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1

Adaptive optics for large aperture coherent laser radars  

Microsoft Academic Search

When the aperture size of a coherent laser radar is much larger than the turbulence coherence length, the radar's performance is significantly degraded by turbulence-induced beam distortions. This paper addresses the correction of turbulence effects on such large aperture radars by means of adaptive optics. The radar system model is of a ground-based monostatic radar doing angle-angle imaging of a

Naomi E. Zirkind; Jeffrey H. Shapiro

1989-01-01

2

The role of the solvent viscosity on the spatiotemporal instabilities of large aperture dye lasers  

E-print Network

The role of the solvent viscosity on the spatiotemporal instabilities of large aperture dye lasers for publication 27 May 1998 Local intensity fluctuations in a large aperture dye laser have been measured behavior as the molecular polarization orientation driven by the laser field. © 1998 American Institute

Rey Juan Carlos, Universidad

3

Off-axis multipass amplifier as a large aperture driver stage for fusion lasers  

Microsoft Academic Search

A multipass amplifier configuration is described which has potential as a large aperture, high gain driver stage for fusion laser systems. We avoid the present limitations of large aperture switches by using an off-angle geometry that does not require an optical switch. The saturated gain characteristics of this multipass amplifier are optimized numerically. Three potential problems are investigated experimentally, self-lasing,

J. E. Murray; D. C. Downs; J. T. Hunt; G. L. Hermes; W. E. Warren

1981-01-01

4

The role of the molecular dynamics in the local intensity instabilities of large aperture dye lasers  

E-print Network

lasers I. Leyvaa) and J. M. Guerra Departamento de O´ ptica, Facultad de Ciencias Fi´sicas Universidad fluctuations of large aperture dye lasers, and find dependencies on solvent viscosity and active molecular size dye lasers are used in a great deal of practical applications, from isotope enrichment to photody

Rey Juan Carlos, Universidad

5

Performance results for Beamlet: A large aperture multipass Nd glass laser  

SciTech Connect

The Beamlet laser is a large aperture, flashlamp pumped Nd: glass laser that is a scientific prototype of an advanced Inertial Fusion laser. Beamlet has achieved third harmonic, conversion efficiency of near 80% with its nominal 35cm {times} 35cm square beam at mean 3{omega} fluences in excess of 8 J/cm{sup 2}(3-ns). Beamlet uses an adaptive optics system to correct for aberrations and achieve less than 2 {times} diffraction limited far field spot size.

Campbell, J.H.; Barker, C.E.; VanWonterghem, B.M.; Speck, D.R.; Behrendt, W.C.; Murray, J.R.; Caird, J.A.; Decker, D.E.; Smith, I.C.

1995-04-11

6

Fabrication of large-aperture random phase plate for uniform illumination on laser fusion target  

NASA Astrophysics Data System (ADS)

We have fabricated a large aperture random phase plate (RPP) in Chinese K9 glass substrate for target-plane laser beam smoothing at 1.06 micrometer wavelength, by using large aperture photolithography and dilute HF etching processes. The RPP's clear aperture is (phi) 250 mm. The measured average step height is 1.060 micrometer, which has a relative standard deviation of 1.24% at 5 locations on the RPP to the theoretical value. A focal spot with very sharp edges and nearly flat-top overall envelope intensity distribution is obtained at the focal-plane of a focusing lens. These results show that our fabrication techniques for RPP is effective, and is easily scaleable to even larger apertures.

Huang, Huijie; Lu, Dunwu; Wang, Runwen; Zhao, Yongkai; Liu, Zengshui

2000-04-01

7

Off-axis multipass amplifier as a large aperture driver stage for fusion lasers.  

PubMed

A multipass amplifier configuration is described which has potential as a large aperture, high gain driver stage for fusion laser systems. We avoid the present limitations of large aperture switches by using an off-angle geometry that does not require an optical switch. The saturated gain characteristics of this multipass amplifier are optimized numerically. Three potential problems are investigated experimentally, self-lasing, output beam quality, and amplified spontaneous emission output. The results indicate comparable cost for comparable performance to a linear chain, with some operational advantage for the multipass driver stage. PMID:20309212

Murray, J E; Downs, D C; Hunt, J T; Hermes, G L; Warren, W E

1981-03-01

8

Novel large aperture EBCCD  

NASA Astrophysics Data System (ADS)

A novel large aperture electron bombardment charge coupled device (EBCCD) has been developed. The diameter of its photocathode is 10 cm and it is the first EBCCD with such a large aperture. Its gain shows good linearity as a function of applied voltage up to -12 kV, where the gain is 2400. The spatial resolution was measured using ladder pattern charts. It is better than 2 line pairs/mm, which corresponds to 3.5 times the CCD pixel size. The spatial resolution was also measured with a copper foil pattern on a fluorescent screen irradiated with X-rays (14 and 18 keV) and a 60 keV gamma-ray from an americium source. The result was consistent with the measurement using ladder pattern charts. The output signal as a function of input light intensity shows better linearity than that of image intensifier tubes (IIT) as expected. We could detect cosmic rays passing through a scintillating fiber block and a plastic scintillator as a demonstration for a practical use in particle physics experiments. This kind of large aperture EBCCD can, for example, be used as an image sensor for a detector with a large number of readout channels and is expected to be additionally applied to other physics experiments.

Suzuki, Atsumu; Aoki, Shigeki; Haba, Junji; Sakuda, Makoto; Suyama, Motohiro

2011-02-01

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

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

Microsoft Academic Search

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

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

2006-01-01

12

MRF applications: on the road to making large-aperture ultraviolet laser resistant continuous phase plates for high-power lasers  

Microsoft Academic Search

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

Joseph A. Menapace; Pete J. Davis; William A. Steele; M. Roman Hachkowski; Andrew Nelson; Kai Xin

2007-01-01

13

MRF applications: on the road to making large-aperture ultraviolet laser resistant continuous phase plates for high-power lasers  

NASA Astrophysics Data System (ADS)

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 microns. 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, Joseph A.; Davis, Pete J.; Steele, William A.; Hachkowski, M. Roman; Nelson, Andrew; Xin, Kai

2007-01-01

14

Suppression of transverse stimulated Raman scattering with laser-induced damage array in a large-aperture potassium dihydrogen phosphate crystal.  

PubMed

A laser-induced damage array composed of numerous pinpoints is generated in a large-aperture KDP crystal to suppress the transverse stimulated Raman scattering (TSRS). The 36 cm 8.5 mm 7 mm damage array is used to block the propagation of the TSRS photons within the crystal and decrease the TSRS gain length. Then several series of experiments were conducted on a large-aperture laser system to test this method and experimental results show that the amplification of TSRS is significantly suppressed by the laser-induced damage array. PMID:24514625

Han, Wei; Wang, Fang; Zhou, Lidan; Li, Fuquan; Feng, Bin; Cao, Huabao; Zhao, Junpu; Li, Sheng; Zheng, Kuixing; Wei, Xiaofeng; Gong, Mali; Zheng, Wanguo

2013-12-16

15

A flat laser array aperture  

NASA Astrophysics Data System (ADS)

We describe a design concept for a flat (or conformal) thin-plate laser phased-array aperture. The aperture consists of a substrate supporting a grid of single-mode optical waveguides fabricated from a linear electro-optic material. The waveguides are coupled to a single laser source or detector. An arrangement of electrodes provides for two-dimensional beam steering by controlling the phase of the light entering the grid. The electrodes can also be modulated to simultaneously provide atmospheric turbulence modulation for long-range free-space optical communication. An approach for fabrication is also outlined.

Papadakis, Stergios J.; Ricciardi, Gerald F.; Gross, Michael C.; Krill, Jerry A.

2010-04-01

16

Large aperture kinoform phase plates in fused silica for spatial beam smoothing on Nova and the Beamlet Lasers  

SciTech Connect

It is now widely recognized that spatial beam smoothing (homogenization) is essential in coupling the laser energy to the inertial confinement fusion (ICF) targets. For the indirect drive approach to ICF, it is desirable to distribute the laser energy into a uniformly speckled profile that has a flat-top super-Gaussian envelope (8th power or higher) and contains greater than 95% of the energy inside the super-Gaussian profile. Spatial smoothing is easily achieved by introducing a binary random phase plate (RPP) in the beam. This produces a homogenized far-field pattern which consists of an overall envelope function determined by the RPP element superimposed with a fine scale speckle pattern arising due to the interference among the various RPP elements. Although easy to fabricate and currently in routine use in many fusion laboratories, the binary RPPs do not meet the ICF requirements stated above since the far-field intensity profile is restricted to essentially an Airy function containing only 84% (an upper limit) of the energy inside the central spot. Approaches using lenslet arrays (refractive or diffractive) have limited use since they operate in the quasi-far-field and have a short depth of focus. The limitations of the RPPs can be overcome by relaxing the binary phase constraint. We have recently presented 5 continuously varying phase screens for tailoring the focal plane irradiance profiles. Called kinoform phase plates (KPPs), these phase screens offer complete flexibility in tailoring the focal plane envelope and, at the same time, increasing the energy efficiency inside the focal spot. In this paper we discuss the design and fabrication of such kinoform phase plates in fused silica for spatial beam smoothing on the Nova and the Beamlet lasers. Since the phase plates are used at the end of the laser chain, KPPs on Nova and Beamlet have to be fabricated on large aperture optics (65-cm diameter and 40-cm square substrates respectively). The following section presents a brief review of process for designing the KPPs. In section 3, we discuss the fabrication of large aperture KPPs in fused silica substrates. The optical performance of these KPPs is discussed in section 4 which is followed by a summary.

Rushford, M.C.; Dixit, S.N.; Thomas, I.M.; Martin, A.M.; Perry, M.D.

1997-03-01

17

Combined phase, near field, and far field diagnostic for large-aperture laser systems  

NASA Astrophysics Data System (ADS)

A method is described for extracting near field, far field and phase information from an interferogram of a laser system output generated by a self referencing, radial shear interferometer. The interferogram may be used as an amplitude mask of a coherent beam. This beam is numerically propagated to the far field where the laser output and its complex conjugate can be separated. The near field and optical phase difference map may then be extracted from the complex representation of the laser output obtained by propagating back to the near field. The practical application of this method and its limitations are discussed and compared with images from equivalent plane far field and near field cameras on the HELEN 2TW Nd:glass laser system.

Barnes, Andrew R.; Smith, I. C.

1999-07-01

18

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

19

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

20

the Large Aperture GRB Observatory  

SciTech Connect

The Large Aperture GRB Observatory (LAGO) aims at the detection of high energy photons from Gamma Ray Bursts (GRB) using the single particle technique (SPT) in ground based water Cherenkov detectors (WCD). To reach a reasonable sensitivity, high altitude mountain sites have been selected in Mexico (Sierra Negra, 4550 m a.s.l.), Bolivia (Chacaltaya, 5300 m a.s.l.) and Venezuela (Merida, 4765 m a.s.l.). We report on the project progresses and the first operation at high altitude, search for bursts in 6 months of preliminary data, as well as search for signal at ground level when satellites report a burst.

Bertou, Xavier [Centro Atomico Bariloche (Argentina)

2009-04-30

21

Large-aperture approximation for not-so-large apertures  

NASA Astrophysics Data System (ADS)

In-flight wavefront measurements around a flat-window turret at subsonic Mach numbers are analyzed in instantaneous and time-averaged sense. In addition to the root-mean-squared levels of aero-optical distortions, higher-order spatial statistics are calculated, and their dependence as a function of the viewing angle is discussed. Given the optical data obtained, the applicability of the commonly used large aperture approximation (LAA) is revisited. We show that, for all angles, the LAA consistently underestimates the time-averaged Strehl ratio, so the LAA should be used very cautiously. Some reasons for these discrepancies are traced to non-Gaussian spatial distribution of the optical wavefronts. A different approximation for computing time-averaged Strehl ratios is proposed, and the results are discussed.

