Hu, Xinqi

2013-09-01

122

Large-Optics white light interferometer for laser wavefront test: apparatus and application  

NASA Astrophysics Data System (ADS)

There is transmitting optics of 250mm aperture with about 8 microradians in SILEX system. This is often large aperture and diffraction-limited laser beam in the laser communications. Large-Optics white light interferometer using double-shearing structure has been submitted to analysis the laser wavefront before. Six optical plates of 490 millimeters apertures are manufactured now one of which is also aperture-divided so that the precision of measured wave front is higher than the full aperture design. It is suitable for measurement of minimum diffraction-limited laser wave front and any wavelength. The interference is happened between equal optical path of the reflection and the other. The plates are the basic structures which are precisely parallel or perpendicular needed for either two plates. There are several tools equipped with the interferometer including white light test source and collimators and so on to confirm the precision of several seconds angle. The apparatus and application is explained in detail in this paper. The adjustment is important for the realization of white light test.

Luan, Zhu; Liu, Liren; Wang, Lijuan; Liu, De'an

2008-08-01

123

A free-air ionization chamber with a large aperture diaphragm  

NASA Astrophysics Data System (ADS)

Calculations of the electric field distributions in free-air ionization chambers reveal that the distortion of the charge collection volume is small even for wide X-ray beam passage if the diaphragm and the X-ray shielding box are kept at a potential equal to half that applied to the high-voltage electrode. Applying this potential to the diaphragm and the shielding box permits a larger aperture diaphragm to be used. This will allow a wider X-ray beam to enter the chamber, thus generating a larger signal. In addition, the distance between the diaphragm and the charge collection volume can be shortened to reduce the amount of X-ray attenuation. It is also possible to calibrate a dosimeter against a free-air ionization chamber that has a diaphragm whose aperture size is equal to the size of the dosimeter in an X-ray field that is collimated to the same size. This is important since free-air ionization chambers are not sensitive to X-rays that are incident at large angles, such as those scattered by the collimator, filters and air.

Takata, N.

2010-07-01

124

Recent enhancements of the Phased Array Mirror Extendible Large Aperture (PAMELA) telescope testbed at MSFC  

NASA Astrophysics Data System (ADS)

Recent incremental upgrades to the Phased Array Mirror Extendible Large Aperture (PAMELA) telescope testbed have enabled the demonstration of phasing (with a monochromatic source) of clusters of primary mirror segments down to the diffraction limit. PAMELA upgrades include an improved Shack-Hartmann wavefront sensor, passive viscoelastic damping treatments for the voice-coil actuators, and mechanical improvement of mirror surface figures. This report summarizes the recent PAMELA upgrades and presents a status of this unique testbed for wavefront sensing and control. The Marshall Space Flight Center acquired the PAMELA telescope in 1993 after Kaman Aerospace was unable to complete integration and testing under the limited SDIO and DARPA funding. The PAMELA is a 36-segment, half-meter aperture, adaptive telescope which utilizes a Shack-Hartmann wavefront sensor, inductive coil edge sensors, voice coil actuators, imaging CCD cameras and interferometry for figure alignment, wavefront sensing and control. MSFC originally obtained the PAMELA to supplement its research in the interactions of control systems with flexible structures. In August 1994, complete tip, tilt and piston control was successfully demonstrated using the Shack-Hartmann wavefront sensor and the inductive edge sensors.

Rakoczy, John M.; Montgomery, Edward E.; Lindner, Jeffrey L.

2000-08-01

125

Design concepts for future large-aperture wide-field-of-view UVIS optical systems  

NASA Astrophysics Data System (ADS)

The Hubble Space Telescope (HST) has provided superb imaging and spectroscopic capability for studying galaxies, stars, and nebulae in the ultraviolet and visible (UVIS) wavelength regions, as well as in the near infrared. The HST is a 2.4-meter telescope with imaging, spectroscopic, and limited coronagraphic instrumentation. NASA plans to discontinue its operations in 2010. Next generation ultraviolet and visible telescope capability to replace HST is currently under discussion. The new facility would include a very large aperture collector, ultra wide field of view (WFOV) imagery, precise wavefront control, and high UVIS efficiency. Such a facility would combine ultra wide FOV imagery that is diffraction-limited at Lyman-? (? = 122 nm) with efficient broad spectral coverage. The design must also provide spectroscopic, and possibly coronagraphic, capability in addition to imagery. This paper will discuss design trades for such capabilities and present design configurations. The paper will also identify key technologies needed to support the implementation of the new facility.

Woodruff, Robert A.

2003-02-01

126

Development of a Large Aperture Nb3Sn Racetrack Quadrupole Magnet  

SciTech Connect

The U.S. LHC Accelerator Research Program (LARP), a collaboration between BNL, FNAL, LBNL, and SLAC, has among its major objectives the development of advanced magnet technology for an LHC luminosity upgrade. The LBNL Superconducting Magnet Group supports this program with a broad effort involving design studies, Nb{sub 3}Sn conductor development, mechanical models, and basic prototypes. This paper describes the development of a large aperture Nb{sub 3}Sn racetrack quadrupole magnet using four racetrack coils from the LBNL Subscale Magnet (SM) Program. The magnet provides a gradient of 95 T/m in a 110 mm bore, with a peak field in the conductor of 11.2 T. The coils are pre-stressed by a mechanical structure based on a pre-tensioned aluminum shell, and axially supported with aluminum rods. The mechanical behavior has been monitored with strain gauges and the magnetic field has been measured. Results of the test are reported and analyzed.

Ferracin, Paolo; Bartlett, Scott E.; Caspi, Shlomo; Dietderich, Daniel R.; Gourlay, Steve A.; Hannaford, Charles R.; Hafalia, Aurelio R.; Lietzke, Alan F.; Mattafirri, Sara; McInturff, Alfred D.; Nyman, Mark; Sabbi, Gianluca

2005-06-01

127

Characterizing the divergence properties of the laser diode beams propagation through collimator and aperture ABCD optical system  

Microsoft Academic Search

The propagation properties of Gaussian laser beams through a complete optical path including free space and the optics of transmitter and receiver containing a collimator, an aperture and a lens is studied. Based on the Collins integral and using the second order moment method, analytical formulas for intensity distribution and Power In Bucket (PIB) along the propagation path are derived.

M. Reza Hedayati Rad; F. D. Kashani; M. M. Eftekhari; M. Reza Mahzoun

2010-01-01

128

Path-average rainfall estimation from optical extinction measurements using a large-aperture scintillometer  

NASA Astrophysics Data System (ADS)

The potential of a near infrared large-aperture boundary layer scintillometer as path-average rain gauge is investigated. The instrument was installed over a 2.4 km path in Benin as part of the AMMA Enhanced Observation Period during 2006 and 2007. Measurements of the one-minute average received signal intensity were collected for 6 rainfall events during the dry season and 16 events during the wet season. Using estimates of the signal base level just before the onset of the rain events, the optical extinction coeffcient is estimated from the path-integrated attenuation for each minute. The corresponding path-average rain rates are computed using a power-law relation between the optical extinction coeffcient and rain rate obtained from measurements of raindrop size distributions with an optical spectropluviometer. Comparisons of five-minute rainfall estimates with measurements from two nearby rain gauges show that the temporal dynamics are generally captured well by the scintillometer. However, the instrument has a tendency to underestimate rain rates and event total rain amounts with respect to the gauges. It is shown that this underestimation can be explained partly by systematic differences between the actual and the employed mean power-law relation between rain rate and specific attenuation, partly by unresolved spatial and temporal rainfall variations along the scintillometer path. Occasionally, the signal may even be lost completely. It is demonstrated that if these effects are properly accounted for, by employing appropriate relations between rain rate and specific attenuation and by adapting the path length to the local rainfall climatology, scintillometer-based rainfall estimates can be within 20% of those estimated using rain gauges. These results demonstrate the potential of large-aperture scintillometers to estimate path-average rain rates at hydrologically relevant scales.

Uijlenhoet, Remko; Cohard, Jean-Martial; Gosset, Marielle

2010-05-01

129

A CLOSE COMPANION SEARCH AROUND L DWARFS USING APERTURE MASKING INTERFEROMETRY AND PALOMAR LASER GUIDE STAR ADAPTIVE OPTICS  

SciTech Connect

We present a close companion search around 16 known early L dwarfs using aperture masking interferometry with Palomar laser guide star adaptive optics (LGS AO). The use of aperture masking allows the detection of close binaries, corresponding to projected physical separations of 0.6-10.0 AU for the targets of our survey. This survey achieved median contrast limits of {Delta}K {approx} 2.3 for separations between 1.2 {lambda}/D-4{lambda}/D and {Delta}K {approx} 1.4 at 2/3 {lambda}/D. We present four candidate binaries detected with moderate-to-high confidence (90%-98%). Two have projected physical separations less than 1.5 AU. This may indicate that tight-separation binaries contribute more significantly to the binary fraction than currently assumed, consistent with spectroscopic and photometric overluminosity studies. Ten targets of this survey have previously been observed with the Hubble Space Telescope as part of companion searches. We use the increased resolution of aperture masking to search for close or dim companions that would be obscured by full aperture imaging, finding two candidate binaries. This survey is the first application of aperture masking with LGS AO at Palomar. Several new techniques for the analysis of aperture masking data in the low signal-to-noise regime are explored.

Bernat, David [Department of Astronomy, Cornell University, Ithaca, NY 14853 (United States); Bouchez, Antonin H.; Cromer, John L.; Dekany, Richard G.; Moore, Anna M. [California Institute of Technology, Pasadena, CA 91125 (United States); Ireland, Michael; Tuthill, Peter [Sydney Institute for Astrophysics, School of Physics, University of Sydney (Australia); Martinache, Frantz [National Astronomical Observatory of Japan, Subaru Telescope, Hilo, HI 96720 (United States); Angione, John; Burruss, Rick S.; Guiwits, Stephen R.; Henning, John R.; Hickey, Jeff; Kibblewhite, Edward; McKenna, Daniel L.; Petrie, Harold L.; Roberts, Jennifer; Shelton, J. Chris; Thicksten, Robert P.; Trinh, Thang [Palomar Laser Guide Star Adaptive Optics Team, Palomar Observatory, California Institute of Technology, Palomar Mountain, CA 92060 (United States)

2010-06-01

130

The Large Aperture Gamma Ray Observatory as an Observational Alternative at High Altitude  

NASA Astrophysics Data System (ADS)

Although satellite observations have revealed some mysteries about the origin and location of cosmic rays at low energies, questions remain to be resolved in higher energy ranges (>1 GeV). However, the flow of particles at high energies is very low, large sensitive areas are necessary, so that the detection of secondary particles from observatories on the surface of the earth is a technically viable solution. While the Pierre Auger Observatory has such capacity given its 16000 m^2 of detectors, low height above sea level greatly reduces its detection capability. The Large Aperture Gamma Ray Observatory (LAGO) is an observational alternative that attempts to overcome this limitation. This project was started in 2005, placing water Cherenkov Detectors at high altitude. Observation sites have been selected with some basic requirements: altitude, academic and technical infrastructure, existence of a research group responsible for assembly and maintenance of the detectors and the analysis, visualization, divulgation and data storage. This paper presents the general status of the observatories of Sierra Negra-México, Chacaltaya-Bolívia, Marcapomacocha-Perú, Mérida-Venezuela and Bucaramanga-Colombia.

Rosales, M.

2011-10-01

131

A New Type of X-ray Condenser Lenses with Large Apertures Fabricated by Rolling of Structured Films  

SciTech Connect

In order to meet the demand for X-ray lenses with large apertures and, hence, photon flux, a new type of X-ray lenses has been developed: Rolled prismatic X-ray lenses feature a vast number of refracting surfaces to increase transparency and aperture, respectively. Prototypes of such lenses have been fabricated by molding and rolling of a structured polyimide film. In this work, rolled prismatic X-ray lenses are pictured, and results of first tests performed at the ANKA storage ring in Karlsruhe are presented.

Simon, M.; Reznikova, E.; Nazmov, V.; Grund, T. [Institut fuer Mikrostrukturtechnik, Forschungszentrum Karlsruhe GmbH Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Last, A. [Institut fuer Mikrostrukturtechnik, Universitaet Karlsruhe Kaiserstrasse 12, 76131 Karlsruhe (Germany)

2010-04-06

132

The pre-research of the deploy technology for the large aperture space astronomical telescope  

NASA Astrophysics Data System (ADS)

The spherical primary mirror (Mb) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is segmented and composed of 37 hexagonal sub-mirrors, and segmented active optics method is successfully developed in it. LAMOST project has passed through the project acceptance in 2009. The success of LAMOST makes deployable primary mirror possible. The deployable large aperture space astronomical telescope is one of the most development potential space observation spacecrafts in the future. This paper is targeted at the reflecting Schmidt telescope LAMOST, which has a 6.67X6.05m primary mirror. The feasibility of the deployable structure of the large reflecting space telescope's primary mirror has been mainly researched. The analysis of the design scheme for the deployable primary mirror has been carried out, and according to the feature and the design of LAMOST, a subdivision type deployment scheme has been given; The locating principle of the both side wings and the locking device after deployment has been analyzed; In addition the problems in the process of deployment is also preliminary discussed. This paper is targeted at the reflecting Schmidt telescope LAMOST, which has a 6.67X6.05 primary mirror. The feasibility of the deployable structure of the large reflecting telescope's primary mirror has been mainly researched. The analysis of the design scheme for the deployable primary mirror has been carried out, and according to the feature and the design of LAMOST, a subdivision type deployment scheme has been given; The locating principle of the both side wings and the locking device after deployment has been analyzed; In addition the problems in the process of deployment have been preliminary discussed.

Jiang, Fanghua; Zuo, Heng; Li, Guoping

2012-09-01

133

Advanced Phase Change Media for Blue Laser Recording of 18 GB Capacity for 0.65 Numerical Aperture and 30 GB Capacity for 0.85 Numerical Aperture  

NASA Astrophysics Data System (ADS)

We attempted to improve phase change media to achieve larger capacity for systems with blue lasers using numerical apertures (NA) of both 0.85 and 0.65. It was found that the Bi-added GeTe-rich pseudo-binary composition promised high erase ratio even when we did not use any interface layers on a recording layer. The use of an absorption control layer (ACL) was also attempted to suppress the cross erase (XE). It was found that the ACL was very effective in suppressing the XE. The advanced phase change media that used the above novel technologies showed good analog performance. The advanced media also showed bER of less than 1.0× 10-4, promising 18 GB capacity for an NA of 0.65 and 30 GB capacity for an NA of 0.85.

Yusu, Keiichiro; Ashida, Sumio; Nakamura, Naomasa; Oomachi, Noritake; Morishita, Naoki; Ogawa, Akihito; Ichihara, Katsutaro

2003-02-01

134

Large aperture ratio machining of the Z-cut quartz base on MEMS technology  

NASA Astrophysics Data System (ADS)

It is difficult to process quartz to get a large aperture ratio micropore(?127?m) by the mechanical tools, but it is possible processed by MEMS technology. The fluorine etching technology is used in experiments. The etching rate of quartz is proportional to the concentration of the HF acid. The etching rate of the mixtures of different proportions of the HF acid (49%) and the NH4F solution (35%) can be acquired, and the etching rate is lower if NH4F solution (35%) replace by the saturated NH4F solution. The experimental results conform to the chemical equation of Judge J S. In the experiment of the micropore etch, the wafers are respectively put in the mixtures of 1:1 and 3:2 ratio of the hydrofluoric acid (49%) and the ammonium fluoride solution (40%), and the morphology of micropore can be observed by the scanning electron microscopy and the confocal microscopy, and then the deepest depth of the micropore is tested by the confocal microscopy, the relationship between etching rate and the proportional of mixed solution can be got.

Xie, Haihe; Jiang, Xiaogfeng; Lin, Chun; Lu, Xizhao; Huang, Yuanqing

2012-10-01

135

Three years of Large Aperture Scintillometer measurements over a patchy savanna in West Africa  

NASA Astrophysics Data System (ADS)

In the context of the West African Monsoon, energy balance at the surface is expected to play a major role, but turbulent fluxes are often difficult to monitor over long period with sufficient accuracy. Within the framework of the "AMMA-CATCH" program, a Large Aperture Scintillometer (LAS) has been installed over a small catchment (12 km2 ), located in the north of Benin, a region exposed to sudanian climate. This presentation will focus on the methodology we applied to derive the sensible heat flux from scintillometer measurements. For this, we need to characterize the annual cycle of aerodynamic parameters. Footprint analysis has been carried through to precise the aggregation of local parameters needed in the computation of H. Then, the result of a three years time series of sensible heat flux will be presented and analysed. It is compared to local and aggregated net radiation measurements to analyse the energy balance partition. For the first time, we dispose of a full year time series of aggregated sensible heat flux, which can provide a complete annual cycle of AET at hour scale.

Guyot, A.; Cohard, J.-M.; Anquetin, S.; Galle, S.

2009-04-01

136

A Large Aperture Infrasound Array in the Netherlands for interferometric studies  

NASA Astrophysics Data System (ADS)

To measure infrasound, microbarometer arrays are installed all over the world. In the framework of the radio-astronomical 'Low Frequency Array' (LOFAR) initiative of the Netherlands, the 'Large Aperture Infrasound Array' (LAIA) is being installed by the KNMI. LAIA will consist of thirty receivers and will have an aperture of 100 km. The in-house developed microbarometers are able to measure infrasound up to a period of 1000 seconds, which is in the acoustic-gravity wave regime. The propagation of the infrasound depends on the temperature and the wind in the atmosphere. There are several models of the distribution of temperature and wind at different altitudes. A goal of this research is to probe the atmosphere to retrieve information of wind and temperature in the atmosphere through actual observations. Is it possible to probe the atmosphere with infrasound in order to evaluate the model of the atmosphere and even retrieve such information on finer temporal and spatial scale? We need knowledge about the source, if we want to isolate the influence of the atmosphere on infrasound propagation. A way to separate the influence of the atmosphere without knowing the sound source in detail is to use interferometry. Via crosscorrelation of the ambient noise between several infrasound receivers the time lags of the infrasound can be determined. Through these lags and with the distances between the receivers it is possible to estimate a velocity model and consequently the parameters of the model of the atmosphere. In this paper, LAIA will be introduced and the implementation and the evaluation of the interferometric approach will be described. For this reason a model of the atmosphere was simulated. The interferometry was applied to the data obtained from this simulation in collaboration with the TU Delft. In further experiments the interferometry will also be applied to measured data from LAIA. This will enable the evaluation of atmospheric models. Furthermore, the results will directly be applicable to the verification of the 'Comprehensive Nuclear-Test-Ban Treaty' (CTBT), where uncertainties in the atmospheric propagation of infrasound play a dominant role.

Fricke, Julius; Evers, Läslo; Simons, Dick; Wapenaar, Kees

2010-05-01

137

Footprint variability analysis of a Large Aperture Scintillometer over a complex terrain  

NASA Astrophysics Data System (ADS)

Surface flux measurement of scalar at a given height is representative of an area usually called « footprint ». Its extent is related to atmospheric conditions (Stability, wind speed, wind direction and wind diffusivity), to aerodynamic properties of the measurement site (Surface roughness), and to the instrumental setup (Sensor height). Several models have been developed to describe this function of inversion. Those provide a theoretical footprint. This study is an application of the Hsieh model in the case of a Large Aperture Scintillometer (LAS). The footprint model is combined with the LAS weighed function to produce the LAS footprint. To take into account the land partition in the footprint area to calculate the aggregated aerodynamic parameters required by the Hsieh model, we apply an iterative procedure to calculate the final footprint. A first sensibility analysis is presented. It shows that LAS are less sensible to wind direction if compared with eddy correlation measurement systems. In the framework of the « AMMA-CATCH » program, a LAS has been installed over an heterogeneous catchment in North Benin under a sudanian climate. The footprint analysis shows that the LAS footprint (~1km2) and the catchment (12km2) have the same land partition whatever the wind conditions. In the context of complex terrain, most of the parameters required in the Hsieh model are not constant along the scintillometer transect, because of the topography of the catchment under the scintillometer beam. Moreover, topography induces local deviation of the synoptic wind conditions. We propose a first sensitivity study to investigate the footprint variability induced by height variation of the beam over the ground. In addition, first results from Large Eddy Simulation are used to analyse surface wind deviations due to topography effect. All sensitivity studies are evaluated by their implication on the footprint extent and on its land use partition.

Guyot, A.; Cohard, J.-M.; Doukoure, M.; Anquetin, S.; Galle, S.; Zin, I.

2009-04-01

138

Full-aperture tilt measurement technique with a laser guide star  

NASA Astrophysics Data System (ADS)

A technique for measuring a full aperture tilt (FAT) with a laser guide star (LGS) is proposed. It is shown that information about a FAT is lost in a conventional LGS scheme because of the reciprocity of propagation paths. As a consequence neither the conventional LGS scheme nor its modifications with the receiver coaxial with the transmitter can be used to sense the FAT. A bistatic scheme that permits us to overcome the above difficulty is considered. This scheme permits us to single out the tilt component corresponding to the transmitting beam which is highly correlated with the FAT for a natural star. The tilt component corresponding to the reflected wave can be averaged out by averaging a LGS image motion over its angular extent. Such an averaging, however, does not affect the tilt component corresponding to the transmitting beam. This tilt conservation effect occurs due to the fact that a random motion of the transmitting beam causes a displacement of the LGS as a whole. The accuracy of measuring a FAT with a LGS is determined and the requirements for the measurement scheme are discussed.

Belen'kii, Mikhail S.

1995-06-01

139

Dynamic aperture optical arrays based on polymeric MEMS actuators for large scale coding elements with application in visible to MWIR  

NASA Astrophysics Data System (ADS)

Extension of coded apertures to the MWIR introduces the effects of diffraction and other distortions not observed in shorter wavelength systems. A new approach is being developed under the DARPA/SPO funded LACOSTE (Large Area Coverage Optical search-while Track and Engage) program, that addresses the effects of diffraction while gaining the benefits of coded apertures, thus providing flexibility to vary resolution, possess sufficient light gathering power, and achieve a wide field of view (WFOV). The photonic MEMS "eyelid" array technology is currently being instantiated in this DARPA Surveillance program study as the "heart", mediating the flow of the incoming signal. However, speed, lifetime, packaging and scalability are critical factors for the MEMS "eyelid" technology which will determine system efficacy as well as military and commercial usefulness. The electronic eyelid array is the fundamental addressable unit for adaptive code generation and will allow the system to multiplex in time for increased resolution. The binary code which determines whether a 500?m eyelid is open or closed is referred to as the "eyelid code." Groups of eyelids can work together as a "super aperture" by virtue of a "macro-code." A macro code becomes relevant to describe how dispersed eyelids across the 0.19m x 0.19m aperture will function together. Dynamic aperture arrays were fabricated on both quartz and sapphire substrates for operation in the visible to MWIR. Both 8x8 and 40x40 element arrays were designed, fabricated, and tested with macro-codes consisting of 4, 8, and 16 unique combinations. The die were packaged and tested in ambient for robust eyelid operations. The point spread function was also measured in an optical setup with the eyelid arrays located in the aperture plane.

Goodwin, S.; Carlson, J.; Rogers, S.; Kim, J.; Kim, C.; Brady, D.; Stoner, B. R.

2007-10-01

140

LCLS X-ray mirror measurements using a large aperture visible light interferometer  

SciTech Connect

Synchrotron or FEL X-ray mirrors are required to deliver an X-ray beam from its source to an experiment location, without contributing significantly to wave front distortion. Accurate mirror figure measurements are required prior to installation to meet this intent. This paper describes how a 300 mm aperture phasing interferometer was calibrated to <1 nm absolute accuracy and used to mount and measure 450 mm long flats for the Linear Coherent Light Source (LCLS) at Stanford Linear Accelerator Center. Measuring focus mirrors with an interferometer requires additional calibration, because high fringe density introduces systematic errors from the interferometer's imaging optics. This paper describes how these errors can be measured and corrected. The calibration approaches described here apply equally well to interferometers larger than 300 mm aperture, which are becoming more common in optics laboratories. The objective of this effort was to install LCLS flats with < 10 nm of spherical curvature, and < 2 nm rms a-sphere. The objective was met by measuring the mirrors after fabrication, coating and mounting, using a 300 mm aperture phasing interferometer calibrated to an accuracy < 1 nm. The key to calibrating the interferometer accurately was to sample the error using independent geometries that are available. The results of those measurements helped identify and reduce calibration error sources. The approach used to measure flats applies equally well to focus mirrors, provided an additional calibration is performed to measure the error introduced by fringe density. This calibration has been performed on the 300 mm aperture interferometer, and the measurement correction was evaluated for a typical focus mirror. The 300 mm aperture limitation requires stitching figure measurements together for many X-ray mirrors of interest, introducing another possible error source. Stitching is eliminated by applying the calibrations described above to larger aperture instruments. The authors are presently extending this work to a 600 mm instrument. Instruments with 900 mm aperture are now becoming available, which would accommodate the largest mirrors of interest.

McCarville, T; Soufli, R; Pivovaroff, M

2011-03-02

141

System Aspects of Dual-Layer Phase-Change Recording with High Numerical Aperture Optics and Blue Laser  

NASA Astrophysics Data System (ADS)

In this publication, key technologies for blue laser recording and dual layer phase-change disks with a total capacity of 50 Gbytes are explained and system margins are evaluated. Key challenges are the phase-change recording layer design, a robust read and write system with low intrinsic noise and the optical pickup design including, e.g., high numerical aperture (NA) objective lens, spherical aberration compensation devices and beam shaping optics. Blue-laser dual-layer technology will be emerging as the next-generation optical data storage standard beyond compact discs (CDs) and digital versatile discs (DVDs).

Richter, Hartmut; Hofmann, Holger; Knittel, Joachim; Kawakubo, Osamu; Kashiwagi, Toshiyuki; Mijiritskii, Andrei; Hellmig, Jochen

2003-02-01

142

A Field Cancellation Algorithm for Constructing Economical Planar Permanent Magnet (PM) Multipoles With Large High Quality Field Apertures  

SciTech Connect

In recent years studies have been initiated on a new class of multipole field generators consisting of cuboid planar permanent magnet (PM) pieces arranged in biplanar arrays of 2-fold rotational symmetry. These structures, first introduced for Free Electron Laser (FEL) applications, are based on reducing the rotational symmetry of conventional N-pole field generators from N-fold to 2-fold. One consequence of this reduction is a large higher-multipole content in a planar PM multipole's field at distances relatively close to the structure's axis, making it generally unsuitable for applications requiring a large high-quality field aperture. In this paper we outline an economical field-cancellation algorithm that can substantially decrease the harmonic content of a planar PM's field without breaking its biplanar geometry or 2-fold rotational symmetry. An economical field-cancellation algorithm has been described which will allow the fabrication of bi-planar quadrupoles and sextupoles with high-quality fields using a manageably small number of PM pieces. For higher order N-poles the number of pieces required to cancel a given number of successively-higher multipole components will also increase linearly; nevertheless, the practicability of fabricating octupoles and higher N-poles of this type should be considered a subject of continuing r&d. Since the removal of a large number of successive multipole components essentially increases the transverse region over which the N-pole's field is dominated by its leading N-pole field component, the fabrication of quadrupoles and sextupoles of the type described in this paper should lead to their introduction in storage ring applications. One potentially important application in this area is as distributed focusing elements installed into very-short-period, small-gap undulators (e.g., as a FODO lattice). The installation is rendered feasible by the very small vertical height of the biplanar N-poles (on the order of a millimeter), which, notwithstanding, doesn't prevent them from attaining focusing gradients on the order of several hundred T/m. If proven, this would allow short-period undulators of substantial length (viz., >>b) to be operated on storage rings, potentially transforming the optimality and economy of synchrotron radiation sources toward more favorable regimes.

Tatchyn, Roman; /SLAC

2011-08-12

143

High fidelity large aperture periodically poled Rb:KTiOPO4 for high energy frequency conversion  

Microsoft Academic Search

We demonstrate periodic poling of 5 mm thick Rb-doped KTiOPO4 crystals at room temperature. The ferroelectric domain grating is shown to be uniform and homogeneous across the whole crystal aperture. OCIS codes: (160.2260) Ferroelectrics; (190.4410) Nonlinear optics, parametric processes

Andrius Zukauskas; Nicky Thilmann; Valdas Pasiskevicius; Fredrik Laurell; Carlota Canalias

2011-01-01

144

Comparison of nxn grille CTF measurement for VESA standard and large-sample aperture methods  

Microsoft Academic Search

An alternative method for measuring the contrast transfer function (CTF) of a pixilated display is proposed that reduces the amount of time required to perform a high sample rate-small aperture luminance scan as outlined in the Video Electronics Standards Association (VESA) standard for measuring the contrast of an n X n grille. The alternative method proposed by the Night Vision

Russell S. Draper; Charles E. Bradford; David A. Fellowes

2002-01-01

145

Artificial eyelid dynamic aperture optical arrays for large scale coding elements with application in the visible to MWIR  

NASA Astrophysics Data System (ADS)

The use of coded apertures in a large area MWIR system introduces a number of difficulties including the effects of diffraction and other distortions not observed in shorter wavelength systems. A new approach is being developed that addresses the effects of diffraction while gaining the benefits of coded apertures, thus providing the flexibility to vary resolution, possess sufficient light gathering power, and achieve a wide field of view (WFOV). The photonic MEMS artificial eyelid array technology is currently being applied as the coded aperture in this program for surveillance enabling technology development. Speed, lifetime, packaging and scalability are all critical factors for the MEMS eyelid technology to determine system efficacy as well as military and commercial usefulness. The electronic eyelid is the fundamental addressable unit for adaptive code generation and will allow the system to multiplex in time for increased resolution. The proposed system consists of four subsystems in parallel with each subsystem consisting of four subapertures. Each sub-aperture contains an artificial eyelid array capable of 36 different, independent patterns of open 500µm eyelids corresponding to 36 different look directions. Dynamic aperture arrays were fabricated on both quartz and sapphire substrates for operation in the visible to MWIR. Both 8x8 and 40x40 element arrays were designed, fabricated, and tested with the capability of 4, 8, and 16 unique pattern combinations. Process and device improvements have been implemented to improve the yield of the MEMS arrays. In addition to mechanical evaluations, the eyelid arrays were tested optically to demonstrate the capability of multiple look directions.

Goodwin, Scott; Stoner, Brian R.; Carlson, Jim; Rogers, Stanley

2008-08-01

146

Design and experiment of a large aperture digital beam deflector based on electro-optic crystal switch array  

NASA Astrophysics Data System (ADS)

A large aperture two-dimensional (2D) digital beam deflector based on electro-optic (EO) crystal switch array has been proposed and experimentally demonstrated. The deflector employs cascaded beams splitting units, which consist of LiNbO3 EO switches and polarizing beam splitters, and a deflecting prism array to produce a 2D array of beam positions with a wide field of view. Design, construction, and performance of a 3×3 rectangle scanning array with a clear aperture of 6.5 mm are described in detail. Transmission efficiency, half-wave voltage, and scanning speed are measured to describe the performance of the EO switches. The effect of deviation of the input light from the optical axis is analyzed and a technique to diminish this effect is also proposed.

Yan, A. M.; Zhi, Y. N.; Sun, J. F.; Liu, L. R.

2012-05-01

147

Large-volume ionization chamber with variable apertures for air-kerma measurements of low-energy radiation sources  

SciTech Connect

This report describes the design and initial measurement results of a large-volume ionization chamber designed to realize the air kerma from therapeutic radiation sources emitting photons with energies up to about 70 keV. The measured ionization current is used to provide absolute source calibrations by the most widely used brachytherapy source strength metric called air-kerma strength. The variable-aperture free-air chamber (VAFAC), named because of its variable aperture stand, will provide insight into the angular dependence of air-kerma strength measurements. Another unique feature of this ionization chamber is its seed holder design that reduces unwanted scatter, ensures vertical positioning, and rotates the seed with a positional accuracy of 0.3 deg. Benchmark experiments show that the VAFAC agrees well with existing National Institute of Standards and Technology standards and is capable of measuring clinical-strength seeds with repeatabilities of less than 2% at the 1{sigma} level (k=1)

Culberson, W.S.; DeWerd, L.A.; Anderson, D.R.; Micka, J.A. [Department of Medical Physics, University of Wisconsin-Madison, 1300 University Avenue, Madison, Wisconsin 53706 (United States)

2006-01-15

148

Full aperture backscatter station imager diagnostics system for far-field imaging of laser plasma instabilities on Nova  

SciTech Connect

In ICF, the understanding of laser plasma scattering processes is essential for laser target coupling and for controlling the symmetry of indirect drive implosions. The existing Nova full aperture backscatter station has been useful in understanding laser plasma instabilities occurring in hohlraums by measuring the quantity, spectral distribution, and near-field spatial distributions of Brillouin and more recently Raman backscatter. Equally important is an understanding of the far-field spatial intensity distribution which could help in understanding filamentation, threshold and saturation processes. This article describes a broadband, color-corrected far-field imager and associated diagnostics capable of imaging the source of scattered light to better than 25 {mu}m resolution. Brillouin and Raman backscatter can be imaged through the Nova beam-7 focusing lens or the imager can be used like a microscope to image side scatter from other beams. {copyright} {ital 1997 American Institute of Physics.}

Wilke, M.D.; Fernandez, J.C.; Berggren, R.R.; Horton, R.F.; Montgomery, D.S.; Faulkner, J.A.; Looney, L.D.; Jimerson, J.R. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1997-01-01

149

Simulation studies of space-charge-dominated beam transport in large aperture ratio quadrupoles  

SciTech Connect

For many cases of interest in the design of heavy-ion fusion accelerators, the maximum transportable current in a magnetic quadrupole lattice scales as ({alpha}/L){sup 2} where {alpha} is the useful dynamic aperture and L is the half-lattice period. There are many cost benefits to maximizing the usable aperture which must be balanced against unwanted effects such as possible emittance growth and particle loss from anharmonic fringe fields. We have used two independent simulation codes to model space-charge dominated beam transport both in an azimuthally-pure quadrupole FODO lattice design and in a more conventional design. Our results indicate that careful matching will be necessary to minimize emittance growth and that ({alpha}/L) ratios of 0.2 or larger are possible for particular parameters.

Fawley, W.M.; Laslett, L.J.; Celata, C.M.; Faltens, A. [Lawrence Berkeley Lab., CA (United States); Haber, I. [Naval Research Lab., Washington, DC (United States)

1993-05-01

150

A Large Aperture Fabry-Perot Tunable Filter Based On Micro Opto Electromechanical Systems Technology  

NASA Astrophysics Data System (ADS)

A research and development effort sponsored by the NASA Goddard Spaceflight Center (GSFC) is focused on applying Micro Opto Electromechanical Systems (MOEMS) technology to create a miniature Fabry-Perot tunable filter for space and ground-based near infrared imaging spectrometer applications. Unlike previous devices developed for small-aperture telecommunications systems, the GSFC research is directed toward a novel 12 - 40 mm aperture for astrophysical studies, including emission line imaging of galaxies and nebulae, and multi-spectral redshift surveys in the 1.1 - 2.3 um wavelength region. The MOEMS design features integrated electrostatic scanning of the 11-um optical gap, and capacitance micrometry for closed loop control of parallelism within a 10-nm tolerance. The low thermal mass and inertia inherent in MOEMS devices allows for rapid cooling to the proposed 30 K operating temperature, and high frequency response. Achieving the proposed 6-nm aperture flatness (with an effective finesse of 50) represents the primary technical challenge in the current 12-mm prototype.

Palmer, J. A.; Greenhouse, M. A.; Mott, D. B.; Barclay, R. B.; Powell, W. D.; Hsieh, W. T.

2002-12-01

151

Operation of a DC large aperture volume-production H sup minus source  

SciTech Connect

In testing a multicusp volume-production H{sup {minus}} ion source (20 cm diameter, 23 cm long), we optimized the gas pressure, the plasma electrode bias potential and the magnetic filter. At the optimum pressure of 9 mT, the H{sup {minus}} beam output increased linearly with discharge power. The maximum H{sup {minus}} beam, measured with a current transformer downstream of the accelerator, was 100 mA while using a 6.67 cm{sup 2} aperture. Presently we are limited by overheating of the cathodes by the plasma ions. Under similar discharge conditions the maximum H{sup {minus}} current density was found to vary as a{sup {minus}0.7} where a is the aperture radius. Results from emittance measurements showed that the effective H{sup {minus}} ion temperature increased with a for a {gt} 0.8 cm. Thus the brightness of the beam decreased with increasing aperture radius. Operating the source with cesium would increase the H{sup {minus}} output however our accelerator must be improved to avoid breakdowns caused by the cesium contamination. 8 refs., 6 figs.

Kwan, J.W.; Ackerman, G.D.; Anderson, O.A.; Chan, C.F.; Cooper, W.S.; deVries, G.J.; Leung, K.N.; Lietzke, A.F.; Steele, W.F.

1989-04-01

152

Operation of a dc large aperture volume-production H sup minus source  

SciTech Connect

In testing a multicusp volume-production H{sup {minus}} ion source (20 cm diameter, 23 cm long), we optimized the gas pressure, the plasma electrode bias potential, and the magnetic filter. At the optimum pressure of 9 mTorr, the H{sup {minus}} beam output increased linearly with discharge power. The maximum H{sup {minus}} beam, measured with a current transformer downstream of the accelerator, was 100 mA while using a 6.67-cm{sup 2} aperture. Presently we are limited by overheating of the cathodes by the plasma ions. Under similar discharge conditions the maximum H{sup {minus}} current density was found to vary as {ital a}{sup {minus}0.7}, where {ital a} is the aperture radius. Results from emittance measurements showed that the effective H{sup {minus}} ion temperature increased with {ital a} for {ital a}{gt}0.8 cm. Thus, the brightness of the beam decreased with increasing aperture radius. Operating the source with cesium would increase the H{sup {minus}} output; however, our accelerator must be improved to avoid breakdowns caused by the cesium contamination.