Porter, Chris; Gordeyev, Stanislav; Jumper, Eric

2013-07-01

22

Apodizing induced-absorption apertures with a large optical beam diameter and their application in high-power 1. 06. mu. laser systems  

SciTech Connect

Soft apodizing apertures were developed and investigated. They were based on the absorption induced in CaF/sub 2/:Pr by ionizing radiation and their diameters were 2--5 cm. The transmission profiles of the apertures were determined at the wavelength of 1.06 ..mu... The optical quality of the apertures was determined, measurements were made of the damage thresholds and their use in high-power laser systems was studied. The damage threshold of CaF/sub 2/:Pr apertures in focused laser beams was higher than the damage thresholds of laser glasses and these apertures did not bleach right up to the damage threshold. An increase in the efficiency of conversion to the second harmonic was observed when a soft aperture was placed in a laser beam.

Gorshkov, B.G.; Ivanchenko, V.K.; Karpovich, V.K.; Krasyuk, I.K.; Lukishova, S.G.; Margolin, D.M.; Pashinin, P.P.; Simun, E.A.; Sokolov, V.A.; Terekhov, V.D.

1985-07-01

23

Performance of a prototype for a large-aperture multipass Nd:glass laser for inertial confinement fusion  

SciTech Connect

The Beamlet is a single-beam prototype of future multibeam megajoule-class Nd:glass laser drivers for inertial confinement fusion. It uses a multipass main amplifier, adaptive optics, and efficient, high-fluence frequency conversion to the third harmonic. The Beamlet amplifier contains Brewster-angle glass slabs with a clear aperture of 39 cm{times}39 cm and a full-aperture plasma-electrode Pockels cell switch. It has been successfully tested over a range of pulse lengths from 1{endash}10 ns up to energies at 1.053 {mu}m of 5.8 kJ at 1 ns and 17.3 kJ at 10 ns. A 39-actuator deformable mirror corrects the beam quality to a Strehl ratio of as much as 0.4. The 1.053-{mu}m output has been converted to the third harmonic at efficiencies as high as 80{percent} and fluences as high as 8.7 J/cm{sup 2} for 3-ns pulses. {copyright} 1997 Optical Society of America

Van Wonterghem, B.M.; Murray, J.R.; Campbell, J.H.; Speck, D.R.; Barker, C.E.; Smith, I.C.; Browning, D.F.; Behrendt, W.C. [Lawrence Livermore National Laboratory, University of California, P. O. Box 808, Livermore, California 94551 (United States)

1997-07-01

24

Eyeglass. 1. Very large aperture diffractive telescopes  

Microsoft Academic Search

The Eyeglass is a very large aperture (25100-m) space telescope consisting of two distinct spacecraft, separated in space by several kilometers. A diffractive lens provides the telescope{close_quote}s large aperture, and a separate, much smaller, space telescope serves as its mobile eyepiece. Use of a transmissive diffractive lens solves two basic problems associated with very large aperture space telescopes; it is

Roderick A. Hyde

1999-01-01

25

Finite-aperture tapered unstable resonator lasers  

NASA Astrophysics Data System (ADS)

The development of high power, high brightness semiconductor lasers is important for applications such as efficient pumping of fiber amplifiers and free space communication. The ability to couple directly into the core of a single-mode fiber can vastly increase the absorption of pump light. Further, the high mode-selectivity provided by unstable resonators accommodates single-mode operation to many times the threshold current level. The objective of this dissertation is to investigate a more efficient semiconductor-based unstable resonator design. The tapered unstable resonator laser consists of a single-mode ridge coupled to a tapered gain region. The ridge, aided by spoiling grooves, provides essential preparation of the fundamental mode, while the taper provides significant amplification and a large output mode. It is shown a laterally finite taper-side mirror (making the laser a "finite-aperture tapered unstable resonator laser") serves to significantly improve differential quantum efficiency. This results in the possibility for higher optical powers while still maintaining single-mode operation. Additionally, the advent of a detuned second order grating allows for a low divergent, quasicircular output beam emitted from the semiconductor surface, easing packaging tolerances, and making two dimensional integrated arrays possible. In this dissertation, theory, design, fabrication, and characterization are presented. Material theory is introduced, reviewing gain, carrier, and temperature effects on field propagation. Coupled-mode and coupled wave theory is reviewed to allow simulation of the passive grating. A numerical model is used to investigate laser design and optimization, and effects of finite-apertures are explored. A microfabrication method is introduced to create the FATURL in InAlGaAs/-InGaAsP/InP material emitting at about 1410 nm. Fabrication consists of photolithography, electron-beam lithography, wet etch and dry etching processes, metal and dielectric electron-beam evaporation, and rapid-thermal annealing. FATURLs are compared to infinite aperture TURLs, and show significant improvements in differential quantum efficiency (more than 40%) under pulsed-current operation. Far-field measurements show diffraction-limited divergence up to at least 2.3 x Ith, and spectral characteristics show good control over the longitudinal mode spectrum. Finally, several modifications to the laser design and fabrication are presented to improve laser performance.

Bedford, Robert George

26

Progress toward large-aperture membrane mirrors  

Microsoft Academic Search

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

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

2000-01-01

27

Intracavity frequency doubling in a wide-aperture argon laser  

SciTech Connect

The four-mirror cavity with a BBO crystal for frequency doubling in a wide-aperture argon laser is optimised. The dependences of the second-harmonic power on the displacement of a focusing mirror, the displacement of the crystal, and the discharge current are measured. These dependences are in good agreement with calculations. After optimisation, {approx}1 W of UV laser radiation at 244 nm was obtained with the conversion efficiency twice as large as that for the known similar lasers. It is shown that the increase in the efficiency was achieved mainly due to the increase in the discharge-tube aperture. (nonlinear optical phenomena)

Abdullina, S R; Babin, S A; Vlasov, Aleksandr A; Kablukov, S I [Institute of Automation and Electrometry, Siberian Branch, Russian Academy of Sciences, Novosibirsk (Russian Federation)

2005-09-30

28

Large-aperture telescopic laser system with phase-conjugation compensation of distortions of a segmented main mirror  

Microsoft Academic Search

A telescopic laser system with phase-conjugation compensation of distortions of a segmented main mirror (diameter 30 cm, focal length 1.2 m) was constructed. Experimental results agreed with numerical modeling and demonstrated the feasibility of forming a diffraction-quality image when the segments of the main mirror were tilted at angles up to 1.5 10 ? 4 rad and longitudinal displacements

Michail V Vasilev; Vladimir Yu Venediktov; Alexey A Leshchev; P M Semenov; V G Sidorovich; O V Solodyankin

1991-01-01

29

BRIEF COMMUNICATIONS: Wide-aperture source of x-ray radiation for preionization of the large-volume electric-discharge lasers  

Microsoft Academic Search

A high-voltage diffuse discharge at atmospheric pressure in a system formed by a row of thin wires and a planar grid was found to be a highly efficient source of x-ray radiation. The aperture of this source was 40 200 cm and the dose delivered to the active medium of an electric-discharge CO2 laser with the volume up to

S. N. Buranov; V. V. Gorokhov; V. I. Karelin; A. I. Pavlovskii; P. B. Repin

1991-01-01

30

Eyeglass: A Very Large Aperture Diffractive Space Telescope  

Microsoft Academic Search

Eyeglass is a very large aperture (25 - 100 meter) space telescope consisting of two distinct spacecraft, separated in space by several kilometers. A diffractive lens provides the telescope's large aperture, and a separate, much smaller, space telescope serves as its mobile eyepiece. Use of a transmissive diffractive lens solves two basic problems associated with very large aperture space telescopes;

Roderick A. Hyde; Shamasundar N. Dixit; Andrew H. Weisberg; Michael C. Rushford

2002-01-01

31

Computer simulation of a multiple-aperture coherent laser radar  

Microsoft Academic Search

This paper presents the construction of a 2D multiple aperture coherent laser radar simulation that is capable of including the effects of the time evolution of speckle on the laser radar output. Every portion of a laser radar system is modeled in software, including quarter and half wave plates, beamsplitters (polarizing and non-polarizing), the detector, the laser source, and all

Kevin J. Gamble

1996-01-01

32

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

NASA Astrophysics Data System (ADS)

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 have windows approaching twenty inches in diameter. These sensor windows typically operate in hostile environments including very high pressure differentials, large thermal gradients, and severe rain and sand abrasion. EMI/EMC protection and de-icing capabilities are also commonly required. For airborne applications and to minimize thermal gradients, thinner, lightweight, high strength windows are also necessary. Sapphire is an ideal window material to satisfy these requirements due to its high strength, UV-MWIR bandpass, minimal optical scatter, excellent index of refraction homogeneity and very high scratch/impact resistance. Associated optical fabrication, grid lithography and optical coating processes have been developed at Hughes Danbury for sapphire windows. This paper addresses the development of a family of large aperture, broadband sapphire windows which also provide EMI/EMC protection and de-icing capabilities. The resulting design configuration and performance characteristics are also addressed. Future technology development requirements are also discussed.

Askinazi, Joel

1997-06-01

33

TECHNOLOGY DEVELOPMENT PROJECT PLAN Advanced Technology Large Aperture Space Telescope  

E-print Network

TECHNOLOGY DEVELOPMENT PROJECT PLAN for the Advanced Technology Large Aperture Space Telescope, and Ronald Polidan. #12;Advanced Technology Large-Aperture Space Telescope (ATLAST) 22 TABLE OF CONTENTS 1 (ATLAST) A Roadmap for UVIOR Technology, 2010-2020 24 April, 2009 T. Tupper Hyde, ATLAST Technologist

Sirianni, Marco

34

Mode-volume enhancement in an apertured laser  

NASA Astrophysics Data System (ADS)

In a laser TEM00-mode selection by the use of a hard intracavity aperture gives rise to losses that are experimentally observable and to an increase in the fundamental-mode volume that is more difficult to observe. We use the parasitic resonances that are characteristic of multicavity lasers to demonstrate this volume enhancement in a He-Ne laser operating at 3.39 (mu)m. The increase in mode volume in the apertured laser can increase the output power by a factor of 3 with respect to that of the nonapertured laser.

Ait-Ameur, K.; Stphan, G.

1995-11-01

35

2D angular synthetic aperture laser optical feedback imaging  

Microsoft Academic Search

For synthetic aperture (SA) operation in the optical domain, microchip laser sources seem to be relevant by reasons of their compactness and their high temporal and spatial coherence (laser linewidth less than 1 kHz and laser beam divergence close to the diffraction limit). The main objective of this study is to combine the high resolution of SA experiment (i.e. beyond

E. Lacot; O. Hugon; O. Jacquin

2009-01-01

36

Study on the precision measurement of high-flux large aperture sampling grating  

NASA Astrophysics Data System (ADS)

This paper describes an effective method for the measurements of large aperture sampling grating, the sampling efficiency the sampling focal length and the sampling angle. By using a 351nm collimation laser source to scan the full aperture of the sampling grating in every subregion, the diffraction power of "0" order and "+1" order can be obtained synchronously by two standard integrating balls, And then by calculating the sampling efficiency of this subregion and splicing the acquisition data, we can get the averaged grating sampling efficiency in the full aperture.Based on this method, we can effectively eliminate the effect of the output instability of laser source, decrease the uncertainty of test results. According to the fabrication principle of the sampling grating, measurements for the sampling focal length and the sampling angle can be performed. Test rersults indicate that this method can be used to measure large aperture sampling gratings

Yuan, Haoyu; Chen, Yong-quan; Peng, Zhi-tao; Duan, Ya-xuan; Wu, Jianhong; Fu, Shaojun

2012-10-01

37

The design of a large aperture infrared optical system  

Microsoft Academic Search

The paper considers the optical design of a large aperture telescope for near infrared imaging onto a linear array of detectors. The design must satisfy a number of optical system variables which include aperture, obscuration, field of view, image quality, focal surface, color correction, system throughput, off-axis energy rejection, and maximum mirror dimension. The ring field infrared telescope design uses

R. R. Altenhof

1975-01-01

38

Large-Aperture Segmented Mirror Telescope Design Concept  

E-print Network

Large-Aperture Segmented Mirror Telescope Design Concept (Image courtesy of John Frassanito (ATLAS) Telescope: A Technology Roadmap for the Next Decade Principal Investigator: Dr. Marc Postman Telescope .......................................2 2 Science Objectives and Expected Impact of an ATLAS

Sirianni, Marco

39

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

Microsoft Academic Search

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

Stephen A. Hanes

2003-01-01

40

The balloon-borne large aperture submillimeter telescope (BLAST)  

Microsoft Academic Search

This thesis presents a description of the instrumentation and Galactic science from the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). BLAST was designed to conduct large area submillimeter surveys to constrain the star formation history of the high-redshift universe and to probe the earliest stages of star formation within our own galaxy. It operates on a balloon platform at an altitude

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

2007-01-01

41

Large diffractive/refractive apertures for space and airborne telescopes  

NASA Astrophysics Data System (ADS)

Recent work, specifically the Lawrence Livermore National Laboratory (LLNL) Eyeglass and the DARPA MOIRE programs, have evaluated lightweight, easily packaged and deployed, diffractive/refractive membrane transmissive lenses as entrance apertures for large space and airborne telescopes. This presentation describes a new, innovative approach to the theory of diffractive and refractive effects in lenses used as telescope entrance apertures and the fabrication of the necessary large membrane optics. Analyses are presented to indicate how a broadband, highly transmissive diffractive / refractive membrane lens can be developed and fabricated, and potential applications in defense and astronomy are briefly discussed.

MacEwen, Howard A.; Breckinridge, James B.

2013-05-01

42

Full-aperture, high-power semiconductor laser  

NASA Astrophysics Data System (ADS)

A single quantum well laser with a 2-mm-wide aperture has exhibited low threshold current density and nearly 100% packing fraction. The lateral structure relies on epitaxial growth on a corrugated substrate to frustrate radiative lateral processes and it thus eliminates the need for isolation at least for incoherent operation. Threshold current densities are comparable to those for low-power devices, and slope efficiencies remain undiminished to our current limit where 10.7 W per facet is attained. The aperture size is limited only by our fixturing arrangement.

Waters, R. G.; Dalby, R. J.; Emanuel, M. A.

1989-06-01

43

Polarimetric Calibration of Large-Aperture Telescopes II: The sub-aperture method  

E-print Network

A new method for absolute polarimetric calibration of large telescopes is presented. The proposed method is highly accurate and is based on the calibration of a small sub-aperture, which is then extended to the full system by means of actual observations of an astronomical source. The calibration procedure is described in detail along with numerical simulations that explore its robustness and accuracy. The advantages and disadvantages of this technique with respect to other possible alternatives are discussed.

H. Socas-Navarro

2004-10-23

44

Self-Referencing Hartmann Test for Large-Aperture Telescopes  

NASA Technical Reports Server (NTRS)

A method is proposed for end-to-end, full aperture testing of large-aperture telescopes using an innovative variation of a Hartmann mask. This technique is practical for telescopes with primary mirrors tens of meters in diameter and of any design. Furthermore, it is applicable to the entire optical band (near IR, visible, ultraviolet), relatively insensitive to environmental perturbations, and is suitable for ambient laboratory as well as thermal-vacuum environments. The only restriction is that the telescope optical axis must be parallel to the local gravity vector during testing. The standard Hartmann test utilizes an array of pencil beams that are cut out of a well-corrected wavefront using a mask. The pencil beam array is expanded to fill the full aperture of the telescope. The detector plane of the telescope is translated back and forth along the optical axis in the vicinity of the nominal focal plane, and the centroid of each pencil beam image is recorded. Standard analytical techniques are then used to reconstruct the telescope wavefront from the centroid data. The expansion of the array of pencil beams is usually accomplished by double passing the beams through the telescope under test. However, this requires a well-corrected, autocollimation flat, the diameter or which is approximately equal to that of the telescope aperture. Thus, the standard Hartmann method does not scale well because of the difficulty and expense of building and mounting a well-corrected, large aperture flat. The innovation in the testing method proposed here is to replace the large aperture, well-corrected, monolithic autocollimation flat with an array of small-aperture mirrors. In addition to eliminating the need for a large optic, the surface figure requirement for the small mirrors is relaxed compared to that required of the large autocollimation flat. The key point that allows this method to work is that the small mirrors need to operate as a monolithic flat only with regard to tip/tilt and not piston because in collimated space piston has no effect on the image centroids. The problem of aligning the small mirrors in tip/tilt requires a two-part solution. First, each mirror is suspended from a two-axis gimbal. The orientation of the gimbal is maintained by gravity. Second, the mirror is aligned such that the mirror normal is parallel to gravity vector. This is accomplished interferometrically in a test fixture. Of course, the test fixture itself needs to be calibrated with respect to gravity.

Korechoff, Robert P.; Oseas, Jeffrey M.

2010-01-01

45

Strong terahertz radiation from air plasmas generated by an aperture-limited Gaussian pump laser beam  

SciTech Connect

Terahertz radiation generated by focusing the fundamental laser pulse and its second harmonic into ambient air strongly saturates with increasing pump laser energy. We demonstrate a simple method to control the Gaussian pump laser beam to improve the output of terahertz radiation with an adjustable aperture. With the optimal aperture-limited pump laser beams, the terahertz wave amplitudes can be enhanced by more than eight times depending on the pump laser parameters than those of aperture-free cases.

Peng Xiaoyu; Toncian, Toma; Jung, Ralph; Willi, Oswald [Institut fuer Laser-und Plasmaphysik, Heinrich-Heine-Universitaet Duesseldorf, Duesseldorf, 40225 (Germany); Li Chun; Li Yutong; Wang Weimin; Wang Shoujun; Liu Feng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100080 (China); Chen Min; Pukhov, Alexander [Institut fuer Theoretische physik I, Heinrich-Heine-Universitaet Duesseldorf, Duesseldorf, 40225 (Germany); Sheng Zhengming; Zhang Jie [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100080 (China); Department of Physics, Shanghai Jiao Tong University, Shanghai, 200240 (China)

2009-03-09

46

The balloon-borne large aperture sub-millimeter telescope  

Microsoft Academic Search

The balloon-borne large aperture sub-millimeter telescope (BLAST) is a new instrument to study galaxies at high redshift and to help answer questions about our galaxy and star formation. BLAST will fly from a long duration balloon. The telescope design incorporates a 2-m primary mirror with large-format bolometer arrays operating at 250, 350 and 500 ?m with 149, 88 and 43

G. S. Tucker; P. A. R. Ade; J. J. Bock; M. Devlin; M. Griffin; J. Gundersen; M. Halpern; P. Hargrave; D. Hughes; J. Klein; P. Mauskopf; C. B. Netterfield; L. Olmi; D. Scott

2004-01-01

47

Mission definition for a large-aperture microwave radiometer spacecraft  

NASA Technical Reports Server (NTRS)

An Earth-observation measurements mission is defined for a large-aperture microwave radiometer spacecraft. This mission is defined without regard to any particular spacecraft design concept. Space data application needs, the measurement selection rationale, and broad spacecraft design requirements and constraints are described. The effects of orbital parameters and image quality requirements on the spacecraft and mission performance are discussed. Over the land the primary measurand is soil moisture; over the coastal zones and the oceans important measurands are salinity, surface temperature, surface winds, oil spill dimensions and ice boundaries; and specific measurement requirements have been selected for each. Near-all-weather operation and good spatial resolution are assured by operating at low microwave frequencies using an extremely large aperture antenna in a low-Earth-orbit contiguous mapping mode.

Keafer, L. S., Jr.

1981-01-01

48

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

49

Silicon Powder Filters for Large-Aperture Cryogenic Receivers  

NASA Astrophysics Data System (ADS)

Upcoming experiments probing for the existence of B-mode polarization in the cosmic microwave background (CMB) will require large arrays of background-limited detectors. This will necessitate the use of cryogenic receivers with large-aperture vacuum windows and correspondingly large low-pass infrared-blocking filters to minimize thermal load. Large-diameter filters composed of absorptive dielectrics are difficult to conductively cool adequately, and thus tend to heat up and re-radiate towards the focal plane. Reflective metal-mesh filters are challenging to manufacture at such large apertures and with feature sizes small enough to effectively block 300K thermal radiation. In order to overcome these difficulties, we have developed a novel type of thermal filter that scatters, rather than reflects or absorbs, unwanted infrared radiation. Comprised of ultra-pure silicon powder distributed within a polymethylpentene (PMP) substrate, these filters are not absorptive in the infrared while being transparent to microwaves, and are comparatively straightforward to produce. By adjusting the size of the silicon particles, the frequency cut-off of these low-pass filters is fully tunable. Small scale (70mm diameter, 3mm thickness) prototypes have exhibited <10% transmission throughout the infrared spectrum and <1% transmission at the peak of the 300K blackbody spectrum, while maintaining an estimated 97% transmission in the microwave regime.

Boone, Fletcher; Essinger-Hileman, T.; Bennett, C. L.; Marriage, T.; Xu, Z.

2014-01-01

50

Bridgman growth of large-aperture yttrium calcium oxyborate crystal  

SciTech Connect

Highlights: ? YCOB is a novel non-linear optical crystal possessing good thermal, mechanical and nonlinear optical properties. ? Large size crystal growth is key technology question for YCOB crystal. ? YCOB crystals 3 in. in diameter were grown with modified vertical Bridgman method. ? It is a more effective growth method to obtain large size and high quality YCOB crystal. -- Abstract: Large-aperture yttrium calcium oxyborate YCa{sub 4}O(BO{sub 3}){sub 3} (YCOB) crystals with 3 in. in diameter were grown with modified vertical Bridgman method, and the large crystal plate (63 mm 68 mm 20 mm) was harvested for high-average power frequency conversion system. The crack, facet growth and spiral growth can be effectively controlled in the as-grown crystal, and Bridgman method displays more effective in obtain large size and high quality YCOB crystal plate than Czochralski technique.

Wu, Anhua, E-mail: wuanhua@mail.sic.ac.cn [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China)] [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China); Jiang, Linwen; Qian, Guoxing; Zheng, Yanqing; Xu, Jun; Shi, Erwei [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China)] [Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050 (China)

2012-09-15

51

Science drivers and requirements for an Advanced Technology Large Aperture Space Telescope (ATLAST): Implications for technology  

E-print Network

Science drivers and requirements for an Advanced Technology Large Aperture Space Telescope (ATLAST, MS SD70 SOMTC, Huntsville, AL USA 35812-0262 ABSTRACT The Advanced Technology Large-Aperture Space to current generation observatory-class space missions. Keywords: Advanced Technology Large-Aperture Space

Sirianni, Marco

52

The COronal Solar Magnetism Observatory (COSMO) Large Aperture Coronagraph  

NASA Astrophysics Data System (ADS)

The COSMO is a facility dedicated to observing coronal and chromospheric magnetic fields. It will be located on a mountaintop in the Hawaiian Islands and will replace the current Mauna Loa Solar Observatory (MLSO). COSMO will provide unique observations of the global coronal magnetic fields and its environment to enhance the value of data collected by other observatories on the ground (e.g. SOLIS, BBO NST, Gregor, ATST, EST, Chinese Giant Solar Telescope, NLST, FASR) and in space (e.g. SDO, Hinode, SOHO, GOES, STEREO, Solar-C, Solar Probe+, Solar Orbiter). COSMO will employ a fleet of instruments to cover many aspects of measuring magnetic fields in the solar atmosphere. The dynamics and energy flow in the corona are dominated by magnetic fields. To understand the formation of CMEs, their relation to other forms of solar activity, and their progression out into the solar wind requires measurements of coronal magnetic fields. The large aperture coronagraph, the Chromospheric and Prominence Magnetometer and the K-Coronagraph form the COSMO instrument suite to measure magnetic fields and the polarization brightness of the low corona used to infer electron density. The large aperture coronagraph will employ a 1.5 meter fuse silica singlet lens, birefringent filters, and a spectropolarimeter to cover fields of view of up to 1 degree. It will observe the corona over a wide range of emission lines from 530.3 nm through 1083.0 nm allowing for magnetic field measurements over a wide range of coronal temperatures (e.g. FeXIV at 530.3 nm, Fe X at 637.4 nm, Fe XIII at 1074.7 and 1079.8 nm. These lines are faint and require the very large aperture. NCAR and NSF have provided funding to bring the large aperture coronagraph to a preliminary design review state by the end of 2013. As with all data from Mauna Loa, the data products from COSMO will be available to the community via the Mauna Loa website: http://mlso.hao.ucar.edu

Tomczyk, Steve; Gallagher, Dennis; Wu, Zhen; Zhang, Haiying; Nelson, Pete; Burkepile, Joan; Kolinksi, Don; Sutherland, Lee

2013-04-01

53

Optimal strategy for fabrication of large aperture aspheric surfaces.  