Kwan, J.W.; Ackerman, G.D.; Anderson, O.A.; Chan, C.F.; Cooper, W.S.; deVries, G.J.; Leung, K.N.; Lietzke, A.F.; Steele, W.F. (Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (US) )

1990-01-01

153

Novel Adaptive Optics concepts : wavefront sensing with sodium laser guide stars at Extemely Large Telescopes and simultaneous differential imaging  

Microsoft Academic Search

Since more than 15 years, Adaptive Optics (AO) is a proven concept to reach diffraction limited imaging at modern astronomical telescopes. In the case of next generation telescopes (Extremely Large Telescopes (ELTs)) with aperture diameters of up to 100m, sodium laser guide star based multi-conjugated-AO systems will be a basic requirement to exploit their full capability in terms of resolution

Stephan Albert Kellner

2005-01-01

154

Microscopic characterization of laser-induced damage performance of large-size KDP and DKDP nonlinear crystals  

Microsoft Academic Search

KDP and DKDP are unique materials for frequency conversion in large-aperture laser systems. Under high power irradiation, a threshold exists above which multiple damage sites are formed in the bulk of crystal plates thus obstructing beam propagation and creating undesirable beam modulations. Damage testing has focused on measuring the irradiation threshold fluences that lead to irreversible material modifications. However, small

Paul DeMange; Christopher W. Carr; Harry B. Radousky; Stavros G. Demos

2004-01-01

155

Amplification of femtosecond pulses to above 1 J with large aperture Cr:LiSrAIF{sub 6} amplifiers  

SciTech Connect

The authors have developed a chirped pulse amplification system capable of producing femtosecond pulses with energy above one joule. This is accomplished by using a large aperture, flashlamp pumped Cr-LiSrAlF{sub 6} (Cr:LiSAF) amplifier. Optimum design of the 19 mm diameter amplifier results in a single pass gain of 5 with good beam quality. This amplifier produces 1.05 J pulses after compression with a width of < 125 fs at a repetition rate of 0.05 Hz.

Ditmire, T.; Perry, M.D.

1995-01-01

156

Focusing of doughnut laser beams by a high numerical-aperture objective in free space  

Microsoft Academic Search

We report on, in this letter, a phenomenon that the central zerointensity point of a doughnut beam, caused by phase singularity, disappears in the focus, when such a beam is focused by a high numerical-aperture objective in free space. In addition, the focal shape of the doughnut beam of a given topological charge exhibits the increased ring intensity in the

Djenan Ganic; Xiaosong Gan; Min Gu

2003-01-01

157

Large Aperture Diagnostic System for Gain and Wavefront Measurements on NIF/LMJ Amplifiers.  

National Technical Information Service (NTIS)

We are in the midst of constructing an amplifier laboratory (Arnplab) that will be the physics and engineering proving ground for fill sized segmented glass amplifiers of designs that will outfit the National Ignition Facility (NIF) and Laser Megajoule (L...

L. E. Zapata R. McCracken A. Erlandson J. L. Guenet E. Grebot S. Seznec

1997-01-01

158

Anisotropic self-lasing in large-aperture Ti:sapphire crystals  

Microsoft Academic Search

Summary form only given. The Ti:sapphire lasers of a 100 TW-Petawatt power level need active crystals of 30-100 mm diameter. Because of high amplification gain those crystals are subjected to a high parasitic lasing. We have currently upgraded our Ti:sapphire laser system for 30 TW in a 10-Hz mode and 100 TW in a single shot mode. The last power

M. P. Kalachnikov; V. Karpov; H. Schonnagel

2002-01-01

159

Modal phase correction for large-aperture ground-based telescope with multiguide stars  

Microsoft Academic Search

Simple analytical expressions for parameter Strehl of ground-based astronomical telescope: (i) without adaptive correction, (ii) phase correction with use single laser guide star, (iii) phase correction with use multi-guide stars (square matrix system of guide stars with variable number of elements) are obtained. Models of the vertical dependence of the structure parameter of refractive index of the turbulent atmosphere for

Lidia A. Bolbasova; Vladimir P. Lukin

2009-01-01

160

Experimental Instrumentation System for the Phased Array Mirror Extendible Large Aperture (PAMELA) Test Program.  

National Technical Information Service (NTIS)

Adaptive optics are used in telescopes for both viewing objects with minimum distortion and for transmitting laser beams with minimum beam divergence and dance. In order to test concepts on a smaller scale, NASA MSFC is in the process of setting up an ada...

W. H. Boykin

1993-01-01

161

Laser scanning system for large diameter measurement  

NASA Astrophysics Data System (ADS)

In this paper, it is described the work principle and total structure and design of the laser-scanned measuring systerm for the large diameter. Signal characteristics of scanning system is described,the circuit and method for boundaries detection and drift errors. The feasibility of the system is tested by practice, the accuracy of boundary distinguishing is up to +/-1?m,and continuous working errors up to +/-5?m,measurement range up to 0~400mm. This system shows a better method for measuring large diameters.

Chen, Liang; Zhang, Shuqin; Ji, Shangzhong; Chang, Benkang; Yu, Jun

2009-11-01

162

Development of a high-power vertical-cavity surface-emitting laser array with ion-implanted current apertures  

NASA Astrophysics Data System (ADS)

Vertical-Cavity Surface-Emitting Lasers (VCSELs) are very attractive to high power light sources owing to the advantageous configuration of two-dimensional arrays and being free from catastrophic optical damage. Although oxideconfined VCSELs have been employed in most of applications with VCSELs, ion-implanted VCSELs have a potential to be the better light sources for high power applications. In spite of the fact, the detailed characteristics of the ionimplanted VCSELs had been researched only in ten milliwatt-class output power. Here we report on a high power VCSEL-array with proton-implanted current apertures. A peak output power of over 40 W under short-pulse operation has been achieved. This is the first demonstration of ten watt-class output power for ion-implanted VCSELs.

Naito, Hideyuki; Miyamoto, Masahiro; Aoki, Yuta; Higuchi, Akira; Torii, Kousuke; Nagakura, Takehito; Morita, Takenori; Maeda, Junya; Miyajima, Hirofumi; Yoshida, Harumasa

2013-03-01

163

Optical breakdown of window surfaces of wide-aperture TEA CO2 lasers by microsecond pulses  

NASA Astrophysics Data System (ADS)

It has been established, that the surface destruction has 3 stages: breakdown origin (the distance is 3 - 5 mm from the surface timed up to 1 microsecond(s) regarding leading edge of laser pulse); evaporation (timed for 3 - 5 microsecond(s) ); interaction of the adsorbents with plasma torch and laser radiation, heating and cracking under the influence of UF plasma radiation.

Kazantsev, Sergei G.

1999-01-01

164

Mg-doped congruent LiTaO3 crystal for large-aperture quasi-phase matching device.  

PubMed

Mg-doped congruent composition LiTaO(3) (MgLT) crystal, which can be grown by a conventional Czochralski method, has improved properties such as transparent range, thermal conductivity, and coercive field compared to conventional undoped congruent LiTaO(3). In this paper, various properties of MgLT including Mg-doping dependence are characterized, and also compared to that of undoped congruent LiTaO(3), LiNbO(3), and Mg-doped congruent LiNbO(3), as a material of high power quasi-phase matching (QPM) device. Up to 3-mm-thick periodically poled MgLT crystal is shown to demonstrate the possibility of large-aperture QPM-MgLT devices. Subsequently, optical parametric oscillation experiments by using periodically poled MgLT are demonstrated to discuss an efficient QPM condition. PMID:18852804

Ishizuki, Hideki; Taira, Takunori

2008-10-13

165

Concept study of an Extremely Large Hyper Telescope (ELHyT) with 1200m sparse aperture for direct imaging at 100 micro-arcsecond resolution  

NASA Astrophysics Data System (ADS)

The hypertelescope construction initiated in the Southern Alps (Labeyrie et al., this conference) has provided some preliminary operating experience indicating that larger versions, up to perhaps 1200m, are probably feasible at suitable sites. The Arecibo-like architecture of such instruments does not require the large mount and dome which dominate the cost of a 40m ELT. For the same cost, an "Extremely Large Hyper Telescope” ( ELHyT) may therefore have a larger collecting area. It may thus in principle reach higher limiting magnitudes, both for seeing-limited and, if equipped with a Laser Guide Star and adaptive phasing, for high-resolution imaging with gain as the size ratio, i.e. about 30 with respect to a 40m ELT. Like the radio arrays of antennas, such instruments can be grown progressively. Also, they can be up-graded with several focal gondolas, independently tracking different sources. Candidate sites have been identified in the Himalaya and the Andes. We describe several design options and compare the science achievable for both instruments, ELTs and ELHyTs. The broad science addressed by an ELHyT covers stellar chromospheres, transiting exoplanets and those requiring a high dynamic range, achieved by array apodization or coronagraphy. With a Laser Guide Star, it extends to faint compact sources beyond the limits of telescopes having a smaller collecting area, supernovae, active galactic nuclei, gamma ray bursts. The sparse content of remote galaxies seen in the Hubble Deep Field appears compatible with the crowding limitations of an ELHyT having 1000 apertures.

Labeyrie, Antoine; Mourard, Denis; Allouche, Fatmé; Chakraborthy, Rijuparna; Dejonghe, Julien; Surya, Arun; Bresson, Yves; Aime, Claude; Mary, David; Carlotti, Alexis

2012-07-01

166

The study on servo-control system in the large aperture telescope  

NASA Astrophysics Data System (ADS)

Large astronomical telescope or extremely enormous astronomical telescope servo tracking technique will be one of crucial technology that must be solved in researching and manufacturing. To control technique feature of large astronomical telescope or extremely enormous astronomical telescope, this paper design a sort of large astronomical telescope servo tracking control system. This system composes a principal and subordinate distributed control system, host computer sends steering instruction and receive slave computer functional mode, slave computer accomplish control algorithm and execute real-time control. Large astronomical telescope servo control use direct drive machine, and adopt DSP technology to complete direct torque control algorithm, Such design can not only increase control system performance, but also greatly reduced volume and costs of control system, which has a significant occurrence. The system design scheme can be proved reasonably by calculating and simulating. This system can be applied to large astronomical telescope.

Hu, Wei; Zhang, Zhenchao; Wang, Daxing

2008-08-01

167

Measurement of wavefront structure from large aperture optical components by phase shifting interferometry  

SciTech Connect

This paper discusses the results of high spatial resolution measurement of the transmitted or reflected wavefront of optical components using phase shifting interferometry with a wavelength of 6328 {angstrom}. The optical components studied range in size from approximately 50 mm {times} 100 mm to 400 mm {times} 750 mm. Wavefront data, in the form of 3-D phase maps, have been obtained for three regimes of scale length: ``micro roughness``, ``mid-spatial scale``, and ``optical figure/curvature.`` Repetitive wavefront structure has been observed with scale lengths from 10 mm to 100 mm. The amplitude of this structure is typically {lambda}/100 to {lambda}/20. Previously unobserved structure has been detected in optical materials and on the surfaces of components. We are using this data to assist in optimizing laser system design, to qualify optical components and fabrication processes under study in our component development program.

Wolfe, C.R.; Lawson, J.K.; Kellam, M.; Maney, R.T.; Demiris, A.

1995-05-12

168

The role of small-scale aperture variability on the formation of large-scale dissolution channels in rough-walled fractures exposed to reactive fluid flow  

NASA Astrophysics Data System (ADS)

Flow of reactive fluids through variable-aperture fractures can lead to geochemical alteration of the fracture surfaces resulting in localized changes in fracture permeability. For a pore fluid that is undersaturated with respect to the minerals forming the fracture surfaces, chemical reactions lead to dissolution and increases in local fracture apertures. Local dissolution rates tend to be positively correlated with fracture aperture, (i.e. larger flow rates lead to locally higher flow rates and faster dissolution) resulting in a positive feedback mechanism that can lead to instabilities in the reaction front. Under certain conditions, reaction front instabilities lead to the formation of distinct dissolution channels that significantly alter the large-scale transport properties of fractured media. The formation of dissolution channels and the rate of their propagation are sensitive to parameters including the dimensionless Peclet and Damkohler numbers (Pe=advective/diffusive transport Da=surface reaction rate/advective transport), and the statistics (mean and variance), spatial correlation structure, and size of the fracture aperture field. We have developed an enhanced computational model of reactive fluid flow through variable aperture fractures in which the small-scale variability of the fracture aperture is represented explicitly. Fluid flow, transport of dissolved components and surface reactions are all calculated using depth-averaged formulations of the governing equations, which allows us to explore the influence of small-scale aperture variability on the formation of dissolution at scales much larger than the aperture correlation length. Enhancements to this code include implementation of a higher order advection scheme to minimize the influence of numerical dispersion and parallelization of the algorithm to allow large-scale simulations (>>10 million nodes). Direct comparison to dissolution experiments has demonstrated that this model effectively simulates the observed behavior over a range of Pe and Da. We present results from a series of fracture dissolution simulations in which we systematically varied Pe, Da, and fracture size in synthetic fractures with identical aperture statistics (mean and variance) and correlation structure. Results demonstrate that the length scale required for development of distinct dissolution channels increases for larger Pe and smaller Da. Furthermore, the spacing of distinct dissolution channels scales with the length of the longest channels. These results suggest the potential for the development of generalized scaling relationships to quantify the channeling induced by reactive fluid flow in variable aperture fractures. This work was performed under the auspices of the DOE by the University of California, Lawrence Livermore National Laboratory under contract No. 7405-Eng-48.

Detwiler, R. L.; Ezzedine, S. M.; Rajaram, H.; Morris, J. P.

2005-12-01

169

New large optical cavity laser with distributed active layers  

SciTech Connect

A new semiconductor current injection laser having multiple active layers distributed within a large optical cavity (LOC) waveguide is shown to operate as an efficient, low-threshold, high-peak power laser diode. The use of distributed active layers in LOC laser structure leads to improved efficiency in utilizing the injected carriers when compared to the conventional single active layer LOC laser structure.

Tsang, W.T.; Olsson, N.A.

1983-05-15

170

Large-scale temporal and spatial imaging of soil brightness temperature with an L-band synthetic aperture microwave radiometer  

Microsoft Academic Search

The Microwave Remote Sensing Lab (MIRSL) at the University of Massachusetts has developed a second-generation L-band synthetic aperture microwave radiometer referred to as the Electronically Steered Thinned Array Radiometer, or ESTAR, which measures soil moisture or ocean salinity from an airborne platform. This dissertation reviews the basics of synthetic aperture microwave radiometry, then details recent modifications to the ESTAR instrument,

John D. Isham

1999-01-01

171

Advances in the development of x-ray refractive large aperture rolled prism lenses  

Microsoft Academic Search

At the Institute of Microstructure Technology (IMT) at Karlsruhe Institute of Technology (KIT) X-ray refractive line focus lenses have been developed. They consist of a large number of concave bi-parabolic lens elements made of SU8. To form a point focus two of these lens stacks, tilted by 90° with respect to each other around the optical axis, need to be

H. Vogt; R. Eisenhower; A. Last; K. U. Mettendorf; J. Mohr; V. Nazmov; M. Simon

2011-01-01

172

Laser aperture diagnostics system for gain and wavefront measurements on NIF\\/LMJ amplifiers  

Microsoft Academic Search

We are in the midst of constructing an amplifier laboratory (Arnplab) that will be the physics and engineering proving ground for fill sized segmented glass amplifiers of designs that will outfit the National Ignition Facility (NIF) and Laser Megajoule (LMJ) projects. Amplab will demonstrate the cornerstone mechanical, electrical and optical concepts that support the NW and LMJ amplifier schemes. Here

1996-01-01

173

Research of active panel technology for large aperture millimeter-wave/sub-millimeter-wave telescope  

NASA Astrophysics Data System (ADS)

As Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) project was completed successfully, indicating the key technology of active optics has been mastered by the Chinese astronomical community, experts of Nanjing Institute of Astronomical Optics and Technology (NIAOT), builders of this project, started to consider how to use the technology developed in large optical telescope such as LAMOST to improve the performance of millimeterwave / sub-millimeter-wave telescope. In order to do more research work about active optics of millimeter submillimeter band and improve the performance of Delingha 13.7m millimeter-wave telescope, researchers of NIAOT intend to upgrade the reflect panel accuracy of this telescope. This paper will introduce the preliminary work of the accuracy-upgrading task, numerical simulation of the 13.7m telescope. In this presentation, the primary reflector finite element model (FEM) construction, gravity and thermal deformation, and modal analyze are described. The result shows that the gravity and thermal distortion of the reflector are contributed mostly by the back-structure and the active support for the panels is very necessary to restrain this kind of distortion.

Wu, Xuhao; Cui, Xiangqun

2010-05-01

174

Study on the Stressed Mirror Polishing with a Continuous Polishing Machine for Large Aperture Off-axis Aspheric Mirrors  

NASA Astrophysics Data System (ADS)

A special stressed annular polishing technique is proposed to mill the off-axis aspheric sub-mirrors of a large segmented mirror with an annular polishing machine. Based on the basic principle of stressed annular polishing technique, a set of special stressing mechanisms are designed to convert milling the aspheric surfaces of sub-mirrors with different off-axis distances into milling the spherical surfaces with identical radii of curvature, so that they can be pol- ished simultaneously on a continuous polishing machine. It took about contin- uous 40 hours to polish a scaled-down mirror of the planning Chinese Future Giant Telescope (CFGT) using this technique. This mirror has the 330 mm di- ameter, 3.6 m off-axis distance, and the 21.6 m radius of curvature, and its max- imum asphericity is 16 micron. The experiment shows that this method has a high effciency, suits batch manufacturing, especially the batch manufacturing of aspheric sub-mirrors of the segmented primary mirror of an extremely large aperture telescope.

Li, Xin-nan; Zhang, Hai-ying; Cui, Xiang-qun; Jiang, Zi-bo; Zheng, Yi; Liu, Xing-tao; Ni, Hou-kun

2012-10-01

175

Design of large aperture four group elements mid-wave infrared zoom lens  

NASA Astrophysics Data System (ADS)

Zoom lens with variable focal length is well fit for researching objectives far and near. Design of zoom lens working at mid-wave infrared wavelength (7.7-10.3_m) and its view field 10 degrees is presented. Determination of the initial configuration of the variable and the compensate groups are discussed according to the mechanism compensate curves. The compensate group is determined with positive power. Its focal length changes during a large scope, which is from 300mm to 100mm. And the corresponding F number variables from 3.75 to 1.25. So the residual aberration needs to be carefully corrected. The optimized zoom lens is composed of four group elements, and its performance reaches diffraction limited at each focal position.

Ji, Yiqun; Shi, Rongbao; He, Hucheng; Shen, Weimin

2012-10-01

176

Optimization of Deposition Uniformity for Large Aperture NIF Substrates in a Planetary Rotation System  

SciTech Connect

Multilayer coatings on large substrates with increasingly complex spectral requirements are essential for a number of optical systems, placing stringent requirements on the error tolerances of individual layers. Each layer must be deposited quite uniformly over the entire substrate surface since any nonuniformity will add to the layer-thickness error level achieved. A deposition system containing a planetary rotation system with stationary uniformity masking is modeled, with refinements of the planetary gearing, source placement, and uniformity mask shape being utilized to achieve an optimal configuration. The impact of improper planetary gearing is demonstrated theoretically, as well as experimentally, providing more comprehensive requirements than simply avoiding repetition of previous paths through the vapor plume, until all possible combinations of gear teeth have been used. Deposition efficiency and the impact on the uniformity achieved are used to validate improved source placement.

Oliver, J.B.; Talbot, D.

2003-05-06

177

Temporal-spatial characteristics of area-averaged sensible heat flux by Large Aperture Scintillometer over Hai River Basin  

NASA Astrophysics Data System (ADS)

Due to the wide and deep application of Large Aperture Scintillometer (LAS), the scintillation method exhibits as a robust technique in measuring area-averaged sensible heat fluxes. As the path length of LAS is comparable to the pixel size of satellite images and grid scale of hydrological models, the measurements are helpful for validation. Meanwhile LAS has the potential to explore the scale effect, especially to bridge the gap from local to regional flux measurement. In our analysis, the ground measurements including LAS, Eddy Covariance (EC) system and Automatic Weather System(AWS), as well as TM/MODIS satellite in Miyun, Guantao and Daxing sites over Hai River Basin from 2008-2009 were selected, which can represent three different heterogeneous surfaces in Hai River Basin. After data processing and quality control, continuous sensible heat flux (Hlas) data on Kilometers Scale were obtained over various surfaces. Based on the footprint model of LAS, the distribution of source area for LAS measurements had been analyzed over Miyun, Guantao and Daxing sites in January, April, July and October, 2008. And then the daily variation of Hlas in January, April, July and October in 2008 over the three sites have been analyzed; the value and tendency of variation in these months are different among these sites, which are in accordance with the local crop phenophases. From the comparison of daily mean net radiation (Rn) and Hlas from 2008-2009 over the three sites, it can be seen the seasonal variation of Hlas are consistent in these two years, however, Miyun site shows a single peak while Guantao and Daxing sites show double-peak variation of Hlas, which mainly due to the different crop phenophases and irrigation conditions. At last, the difference between Hlas and Hec in Miyun and Guantao sites had been discussed separately. In accordance with the underlying surfaces, the reasons for the difference between Hlas and Hec can be attributed to the energy balance ratio of EC, the heterogeneity of the underlying surfaces as well as the relative weights of the overlap area between EC and LAS measurements. While in Guantao site, apart from the above reasons mentioned in Miyun site, the atmospheric instability may be one of the main reasons that contribute to the difference between Hlas and Hec. Key words: Large aperture scintillometer, Hai River Basin, Data processing and quality control, Temporal-spatial characteristics

Bai, J.; Liu, S. M.; Xu, Z. W.; Jia, L.; Ding, X. P.

2010-09-01

178

Resolution enhanced sparse aperture imaging  

Microsoft Academic Search

The resolution of a conventional diffraction limited imaging system is proportional to its entrance pupil diameter. The primary goal of multiple aperture imaging is to enhance resolution by increasing the effective aperture diameter, while also minimizing the total image collection area, the latter being desirable because of the cost and weight of large single aperture imaging systems. Provided is a

Nick Miller; Bradley Duncan; Matthew P. Dierking

2006-01-01

179

Combining a large aperture scintillometer and estimates of available energy to derive evapotranspiration over several agricultural fields in a semi-arid region  

Microsoft Academic Search

The objective of the present study was to investigate the potential of a large aperture scintillometer (LAS) combined with a simple available energy model to estimate area-averaged latent heat flux in difficult environmental conditions. The difficulties are related to the sparseness of the vegetation, the heterogeneity of the soil characteristics, and, most importantly, the heterogeneity in terms of soil moisture

JAMAL EZZAHAR; ABDELGHANI CHEHBOUNI; SALAH ER-RAKI; LAHOUCINE HANICH

2009-01-01

180

Active beam controlling of high power Q-switched Nd:YAG lasers for stable fiber coupling with small numerical aperture for material processing  

NASA Astrophysics Data System (ADS)

For mobile surface treatment it is convenient to work with flexible fiber coupled lasers. To keep the focusing optic sufficiently small it is necessary to have small fiber core diameters and a small outgoing numerical aperture. The knowledge of the resonator beam parameters is essential for long term stable fiber coupling conditions. We demonstrate that the out-coupling beam diameter is suitable as a control process variable for this purpose. For high power side pumped Nd:YAG lasers it is necessary to have an effective rod cooling to compensate thermal lensing. By adapting the rod cooling to the thermal lensing it is possible to keep the beam diameter constant. In this case the water flow of the rod cooling circuit has to be independent from pump diode cooling circuit and has to be controlled by a beam profile measurement inside the resonator. The half angle of the laser beam outside the resonator is dependent on the resonator length and the pump power and therefore the thermal lensing. If the beam diameter on the mirror is constant, the numerical aperture of the laser is also constant. If the beam diameter changes due to diode degradation or other effects inside the resonator, the diameter as a process control variable should control the flow of the rod cooling. Thus, the thermal lensing could be adapted, to control the beam diameter and as a result the numerical aperture for the fiber.

Goehre, Mario; Becker, Christoph

2013-02-01

181

Large linewidth-enhancement factor in a microchip laser  

SciTech Connect

We evidence experimentally that the linewidth-enhancement factor {alpha} can take a rather large value ({alpha}{approx_equal}1) for a nonsemiconductor laser, here a Nd{sup 3+}: YAG microchip laser. This measure is performed using an original and simple method adapted to this kind of laser and based on the variations of the laser relaxation frequency when the laser is subjected to an optical feedback.

Szwaj, Christophe; Lacot, Eric; Hugon, Olivier [Laboratoire de Physique des Lasers, Atomes et Molecules, UMR CNRS 8523, CERLA, FR CNRS 1416, Universite des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq Cedex (France); Laboratoire de Spectrometrie Physique, UMR CNRS 5588, Universite Joseph Fourier, F-38402 Saint Martin d'Heres (France)

2004-09-01

182

Processing method and process modeling of large aperture transparent magnesium aluminate spinel domes  

NASA Astrophysics Data System (ADS)

Polycrystalline spinel serves as an alternative to materials such as sapphire and magnesium fluoride that are currently being used in electromagnetic window applications such as missile domes, where high strength, high hardness and high transmittance in the visible and infrared spectra are required. The cubic crystal lattice of spinel imparts an isotropy to the bulk optical property, which eliminates optical distortion due to birefringence that occurs in sapphire and other non-cubic materials. The current study is to find a reliable manufacturing process to produce large magnesium aluminate spinel domes from powder consolidation efficiently. A binder-less dry ball milling process was used to deflocculate the spinel powder to increase its fluidity in an effort to ease the shape-forming. Dry ball milling time trials were conducted at several intervals to determine the appropriate level of time required to break up both the hard and soft agglomerates associated with the virgin spinel powder. The common problems encountered in dry powder shape-forming are crack growth and delamination of the green body during cold isostatic pressing (CIPing). The cracking and the delamination are due to the buildup of stress gradients on the green body that are created by the frictional force between the powder and the die wall or mold wall. To understand the stresses during the CIPing process, a finite element analysis of stresses on the green body was conducted. The simulation was used to evaluate the effect of die tooling and process characteristics on the development of stress gradients in the green body dome. Additionally, the effect of friction between the die wall and powder was examined by the simulation. It was found that by mitigating the frictional forces, cracking and delamination on the green body could be eliminated. A stepped-pressure CIPing technique was developed to reduce stress gradient build-up during CIPing. Also, oleic acid lubricant was applied to the die wall to reduce the wall friction between the powder and the die itself. As a result of these two above-mentioned methods, it was demonstrated that it is possible to consolidate a binder-free powder into large defect-free domes.

Yu, Jian; McWilliams, Brandon; Kilczewski, Steven; Gilde, Gary; Lidie, Ashley; Sands, James

2009-05-01

183

Towards predicting the laser damage threshold of large-area optics  

SciTech Connect

As the size of optics increases, such as in the optical coatings being developed for the National Ignition Facility in US and the Laser MegaJoules in France, the difficulty also increases in measuring and defining their laser damage threshold. Measuring the threshold on small witness samples ({le}cm) rather than full aperture optic (=m) is advantageous, and in this article, the threshold of large-area components is addressed in two ways. First, a model based on the R-on-l threshold distribution is shown to predict the threshold of a large optic with a high degree of confidence. The average R-on-l threshold provides a reliable, accurate value to evaluate coatings. An automated damage test bench has been developed at CEA. Secondly, the damage threshold has to be defined according to final use of the component. LLNL has defined a functional damage threshold to set limits on maximum damage size. An empirical power law dependence of average damage size on peak fluence was found; this can be used to predict the damage behavior of large-aperture optics exhibiting the same damage morphology.

Hue, J. [CEA Centre d`Etudes Nucleaires de Grenoble, 38 (France). Lab. d`Electronique et de Technologie de l`Informatique; Genin, F.Y.; Maricle, S.M.; Kozlowski, M.R. [Lawrence Livermore National Lab., CA (United States)

1996-10-01

184

From monolithics to tethers to freeflyers: the spectrum of large aperture sensing from space  

NASA Astrophysics Data System (ADS)

As part of The National Aeronautics and Space Administration's (NASA's) endeavor to push the envelope and go where we have never been before, the Space Science Enterprise has laid out a vision which includes several missions that revolutionize the collection of scientific data from space. Many of the missions designed to meet the objectives of these programs depend heavily on the ability to perform space-based interferometry, which has recently become a rapidly growing field of investigation for both the scientific and engineering communities. While scientists are faced with the challenges of designing high fidelity optical systems capable of making detailed observations, engineers wrestle with the problem of providing space-based platforms that can permit this data gathering to occur. Observational data gathering is desired at a variety of spectral wavelengths and resolutions, calling for interferometers with a range of baseline requirements. Approaches to configuration design are as varied as the missions themselves from large monolithic spacecraft to multiple free-flying small spacecraft and everything in between. As will be discussed, no one approach provides a ?panacea? of solutions rather each has its place in terms of the mission requirements. The purpose here is to identify the advantages and disadvantages of the various approaches, to discuss the driving factors in design selection and determine the relative range of applicability of each design approach.

Leitner, Jesse; Quinn, Dave; Matsumura, Mark M.

2003-02-01

185

The ExaVolt Antenna: A large-aperture, balloon-embedded antenna for ultra-high energy particle detection  

NASA Astrophysics Data System (ADS)

We describe the scientific motivation, experimental basis, design methodology, and simulated performance of the ExaVolt Antenna (EVA) mission, and planned ultra-high energy (UHE) particle observatory under development for NASA's suborbital super-pressure balloon program in Antarctica. EVA will improve over ANITA's integrated totals - the current state-of-the-art in UHE suborbital payloads - by 1-2 orders of magnitude in a single flight. The design is based on a novel application of toroidal reflector optics which utilizes a super-pressure balloon surface, along with a feed-array mounted on an inner membrane, to create an ultra-large radio antenna system with a synoptic view of the Antarctic ice sheet below it. Radio impulses arise via the Askaryan effect when UHE neutrinos interact within the ice, or via geosynchrotron emission when UHE cosmic rays interact in the atmosphere above the continent. EVA's instantaneous antenna aperture is estimated to be several hundred m2 for detection of these events within a 150-600 MHz band. For standard cosmogenic UHE neutrino models, EVA should detect of order 30 events per flight in the EeV energy regime. For UHE cosmic rays, of order 15,000 geosynchrotron events would be detected in total, several hundred above 10 EeV, and of order 60 above the GZK cutoff energy.

Gorham, P. W.; Baginski, F. E.; Allison, P.; Liewer, K. M.; Miki, C.; Hill, B.; Varner, G. S.

2011-12-01

186

Determination of Area-Averaged Sensible Heat Fluxes with a Large Aperture Scintillometer over a Heterogeneous Surface Flevoland Field Experiment  

NASA Astrophysics Data System (ADS)

To test the applicability of the scintillation method over a heterogeneous area an experiment was carried out in the summer of 1998 in Flevoland (The Netherlands). In the patchy area only four crops were grown namely sugar beet, potatoes, wheat and onions. From eddy covariance measurements it was found that the heterogeneity was mainly caused by differences in thermal properties. No variations in the aerodynamics roughness length were observed. Two large aperture scintillometers were installed at a height of 11.6 and 20.4 m. A good resemblance was found between the sensible heat fluxes derived from both LAS instruments and the area-averaged fluxes obtained from the in-situ eddy covariance measurements. The slight underestimation of the lower LAS could be assessed using a blending height model and an analytical footprint model. The results also indicated that when scintillometer measurements are made below the blending height the violation to Monin-Obukhov Similarity Theory is small and that reasonable fluxes can be obtained from path-averaged structure parameters.

Meijninger, W. M. L.; Hartogensis, O. K.; Kohsiek, W.; et al.

187

Three-dimensional shape measurement of large-aperture aspheric mirrors by off-axis null Ronchi test.  

PubMed

An off-axis null Ronchi test is presented to measure the three-dimensional (3D) shape of a large-aperture aspheric mirror. The method designs curved fringe patterns as null sinusoidal gratings by means of phase information and ray tracing. In the process of measurement, the curved fringe patterns are displayed on a transmission-type liquid crystal display (T-LCD) screen, and a CCD camera records the fringe patterns containing the information of deviations of the mirror. The slopes of the deviations of the mirror are obtained by using the recorded fringe patterns. The deviations are restored by integrating, and then the 3D shape of the mirror can be reconstructed. Compared with the classical null Ronchi test, the method can provide enough measured data points and avoid the jagged edges of bands on the null gratings. Moreover, the method can conveniently change period and direction of the curved fringes and accurately control phase shifting. Computer simulations and a preliminary experiment are presented to show the performance of the method. PMID:22441472

Guo, Chunfeng; Su, Xianyu; Chen, Wenjing; Lei, Baiping; Wu, Fan

2012-03-20

188

Compact, wide aperture X-ray preionized XeCl laser with high specific optical power  

NASA Astrophysics Data System (ADS)

An X-ray preionized, discharge-pumped XeCl laser with a variable beam cross-section of up to 6×6 cm2 is described. It uses flat electrodes and the beam width is determined by X-ray collimation. Its operation characteristics concerning reduced electric field strength ( E/p) and X-ray dose are discussed in detail. The inductance of the discharge loop is minimized using a water capacitor arrangement. A very high specific optical power (90 MW/l) is achieved in an active volume of 1.2 l. The pulse energy exceeds 5 J in a 45 ns pulse (FWHM).

Steyer, M.; Stankov, K. A.; Mizoguchi, H.; Ouyang, B.; Schäfer, F. P.

1989-10-01

189

Transverse Mode Structure and Pattern Formation in Oxide Confined Vertical Cavity Semiconductor Lasers  

SciTech Connect

We analyze the transverse profiles of oxide-confined vertical cavity laser diodes as a function of aperture size. For small apertures we demonstrate that thermal lensing can be the dominant effect in determining the transverse resonator properties. We also analyze pattern formation in lasers with large apertures where we observe the appearance of tilted waves.

Choquette, K.D.; Geib, K.M.; Hegarty, S.P.; Hou, H.Q.; Huyet, G.; McInerney, J.G.; Porta, P.

1999-07-06

190

Transverse-mode structure and pattern formation in oxide-confined vertical-cavity semiconductor lasers  

SciTech Connect

We analyze the transverse profiles of oxide-confined vertical-cavity laser diodes as a function of aperture size. For small apertures we demonstrate that thermal lensing can be the dominant effect in determining the transverse resonator properties. We also analyze pattern formation in lasers with large apertures where we observe the appearance of tilted waves. {copyright} 1999 Optical Society of America

Hegarty, S.P. [Department of Physics, National University of Ireland, University College Cork, Cork (Ireland); Huyet, G. [University of Strathclyde, G4 0NG, Glasgow, Scotland (United Kingdom); Porta, P.; McInerney, J.G. [Department of Physics, National University of Ireland, University College Cork, Cork (Ireland); Choquette, K.D.; Geib, K.M.; Hou, H.Q. [Photonics Research Department, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

1999-11-01

191

Antares laser power amplifier  

Microsoft Academic Search

The design of the Antares laser power amplifier is discussed. The power amplifier is the last stage of amplification in the 100 kJ Antares laser. A single, cylindrical, grid control, cold cathode electron gun, surrounded by 12 large aperture CO2 electron beam sustained laser discharge sectors is described. A large scale interaction between optical, mechanical, and electrical disciplines required to

R. D. Stine; G. F. Ross; C. J. Silvernail

1979-01-01

192

High-resolution adaptive optics scanning laser ophthalmoscope with dual deformable mirrors for large aberration correction  

SciTech Connect

Scanning laser ophthalmoscopes with adaptive optics (AOSLO) have been shown previously to provide a noninvasive, cellular-scale view of the living human retina. However, the clinical utility of these systems has been limited by the available deformable mirror technology. In this paper, we demonstrate that the use of dual deformable mirrors can effectively compensate large aberrations in the human retina, making the AOSLO system a viable, non-invasive, high-resolution imaging tool for clinical diagnostics. We used a bimorph deformable mirror to correct low-order aberrations with relatively large amplitudes. The bimorph mirror is manufactured by Aoptix, Inc. with 37 elements and 18 {micro}m stroke in a 10 mm aperture. We used a MEMS deformable mirror to correct high-order aberrations with lower amplitudes. The MEMS mirror is manufactured by Boston Micromachine, Inc with 144 elements and 1.5 {micro}m stroke in a 3 mm aperture. We have achieved near diffraction-limited retina images using the dual deformable mirrors to correct large aberrations up to {+-} 3D of defocus and {+-} 3D of cylindrical aberrations with test subjects. This increases the range of spectacle corrections by the AO systems by a factor of 10, which is crucial for use in the clinical environment. This ability for large phase compensation can eliminate accurate refractive error fitting for the patients, which greatly improves the system ease of use and efficiency in the clinical environment.