PubMed

Aspheric surfaces are widely used because of their desirable characteristics. Such a surface can obtain nearly perfect imaging quality with fewer optical elements and reduce the size and mass of optical systems. Various machine systems have been developed based on modern deterministic polishing technologies for large aperture aspheric surfaces. Several factors affect the final precision of large aperture aspheric surfaces, such as the velocity limit of the machine and the path design. Excess velocity, which will be truncated automatically by the computer numerical control system, may cause the dwell time to deviate from the desired time. When a path designed on a two-dimensional surface map with equidistant pitch is projected onto an aspheric surface, the pitch changes as a result of the varied curvature of the aspheric surface. This may affect the removal map and cause some ripple errors. A multiregion distribution strategy, which includes velocity checking, is proposed in this study to avoid exceeding the velocity limits. The strategy can be used to modify local errors and edge effects. A three-dimensional spiral path generation method is also presented using an iterative method to ensure uniformity in the space length of the adjacent circle of the spiral path. This process can reduce the ripple error caused by the overlapping of tool paths. A polishing experiment was conducted, and the results proved the validity of the proposed strategies. PMID:24514001

Feng, Yunpeng; Cheng, Haobo; Wang, Tan; Dong, Zhichao; Tam, Hon-Yuen

2014-01-01

54

CALISTO: The Cryogenic Aperture Large Infrared Space Telescope Observatory  

NASA Astrophysics Data System (ADS)

CALISTO, the Cryogenic Aperture Large Infrared Space Telescope Observatory, will enable extraordinarily high sensitivity far-infrared continuum and moderate (R 1000) resolution spectroscopic observations from 20m into the submillimeter, wavelengths between those accessible by JWST and future ground based facilities,. Such observations will provide vital information about a wide range of important astronomical questions including (1) the formation of the first structure in the universe traced by H2 emission; (2) the evolution of galaxies and the star formation that takes place within them; (3) the formation of planetary systems through observations of protostellar and debris disks; (4) the outermost portions of our solar system through observations of Trans-Neptunian Objects (TNOs) and the Oort cloud. With low emissivity optics cooled to below 5 K, the photon fluctuations from the astronomical background (Zodiacal, Galactic, and extragalactic) exceed those of the telescope. Detectors with a noise equivalent power below that set by the background allow us to achieve astronomical background sensitivity through the submillimeter/far-infrared region. CALISTO builds on studies for the SAFIR (Single Aperture Far Infrared) telescope mission, employing a 4m x 6m off-axis Gregorian telescope which has a simple deployment from an Atlas V launch vehicle. The telescope and cold stop have minimal sidelobes and scattering, enabling astronomical background limited observations over a large fraction of the sky. We discuss CALISTO optics, performance, instrument complement, and mission design, and give an overview of key science goals and required technology development to enable this important future mission.

Goldsmith, Paul

55

The Balloon-borne Large Aperture Sub-millimetre Telescope  

E-print Network

The Balloon-borne Large-Aperture Sub-millimetre Telescope (BLAST) will operate on a Long Duration Balloon platform with large format bolometer arrays at 250, 350 and 500 microns, initially using a 2m mirror, with plans to increase to 2.5m. BLAST is a collaboration between scientists in the USA, Canada, UK, Italy and Mexico. Funding has been approved and it is now in its building phase. The test flight is scheduled for 2002, with the first long duration flight the following year. The scientific goals are to learn about the nature of distant extragalactic star forming galaxies and cold pre-stellar sources by making deep maps both at high and low galactic latitudes. BLAST will be useful for planning Herschel key projects which use SPIRE.

Douglas Scott; the BLAST Team

2001-04-03

56

Towards laser guide stars for multi-aperture interferometry: an application to the hypertelescope  

NASA Astrophysics Data System (ADS)

Optical interferometry has been successful at achieving milliarcsecond resolution on bright stars. Imaging performance can improve greatly by increasing the number of baselines, which has motivated proposals to build large (100 m) optical interferometers with tens to hundreds of telescopes. It is also desirable to adaptively correct atmospheric turbulence to obtain direct phased images of astrophysical sources. When a natural guide star is not available, we investigate the feasibility of using a modified laser-guide-star technique that is suitable for large diluted apertures. The method consists of using subsets of apertures to create an array of artificial stars in the sodium layer and collecting back-scattered light with the same subapertures. We present some numerical and laboratory simulations that quantify the requirements and sensitivity of the technique.

Nuez, Paul D.; Labeyrie, Antoine; Riaud, Pierre

2014-04-01

57

Factors affecting the performance of large-aperture microphone arrays  

NASA Astrophysics Data System (ADS)

Large arrays of microphones have been proposed and studied as a possible means of acquiring data in offices, conference rooms, and auditoria without requiring close-talking microphones. When such an array essentially surrounds all possible sources, it is said to have a large aperture. Large-aperture arrays have attractive properties of spatial resolution and signal-to-noise enhancement. This paper presents a careful comparison of theoretical and measured performance for an array of 256 microphones using simple delay-and-sum beamforming. This is the largest currently functional, all digital-signal-processing array that we know of. The array is wall-mounted in the moderately adverse environment of a general-purpose laboratory (8 m8 m3 m). The room has a T60 reverberation time of 550 ms. Reverberation effects in this room severely impact the array's performance. However, the width of the main lobe remains comparable to that of a simplified prediction. Broadband spatial resolution shows a single central peak with 10 dB gain about 0.4 m in diameter at the -3 dB level. Away from that peak, the response is approximately flat over most of the room. Optimal weighting for signal-to-noise enhancement degrades the spatial resolution minimally. Experimentally, we verify that signal-to-noise gain is less than proportional to the square root of the number of microphones probably due to the partial correlation of the noise between channels, to variation of signal intensity with polar angle about the source, and to imperfect correlation of the signal over the array caused by reverberations. We show measurements of the relative importance of each effect in our environment.

Silverman, Harvey F.; Patterson, William R.; Sachar, Joshua

2002-05-01

58

Factors affecting the performance of large-aperture microphone arrays.  

PubMed

Large arrays of microphones have been proposed and studied as a possible means of acquiring data in offices, conference rooms, and auditoria without requiring close-talking microphones. When such an array essentially surrounds all possible sources, it is said to have a large aperture. Large-aperture arrays have attractive properties of spatial resolution and signal-to-noise enhancement. This paper presents a careful comparison of theoretical and measured performance for an array of 256 microphones using simple delay-and-sum beamforming. This is the largest currently functional, all digital-signal-processing array that we know of. The array is wall-mounted in the moderately adverse environment of a general-purpose laboratory (8 m x 8 m x 3 m). The room has a T60 reverberation time of 550 ms. Reverberation effects in this room severely impact the array's performance. However, the width of the main lobe remains comparable to that of a simplified prediction. Broadband spatial resolution shows a single central peak with 10 dB gain about 0.4 m in diameter at the -3 dB level. Away from that peak, the response is approximately flat over most of the room. Optimal weighting for signal-to-noise enhancement degrades the spatial resolution minimally. Experimentally, we verify that signal-to-noise gain is less than proportional to the square root of the number of microphones probably due to the partial correlation of the noise between channels, to variation of signal intensity with polar angle about the source, and to imperfect correlation of the signal over the array caused by reverberations. We show measurements of the relative importance of each effect in our environment. PMID:12051434

Silverman, Harvey F; Patterson, William R; Sachar, Joshua

2002-05-01

59

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

60

Large aperture magnets for a future high power proton synchrotron  

SciTech Connect

A high intensity, high power proton synchrotron is currently under consideration at Fermilab. The machine--known as the Proton Driver--would accelerate 3 x 10{sup 13} protons from 400 MeV to 12 GeV (stage I) or 16 GeV (stage II) and ultimately deliver in excess of 1 MW of beam power. To minimize losses and insure beam stability, the space charge-induced tune shift must be kept well below 0.5. This is accomplished by spreading out bunches both longitudinally and transversely. While the former strategy favors high voltage low frequency RF, the latter leads to magnets with unconventionally large apertures. This requirement, combined with a 1.5 T bending field and rapid cycling operation results in a number of serious but not insurmountable challenges. In this paper, they discuss the design of the Proton Driver magnets and the rationale behind it.

Jean-Francois Ostiguy and Frederick M. Mills

2001-08-14

61

Phased Array Mirror Extendible Large Aperture (PAMELA) Optics Adjustment  

NASA Technical Reports Server (NTRS)

Scientists at Marshall's Adaptive Optics Lab demonstrate the Wave Front Sensor alignment using the Phased Array Mirror Extendible Large Aperture (PAMELA) optics adjustment. The primary objective of the PAMELA project is to develop methods for aligning and controlling adaptive optics segmented mirror systems. These systems can be used to acquire or project light energy. The Next Generation Space Telescope is an example of an energy acquisition system that will employ segmented mirrors. Light projection systems can also be used for power beaming and orbital debris removal. All segmented optical systems must be adjusted to provide maximum performance. PAMELA is an on going project that NASA is utilizing to investigate various methods for maximizing system performance.

1995-01-01

62

APPLICATION OF LARGE APERTURE EMATS TO WELD INSPECTION  

SciTech Connect

One of the most significant developments in EMAT operation is the incorporation of phased array techniques. Phased array EMATs enable electronic beam steering and focusing while operating with temporally short pulses for good range resolution. Using phased array EMAT operation, multiple high powered pulsers are combined in the generation of the ultrasonic wave and multiple elements are combined in the reception of the ultrasonic wave, for improved sensitivity. EMATs make it practical to operate with shear horizontal (SH) waves and scan over a metal part's surface. An EMAT generated line force at the surface launches shear horizontal waves with uniform amplitude for beam angles from -90 deg. to 90 deg. Shear horizontal waves also reflect without mode conversion from surfaces that are parallel to the polarization of the shear wave displacements. The combination of these advantages makes phased array EMATs well suited for weld inspection. Recently, BWXT Services has developed a 32 active channel EMAT phased array system for operation up to 5 MHz. In addition, each element can be constructed with several sub-elements, alternating in polarity, to effectively multiply the number of active elements for a restricted range of beam angles. For example by using elements comprised of 4 sub elements, a 128 active element aperture designed for operation with a nominal 60 deg. beam angle provides good beam steering and focusing performance for 45 deg. to 70 deg. beam angles. The large active apertures allow the use of highly focused beams for good defect detection and high resolution imaging of weld defects. Application of this system to weld inspections has verified that good defect detection and imaging is possible. In addition, operation with SH waves has proven to provide improved detection of lack of fusion at the cap and root of the weld for certain weld geometries. The system has also been used to demonstrate the inspection of submerged metal arc welds while welding.

Maclauchlan, D. T.; Clark, S. P.; Hancock, J. W. [NDE and IS Group, BWXT Services, Lynchburg, VA 24502 (United States)

2008-02-28

63

MOIRE: ground demonstration of a large aperture diffractive transmissive telescope  

NASA Astrophysics Data System (ADS)

The desire to field space-based telescopes with apertures in excess of 10 meter diameter is forcing the development of extreme lightweighted large optomechanical structures. Sparse apertures, shell optics, and membrane optics are a few of the approaches that have been investigated and demonstrated. Membrane optics in particular have been investigated for many years. The MOIRE approach in which the membrane is used as a transmissive diffractive optical element (DOE) offers a significant relaxation in the control requirements on the membrane surface figure, supports extreme lightweighting of the primary collecting optic, and provides a path for rapid low cost production of the primary optical elements. Successful development of a powered meter-scale transmissive membrane DOE was reported in 2012. This paper presents initial imaging results from integrating meter-scale transmissive DOEs into the primary element of a 5- meter diameter telescope architecture. The brassboard telescope successfully demonstrates the ability to collect polychromatic high resolution imagery over a representative object using the transmissive DOE technology. The telescope includes multiple segments of a 5-meter diameter telescope primary with an overall length of 27 meters. The object scene used for the demonstration represents a 1.5 km square complex ground scene. Imaging is accomplished in a standard laboratory environment using a 40 nm spectral bandwidth centered on 650 nm. Theoretical imaging quality for the tested configuration is NIIRS 2.8, with the demonstration achieving NIIRS 2.3 under laboratory seeing conditions. Design characteristics, hardware implementation, laboratory environmental impacts on imagery, image quality metrics, and ongoing developments will be presented.

Atcheson, Paul; Domber, Jeanette; Whiteaker, Kevin; Britten, Jerald A.; Dixit, Shamasundar N.; Farmer, Brandon

2014-08-01

64

CALISTO: the Cryogenic Aperture Large Infrared Space Telescope Observatory  

NASA Astrophysics Data System (ADS)

CALISTO, the Cryogenic Aperture Large Infrared Space Telescope Observatory, will enable extraordinarily high sensitivity far-infrared continuum and moderate (R ~ 1000) resolution spectroscopic observations at wavelengths from ~30µm to ~300 ?m - the wavelengths between those accessible by JWST and future ground based facilities. CALISTO's observations will provide vital information about a wide range of important astronomical questions including (1) the first stars and initial heavy element production in the universe; (2) structures in the universe traced by H2 emission; (3) the evolution of galaxies and the star formation within them (4) the formation of planetary systems through observations of protostellar and debris disks; (5) the outermost portions of our solar system through observations of Trans-Neptunian Objects (TNOs) and the Oort cloud. With optics cooled to below 5 K, the photon fluctuations from the astronomical background (Zodiacal, Galactic, and extragalactic) exceed those from the telescope. Detectors with a noise equivalent power below that set by the background will make possible astronomical-background-limited sensitivity through the submillimeter/far-infrared region. CALISTO builds on studies for the SAFIR (Single Aperture Far Infrared) telescope mission, employing a 4m x 6m off-axis Gregorian telescope which has a simple deployment using an Atlas V launch vehicle. The unblocked telescope with a cold stop has minimal sidelobes and scattering. The clean beam will allow astronomical background limited observations over a large fraction of the sky, which is what is required to achieve CALISTO's exciting science goals. The maximum angular resolution varies from 1.2" at 30 µm to 12" at 300 ?m. The 5? 1 hr detectable fluxes are ?S(d?/? = 1.0) = 2.2x10-20 Wm-2, and ?S(d?/? = 0.001) = 6.2x10-22 Wm-2. The 8 beams per source confusion limit at 70 ?m is estimated to be 5 ?Jy. We discuss CALISTO optics, performance, instrument complement, and mission design, and give an overview of key science goals and required technology development to enable this promising far IR/submm mission.

Goldsmith, Paul F.; Bradford, Matt; Dragovan, Mark; Paine, Chris; Satter, Celeste; Langer, Bill; Yorke, Harold; Huffenberger, Kevin; Benford, Dominic; Lester, Dan

2008-07-01

65

The Balloon-borne Large Aperture Submillimeter Telescope: BLAST  

E-print Network

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a sub-orbital 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 3 arrays, observes simultaneously in broad-band (30%) spectral-windows at 250, 350, and 500 microns. The optical design is based on a 2m 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"; post-flight pointing reconstruction to ~5" rms is achieved. The on-board telescope control software permits autonomous execution of a pre-selected 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-hour flight from ESRANGE (Kiruna), Sweden to Victoria Island, northern Canada in June 2005; and a 250-hour, circumpolar-flight from McMurdo Station, Antarctica, in December 2006.

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

2007-11-21

66

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

67

A compact, large-aperture tunable lens with adaptive spherical correction  

E-print Network

In this paper, we present the proof of concept of a very fast adaptive glass membrane lens with a large aperture/diameter ratio, spherical aberration correction and integrated actuation. The membrane is directly deformed using two piezo actuators that can tune the focal length and the conical parameter. This operating principle allows for a usable aperture of the whole membrane diameter. Together with the efficient actuation mechanism, the aperture is around 2/3 of the total system diameter - at a thickness of less than 2mm. The response time is a few milliseconds at 12mm aperture, which is fast compared to similar systems.

Wapler, Matthias C; Wallrabe, Ulrike

2014-01-01

68

Experimental instrumentation system for the Phased Array Mirror Extendible Large Aperture (PAMELA) test program  

NASA Technical Reports Server (NTRS)

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 adaptive optics test facility with precision (fraction of wavelengths) measurement equipment. The initial system under test is the adaptive optical telescope called PAMELA (Phased Array Mirror Extendible Large Aperture). Goals of this test are: assessment of test hardware specifications for PAMELA application and the determination of the sensitivities of instruments for measuring PAMELA (and other adaptive optical telescopes) imperfections; evaluation of the PAMELA system integration effort and test progress and recommended actions to enhance these activities; and development of concepts and prototypes of experimental apparatuses for PAMELA.

Boykin, William H., Jr.

1993-01-01

69

Time-gated ballistic imaging using a large aperture switching beam.  

PubMed

Ballistic imaging commonly denotes the formation of line-of-sight shadowgraphs through turbid media by suppression of multiply scattered photons. The technique relies on a femtosecond laser acting as light source for the images and as switch for an optical Kerr gate that separates ballistic photons from multiply scattered ones. The achievable image resolution is one major limitation for the investigation of small objects. In this study, practical influences on the optical Kerr gate and image quality are discussed theoretically and experimentally applying a switching beam with large aperture (D = 19 mm). It is shown how switching pulse energy and synchronization of switching and imaging pulse in the Kerr cell influence the gate's transmission. Image quality of ballistic imaging and standard shadowgraphy is evaluated and compared, showing that the present ballistic imaging setup is advantageous for optical densities in the range of 8 < OD < 13. Owing to the spatial transmission characteristics of the optical Kerr gate, a rectangular aperture stop is formed, which leads to different resolution limits for vertical and horizontal structures in the object. Furthermore, it is reported how to convert the ballistic imaging setup into a schlieren-type system with an optical schlieren edge. PMID:24664055

Mathieu, Florian; Reddemann, Manuel A; Palmer, Johannes; Kneer, Reinhold

2014-03-24

70

ULTIMA free-flying large-aperture space telescope  

Microsoft Academic Search

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,

Jonathan W. Campbell; Charles R. Taylor

1997-01-01

71

Analysis of the Systematic Errors Found in the Kipp & Zonen Large-Aperture Scintillometer  

Microsoft Academic Search

Studies have shown a systematic error in the Kipp & Zonen large-aperture scintillometer (K&ZLAS) measurements of the sensible heat flux, H. We improved on these studies and compared four K&ZLASs with a Wageningen large-aperture scintillometer at the Chilbolton Observatory. The scintillometers were installed such that their footprints were the same and independent flux measurements were made along the measurement path.

B. van Kesteren; O. K. Hartogensis

2011-01-01

72

Analysis of the Systematic Errors Found in the Kipp & Zonen Large-Aperture Scintillometer  

Microsoft Academic Search

Studies have shown a systematic error in the Kipp & Zonen large-aperture scintillometer (K&ZLAS) measurements of the sensible heat flux, H. We improved on these studies and compared four K&ZLASs with a Wageningen large-aperture scintillometer at the Chilbolton Observatory. The scintillometers were installed such that their footprints were the same and independent flux measurements were made along the measurement path.

B. van Kesteren; O. K. Hartogensis

2010-01-01

73

Analysis of the Systematic Errors Found in the Kipp & Zonen Large-Aperture Scintillometer  

Microsoft Academic Search

Studies have shown a systematic error in the Kipp & Zonen large-aperture scintillometer (K&ZLAS) measurements of the sensible\\u000a heat flux, H. We improved on these studies and compared four K&ZLASs with a Wageningen large-aperture scintillometer at the Chilbolton\\u000a Observatory. The scintillometers were installed such that their footprints were the same and independent flux measurements\\u000a were made along the measurement path.

B. Van Kesteren; O. K. Hartogensis

2011-01-01

74

The scaling relationship between telescope cost and aperture size for very large telescopes  

NASA Technical Reports Server (NTRS)

Cost data for ground-based telescopes of the last century are analyzed for trends in the relationship between aperture size and cost. We find that for apertures built prior to 1980, costs scaled as aperture size to the 2.8 power, which is consistent with the precious finding of Meinel (1978). After 1980, 'traditional' monolithic mirror telescope costs have scaled as aperture to the 2.5 power. The large multiple mirror telescopes built or in construction during this time period (Keck, LBT, GTC) appear to deviate from this relationship with significant cost savings as a result, although it is unclear what power law such structures follow. We discuss the implications of the current cost-aperture size data on the proposed large telescope projects of the next ten to twenty years. Structures that naturally tend towards the 2.0 power in the cost-aperture relationship will be the favorable choice for future extremely large apertures; out expectation is that space-based structures will ultimately gain economic advantage over ground-based ones.

van Belle, Gerard T.; Meinel, Aden Baker; Meinel, Marjorie Pettit

2004-01-01

75

The scaling relationship between telescope cost and aperture size for very large telescopes  

NASA Astrophysics Data System (ADS)

Cost data for ground-based telescopes of the last century are analyzed for trends in the relationship between aperture size and cost. We find that for apertures built prior to 1980, costs scaled as aperture size to the 2.8 power, which is consistent with the previous finding of Meinel (1978). After 1980, 'traditional' monolithic mirror telescope costs have scaled as aperture to the 2.5 power. The large multiple mirror telescopes built or in construction during this time period (Keck, LBT, GTC) appear to deviate from this relationship with significant cost savings as a result, although it is unclear what power law such structures follow. We discuss the implications of the current cost-aperture size data on the proposed large telescope projects of the next ten to twenty years. Structures that naturally tend towards the 2.0 power in the cost-aperture relationship will be the favorable choice for future extremely large apertures; our expectation is that space-based structures will ultimately gain economic advantage over ground-based ones.

van Belle, Gerard T.; Meinel, Aden B.; Meinel, Marjorie P.