Chen, D; Jones, S M; Silva, D A; Olivier, S S

2007-01-25

193

Determining meteoroid bulk densities using a plasma scattering model with high-power large-aperture radar data  

NASA Astrophysics Data System (ADS)

We present an improved technique for calculating bulk densities of low-mass (<1 g) meteoroids using a scattering model applied to the high-density plasma formed around the meteoroid as it enters Earth's atmosphere. These plasmas, referred to as head echoes, travel at or near the speed of the meteoroid, thereby allowing the determination of the ballistic coefficient (mass divided by physical cross-section), which depends upon speed and deceleration. Concurrently, we apply a scattering model to the returned signal strength of the head echo in order to correlate radar-cross-section (RCS) to plasma density and meteoroid mass. In this way, we can uniquely solve for the meteoroid mass, radius and bulk density independently. We have applied this new technique to head echo data collected in 2007 and 2008 simultaneously at VHF (160 MHz) and UHF (422 MHz) at ALTAIR, which is a high-power large-aperture radar located on the Kwajalein Atoll. These data include approximately 20,000 detections with dual-frequency, dual-polarization, and monopulse (i.e. angle) returns. From 2000 detections with the smallest monopulse errors, we find a mean meteoroid bulk density of 0.9 g/cm3 with observations spanning almost three orders of magnitude from 0.01 g/cm3 to 8 g/cm3. Our results show a clear dependence between meteoroid bulk density and altitude of head echo formation, as well as dependence between meteoroid bulk density and 3D speed. The highest bulk densities are detected at the lowest altitudes and lowest speeds. Additionally, we stipulate that the approximations used to derive the ballistic parameter, in addition to neglecting fragmentation, suggest that the traditional ballistic parameter must be used with caution when determining meteoroid parameters.

Close, Sigrid; Volz, Ryan; Loveland, Rohan; Macdonell, Alex; Colestock, Patrick; Linscott, Ivan; Oppenheim, Meers

2012-09-01

194

A conceptual design for a Cassegrain-mounted high-resolution optical spectrograph for large-aperture telescopes  

NASA Astrophysics Data System (ADS)

We present a conceptual design for a high-resolution optical spectrograph appropriate for mounting at Cassegrain on a large aperture telescope. The design is based on our work for the Gemini High Resolution Optical Spectrograph (CUGHOS) project. Our design places the spectrograph at Cassegrain focus to maximize throughput and blue wavelength coverage, delivering R=40,000 resolving power over a continuous 320-1050 nm waveband with throughputs twice those of current instruments. The optical design uses a two-arm, cross-dispersed echelle format with each arm optimized to maximize efficiency. A fixed image slicer is used to minimize optics sizes. The principal challenge for the instrument design is to minimize flexure and degradation of the optical image. To ensure image stability, our opto-mechanical design combines a cost-effective, passively stable bench employing a honeycomb aluminum structure with active flexure control. The active flexure compensation consists of hexapod mounts for each focal plane with full 6-axis range of motion capability to correct for focus and beam displacement. We verified instrument performance using an integrated model that couples the optical and mechanical design to image performance. The full end-to-end modeling of the system under gravitational, thermal, and vibrational perturbations shows that deflections of the optical beam at the focal plane are <29 ?m per exposure under the worst case scenario (<10 ?m for most orientations), with final correction to 5 ?m or better using open-loop active control to meet the stability requirement. The design elements and high fidelity modeling process are generally applicable to instruments requiring high stability under a varying gravity vector.

Froning, Cynthia S.; Osterman, Steven; Burgh, Eric; Beasley, Matthew; Scowen, Paul; Veach, Todd; Jordan, Steven; Ebbets, Dennis; Lieber, Michael; deCino, James; Castilho, Bruno Vaz; Gneiding, Clemens; César de Oliveira, Antonio

2013-09-01

195

Evaluation of sensible heat fluxes derived from Large Aperture Scintillometer measurements over irrigated and dryland cotton during BEAREX08  

NASA Astrophysics Data System (ADS)

The path integrating capabilities of scintillometer over heterogeneous landscapes makes it a powerful tool for validating satellite-based evapotranspiration (ET) maps. Numerous studies have evaluated the accuracy of sensible heat fluxes (H) derived from Large Aperture Scintillometer (LAS) measurements using eddy covariance (EC) measurements. EC systems have the energy balance closure problem (Rn-H-LE-G?0) up to 20 percent. For that reason we chose to evaluate the accuracy of the LAS-based ET fluxes against lysimeter data. Data used in this study was collected during the Bushland Evapotranspiration and Agricultural Remote Sensing Experiment 2008 (BEAREX08). The BEAREX08 was conducted at the USDA-ARS Conservation and Production Research Laboratory (CPRL) in Bushland [350 11' N, 1020 06' W; 1,170 m elevation MSL] located in the semi-arid Southern High Plains of Texas, USA during the 2008 summer cropping season. The CPRL is equipped with four large (3 x 3 x 2.5 m) monolithic lysimeters, with each lysimeter located in the center of 210 x 225 m fields arranged in a block pattern. One LAS was deployed across two dryland lysimeter fields (designated as NW and SW) and another on two irrigated lysimeter fields (designated as NE and SE), and all four fields were planted to cotton. The structure parameter of the refractive index of air was monitored at a 1-min interval and averaged for 15-minute periods between 10 July and 30 August, synchronized with weather station and lysimeter measurements. In addition, net radiation (Rn) and soil heat fluxes (G) were measured in all four lysimeter fields. Sensible heat fluxes (H) were derived from LAS measurements using a heat flux source area function and estimated ET fluxes as a residual from the energy balance were compared against lysimeter data. Trends in the LAS-based ET fluxes closely followed those in the observed data. However, LAS-based ET fluxes were over predicted by 10-35%. Differences between lysimeter- and LAS-based ET estimates over dryland cotton may be partly due to non-uniform vegetation growth on the NW and SW lysimeter fields. Overall, results indicate that the LAS is a promising tool for estimating ET fluxes.

Gowda, P.; Hartogensis, O.; Howell, T.; Scanlon, B.

2009-09-01

196

Simultaneous design of an optical system and null tests of the components: examples and results from the Large-aperture Synoptic Survey Telescope  

NASA Astrophysics Data System (ADS)

Optical null tests for three lenses and two subsystems were incorporated into the optical design procedure for the Large-aperture Synoptic Survey Telescope [1]. The "skip surfaces" feature in the OSLO optical design program was crucial. The resulting optical tests were extremely simple, requiring only a retro reflecting spherical or flat mirror. This is only possible because the optical tests were simultaneously designed and optimized as the telescope was designed.

Seppala, Lynn G.

2010-07-01

197

Determination of Area-Averaged Water Vapour Fluxes with Large Aperture and Radio Wave Scintillometers over a Heterogeneous Surface – Flevoland Field Experiment  

Microsoft Academic Search

A large aperture scintillometer (LAS) andradio wave scintillometer (RWS)were installed over a heterogeneous areato test the applicability of the scintillation method.The heterogeneity in the area, whichconsisted of many plots, was mainly caused bydifferences in thermal properties ofthe crops; the variations in theaerodynamic roughness lengthwere small. The water vapour fluxesderived from the combined LAS-RWSsystem, also known as the two-wavelengthmethod, agreed fairly

W. M. L. Meijninger; A. E. Green; O. K. Hartogensis; W. Kohsiek; J. C. B. Hoedjes; R. M. Zuurbier; H. A. R. De Bruin

2002-01-01

198

Determination of Area-Averaged Water Vapour Fluxes with Large Aperture and Radio Wave Scintillometers over a Heterogeneous Surface Flevoland Field Experiment  

Microsoft Academic Search

A large aperture scintillometer (LAS) andradio wave scintillometer (RWS)were installed over a heterogeneous areato test the applicability of the scintillation method.The heterogeneity in the area, whichconsisted of many plots, was mainly caused bydifferences in thermal properties ofthe crops; the variations in theaerodynamic roughness lengthwere small. The water vapour fluxesderived from the combined LAS-RWSsystem, also known as the two-wavelengthmethod, agreed fairly

W. M. L. Meijninger; A. E. Green; O. K. Hartogensis

2002-01-01

199

Study of 2-in1 large-aperture Nb3Sn IR quadrupoles for the LHC luminosity upgrade  

SciTech Connect

Double-aperture Nb{sub 3}Sn quadrupoles with asymmetric coils and with cold and warm iron yokes were studied for the dipole-first upgrade scenario of the LHC Interaction Regions (IR). This paper describes the magnet design concepts and discusses their performance parameters, including field gradient and field quality limitations.

Kashikhin, V.V.; Zlobin, A.V.; /Fermilab

2006-06-01

200

Wavelength tunable, high energy femtosecond laser pulses directly generated from large-mode-area photonic crystal fiber  

NASA Astrophysics Data System (ADS)

Wavelength tunable high energy ultrashort laser pulses are generated from a large-mode-area photonic crystal fiber in anomalous dispersion (AD) regime. A simplified laser cavity design with one fine polished facet of the fiber as a cavity mirror is used. The intra-cavity dispersion compensation is achieved by a grating pair, the spatial dispersed light from which also have optical spectrum filtering effects combined with the limited aperture of the fiber core. The laser system is able to generate ultrashort pulses ranging from 494 fs (with 56 nJ pulse energy) to 1.24 ps (with 49 nJ pulse energy) at 55 MHz repetition rate. The filtering mechanism benefits the generation of high energy pulses with narrowing pulse duration in AD regime. An undulation in frequency and time domain is also observed with the increase of the pump power. Furthermore, this laser system is directly used as seed for supercontinuum generation.

Zhang, Chi; Zhang, Yu-ying; Hu, Ming-lie; Wang, Si-jia; Song, You-jian; Chai, Lu; Wang, Ching-yue

2012-05-01

201

Large scale laser microstructuring of gravure print rollers  

NASA Astrophysics Data System (ADS)

Application of lasers for print form fabrication plays an increasingly important role in the printing industry due to the high machining rate, the high spatial resolution and the ability of digital modulation. This paper gives an overview of our laser based processes in gravure and embossing with a focus on micro-structuring of gravure print forms by direct laser ablation. The precise large scale micro-fabrication by laser engraving is the fastest and most versatile process for gravure cylinder fabrication (ablation rate up to 1 cm3/min). Direct laser engraving into metallic cylinders is performed with high power Q-switched Nd:YAG laser systems and fiber lasers at up to 100 kHz repetition rate, tuned for high reproducibility and stability of the mean pulse energy (?2 < 0.6%). Flexible aspect ratios and designs of the cell profile are achieved by fast modulation of the laser beam profile for each single pulse. This allows for optimization of the cell shape to get the best ink transfer interaction on a specific print substrate. New experiments with high power fiber lasers (cw lasers and pulsed MOPA systems > 500W@ 100kHz) resulted in improved cell precision, screen resolution and production efficiency. Future large scale cylinder engraving with ultra short pulse lasers (ps) is discussed.

Hennig, Guido; Selbmann, Karl-Heinz; Pfinninger, Silke; Brendel, Johannes; Brüning, Stephan

2008-03-01

202

Performance of a 80 W copper vapor laser with “alignment free” unstable CAT-EYE resonator and other configurations using intra-cavity apertures  

NASA Astrophysics Data System (ADS)

Performance of a kinetically enhanced copper vapor laser (KE-CVL) with various stable/unstable “alignment free” CAT-EYE resonator configurations are presented here in this paper. The laser used in the experiment was a 45 mm bore (˜2 l discharge volume) kinetically enhanced copper vapor laser developed in our laboratory and capable of generating maximum power of ˜80 W (at ˜9.8 kHz). The efficiency of the laser was ˜1.4% and beam divergence of ˜3.5 mrad in a plane plane standard multimode cavity. For the first time performance of unstable CAT-EYE resonator is demonstrated with a CVL/KE-CVL. On using unstable CAT-EYE resonator the divergence of the laser beam reduced to ˜0.22 mrad (˜20-fold reduction as compared to conventional plane plane cavity), ˜40 W output power and with excellent misalignment tolerance. The laser output power was found to be within ˜5% drift/decline with misalignment angle of about 4 mrad between the mirrors. This is a significant improvement in comparison to standard conventional unstable resonator (M ˜ 50) CVL where ˜0.5 mrad divergence is achieved with power drift/decline of about 45% at ˜4 mrad misalignment angle. Off-axis unstable CAT-EYE unstable resonator was also demonstrated for the first time with further reduction in beam divergence to ˜0.13 mrad and with output power of ˜28 W. The misalignment tolerance was found to be highest in case of off-axis unstable CAT-EYE resonator with decline/drift in laser power of only ˜10% for misalignment angle as high as ˜8 mrad. Performance with intra-cavity apertures in plane plane type CAT-EYE resonator for transverse mode control is also presented for the first time in CVLs. It is observed that the laser beam divergence reduces significantly to 1.25 mrad (a factor of 2) on using an aperture of ˜3.5 mm at the CAT-EYE reflector as compared to its normal (R = F = d) configuration without aperture. In case of stable CAT-EYE resonator the average beam divergence reduces from 8 mrad to 4 mrad (factor of 2) on using intra-cavity aperture of about 3 mm. It was also observed that high misalignment tolerance was retained on using intra-cavity apertures in almost all the CAT-EYE resonators. Use of intra-cavity mesh was also demonstrated for the first time with stable CAT-EYE resonator for improving the beam focus-ability. Average beam divergence was reduced by a factor of 2.5 (from 8 mrad to 3 mrad) on using intra-cavity mesh. These new configurations in CAT-EYE resonators in KE-CVLs are found to be effective in improving and controlling the laser beam divergence significantly with additional characteristic of high misalignment tolerance.

Singh, Bijendra; Daultabad, S. R.; Subramaniam, V. V.; Chakraborty, Ashim

2008-12-01

203

Large area electron beam pumped krypton fluoride laser amplifier  

SciTech Connect

Nike is a recently completed multi-kilojoule krypton fluoride (KrF) laser that has been built to study the physics of direct drive inertial confinement fusion. This paper describes in detail both the pulsed power and optical performance of the largest amplifier in the Nike laser, the 60 cm amplifier. This is a double pass, double sided, electron beam-pumped system that amplifies the laser beam from an input of 50 J to an output of up to 5 kJ. It has an optical aperture of 60 cm {times} 60 cm and a gain length of 200 cm. The two electron beams are 60 cm high {times} 200 cm wide, have a voltage of 640 kV, a current of 540 kA, and a flat top power pulse duration of 250 ns. A 2 kG magnetic field is used to guide the beams and prevent self-pinching. Each electron beam is produced by its own Marx/pulse forming line system. The amplifier has been fully integrated into the Nike system and is used on a daily basis for laser-target experiments. {copyright} {ital 1997 American Institute of Physics.}

Sethian, J.D.; Obenschain, S.P.; Gerber, K.A.; Pawley, C.J.; Serlin, V.; Sullivan, C.A. [Plasma Physics Division, Naval Research Laboratory, Washington DC 20375 (United States); Webster, W. [Research Support Instruments, 4325-B Forbes Boulevard, Lanham, Maryland 20706 (United States); Deniz, A.V.; Lehecka, T. [Science Applications International Corporation, 1710 Goodridge Drive, McLean, Virginia 22102 (United States); McGeoch, M.W. [PLEX Corporation, 21 Addington Road, Brookline, Massachusetts 02146 (United States); Altes, R.A.; Corcoran, P.A.; Smith, I.D. [Pulse Sciences, Incorporated, 600 McCormick Street, San Leandro, California 94577 (United States); Barr, O.C. [Pharos Technical Enterprises, 1603 Barcelona Street, Livermore, California 94550 (United States)

1997-06-01

204

Development of a Sparse Aperture Test-Bed Utilizing Pupil-Plane Imaging.  

National Technical Information Service (NTIS)

Sparse aperture imaging provides the opportunity to achieve high resolutions image with groups of smaller apertures rather than a large single aperture. Eliminating large monolithic apertures provides both a cost and weight reduction among other possible ...

D. Jameson D. Rabb J. Roche

2008-01-01

205

Large aperture multi-pass amplifiers for high peak power lasers  

NASA Astrophysics Data System (ADS)

We demonstrate theoretically and experimentally the optimal conditions whereby amplification using the Extraction During Pumping (EDP) technique can deliver up to four times more energy than a conventional amplifier. The existence of an optimal combination of incident pump fluence and pump area is shown. This allows kJ level energy extraction with existing technology.

Chvykov, Vladimir; Krushelnick, Karl

2012-04-01

206

Optimization of deposition uniformity for large-aperture National Ignition Facility substrates in a planetary rotation system.  

PubMed

Multilayer coatings on large substrates with increasingly complex spectral requirements are essential for a number of optical systems, placing stringent requirements on the error tolerances of individual layers. Each layer must be deposited quite uniformly over the entire substrate surface since any nonuniformity will add to the layer-thickness error level achieved. A deposition system containing a planetary rotation system with stationary uniformity masking is modeled, with refinements of the planetary gearing, source placement, and uniformity mask shape being utilized to achieve an optimal configuration. The impact of improper planetary gearing is demonstrated theoretically, as well as experimentally, providing more comprehensive requirements than simply avoiding repetition of previous paths through the vapor plume, until all possible combinations of gear teeth have been used. Deposition efficiency and the impact of changing vapor plume conditions on the uniformity achieved are used to validate improved source placement. Uniformity measurements performed on a mapping laser photometer demonstrate nonuniformities of less than 0.5% for 0.75 m optics in a 72 in. (1.8 m) coating chamber. PMID:16639459

Oliver, James B; Talbot, David

2006-05-01

207

Instrument Design of the Large Aperture Solar UV Visible and IR Observing Telescope (SUVIT) for the SOLAR-C Mission  

NASA Astrophysics Data System (ADS)

We present an instrumental design of one major solar observation payload planned for the SOLAR-C mission: the Solar Ultra-violet Visible and near IR observing Telescope (SUVIT). The SUVIT is designed to provide high-angular-resolution investigation of the lower solar atmosphere, from the photosphere to the uppermost chromosphere, with enhanced spectroscopic and spectro-polarimetric capability in wide wavelength regions from 280 nm (Mg II h&k lines) to 1100 nm (He I 1083 nm line) with 1.5 m class aperture and filtergraphic and spectrographic instruments.

Suematsu, Y.; Katsukawa, Y.; Shimizu, T.; Ichimoto, K.; Takeyama, N.

2012-12-01

208

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Optical surface breakdown of alkali halide crystals by microsecond pulses from a wide-aperture CO2 laser  

NASA Astrophysics Data System (ADS)

A study was made of the dynamics of temporal and spatial changes in the spectral characteristics of plasmas. A three-stage mechanism of the damage to surfaces of alkali halide crystals by microsecond pulses from a TEA CO2 laser was proposed: breakdown initiation (at a distance of 3-5 mm from the surface with a time delay up to 1 ?s relative to the leading edge of a laser pulse), evaporation (after a further delay of 3-5 ?s), and interaction of the adsorbates with a plasma jet and with the laser radiation, as well as heating and cracking of a crystal by the UV plasma radiation.

Kazantsev, S. G.

1998-04-01

209

Large-scale temporal and spatial imaging of soil brightness temperature with an L-band synthetic aperture microwave radiometer  

NASA Astrophysics Data System (ADS)

The Microwave Remote Sensing Lab (MIRSL) at the University of Massachusetts has developed a second-generation L-band synthetic aperture microwave radiometer referred to as the Electronically Steered Thinned Array Radiometer, or ESTAR, which measures soil moisture or ocean salinity from an airborne platform. This dissertation reviews the basics of synthetic aperture microwave radiometry, then details recent modifications to the ESTAR instrument, including the change to a horizontally polarized antenna, and improvements to the instrument's thermal control. The dissertation discusses calibration methods, including corrections to the null feedback radiometer (NFR) data used to form the system response matrix, or G-matrix. It also describes image calibration, noting steps taken to reduce image ripple. Results obtained during the Southern Great Plains 1997 (SGP'97) hydrology experiment in Oklahoma are discussed and compared to rainfall data obtained from the Oklahoma Mesonet system of weather stations. This data set is the largest one of its type obtained by ESTAR to date, in terms of area of geographical and temporal coverage.

Isham, John D.

210

Comparison of CNES spherical and NASA hemispherical large aperture integrating sources. I - Using a laboratory transfer spectroradiometer. II - Using the SPOT-2 satellite instruments  

NASA Astrophysics Data System (ADS)

CNES spherical and NASA hemispherical large aperture calibration sources are examined using a laboratory transfer spectroradiometer and SPOT-2 instruments. The sources, collected at Matra in France during October 1987, are compared in terms of absolute calibration, linearity, and uniformity. The laboratory transfer spectroradiometer data reveal that the calibration results correspond to within about 7 percent absolute accuracy level and the linearity of the CNES source with lamp level is good. It is observed using the satellite data that both sources have an excellent uniformity over a 4 deg field of view.

Guenther, B.; McLean, J.; Leroy, M.; Henry, P.

1990-02-01

211

Tests of A Displaced-beam Small Aperture Laser Scintillometer To Determine Surface Fluxes and Dissipation Rate of Tke  

Microsoft Academic Search

Comparisons between surface fluxes of sensible heat and momentum derived from a displaced-beam small aperture scintillometer (DBSAS) and eddy-correlation mea- surements (or flux-profile methods) will be presented. Furthermore, similar compar- isons for the dissipation rate of turbulent kinetic energy and temperatures structure parameter will be shown. Although the results are very promising, some systematic de- viations are observed. The cause

H. A. R. de Bruin; O. K. Hartogensis; F. Beyrich; W. M. L. Meininger; A.-S. Smedman

2002-01-01

212

Optical delay control of large-spectral-bandwidth laser pulses  

SciTech Connect

In this Rapid Communication we report an experimental observation of temporal delay control of large-spectral-bandwidth multimode laser pulses by means of electromagnetically induced transparency. We achieved optically controllable retardation of laser pulses with an input spectral bandwidth of 3.3 GHz with limited temporal distortion and excellent values of the delay-bandwidth product. The experimental results compare favorably with a theoretical analysis.

Ignesti, E.; Tognetti, M. V.; Buffa, R. [Dipartimento di Fisica, Universita di Siena, Via Roma 56, I-53100 Siena (Italy); Cavalieri, S.; Fini, L.; Sali, E. [Dipartimento di Fisica, Universita di Firenze, Via G. Sansone 1, Sesto Fiorentino, I-50019 Firenze (Italy); European Laboratory for Non-Linear Spectroscopy (LENS), Universita di Firenze, Via N. Carrara 1, Sesto Fiorentino, I-50019 Firenze (Italy); Eramo, R. [Dipartimento di Fisica, Universita di Firenze, Via G. Sansone 1, Sesto Fiorentino, I-50019 Firenze (Italy); European Laboratory for Non-Linear Spectroscopy (LENS), Universita di Firenze, Via N. Carrara 1, Sesto Fiorentino, I-50019 Firenze (Italy); INFM-CRS-Soft Matter (CNR) c/o Universita la Sapienza, Piazzale A. Moro 2, I-00185 Roma (Italy)

2009-07-15

213

Scale-factor corrections in large ring lasers  

NASA Astrophysics Data System (ADS)

The authors report on fluctuations of the geometric scale factor of a very large ring laser situated 30 m underground in the Cashmere Cavern in Christchurch (New Zealand). Variations in temperature and atmospheric pressure cause thermoelastic deformations to the cavern, which lead to changes of the area and perimeter of the ring laser structure. In situ beam monitoring has been used to partially correct for these effects.

Pritsch, B.; Schreiber, K. U.; Velikoseltsev, A.; Wells, J.-P. R.

2007-08-01

214

Pulsed RGB lasers for large-screen video displays  

NASA Astrophysics Data System (ADS)

Acousto-optic spatial light modulators present new opportunities to create bright video displays with pulsed lasers. Operating characteristics of coherent red, green, and blue light sources to support NTSC, PAL, and HDTV video standards are presented. We describe rear-projection systems under development at COLOR that employ pulsed RGB lasers to produce very bright images suitable for both outdoor and brightly lit indoor large screen display applications.

Martinsen, Robert J.; Karakawa, Masayuki; McDowell, Stephen R.

1997-01-01

215

Large Signal Resonance and Laser Dilatometer Methods  

NASA Astrophysics Data System (ADS)

In many piezoelectric devices maximum deformations are desirable. They can only be achieved under high field strengths (1-2 kV mm-1) and cause large mechanical stress amplitudes in the piezoelectric material. This calls for piezoelectric materials with a strong piezoelectric effect that are capable of withstanding both high electric field strengths and large mechanical stresses. Under these large signal conditions, the properties of piezoelectric materials are considerably non-linear and show hysteretic behaviour. As discussed in Chap. 3.3, the non-linear behaviour can be attributed to the motion of non 180° domain walls. Therefore, the non-linearity of the piezoelectric response and the accompanying hysteresis can be described with the aid of Rayleigh's law (Equations (3.48) and (3.49) in Chap. 3.3). The most important aspect of the Rayleigh-like behaviour is the fact that hysteresis and non-linearity in soft piezoelectric ceramics are essentially linked, as can be seen in Fig. 19.7, that is, both hysteresis and non-linearity are results of the same-domain wall pinning processes. Since the hysteretic response is closely related to the electrical and mechanical losses occurring in piezoelectric ceramics or ferroelectric perovskites, in general, the performance of power ceramics can be tested substantially by measuring either the dielectric losses at large field amplitudes or the mechanical losses at large mechanical stress amplitudes. However, to perform these measurements, it is not sufficient to extend simply the standard small-signal capacitance/loss tangent techniques according to IRE or IEEE standards [1] or the impedance measurement techniques as described in Chap. 18 to higher-signal amplitudes. For then the measurement results would be considerably falsified by an overheating of the test samples. With this in mind, pulsed test signals are mostly used [2].

Wolff, A.

216

Achieving high focusing power for a large-aperture liquid crystal lens with novel hole-and-ring electrodes.  

PubMed

Aiming to equip commercial camera modules, such as the optical imaging systems with a CMOS sensor module in 3 Mega pixels, an ultra thin liquid crystal lens with designed hole-and-ring electrodes is proposed in this study to achieve high focusing power. The LC lens with proposed electrodes improves the central intensity of electric field which leads to better focusing quality. The overall thickness of the LC lens can be as thin as 1.2 mm and the shortest focal length of the 4 mm-aperture lens occurs at 20 cm under an applied voltage of 30 V at 1 KHz. The inner ring electrode requires only 40% of applied voltage of the external hole electrode. The applied voltages for this internal ring and external hole electrodes can simply be realized by a pre-designed parallel resistance pair and a single voltage source. Experiments are conducted for validation and it shows that the designed LC lens owns good image clearness and contrast at the focal plane. The proposed design reduces the thickness of LC lens and is capable of achieving relative higher focusing power than past studies with lower applied voltage. PMID:19582020

Chiu, Chi-Wei; Lin, Yu-Cheng; Chao, Paul C-P; Fuh, Andy Y-G

2008-11-10

217

Integration of optical inspection and metrology functions into DUV femtosecond laser repair tool for large-area FPD photomasks  

NASA Astrophysics Data System (ADS)

In this paper we describe the early stages of introduction of the inspection and metrology capabilities for the large area mask repair tools. Commercially available MRT platform was used as a basis for integration of defect repair, metrology, review, inspection, and verification functions into a single MiRT prototype system. This system was designed for large area LCD/PDP photomasks of Generation 7 and beyond. Advanced DUV femtosecond laser technology was developed for repair of both clear and opaque defects on Chrome-on-Glass masks using laser CVD and laser ablation. Specifics of the system design and architecture is discussed. Laser processing module was based on the projection optics with imaged aperture. Image formation in such optical system is reviewed and outcome of the computer simulation is compared with the experimental data. For the first time, we report results of the feasibility study of grayscale photomask repair using laser CVD technology. By carefully controlling process parameters, we were able to deposit films with different thickness and therefore variable transmittance. We also discuss die-to-database inspection of half-tone masks and capabilities of the integrated metrology and review of the repaired photomask sites. Proprietary die-to-database inspection and verification algorithms combined with distributed super-fast computer architecture allowed effective process control with accurate, repeatable, and timely measurements. Different subsystems that enable integration of repair, metrology, and inspection functions into the MiRT system are discussed.

Treyger, Leon; Heyl, Jon; Ronning, Donald; Ducharme, Donald

2007-05-01

218

Diffraction smoothing aperture for an optical beam  

DOEpatents

The disclosure is directed to an aperture for an optical beam having an irregular periphery or having perturbations imposed upon the periphery to decrease the diffraction effect caused by the beam passing through the aperture. Such apertures are particularly useful with high power solid state laser systems in that they minimize the problem of self-focusing which frequently destroys expensive components in such systems.

Judd, O' Dean P. (Los Alamos, NM); Suydam, Bergen R. (Los Alamos, NM)

1976-01-01

219

Large-screen projection displays with laser brightness amplifiers  

NASA Astrophysics Data System (ADS)

One of the most difficult problems of large-screen projection displays is overloading of a panel to be projected with illuminating light. The problem can be solved by using, on the way from a panel to be projected to a screen, an optical amplifier with high enough amplification. The prospects of using laser amplifiers in projection displays are discussed. Among all laser amplifiers the most suitable for application as optical amplifiers in projection systems are now pulsed metal vapor laser and metal halide laser amplifiers. They have rather high gain enabling amplification in the range from 102 to 104 and high average output power sufficient to illuminate a large screen. The main characteristics of these amplifiers are described. The results of experimental investigations of projection systems with copper, copper bromide, gold and some other metal vapor amplifiers are reported. In all cases good quality amplified images were obtained. Average power at the output of amplifiers was under typical conditions of operation comparable with the output power of a laser with the same amplifying element. Measurement of contrast of amplified images showed that under normal conditions of operation it is close to the contrast of the input picture even at strong saturation of the amplifying medium. The influence of the amplifier saturation is briefly discussed. The results of experiments with TV projection systems using two types of liquid crystal spatial light modulators are presented and prospects of large-screen projection displays development are discussed.

Petrash, Gueorgii G.; Chvykov, Vladimir V.; Zemskov, Konstantin I.

1997-05-01

220

A Field Cancellation Algorithm for Constructing Economical Planar Permanent Magnet (PM) Multipoles With Large High Quality Field Apertures  

Microsoft Academic Search

In recent years studies have been initiated on a new class of multipole field generators consisting of cuboid planar permanent magnet (PM) pieces arranged in biplanar arrays of 2-fold rotational symmetry. These structures, first introduced for Free Electron Laser (FEL) applications, are based on reducing the rotational symmetry of conventional N-pole field generators from N-fold to 2-fold. One consequence of

Roman Tatchyn

2011-01-01

221

Development and Testing of a Power Trough System Using a Structurally-Efficient, High-Performance, Large-Aperture Concentrator with Thin Glass Reflector and Focal Point Rotation  

SciTech Connect

Industrial Solar Technology has assembled a team of experts to develop a large-aperture parabolic trough for the electric power market that moves beyond cost and operating limitations of 1980's designs based on sagged glass reflectors. IST's structurally efficient space frame design will require nearly 50% less material per square meter than a Solel LS-2 concentrator and the new trough will rotate around the focal point. This feature eliminates flexhoses that increase pump power, installation and maintenance costs. IST aims to deliver a concentrator module costing less than $100 per square meter that can produce temperatures up to 400 C. The IST concentrator is ideally suited for application of front surface film reflectors and ensures that US corporations will manufacture major components, except for the high temperature receivers.

May, E. K.; Forristall, R.

2005-11-01

222

Increasing the focused response of impulse radiating antennas through polarization control of aperture fields  

Microsoft Academic Search

Wide-band, focused aperture antennas like impulse radiating antennas (IRAs) can see improved aperture efficiency through control of the aperture shape and aperture field distribution. The shape of the aperture fields is largely dictated by the transverse electromagnetic mode distribution on the nondispersive feed of the IRA. In this paper we consider reshaping the aperture field by controlling the polarization of

J. Scott Tyo; M. Dogan; J. H. Boddeker; C. J. Buchenauer

2006-01-01

223

Laser scanning system for inspecting large underwater hydroelectric structures  

NASA Astrophysics Data System (ADS)

A novel robotic laser scanning system for the inspection of large underwater hydroelectric structures is proposed. This system has been developed at the Hydro Quebec Research Institute and consists of a laser camera mounted on a 2-D Cartesian manipulator. Mechanical, electronic, and software design aspects; overall operational modalities; and proof of concept results are presented. We evaluated the performances of the system in the course of laboratory experiments and inspection trials carried out under normal operating conditions at the site of three of Hydro Quebec's hydroelectric dams.

Mirallès, François; Beaudry, Julien; Blain, Michel; de Santis, Romano M.; Houde, Régis; Hurteau, Richard; Robert, André; Sarraillon, Serge; Soucy, Nathalie

2010-04-01

224

Laterally periodic resonator for large-area gain lasers  

NASA Astrophysics Data System (ADS)

Laterally periodic resonators, which can be constructed by use of transversely periodic phase- or amplitude-modulating elements in a cavity, are proposed for stabilization and generation of transversely coherent output from large-area gain. Lasers with periodic resonators have the combined features of conventional cavities and laser arrays. Significant low-order transverse modes and mode discrimination of a sample resonator with intracavity periodic phase elements are investigated numerically by the iteration method. Wave-propagation calculations are carried out by use of a fast Fourier transform, and a modified Prony method is used to evaluate wave functions and losses of transverse modes. Results of numerical calculations are consistent with expectations.

Feng, Yan; Ueda, Ken-Ichi

2003-03-01

225

Radiative shocks on large scale lasers. Preliminary results  

NASA Astrophysics Data System (ADS)

Radiative shocks, those structure is strongly influenced by the radiation field, are present in various astrophysical objects (circumstellar envelopes of variable stars, supernovae ...). Their modeling is very difficult and thus will take benefit from experimental informations. This approach is now possible using large scale lasers. Preliminary experiments have been performed with the nanosecond LULI laser at Ecole Polytechnique (France) in 2000. A radiative shock has been obtained in a low pressure xenon cell. The preparation of such experiments and their interpretation is performed using analytical calculations and numerical simulations.

Leygnac, S.; Bouquet, S.; Stehle, C.; Barroso, P.; Batani, D.; Benuzzi, A.; Cathala, B.; Chièze, J.-P.; Fleury, X.; Grandjouan, N.; Grenier, J.; Hall, T.; Henry, E.; Koenig, M.; Lafon, J. P. J.; Malka, V.; Marchet, B.; Merdji, H.; Michaut, C.; Poles, L.; Thais, F.

2001-05-01

226

Nuclear-pumped lasers for large-scale applications  

SciTech Connect

Efficient initiation of large-volume chemical lasers may be achieved by neutron induced reactions which produce charged particles in the final state. When a burst mode nuclear reactor is used as the neutron source, both a sufficiently intense neutron flux and a sufficient short initiation pulse may be possible. Proof-of-principle experiments are planned to demonstrate lasing in a direct nuclear-pumped large-volume system: to study the effects of various neutron absorbing materials on laser performance; to study the effects of long initiation pulse lengths; to determine the performance of large-scale optics and the beam quality that may bo obtained; and to assess the performance of alternative designs of burst systems that increase the neutron output and burst repetition rate. 21 refs., 7 figs., 5 tabs.

Anderson, R.E.; Leonard, E.M.; Shea, R.E.; Berggren, R.R.

1988-01-01

227

Single-pulse driven plasma Pockels cell with 350mm×350mm aperture  

NASA Astrophysics Data System (ADS)

Large-aperture plasma Pockels cell is one of important components for inertial confinement fusion laser facility. We demonstrate a single-pulse driven PPC with 350mm×350mm aperture. It is different to the PPC of NIF and LMJ for its simple operation to perform Pockels effect. With optimized operation parameters, the PPC meets the optical switching requirement of SGII update laser facility. Only driven by one high voltage pulser, the simplified PPC system would be provided with less associated diagnostics, less the maintenance, and higher reliability.

Zhang, Xiongjun; Wu, Dengsheng; Zhang, Jun; Lin, Donghui; Zheng, Kuixing; Jing, Feng

2010-08-01

228

Invited review article: Large ring lasers for rotation sensing.  

PubMed

Over the last two decades a series of large ring laser gyroscopes have been built having an unparalleled scale factor. These upscaled devices have improved the sensitivity and stability for rotation rate measurements by six orders of magnitude when compared to previous commercial developments. This progress has made possible entirely new applications of ring laser gyroscopes in the fields of geophysics, geodesy, and seismology. Ring lasers are currently the only viable measurement technology, which is directly referenced to the instantaneous rotation axis of the Earth. The sensor technology is rapidly developing. This is evidenced by the first experimentally viable proposals to make terrestrial tests of general relativistic effects such as the frame dragging of the rotating Earth. PMID:23635174

Schreiber, Karl Ulrich; Wells, Jon-Paul R

2013-04-01

229

Invited Review Article: Large ring lasers for rotation sensing  

NASA Astrophysics Data System (ADS)

Over the last two decades a series of large ring laser gyroscopes have been built having an unparalleled scale factor. These upscaled devices have improved the sensitivity and stability for rotation rate measurements by six orders of magnitude when compared to previous commercial developments. This progress has made possible entirely new applications of ring laser gyroscopes in the fields of geophysics, geodesy, and seismology. Ring lasers are currently the only viable measurement technology, which is directly referenced to the instantaneous rotation axis of the Earth. The sensor technology is rapidly developing. This is evidenced by the first experimentally viable proposals to make terrestrial tests of general relativistic effects such as the frame dragging of the rotating Earth.

Schreiber, Karl Ulrich; Wells, Jon-Paul R.

2013-04-01

230

High power optical sources of femtosecond pulses on the base of hybrid laser systems with wide-aperture gas laser amplifiers  

NASA Astrophysics Data System (ADS)

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~1014 - 1015 W now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)laser excited by VUV radiation of an e-beam pumped Xe2 lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(CA) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High- Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm3, e-beam pulse duration ~ 100- 200 ns. A possibility of using Kr2F as an active medium with saturation energy 0.2 J/cm2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing ~50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute. Preliminary experiments on amplification of UV femtosecond pulses were carried out with electric discharge KrF laser amplifier.

Ionin, A. A.; Konyashchenko, A. V.; Koval'chuk, B. M.; Krokhin, O. N.; Losev, V. F.; Mesyats, G. A.; Mikheev, L. D.; Molchanov, A. G.; Novoselov, Yu. N.; Seleznev, L. V.; Sinitsyn, D. V.; Starodub, A. N.; Tarasenko, V. F.; Yakovlenko, S. I.; Zvorykin, V. D.