2004-10-01

76

Large Aperture Scanning Lidar Based on Holographic Optical Elements  

NASA Technical Reports Server (NTRS)

Lidar remote sensing instruments can make a significant contribution to satisfying many of the required measurements of atmospheric and surface parameters for future spaceborne platforms, including topographic altimeters, atmospheric profiles of, wind, humidity, temperature, trace molecules, aerosols, and clouds. It is highly desirable to have wide measurement swaths for rapid coverage rather than just the narrow ribbon of data that is obtained with a nadir only observation. For most applications global coverage is required, and for wind measurements scanning or pointing is required in order to retrieve the full 3-D wind vector from multiple line-of-sight Doppler measurements. Conventional lidar receivers make up a substantial portion of the instrument's size and weight. Wide angle scanning typically requires a large scanning mirror in front of the receiver telescope, or pointing the entire telescope and aft optics assembly, Either of these methods entails the use of large bearings, motors, gearing and their associated electronics. Spaceborne instruments also need reaction wheels to counter the torque applied to the spacecraft by these motions. NASA has developed simplified conical scanning telescopes using Holographic Optical Elements (HOEs) to reduce the size, mass, angular momentum, and cost of scanning lidar systems. NASA has developed two operating lidar systems based on 40 cm diameter HOEs. The first such system, named Prototype Holographic Atmospheric Scanner for Environmental Remote Sensing (PHASERS) was a joint development between NASA Goddard Space Flight Center (GSFC) and the University of Maryland College Park. PHASERS is based on a reflection HOE for use at the doubled Nd:YAG laser wavelength of 532 nm and has recently undergone a number of design changes in a collaborative effort between GSFC and Saint Anselm College in New Hampshire. The next step was to develop IR transmission HOEs for use with the Nd:YAG fundamental in the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE). The HOE spins like a compact disk in a large ring ball bearing. In an aircraft the HOE faces down, looking out through a window at an angle of 45 degrees off-nadir. The HOE diffracts 85% of the incident 532 nm light into a 160 micron spot at a focal length of 1 meter. HARLIE is a field deployable lidar measuring aerosol, cloud, and boundary layer backscatter for atmospheric research. It has flown several times and is also used from a ground-based trailer in an upward-looking mode. The HOE generates a 45 degree conical scan pattern by rotating at speeds up to 30 rpm. Like PHASERS, the HOE in HARLIE serves both as the laser collimating lens as well as the receiver telescope primary optic. The telescope is coupled to the receiver package via fiber optic. The transmitter is a diode pumped Nd:YAG laser operating at 1064 nm, delivering 1 mJ pulses at a 5 KHz rep-rate. The receiver has a 200 microradian field-of-view and a 0.5 nm optical bandpass. The photon counting data system utilizes a single Geiger-mode silicon avalanche photodiode detector, This new technology has also presented us with new data visualization challenges as well as new measurement techniques. The backscatter data obtained from a stationary (i.e. ground-based) scanning HOE lidar is on the surface of a cone, which when viewed over many consecutive scans can reveal atmospheric motions on this surface over time as the atmosphere advects over the site. In a moving platform such as an airplane or satellite, the data from consecutive scans cover different areas under the flight path, revealing atmospheric structure in 3-dimensions. An example of a visualization of HARLIE ground-based data is presented, showing aerosol backscatter on a 90 degree conical surface generated from one 360 degree scan of the lidar during the HOLO-1 field campaign on the afternoon of 10 March 1999. Higher backscatter levels are rendered as lighter signal against a dark background. Breaking Kelvin-Helmholtz waves are evident on the north side of the scan at an altitude of 10-11 km. Time

Schwemmer, Geary K.; Miller, David O.; Wilkerson, Thomas D.; Andrus, Ionio; Guerra, David V.; Einaudi, Franco (Technical Monitor)

2001-01-01

77

Theoretical model to suppress parasitic lasing in large-aperture Ti:sapphire amplifiers using a temporal dual-pulse pump  

NASA Astrophysics Data System (ADS)

Transverse parasitic lasing (PL) in large-aperture Ti:sapphire (Ti:S) crystals is a critical factor that limits the energy achievable with the chirped-pulse amplification (CPA) technique. We propose a method to suppress PL effects in large-aperture Ti:S amplifiers by using a temporal dual-pulse pump. Theoretical simulations based on the experimental parameters in 2.0 PW Ti:S laser system are performed to predict the transverse gain as a function of pumping time and output energy. By optimizing the temporal profile of the pump beam as well as the time delay between the input seed and pump pulses, we can minimize PL effects in Ti:S crystals. This method is applicable to larger-aperture Ti:S crystals pumped at higher pump fluence and energy, and is potential to develop a ~10 PW laser system.

Chu, Yuxi; Liang, Xiaoyan; Yu, Lianghong; Xu, Lu; Li, Ruxin; Xu, Zhizhan

2014-05-01

78

A Large Aperture Ultrasonic Array System for Hyperthermia Treatment of Deep-Seated Tumors  

Microsoft Academic Search

A computer controlled hyperthermia system has been developed for clinical evaluation. It is composed of a large aperture ultrasonic array applicator, an ultrasonic annular phased array imager and a multi-channel thermometry system. The applicator has a 50cm aperture which contains 30 broadband ultrasound transducers that operate from 500KHz to 1MHz. Each transducer is independently controllable in power, phase and mechanical

E. Seppi; E. Shapiro; L. Zitelli; S. Henderson; A. Wehlau; G. Wu; C. Dittmer

1985-01-01

79

Fourier algorithm method for reconstruction of large-aperture digital holograms based on phase compensation.  

PubMed

To simplify the reconstruction calculation of a large-aperture digital hologram we propose a novel Fourier-transformation reconstruction algorithm. When the reconstructed wave is the same as or similar to the reference wave, the higher-order phase term of reconstruction can be compensated for. For example, the variation between the higher-order phase term and the aperture angle with a different field of view in in-line phase-shifting digital holography is analyzed. PMID:15035488

Lu, Xiaoxu; Zhang, Yimo; Zhong, Liyun; Luo, Yinlong; She, Canling

2004-03-15

80

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

81

Analysis of fratricide effect observed with GeMS and its relevance for large aperture astronomical telescopes  

NASA Astrophysics Data System (ADS)

Large aperture ground-based telescopes require Adaptive Optics (AO) to correct for the distortions induced by atmospheric turbulence and achieve diffraction limited imaging quality. These AO systems rely on Natural and Laser Guide Stars (NGS and LGS) to provide the information required to measure the wavefront from the astronomical sources under observation. In particular one such LGS method consists in creating an artificial star by means of fluorescence of the sodium atoms at the altitude of the Earth's mesosphere. This is achieved by propagating one or more lasers, at the wavelength of the Na D2a resonance, from the telescope up to the mesosphere. Lasers can be launched from either behind the secondary mirror or from the perimeter of the main aperture. The so-called central- and side-launch systems, respectively. The central-launch system, while helpful to reduce the LGS spot elongation, introduces the so-called "fratricide" effect. This consists of an increase in the photon-noise in the AO Wave Front Sensors (WFS) sub-apertures, with photons that are the result of laser photons back-scattering from atmospheric molecules (Rayleigh scattering) and atmospheric aerosols (dust and/or cirrus clouds ice particles). This affects the performance of the algorithms intended to compute the LGS centroids and subsequently compute and correct the turbulence-induced wavefront distortions. In the frame of the Thirty Meter Telescope (TMT) project and using actual LGS WFS data obtained with the Gemini Multi-Conjugate Adaptive Optics System (Gemini MCAO a.k.a. GeMS), we show results from an analysis of the temporal variability of the observed fratricide effect, as well as comparison of the absolute magnitude of fratricide photon-flux level with simulations using models that account for molecular (Rayleigh) scattering and photons backscattered from cirrus clouds.

Otarola, Angel; Neichel, Benoit; Wang, Lianqi; Boyer, Corinne; Ellerbroek, Brent; Rigaut, Franois

2013-12-01

82

Wide-aperture laser diode array in the external V-shaped cavity  

NASA Astrophysics Data System (ADS)

The operation of a wide-aperture laser diode array with the radiation wavelength 980 nm in external V-shaped symmetric and asymmetric cavities is experimentally studied. The regimes of stable oscillation are studied as functions of the feedback beam direction. The spectra and the intensity distribution of radiation in the far zone are presented for the laser diode in symmetric and asymmetric cavities. Tuning of the radiation wavelength is demonstrated using the Littman geometry in the asymmetric cavity.

Svetikov, V. V.; Nurligareev, D. Kh

2014-09-01

83

Estimation of catchment averaged sensible heat fluxes using a Large Aperture Scintillometer  

Microsoft Academic Search

Evapotranspiration rates at the catchment scale are very difficult to quantify. One possible manner to continuously observe this variable could be the estimation of sensible heat fluxes (H) across large distances (in the order of kilometers) using a Large Aperture Scintillometer (LAS), and inverting these observations into evapotranspiration rates, under the assumption that the LAS observations are representative for the

Bruno Samain; Bram Ferket; Willem Defloor; Valentijn R. N. Pauwels

2010-01-01

84

Estimation of catchment averaged sensible heat fluxes using a large aperture scintillometer  

Microsoft Academic Search

Evapotranspiration rates at the catchment scale are very difficult to quantify. One possible manner to continuously observe this variable could be the estimation of sensible heat fluxes (H) across large distances (in the order of kilometers) using a large aperture scintillometer (LAS), and inverting these observations into evapotranspiration rates, under the assumption that the LAS observations are representative for the

Bruno Samain; Bram V. A. Ferket; Willem Defloor; Valentijn R. N. Pauwels

2011-01-01

85

Optical Performance of Designs for a Large Aperture Far-Infrared Telescope  

NASA Astrophysics Data System (ADS)

We have developed two designs for a large single aperture far-infrared space telescope. Achieving the ultimate sensitivity in the far infrared (30 to 300 microns wavelength) requires a telescope cooled to 4 K with a large collecting area. The performance of the system can be degraded by radiation from dust in the solar system (zodi), from the Milky Way, and from the spacecraft. It is thus critical to understand the response of any telescope design at angles far from the direction of peak response. We have carried out detailed calculations of the radiation pattern from two different telescope designs for a 10m diameter aperture. This is the nominal diameter of the Single Aperture Far InfraRed (SAFIR) telescope, but can easily be extended to the 6m by 4m aperture proposed for the Cryogenic Aperture Large Infrared Space Telescope Observatory (CALISTO). The first design is the on-axis (symmetric) telescope as described in the SAFIR Vision Mission (VM) Report, while the second is off-axis (unobscured). The calculations, which have been carried out at a wavelength of 1mm, utilize a combination of physical optics/physical theory of diffraction (PO/PTD) and geometrical optics/geometrical theory of diffraction (GO/GTD). The on-axis SAFIR VM design has a relatively large subreflector (0.09 fractional area obscuration) and its feed legs obscure 0.027 of the collecting area. Relative to this inefficient geometry, the unobscured design has higher gain by a factor of 1.45 (1.6 dB) with a 12 dB edge taper Gaussian illumination. It is also characterized by a far lower sidelobe level. The off-axis design is preferable in terms of aperture efficiency and its lower scattered radiation at large angles from the main beam, thus minimizing coupling to the sunshield and allowing observation of a large portion of the sky without compromising sensitivity as a result of extraneous pickup.

Goldsmith, Paul; Khayatian, B.; Bradford, C. M.; Dragovan, M.; Imbriale, W.; Lee, R.; Paine, C.; Yorke, H.; Zmuidzinas, J.

2006-12-01

86

Synthesis of a large communications aperture using small antennas  

NASA Technical Reports Server (NTRS)

In this report we compare the cost of an array of small antennas to that of a single large antenna assuming both the array and single large antenna have equal performance and availability. The single large antenna is taken to be one of the 70-m antennas of the Deep Space Network. The cost of the array is estimated as a function of the array element diameter for three different values of system noise temperature corresponding to three different packaging schemes for the first amplifier. Array elements are taken to be fully steerable paraboloids and their cost estimates were obtained from commercial vendors. Array loss mechanisms and calibration problems are discussed. For array elements in the range 3 - 35 m there is no minimum in the cost versus diameter curve for the three system temperatures that were studied.

Resch, George M.; Cwik, T. W.; Jamnejad, V.; Logan, R. T.; Miller, R. B.; Rogstad, Dave H.

1994-01-01

87

The measurement and analysis of wavefront structure from large aperture ICF optics  

SciTech Connect

This paper discusses the techniques, developed over the past year, for high spatial resolution measurement and analysis of the transmitted and/or reflected wavefront of large aperture ICF optical components. Parts up to 400 mm {times} 750 mm have been measured and include: laser slabs, windows, KDP crystals and lenses. The measurements were performed using state-of-the-art commercial phase shifting interferometers at a wavelength of 633 {mu}m. Both 1 and 2-D Fourier analysis have been used to characterize the wavefront; specifically the Power Spectral Density, (PSD), function was calculated. The PSDs of several precision optical components will be shown. The PSD(V) is proportional to the (amplitude){sup 2} of components of the Fourier frequency spectrum. The PSD describes the scattered intensity and direction as a function of scattering angle in the wavefront. The capability of commercial software is limited to 1-D Fourier analysis only. We are developing our own 2-D analysis capability in support of work to revise specifications for NIF optics. 2-D analysis uses the entire wavefront phase map to construct 2D PSD functions. We have been able to increase the signal-to-noise relative to 1-D and can observe very subtle wavefront structure.

Wolfe, C.R.; Lawson, J.K.