2007-08-01

231

Measuring large amplitudes of mechanical vibrations with laser interferometers  

NASA Astrophysics Data System (ADS)

Heterodyne methods of laser interferometry are the most promising methods of measuring large mechanical vibrations, their main advantages being that they are contactless and remote operational, and their main features being high accuracy and reproducibility of readings. However, use of a square-law photodetector and a frequency detector with a laser interferometer requires conversion to single-frequency laser radiation to two-frequency one. An attendant problem is to provide a stable and efficient wideband heterodyne with wide dynamic range for a reference signal with a Doppler frequency shift sufficiently large relative to the frequency of the probing signal. One known method of such interferometry which meets these requirements involves use of an oscillograph and an electronic-counter frequency meter. The principle of this method is outlined on the example of one mirror of a two-beam interferometer, assuming that its vibrations are harmonic. The interferometer for this application consists of a light splitter, a reference mirror, and a movable mirror with a Teflon membrane controlled by a sine-wave generator. The light source is an LG-79/1 He-Ne laser. The photodetector is an FD-21 KP photodiode with a time constant of 6 ns. Vibrations are measured with a Ch3-34A frequency meter.

Bondarenko, A. N.; Trotsenko, V. P.

1984-09-01

232

Criteria for formation of low-frequency sound under wide-aperture repetitively pulsed laser irradiation of solids  

SciTech Connect

The criteria for merging shock waves formed by optical breakdowns on the surface of solids have been investigated. Targets made of different materials were successively irradiated by two CO{sub 2}-laser pulses with energies up to 200 J and a duration of {approx}1 {mu}s. It is shown that the criteria under consideration can be applied to different targets and irradiation regimes and make it possible to calculate the parameters of repetitively pulsed laser radiation that are necessary to generate low-frequency sound and ultrasound in air.

Tishchenko, V N; Posukh, V G; Gulidov, A I; Zapryagaev, V I; Pavlov, A A; Boyarintsev, Ye L; Golubev, M P; Kavun, I N; Melekhov, A V; Golobokova, L S; Miroshnichenko, I B; Pavlov, Al A; Shmakov, A S

2011-10-31

233

Radio frequency electromagnetic fields in large conducting enclosures: effects of apertures and human bodies on propagation and field-statistics  

Microsoft Academic Search

Radio frequency propagation in an electrically large resonant chamber (a screened room) was simulated by two models: a statistical combination of multiple resonant modes and a computational electromagnetic simulation [the transmission line matrix (TLM) method]. The purpose of this work was to investigate the effects of passengers and windows on electromagnetic fields (EMF) in aircraft and other vehicles. Comparison of

Martin P. Robinson; Janet Clegg; Andy C. Marvin

2006-01-01

234

The development of TW and PW optical sources of femtosecond pulses on the base of hybrid laser systems with wide-aperture gas laser amplifiers  

NASA Astrophysics Data System (ADS)

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~1014 - 1015 W being now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by a solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)-laser excited by VUV radiation of an e-beam pumped Xe2 lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(C-A) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High-Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm3, e-beam pulse duration ~ 100-200 ns. A possibility of using Kr2F as an active medium with saturation energy 0.2 J/cm2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing 50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute.

Ionin, A. A.; Konyashchenko, A. V.; Koval'chuk, B. M.; Krokhin, O. N.; Losev, V. F.; Mesyats, G. A.; Mikheev, L. D.; Molchanov, A. G.; Novoselov, Yu. N.; Starodub, A. N.; Tarasenko, V. F.; Yakovlenko, S. I.; Zvorykin, V. D.

2007-05-01

235

High-power optical sources of femtosecond pulses on the base of hybrid laser systems with wide-aperture gas laser amplifiers  

NASA Astrophysics Data System (ADS)

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~1014 - 1015 W now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)-laser excited by VUV radiation of an e-beam pumped Xe2 lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(CA) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High- Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm3, e-beam pulse duration ~ 100- 200 ns. A possibility of using Kr2F as an active medium with saturation energy 0.2 J/cm2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing ~50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute. Preliminary

Ionin, A. A.; Konyashchenko, A. V.; Koval'chuk, B. M.; Krokhin, O. N.; Losev, V. F.; Mesyats, G. A.; Mikheev, L. D.; Molchanov, A. G.; Novoselov, Yu. N.; Seleznev, L. V.; Sinitsyn, D. V.; Starodub, A. N.; Tarasenko, V. F.; Yakovlenko, S. I.; Zvorykin, V. D.

2007-03-01

236

Study on Stressed Mirror Polishing with Continoues Polishing Machine for Large Aperture Off-axis Aspheric Mirror  

NASA Astrophysics Data System (ADS)

In this paper, a special technique is proposed to polish the off-axis aspherical mirror for a large segmented mirror. It is based on a process of stressed mirror polishing with the continoues polishing machine. During the polishing procedure, a stressing fixture attached to the mirror segment was designed to transform the surface shape of aspheric mirror to a destined sphere. So segments can be polished into same sphere on an contineous polishing machine (CPM). It took about 40 hours to continuously polish a scaled-down sub-mirror of CFGT using the technique.The mirror is 330 mm in diameter, 3.6 m in off-axis distance and 21.6 m in radius of curverture. The maximum asphericity is about 16 microns. High polishing efficiency was shown and it might met the needs of manufacturing of a large segmented telescope mirror.

Li, X. N.; Zhang, H. Y.; Cui, X. Q.; Jiang, Z. B.; Zheng, Y.; Liu, X. T.; Ni, H. K.

2012-03-01

237

Recent Advances in Laser Metrology and Correction of High Numerical Aperture Laser Beams Using Quadri-Wave Lateral Shearing-Interferometry - Poster Paper  

NASA Astrophysics Data System (ADS)

We present a new scheme to measure and correct the wave front of high numerical aperture focusing optics without any re-collimation optics. This scheme is based on the ability of Lateral Shearing Interferometry to sample wave fronts with short radius of curvature. Combining a SID4 interferometer close to the focal region with a deformable mirror leads to diffraction limited spots. Wave front correction is also done with a parallel beam line using the corrected beam as a reference. This avoids keeping the wave front sensor in the interaction area. In both cases, no difference in far-field patterns was observed.

Wattellier, Benoit; Doudet, Ivan; Boucher, William

2008-01-01

238

Optimization of deposition uniformity for large-aperture National Ignition Facility substrates in a planetary rotation system  

SciTech Connect

Multilayer coatings on large substrates with increasingly complex spectral requirements are essential for a number of optical systems, placing stringent requirements on the error tolerances of individual layers. Each layer must be deposited quite uniformly over the entire substate surface since any nonuniformity will add to the layer-thickness error level achieved. A deposition system containing a planetary rotation system with stationary uniformity masking is modeled, with refinements of the planetary gearing, source placement, and uniformity mask shape being utilized to achieve an optimal configuration. The impact of improper planetary gearing is demonstrated theoretically, as well as experimentally, providing more comprehensive requirements than simply avoiding repetition of previous paths through the vapor plume, until all possible combinations of gear teeth have been used. Deposition efficiency and the impact of changing vapor plume conditions on the uniformity achieved are used to validate improved source placement.

Oliver, J.B.; Talbot, D.

2006-05-17

239

Analysis of quantitative differences in large-aperture size for free-space optical communication systems with circle polarization shift keying and on-off keying in atmospheric turbulence channels  

NASA Astrophysics Data System (ADS)

A theoretical model is proposed to study quantitative differences in the size of large-aperture between circle polarization shift keying (CPolSK) and on-off keying (OOK). The quantitative differences can be analyzed with the impact from atmospheric condition, link length, and communication wavelength. Numerical results show that FSO CPolSK systems with longer communication wavelength can reduce the size even smaller than the systems using OOK, while it can be not obvious with increasing link length. Meanwhile, increasing average signal-to-noise ratio (SNR) leads to a reduction of the difference in aperture size. These results can be helpful for FSO systems design.

Liu, Chao; Yu, Xuelian; Yao, Yong

2010-11-01

240

Large area uniform nanostructures fabricated by direct femtosecond laser ablation.  

PubMed

An approach for fabricating large area uniform nanostructures by direct femtosecond (fs) laser ablation is presented. By the simple scanning technique with appropriate irradiation conditions, arbitrary size of uniform, complanate nano-grating, nano-particle, and nano-square structures can be produced on wide bandgap materials as well as graphite. The feature sizes of the formed nanostructures, which can be tuned in a wide range by varying the irradiation wavelength, is about 200 nm with 800 nm fs laser irradiation. The physical properties of the nano-structured surfaces are changed greatly, especially the optical property, which is demonstrated by the extraordinary enhancement of light transmission of the treated area. This technique is efficient, universal, and environmentally friendly, which exhibits great potential for applications in photoelectron devices. PMID:19582029

Huang, Min; Zhao, Fuli; Cheng, Ya; Xu, Ningsheng; Xu, Zhizhan

2008-11-10

241

Large amplitude electromagnetic solitons in intense laser plasma interaction  

NASA Astrophysics Data System (ADS)

This paper shows that the standing, backward- and forward-accelerated large amplitude relativistic electromagnetic solitons induced by intense laser pulse in long underdense collisionless homogeneous plasmas can be observed by particle simulations. In addition to the inhomogeneity of the plasma density, the acceleration of the solitons also depends upon not only the laser amplitude but also the plasma length. The electromagnetic frequency of the solitons is between about half and one of the unperturbed electron plasma frequency. The electrostatic field inside the soliton has a one-cycle structure in space, while the transverse electric and magnetic fields have half-cycle and one-cycle structure respectively. Analytical estimates for the existence of the solitons and their electromagnetic frequencies qualitatively coincide with our simulation results.

Li, Bai-Wen; S, Ishiguro; M, Skoric M.

2006-09-01

242

Laterally periodic resonator for large-area gain lasers.  

PubMed

Laterally periodic resonators, which can be constructed by use of transversely periodic phase- or amplitude-modulating elements in a cavity, are proposed for stabilization and generation of transversely coherent output from large-area gain. Lasers with periodic resonators have the combined features of conventional cavities and laser arrays. Significant low-order transverse modes and mode discrimination of a sample resonator with intracavity periodic phase elements are investigated numerically by the iteration method. Wave-propagation calculations are carried out by use of a fast Fourier transform, and a modified Prony method is used to evaluate wave functions and losses of transverse modes. Results of numerical calculations are consistent with expectations. PMID:19461774

Feng, Yan; Ueda, Ken-Ichi

2003-03-24

243

Tunnel contact junction native-oxide aperture and mirror vertical-cavity surface-emitting lasers and resonant-cavity light-emitting diodes  

NASA Astrophysics Data System (ADS)

Vertical-cavity surface-emitting lasers (VCSELs) and resonant-cavity light-emitting diodes (RCLEDs) are demonstrated with high index contrast distributed Bragg reflectors (DBRs) on either side of a ?-thickness cavity (?~980 nm). The devices, with tunnel contact junctions making possible lateral electron current excitation, have a lower 6.5 period native-oxide-based AlxOy/GaAs DBR and an upper reflector that is either a 2-4 period AlxOy/GaAs DBR, a 1-2 period SiO2/ZnSe DBR, a ?/4-thickness layer of AlxOy (antireflecting), or no mirror at all. The AlxOy/GaAs DBRs and a buried-oxide-defined current aperture are formed by selective oxidation of the high Al composition AlxGa1-xAs layers. Device characteristics are observed as a function of the upper DBR periodicity (reflectivity). Devices with upper reflectivities of R>~99% operate as VCSELs while those with less reflectivity R<~96% operate as RCLEDs, some with external differential quantum efficiencies as high as ?~27% and narrow spectral emission (??~50 Å).

Wierer, J. J.; Kellogg, D. A.; Holonyak, N.

1999-02-01

244

Confocal scanning laser ophthalmoscopic imaging resolution of secondary retinal effects induced by laser radiation  

Microsoft Academic Search

We have evaluated secondary laser induced retinal effects in non-human primates with a Rodenstock confocal scanning laser ophthalmoscope. A small eye animal model, the Garter snake, was employed to evaluate confocal numerical aperture effects in imaging laser retinal damage in small eyes vs. large eyes. Results demonstrate that the confocal image resolution in the Rhesus monkey eye is sufficient to

Harry Zwick; David J. Lund; Bruce E. Stuck; Joseph A. Zuclich; R. Elliott; Steven T. Schuschereba; Donald A. Gagliano; M. Belkin; Randolph D. Glickman

1996-01-01

245

Lasers for coherent optical satellite links with large dynamics  

NASA Astrophysics Data System (ADS)

We present the experimental realization of a laser system for ground to satellite optical Doppler ranging at the atmospheric turbulence limit. Such a system needs to display good frequency stability (a few parts in 10^{-14}) whilst allowing large and well controlled frequency sweeps of +/- 12 GHz at rates exceeding 100 MHz/s. Furthermore it needs to be sufficiently compact and robust for transportation to different astronomical observation sites where it is to be interfaced with satellite ranging telescopes. We demonstrate that our system fulfills those requirements and should therefore allow operation of ground to low Earth orbit satellite coherent optical links limited only by atmospheric turbulence.

Chiodo, Nicola; Djerroud, Khelifa; Acef, Ouali; Clairon, André; Wolf, Peter

2013-10-01

246

The chaotic dynamical aperture  

SciTech Connect

Nonlinear magnetic forces become more important for particles in the modern large accelerators. These nonlinear elements are introduced either intentionally to control beam dynamics or by uncontrollable random errors. Equations of motion in the nonlinear Hamiltonian are usually non-integrable. Because of the nonlinear part of the Hamiltonian, the tune diagram of accelerators is a jungle. Nonlinear magnet multipoles are important in keeping the accelerator operation point in the safe quarter of the hostile jungle of resonant tunes. Indeed, all the modern accelerator design have taken advantages of nonlinear mechanics. On the other hand, the effect of the uncontrollable random multipoles should be evaluated carefully. A powerful method of studying the effect of these nonlinear multipoles is using a particle tracking calculation, where a group of test particles are tracing through these magnetic multipoles in the accelerator hundreds to millions of turns in order to test the dynamical aperture of the machine. These methods are extremely useful in the design of a large accelerator such as SSC, LEP, HERA and RHIC. These calculations unfortunately take tremendous amount of computing time. In this paper, we try to apply the existing method in the nonlinear dynamics to study the possible alternative solution. When the Hamiltonian motion becomes chaotic, the tune of the machine becomes undefined. The aperture related to the chaotic orbit can be identified as chaotic dynamical aperture. We review the method of determining chaotic orbit and apply the method to nonlinear problems in accelerator physics. We then discuss the scaling properties and effect of random sextupoles.

Lee, S.Y.; Tepikian, S.

1985-10-01

247

Synthetic Aperture Image Holography.  

National Technical Information Service (NTIS)

The paper describes the underwater imaging method of 'Synthetic Aperture Image Holography' which has real-time imaging capability. The method utilizes image holography and computer synthetic aperture techniques. The imaging system consists of the acoustic...

T. Sato J. S. Jaffe

1985-01-01

248

Beaming matter waves from a subwavelength aperture  

SciTech Connect

We show theoretically that the shape of a beam of matter waves (cold atoms) emerging from one subwavelength aperture pierced in a film can be collimated within a few degrees. By means of an external laser field, a potential well for the atoms in the direction perpendicular to the surface is created. In this way, a running surface matter wave can be excited when atoms diffract from the aperture. If the aperture is surrounded with a finite array of indentations, coherent scattering of the surface matter wave with these indentations molds the angular distribution of the matter wave in the far field.

Fernandez-Dominguez, A. I.; Moreno, Esteban; Garcia-Vidal, F. J. [Departamento de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Martin-Moreno, L. [Departamento de Fisica de la Materia Condensada, Universidad de Zaragoza-CSIC, E-50009 Zaragoza (Spain)

2006-08-15

249

Synthetic Aperture Sonar.  

National Technical Information Service (NTIS)

The report discusses synthetic-aperture imagery applied to the Seabed Treaty verification problem. It presents the basic theory of the synthetic-aperture side-looking sonar and shows the transition region from real to synthetic aperture in terms of resolu...

J. N. Bucknam A. M. Chwastyk H. D. Black F. C. Paddison

1971-01-01

250

Confocal scanning beam laser microscope\\/macroscope: applications requiring large data sets  

Microsoft Academic Search

A new confocal scanning beam laser microscope\\/macroscope is described that combines the rapid scan of a scanning beam laser microscope with the large specimen capability of a scanning stage microscope. This instrument combines an infinity-corrected confocal scanning laser microscope with a scanning laser macroscope that uses a telecentric f*(theta) laser scan lens to produce a confocal imaging system with a

Arthur E. Dixon; Savvas Damaskinos; Alfonso Ribes; Eileen Seto; Marie-Claude Beland; Tetsu Uesaka; Brian Dalrymple; Sid P. Duttagupta; Philippe M. Fauchet

1995-01-01

251

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Size effect and the optical strength of infrared optical materials in the case of large irradiation spots  

NASA Astrophysics Data System (ADS)

A study was made of the dependences of the optical breakdown thresholds on the irradiated volume of KCl, NaCl, BaF2, and ZnSe single crystals when the laser beam aperture was varied from 80 ?m to 30 cm.

Kazantsev, S. G.

1997-03-01

252

Characterisation and calibration of a large aperture (1.6 m) ka-band indoor passive millimetre wave security screening imager  

NASA Astrophysics Data System (ADS)

A large 1.6 m aperture mechanically scanning quasi-optical millimetre wave imaging system designed for active use [1] has been investigated for its passive millimetre wave (PMMW) imaging capabilities. This raises new challenges for this imager, as the person / background contrast in indoor security scenarios at these frequencies is in the region of 6-7 K. The system is sensitive over 24 - 28 GHz and has a radiometric sensitivity measured at 6.5 K in a single frame, at a frame rate of 8.8 Hz. It was found that the focal plane receiver array radiated an excess noise ratio (ENR) of typically 9 dB. This radiation re-entered the focal plane array receivers after reflection from the imager optical components typically with a standard deviation of 17 K over the mechanical scan associated with a single image frame. Reflected from subjects in the field of view, it was typically 400 K from a 100 % reflective surface, and 40 K to 100 K from a human subject. This radiation, termed self-emission in this paper, is a feature of many PMMW imaging systems that use highgain electronic amplifiers in their receiving systems. The effectiveness in the use of a calibration mechanism to subtract self-emission reflected from the optical components and a large area quarter wave plate to minimising the amount of self-emission reflected back from subjects is demonstrated. The present system would benefit greatly from replacement amplifiers of larger bandwidth, lower self-emission and lower noise figure. It was also found that the millimetre wave emission from fluorescent room lighting entered the optics of the imager and modulated the received signals at 100 Hz. The mean level of emission was measured at 10 K with a ?10 K modulation at 100 Hz for per mode for a 100 % reflecting surface in the room. The best solution to the problem of emission from fluorescent lights was to turn them off and use incandescent lighting.

Salmon, Neil A.; Kirkham, Louise; Wilkinson, Peter N.

2012-10-01

253

Large Deformation Change in Iridium Isotopes from Laser Spectroscopy  

SciTech Connect

Laser spectroscopy measurements have been performed on neutron-deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d{sup 7}6s{sup 2} {sup 4}F{sub 9/2} {yields}5d{sup 7}6s6p {sup 6}F{sub 11/2} have been studied for the {sup 182-189}Ir, {sup 186}Ir{sup m} and {sup 191,193}Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the hyperfine splitting measurements and the changes of the mean square charge radii from the isotope shift measurements. A large deformation change between {sup 187}Ir and {sup 186}Ir and between {sup 186}Ir{sup m} and {sup 186}Ir{sup g} has been observed.

D. Verney; L. Cabaret; J. Crawford; H.T. Duong; J. Genevey; G. Hubert; F. Ibrahim; M. Krieg; F. Le Blanc; J.K.P. Lee; G. Le Scornet; D. Lunney; J. Obert; J. Oms; J. Pinard; J.C. Putaux; B. Roussiere; J. Sauvage; V. Sebastian

1999-12-31

254

Large deformation change in iridium isotopes from laser spectroscopy  

SciTech Connect

Laser spectroscopy measurements have been performed on neutron-deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d{sup 7}6s{sup 2} {sup 4}F{sub 9/2}{yields}5d{sup 7}6s6p {sup 6}F{sub 11/2} have been studied for the {sup 182-189}Ir, {sup 180}Ir{sup m} and {sup 191,193}Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the hyperfine splitting measurements and the changes of the mean square charge radii from the isotope shift measurements. A large deformation change between {sup 187}Ir and {sup 186}Ir and between {sup 186}Ir{sup m} and {sup 186}Ir{sup g} has been observed.

Verney, D.; Le Blanc, F.; Obert, J.; Oms, J.; Putaux, J. C.; Roussiere, B.; Sauvage, J. [Institut de Physique Nucleaire, IN2P3-CNRS, 91406 Orsay Cedex (France); Cabaret, L.; Duong, H. T.; Pinard, J. [Laboratoire Aime Cotton, 91405 Orsay Cedex (France); Crawford, J.; Lee, J. K. P. [Physics Department, Mc Gill University, H3A2T8 Montreal (Canada); Genevey, J.; Ibrahim, F. [Institut des Sciences Nucleaires, IN2P3-CNRS, 38026 Grenoble Cedex (France); Hubert, G.; Krieg, M.; Sebastian, V. [Institut fuer Physik der Univeristaet Mainz (Germany); Le Scornet, G.; Lunney, D. [CSNSM, IN2P3-CNRS, 91405 Orsay Cedex (France)

1999-11-16

255

Laser deposition of large-area thin films  

SciTech Connect

A new method for fabricating large-area thin films of uniform thickness on a rotating substrate is proposed. Its distinctive features are (i) the presence of a diaphragm, partially transmitting the evaporated material, between the target and substrate and (ii) the translatory motion of the rotating substrate with respect to the target at a certain velocity. The method proposed makes it possible to obtain thin films of uniform thickness on substrates with sizes limited by only the deposition chamber size. The method is experimentally verified by depositing thin CuO films on silicon substrates placed over the radius of a disk 300 mm in diameter. The deviation of the film thickness from the average value does not exceed {+-}3% throughout the entire radius, which confirms good prospects of this method for microelectronics, optical industry, and other modern technologies. (laser technology)

Kuzanyan, A S; Petrosyan, V A; Pilosyan, S Kh; Nesterov, V M

2011-03-31

256

Matrix formulation of axis-symmetric laser beams through a paraxial ABCD system containing hard-edged apertures: A comparative study  

NASA Astrophysics Data System (ADS)

A matrix formulation is presented, which enables us to study the propagation of axis-symmetric beams through a paraxial optical ABCD system containing hard-edged aperture. Numerical calculation results of super-Gaussian beams passing through a multi-aperture-lens system are given to illustrate the advantage of the method. A comparison of the matrix formulation, complex Gaussian expansion and direct numerical integration of the Collins formula is made, where the propagation of apertured Laguerre-Gaussian beams is chosen as an illustrative example. It is shown that the matrix formulation provides satisfactory results in both Fraunhofer and Fresnel regions, and reduces the computational time greatly in comparison with the direct integrationE However, this method is suited only to axis-symmetric optical beams and systems. By using the complex Gaussian expansion discrepancies exist in the near zone closer to the aperture, but usually its computational efficiency is higher than the matrix formulation.

Ji, Xiaoling; Lu, Baida

2005-06-01

257

Correlation of Laser-Induced Damage to Phase Objects in Bulk Fused Silica.  

National Technical Information Service (NTIS)

The Optical Sciences Laser (OSL) Upgrade facility, described in last year's proceedings, is a kJ-class, large aperture (100cm(sup 2)) laser system that can accommodate prototype optical components for large-scale inertial confinement fusion lasers. High-e...

M. C. Nostrand C. J. Cerjan M. A. Johnson T. I. Suratwala T. L. Weiland W. D. Sell J. L. Vickers R. L. Luthi J. R. Stanley T. G. Parham C. B. Thorsness

2004-01-01

258

A comparison of detection sensitivity between ALTAIR and Arecibo meteor observations: Can high power and large aperture radars detect low velocity meteor head-echoes  

NASA Astrophysics Data System (ADS)

Meteor head-echo observations using High Power and Large Aperture (HPLA) radars have been routinely used for micrometeor studies for over a decade. The head-echo is a signal from the radar-reflective plasma region traveling with the meteoroid and its detection allows for very precise determination of instantaneous meteor altitude, velocity and deceleration. Unlike specular meteor radars (SMR), HPLA radars are diverse instruments when compared one to another. The operating frequencies range from 46 MHz to 1.29 GHz while the antenna configurations changes from 18,000 dipoles in a 300 m×300 m square array, phase arrays of dipoles to single spherical or parabolic dishes of various dimensions. Hunt et al. [Hunt, S.M., Oppenheim, M., Close, S., Brown, P.G., McKeen, F., Minardi, M., 2004. Icarus 168, 34-42] and Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi: 10.1016/j.icarus.2006.09.07] recently showed, by utilizing a head-echo plasma-based model, the presence of instrumental biases in the ALTAIR VHF radar system against detecting meteors produced by very small particles (<1 ?g) moving at slow (˜20 km/s) velocities due to the low head echo radar cross-section (RCS) associated with these particles. In this paper we apply the same methodology to the Arecibo 430 MHz radar and compare the results with those presented by Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi: 10.1016/j.icarus.2006.09.07]. We show that, if the methodology applied by Hunt et al. [Hunt, S.M., Oppenheim, M., Close, S., Brown, P.G., McKeen, F., Minardi, M., 2004. Icarus 168, 34-42] and Close et al. [Close, S., Brown, P., Campbell-Brown, M., Oppenheim, M., Colestock, P., 2007. Icarus, doi: 10.1016/j.icarus.2006.09.07] is accurate, for particles at least 1 ?g or heavier, while the bias may exist for the ALTAIR measurements, it does not exist in the Arecibo data due to its greater sensitivity.

Janches, Diego; Close, Sigrid; Fentzke, Jonathan T.

2008-01-01

259

Stability design considerations for mirror support systems in ICF lasers  

SciTech Connect

Some of the major components of laser systems used for Inertial Confinement Fusion (ICF) are the large aperture mirrors which direct the path of the laser. These mirrors are typically supported by systems which consist of mirror mounts, mirror enclosures, superstructures, and foundations. Stability design considerations for the support systems of large aperture mirrors have been developed based on the experience of designing and evaluating similar systems at the Lawrence Livermore National Laboratory (LLNL). Examples of the systems developed at LLNL include Nova, the Petawatt laser, Beamlet, and the National Ignition Facility (NIF). The structural design of support systems of large aperture mirrors has typically been controlled by stability considerations in order for the large laser system to meet its performance requirements for alignment and positioning. This paper will discuss the influence of stability considerations and will provide guidance on the structural design and evaluation of mirror support systems in ICF lasers so that this information can be used on similar systems.

Tietbohl, G.L.; Sommer, S.C.

1996-10-01

260

Processing and Application of ICESat Large Footprint Full Waveform Laser Range Data  

Microsoft Academic Search

In the last two decades, laser scanning systems made the transition from scientific research to the commercial market. Laser scanning has a large variety of applications such as digital elevation models, forest inventory and man-made object reconstruction, and became the most required input data for flood plain and hydraulic models. This system is generally called as a discrete laser scanning

V. H. Duong

2010-01-01

261

The Antares laser power amplifier  

Microsoft Academic Search

The overall design of the Antares laser power amplifier is discussed. The power amplifier is the last stage of amplification in the 100-kJ Antares laser. In the power amplifier a single, cylindrical, grid-controlled cold-cathode, electron gun is surrounded by 12 large-aperture CO2 electron-beam sustained laser discharge sectors. Each power amplifier will deliver 18 kJ and the six modules used in

R. D. Stine; G. F. Ross; C. Silvernail

1979-01-01

262

Aperture averaging for studies of atmospheric turbulence and optimization of free space optical communication links  

NASA Astrophysics Data System (ADS)

Even after several decades of study, inconsistencies remain in the application of atmospheric turbulence theories to experimental systems, and the demonstration of acceptable correlations with experimental results. We have developed a flexible empirical approach for improving link performance through image analysis of intensity scintillation patterns coupled with frame aperture averaging on a free space optical (FSO) communication link. Aperture averaging calculations are invaluable in receiver design. A receiver must be large enough to collect sufficient power and reduce scintillation effects at a given range, but must also be of practical size. We have constructed an imaging system for measuring the effects of atmospheric turbulence and obscuration on FSO links. A He-Ne laser beam propagates over a range of 863 meters in atmospheric turbulence conditions that vary diurnally and seasonally from weak to strong. A high performance digital camera with a frame-grabbing computer interface is used to capture received laser intensity distributions at rates up to 30 frames per second and various short shutter speeds, down to 1/16,000s per frame. The captured image frames are analyzed in Labview to evaluate the turbulence parameter Cn2, temporal and spatial intensity variances, and aperture averaging. The aperture averaging results demonstrate the expected reduction in intensity fluctuations with increasing aperture diameter, and show quantitatively the differences in behavior between various strengths of turbulence. The reduction in scintillation with aperture size guides the selection of optimum receiver aperture. Spatial and temporal variance analyses within single frames and between frames are compared and show good agreement.

Yuksel, Heba; Davis, Christopher C.

2005-08-01

263

Calculation of the Illumination Symmetry of a Spherical Target in Multichannel Laser Devices.  

National Technical Information Service (NTIS)

The illumination symmetry of a spherical target irradiated by a laser system with a large number of output beams was investigated. A series of illumination geometries was considered, including those satisfying the aperture separation condition. A computer...

A. E. Danilov N. N. Demchenko V. B. Rozanov G. V. Sklizkov S. I. Fedotov

1977-01-01

264

Mirror Quality Required by the Antares Laser System.  

National Technical Information Service (NTIS)

The Antares laser system is a large (100 kJ) CO sub 2 pulse laser operating at 10.6 mu m. The system has 72 beam lines, each with an aperture of 900 cm exp 2 . The system will be composed primarily of large copper-faced mirrors whose principal dimensions ...

W. C. Sweatt

1979-01-01

265

Laser-assisted vitrification of large equine embryos.  

PubMed

The major difficulty in providing the benefits of embryo cryopreservation for equine agriculture is the mismatch between the optimal embryo age for collection from the mare (7-8 days after ovulation was detected) and the optimal age for freezing under current methods (6.5 days after ovulation). To overcome this limitation, we tested a method to enhance penetration of cryopreservative across the capsule and trophoblast of day 7 and 8 embryos combined with rapid freezing by vitrification. Six small embryos (<300 ?m in diameter) were collected on day 6-7 after ovulation and twelve larger embryos were recovered on day 7-8. In the treatment group, replacement of blastocoelic fluid with cryopreservative solution was facilitated by a laser system used to create a small opening in the embryonic capsule and trophectoderm. All embryos were vitrified using a CryoLeaf freezing support. After recovery from freezing and embryo transfer, three of four small untreated embryos (<300 ?m in diameter, 75%) and four of nine large blastocysts in the treatment group (>300 ?m in diameter, 44%) resulted in a vesicle as detected by ultrasonography approximately one week after transfer. However, only one recipient mare was still pregnant on day 23, and she delivered a live foal. Further investigation is required to determine why most of the embryos in this experiment were lost between day 13 and day 23 of gestation. PMID:21535240

Scherzer, J; Davis, C; Hurley, D J

2011-04-28

266

Asperity Height and Aperture of an Artificial Tensile Fracture of Metric Size  

Microsoft Academic Search

Summary  A tensile fracture of about 1?m in length was created by indenting wedges in a block of granite, and the heights of the two\\u000a fracture surfaces were measured using a large, non-contact surface profile measurement system with a laser profilometer to\\u000a determine the aperture distribution of the fracture. Based on the measured data, the frequency characteristics of the asperity\\u000a heights,

K. Sakaguchi; J. Tomono; K. Okumura; Y. Ogawa; K. Matsuki

2008-01-01

267

Adaptive coded aperture projection  

Microsoft Academic Search

With adaptive coded aperture projection, we present solutions for taking projectors to the next level. By placing a programmable liquid crystal array at a projectors aperture plane we show how the depth of field (DOF) of a projection can be greatly enhanced. This allows focussed imagery to be shown on complex screens with varying distances to the projectors focal plane,

Max Grosse; Gordon Wetzstein; Oliver Bimber; Anselm Grundhöfer

2009-01-01

268

Electron Microscope Aperture System.  

National Technical Information Service (NTIS)

An electron microscope is described, which includes an electron source, a condenser lens having either a circular aperture for focusing a solid cone of electrons onto a specimen or an annular aperture for focusing a hollow cone of electrons onto the speci...

K. Heinemann

1972-01-01

269

Electron Microscope Aperture System.  

National Technical Information Service (NTIS)

An electron microscope is described which includes an electron source, a condenser lens having either a circular aperture for focusing a solid cone of electrons onto a specimen or an annular aperture for focusing a hollow cone of electrons onto the specim...

K. Heinemann

1973-01-01

270

Laser conditioning study of KDP on the optical sciences laser using large area beams  

SciTech Connect

Considerable attention has been paid over the years to the problem of growing high purity KDP and KD*P to meet threshold requirements on succeeding generations of inertial confinement fusion lasers at LLNL. While damage thresholds for these materials have increased over time, the current National Ignition Facility (NIF) maximum fluence requirement (redline) for KD*P frequency triplers of 14.3 J/cm{sup 2} at 351 nm, 3 ns has not been reached without laser (pre)conditioning. It is reasonable to assume that, despite the rapid increase in damage thresholds for rapidly grown crystals, -a program of large scale conditioning of the 192 NIF triplers will be required. Small area ramp (R/1) tests on single sites indicate that KDP damage thresholds can be raised on average up to 1.5X the unconditioned values. Unpublished LLNL 3{omega} raster conditioning studies on KDP, however, have not conclusively shown that off-line conditioning is feasible for KD*P. Consequently, investigating the feasibility of on-line conditioning of NIF triplers at 3{omega} has become a high priority for the KDP damage group at LLNL. To investigate the feasibility of on-line conditioning we performed a series of experiments using the Optical Sciences Laser (OSL) on numerous samples of conventional and rapid growth KDP and KD*P. The experiment entailed exposing sites on each sample to a range of ramped shot (N/l) sequences starting at average fluences of -2 J/cm{sup 2} (in a 7 mm ``top hat`` beam @ 351 nm, 3 ns) up to peak fluences of approximately 13 J/cm{sup 2}. Test results indicated that the most effective conditioning procedure entailed a 7-8 shot ramp starting at 2 J/cm{sup 2} and ending at 12-13 J/cm{sup 2}. The pinpoint onset fluence for the 8/1 tests was 1.4 times that of the unconditioned site. Damage evolution appears to be exponential as a function of increasing fluence. When damage occurs after conditioning however, pinpoint density evolution exhibits a greater slope than less conditioned sites. The overall reduction in the total pinpoint number can be as high as 30OX. Despite laser conditioning , the pinpoint onset for the samples considered is below the NIF redline fluence of 14.3 J/cm{sup 2}. In addition, the exponential pinpoint evolution curves indicate that damage levels at NIF redline fluences will be on the order of 10{sup 4} pinpoints/mm{sup 2}. This suggests that there will be significant damage in NIP triplers, however, substantial damage has not been observed in the large Beamlet tripler (conventionally grown KD*P) under similar exposure conditions. By applying the OSL damage evolution curves to model NIF THG output spatial profiles it is possible to show damage in NIF triplers will be slight, consisting of isolated clusters with a few pinpoints at high fluence portions of the beam. This prediction has been verified by scatter mapping the 37 cm Beamlet tripler crystal. These results will be discussed in a future memo. These results indicate the feasibility of on-line conditioning for the NIF laser.

Runkel, M.; DeYoreo, J.; Sell, W.; Milam, D.

1997-12-20

271

Heat assisted magnetic recording (HAMR) with nano-aperture VCSELs for 10 Tb/in2 magnetic storage density  

NASA Astrophysics Data System (ADS)

We have conducted a thorough experimental analysis of nano-aperture VCSELs for use in heat-assisted magnetic recording (HAMR). To the best of our knowledge, this is the first study to both explore the impact of magnetic media proximity on VCSEL aperture power throughput and to use statistical methods to simultaneously characterize thousands of aperture designs. To achieve areal recording densities beyond 1 Tb/in2, high anisotropy magnetic materials are required to overcome the super-paramagnetic effect. These require high switching fields which are not conventionally available. Heat assisted magnetic recording (HAMR) is a potential technology to reduce the coercivity of the media and thus the required switching field by localized heating to enable writing of bits. The challenges being faced by this technology are to develop a precise method of delivering light to a very small, sub wavelength bit area with sufficient power through a near field aperture, and the fabrication of a laser source which can be integrated with current write heads used in hard disk drives. The focus of our work is to characterize nano-aperture VCSELs and test their potential application to HAMR. We have fabricated 850 nm VCSELs with large arrays of differently shaped nano-apertures in the gold layer on top of each VCSEL. The focusing and transmission characteristics of differently shaped nano-apertures are compared by simulations and experiments. C-shaped and H-shaped nano-apertures have also been fabricated in a gold layer deposited on a SiO2 substrate to observe the effect of close proximity of magnetic media (FePt) on the performance of nano-apertures, and polarization effects have also been characterized.

Hussain, Sajid; Kundu, Shreya; Bhatia, C. S.; Yang, Hyunsoo; Danner, Aaron J.

2013-03-01

272

Performance of a 80 W copper vapor laser with “alignment free” unstable CAT-EYE resonator and other configurations using intra-cavity apertures  

Microsoft Academic Search

Performance of a kinetically enhanced copper vapor laser (KE-CVL) with various stable\\/unstable “alignment free” CAT-EYE resonator configurations are presented here in this paper. The laser used in the experiment was a 45mm bore (?2l discharge volume) kinetically enhanced copper vapor laser developed in our laboratory and capable of generating maximum power of ?80W (at ?9.8kHz). The efficiency of the laser

Bijendra Singh; S. R. Daultabad; V. V. Subramaniam; Ashim Chakraborty

2008-01-01

273

Effects of large-area irradiated laser phototherapy on peripheral nerve regeneration across a large gap in a biomaterial conduit.  

PubMed

This paper proposes a novel biodegradable nerve conduit comprising 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) cross-linked gelatin, annexed with ?-tricalcium phosphate (TCP) ceramic particles (EDC-Gelatin-TCP, EGT). In this study, the EGT-implant site in rats was irradiated using a large-area 660 nm AlGaInP diode laser (50 mW) to investigate the feasibility of laser stimulation in the regeneration of a 15-mm transected sciatic nerve. The animals were divided into three groups: a sham-irradiated group (EGT/sham); an experimental group undergoing low-level laser (LLL) therapy (EGT/laser); a control group undergoing autologous nerve grafts (autografts). Twelve weeks after implantation, walking track analysis showed a significantly higher sciatic functional index (p < 0.05) and improved toe spreading development in the EGT/laser and autograft groups than in the EGT/sham group. In electrophysiological measurement, both the mean peak amplitude and the area under the compound muscle action potential curves in the EGT/laser and autograft groups showed significantly improved functional recovery than the EGT/sham group (p < 0.05). Compared with the EGT/sham group, the EGT/laser and autograft groups displayed a reduction in muscular atrophy. Histomorphometric assessments revealed that the EGT/laser group had undergone more rapid nerve regeneration than the EGT/sham group. The laser-treated group also presented greater neural tissue area as well as larger axon diameter and thicker myelin sheath than the tube group without the laser treatment, indicating improved nerve regeneration. Thus, these assessments demonstrate that LLL therapy can accelerate the repair of a transected peripheral nerve in rats after being bridged with EGT conduit. PMID:22887896

Shen, Chiung-Chyi; Yang, Yi-Chin; Liu, Bai-Shuan

2012-08-10

274

Broadband synthetic aperture geoacoustic inversion.  

PubMed

A typical geoacoustic inversion procedure involves powerful source transmissions received on a large-aperture receiver array. A more practical approach is to use a single moving source and/or receiver in a low signal to noise ratio (SNR) setting. This paper uses single-receiver, broadband, frequency coherent matched-field inversion and exploits coherently repeated transmissions to improve estimation of the geoacoustic parameters. The long observation time creates a synthetic aperture due to relative source-receiver motion. This approach is illustrated by studying the transmission of multiple linear frequency modulated (LFM) pulses which results in a multi-tonal comb spectrum that is Doppler sensitive. To correlate well with the measured field across a receiver trajectory and to incorporate transmission from a source trajectory, waveguide Doppler and normal mode theory is applied. The method is demonstrated with low SNR, 100-900?Hz LFM pulse data from the Shallow Water 2006 experiment. PMID:23862809

Tan, Bien Aik; Gerstoft, Peter; Yardim, Caglar; Hodgkiss, William S

2013-07-01

275

Active compensation of large dispersion of femtosecond pulses for precision laser ranging.  

PubMed

We describe an active way of compensation for large dispersion induced in the femtosecond light pulses travelling in air for laser ranging. The pulse duration is consistently regulated at 250 fs by dispersion control, allowing sub-micrometer resolution in measuring long distances by means of time-of-flight measurement. This method could facilitate more reliable applications of femtosecond pulses for satellite laser ranging, laser altimetry and active LIDAR applications. PMID:21369227

Lee, Sang-Hyun; Lee, Joohyung; Kim, Young-Jin; Lee, Keunwoo; Kim, Seung-Woo

2011-02-28

276

Computer-controlled measurements of laser-induced damage statistics on large optics  

Microsoft Academic Search

This paper presents data reduction on an experimental set-up that we have recently developed at CESTA, France. It has been implemented to analyze laser-induced damage on optics dedicated to the Megajoule laser project. Our goal is to measure the damage fluence on samples under tests, using a statistical approach on a very large number of sites. The laser-induced damage density

Michel A. Josse; Roger Courchinoux; Laurent Lamaignere; Jean-Christophe Poncetta; Thierry Donval; Herve Bercegol

2005-01-01

277

Sideband analysis and seismic detection in a large ring laser  

NASA Astrophysics Data System (ADS)

A ring laser unlocked by the Earth's Sagnac effect has attained a frequency resolution of 1 part in 3 \\times 1021 and a rotational resolution of 300 prad. We discuss both theoretically and experimentally the sideband structure of the Earth rotation-induced spectral line induced in the microhertz-hertz region by frequency modulation associated with extra mechanical motion, such as seismic events. The relative sideband height is an absolute measure of the rotational amplitude of that Fourier component. An initial analysis is given of the ring laser record from the Arthur's Pass-Coleridge seismic event of 18 June 1994.

Stedman, G. E.; Li, Z.; Bilger, H. R.

1995-08-01

278

Sideband analysis and seismic detection in a large ring laser.  

PubMed

Aring laser unlocked by the Earth's Sagnac effect has attained a frequency resolution of 1 part in 3 × 10(21) and a rotational resolution of 300 prad. We discuss both theoretically and experimentally the sideband structure of the Earth rotation-induced spectral line induced in the microhertz-hertz region by frequency modulation associated with extra mechanical motion, such as seismic events. The relative sideband height is an absolute measure of the rotational amplitude of that Fourier component. An initial analysis is given of the ring laser record from the Arthur's Pass-Coleridge seismic event of 18 June 1994. PMID:21060358

Stedman, G E; Li, Z; Bilger, H R

1995-08-20

279

Large area laser surface micro/nanopatterning by contact microsphere lens arrays  

NASA Astrophysics Data System (ADS)

Laser surface micro/nanopatterning by particle lens arrays is a well-known technique. Enhanced optical fields can be achieved on a substrate when a laser beam passes through a self-assembled monolayer of silica microspheres placed on the substrate. This enhanced optical field is responsible for ablative material removal from the substrate resulting in a patterned surface. Because of the laser ablation, the microspheres are often ejected from the substrate during laser irradiation. This is a major issue impeding this technique to be used for large area texturing. We explored the possibility to retain the spheres on the substrate surface during laser irradiation. A picosecond laser system (wavelength of 515 nm, pulse duration 6.7 ps, repetition rate 400 kHz) was employed to write patterns through the lens array on a silicon substrate. In this experimental study, the pulse energy was found to be a key factor to realize surface patterning and retain the spheres during the process. When the laser pulse energy is set within the process window, the microspheres stay on the substrate during and after laser irradiation. Periodic patterns of nanoholes can be textured on the substrate surface. The spacing between the nanoholes is determined by the diameter of the microspheres. The depth of the nanoholes varies, depending on the number of laser pulses applied and pulse energy. Large area texturing can be made using overlapping pulses obtained through laser beam scanning.

Sedao, X.; Derrien, T. J.-Y.; Romer, G. R. B. E.; Pathiraj, B.; Huis in `t Veld, A. J.

2013-06-01

280

Study of laser-induced damage to large core silica fiber by Nd:YAG and Alexandrite lasers  

NASA Astrophysics Data System (ADS)

As a continuation of our earlier study at 2.1 ?m wavelength, we have investigated the laser damage to several types of step-index, large core (1500 ?m) silica fibers at two new wavelengths by high power long pulsed Nd:YAG (1064 nm) and Alexandrite (755 nm) lasers. It was observed that fibers with different designs showed a significant difference in performance at these wavelengths. We will also report a correlation of damage to the fibers between the two laser wavelengths. The performance analyses of different fiber types under the given test conditions will enable optimization of fiber design for specific applications.

Sun, Xiaoguang; Li, Jie; Hokansson, Adam; Whelan, Dan; Clancy, Michael

2009-02-01

281

FUNDAMENTAL STUDIES OF IGNITION PROCESSES IN LARGE NATURAL GAS ENGINES USING LASER SPARK IGNITION  

Microsoft Academic Search

The current report details project progress made during the first quarterly reporting period of the DOE sponsored project ''Fundamental studies of ignition processes in large natural gas engines using laser spark ignition''. The goal of the overall research effort is to develop a laser ignition system for natural gas engines, with a particular focus on using fiber optic delivery methods.

Azer Yalin; Morgan Defoort; Bryan Willson

2005-01-01

282

Development and utilization of a laser velocimeter system for a large transonic wind tunnel  

Microsoft Academic Search

The need for measurements of the velocity flow field about spinner propeller nacelle configurations at Mach numbers to 0.8 was met by a specially developed laser velocimeter system. This system, which uses an argon ion laser and 4 beam 2 color optics, was required to operate in the hostile environment associated with the operation of a large transonic wind tunnel.

R. J. Freedman; J. P. Greissing

1982-01-01

283

Fail safe system for suppressing stimulated Brillouin scattering in large optics on the Nova laser  

SciTech Connect

We have designed and are testing a fail safe'' system on Nova to suppress stimulated Brillouin scattering (SBS) in large optics at the output of the laser. The system increases the laser bandwidth to prevent SBS and prevents pulses with insufficient bandwidth from being injected into the amplifier chain. It is thus fail safe. The system design and experimental measurements will be presented.

Thompson, C.E.; Browning, D.F.; Padilla, E.H.; Weiland, T.L.; Wintemute, J.D.

1992-01-08

284

Fail safe system for suppressing stimulated Brillouin scattering in large optics on the Nova laser  

SciTech Connect

We have designed and are testing a ``fail safe`` system on Nova to suppress stimulated Brillouin scattering (SBS) in large optics at the output of the laser. The system increases the laser bandwidth to prevent SBS and prevents pulses with insufficient bandwidth from being injected into the amplifier chain. It is thus fail safe. The system design and experimental measurements will be presented.

Thompson, C.E.; Browning, D.F.; Padilla, E.H.; Weiland, T.L.; Wintemute, J.D.

1992-01-08

285

The laser interferometer system for the large optics diamond turning machine  

SciTech Connect

The purpose of this report is to describe the Laser Interferometer System designed for the Large Optics Diamond Turning Machine (LODTM). To better understand the laser interferometer system, it is useful to begin with an overview of the LODTM metrology system.

Baird, E D; Donaldson, R R; Patterson, S R

1999-06-29

286

Research of large energy and high power Nd:Ce:YAG laser  

NASA Astrophysics Data System (ADS)

Currently, the output laser energy was enlarged mostly by using laser application technology and different pump styles were used, which made the laser volume large. In this thesis, the output laser energy was increased by improving the quality of laser crystal and using new style doped laser crystal, which can increase the capacity usage ratio of solid laser, and the beam quality was improved as well. In the paper, a new double-doped Nd:Ce:YAG laser crystal pumped by Xe-lamp and the plane-plane resonant was used as main oscillator of laser. There were two advantages using the method. Firstly, the absorption spectrum and emission band spectrum of Ce3+ were analyzed, which can create energy transition between Ce3+ and Nd3+. The Ce3+ ion in double-doped laser crystal can absorb pump light at ultraviolet band and create stimulated emission, which located at the absorption band of Nd3+ and made more Nd3+ ion create energy level transition. The inverted population increased. As result the capacity usage ratio of pumped energy was increased and the output energy of laser was enlarged. Secondly for the advantage of the limitation of plane-plane resonant to laser beam was strong, the angle of divergence was small at far field and the beam quality was good. Finally the pulsed laser energy was compressed to spike pulse by using passive Q-switched, and the peak power was increased. The experiments were carried out under the condition of passive Q-switched. When the input voltage was 800V, the laser beam was obtained at the oscillator stage, whose output energy was 651.5mJ. The pulse width was 20ns. The slope efficiency was 0.49%. Angle of divergence was better than 1.2 mrad. And peak power was 32.5KW. The experiment result is accordant with theoretical analyses. This solid laser has important potential application.

Zhao, Zhen-Yu; Nie, Jin-Song

2011-06-01

287

Laser safety training programs for a large and diverse research and development laboratory  

NASA Astrophysics Data System (ADS)

Sandia National Laboratories is a large multiprogram Research and Development laboratory which is operated by a contractor for the US Department of Energy. In the Laboratories, lasers are both the subject of research and the tools that are used in other research, development, and testing activities. Since 1979, laser safety training has been the primary focus of the Laboratories' laser safety program. Approximately 1100 personnel have been trained in formal courses during that time period. The formal course, presented on site by a contractor, consists of two full days of instruction. The course contents include the following topics: Laser technology and safety overview; Federal and ANSI laser standards summaries; Biological effects of laser radiation; Classification of lasers; Laser hazard analysis; Review of ANSI Z136.1 control measures; Laser eye protection. Recent emphasis on regulatory requirements, conduct of operations, and quality management has revealed a need to change the laser safety training curriculum. A new course for users of low power lasers (Class 2 and 3a) is being developed. A refresher course, a management awareness (self-study) course, and major changes in the current course are planned.

Stocum, W. E.

288

Filamentation Analysis in Large-Mode-Area Fiber Lasers  

SciTech Connect

Starting from the paraxial wave equation, an analytic expression for filament threshold in fiber lasers is derived. The occurrence of filamentation is determined by the larger of two thresholds, one of perturbative gain and one of spatial confinement. The threshold value is around a few megawatts, depending on the parameters of the fiber.

Sun, L.; Marciante, J.R.

2007-10-04

289

Shock wave absorber having apertured plate  

DOEpatents

The shock or energy absorber disclosed herein utilizes an apertured plate maintained under the normal level of liquid flowing in a piping system and disposed between the normal liquid flow path and a cavity pressurized with a compressible gas. The degree of openness (or porosity) of the plate is between 0.01 and 0.60. The energy level of a shock wave travelling down the piping system thus is dissipated by some of the liquid being jetted through the apertured plate toward the cavity. The cavity is large compared to the quantity of liquid jetted through the apertured plate, so there is little change in its volume. The porosity of the apertured plate influences the percentage of energy absorbed.

Shin, Y.W.; Wiedermann, A.H.; Ockert, C.E.

1983-08-26

290

Shock wave absorber having apertured plate  

DOEpatents

The shock or energy absorber disclosed herein utilizes an apertured plate maintained under the normal level of liquid flowing in a piping system and disposed between the normal liquid flow path and a cavity pressurized with a compressible gas. The degree of openness (or porosity) of the plate is between 0.01 and 0.60. The energy level of a shock wave travelling down the piping system thus is dissipated by some of the liquid being jetted through the apertured plate toward the cavity. The cavity is large compared to the quantity of liquid jetted through the apertured plate, so there is little change in its volume. The porosity of the apertured plate influences the percentage of energy absorbed.

Shin, Yong W. (Western Springs, IL); Wiedermann, Arne H. (Chicago Heights, IL); Ockert, Carl E. (Vienna, VA)

1985-01-01

291

Experimental and numerical studies of mode-locked fiber laser with large normal and anomalous dispersion.  

PubMed

An ytterbium-doped mode-locked fiber laser was demonstrated with a chirped fiber Bragg grating for dispersion management. The cavity net dispersion could be changed from large normal dispersion (2.4 ps(2)) to large anomalous dispersion (-2.0 ps(2)), depending on the direction of the chirped Bragg grating in laser cavity. The proposed fiber lasers with large normal dispersion generated stable pulses with a pulse width of <1.1 ns and a pulse energy of 1.5 nJ. The laser with large anomalous dispersion generated wavelength-tunable soliton with a pulse width of 2.7 ps and pulse energy of 0.13 nJ. A theoretical model was established and used to verify the experimental observations. PMID:23736423

Zhang, Lei; El-Damak, A R; Feng, Yan; Gu, Xijia

2013-05-20

292

Computer-controlled measurements of laser-induced damage statistics on large optics  

NASA Astrophysics Data System (ADS)

This paper presents data reduction on an experimental set-up that we have recently developed at CESTA, France. It has been implemented to analyze laser-induced damage on optics dedicated to the Megajoule laser project. Our goal is to measure the damage fluence on samples under tests, using a statistical approach on a very large number of sites. The laser-induced damage density is accurately plotted as a function of laser fluence, by measuring the fluence of every single shot during the scan. This improvement of accuracy modifies dramatically the interpretation of the results that can be made, compared to raw data, considering the mean fluence only.

Josse, Michel A.; Courchinoux, Roger; Lamaignere, Laurent; Poncetta, Jean-Christophe; Donval, Thierry; Bercegol, Herve

2005-02-01

293

Parallel optical nanolithography using nanoscale bowtie apertures  

NASA Astrophysics Data System (ADS)

Over the past two decades various branches of science and engineering have developed techniques for producing nanoscopic light sources for different applications such as imaging, detection and fabrication. These areas include near-field scanning optical microscopy (NSOM), surface-enhanced Raman scattering and detection (SERS), plasmonics and so on. In particular nanolithography techniques have been developed to produce feature sizes in the sub-100 nm length scales. These processes include variations of standard photolithography process to achieve high resolution, optical fiber-based near-field lithography, surface plasmon assisted nanolithography, interference optical lithography and so on. This work presents a study of the viability of using nanoscale bowtie apertures for nanolithography. Bowtie apertures exhibit a unique property of supporting a propagating TE10 mode at wavelengths of light in the visible and near-UV regimes. The energy of this mode is concentrated in the gap region of the aperture and thus these apertures have the potential to produce high intensity nanoscale light spots that can be used for nano-patterning applications. We demonstrate this capability of nanoscale bowtie apertures by patterning photoresist to obtain resolution less than 100 nm. Initially we present the results from static lithography experiments and show that the ridge apertures of different shapes -- C, H and bowtie produce holes in the photoresist of dimensions around 50-60 nm. Subsequently we address the issues involved in using these apertures for nano directwriting. We show that chromium thin-films offer a viable solution to produce high quality metal films of surface roughness less than 1 nm over an area of 25 mum2. This is indeed important to achieve intimate contact between the apertures and the photoresist surface. We also explain ways to decrease friction between the mask and photoresist surfaces during nano direct-writing. In addition, to decrease the contact force needed to bring an array of bowtie apertures into intimate contact with the photoresist surface we present an optical interference based alignment system that aligns the mask and photoresist surfaces to within 0.1 mrad of parallelism. In this work we show that bowtie apertures can be used to produce patterns in the photoresist of dimensions in the order of 85-90 nm. We also demonstrate parallel optical nanolithography using an array of bowtie apertures that opens up the possibility of using arrays of bowtie apertures to produce a large number of nanoscale light spots for parallel nano-manufacturing.

Uppuluri, Sreemanth M. V.

294

Physical Design of Parameters of Nd:Yag Disk Laser.  

National Technical Information Service (NTIS)

Using a large Nd:YAG crystal grown by the temperature gradient method, researchers built a 40 mm aperture disk laser. The key problems that had to be resolved to set up the disk laser were suppression of parasitic oscillation in the disk and removal of wa...

M. Zhang W. Cao Q. Chen F. Tang

1987-01-01

295

A smart car for the surface shape measurement of large antenna based on laser tracker  

NASA Astrophysics Data System (ADS)

The geometric accuracy of the surface shape of large antenna is an important indicator of antenna’s quality. Currently, high-precision measurement of large antenna surface shape can be performed in two ways: photogrammetry and laser tracker. Photogrammetry is a rapid method, but its accuracy is not enough good. Laser tracker can achieve high precision, but it is very inconvenient to move the reflector (target mirror) on the surface of the antenna by hand during the measurement. So, a smart car is designed to carry the reflector in this paper. The car, controlled by wireless, has a small weight and a strong ability for climbing, and there is a holding bracket gripping the reflector and controlling reflector rise up and drop down on the car. During the measurement of laser tracker, the laser beam between laser tracker and the reflector must not be interrupted, so two high-precision three-dimensional miniature electronic compasses, which can real-time monitor the relative angle between the holding bracket and the laser tracker’s head, are both equipped on the car and the head of laser tracker to achieve automatic alignment between reflector and laser beam. With the aid of the smart car, the measurement of laser tracker has the advantages of high precision and rapidity.

Gu, Yonggang; Hu, Jing; Jin, Yi; Zhai, Chao

2012-09-01

296

Development of laser guide stars and adaptive optics for large astronomical telescopes  

SciTech Connect

We describe a feasibility experiment to demonstrate high-order adaptive optics using a sodium-layer laser guide star. We use the copper-vapor-pumped dye lasers developed for LLNL's atomic Vapor Laser Isotope Separation program to create the laser guide star. Closed-loop adaptive corrections will be accomplished using a 69-subaperture adaptive optics system on a one-meter telescope at LLNL. The laser bream is projected upwards from a beam director approximately 5 meters away from the main telescope, and is expected to form a spot 1-2 meters in diameter at the atmospheric sodium layer (95 km altitude). We describe the overall system architecture and adaptive optics components, and analyze the expected performance. Our long-term goal is to develop sodium-layer laser guide stars and adaptive optics for large astronomical telescopes. We discuss preliminary design trade-offs for the Keck Telescope at Mauna Kea.

Max, C.E.; Avicola, K.; Bissinger, H.; Brase, J.M.; Gavel, D.T.; Friedman, H.; Morris, J.R.; Olivier, S.S.; Rapp, D.; Salmon, J.T.; Waltjen, K.

1992-06-29

297

Development of laser guide stars and adaptive optics for large astronomical telescopes  

SciTech Connect

We describe a feasibility experiment to demonstrate high-order adaptive optics using a sodium-layer laser guide star. We use the copper-vapor-pumped dye lasers developed for LLNL`s atomic Vapor Laser Isotope Separation program to create the laser guide star. Closed-loop adaptive corrections will be accomplished using a 69-subaperture adaptive optics system on a one-meter telescope at LLNL. The laser bream is projected upwards from a beam director approximately 5 meters away from the main telescope, and is expected to form a spot 1-2 meters in diameter at the atmospheric sodium layer (95 km altitude). We describe the overall system architecture and adaptive optics components, and analyze the expected performance. Our long-term goal is to develop sodium-layer laser guide stars and adaptive optics for large astronomical telescopes. We discuss preliminary design trade-offs for the Keck Telescope at Mauna Kea.

Max, C.E.; Avicola, K.; Bissinger, H.; Brase, J.M.; Gavel, D.T.; Friedman, H.; Morris, J.R.; Olivier, S.S.; Rapp, D.; Salmon, J.T.; Waltjen, K.

1992-06-29

298

Development of laser guide stars and adaptive optics for large astronomical telescopes  

NASA Astrophysics Data System (ADS)

A feasibility experiment to demonstrate high-order adaptive optics using a sodium-layer laser guide star is described. The copper-vapor-pumped dye lasers developed for LLNL's atomic Vapor Laser Isotope Separation program is used to create the laser guide star. Closed-loop adaptive corrections will be accomplished using a 69-subaperture adaptive optics system on a one-meter telescope at LLNL. The laser beam is projected upwards from a beam director approximately 5 meters away from the main telescope, and is expected to form a spot 1-2 meters in diameter at the atmospheric sodium layer (95 km altitude). The overall system architecture and adaptive optics components are described, and the expected performance is analyzed. Our long-term goal is to develop sodium-layer laser guide stars and adaptive optics for large astronomical telescopes. Preliminary design trade-offs for the Keck Telescope at Mauna Kea are discussed.

Max, C. E.; Avicola, K.; Bissinger, H.; Brase, J. M.; Gavel, D. T.; Friedman, H.; Morris, J. R.; Olivier, S. S.; Rapp, D.; Salmon, J. T.

1992-06-01

299

Highly efficient resonantly pumped Er:YAG large area waveguide laser with diffraction limited output  

NASA Astrophysics Data System (ADS)

We demonstrated nearly a quantum defect limited CW operation of a 41-mm-long Er:YAG large area crystalline waveguide laser with a diffraction limited output, which was resonantly pumped by a fiber laser at 1532 nm. Using a Er(0.25%):YAG, 62 ?m x 62 ?m waveguide, surrounded by a 3 x 5 mm rectangular cladding of undoped YAG, an output power of 9.1 W with slope efficiency of 92.8% has been achieved. The output laser beam had a Gaussian profile with a ~ 2.8 x 10-2 rad divergence, which is in good agreement with the divergence expected from a waveguide with a low NA value. The waveguide laser operated simultaneously at two wavelengths, 1617 nm and 1645 nm, when the transmission of the laser cavity output coupler was less than 20-25%, and operated only at 1617 nm when the laser output mirror had a higher transmission.

Ter-Gabrielyan, N.; Fromzel, V.; Dubinskii, Mark; Mu, X.; Meissner, H.

2013-05-01

300

Laser Plasma Particle Accelerators: Large Fields for Smaller Facility Sources  

SciTech Connect

Compared to conventional particle accelerators, plasmas can sustain accelerating fields that are thousands of times higher. To exploit this ability, massively parallel SciDAC particle simulations provide physical insight into the development of next-generation accelerators that use laser-driven plasma waves. These plasma-based accelerators offer a path to more compact, ultra-fast particle and radiation sources for probing the subatomic world, for studying new materials and new technologies, and for medical applications.

Geddes, Cameron G.R.; Cormier-Michel, Estelle; Esarey, Eric H.; Schroeder, Carl B.; Vay, Jean-Luc; Leemans, Wim P.; Bruhwiler, David L.; Cary, John R.; Cowan, Ben; Durant, Marc; Hamill, Paul; Messmer, Peter; Mullowney, Paul; Nieter, Chet; Paul, Kevin; Shasharina, Svetlana; Veitzer, Seth; Weber, Gunther; Rubel, Oliver; Ushizima, Daniela; Bethel, Wes; Wu, John

2009-03-20

301

Laser Plasma Particle Accelerators: Large Fields for Smaller Facility Sources  

Microsoft Academic Search

Compared to conventional particle accelerators, plasmas can sustain accelerating fields that are thousands of times higher. To exploit this ability, massively parallel SciDAC particle simulations provide physical insight into the development of next-generation accelerators that use laser-driven plasma waves. These plasma-based accelerators offer a path to more compact, ultra-fast particle and radiation sources for probing the subatomic world, for studying

Cameron G. R. Geddes; Estelle Cormier-Michel; Eric H. Esarey; Carl B. Schroeder; Jean-Luc Vay; Wim P. Leemans; David L. Bruhwiler; John R. Cary; Ben Cowan; Marc Durant; Paul Hamill; Peter Messmer; Paul Mullowney; Chet Nieter; Kevin Paul; Svetlana Shasharina; Seth Veitzer; Gunther Weber; Oliver Rubel; Daniela Ushizima; Wes Bethel; John Wu

2009-01-01

302

FDTD method for laser absorption in metals for large scale problems.  

PubMed

The FDTD method has been successfully used for many electromagnetic problems, but its application to laser material processing has been limited because even a several-millimeter domain requires a prohibitively large number of grids. In this article, we present a novel FDTD method for simulating large-scale laser beam absorption problems, especially for metals, by enlarging laser wavelength while maintaining the material's reflection characteristics. For validation purposes, the proposed method has been tested with in-house FDTD codes to simulate p-, s-, and circularly polarized 1.06 ?m irradiation on Fe and Sn targets, and the simulation results are in good agreement with theoretical predictions. PMID:24150386

Deng, Chun; Ki, Hyungson

2013-10-21

303

Multiple Instrument Distributed Aperture Sensor (MIDAS) for planetary remote sensing  

NASA Astrophysics Data System (ADS)

An innovative approach that enables greatly increased return from planetary science remote sensing missions is described. Our concept, called Multiple Instrument Distributed Aperture Sensor (MIDAS), provides a large-aperture, wide-field telescope at a fraction of the cost, mass and volume of conventional space telescopes, by integrating advanced optical interferometry technologies. All optical assemblies are integrated into MIDAS as the primary remote sensing science payload, thereby reducing the cost, resources, complexity, integration and risks of a set of back-end science instruments (SI"s) tailored to a specific mission, such as advanced SI"s now in development for future planetary remote sensing missions. MIDAS interfaces to multiple SI"s for redundancy and to enable synchronized concurrent science investigations, such as with multiple highly sensitive spectrometers. Passive imaging modes with MIDAS enable high resolution remote sensing at the diffraction limit of the overall synthetic aperture, sequentially by each science instrument as well as in somewhat lower resolution by multiple science instruments acting concurrently on the image, such as in different wavebands. Our MIDAS concept inherently provides nanometer-resolution hyperspectral passive imaging without the need for any moving parts in the science instruments. In its active remote sensing modes using an integrated laser subsystem, MIDAS enables LIDAR, vibrometry, illumination, various active laser spectroscopies such as ablative, breakdown, fluorescence, Raman and time-resolved spectroscopy. The MIDAS optical design also provides high-resolution imaging for long dwell times at high altitudes, thereby enabling real-time, wide-area remote sensing of dynamic changes in planet surface processes. These remote sensing capabilities significantly enhance astrobiologic, geologic, atmospheric, and similar scientific objectives for planetary exploration missions.

Pitman, Joseph T.; Duncan, Alan; Stubbs, David; Sigler, Robert D.; Kendrick, Richard L.; Smith, Eric H.; Mason, James E.; Delory, Gregory; Lipps, Jere H.; Manga, Michael; Graham, James R.; de Pater, Imke; Reiboldt, Sarah; Marcus, Philip; Bierhaus, Edward; Dalton, James B.; Fienup, James R.; Yu, Jeffrey W.

2004-12-01

304

Comparison of laser-induced surface damage density measurements with small and large beams: toward representativeness  

SciTech Connect

Pulsed laser damage density measurements obtained with diverse facilities are difficult to compare, due to the interplay of numerous parameters, such as beam area and pulse geometry, which, in operational large beam conditions, are very different from laboratory measurements. This discrepancy could have a significant impact; if so, one could not even pretend that laser damage density control is a real measurement process. In this paper, this concern is addressed. Tests with large beams of centimeter size on a high-power laser facility have beam performed according to a parametric study and are compared to small beam laboratory tests. It is shown that laser damage densities obtained with large and small beams are equal, within calculated error bars.

Lamaignere, Laurent; Dupuy, Gabriel; Donval, Thierry; Grua, Pierre; Bercegol, Herve

2011-02-01

305

Confocal coded aperture imaging  

DOEpatents

A method for imaging a target volume comprises the steps of: radiating a small bandwidth of energy toward the target volume; focusing the small bandwidth of energy into a beam; moving the target volume through a plurality of positions within the focused beam; collecting a beam of energy scattered from the target volume with a non-diffractive confocal coded aperture; generating a shadow image of said aperture from every point source of radiation in the target volume; and, reconstructing the shadow image into a 3-dimensional image of the every point source by mathematically correlating the shadow image with a digital or analog version of the coded aperture. The method can comprise the step of collecting the beam of energy scattered from the target volume with a Fresnel zone plate.

Tobin, Jr., Kenneth William (Harriman, TN); Thomas, Jr., Clarence E. (Knoxville, TN)

2001-01-01

306

Polarizing aperture stereoscopic cinema camera  

NASA Astrophysics Data System (ADS)

The art of stereoscopic cinematography has been held back because of the lack of a convenient way to reduce the stereo camera lenses' interaxial to less than the distance between the eyes. This article describes a unified stereoscopic camera and lens design that allows for varying the interaxial separation to small values using a unique electro-optical polarizing aperture design for imaging left and right perspective views onto a large single digital sensor, the size of the standard 35 mm frame, with the means to select left and right image information. Even with the added stereoscopic capability, the appearance of existing camera bodies will be unaltered.

Lipton, Lenny

2012-07-01

307

X-ray lasing - The Novette laser  

NASA Astrophysics Data System (ADS)

The design and operational history of the Novette laser system, which served as a test bed for the Nova laser, are described. In the Novette, full-power harmonic conversion with large-aperture arrays of KDP crystals generates beams of green (0.53-micron) and ultraviolet (0.35- and 0.26- micron) light. Other innovations include segmented laser-amplifier disks which can be scaled up to almost arbitrarily large apertures; neutral-solution antireflection coatings on laser optics which more than triple the nominal damage threshold for 1-ns pulses (now 15 J/sq cm); and Nova-style digital control and diagnostic techniques. In addition to completing the inertial confinement fusion (ICF) experiments planned for its two-year lifetime, the Novette performed target experiments clarifying the physics of laser-plasma coupling, including the first demonstration of X-ray lasing. As many as six full-power shots a day were achieved.

1985-11-01

308

Study on the algorithm in the measurement of large annular planes with a laser tracker  

NASA Astrophysics Data System (ADS)

To measure the flatness of the large annular planes, a method with laser tracker on the basis of multi-station and time-sharing measurement principle is proposed in this paper. The laser tracker is used to measure the flatness of large annular planes at different base stations. Based on the redundancy principle, the space coordinates of each measuring point can be determined by large amount of measured data. In the paper, the results of computer simulation for the principle are obtained with several iterative nonlinear algorithms, and it is shown that the method is feasible.

Zhu, Wen; Fan, Tian-quan; Cao, Xue-dong; Li, Jie; Wu, Shibin

2013-09-01

309

Fabrication of large curvature microlens array using confined laser swelling method.  

PubMed

This Letter proposes a confined laser swelling method to fabricate large curvature microlens arrays. Unlike the polymers in conventional free laser swelling, the swelling polymer, which is methyl red-doped polymethyl methacrylate here, is confined between walls formed by a substrate and a flexible cover layer. Because swelling occurs in an enclosed space, decomposed segments remain in the matrix, resulting in a large hump at the side of the flexible cover layer. The results show that these humps are tens of times higher than those acquired by conventional methods and this method has potential for high efficiency large curvature microlens fabrication. PMID:24104643

Shao, Jinyou; Ding, Yucheng; Zhai, Haipeng; Hu, Bing; Li, Xiangming; Tian, Hongmiao

2013-08-15

310

The Use of Large Transparent Ceramics in a High Powered, Diode Pumped Solid State Laser  

SciTech Connect

The advent of large transparent ceramics is one of the key enabling technological advances that have shown that the development of very high average power compact solid state lasers is achievable. Large ceramic neodymium doped yttrium aluminum garnet (Nd:YAG) amplifier slabs are used in Lawrence Livermore National Laboratory's (LLNL) Solid State Heat Capacity Laser (SSHCL), which has achieved world record average output powers in excess of 67 kilowatts. We will describe the attributes of using large transparent ceramics, our present system architecture and corresponding performance; as well as describe our near term future plans.

Yamamoto, R; Bhachu, B; Cutter, K; Fochs, S; Letts, S; Parks, C; Rotter, M; Soules, T

2007-09-24

311

Rapid Fabrication of Large-Area Concave Microlens Arrays on PDMS by a Femtosecond Laser.  

PubMed

A fast and single-step process is developed for the fabrication of low-cost, high-quality, and large-area concave microlens arrays (MLAs) by the high-speed line-scanning of femtosecond laser pulses. Each concave microlens can be generated by a single laser pulse, and over 2.78 million microlenses were fabricated on a 2 × 2 cm(2) polydimethylsiloxane (PDMS) sheet within 50 min, which greatly enhances the processing efficiency compared to the classical laser direct writing method. The mechanical pressure induced by the expansion of the laser-induced plasmas as well as a long resolidifing time is the reason for the formation of smooth concave spherical microstructures. We show that uniform microlenses with different diameters and depths can be controlled by adjusting the power of laser pulses. Their high-quality optical performance is also demonstrated in this work. PMID:24070159

Yong, Jiale; Chen, Feng; Yang, Qing; Du, Guangqing; Bian, Hao; Zhang, Dongshi; Si, Jinhai; Yun, Feng; Hou, Xun

2013-09-26

312

Development of a Durable, Large Area Cathode for Repetitive, Uniform Electron Beam Generation.  

National Technical Information Service (NTIS)

Electra is a large-aperture, krypton-fluoride laser under development for inertial fusion energy research. The laser will require dual 500 kV, 36 A/sq cm, uniform electron beams operating at 5 Hz. Experimental studies have been performed to develop an app...

F. Hegeler J. D. Sethian M. Friedman M. C. Myers

2002-01-01

313

Bistatic synthetic aperture radar  

Microsoft Academic Search

Synthetic aperture radar (SAR) is becoming increasingly important in many military ground surveillance and targeting roles because of its ability to operate in all weather, day and night, and to detect, classify and geolocate objects at long stand-off ranges. Bistatic SAR, where the transmitter and receiver are on separate platforms, is seen as a potential means of countering vulnerability. This

A. M. Horne; G. Yates

2002-01-01

314

Piezoceramic actuated aperture antennae  

Microsoft Academic Search

Recently, it has been demonstrated that aperture antennae can have their performance improved by employing shape control on the antenna surface. The antennae previously studied were actuated utilizing polyvinylidene fluoride (PVDF). Since PVDF is a polymer with limited control authority, these antennae can only be employed in space based applications. This study examines more robust antenna structures devised of a

Hwan-Sik Yoon; Gregory Washington

1998-01-01

315

Controle modal des diodes laser a large fenetre d'emission  

Microsoft Academic Search

Les diodes laser a large fenetre d'emission (BA) constituent des sources permettant d'obtenir des puissances elevees a faible cout. Leur emission est cependant composee de nombreux modes lateraux et longitudinaux, reduisant la qualite du faisceau emis. Nous considerons l'utilisation, en cavite externe, de reseaux possedant un profil spatial de reflectivite, afin de controler les modes de ces lasers. Le chapitre

Jean-Francois Lepage

2003-01-01

316

Femtosecond laser machining and lamination for large-area flexible organic microfluidic chips  

Microsoft Academic Search

A hybrid process compatible with reel-to-reel manufacturing is developed for ultra low-cost large-scale manufacture of disposable microfluidic chips. It combines ultra-short laser microstructuring and lamination technology. Microchannels in polyester foils were formed using focused, high-intensity femtosecond laser pulses. Lamination using a commercial SU8-epoxy resist layer was used to seal the microchannel layer and cover foil. This hybrid process also enables

C. Khan Malek; L. Robert; R. Salut

2009-01-01

317

Femtosecond laser machining and lamination for large-area flexible organic microfluidic chips  

NASA Astrophysics Data System (ADS)

A hybrid process compatible with reel-to-reel manufacturing is developed for ultra low-cost large-scale manufacture of disposable microfluidic chips. It combines ultra-short laser microstructuring and lamination technology. Microchannels in polyester foils were formed using focused, high-intensity femtosecond laser pulses. Lamination using a commercial SU8-epoxy resist layer was used to seal the microchannel layer and cover foil. This hybrid process also enables heterogeneous material structuration and integration.