1995-05-30

88

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

89

COMPONENTS OF LASER SYSTEMS: Pumping of the GARPUN wide-aperture excimer laser by counterpropagating electron beams  

NASA Astrophysics Data System (ADS)

The transport of high-current electron beams from vacuum diodes to the laser chamber of the GARPUN wide-aperture excimer laser was investigated experimentally and theoretically. The processes involving the transport of fast electrons in argon and krypton in a longitudinal magnetic field were also studied. Pumping by counter-propagating electron beams resulted in the deposition of up to 2.1 kJ of energy into the active medium of the laser, which corresponded to a specific excitation power of ~0.8 MW cm-3 with an inhomogeneity of less than 20% over a 12 cm 18 cm aperture. The efficiency of the energy deposition by electron beams was ~60% and the overall efficiency of the laser pumping system was ~16%.

Arlantsev, S. V.; Grigor'yants, E. A.; Vadkovskii, A. D.; Zvorykin, V. D.; Metreveli, G. E.

1994-03-01

90

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

91

A Balloon-borne Large Aperture Submillimeter Telescope  

E-print Network

A new generation of sub-orbital platforms will be operational in the next few years. These new telescopes will operate from airborne and balloon-borne platforms where the atmosphere is transparent enough to allow sensitive measurements to be made in the submillimeter bands. The telescopes will take advantage of state-of-the-art instrumentation including large format bolometer arrays and spectrometers. Other papers in this volume will deal specifically with the potential of these bands. In this paper will review the capabilities the BLAST balloon-borne telescope.

Mark J. Devlin

2000-12-14

92

High power density vertical-cavity surface-emitting lasers with ion implanted isolated current aperture.  

PubMed

We report on GaAs-based high power density vertical-cavity surface-emitting laser diodes (VCSELs) with ion implanted isolated current apertures. A continuous-wave output power of over 380 mW and the power density of 4.9 kW/cm2 have been achieved at 15 C from the 100-?m-diameter aperture, which is the highest output characteristic ever reported for an ion implanted VCSEL. A high background suppression ratio of over 40 dB has also been obtained at the emission wavelength of 970 nm. The ion implantation technique provides an excellent current isolation in the apertures and would be a key to realize high power output from a VCSEL array. PMID:22418178

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

2012-02-13

93

Electro-mechanical Simulation of a Large Aperture MOEMS Fabry-Perot Tunable Filter  

E-print Network

variable interference filters have typically been restricted to circular variable filters or linear variable filters. These options require an optical design that includes a small (1-2 mm diameter) pupilElectro-mechanical Simulation of a Large Aperture MOEMS Fabry-Perot Tunable Filter Jonathan L. Kuhn

Satyapal, Shobita

94

LAPCAT: the Large Antarctic Plateau Clear-Aperture Telescope John Storeya*  

E-print Network

technologies in an Antarctic environment, LAPCAT also paves the way for the eventual construction of a secondLAPCAT: the Large Antarctic Plateau Clear-Aperture Telescope John Storeya* , Roger Angelb , Jon, and that the design of precision instruments to work under Antarctic conditions is possible. Dome C (75 O 6 south, 123

Ashley, Michael C. B.

95

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

Microsoft Academic Search

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

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

2009-01-01

96

Using GPS to Synthesize A Large Antenna Aperture When The Elements Are Mobile  

E-print Network

Using GPS to Synthesize A Large Antenna Aperture When The Elements Are Mobile Shau-Shiun Jan, Per antenna elements, where the Global Positioning System (GPS) is used to estimate the current location and velocity of those elements. GPS is also used to synchronize the clocks carried by the mobiles

Stanford University

97

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

98

Polarimetric Calibration of Large-Aperture Telescopes I: The Beam-Expansion Method  

E-print Network

This paper describes a concept for the high-accuracy absolute calibration of the instrumental polarization introduced by the primary mirror of a large-aperture telescope. This procedure requires a small aperture with polarization calibration optics (e.g., mounted on the dome) followed by a lens that opens the beam to illuminate the entire surface of the mirror. The Jones matrix corresponding to this calibration setup (with a diverging incident beam) is related to that of the normal observing setup (with a collimated incident beam) by an approximate correction term. Numerical models of parabolic on-axis and off-axis mirrors with surface imperfections are used to explore its accuracy.

H. Socas-Navarro

2004-10-23

99

Tethered Formation Configurations: Meeting the Scientific Objectives of Large Aperture and Interferometric Science  

NASA Technical Reports Server (NTRS)

With the success of the Hubble Space Telescope, it has become apparent that new frontiers of science and discovery are made every time an improvement in imaging resolution is made. For the HST working primarily in the visible and near-visible spectrum, this meant designing, building and launching a primary mirror approximately three meters in diameter. Conventional thinking tells us that accomplishing a comparable improvement in resolution at longer wavelengths for Earth and Space Science applications requires a corresponding increase in the size of the primary mirror. For wavelengths in the sub-millimeter range, a very large telescope with an effective aperture in excess of one kilometer in diameter would be needed to obtain high quality angular resolution. Realistically a single aperture this large is practically impossible. Fortunately such large apertures can be constructed synthetically. Possibly as few as three 3 - 4 meter diameter mirrors flying in precision formation could be used to collect light at these longer wavelengths permitting not only very large virtual aperture science to be carried out, but high-resolution interferometry as well. To ensure the longest possible mission duration, a system of tethered spacecraft will be needed to mitigate the need for a great deal of propellant. A spin-stabilized, tethered formation will likely meet these requirements. Several configurations have been proposed which possibly meet the needs of the Space Science community. This paper discusses two of them, weighing the relative pros and cons of each concept. The ultimate goal being to settle on a configuration which combines the best features of structure, tethers and formation flying to meet the ambitious requirements necessary to make future large synthetic aperture and interferometric science missions successful.

Farley, Rodger E.; Quinn, David A.

2004-01-01

100

Tethered Formation Configurations: Meeting the Scientific Objectives of Large Aperture and Interferometric Science  

NASA Technical Reports Server (NTRS)

With the success of the Hubble Space Telescope, it has become apparent that new frontiers of science and discovery are made every time an improvement in imaging resolution is made. For the HST working primarily in the visible and near-visible spectrum, this meant designing, building, and launching a primary mirror approximately three meters in diameter. Conventional thinking tells us that accomplishing a comparable improvement in resolution at longer wavelengths for Earth and Space Science applications requires a corresponding increase in the size of the primary mirror. For wavelengths in the sub-millimeter range, a very large telescope with an effective aperture in excess of one kilometer in diameter would be needed to obtain high quality angular resolution. Realistically a single aperture this large is practically impossible. Fortunately such large apertures can be constructed synthetically. Possibly as few as three 34 meter diameter mirrors flying in precision formation could be used to collect light at these longer wavelengths permitting not only very large virtual aperture science to be carried out, but high-resolution interferometry as well. To ensure the longest possible mission duration, a system of tethered spacecraft will be needed to mitigate the need for a great deal of propellant. A spin-stabilized, tethered formation will likely meet these requirements. Several configurations have been proposed which possibly meet the needs of the Space Science community. This paper discusses two of them, weighing the relative pros and cons of each concept. The ultimate goal being to settle on a configuration which combines the best features of structure, tethers, and formation flying to meet the ambitious requirements necessary to make future large synthetic aperture and interferometric science missions successful.

Farley, Rodger E.; Quinn, David A.; Brodeur, Stephen J. (Technical Monitor)

2001-01-01

101

Distributed aperture effect in laser rods with negative lenses A discussion  

NASA Astrophysics Data System (ADS)

The difference between a ray transfer matrix in a lenslike medium and a section of lenslike medium immersed in vacuum is demonstrated. The distributed aperture and useful volume are calculated for a laser rod with negative lenses ground on the ends, using a multiplication of ray transfer matrices and the deductive method used by Barnes and Scalise. The results we obtained are different from their results.

Shie, C.-D.; Peng, K.-S.

1980-01-01

102

The Balloon-borne Large Aperture Submillimeter Telescope Peter Adea, Itziar Aretxagab, James Bockc, Jaspaul Chungd, Mark Devline, Simon Dickere,  

E-print Network

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) Peter Adea, Itziar Aretxagab with unprecedented image fidelity. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) will be one of the first experiments to make full use of this new capability. The high altitude ( 35 km) of the balloon

Aretxaga, Itziar

103

Design and development of control software in the experiment system of synthetic aperture laser imaging radar  

NASA Astrophysics Data System (ADS)

A control software experiment system of synthetic aperture imaging ladar is developed based on multithreading parallel mechanism of Labview8.6 and SCPI (standard commands for programmable instruments) protocol. Firstly, hardware composition and software function requirement of the system are analyzed. Then, the control module of the laser and stepper motor and the data communication module of oscillograph are developed separately and the three modules are integrated to realize the gather and compute of the return signal. Finally, by the result of experiment, the control software worked steady and real timely and it can operate the laser, stepper motor and oscillograph successfully.

Wu, Yapeng; Zhou, Yu; Zhi, Ya'nan; Sun, Jianfeng; Lu, Wei; Liu, Liren

2010-08-01

104

A Large Aperture Lidar Observatory for Exploring the Interaction of Our Atmosphere with Space (Invited)  

NASA Astrophysics Data System (ADS)

The mesopause region has been the subject of intensive study during the past decade because it is recognized as a critical region connecting our sensible atmosphere to the near-space environment. Processes in this region include a host of wave dynamics, heat and constituent transport, turbulence, polar mesospheric cloud formation, and the influx of meteoric material. Moreover, the neutral gas properties above the mesopause from 100 - 200 km altitude are poorly characterized and are influenced by additional processes that include solar EUV absorption / ionization, eddy to molecular diffusion, neutral wind dynamo action, and geomagnetic activity. Thus, this altitude region is a complex confluence of space and atmosphere processes that ultimately determine its properties. Fundamentally these processes are operating in any planetary atmosphere and must be understood in order to advance understanding of habitability and sustainability of a planetary system. While observational and modeling capabilities are evolving, progress in characterizing neutral properties and related processes in the mesopause region and above has been inhibited because they cannot be observed in sufficient detail and at high enough altitudes with existing instrumentation. This is especially true of the neutral atmosphere from 50 - 1000 km, where observations of its properties, dynamics and thermal structure are either sparse or nonexistent. A Large-Aperture Lidar Observatory (LALO) would enable significant progress by providing critical measurements of atmospheric constituents and parameters at greatly enhanced resolution and at much higher altitudes than is possible today. A large telescope in combination with modern high-power lasers, would enable observations of the neutral atmosphere to 1000 km altitude with a sensitivity and resolution approximately 1000 times better than can be achieved with the most powerful lidar systems in operation today. There are no technology barriers to realizing this goal. The knowledge obtained would improve our ability to understand the Earth's atmosphere to its fullest extent and would have a transformational effect on upper atmosphere research in a manner similar to that experienced by ionosphere research with the implementation of large-scale incoherent scatter radars. It would also have direct applications to studies of other planets in our solar system and to the exploration of nearby exoplanets within our galaxy.

Thayer, J. P.; Gardner, C. S.; Swenson, G. R.

2013-12-01

105

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

NASA Astrophysics Data System (ADS)

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 (OTF) and signal-to-noise ratio (SNR) performance metrics. The performance impacts of the misalignments are shown to be dependent upon the Fried parameter (effective telescope diameter), the source object brightness, and the control system time delay. The degree of performance degradation is directly related to the relative value of the Fried parameter to the deformable mirror displacement (misalignment cases) and the effective actuator spacing (actuator failure cases). The results indicate that the impact of misalignments and failures is small when seeing conditions are good or the percentage misalignments and failures are small.

Hogan, Timothy D.

1993-12-01

106

The Advanced Technology Large Aperture Space Telescope (ATLAST): Science Drivers and Technology Developments  

NASA Technical Reports Server (NTRS)

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers and the resulting performance requirements for ATLAST (8 to 16 milliarcsecond angular resolution, diffraction limited imaging at 0.5 m wavelength, minimum collecting area of 45 square meters, high sensitivity to light wavelengths from 0.1 m to 2.4 m, high stability in wavefront sensing and control). We also discuss the priorities for technology development needed to enable the construction of ATLAST for a cost that is comparable to current generation observatory-class space missions. Keywords: Advanced Technology Large-Aperture Space Telescope (ATLAST); ultraviolet/optical space telescopes; astrophysics; astrobiology; technology development.