Malek, C. Khan; Robert, L.; Salut, R.

2009-04-01

318

Pattern Formation in the Transverse Section of a Laser with a Large Fresnel Number  

SciTech Connect

We experimentally investigate pattern formation in a single-wavelength long laser cavity with a large Fresnel number. Near the laser threshold, we observe a single frequency spatially periodic structure corresponding to titled waves theoretically predicted by the Maxwell-Bloch equations. We also show the presence of secondary instabilities at other wavelengths and polarization instabilities at the same wavelength for different parameter values. {copyright} {ital 1999} {ital The American Physical Society }

Hegarty, S.P.; Huyet, G.; McInerney, J.G. [Physics Department, National University of Ireland, University College, Cork (Ireland); Choquette, K.D. [Photonics Research Department, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

1999-02-01

319

Off-axis field approximations for ion traps with apertures  

NASA Astrophysics Data System (ADS)

In recent work (Int. J. Mass Spec., vol. 282, pp. 112-122) we have considered the effect of apertures on the fields inside rf traps at points on the trap axis. We now complement and complete that work by considering off-axis fields in axially symmetric (referred to as "3D") and in two dimensional ("2D") ion traps whose electrodes have apertures, i.e., holes in 3D and slits in 2D. Our approximation has two parts. The first, EnoAperture, is the field obtained numerically for the trap under study with apertures artificially closed. We have used the boundary element method (BEM) for obtaining this field. The second part, EdueToAperture, is an analytical expression for the field contribution of the aperture. In EdueToAperture, aperture size is a free parameter. A key element in our approximation is the electrostatic field near an infinite thin plate with an aperture, and with different constant-valued far field intensities on either side. Compact expressions for this field can be found using separation of variables, wherein the choice of coordinate system is crucial. This field is, in turn, used four times within our trap-specific approximation. The off-axis field expressions for the 3D geometries were tested on the quadrupole ion trap (QIT) and the cylindrical ion trap (CIT), and the corresponding expressions for the 2D geometries were tested on the linear ion trap (LIT) and the rectilinear ion trap (RIT). For each geometry, we have considered apertures which are 10%, 30%, and 50% of the trap dimension. We have found that our analytical correction term EdueToAperture, though based on a classical small-aperture approximation, gives good results even for relatively large apertures.

Chattopadhyay, Madhurima; Mohanty, Atanu K.

2009-12-01

320

Desorption of large organic molecules by laser-induced plasmon excitation  

SciTech Connect

Ejection of large organic molecules from surfaces by laser-induced electronic-excited desorption has attracted considerable interest in recent years. In addition to the importance of this effect for fundamental investigations of the ejection process, this desorption technique has been applied to the study of large, fragile molecules by mass spectrometry. In this paper, we present a new method to induce electronic excitation on the metal surface for the desorption of large organic molecules. 3 refs., 3 figs.

Lee, I.; Callcott, T.A. (Oak Ridge National Lab., TN (USA) Tennessee Univ., Knoxville, TN (USA). Dept. of Physics and Astronomy); Arakawa, E.T. (Oak Ridge National Lab., TN (USA))

1991-01-01

321

Polymeric aperture masks for high performance organic integrated circuits  

Microsoft Academic Search

The use of polymeric aperture masks to fabricate high performance pentacene-based integrated circuits is presented. The aperture masks are fabricated using a laser ablation process with capabilities of generating 10 mum features. A mask set consisting of 4-6 aligned layers has been fabricated and has been used to demonstrate functional rf-powered integrated circuits with 20 mum gate lengths. Devices consisted

Dawn V. Muyres; Paul F. Baude; Steven Theiss; Michael Haase; Tommie W. Kelley; Patrick Fleming

2004-01-01

322

Apodised aperture using rotation of plane of polarization  

DOEpatents

An apodised aperture based on the rotation of plane of polarization producing desirable characteristics on a transmitted light beam such as beam profiling in high flux laser amplifier chains is described. The apodised aperture is made with a lossless element by using one or more polarizers and/or analyzers and magneto-optical Faraday means for selectively rotating the plane of polarized radiation over the cross section to effect the desired apodisation. (auth)

Simmons, W.W.; Leppelmeier, G.W.; Johnson, B.C.

1975-09-01

323

Recommendations for the design and the installation of large laser scanning microscopy systems  

NASA Astrophysics Data System (ADS)

Laser Scanning Microscopy (LSM) has since the inventions of the Confocal Scanning Laser Microscope (CLSM) and the Multi Photon Laser Scanning Microscope (MPLSM) developed into an essential tool in contemporary life science and material science. The market provides an increasing number of turn-key and hands-off commercial LSM systems, un-problematic to purchase, set up and integrate even into minor research groups. However, the successful definition, financing, acquisition, installation and effective use of one or more large laser scanning microscopy systems, possibly of core facility character, often requires major efforts by senior staff members of large academic or industrial units. Here, a set of recommendations is presented, which are helpful during the process of establishing large systems for confocal or non-linear laser scanning microscopy as an effective operational resource in the scientific or industrial production process. Besides the description of technical difficulties and possible pitfalls, the article also illuminates some seemingly "less scientific" processes, i.e. the definition of specific laboratory demands, advertisement of the intention to purchase one or more large systems, evaluation of quotations, establishment of contracts and preparation of the local environment and laboratory infrastructure.

Helm, P. Johannes

2012-02-01

324

Subpicosecond, high-brightness excimer laser systems  

SciTech Connect

Subpicosecond, high-brightness excimer laser systems are being used to explore the interaction of intense coherent ultraviolet radiation with matter. Applications of current systems include generation of picosecond x-ray pulses, investigation of possible x-ray laser pumping schemes, studies of multiphoton phenomena in atomic species, and time-resolved photochemistry. These systems, based on the amplification of subpicosecond pulses in small aperture (/approximately/1 cm/sup 2/) XeCl or KrF amplifiers, deliver focal spot intensities of /approximately/10/sup 17/ W/cm/sup 2/. Scaling to higher intensities, however, will require an additional large aperture amplifier which preserves near-diffraction-limited beam quality and subpicosecond pulse duration. We describe here both a small aperture KrF system which routinely provides intensities >10/sup 17/ W/cm/sup 2/ to several experiments, and a large aperture XeCl system designed to deliver /approximately/1 J subpicosecond pulses and yield intensities on target in excess of 10/sup 19/W/cm/sup 2/. We also discuss the effects of two-photon absorption on large-aperture, high-brightness excimer lasers. 4 refs., 2 figs.

Taylor, A.J.; Gosnell, T.R.; Roberts, J.P.; Lester, C.S.; Gibson, R.B.; Harper, S.E.; Tallman, C.R.

1988-01-01

325

Effect of fracture aperture variations on the dispersion of contaminants  

Microsoft Academic Search

Dispersion of dissolved contaminants in fractured rocks is strongly dependent on the variability of fracture aperture. Large fracture aperture regions result in significant channeling of the fluid flow, accelerating the movement of solutes in a particular direction, which may differ locally with respect to the main flow direction from high to low hydraulic potential. This may result in very early

Arturo A. Keller; Paul V. Roberts; Martin J. Blunt

1999-01-01

326

Full-aperture wavefront reconstruction from annular subaperture interferometric data by use of Zernike annular polynomials and a matrix method for testing large aspheric surfaces  

Microsoft Academic Search

We propose a more accurate and efficient reconstruction method used in testing large aspheric surfaces with annular subaperture interferometry. By the introduction of the Zernike annular polynomials that are orthogonal over the annular region, the method proposed here eliminates the coupling problem in the earlier reconstruction algorithm based on Zernike circle polynomials. Because of the complexity of recurrence definition of

Hou Xi; Wu Fan; Yang Li; Wu Shibin; Chen Qiang

2006-01-01

327

Aperture averaging analysis and aperture shape invariance of received scintillation in free-space optical communication links  

NASA Astrophysics Data System (ADS)

Intensity scintillation and beam wander caused by atmospheric turbulence are two significant phenomena that affect free space optical (FSO) communication links. We have constructed an imaging system for measuring the effects of atmospheric turbulence and obscuration on FSO links. A He-Ne laser beam propagates over a range of 863 meters in atmospheric turbulence conditions that vary diurnally and seasonally from weak to strong. A high performance digital camera with a frame-grabbing computer interface is used to capture received laser intensity distributions at rates up to 30 frames per second and various short shutter speeds, down to 1/16,000s per frame. The captured image frames are analyzed in Labview to evaluate the turbulence index parameter, temporal and spatial intensity variances, and aperture averaging. The aperture averaging results demonstrate the expected reduction in intensity fluctuations with increasing aperture diameter, and show quantitatively the differences in behavior between various strengths of turbulence. This paper will present the most accurate empirical data to date for the weak and intermediate turbulence regime. Such results can help build upon existing empirical data and lead to the development of new theories. Aperture averaging of the received irradiance is also shown to be independent of the shape of the receiver aperture, and depends only on its area. This finding allows the use of refractive or catadioptric receivers, whichever is convenient, and the same amount of aperture averaging will be achieved for equal unobscured aperture areas. This can make the telescope design for an FSO receiver more compact.

Yuksel, Heba; Davis, Christopher C.

2006-09-01

328

Laser heating of large noble gas clusters: from the resonant to the relativistic interaction regimes  

NASA Astrophysics Data System (ADS)

Wide-ranging measurements of sub-picosecond laser interactions with large noble gas cluster targets have been conducted in order to help clarify the nature and extent of the underlying laser plasma heating. Within the sub-relativistic vacuum irradiance range of 1016 1017 W cm-2, we find that electron temperatures measured with continuum x-ray spectroscopy exhibit a pronounced multi-keV enhancement. Analysis indicates this behaviour to be consistent with collisional or collisionless resonant heating mechanisms. We also present the first measurements of laser-to-cluster energy deposition at relativistic vacuum irradiances, our data demonstrating absorption fractions of 90% or more. Optical probing was used to resolve the onset of a supersonic ionization front resulting from this very high absorption, and shows that despite significant pre-focus heating, the greatest plasma energy densities can be generated about the vacuum focus position. Electron energy spectra measurements confirm that laser plasma super-heating occurs, and together with ion data establish that relativistic laser plasma coupling in atomic clusters can take place without significant MeV particle beam production. In conjunction with optical self-emission data, the optical probing also indicates laser pre-pulse effects at peak vacuum irradiance of 5 × 1019 W cm-2. Laser absorption, plasma heating and energy transport data are supported throughout with analytical and numerical modelling. © British Crown Copyright 2008/MOD

Gumbrell, E. T.; Moore, A. S.; Lazarus, J. A.; Clark, E. L.; Nilson, P. M.; Garbett, W. J.; Comley, A. J.; Robinson, J. S.; Hohenberger, M.; Edwards, R. D.; Eagleton, R. E.; Clarke, R. J.; Symes, D. R.; Smith, R. A.

2008-12-01

329

Toward a spaceworthy picometer laser gauge  

Microsoft Academic Search

Metrology will be an enabling technology for a new generation of astronomical missions having large and distributed apertures and delivering unprecedented performance. The x-ray interferometer Black Hole Imager, the UV interferometer Stellar Imager, and other missions will require measurements of incremental distance as accurate as 0.1 picometer, and absolute distance capability. Our Tracking Frequency laser distance Gauge (TFG) was developed

James D. Phillips; Robert D. Reasenberg

2004-01-01

330

Beam characteristics of a large-bore copper laser with radiatively cooled plasma  

NASA Astrophysics Data System (ADS)

In a large-bore copper vapor laser (CVL), excessive gas heating at the axial region of the discharge lowers its efficiency by thermally populating the metastable lower laser levels. The associated lower gas density also lengthens the discharge field- diffusion time, leading to weaker axial pumping and undesired beam characteristics. A novel approach to circumvent this obstacle has been developed by cooling the plasma radiatively via a series of segmented metal plates (septa) placed vertically along the length of the tube. This improved tube design significantly lowers the average gas temperature and shortens the radial delay. A 27% increase in laser power was observed with the addition of septa. We have characterized the beam intensity profile, spatial and temporal pulse variation, and beam polarization through extensive laboratory measurements. A detailed computational model of the laser has been used to characterize and interpret the laboratory results.

Chang, Jim J.; Boley, Charles D.; Martinez, Mark W.; Molander, William A.; Warner, Bruce E.

1994-05-01

331

Thermal waveguiding in oxide-defined, narrow-stripe, large-optical-cavity lasers  

SciTech Connect

The characteristics of oxide-defined, narrow-stripe large-optical-cavity (LOC) AlGaAs lasers are described. Compared with regular narrow-stripe double heterostructure (DH) lasers, the LOC version exhibits more narrowing of the near-field and far-field distributions, higher astigmatism, higher differential quantum efficiency, and higher incidence of sustained pulsations. We have found that these phenomena can be explained in terms of the formation of a thermal waveguide. There is often a striking similarity in characteristics of narrow-stripe LOC and degraded narrow- stripe DH lasers. We suggest that a thermal waveguiding effect is an important factor in determining the behavior of degraded semiconductor lasers.

Chen, Y.C.; Reisinger, A.R.; Chinn, S.R.

1982-07-15

332

Beam characteristics of a large-bore copper laser with a radiatively cooled plasma  

SciTech Connect

In a large-bore copper vapor laser (CVL), excessive gas heating at the axial region of the discharge lowers its efficiency by thermally populating the metastable lower laser levels. The associated lower gas density also lengthens the discharge field-diffusion time, leading to weaker axial pumping and undesired beam characteristics. The authors` laboratory has developed a novel approach to circumvent this obstacle by cooling the plasma radiatively via a series of segmented metal plates (septa) placed vertically along the length of the tube. This improved tube design significantly lowers the average gas temperature and shortens the radial delay. A 27% increase in laser power was observed with the addition of septa. The authors have characterized the beam intensity profile, spatial and temporal pulse variation, and beam polarization through extensive laboratory measurements. A detailed computational model of the laser has been used to characterize and interpret the laboratory results.

Chang, J.J.; Boley, C.D.; Molander, W.A.; Warner, B.E. [Lawrence Livermore National Lab., CA (United States); Martinez, M.W. [Martin Marietta Energy Systems, Inc., Oak Ridge, TN (United States)

1994-01-18

333

Wide-aperture detector of terahertz radiation based on GaAs\\/InGaAs transistor structure with large-area slit grating gate  

Microsoft Academic Search

Terahertz photoresponse of a GaAs\\/InGaAs transistor structure with large-area slit grating gate has been measured. Peaks in\\u000a the photoresponse curve are assigned to plasmon resonances excited in the structure. More effective excitation of plasmon\\u000a resonances is achieved in a grating gate structure with narrow slits, which increase the photoresponse amplitude by an order\\u000a of magnitude.

K. V. Marem’yanin; D. M. Ermolaev; D. V. Fateev; S. V. Morozov; N. A. Maleev; V. E. Zemlyakov; V. I. Gavrilenko; V. V. Popov; S. Yu. Shapoval

2010-01-01

334

Strongly Enhanced Transmission through a Subwavelength Aperture.  

NASA Astrophysics Data System (ADS)

The optical throughput of a subwavelength aperture in a metal film is strongly enhanced, by up to a factor 150, by a resonant interaction of the incident light with surface plasmons, excitation modes at the metal surface. This occurs through grating coupling at a periodically corrugated metal surface. The strength of the interaction, and thus of the transmission enhancement, is determined by the topography of the surface surrounding the aperture. In a systematic study, we find that the optimal surface corrugation is axially symmetric, consisting of a set of concentric circular grooves around the central aperture, with a groove depth a few times the skin depth of the metal. We present a model of the surface plasmon modes which give rise to the large transmission enhancement. URL:http://www.neci.nj.nec.com/homepages/thio/arrays.html

Thio, Tineke; Pellerin, K. M.; Linke, R. A.; Ebbesen, T. W.; Lezec, H. J.

2002-03-01

335

The aperture problem in contoured stimuli  

PubMed Central

A moving object elicits responses from V1 neurons tuned to a broad range of locations, directions, and spatiotemporal frequencies. Global pooling of such signals can overcome their intrinsic ambiguity in relation to the object’s direction/speed (the “aperture problem”); here we examine the role of low-spatial frequencies (SF) and second-order statistics in this process. Subjects made a 2AFC fine direction-discrimination judgement of ‘naturally’ contoured stimuli viewed rigidly translating behind a series of small circular apertures. This configuration allowed us to manipulate the scene in several ways; by randomly switching which portion of the stimulus was presented behind each aperture or by occluding certain spatial frequency bands. We report that global motion integration is (a) largely insensitive to the second-order statistics of such stimuli and (b) is rigidly broadband even in the presence of a disrupted low SF component.

Kane, David; Bex, Peter J.; Dakin, Steven C.

2010-01-01

336

Z-Beamlet: a multikilojoule, terawatt-class laser system  

SciTech Connect

A large-aperture (30-cm) kilojoule-class Nd:glass laser system known as Z-Beamlet has been constructed to perform x-ray radiography of high-energy-density science experiments conducted on the Z facility at Sandia National Laboratories, Albuquerque, New Mexico. The laser, operating with typical pulse durations from 0.3 to 1.5 ns, employs a sequence of successively larger multipass amplifiers to achieve up to 3-kJ energy at 1054 nm. Large-aperture frequency conversion and long-distance beam transport can provide on-target energies of up to 1.5 kJ at 527 nm.

Rambo, Patrick K.; Smith, Ian C.; Porter, John L. Jr.; Hurst, Michael J.; Speas, C. Shane; Adams, Richard G.; Garcia, Antonio J.; Dawson, Ellis; Thurston, Benjamin D.; Wakefield, Colleen; Kellogg, Jeff W.; Slattery, Michael J.; Ives III, Harry C.; Broyles, Robin S.; Caird, John A.; Erlandson, Alvin C.; Murray, James E.; Behrendt, William C.; Neilsen, Norman D.; Narduzzi, Joseph M

2005-04-20

337

Gaseous saturable absorbers for the Helios CO2 laser systems  

Microsoft Academic Search

Saturable absorbers are widely used to suppress parasitic oscillations in large-aperture, high-power CO2 fusion-laser systems. This paper reports experimental results on SF6-based gaseous saturable absorbers used for parasitic suppression in the eight-beam, 10 kJ Helios fusion-laser system. The gas mix effectively quenches self-lasing in the 9 and 10 microns branches of the CO2 laser spectrum while simultaneously allowing high transmission

R. F. Haglund Jr.; A. V. Nowak; S. J. Czuchlewski

1981-01-01

338

Volume self-sustained discharge stability in gas lasers  

NASA Astrophysics Data System (ADS)

An experimental investigation of the basic mechanisms of volume self-sustained discharge (VSD) in CO2 and N2O laser gas mixtures is reported. The influence of low-ionization additives on the VSD stability is reported. A principle for obtaining a discharge for pumping gas lasers is suggested that will make it possible to create high-power, compact, and pulsed CO2 and N2O lasers with large apertures and simple design.

Apollonov, V. V.; Baitsur, G. G.; Ermachenko, A. V.; Firsov, K. N.; Semenov, S. K.

339

Multiple instrument distributed aperture sensor (MIDAS) science payload concept  

NASA Astrophysics Data System (ADS)

We describe the Multiple Instrument Distributed Aperture Sensor (MIDAS) concept, an innovative approach to future planetary science mission remote sensing that enables order of magnitude increased science return. MIDAS provides a large-aperture, wide-field, diffraction-limited telescope at a fraction of the cost, mass and volume of conventional space telescopes, by integrating advanced optical interferometry technologies. All telescope optical assemblies are integrated into MIDAS as the primary remote sensing science payload, thereby reducing the cost, resources, complexity, I&T and risks of a set of back-end science instruments (SI's) tailored to a specific mission. MIDAS interfaces to multiple science instruments, enabling sequential and concurrent functional modes, thereby expanding the potential planetary science return many fold. Passive imaging modes with MIDAS enable remote sensing at diffraction-limited resolution sequentially by each science instrument, or at lower resolution by multiple science instruments acting concurrently on the image, such as in different wavebands. Our MIDAS concept inherently provides nanometer-resolution hyperspectral passive imaging without the need for any moving parts in the science instruments. For planetary science missions, the MIDAS optical design provides high-resolution imaging for long dwell times at high altitudes, thereby enabling real-time, wide-area remote sensing of dynamic surface characteristics. In its active remote sensing modes, using an integrated solid-state laser source, MIDAS enables LIDAR, vibrometry, surface illumination, and various active or ablative spectroscopies. Our concept is scalable to apertures well over 10m, achieved by autonomous deployments or manned assembly in space. MIDAS is a proven candidate for future planetary science missions, enabled by our continued investments in focused MIDAS technology development areas. In this paper we present the opto-mechanical design for a 1.5m MIDAS point design, including its accommodation of back-end science instruments.

Stubbs, David M.; Duncan, Alan L.; Pitman, Joe T.; Sigler, Robert D.; Kendrick, Richard L.; Chilese, John F.; Smith, Eric H.

2004-10-01

340

Use of Zernike Polynomials and Interferometry in the Optical Design and Assembly of Large Carbon-Dioxide Laser Systems.  

National Technical Information Service (NTIS)

This paper describes the need for non-raytracing schemes in the optical design and analysis of large carbon-dioxide lasers like the Gigawatt, Gemini, and Helios lasers currently operational at Los Alamos, and the Antares laser fusion system under construc...

V. K. Viswanathan

1981-01-01

341

Use of Zernike polynomials and interferometry in the optical design and assembly of large carbon-dioxide laser systems  

Microsoft Academic Search

This paper describes the need for non-raytracing schemes in the optical design and analysis of large carbon-dioxide lasers like the Gigawatt, Gemini, and Helios lasers currently operational at Los Alamos, and the Antares laser fusion system under construction. The scheme currently used at Los Alamos involves characterizing the various optical components with a Zernike polynomial set obtained by the digitization

Viswanathan

1981-01-01

342

Self-locked operation of large He-Ne ring laser gyroscopes  

NASA Astrophysics Data System (ADS)

Helium-neon ring laser gyroscopes have been observed to produce a stable and useful Sagnac beat signal while operating with multiple longitudinal modes through a mode-locking mechanism. The parameter space pertaining to stable operation with respect to gas pressure and intra-cavity power has been explored experimentally. Two regions of stability have been identified. The stability of large ring lasers operating with mode-locking has been characterized. Mode-locked operation presents no statistically significant difference in performance compared with single-mode operation. It is shown that the time required for establishing stable mode-coupled operation can be a practical disadvantage for the ultra-large ring lasers.

Holdaway, J.; Hurst, R. B.; Graham, R.; Rabeendran, N.; Schreiber, K. U.; Wells, J.-P. R.

2012-06-01

343

Tunable optical diffusers for high-power laser applications based on magnetically actuated membranes  

Microsoft Academic Search

A dynamic laser beam shaper based on MEMS technology is presented. A magnetically actuated deformable single crystal silicon micromembrane is deformed in resonance to diffuse and homogenize laser beams. The large aperture mirror shows line generation with angles up to 1° and line smoothing capabilities. High power density handling is demonstrated up to 140 W\\/cm2.

J. Masson; A. Bich; W. Noell; R. Voelkel; K. J. Weible; N. F. de Rooij

2010-01-01

344

Laser radar IV; Proceedings of the Meeting, Orlando, FL, Mar. 29, 30, 1989  

NASA Astrophysics Data System (ADS)

Various papers on laser radars are presented. Individual topics considered include: frequency chirp of a low-pressure hybrid TE CO2 laser, design of a high-power isotopic CO2 laser amplifier, monolithic beam steering for large aperture laser radar, laser radar receiver using a Digicon detector, all-solid-state CO2 laser driver, noise in an acoustooptic-modulated laser source, laser signature prediction using the Value computer program, laser radar acquisition and tracking, concept of a moving target indicator search ladar, system design philosophy for laser radar wavelength determination, imaging three-frequency CO2 laser radar, backscatter-modulation semiconductor laser radar, three-dimensional imaging using a single laser pulse, design and manufacture of a high-resolution laser radar scanner, calculations of vibrational signatures for coherent ladar, coherent subaperture ultraviolet imagery, and range-Doppler resolution degradation associated with amplitude distortion.

Becherer, Richard J.

1989-09-01

345

Aperture weighting technique for video synthetic aperture radar  

NASA Astrophysics Data System (ADS)

We present a technique for aperture weighting for use in video synthetic aperture radar (SAR). In video SAR the aperture required to achieve the desired cross range resolution typically exceeds the frame rate period. As a result, there can be a significant overlap in the collected phase history used to form consecutive images in the video. Video SAR algorithms seek to exploit this overlap to avoid unnecessary duplication of processing. When no aperture weighting or windowing is used one can simply form oversampled SAR images from the non-overlapping sub-apertures using coherent back projection (or other similar techniques). The resulting sub-aperture images may be coherently summed to produce a full resolution image. A simple approach to windowing for sidelobe control is to weight the sub-apertures during summation of the images. Our approach involves producing two or more weighted images for each sub-aperture which can be linearly combined to approximate any desired aperture weighting. In this method we achieve nearly the same sidelobe control as weighting the phase history data and forming a new image for each frame without losing the computation savings of the sub-aperture image combining approach.

Hawley, Robert W.; Garber, Wendy L.

2011-05-01

346

Retouching the Lenses of Large Objectives with the Aid of an Unequal Arm Laser Interferometer.  

National Technical Information Service (NTIS)

A description of a scheme for manually retouching the lenses of large objectives using an unequal arm interferometer which contains a gas laser as a source of monochromatic light is given. The proposed technique makes it possible to perform rapid quantita...

V. A. Savin V. N. Esina V. Y. Yurchenko

1972-01-01

347

Laser Ablation of a Large Tongue Hemangioma with Remifentanil Analgosedation in the ORL Endoscopy Suite  

Microsoft Academic Search

We present a unique, practical, and safe approach to the clinical management of a young male with a large tongue hemangioma who presented for serial surgical treatment of the lesion. Laser ablation was undertaken in the operating room under topical anesthesia with remifentanil analgosedation without the use of supplemental oxygen. Significant involution of the hemangioma was achieved without complication while

Joshua H. Atkins; Jeff E. Mandel; Natasha Mirza

2011-01-01

348

Advanced laser micro-structuring of super-large-area optical films  

Microsoft Academic Search

A novel laser micro-machining technique to produce high density micro-structures called Synchronized Image Scanning (SIS) was introduced a couple of years ago. Over this period of time, the technique was refined in a major effort to meet the needs of various industries. There is an increasing demand for micro-structuring of large and super large area optical films, e.g. for Rear

Karl L. Boehlen; Ines B. Stassen Boehlen; Ric M. Allott

2005-01-01

349

Tunnel contact junction native-oxide aperture and mirror vertical-cavity surface-emitting lasers and resonant-cavity light-emitting diodes  

Microsoft Academic Search

Vertical-cavity surface-emitting lasers (VCSELs) and resonant-cavity light-emitting diodes (RCLEDs) are demonstrated with high index contrast distributed Bragg reflectors (DBRs) on either side of a lambda-thickness cavity (lambda~980 nm). The devices, with tunnel contact junctions making possible lateral electron current excitation, have a lower 6.5 period native-oxide-based AlxOy\\/GaAs DBR and an upper reflector that is either a 2-4 period AlxOy\\/GaAs DBR,

J. J. Wierer; D. A. Kellogg; N. Holonyak

1999-01-01

350

LLNL medical and industrial laser isotope separation: large volume, low cost production through advanced laser technologies  

SciTech Connect

The goal of this LDRD project was to demonstrate the technical and economical feasibility of applying laser isotope separation technology to the commercial enrichment (>lkg/y) of stable isotopes. A successful demonstration would well position the laboratory to make a credible case for the creation of an ongoing medical and industrial isotope production and development program at LLNL. Such a program would establish LLNL as a center for advanced medical isotope production, successfully leveraging previous LLNL Research and Development hardware, facilities, and knowledge.

Comaskey, B.; Scheibner, K. F.; Shaw, M.; Wilder, J.

1998-09-02

351

Science with large-aperture infrared interferometry — size does matter or talking about a new tool to study the galactic center  

NASA Astrophysics Data System (ADS)

We report on the recent pioneering successes in observing sources at the center of our Galaxy with infrared long-baseline interferometry. The 1st generation beam-combiners AMBER and MIDI of the VLTI have been used to resolve the IR-brightest sources in the central parsec at low spectral resolution. In the NIR, a program was initiated to study the supergiant GCIRS 7, and first data might indicate a resolved circumstellar shell. Nevertheless the large amount of correlated flux on the 50 m baseline gives strong experimental support for future phase-referencing missions based on this star. Further, the results of a detailed MIDI-study of the complex dusty environment of the enigmatic GCIRS 3 are presented. The spatial and spectral information provided by the interferometer allows for the first time to estimate the physical properties of the illuminating source, deeply embedded in dust, and has led to new insights in the dust chemistry in the central parsec. Current, and near-future interferometric technology is discussed with respect to Galactic center observations.

Pott, Jörg-Uwe; Eckart, Andreas; Ghez, Andrea; Kraus, Stefan

2008-10-01

352

Aperture shape optimization for IMRT treatment planning  

NASA Astrophysics Data System (ADS)

We propose an algorithm for aperture shape optimization (ASO) for step and shoot delivery of intensity-modulated radiotherapy. The method is an approach to direct aperture optimization (DAO) that exploits gradient information to locally optimize the positions of the leafs of a multileaf collimator. Based on the dose-influence matrix, the dose distribution is locally approximated as a linear function of the leaf positions. Since this approximation is valid only in a small interval around the current leaf positions, we use a trust-region-like method to optimize the leaf positions: in one iteration, the leaf motion is confined to the beamlets where the leaf edges are currently positioned. This yields a well-behaved optimization problem for the leaf positions and the aperture weights, which can be solved efficiently. If, in one iteration, a leaf is moved to the edge of a beamlet, the leaf motion can be confined to the neighboring beamlet in the next iteration. This allows for large leaf position changes over the course of the algorithm. In this paper, the ASO algorithm is embedded into a column-generation approach to DAO. After a new aperture is added to the treatment plan, we use the ASO algorithm to simultaneously optimize aperture weights and leaf positions for the new set of apertures. We present results for a paraspinal tumor case, a prostate case and a head and neck case. The computational results indicate that, using this approach, treatment plans close to the ideal fluence map optimization solution can be obtained.

Cassioli, A.; Unkelbach, J.

2013-01-01

353

Aperture shape optimization for IMRT treatment planning.  

PubMed

We propose an algorithm for aperture shape optimization (ASO) for step and shoot delivery of intensity-modulated radiotherapy. The method is an approach to direct aperture optimization (DAO) that exploits gradient information to locally optimize the positions of the leafs of a multileaf collimator. Based on the dose-influence matrix, the dose distribution is locally approximated as a linear function of the leaf positions. Since this approximation is valid only in a small interval around the current leaf positions, we use a trust-region-like method to optimize the leaf positions: in one iteration, the leaf motion is confined to the beamlets where the leaf edges are currently positioned. This yields a well-behaved optimization problem for the leaf positions and the aperture weights, which can be solved efficiently. If, in one iteration, a leaf is moved to the edge of a beamlet, the leaf motion can be confined to the neighboring beamlet in the next iteration. This allows for large leaf position changes over the course of the algorithm. In this paper, the ASO algorithm is embedded into a column-generation approach to DAO. After a new aperture is added to the treatment plan, we use the ASO algorithm to simultaneously optimize aperture weights and leaf positions for the new set of apertures. We present results for a paraspinal tumor case, a prostate case and a head and neck case. The computational results indicate that, using this approach, treatment plans close to the ideal fluence map optimization solution can be obtained. PMID:23257284

Cassioli, A; Unkelbach, J

2012-12-21

354

Aperture calculation of AURORA2D compact electron storage ring with a superconducting wiggler  

Microsoft Academic Search

Dynamic apertures of AURORA-2D 700 MeV compact electron storage ring with a 7 Tesla wiggler are calculated with a tracking program NABO which uses a sixth order Runge-Kutta method. Also dynamic apertures are calculated by a symplectic tracking program SAD to see the validity of using the Runge-Kutta method. Sufficiently large dynamic apertures are obtained

H. Tsutsui; T. Takayama; T. Hori

1997-01-01

355

Ultrafast laser ablation and machining large-size structures on porcine bone.  

PubMed

When using ultrafast laser ablation in some orthopedic applications where precise cutting/drilling is required with minimal damage to collateral tissue, it is challenging to produce large-sized and deep holes using a tightly focused laser beam. The feasibility of producing deep, millimeter-size structures under different ablation strategies is investigated. X-ray computed microtomography was employed to analyze the morphology of these structures. Our results demonstrated the feasibility of producing holes with sizes required in clinical applications using concentric and helical ablation protocols. PMID:23884158

An, Ran; Khadar, Ghadeer W; Wilk, Emilia I; Emigh, Brent; Haugen, Harold K; Wohl, Gregory R; Dunlop, Brett; Anvari, Mehran; Hayward, Joseph E; Fang, Qiyin

2013-07-01

356

Breaking and Moving Hotspots in a Large Grain Nb Cavity with a Laser Beam  

SciTech Connect

Magnetic vortices pinned near the inner surface of SRF Nb cavities are a possible source of RF hotspots, frequently observed by temperature mapping of the cavities outer surface at RF surface magnetic fields of about 100 mT. Theoretically, we expect that the thermal gradient provided by a 10 W green laser shining on the inner cavity surface at the RF hotspot locations can move pinned vortices to different pinning locations. The experimental apparatus to send the beam onto the inner surface of a photoinjector-type large-grain Nb cavity is described. Preliminary results on the changes in thermal maps observed after applying the laser heating are also reported.

Ciovati, G; Cheng, G; Flood, R J; Jordan, K; Kneisel, P; Morrone, M L; Turlington, L; Wilson, K M; Zhang, S; Anlage, S M; Gurevich, A V

2011-07-25

357

Large-area surface-enhanced Raman scattering-active substrates fabricated by femtosecond laser ablation  

NASA Astrophysics Data System (ADS)

A rapid and simple approach to fabricate large-area surface-enhanced Raman scattering-active (SERS-active) substrates is reported. The substrates are fabricated by using femtosecond laser (fs-laser) direct writing on Silicon wafers, followed by thin-film coating of metal such as gold. The substrates are demonstrated to exhibit signal homogeneity and good enhancement ability for SERS. The maximum enhancement factor (EF) up to 3×107 of such SERS substrates for rhodamine 6G (R6G) at 785 nm excitation wavelength was measured. This technique could demonstrate a functional microchip with SERS capability of signal homogeneity, high sensitivity and chemical stability.

Zhu, ZhiQing; Yan, ZhenDong; Zhan, Peng; Wang, ZhenLin

2013-09-01

358

Fabrication of large-area hydrophobic surfaces with femtosecond-laser-structured molds  

NASA Astrophysics Data System (ADS)

Fast replication of large-area femtosecond-laser-induced surface micro/nanostructures on plastic parts by injection molding is demonstrated. An STAVAX steel mold insert is irradiated by femtosecond laser pulses with linear or circular polarization to form periodic-like nanostructures or nanostructure-covered conical microstructures. It was then used for the process of thermal injection molding. The process provides high-volume manufacturing means to generate hydrophobic enhanced plastic parts, which is expected to be widely used in consumables and chemical/biomedical device industries.

Wu, P. H.; Cheng, C. W.; Chang, C. P.; Wu, T. M.; Wang, J. K.

2011-11-01

359

Fabrication of microstructures with continuous surface profiles and very large sag heights by laser lithography  

NASA Astrophysics Data System (ADS)

The fabrication of microstructures with continuous surface profiles and very large sag heights by a laser lithographic process on a commercially available laser lithography system is presented. The fabricated structures possess sag heights up to 60 ?m with a pitch of 400 ?m. Fabrication imperfections due to nonlinearities in the photoresist response and the isotropy of the development process have been compensated in the exposure data to minimize profile deviations. Therefore, an empirical process model is proposed based on experimentally determined development rates. The achievable accuracy of the data pre shape and exposure method as well as their limitations are discussed.

Dunkel, Jens; Wippermann, Frank; Bräuer, Andreas

2012-02-01

360

Optimal aperture geometry for high transmission through subwavelength aperture arrays  

NASA Astrophysics Data System (ADS)

The optical transmission through a periodic aperture array in a metal film is strongly enhanced by a resonance of the incident light with surface plasmon polaritons on one or both of the metal surfaces. The efficiency of the coupling, and thus the strength of the transmission enhancement, depends sensitively on the geometry of the apertures close to the metal surface. We show that this holds for the case of a single aperture surrounded by a surface corrugation as well as for an array of apertures. URL:http://www.neci.nj.nec.com/homepages/thio/arrays.html *Present address: Physics Department, Univ. of Wisconsin at Madison

Thio, Tineke; Pellerin, K. M.

2003-03-01

361

Management of large prostatic adenoma: Lasers versus bipolar transurethral resection of prostate.  

PubMed

Transurethral resection of prostate (TURP) has long been the most commonly performed surgical procedure for the management of benign prostate enlargement (BPE), but has several associated limitations. Over the years, laser techniques have developed as major contenders as alternative therapies for BPE. However, simultaneously, TURP has also flourished and with relatively recent development of resection in saline (bipolar TURP), the tussle between laser techniques and TURP has further gained momentum. A systematic search was performed on Medline using the various Medical subject headings related to the surgical management of BPE including TURP, bipolar, lasers, holmium laser enucleation of prostate (HoLEP), photo-selective vaporization of prostate (PVP), etc., All articles types including meta-analysis randomized controlled trials, review articles, guidelines from various urological associations, single center studies from 2002 onward were considered for review. Bipolar TURP, HoLEP, and PVP provide equivalent outcomes for large prostate adenoma (<60 g). For extremely large glands (<150 g), HoLEP is a very efficacious endoscopic alternative to open prostatectomy and has proven long-term results over more than a decade. Bipolar TURP and PVP are attractive with a minimal learning curves and equivalent short term durability. Surgical management of large prostate should be individualized based upon patient's comorbidities and surgeon's expertise. PMID:24082445

Gupta, Narmada P; Nayyar, Rishi

2013-07-01

362

Management of large prostatic adenoma: Lasers versus bipolar transurethral resection of prostate  

PubMed Central

Transurethral resection of prostate (TURP) has long been the most commonly performed surgical procedure for the management of benign prostate enlargement (BPE), but has several associated limitations. Over the years, laser techniques have developed as major contenders as alternative therapies for BPE. However, simultaneously, TURP has also flourished and with relatively recent development of resection in saline (bipolar TURP), the tussle between laser techniques and TURP has further gained momentum. A systematic search was performed on Medline using the various Medical subject headings related to the surgical management of BPE including TURP, bipolar, lasers, holmium laser enucleation of prostate (HoLEP), photo-selective vaporization of prostate (PVP), etc., All articles types including meta-analysis randomized controlled trials, review articles, guidelines from various urological associations, single center studies from 2002 onward were considered for review. Bipolar TURP, HoLEP, and PVP provide equivalent outcomes for large prostate adenoma (<60 g). For extremely large glands (<150 g), HoLEP is a very efficacious endoscopic alternative to open prostatectomy and has proven long-term results over more than a decade. Bipolar TURP and PVP are attractive with a minimal learning curves and equivalent short term durability. Surgical management of large prostate should be individualized based upon patient's comorbidities and surgeon's expertise.

Gupta, Narmada P; Nayyar, Rishi

2013-01-01

363

Large-area electron beam diode modeling for KrF Laser IFE  

NASA Astrophysics Data System (ADS)

The KrF Laser Inertial Fusion Energy (IFE) scheme focuses ˜ 60 individually generated 58 kJ laser pulses symmetrically onto a high yield fusion target. The lasers are pumped by large-area electron beam diodes, the technology for which is presently being developed on the Electra^1 and Nike^2 facilities at the Naval Research Laboratory in Washington, DC. An IFE-level diode design is examined via large-scale numerical simulations using the particle-in-cell code LSP. The simulations include detailed geometric representations of the cathode, foils, and support structures (the hibachi) as well as gas transport models. This integrated modeling procedure has been successfully benchmarked against recent Electra large-area diode experiments^3. The simulations provide estimates of the electron beam energy deposited in the gas, foils, and hibachi. The estimates of energy deposition in the laser gas from the simulations will be integrated with existing system designs. [1] J. D. Sethian, et al., IEEE Trans. Plasma Sci. 28, 1333 (2000). [2] J. D. Sethian, et al., Rev. Sci. Instrum. 68, 2357 (1997). [3] D. V. Rose, et al., submitted to J. Appl. Phys. (2003).

Rose, D. V.; Welch, D. R.; Sethian, J. D.; Guiliani, J. L.; Hegeler, F.; Swanekamp, S. B.

2003-10-01

364

Excitation, Fragmentation and Control of Large Finite Systems: C60 in Moderately Strong Laser Fields  

NASA Astrophysics Data System (ADS)

Recent progress in the understanding of the primary excitation mechanisms of the C60 fullerene in intense laser pulses is reported. By analyzing mass spectra as a function of pulse duration, laser intensity and time delay between pump- and probe pulse insight into fundamental photoinduced processes such as ionization and fragmentation is obtained. Using ultrashort sub-10fs pulses excitation times are addressed which lie well below the characteristic time scales for electron-electron and electron-phonon coupling. The measured saturation intensities of multiply charged parent ions indicate that for higher charge states the well known C60 giant plasmon resonance is involved in creating ions and a significant amount of large fragments through a non-adiabatic multi-electron dynamics. To enhance the formation of large fragments femtosecond laser pulses tailored with closed-loop, optimal control feedback were used. A characteristic pulse sequence excites oscillations in C60 with large amplitude by coherent heating of nuclear motion. Again, the experimental findings can be understood by a laser-induced multi-electron excitation via the electronically excited resonance followed by efficient coupling to the radial symmetric breathing vibration of C60.

Laarmann, Tim; Schulz, Claus Peter; Hertel, Ingolf Volker

365

Controle modal des diodes laser a large fenetre d'emission  

NASA Astrophysics Data System (ADS)

Les diodes laser a large fenetre d'emission (BA) constituent des sources permettant d'obtenir des puissances elevees a faible cout. Leur emission est cependant composee de nombreux modes lateraux et longitudinaux, reduisant la qualite du faisceau emis. Nous considerons l'utilisation, en cavite externe, de reseaux possedant un profil spatial de reflectivite, afin de controler les modes de ces lasers. Le chapitre 1 presente d'abord une introduction aux lasers a semi-conducteurs, ainsi qu'un rappel des principales methodes de controle des modes abordees dans la litterature. Le chapitre 2 decrit la fabrication et l'utilisation de reseaux holographiques apodisants dans le but d'obtenir une emission monomode laterale et longitudinale. Nous etudions d'abord les effets d'un profil spatial de reflectivite en cavite externe sur la discrimination envers les modes lateraux. Nous voyons ensuite la modelisation, la fabrication, puis la caracterisation des reseaux holographiques apodisants. Nous presentons finalement les resultats obtenus par l'operation d'une diode laser BA avec les reseaux fabriques. Ces resultats sont compares avec ceux obtenus en utilisant d'autres types de coupleurs externes. Le chapitre 3 traite de la fabrication et de l'usage de reseaux holographiques a double pas, dans le but d'obtenir une emission laser sur deux modes longitudinaux. La theorie et les procedures experimentales relatives a la fabrication de ces reseaux sont d'abord exposees. Nous procedons ensuite a une analyse des proprietes diffractives de ces elements. Le chapitre se termine par une presentation des resultats experimentaux obtenus en utilisant ces coupleurs en cavite externe avec une diode laser. Le chapitre 4 presente une analyse de la stabilite du systeme laser obtenu au chapitre 3. Nous rappelons d'abord la theorie relative a la competition modale dans les lasers et nous voyons, de facon analytique, l'effet de la saturation spatiale sur la saturation mutuelle des modes, dans le cas d'un laser opere en cavite externe. Nous presentons egalement des simulations numeriques du systeme laser. Ces simulations sont basees sur les equations d'evolution, qui sont derivees pour le cas d'un laser a cavites couplees avec retroaction pour deux longueurs d'onde. Nous y mettons en evidence l'influence de phenomenes tels que la saturation spatiale inhomogene, l'emission spontanee et les pertes intracavite sur le comportement du regime d'operation a deux longueurs d'onde.

Lepage, Jean-Francois

366

Optical Transmission Properties of Dielectric Aperture Arrays  

NASA Astrophysics Data System (ADS)

Optical detection devices such as optical biosensors and optical spectrometers are widely used in many applications for the functions of measurements, inspections and analysis. Due to the large dimension of prisms and gratings, the traditional optical devices normally occupy a large space with complicated components. Since cheaper and smaller optical devices are always in demand, miniaturization has been kept going for years. Thanks to recent fabrication advances, nanophotonic devices such as semiconductor laser chips have been growing in number and diversity. However, the optical biosensor chips and the optical spectrometer chips are seldom reported in the literature. For the reason of improving system integration, the study of ultra-compact, low-cost, high-performance and easy-alignment optical biosensors and optical spectrometers are imperative. This thesis is an endeavor in these two subjects and will present our research work on studying the optical transmission properties of dielectric aperture arrays and developing new optical biosensors and optical spectrometers. The first half of the thesis demonstrates that the optical phase shift associated with the surface plasmon (SP) assisted extraordinary optical transmission (EOT) in nano-hole arrays fabricated in a metal film has a strong dependence on the material refractive index value in close proximity to the holes. A novel refractive index sensor based on detecting the EOT phase shift is proposed by building a model. This device readily provides a 2-D biosensor array platform for non-labeled real-time detection of a variety of organic and biological molecules in a sensor chip format, which leads to a high packing density, minimal analyte volumes, and a large number of parallel channels while facilitating high resolution imaging and supporting a large space-bandwidth product (SBP). Simulation (FDTD Solutions, Lumerical Solutions Inc) results indicate an achievable sensitivity limit of 4.37x10-9 refractive index units (RIU) and a dynamic range as large as 0.17 RIU. Subsequently, optical transmission properties through a self-mixing interferometer array are studied and a novel high-resolution cost-effective optical spectrometer is proposed. The miniature interferometer-based spectrometer is made of polymethyl methacrylate (PMMA) with a CCD as the detector. The detected intensity of each CCD pixels contains the spectral information. Since each frequency component in the incoming beam corresponds to a unique phase difference of the two beam portions of each optical interferometer, the total intensity received by each CCD pixel, which is resulted from the addition of the interference signals from all the frequency components in the beam, should also be unique. Therefore, the spectrum calculation is a problem to solve an ill-posed linear system by using Tikhonov regularization method. Simulation results show that the resolution can reach picometer level. Apart from the choice of path difference between the interfering beams, the spectral resolution also depends on the signal-to-noise ratio and analogue-digital conversion resolution (dynamic range) of the CCD chip. In addition, the theory of uniform waveguide scattering is explored to expand the possibility of using such mini-interferometers for performing free-space spectral analysis of waveguide devices. At the same time, the method of least squares is used to correct the pixel non-uniformity of the CCD so as to improve the performance of the spectrometer. The sensor chip and spectrometer chip introduced here are based on the interference of light transmitted through dielectric aperture arrays. Their compact feature renders these devices ideal for miniaturization and integration as the systems in microfluidics architectures and lab-on-chip designs.

Yang, Tao

367

Nanolithography using nanoscale ridge apertures  

NASA Astrophysics Data System (ADS)

There is a continuous effort to develop techniques for nanoscale feature definition below the diffraction limit. Nanolithography has been a key technique because of its precision and cost effective. A sub-wavelength hole in an opaque screen can be used to provide a small light source with the optical resolution beyond the diffraction limit in the near field. However, a nanometer-sized hole in circular or square shapes is plagued by low transmission and poor contrast. This drawback limits the nanoscale apertures from being employed in nanolithography applications. Ridge apertures in C, H and bowtie shapes, on the other hand, have been numerically and experimentally demonstrated to show the ability of achieving both enhanced light transmission and sub-wavelength optical resolution down to nanometer domain benefiting from the existence of waveguide propagation mode confined in the gap between the ridges. In this report, the detailed field distributions in contact nanolithography are analyzed using finite difference time domain (FDTD) simulations. It was found that the high imaging contrast, which is necessary for successful lithography, is achieved close to the mask exit plane and decays quickly with the increase of the distance from the mask exit plane. Simulations are also performed for comparable regular shaped apertures and different shape bowtie apertures. Design rules are proposed to optimize the bowtie aperture for producing a sub-wavelength, high transmission field with high imaging contrast. High resolution contact nanolithography was carried on a home constructed lithography setup. It has been experimentally demonstrated that nanoscale bowtie and C apertures can be used for contact lithography to achieve nanometer scale resolution due to its intrinsic advantages of achieving enhanced optical transmission and concentrating light far beyond the diffraction limit. It also has shown the advantages of bowtie and C apertures over conventional apertures in both transmission enhancement and nanoscale light concentration. Lithographic holes as small as 40 nm x 50 nm and 50 nm x 60 nm for bowtie and C apertures, respectively, has been achieved. To study the properties of nanoscale bowtie apertures, a home-made near-field scanning optical microscope (NSOM) is developed. AFM images of standard calibration samples are used to calibrate the piezoelectric stage and topography resolution. NSOM results of bowtie apertures are also presented to study their transmission enhancement and field localization. Near-field scanning optical microscopy (NSOM) probe integrated with nanometer scale bowtie aperture for enhanced optical transmission is demonstrated. The bowtie-shape aperture allows waveguide propagating mode in the bowtie gap region, which enables simultaneous nanoscale optical resolution and enhanced optical transmission. These unique optical characteristics of bowtie aperture are demonstrated by measuring optical near fields produced by apertures in metal film. It is shown that bowtie aperture probes have one order of magnitude increase in transmission over probes with a regular shape aperture. The imaging results using bowtie aperture are in agreement with those obtained from numerical calculations. Spectroscopic measurements of transmitted field through bowtie shaped nanoscale apertures in visible wavelength region were used to further calibrate the aperture. Resonance in these apertures and its relation with the aperture geometry are investigated. The near-field spectral response is also investigated using Finite Difference Time Domain (FDTD) computation and compared with the spectroscopic measurements. The dependences of the peak wavelength and peak amplitude on the geometry of the bowtie aperture are illustrated. Design rules are proposed to optimize the bowtie aperture for producing a sub-wavelength, high transmission field.

Wang, Liang

368

Equivalent circuit for aperture antennas  

NASA Astrophysics Data System (ADS)

The commonly used equivalent circuit based on a constant-voltage generator does not correctly characterize scattering by an aperture antenna, nor does its dual, the constant-current generator. This long-standing dilemma has been resolved by combining voltage and current sources to form a constant-power source. The power generated by this source is equated to the available power in a plane wave incident on the aperture. The voltage and current of the two sources and their respective internal impedances are then completely determined from the aperture area, the impedance, the aperture efficiency, and the relative power pattern of the antenna.

Love, A. W.

1987-06-01

369

Alignment of a large outdoor antenna surface using a laser tracker  

NASA Astrophysics Data System (ADS)

The Large Millimeter Telescope (LMT) currently employs a 32.5m diameter primary reflector composed of 84 surface segments. Global alignment of the surface is carried out using the best-fit parabola. Surface alignment follows an iterative procedure that consists of measuring the surface with a laser tracker to determine the deviations from the theoretical surface, followed by surface adjustments at the segment level. Global alignment of the primary surface presents many unusual problems related to the measurement of a large object in a non-metrology environment. The LMT antenna is located at high altitude (4700m, 15000ft) in a rural setting, where mean temperatures oscillate around zero degrees centigrade, thus presenting a challenge for traditional sensitive metrology equipment such as the laser tracker. Measurement of the antenna surface with the laser tracker requires the use of fiducial points that can be used to tie the measurement of each segment position to a common reference. Several approaches to the allocation of fiducial markers on and around the antenna are discussed in this paper. In-house data analysis provides a surface error and detailed output for the iterative adjustment of individual segments in order to reduce the global surface error. In this paper we discuss many aspects of the global alignment process with particular emphasis on making optimum use of laser tracker metrology.

Leon-Huerta, Andrea; Lucero Alvarez, Maribel; Hernandez Rios, Emilio; Tzile Torres, Carlos; Cabrera Cuevas, Lizeth; Castro Santos, David; Hernandez Lázaro, Josefina; Gale, David M.; Wilson, Grant; Narayanan, Gopal

2013-04-01

370

Wideband Vivaldi Arrays for Large Aperture Antennas  

NASA Astrophysics Data System (ADS)

Single- and dual-polarized arrays of Vivaldi notch elements have been extensively analyzed by using efficient numerical analyses. From these analyses and from experimental studies, element designs and array configurations have been determined to provide more than two octaves of bandwidth while scanning to 45° from broadside in all directions. Parameter studies illustrating the effects of some key design parameters are presented. Vivaldi notch elements are linearly polarized in their principal planes and elliptically polarized in the intercardinal planes. Nonetheless, it has been shown that full polarization information about the radio source can be extracted from the signals received on orthogonal antennas. A few issues related to fabrication and assembly of dual-polarized arrays are discussed.

Schaubert, D. H.; Chio, T. H.

371

Large-area plasmonic structures fabricated by laser nanopatterning and their applications  

NASA Astrophysics Data System (ADS)

Laser interference lithography is applied to fabricate large-area plasmonic nanostructures. This approach has the advantages of being non-contact process in air and able to achieve large-area and maskless nanolithography at a high speed with low system investment. Single layer Au or Ag noble metallic thin film and Ag/Au, Ag/Ni or Au/Ni bimetallic layer thin films are patterned into nano-dot, nano-rod and nano-nut arrays by laser interference lithography. Plasmonic effects of the fabricated metallic nanostructures are studied. Tunable and multi-peak surface plasmon resonances of these nanostructures can be obtained, which have potential applications in solar cells, bio-sensing and photonic circuits.

Hong, M. H.; Liu, C. H.; Ma, F.; Chen, Z. C.; Luk'yanchuk, B.; Shi, L. P.; Chong, T. C.

2009-02-01

372

Production of large molecular ion crystals via sympathetic cooling by laser-cooled Ba+  

Microsoft Academic Search

We have produced ensembles of cold 16O+2, 40Ar+, 12C16O+2, and various isotopes of barium ions (135Ba+, 136Ba+ and 137Ba+) via sympathetic cooling with laser-cooled 138Ba+ in a linear radiofrequency trap. The sympathetically cooled species were embedded in the centre of large 138Ba+ Coulomb crystals containing up to 2000 ions and were identified by motional resonance excitation. Crystals with molecular fractions

B. Roth; A. Ostendorf; H. Wenz; S. Schiller

2005-01-01

373

Advanced laser micro-structuring of super-large-area optical films  

NASA Astrophysics Data System (ADS)

A novel laser micro-machining technique to produce high density micro-structures called Synchronized Image Scanning (SIS) was introduced a couple of years ago. Over this period of time, the technique was refined in a major effort to meet the needs of various industries. There is an increasing demand for micro-structuring of large and super large area optical films, e.g. for Rear Projection TV, anti counterfeit packaging material and 3D displays. Especially in the display industry, where the screens are ever increasing in size, established micro-structuring methods like e-beam milling, diamond turning or the reflow technique struggle to keep up with the development. This paper explains how it is possible to direct laser etch hundreds of millions of lenses into a 2 m x 1.5 m substrate. It looks at the advances made in SIS in recent years regarding seam reduction, overall accuracy and precision when structuring super large area optical films, and it presents the tools and subsystems needed to generate the features in those films. Furthermore, the potential of this exciting laser micro-machining technique for rapid prototyping for all sorts of optical and non-optical structures is mapped out.

Boehlen, Karl L.; Stassen Boehlen, Ines B.; Allott, Ric M.

2005-01-01

374

Synthetic aperture active sonar imaging  

Microsoft Academic Search

The main problems involved in synthetic aperture sonar imaging are medium instability, slow mapping rate, and platform motion. Proposed solutions to these problems are reviewed, and a new technique for synthetic aperture sonar imaging is presented which allows a fast mapping rate and improved motion compensation. This technique involves using multiple receivers to form a complex-valued preliminary image for each

Bretton L. Douglas; Hua Lee

1992-01-01

375

Reconfigurable aperture decade bandwidth array  

Microsoft Academic Search

A variety of military systems employ multiple antenna apertures on a single platform such as a ship or an aircraft. In order to reduce cost and improve performance characteristics such as the radar cross section (RCS), it is desirable to combine multiple functions into a single aperture. Wide (10:1) bandwidth phased array antennas are needed to accomplish this goal. To

J. C. Veihl; R. E. Hodges; D. McGrath; C. Monzon

2000-01-01

376

High-energy, spatially flat-top green pump laser by beam homogenization for petawatt scale Ti:sapphire laser systems  

Microsoft Academic Search

We have demonstrated that we can homogenize the spatial profile of a high-energy green laser pulse used for pumping a petawatt scale Ti:sapphire amplifier. The second harmonic of a high-energy, large aperture Nd:glass laser system generates laser emission at a green wavelength with 75J single pulse energy. Using a diffractive optical element for beam homogenization, we have obtained a highly

Momoko Tanaka; Hiromitsu Kiriyama; Yoshihiro Ochi; Yoshiki Nakai; Hajime Sasao; Hajime Okada; Hiroyuki Daido; Paul Bolton; Shunichi Kawanishi

2009-01-01

377

A New Approach for Structural Monitoring of Large Dams with a Three-Dimensional Laser Scanner  

PubMed Central

Driven by progress in sensor technology, computer methods and data processing capabilities, 3D laser scanning has found a wide range of new application fields in recent years. Particularly, monitoring the static and dynamic behaviour of large dams has always been a topic of great importance, due to the impact these structures have on the whole landscape where they are built. The main goal of this paper is to show the relevance and novelty of the laserscanning methodology developed, which incorporates different statistical and modelling approaches not considered until now. As a result, the methods proposed in this paper have provided the measurement and monitoring of the large “Las Cogotas” dam (Avila, Spain).

Gonzalez-Aguilera, Diego; Gomez-Lahoz, Javier; Sanchez, Jose

2008-01-01

378

Fabrication of mitigation pits for improving laser damage resistance in dielectric mirrors by femtosecond laser machining  

SciTech Connect

Femtosecond laser machining is used to create mitigation pits to stabilize nanosecond laser-induced damage in multilayer dielectric mirror coatings on BK7 substrates. In this paper, we characterize features and the artifacts associated with mitigation pits and further investigate the impact of pulse energy and pulse duration on pit quality and damage resistance. Our results show that these mitigation features can double the fluence-handling capability of large-aperture optical multilayer mirror coatings and further demonstrate that femtosecond laser macromachining is a promising means for fabricating mitigation geometry in multilayer coatings to increase mirror performance under high-power laser irradiation.

Wolfe, Justin E.; Qiu, S. Roger; Stolz, Christopher J.

2011-03-20

379

Averaging of receiver aperture for flat-topped incidence  

NASA Astrophysics Data System (ADS)

Using a flat-topped profile for the incident beam, the power scintillation index for weak atmospheric turbulence is formulated and analytically evaluated. Through the use of the aperture averaging factor, the averaging effect of the finite receiver aperture on the intensity fluctuations for a flat-topped incident beam is examined. The influence of the order of flatness on the averaging is investigated. At large propagation lengths, increasing the flatness parameter decreases the power scintillations and it is possible to further reduce the scintillation by increasing the receiver aperture. Increasing the structure constant increases this effect.

Kamac?o?lu, Canan; Baykal, Yahya; Yazgan, Erdem

2013-11-01

380

Micromold-Based Laser Shock Embossing of Metallic Foil: Fabrication of Large-Area Three-Dimensional Microchannel Networks  

Microsoft Academic Search

Micromold-based laser shock embossing is a new three-dimensional (3D) forming technique, which utilizes laser-generated shock wave to shape the workpiece. In this article, the microchannel networks mold was produced by micro-wire electrical discharge machining (Micro-WEDM). Large-area three-dimensional microchannel networks were successfully fabricated on metallic foil surface using laser-generated shock wave. The investigation reveals that 3D microchannel networks have a high

Zongbao Shen; Huixia Liu; Xiao Wang; Hejun Wang

2011-01-01

381

Micromould Based Laser Shock Embossing of Metallic Foil: Fabrication of Large-Area Three-Dimensional Microchannel Networks  

Microsoft Academic Search

Micromould based laser shock embossing is a new three-dimensional (3D) forming technique, which utilizes laser-generated shock wave to shape the work piece. In the paper, the microchannel networks mould was produced by micro wire electrical discharge machining (Micro-WEDM). Large-area three-dimensional microchannel networks were successfully fabricated on metallic foil surface using laser-generated shock wave. The investigation reveals that three-dimensional microchannel networks

Zongbao Shen; Huixia Liu; Xiao Wang; Hejun Wang

2011-01-01

382

Generation and characterization of femtosecond petawatt Ti:sapphire laser  

Microsoft Academic Search

A Ti:sapphire laser with output of 0.89PW\\/29.0fs based on the scheme of chirped pulse amplification has been developed. The high gain amplification was achieved in large aperture amplifiers by effective suppression of parasitic lasing.

Xiaoyan Liang; Yuxin Leng; Cheng Wang; Lihuang Lin; Chuang Li; Baozhen Zhao; Yunhua Jiang; Xiaoming Lu; Mingyun Hu; Haihe Lu; Dingjun Yin; Yongliang Jiang; Chunmei Zhang; Xingqiang Lu; Hui Wei; Jianqiang Zhu; Ruxin Li; Zhizhan Xu

2007-01-01

383

Lasers.  

ERIC Educational Resources Information Center

|Examines the nature of laser light. Topics include: (1) production and characteristics of laser light; (2) nine types of lasers; (3) five laser techniques including holography; (4) laser spectroscopy; and (5) laser fusion and other applications. (SK)|

Schewe, Phillip F.

1981-01-01

384

Lasers.  

ERIC Educational Resources Information Center

Examines the nature of laser light. Topics include: (1) production and characteristics of laser light; (2) nine types of lasers; (3) five laser techniques including holography; (4) laser spectroscopy; and (5) laser fusion and other applications. (SK)

Schewe, Phillip F.

1981-01-01

385

Measurements of Green Laser-Beam Propagation and Backscatter in Long-Scale Length Plasmas  

Microsoft Academic Search

Summary form only given. We have implemented a complete set of optical diagnostics at the Omega laser to measure propagation and backscatter of a green (527 nm) high intensity laser beam (1015 W\\/cm2) in large-scale length, laser produced plasmas. The diagnostics include a transmitted beam diagnostic (TBD), a full aperture backscatter station (FABS) as well as a near backscatter imager

C. Niemann; L. Divol; D. Froula; S. Glenzer; G. Gregori; R. Kirkwood; A. Mackinnon; N. Meezan; J. Moody; C. Sorce; R. Bahr; W. Seka

2005-01-01

386

Laser-Sheet Flow Visualization Technique for the Large Wind Tunnels of the National Full-Scale Aerodynamics Complex.  

National Technical Information Service (NTIS)

A flow visualization technique for the large wind tunnels of the National Full Scale Aerodynamics Complex (NFAC) is described. The technique uses a laser sheet generated by the NFAC Long Range Laser Velocimeter (LRLV) to illuminate a smoke-like tracer in ...

M. S. Reinath J. C. Ross

1990-01-01

387

Large-signal dynamics of an ultrafast semiconductor laser at digital modulation rates approaching 10 Gbit/s  

SciTech Connect

High-fidelity pseudorandom digital modulation at 8.2 Gbit/s of an ultrahigh speed semiconductor laser is demonstrated. Studies using simple but representative pulse patterns at 10 Gbit/s give insights into the maximum digital modulation rate attainable from a given laser, as well as relations between large-signal digital performance and small-signal analog response.

Lau, K.Y.; Yariv, A.

1985-07-15

388

Monolithic Ge-on-Si lasers for large-scale electronic-photonic integration  

NASA Astrophysics Data System (ADS)

A silicon-based monolithic laser source has long been envisioned as a key enabling component for large-scale electronic-photonic integration in future generations of high-performance computation and communication systems. In this paper we present a comprehensive review on the development of monolithic Ge-on-Si lasers for this application. Starting with a historical review of light emission from the direct gap transition of Ge dating back to the 1960s, we focus on the rapid progress in band-engineered Ge-on-Si lasers in the past five years after a nearly 30-year gap in this research field. Ge has become an interesting candidate for active devices in Si photonics in the past decade due to its pseudo-direct gap behavior and compatibility with Si complementary metal oxide semiconductor (CMOS) processing. In 2007, we proposed combing tensile strain with n-type doping to compensate the energy difference between the direct and indirect band gap of Ge, thereby achieving net optical gain for CMOS-compatible diode lasers. Here we systematically present theoretical modeling, material growth methods, spontaneous emission, optical gain, and lasing under optical and electrical pumping from band-engineered Ge-on-Si, culminated by recently demonstrated electrically pumped Ge-on-Si lasers with >1 mW output in the communication wavelength window of 1500-1700 nm. The broad gain spectrum enables on-chip wavelength division multiplexing. A unique feature of band-engineered pseudo-direct gap Ge light emitters is that the emission intensity increases with temperature, exactly opposite to conventional direct gap semiconductor light-emitting devices. This extraordinary thermal anti-quenching behavior greatly facilitates monolithic integration on Si microchips where temperatures can reach up to 80 °C during operation. The same band-engineering approach can be extended to other pseudo-direct gap semiconductors, allowing us to achieve efficient light emission at wavelengths previously considered inaccessible.

Liu, Jifeng; Kimerling, Lionel C.; Michel, Jurgen

2012-09-01

389

Two-laser, large-field hyperspectral microarray scanner for the analysis of multicolor microarrays.  

PubMed

We describe the development and operation of a two-laser, large-field hyperspectral scanner for analysis of multicolor genotyping microarrays. In contrast to confocal microarray scanners, in which wavelength selectivity is obtained by positioning band-pass filters in front of a photomultiplier detector, hyperspectral microarray scanners collect the complete visible emission spectrum from the labeled microarrays. Hyperspectral scanning permits discrimination of multiple spectrally overlapping fluorescent labels with minimal use of optical filters, thus offering important advantages over standard filter-based multicolor microarray scanners. The scanner uses two-sided oblique line illumination of microarrays. Two lasers are used for the excitation of dyes in the visible and near-infrared spectral regions. The hyperspectral scanner was evaluated with commercially available two-color calibration slides and with in-house-printed four-color microarrays containing dyes with spectral properties similar to their commercial genotyping array counterparts. PMID:18808153

Erfurth, Florian; Tretyakov, Alexander; Nyuyki, Berla; Mrotzek, Grit; Schmidt, Wolf-Dieter; Fassler, Dieter; Saluz, Hans Peter

2008-09-23

390

A laser-based longitudinal density monitor for the large hadroncollider  

SciTech Connect

We report on the development of an instrument for the measurement of the longitudinal beam profile in the Large Hadron Collider (LHC). The technique used, which has been successfully demonstrated at the Advanced Light Source, mixes the synchrotron radiation with the light from a mode-locked solid state laser oscillator in a non-linear crystal.The up-converted radiation is then detected with a photomultiplier and processed to extract, store and display the required information. A 40MHz laser, phase-locked to the ring radio frequency system, with a 50 pspulse length, would be suitable for measuring the dynamics of the core of each of the LHC 2808 bunches in a time span much shorter than the synchrotron period. The same instrument could also monitor the evolution of the bunch tails, the presence of untrapped particles and their diffusion into nominally empty RF buckets (''ghost bunches'') as required by the CERN specifications.

Beche, J.-F.; Byrd, J.; Datte, P.; De Santis, S.; Placidi, M.; Riot, V.; Schoenlein, R.; Turner, W.; Zolotorev, M.

2004-07-01

391

Large area high efficiency broad bandwidth 800 nm dielectric gratings for high energy laser pulse compression.  

PubMed

We have demonstrated broad bandwidth large area (229 mm x 114 mm) multilayer dielectric diffraction gratings for the efficient compression of high energy 800 nm laser pulses at high average power. The gratings are etched in the top layers of an aperiodic (Nb0.5Ta0.5)2O5-SiO2 multilayer coating deposited by ion beam sputtering. The mean efficiency of the grating across the area is better than 97% at the center wavelength and remains above 96% at wavelengths between 820 nm and 780 nm. The gratings were used to compress 5.5 J pulses from a Ti:sapphire laser with an efficiency above 80 percent. PMID:20052091

Martz, D H; Nguyen, H T; Patel, D; Britten, J A; Alessi, D; Krous, E; Wang, Y; Larotonda, M A; George, J; Knollenberg, B; Luther, B M; Rocca, J J; Menoni, C S

2009-12-21

392

Lateral cavity photonic crystal surface emitting lasers with ultralow threshold and large power  

NASA Astrophysics Data System (ADS)

The Bragg diffraction condition of surface-emitting lasing action is analyzed and ?2-1 mode is chosen for lasing. Two types of lateral cavity photonic crystal surface emitting lasers (LC-PCSELs) based on the PhC band edge mode lateral resonance and vertical emission to achieve electrically driven surface emitting laser without distributed Bragg reflectors in the long wavelength optical communication band are designed and fabricated. Deep etching techniques, which rely on the active layer being or not etched through, are adopted to realize the LC-PCSELs on the commercial AlGaInAs/InP multi-quantum-well (MQW) epitaxial wafer. 1553.8 nm with ultralow threshold of 667 A/cm2 and 1575 nm with large power of 1.8 mW surface emitting lasing actions are observed at room temperature, providing potential values for mass production with low cost of electrically driven PCSELs.

Wang, Yufei; Qu, Hongwei; Zhou, Wenjun; Jiang, Bin; Zhang, Jianxin; Qi, Aiyi; Liu, Lei; Fu, Feiya; Zheng, Wanhua

2012-02-01

393

Sparse aperture endoscope  

DOEpatents

An endoscope is disclosed which reduces the volume needed by the imaging part, maintains resolution of a wide diameter optical system, while increasing tool access, and allows stereographic or interferometric processing for depth and perspective information/visualization. Because the endoscope decreases the volume consumed by imaging optics such allows a larger fraction of the volume to be used for non-imaging tools, which allows smaller incisions in surgical and diagnostic medical applications thus produces less trauma to the patient or allows access to smaller volumes than is possible with larger instruments. The endoscope utilizes fiber optic light pipes in an outer layer for illumination, a multi-pupil imaging system in an inner annulus, and an access channel for other tools in the center. The endoscope is amenable to implementation as a flexible scope, and thus increases it's utility. Because the endoscope uses a multi-aperture pupil, it can also be utilized as an optical array, allowing stereographic and interferometric processing. 7 figs.

Fitch, J.P.

1999-07-06

394

Optica aperture synthesis  

NASA Astrophysics Data System (ADS)

Optical long baseline stellar interferometry is an observational technique in astronomy that already exists for over a century, but is truly blooming during the last decades. The undoubted value of stellar interferometry as a technique to measure stellar parameters beyond the classical resolution limit is more and more spreading to the regime of synthesis imaging. With optical aperture synthesis imaging, the measurement of parameters is extended to the reconstruction of high resolution stellar images. A number of optical telescope arrays for synthesis imaging are operational on Earth, while space-based telescope arrays are being designed. For all imaging arrays, the combination of the light collected by the telescopes in the array can be performed in a number of ways. In this thesis, methods are introduced to model these methods of beam combination and compare their effectiveness in the generation of data to be used to reconstruct the image of a stellar object. One of these methods of beam combination is to be applied in a future space telescope. The European Space Agency is developing a mission that can valuably be extended with an imaging beam combiner. This mission is labeled Darwin, as its main goal is to provide information on the origin of life. The primary objective is the detection of planets around nearby stars - called exoplanets- and more precisely, Earth-like exoplanets. This detection is based on a signal, rather than an image. With an imaging mode, designed as described in this thesis, Darwin can make images of, for example, the planetary system to which the detected exoplanet belongs or, as another example, of the dust disk around a star out of which planets form. Such images will greatly contribute to the understanding of the formation of our own planetary system and of how and when life became possible on Earth. The comparison of beam combination methods for interferometric imaging occupies most of the pages of this thesis. Additional chapters will treat related subjects, being experimental work on beam combination optics, a description of a novel formalism for aberration retrieval and experimental work on nulling interferometry. The Chapters on interferometric imaging are organized in such a way that not only the physical principles behind a stellar interferometer are clear, but these chapters also form a basis for the method of analysis applied to the interferometers - -or rather beam combination methods- under consideration. The imaging process in a stellar interferometer will be treated as the inversion of a linear system of equations. The definition of interferometric imaging in this thesis can be stated to be the reconstruction of a luminosity distribution function on the sky, that is, in angular measure, larger than the angular diffraction limited spot size -or Point-Spread Function (PSF)- of a single telescope in the array and that contains, again in angular measure, spatial structure that is much smaller than the PSF of a single telescope. This reconstruction has to be based on knowledge of the dimensions of the telescope array and the detector. The detector collects intensity data that is formed by observation of the polychromatic luminosity distribution on the sky and is deteriorated by the quantum-nature of light and an imperfect electronic detection process. Therefore, the imaging study presented in this thesis can be regarded to be a study on the signal characteristics of various interferometers while imaging a polychromatic wide-field stellar source. The collection of beam combination methods under consideration consists of four types. Among these are two well-known types, having either co-axially combined beams as in the Michelson-Morley experiment to demonstrate the existence of ether, or beams that follow optical paths as if an aperture mask were placed in front of a telescope, making the beams combine in the focus of that telescope, as suggested by Fizeau. For separated apertures rather than an aperture mask, these optical paths are stated to be homothetic. In short, these two types wi

van der Avoort, Casper

2006-05-01

395

Sparse aperture endoscope  

DOEpatents

An endoscope which reduces the volume needed by the imaging part thereof, maintains resolution of a wide diameter optical system, while increasing tool access, and allows stereographic or interferometric processing for depth and perspective information/visualization. Because the endoscope decreases the volume consumed by imaging optics such allows a larger fraction of the volume to be used for non-imaging tools, which allows smaller incisions in surgical and diagnostic medical applications thus produces less trauma to the patient or allows access to smaller volumes than is possible with larger instruments. The endoscope utilizes fiber optic light pipes in an outer layer for illumination, a multi-pupil imaging system in an inner annulus, and an access channel for other tools in the center. The endoscope is amenable to implementation as a flexible scope, and thus increases the utility thereof. Because the endoscope uses a multi-aperture pupil, it can also be utilized as an optical array, allowing stereographic and interferometric processing.

Fitch, Joseph P. (Livermore, CA)

1999-07-06

396

The proceedings of the 1st international workshop on laboratory astrophysics experiments with large lasers  

SciTech Connect

The world has stood witness to the development of a number of highly sophisticated and flexible, high power laser facilities (energies up to 50 kJ and powers up to 50 TW), driven largely by the world-wide effort in inertial confinement fusion (ICF). The charter of diagnosing implosions with detailed, quantitative measurements has driven the ICF laser facilities to be exceedingly versatile and well equipped with diagnostics. Interestingly, there is considerable overlap in the physics of ICF and astrophysics. Both typically involve compressible radiative hydrodynamics, radiation transport, complex opacities, and equations of state of dense matter. Surprisingly, however, there has been little communication between these two communities to date. With the recent declassification of ICF in the USA, and the approval to commence with construction of the next generation ``superlasers``, the 2 MJ National Ignition Facility in the US, and its equivalent, the LMJ laser in France, the situation is ripe for change. . Given the physics similarities that exist between ICF and astrophysics, one strongly suspects that there should exist regions of overlap where supporting research on the large lasers could be beneficial to the astrophysics community. As a catalyst for discussions to this end, Lawrence Livermore National Laboratory sponsored this workshop. Approximately 100 scientists attended from around the world, representing eight countries: the USA, Canada, UK, France, Germany, Russia, Japan, and Israel. A total of 30 technical papers were presented. The two day workshop was divided into four sessions, focusing on nonlinear hydrodynamics, radiative hydrodynamics, radiation transport, and atomic physics-opacities. Copies of the presentations are contained in these proceedings.

Remington, B.A.; Goldstein, W.H. [eds.] [eds.

1996-08-09

397

The proceedings of the 1st international workshop on laboratory astrophysics experiments with large lasers  

NASA Astrophysics Data System (ADS)

The world has stood witness to the development of a number of highly sophisticated and flexible, high power laser facilities (energies up to 50 kJ and powers up to 50 TW), driven largely by the world-wide effort in inertial confinement fusion (ICF). The charter of diagnosing implosions with detailed, quantitative measurements has driven the ICF laser facilities to be exceedingly versatile and well equipped with diagnostics. Interestingly, there is considerable overlap in the physics of ICF and astrophysics. Both typically involve compressible radiative hydrodynamics, radiation transport, complex opacities, and equations of state of dense matter. Surprisingly, however, there has been little communication between these two communities to date. With the recent declassification of ICF in the USA, and the approval to commence with construction of the next generation 'superlasers', the 2 MJ National Ignition Facility in the US, and its equivalent, the LMJ laser in France, the situation is ripe for change. . Given the physics similarities that exist between ICF and astrophysics, one strongly suspects that there should exist regions of overlap where supporting research on the large lasers could be beneficial to the astrophysics community. As a catalyst for discussions to this end, Lawrence Livermore National Laboratory sponsored this workshop. Approximately 100 scientists attended from around the world, representing eight countries: the USA, Canada, UK, France, Germany, Russia, Japan, and Israel. A total of 30 technical papers were presented. The two day workshop was divided into four sessions, focusing on nonlinear hydrodynamics, radiative hydrodynamics, radiation transport, and atomic physics-opacities. Copies of the presentations are contained in these proceedings.

Remington, B. A.; Goldstein, W. H.

1996-08-01

398

The effect of synchrobetatron coupling on the dynamic aperture  

SciTech Connect

The effect of synchrobetatron coupling on the dynamic aperture was studied by comparing the dynamic aperture for a particle with a large fixed {Delta}p/p, no synchrotron oscillations present, with the dynamic aperture for a particle, with a synchrotron oscillation amplitude, of the same {Delta}p/p. The particle with the synchrotron oscillation present was found to have a smaller dynamic aperture than the particle with the fixed {Delta}p/p. It is suggested that this reduction in dynamic aperture may be due to non-linear coupling between the longitudinal and transverse motions. For RHIC, whose lattice and rf were used in this study, the longitudinal phase space is much larger than the transverse phase space, by a factor of several thousand, and a small amount of coupling can cause considerable growth in the transverse motion. The effect is most pronounced at lower energies in RHIC, where larger momentum spread and transverse amplitudes are required. At {gamma} = 30 in RHIC, with a synchrotron oscillation amplitude of {Delta}p/p = 0.005, the dynamic aperture is reduced by about 6 mm by the presence of the synchrotron oscillations. The effect may be more important for RHIC than for other superconducting proton colliders, because of its relatively low energy and because of the importance of intrabeam scattering for heavy ions. This results in larger dynamic aperture requirements for RHIC both in transverse space and in momentum spread.

Parzen, G.

1992-12-31

399

The effect of synchrobetatron coupling on the dynamic aperture  

SciTech Connect

The effect of synchrobetatron coupling on the dynamic aperture was studied by comparing the dynamic aperture for a particle with a large fixed [Delta]p/p, no synchrotron oscillations present, with the dynamic aperture for a particle with a synchrotron oscillation amplitude of the same [Delta]p/p. The particle with the synchrotron oscillation present was found to have a smaller dynamic aperture than that of the particle with the fixed [Delta]p/p. It is suggested that this reduction in dynamic aperture may be due to a non-linear coupling between the longitudinal and transverse motions. For RHIC, whose lattice and RF were used in this study, the longitudinal phase space is much larger than the transverse phase space by a factor of several thousand, and a small amount of coupling can cause considerable growth in the transverse motion. The effect is most pronounced at lower energies in RHIC, where larger momentum spread and transverse amplitudes are required. At [gamma] = 30 in RHIC, with a synchrotron oscillation amplitude of [Delta]p/p = 0.005, the dynamic aperture is reduced by about 6 mm by the presence of the synchrotron oscillations. The effect may be more important for RHIC than for other superconducting proton colliders, because of its relatively low energy and because of the importance of intrabeam scattering for heavy ions. This results in larger dynamic aperture requirements for RHIC both in transverse space and in momentum spread.

Parzen, G.

1993-03-01

400

The effect of synchrobetatron coupling on the dynamic aperture  

SciTech Connect

The effect of synchrobetatron coupling on the dynamic aperture was studied by comparing the dynamic aperture for a particle with a large fixed {Delta}p/p, no synchrotron oscillations present, with the dynamic aperture for a particle with a synchrotron oscillation amplitude of the same {Delta}p/p. The particle with the synchrotron oscillation present was found to have a smaller dynamic aperture than that of the particle with the fixed {Delta}p/p. It is suggested that this reduction in dynamic aperture may be due to a non-linear coupling between the longitudinal and transverse motions. For RHIC, whose lattice and RF were used in this study, the longitudinal phase space is much larger than the transverse phase space by a factor of several thousand, and a small amount of coupling can cause considerable growth in the transverse motion. The effect is most pronounced at lower energies in RHIC, where larger momentum spread and transverse amplitudes are required. At {gamma} = 30 in RHIC, with a synchrotron oscillation amplitude of {Delta}p/p = 0.005, the dynamic aperture is reduced by about 6 mm by the presence of the synchrotron oscillations. The effect may be more important for RHIC than for other superconducting proton colliders, because of its relatively low energy and because of the importance of intrabeam scattering for heavy ions. This results in larger dynamic aperture requirements for RHIC both in transverse space and in momentum spread.

Parzen, G.

1993-03-01

401

Maskless multiple-beam laser lithography for large-area nanostructure/microstructure fabrication.  

PubMed

This paper reports a maskless multiple-beam laser lithography technique for large-area nanostructure/microstructure fabrication. This lithography technique can flexibly generate arbitrary nanostructures/microstructures over a large area at a high speed. The feature size of the nanostructures/microstructures can be controlled by exposure time and moving speed of the nanostage. Functional predesigned patterns, including split-ring resonator metamaterials for terahertz waves, can be obtained. More complicated structures can be made by single- and double-exposure schemes to make hybrid nanostructures/microstructures and tune surface plasmonic resonance properties. Meanwhile, microstructures with large height to lateral dimension ratios (2.5D microstructures) fabricated on silicon substrates can be used as mold tools for soft lithography. This technology shows its unique capacity to create various nanostructures/microstructures for extensive applications. PMID:22193133

Tang, Min; Chen, Zai Chun; Huang, Zhi Qiang; Choo, Yoo Sang; Hong, Ming Hui

2011-12-10

402

Recent advances in sub-aperture finishing  

NASA Astrophysics Data System (ADS)

Subaperture polishing technologies have radically changed the landscape of precision optics manufacturing and enabled the production of components with higher accuracies and increasingly difficult figure requirements. Magnetorheological Finishing (MRF), for example, is a production-proven, deterministic, subaperture finishing technology that has excelled at overcoming the limitations of traditional polishing. Several recent MRF developments will be presented, including complementing Single Point Diamond Turning (SPDT) technology, transmitted wavefront correction, and finishing of increasingly large apertures. We will also discuss the high precision finishing of challenging optics using a newly developed jet-based technology. A series of examples spanning a wide range of materials, geometries and specifications will be presented. Specific areas to be discussed include micro-optics (i.e., optics less than 5 mm in size), which typically require a very labor-intensive iterative process to finish, and steeply concave optics, such as domes, which are typically not well suited for sub-aperture polishing processes.

Tricard, Marc; Shorey, Aric; Dumas, Paul

2005-10-01

403

Hourglass-shaped aperture for cellular electrophysiological study  

NASA Astrophysics Data System (ADS)

This work presents a simple process of reflow of melted glass by CO2 laser to form an hourglass-shaped aperture for cellular electrophysiological study. The fabricated aperture proves to be smooth, circular, debris-free, and freshly activated. Two-phase flow simulation illuminates details of the reflow process. The resulting seal resistance quality is well suited to measure ion-channel activities; a seal resistance of 1.9 G? for PC-12 cell and a typical resistance of 200 M? for Chinese hamster ovary cells were achieved. This approach can be integrated with microfluidics in a single cell patch or array configuration.

Chen, Chang-Yu; Liu, Kuan-Ting; Jong, De-Shien; Wo, Andrew M.

2007-09-01

404

Medical imaging with coded apertures.  

National Technical Information Service (NTIS)

Now algorithms were investigated for image reconstruction in emission tomography which could incorporate complex instrumental effects such as might be obtained with a coded aperture system. The investigation focused on possible uses of the wavelet transfo...

E. Keto S. Libby

1995-01-01

405

Large-Spot Material Interactions with a High-Power Solid-State Laser Beam  

SciTech Connect

We study the material interactions produced by the beam of a 25-kW solid-state laser, in experiments characterized by relatively large spot sizes ({approx}3 cm) and the presence of airflow. The targets are iron or aluminum slabs, of thickness 1 cm. In the experiments with iron, we show that combustion plays an important role in heating the material. In the experiments with aluminum, we observe a sharp transition from no melting to complete melt-through as the intensity on target increases. A layer of paint greatly reduces the requirements for melt-through. We explain these effects and incorporate them into an overall computational model.

Boley, C D; Fochs, S N; Rubenchik, A M

2008-08-06

406

Dynamic aperture fringe discriminator  

NASA Astrophysics Data System (ADS)

A device for eliminating unwanted reflections from refractive optical elements in an optical system is provided. The device operates to prevent desired multiple fringe patterns from being obscured by reflections from refractive elements positioned in proximity to a focal plane of the system. The problem occurs when an optical beam is projected into, and reflected back out of, the optical system. Surfaces of the refractive elements reflect portions of the beam which interfere with portions of the beam which are transmitted through the refractive elements. Interference between the reflected and transmitted portions of the beam produce multiple fringe sets which tend to obscure desired interference fringes. With the refractive optical element in close proximity to the focal plane of the system, the undesired reflected light reflects at an angle 180 degrees opposite from the desired transmitted beam. The device exploits the 180-degree offset, or rotational shear, of the undesired reflected light by providing an optical stop for blocking one-half of the cross-section of the test beam. By blocking one-half of the test beam, the undesired offset beam is blocked, while the returning transmitted beam passes into the optical system unaffected. An image is thereby produced from only the desired transmitted beam. In one configuration, the blocking device includes a semicircular aperture which is caused to rotate about the axis of the test beam. By rotating, all portions of the test beam are cyclically projected into the optical system to thereby produce a complete test image. The rotating optical stop is preferably caused to rotate rapidly to eliminate flicker in the resulting image.

Steimle, Lawrence J.; Thiessen, David L.

1992-05-01

407

Synthetic aperture sonar image statistics  

Microsoft Academic Search

Synthetic Aperture Sonar (SAS) systems are capable of producing photograph quality seafloor imagery using a lower frequency than other systems of comparable resolution. However, as with other high-resolution sonar systems, SAS imagery is often characterized by heavy-tailed amplitude distributions which may adversely affect target detection systems. The constant cross-range resolution with respect to range that results from the synthetic aperture

Shawn F. Johnson

2009-01-01

408

Large scale microstructuring on silicon surface in air and liquid by femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

Large-scale microstructures were imprinted on the surface of silicon with dimensions of 1 mm × 1 mm by femtosecond laser line-by-line scanning irradiation. The scanning was made under air and under chlor/hydrogen based liquid layers. Scanning electron microscope investigations evidenced homogeneous surface microstructures, such as: ripples with sub-wavelengths dimensions, Si pillars and directional oriented bacilliform structures. The dependence of the surface morphology on laser energy, scanning speed and irradiation media was analyzed. In air, the microstructure changes from directional-arranged bacilliform structures to well-known ripple structures with a width of about 525 nm. When using the liquid media, we observe ripple structures with a width of about 370 nm and an overlapping of those that evolve in certain regions into Si pillars. The surfaces show interesting gradient topography behaviour which could be used as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth. By using chlor and hydrogen based liquids we were able to explore the microstructuring of the silicon by line-by-line irradiation process using the femtosecond laser.

Ulmeanu, M.; Jipa, F.; Radu, C.; Enculescu, M.; Zamfirescu, M.

2012-09-01

409

Coded aperture imaging for fluorescent x-rays  

NASA Astrophysics Data System (ADS)

We employ a coded aperture pattern in front of a charge couple device (CCD) pixilated detector to image fluorescent xrays (6-25KeV) from samples irradiated with synchrotron radiation. Coded apertures encode the angular direction of xrays, and given a known source plane, allow for a large Numerical Aperture x-ray imaging system. The algorithm to develop the free standing coded aperture pattern of the Non-Two-Holes-Touching (NTHT) was developed. The algorithms to reconstruct the x-ray image from the encoded pattern recorded are developed by means of modeling and confirmed by experiments on standard samples. Spatial resolution and efficiency are determined for the next development stage whereby an energy resolving pixilated CCD will be deployed allowing for elemental imaging.

Haboub, A.; MacDowell, A. A.; Marchesini, S.; Parkinson, D. Y.

2012-10-01

410

A low-noise large dynamic-range readout suitable for laser spectroscopy with photodiodes.  

PubMed

An original low-noise large dynamic-range readout system for optical light spectroscopy with PIN diodes is presented. The front-end circuit is equipped with a smart device for automatic cancellation of the large dc offset brought about by the photodiode current. This device sinks away the exact amount of dc current from the preamplifier input, yielding auto zeroing of the output-voltage offset, while introducing the minimum electronic noise possible. As a result the measurement dynamic-range is maximized. Moreover, an auxiliary inspection point is provided which precisely tracks the dc component of the photodiode current. This output allows for precise beam alignment and may also be used for diagnostic purposes. The excellent gain stability and linearity make the circuit perfectly suited for optical-light pulse spectroscopy. Applications include particle sizing in the 100 nm range, two-dimensional characterization of semiconductor detectors, ultra-precise characterization of laser beam stability, confocal microscopy. PMID:23126787

Pullia, A; Sanvito, T; Potenza, M A; Zocca, F

2012-10-01

411

A low-noise large dynamic-range readout suitable for laser spectroscopy with photodiodes  

NASA Astrophysics Data System (ADS)

An original low-noise large dynamic-range readout system for optical light spectroscopy with PIN diodes is presented. The front-end circuit is equipped with a smart device for automatic cancellation of the large dc offset brought about by the photodiode current. This device sinks away the exact amount of dc current from the preamplifier input, yielding auto zeroing of the output-voltage offset, while introducing the minimum electronic noise possible. As a result the measurement dynamic-range is maximized. Moreover, an auxiliary inspection point is provided which precisely tracks the dc component of the photodiode current. This output allows for precise beam alignment and may also be used for diagnostic purposes. The excellent gain stability and linearity make the circuit perfectly suited for optical-light pulse spectroscopy. Applications include particle sizing in the 100 nm range, two-dimensional characterization of semiconductor detectors, ultra-precise characterization of laser beam stability, confocal microscopy.

Pullia, A.; Sanvito, T.; Potenza, M. A.; Zocca, F.

2012-10-01

412

High-power one-, two-, and three-dimensional photonic crystal edge- emitting laser diodes for ultrahigh brightness applications  

Microsoft Academic Search

Direct laser diodes can typically provide only a limited single mode power, while ultrahigh-brightness is required for many of the market-relevant applications. Thus, multistage power conversion schemes are applied, when the laser diodes are used just as a pumping source. In this paper we review the recent advances in ultra-large output aperture edge- emitting lasers based on the photonic band

N. Yu. Gordeev; M. V. Maximova; Y. M. Shernyakov; I. I. Novikov

413

Ceramic Laser Materials  

SciTech Connect

Transparent ceramic materials have several major advantages over single crystals in laser applications, not the least of which is the ability to make large aperture parts in a robust manufacturing process. After more than a decade of working on making transparent YAG:Nd, Japanese workers have recently succeeded in demonstrating samples that performed as laser gain media as well as their single crystal counterparts. Since then several laser materials have been made and evaluated. For these reasons, developing ceramic laser materials is the most exciting and futuristic materials topic in today's major solid-state laser conferences. We have established a good working relationship with Konoshima Ltd., the Japanese producer of the best ceramic laser materials, and have procured and evaluated slabs designed by us for use in our high-powered SSHCL. Our measurements indicate that these materials will work in the SSHCL, and we have nearly completed retrofitting the SSHCL with four of the largest transparent ceramic YAG:Nd slabs in existence. We have also begun our own effort to make this material and have produced samples with various degrees of transparency/translucency. We are in the process of carrying out an extensive design-of-experiments to establish the significant process variables for making transparent YAG. Finally because transparent ceramics afford much greater flexibility in the design of lasers, we have been exploring the potential for much larger apertures, new materials, for example for the Mercury laser, other designs for SSHL, such as, edge pumping designs, slabs with built in ASE suppression, etc. This work has just beginning.

Soules, T F; Clapsaddle, B J; Landingham, R L; Schaffers, K I

2005-02-15

414

Fiber laser annealing of indium-tin-oxide nanoparticles for large area transparent conductive layers and optical film characterization  

NASA Astrophysics Data System (ADS)

Indium tin oxide (ITO) coatings are widely used as transparent electrodes for optoelectronic devices. The most common preparation methods are sputtering, evaporation, and wet chemical deposition. ITO coatings can also be manufactured by solution deposition of ITO nanoparticles followed by furnace thermal annealing with the major motivation to reduce equipment investment. However, conventional furnace annealing is energy intensive, slow, and limited by the peak processing temperature. To overcome these constraints, we suggest using a laser beam for ITO nanoparticle annealing over a large area. It is shown in the present study that a low cost, high power, and high efficiency laser can yield large area functional ITO films in a process that carries substantial promise for potential industrial implementation. Furthermore, laser annealing generates higher electrical conductivity than conventional, thermally annealed nanoparticle films. The optical and electrical properties of the annealed ITO films can also be altered by adjusting laser parameters and environmental gases.

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

2011-07-01

415

Thinning of large-area graphene film from multilayer to bilayer with a low-power CO2 laser.  

PubMed

Bilayer graphene has attracted a great deal of attention for many electronic and optical applications. Although large-area bilayer graphene can be synthesized by chemical vapor deposition (CVD), multilayer growth often occurs and subsequent processes are required to obtain uniform bilayer films. We report an efficient way of thinning multilayer graphene film by low-power CO2 laser irradiation in vacuum. With a laser power density of ~10(2) W cm(-2), pristine graphene film of 4-5 layers can be thinned to a bilayer free of defects in 30 s. Contrary to previous laser-assisted graphene thinning processes, which reduced graphene layers precisely and locally with a high power density and a small beam diameter, our approach enables high-efficiency thinning of large-area graphene film whilst using a significantly reduced power density and an increased laser beam diameter. PMID:23764487

Lin, Zhe; Huang, Ting; Ye, Xiaohui; Zhong, Minlin; Li, Lin; Jiang, Juan; Zhang, Wen; Fan, Lili; Zhu, Hongwei

2013-06-14

416

Thinning of large-area graphene film from multilayer to bilayer with a low-power CO2 laser  

NASA Astrophysics Data System (ADS)

Bilayer graphene has attracted a great deal of attention for many electronic and optical applications. Although large-area bilayer graphene can be synthesized by chemical vapor deposition (CVD), multilayer growth often occurs and subsequent processes are required to obtain uniform bilayer films. We report an efficient way of thinning multilayer graphene film by low-power CO2 laser irradiation in vacuum. With a laser power density of ?102 W cm?2, pristine graphene film of 4–5 layers can be thinned to a bilayer free of defects in 30 s. Contrary to previous laser-assisted graphene thinning processes, which reduced graphene layers precisely and locally with a high power density and a small beam diameter, our approach enables high-efficiency thinning of large-area graphene film whilst using a significantly reduced power density and an increased laser beam diameter.

Lin, Zhe; Huang, Ting; Ye, Xiaohui; Zhong, Minlin; Li, Lin; Jiang, Juan; Zhang, Wen; Fan, Lili; Zhu, Hongwei

2013-07-01

417

Development of large scale production of Nd-doped phosphate glasses for megajoule-scale laser systems  

SciTech Connect

Nd-doped phosphate glasses are the preferred gain medium for high-peak-power lasers used for Inertial Confinement Fusion research because they have excellent energy storage and extraction characteristics. In addition, these glasses can be manufactured defect-free in large sizes and at relatively low cost. To meet the requirements of the future mega-joule size lasers, advanced laser glass manufacturing methods are being developed that would enable laser glass to be continuously produced at the rate of several thousand large (790 x 440 x 44 mm{sup 3}) plates of glass per year. This represents more than a 10 to 100-fold improvement in the scale of the present manufacturing technology.

Ficini, G. [Centre d`Etudes de Limeil-Valenton, Villeneuve, St. Georges (France); Campbell, J.H. [Lawrence Livermore National Lab., CA (United States)

1996-05-01

418

Effect of fracture aperture variations on the dispersion of contaminants  

NASA Astrophysics Data System (ADS)

Dispersion of dissolved contaminants in fractured rocks is strongly dependent on the variability of fracture aperture. Large fracture aperture regions result in significant channeling of the fluid flow, accelerating the movement of solutes in a particular direction, which may differ locally with respect to the main flow direction from high to low hydraulic potential. This may result in very early breakthrough of the contaminants, significantly earlier than in the conventional "parallel plate" simplification of fluid flow in fractured systems. In addition, flow and transport in the low aperture regions can be orders of magnitude smaller, which has major implications for remediating contaminated fractured media. In this study we observed the transport of a nonsorbing solute in a naturally fractured rock which was characterized at very high resolution using computed tomography scanning to determine the fracture aperture distribution. We compared the observed breakthrough curve of the solute at various flow rates with the predicted breakthrough curve using the fracture's geostatistics and small perturbation analysis, as well as direct numerical simulation of flow through the fracture using the measured fracture aperture distribution. The experimentally determined fracture transmissivity and dispersivity are within a factor of 2 of those predicted using either the small perturbation approach (using the fracture geostatistics) or explicit numerical modeling of breakthrough, which differ by around 20%, indicating that the geostatistics of the fracture aperture can be used to predict the approximate shape of the breakthrough curve for a fracture.

Keller, Arturo A.; Roberts, Paul V.; Blunt, Martin J.

1999-01-01

419

On-axis parallel ion speeds near mechanical and magnetic apertures in a helicon plasma device  

SciTech Connect

Using laser-induced fluorescence, measurements of parallel ion velocities were made along the axis of a helicon-generated Ar plasma column whose radius was modified by spatially separated mechanical and magnetic apertures. Ion acceleration to supersonic speeds was observed 0.1-5 cm downstream of both aperture types, simultaneously generating two steady-state double layers (DLs) when both apertures were in place. The DL downstream of the mechanical aperture plate had a larger potential drop, {delta}{phi}{sub DL}=6-9 kT{sub e}, compared to the DL downstream of the magnetic aperture, {delta}{phi}{sub DL}{approx}3 kT{sub e}. In the presheath region upstream of the mechanical aperture, the convective ion speed increased over a collisional distance; from stagnant at 4 cm from the aperture to the 1.4 times the sound speed at the aperture. The dependence of the free- and trapped-ion-velocity-distribution functions on the magnetic-field strength and mechanical-aperture electrical bias are also presented.

Sun Xuan; Cohen, S.A.; Scime, Earl E.; Miah, Mahmood [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2005-10-01

420

Composite field approximations for ion traps with apertures on electrodes  

NASA Astrophysics Data System (ADS)

This paper presents two approximate analytical expressions for nonlinear electric fields in the principal direction in axially symmetric (3D) and two dimensional (2D) ion trap mass analysers with apertures (holes in case of 3D traps and slits in case of 2D traps) on the electrodes. Considered together (3D and 2D), we present composite approximations for the principal unidirectional nonlinear electric fields in these ion traps. The composite electric field E has the formE=Enoaperture+Eaperture,where Enoaperture is the field within an imagined trap which is identical to the practical trap except that the apertures are missing and Eaperture is the field contribution due to apertures on the two trap electrodes. The field along the principal axis of the trap can in this way be well approximated for any aperture that is not too large. To derive Eaperture, classical results of electrostatics have been extended to electrodes with finite thickness and different aperture shapes. Enoaperture is a modified truncated multipole expansion for the imagined trap with no aperture. The first several terms in the multipole expansion are in principle exact (though numerically determined using the BEM), while the last term is chosen to match the field at the electrode. This expansion, once computed, works with any aperture in the practical trap. The composite field approximation for axially symmetric (3D) traps is checked for three geometries: the Paul trap, the cylindrical ion trap (CIT) and an arbitrary other trap. The approximation for 2D traps is verified using two geometries: the linear ion trap (LIT) and the rectilinear ion trap (RIT). In each case, for two aperture sizes (10% and 50% of the trap dimension), highly satisfactory fits are obtained. These composite approximations may be used in more detailed nonlinear ion dynamics studies than have been hitherto attempted.

Chattopadhyay, Madhurima; Verma, Neeraj Kumar; Mohanty, Atanu K.

2009-05-01

421

Slab-coupled 1.3-?m semiconductor laser with single-spatial large-diameter mode  

Microsoft Academic Search

A high brightness semiconductor diode laser structure, which utilizes a slab-coupled optical waveguide region to achieve several potentially important advances in performance, is proposed and experimentally demonstrated using a simple rib waveguide in an InGaAsP-InP quantum-well structure operating at 1.3-?m wavelength. These lasers operate in a large low-aspect-ratio lowest-order spatial mode, which can be butt coupled to a single-mode fiber

J. N. Walpole; J. P. Donnelly; P. J. Taylor; L. J. Missaggia; C. T. Harris; R. J. Bailey; A. Napoleone; S. H. Groves; S. R. Chinn; R. Huang; J. Plant

2002-01-01

422

Wafer-scale laser lithography. I. Pyrolytic deposition of metal microstructures. [For ultra-large scale integrated circuits  

SciTech Connect

Mechanisms for laser-driven pyrolytic deposition of micron-scale metal structures on crystalline silicon have been studied. Models have been developed to predict temporal and spatial propeties of laser-induced pyrolytic deposition processes. An argon ion laser-based apparatus has been used to deposit metal by pyrolytic decomposition of metal alkyl and carbonyl compounds, in order to evaluate the models. These results of these studies are discussed, along with their implications for the high-speed creation of micron-scale metal structures in ultra-large scale integrated circuit systems. 4 figures.

Herman, I.P.; Hyde, R.A.; McWilliams, B.M.; Weisberg, A.H.; Wood, L.L.

1982-01-01

423

Initiation, Growth and Mitigation of UV Laser Induced Damage in Fused Silica  

SciTech Connect

Laser damage of large fused silica optics initiates at imperfections. Possible initiation mechanisms are considered. We demonstrate that a model based on nanoparticle explosions is consistent with the observed initiation craters. Possible mechanisms for growth upon subsequent laser irradiation, including material modification and laser intensification, are discussed. Large aperture experiments indicate an exponential increase in damage size with number of laser shots. Physical processes associated with this growth and a qualitative explanation of self-accelerated growth is presented. Rapid growth necessitates damage growth mitigation techniques. Several possible mitigation techniques are mentioned, with special emphasis on CO{sub 2} processing. Analysis of material evaporation, crack healing, and thermally induced stress are presented.

Rubenchik, A M; Feit, M D

2001-12-21

424

Collimating diode laser beams from a large-area VCSEL-array using microlens array  

SciTech Connect

In this letter, the authors demonstrate the fabrication and bonding of a 1 cm {times} 1 cm monolithic two-dimensional (2-D) vertical-cavity surface-emitting laser (VCSEL) array. They coupled the array to a matched microlens array to individually collimate light from each laser. They found the beam divergence of the collimated array to be 1.6{degree} (1/e{sup 2}) for the entire array. Using a 1-cm diameter F2 lens, they were able to focus the collimated beams to a spot of 400 {micro}m in diameter and to couple more than 75% of the array power into a 1-mm core fiber. The results show that it is possible to uniformly bond large area VCSEL arrays to heat sinks, and to collimate light from each element into parallel beams using a single 2-D microlens array. The results also show that the brightness of the focused beam can be further increased with a lens to near 10{sup 5}-W/cm{sup 2} Steradian, a level that is useful for many high-power applications.

Chen, H.L. [Lawrence Livermore National Lab., CA (United States); Francis, D.; Nguyen, T.; Yuen, W.; Li, G.; Chang-Hasnain, C. [Univ. of California, Berkeley, CA (United States)

1999-05-01

425

Development and utilization of a laser velocimeter system for a large transonic wind tunnel  

NASA Astrophysics Data System (ADS)

The need for measurements of the velocity flow field about spinner propeller nacelle configurations at Mach numbers to 0.8 was met by a specially developed laser velocimeter system. This system, which uses an argon ion laser and 4 beam 2 color optics, was required to operate in the hostile environment associated with the operation of a large transonic wind tunnel. To overcome the conditions present in locating the sensitive optics in close proximity to the wind tunnel, an isolation system was developed. The system protects the velocimeter from the high vibrations, elevated temperatures, destructive acoustic pressures and low atmospheric pressures attendant with the operation of the wind tunnel. The system was utilized to map the flow field in front of, behind and in between the rotating blades of an advanced swept blade propeller model at a Mach number of 0.8. The data collected by the system will be used to correlate and verify computer analyses of propeller nacelle flow fields and propeller performance.

Freedman, R. J.; Greissing, J. P.

1982-06-01

426

Large eddy simulation and laser diagnostic studies on a low swirl stratified premixed flame  

SciTech Connect

This paper presents numerical simulations and laser diagnostic experiments of a swirling lean premixed methane/air flame with an aim to compare different Large Eddy Simulations (LES) models for reactive flows. An atmospheric-pressure laboratory swirl burner has been developed wherein lean premixed methane/air is injected in an unconfined low-speed flow of air. The flame is stabilized above the burner rim in a moderate swirl flow, triggering weak vortex breakdown in the downstream direction. Both stereoscopic (3-component) PIV and 2-component PIV are used to investigate the flow. Filtered Rayleigh scattering is used to examine the temperature field in the leading flame front. Acetone-Planar Laser Induced Fluorescence (PLIF) is applied to examine the fuel distribution. The experimental data are used to assess two different LES models; one based on level-set G-equation and flamelet chemistry, and the other based on finite rate chemistry with reduced kinetics. The two LES models treat the chemistry differently, which results in different predictions of the flame dynamic behavior and statistics. Yet, great similarity of flame structures was predicted by both models. The LES and experimental data reveal several intrinsic features of the low swirl flame such as the W-shape at the leading front, the highly wrinkled fronts in the shear layers, and the existence of extinction holes in the trailing edge of the flame. The effect of combustion models, the numerical solvers and boundary conditions on the flame and flow predictions was systematically examined. (author)

Nogenmyr, K.-J.; Bai, X.S. [Department of Energy Sciences, Lund Institute of Technology, Box 118, 22100 Lund (Sweden); Fureby, C. [Division of Weapons and Protection, The Swedish Defense Research Agency - FOI, Stockholm (Sweden); Petersson, P.; Collin, R.; Linne, M. [Department of Combustion Physics, Lund Institute of Technology, Lund (Sweden)

2008-11-15

427

Large eddy simulation and laser diagnostic studies on a low swirl stratified premixed flame  

SciTech Connect

This paper presents numerical simulations and laser diagnostic experiments of a swirling lean premixed methane/air flame with an aim to compare different Large Eddy Simulations (LES) models for reactive flows. An atmospheric-pressure laboratory swirl burner has been developed wherein lean premixed methane/air is injected in an unconfined low-speed flow of air. The flame is stabilized above the burner rim in a moderate swirl flow, triggering weak vortex breakdown in the downstream direction. Both stereoscopic (3-component) PIV and 2-component PIV are used to investigate the flow. Filtered Rayleigh scattering is used to examine the temperature field in the leading flame front. Acetone-Planar Laser Induced Fluorescence (PLIF) is applied to examine the fuel distribution. The experimental data are used to assess two different LES models; one based on level-set G-equation and flamelet chemistry, and the other based on finite rate chemistry with reduced kinetics. The two LES models treat the chemistry differently, which results in different predictions of the flame dynamic behavior and statistics. Yet, great similarity of flame structures was predicted by both models. The LES and experimental data reveal several intrinsic features of the low swirl flame such as the W-shape at the leading front, the highly wrinkled fronts in the shear layers, and the existence of extinction holes in the trailing edge of the flame. The effect of combustion models, the numerical solvers and boundary conditions on the flame and flow predictions was systematically examined. (author)

Nogenmyr, K.-J.; Bai, X.S. [Department of Energy Sciences, Lund Institute of Technology, Box 118, 22100 Lund (Sweden); Fureby, C. [Division of Weapons and Protection, Swedish Defense Research Agency Y FOI, Stockholm (Sweden); Petersson, P.; Collin, R.; Linne, M. [Department of Combustion Physics, Lund Institute of Technology, Lund (Sweden)

2009-01-15

428

Melt dynamics of aluminum irradiated with ultrafast laser radiation at large intensities  

SciTech Connect

Ablation of bulk aluminum has been investigated in situ using ultrafast laser radiation produced by chirped-pulse amplification technique (t{sub p}=80 fs, lambda=800 nm). Melt dynamics and the contribution of the amplified spontaneous emission (ASE) to the ablation have been studied experimentally and numerically for laser fluences well above ablation threshold (F < or approx. 10{sup 3}xF{sub thr}). Using transient quantitative phase microscopy (TQPm), dimensions and volume of ejected vapor, melt droplets, and liquid jets has been investigated. Computational analysis of the optical phase images has been used to determine the total volume of ejected material. A series of time-resolved phase images of vaporized material and/or melt, which are induced by n=1.8 pulses on an aluminum target, are obtained by means of TQPm up to temporal delay tau=1.65 mus after irradiation. Increase in material ejection rate is observed at delays tauapprox =300 ns and tauapprox =1.1 mus after the incident pulse. For large irradiation intensities a considerable contribution of ASE to ablation dynamics has been detected. Ex situ measurements of the ablated material by means of white-light interferometry and scanning electron microscopy provides corresponding factual removed volumes and highlight the pulse-to-pulse morphology changes.

Mingareev, Ilya [Lehrstuhl fuer Lasertechnik, RWTH Aachen University, 52074 Aachen (Germany); Horn, Alexander [Institute of Physics and Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel, 34132 Kassel (Germany)

2009-07-01

429

Melt dynamics of aluminum irradiated with ultrafast laser radiation at large intensities  

NASA Astrophysics Data System (ADS)

Ablation of bulk aluminum has been investigated in situ using ultrafast laser radiation produced by chirped-pulse amplification technique (tp=80 fs, ?=800 nm). Melt dynamics and the contribution of the amplified spontaneous emission (ASE) to the ablation have been studied experimentally and numerically for laser fluences well above ablation threshold (F<~103×Fthr). Using transient quantitative phase microscopy (TQPm), dimensions and volume of ejected vapor, melt droplets, and liquid jets has been investigated. Computational analysis of the optical phase images has been used to determine the total volume of ejected material. A series of time-resolved phase images of vaporized material and/or melt, which are induced by n=1..8 pulses on an aluminum target, are obtained by means of TQPm up to temporal delay ?=1.65 ?s after irradiation. Increase in material ejection rate is observed at delays ?~300 ns and ?~1.1 ?s after the incident pulse. For large irradiation intensities a considerable contribution of ASE to ablation dynamics has been detected. Ex situ measurements of the ablated material by means of white-light interferometry and scanning electron microscopy provides corresponding factual removed volumes and highlight the pulse-to-pulse morphology changes.

Mingareev, Ilya; Horn, Alexander

2009-07-01

430

Eigenmode confinement in the dielectrically apertured Fabry-Perot microcavity [VCSEL  

Microsoft Academic Search

The three-dimensional (3-D) optical confinement of the dielectrically apertured Fabry-Perot microcavity is analyzed by considering electromagnetic coupling between the confined region and parasitic waveguide modes that exist outside the aperture. If the cavity length is close to one-half the emission wavelength and for large enough aperture sizes, all parasitic waveguide modes can be evanescent except one which couples only weakly

D. G. Deppe; T.-H. Oh; D. L. Huffaker

1997-01-01

431

Mosaic of coded aperture arrays  

DOEpatents

The present invention pertains to a mosaic of coded aperture arrays which is capable of imaging off-axis sources with minimum detector size. Mosaics of the basic array pattern create a circular on periodic correlation of the object on a section of the picture plane. This section consists of elements of the central basic pattern as w