Postman, Marc; Brown, Tom; Sembach, Kenneth; Giavalisco, Mauro; Traub, Wesley; Stapelfeldt, Karl; Calzetti, Daniela; Oegerle, William; Rich, R. Michael; Stahl, H. Phillip; Tumlinson, Jason; Mountain, Matt; Soummer, Remi; Hyde, Tupper

2011-01-01

107

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

108

Advanced Technology Large-Aperture Space Telescope (ATLAST): A Technology Roadmap for the Next Decade  

E-print Network

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a set of mission concepts for the next generation of UVOIR space observatory with a primary aperture diameter in the 8-m to 16-m range that will allow us to perform some of the most challenging observations to answer some of our most compelling questions, including "Is there life elsewhere in the Galaxy?" We have identified two different telescope architectures, but with similar optical designs, that span the range in viable technologies. The architectures are a telescope with a monolithic primary mirror and two variations of a telescope with a large segmented primary mirror. This approach provides us with several pathways to realizing the mission, which will be narrowed to one as our technology development progresses. The concepts invoke heritage from HST and JWST design, but also take significant departures from these designs to minimize complexity, mass, or both. Our report provides details on the mission concepts, shows the extraordinary s...

Postman, Marc

2009-01-01

109

Application of modern Aperture Integration (AI) and Geometrical Theory of Diffraction (GTD) techniques for analysis of large reflector antennas  

NASA Technical Reports Server (NTRS)

The application of aperture integration (AI) and geometrical theory of diffraction (GTO) techniques to analyze large reflector antennas is outlined. The following techniques were used: computer modeling, validation of analysis and computer codes, computer aided design modifications, limitation on the conventional aperture integration (AIC) method, extended aperture integration (AIE) method, the AIE method for feed scattering calculations, near field probing predictions for 15 meter model, limitation on AIC for surface tolerance effects, aperture integration on the surface (AIS) method, and AIC and GTD calculations for compact range reflector.

Rudduck, R. C.

1985-01-01

110

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

NASA Astrophysics Data System (ADS)

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) and focal spot of the SAA structure, was simulated using finite-difference time domain (FDTD) calculations. We found that a far-field laser beam propagating through the SAA structure possesses a sub-micron focal spot as well as high focus intensity. The experimental results demonstrated that silicon can be ablated using an input ablation threshold of an order of 0.05 J/cm2 with a pulse duration at around 120fs. We found the obtained surface hole to have a diameter smaller than 1?m. Different surface ablation results obtained by using different threshold fluences of input laser energy are shown. Possible applications of this technique includes executing high aspect ratio laser drilling for thin film microfabrication, undertaking thru silicon via (TSV) for 3DIC, etc.

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

2010-08-01

111

New multiplexed all solid state pulser for high power wide aperture kinetically enhanced copper vapor laser  

NASA Astrophysics Data System (ADS)

A novel multiplexed scheme is demonstrated to combine two or more pulsed solid state pulsers of moderate capabilities. Pulse power supply comprising of two solid state pulsers of 6 kW rating each in multiplexed mode with common magnetic pulse compression stage was demonstrated and optimized for operating with a wide aperture kinetically enhanced copper vapor laser. Using this new configuration, the multiplexed pulsed power supply was capable of operating efficiently at net repetition-rate of 13 kHz, 12 kW (wall plug average power), 18-20 kV discharge voltage and pulse rise-time of 80 ns. The laser under multiplexed configuration delivered un-interrupted output power of about 80 W with scope of further increase in laser output power in excess of 100 W.

Ghodke, D. V.; Muralikrishnan, K.; Singh, Bijendra

2013-11-01

112

New multiplexed all solid state pulser for high power wide aperture kinetically enhanced copper vapor laser.  

PubMed

A novel multiplexed scheme is demonstrated to combine two or more pulsed solid state pulsers of moderate capabilities. Pulse power supply comprising of two solid state pulsers of ~6 kW rating each in multiplexed mode with common magnetic pulse compression stage was demonstrated and optimized for operating with a wide aperture kinetically enhanced copper vapor laser. Using this new configuration, the multiplexed pulsed power supply was capable of operating efficiently at net repetition-rate of ~13 kHz, 12 kW (wall plug average power), 18-20 kV discharge voltage and pulse rise-time of ~80 ns. The laser under multiplexed configuration delivered un-interrupted output power of about ~80 W with scope of further increase in laser output power in excess of 100 W. PMID:24289383

Ghodke, D V; Muralikrishnan, K; Singh, Bijendra

2013-11-01

113

Recent Enhancements of the Phased Array Mirror Extendible Large Aperture (PAMELA) Telescope Testbed at MSFC  

NASA Technical Reports Server (NTRS)

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 in improved Shack-Hartmann wavefront sensor, passive viscoelastic damping treatments for the voice-coil actuators, mechanical improvement of mirror surface figures, and optical bench baffling. This report summarizes the recent PAMELA upgrades, discusses the lessons learned, and presents a status of this unique testbed for wavefront sensing and control. The Marshall Space Flight Center acquired the Phased Array Mirror Extendible Large Aperture (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; Burdine, Robert (Technical Monitor)

2001-01-01

114

Recent Enhancements of the Phased Array Mirror Extendible Large Aperture (PAMELA) Telescope Testbed at MSFC  

NASA Technical Reports Server (NTRS)

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, mechanical improvement of mirror surface figures, and optical bench baffling. This report summarizes the recent PAMELA upgrades, discusses the lessons learned, and presents a status of this unique testbed for wavefront sensing and control. The Marshall Space Flight Center acquired the Phased Array Mirror Extendible Large Aperture (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; Montgomery, Edward E.; Lindner, Jeff

2000-01-01

115

ATLAST-9.2m: a Large-Aperture Deployable Space Telescope  

NASA Technical Reports Server (NTRS)

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.

Oergerle, William; Feinberg, Lee D.; Purves, Lloyd R.; Hyde, T. Tupper; Thronson, Harley A.; Townsend, Jacqueline A.; Postman, Marc; Bolear, 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.

2010-01-01

116

Simulation analysis of on-orbit adjustment and compensation for large aperture optical system  

NASA Astrophysics Data System (ADS)

With the uprating requirements of space remote sensing, the aperture of the optical remote sensor is getting larger and larger. The influences of both the support of optical elements and gravity deformation on the optical system are difficult to conquer. Therefore, it is necessary to compensate the descending optical performance which is caused by the surface error of primary mirror by means of adjusting the position parameters of the optical elements on-orbit. A large aperture coaxial three-mirror optical system is introduced in the paper. Matlab and MetroPro are used to simulate the surface error of the primary mirror. The surface error of the primary mirror is compensated by adjusting the position freedoms of the secondary mirror. The results show that the adjustment of the position freedoms of the secondary mirror can compensate both the coma and some astigmatism of the primary mirror, but not the spherical aberration.

Liu, Jianfeng; Li, Bo; Sun, Dewei; Ruan, Ningjuan; Zhou, Feng

2014-09-01

117

Large excimer lasers for fusion  

SciTech Connect

Important goals in DOE and DOD programs require multimegajoule laser pulses. For inertial confinement fusion there is also a requirement to deliver the pulse in about 25 nsec with a very particular power vs time profile - all at high overall efficiency and low cost per joule. After exhaustive consideration of various alternatives, our studies have shown that the most cost effective approach to energy scaling is to increase the size of the final amplifiers up to the 200 to 300 kJ level. This conclusion derives largely from the fact that, at a given complexity, costs increase slowly with increasing part size while output energy should increase dramatically. Extrapolations to low cost by drastic cuts in the unit cost of smaller devices through mass production are considered highly risky. At a minimum the requirement to provide, space, optics and mounts for such systems will remain expensive. In recent years there have been dramatic advances in scaling. The Los Alamos LAM has produced over 10 kJ in a single 1/2 nsec pulse. In this paper we explore the issues involved in scaling to higher energy while still maintaining high efficiencies. In the remainder of this paper we will discuss KrF laser scaling for the fusion mission. We will omit most of the discussion of the laser system design, but address only KrF amplifiers.

Jensen, R.J.

1986-01-01

118

A Full Aperture Backscattering Light Diagnostic System Installed on the Shenguang-III Prototype Laser Facility  

NASA Astrophysics Data System (ADS)

A full aperture backscattering light diagnostic system (FABLDS) implemented on the Shen Guang-III Prototype Laser Facility is described in the paper. FABLDS measures both stimulated brillouin scattering (SBS) and stimulated Raman scattering (SRS) with a series of optical detectors. Energy sensors record the integrated energy, and streak cameras coupled with spectrometers measure the temporal spectrum of the backscattering light. This paper provides an overview of the FABLDS and detailed descriptions of the optical path. Special components, including off-axis parabolic mirror, spatial filter and optical light filters, are incorporated along the beam path for purifying the scattering light. Several hohlraum targets were employed, including C5H12 gas-filled targets and empty targets in the experiments. Results presented in the paper indicate that the fraction of backscatter light has been obviously shrinked when the laser is smoothed by continuous phase plates (CPP).

Xu, Tao; Mei, Yu; Wei, Huiyue; Peng, Xiaoshi; Wang, Feng; Yang, Dong; Liu, Shenye; Yan, Yadong

2014-06-01

119

Engineering Specification for Large-aperture UVO Space Telescopes Derived from Science Requirements  

NASA Technical Reports Server (NTRS)

An advanced large aperture UV/optical UVO space telescope is required for the next generation of astrophysics and exoplanet science. The science requirements of proposed exoplanet and astrophysics missions were used to determine the encircled energy, point spread function stability and thermal environment requirements. These requirements then determine the optical wavefront specification for potential telescope assemblies which can fit inside current and planned launch vehicles. The optical wavefront specification becomes the top level of the error budget that is split into various sources that control the structural, thermal and optical design.

Stahl, H. Philip; Arnold, William; Bevan, Ryan M.; Smith, W. Scott.; Kirk, Charles S.; Postman, Mark

2013-01-01

120

Compact large-aperture Fabry-Perot interferometer modules for gas spectroscopy at mid-IR  

NASA Astrophysics Data System (ADS)

VTT has developed Fabry-Prot Interferometers (FPI) for visible and infrared wavelengths since 90's. Here we present two new platforms for mid-infrared gas spectroscopy having a large optical aperture to provide high optical throughput but still enabling miniaturized instrument size. First platform is a tunable filter that replaces a traditional filter wheel, which operates between wavelengths of 4-5 um. Second platform is for correlation spectroscopy where the interferometer provides a comb-like transmission pattern mimicking absorption of diatomic molecules at the wavelength range of 4.7-4.8 um. The Bragg mirrors have 2-4 thin layers of polysilicon and silicon oxide.

Kantojrvi, Uula; Varpula, Aapo; Antila, Tapani; Holmlund, Christer; Mkynen, Jussi; Nsil, Antti; Mannila, Rami; Rissanen, Anna; Antila, Jarkko; Disch, Rolf J.; Waldmann, Torsten A.

2014-03-01

121

The balloon-borne large-aperture submillimeter telescope for polarimetry: BLAST-Pol  

Microsoft Academic Search

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry\\u000a(BLAST-Pol) is a suborbital mapping experiment designed to study the role\\u000aplayed by magnetic fields in the star formation process. BLAST-Pol is the\\u000areconstructed BLAST telescope, with the addition of linear polarization\\u000acapability. Using a 1.8 m Cassegrain telescope, BLAST-Pol images the sky onto a\\u000afocal plane that consists of 280 bolometric

G. Marsden; Peter A. R. Ade; S. Benton; J. J. Bock; Edward L. Chapin; J. Chung; M. J. Devlin; S. Dicker; L. Fissel; M. Griffin; J. O. Gundersen; M. Halpern; P. C. Hargrave; D. H. Hughes; J. Klein; A. Korotkov; C. J. MacTavish; P. G. Martin; T. G. Martin; T. G. Matthews; P. Mauskopf; L. Moncelsi; C. B. Netterfield; G. Novak; E. Pascale; L. Olmi; G. Patanchon; M. Rex; G. Savini; D. Scott; C. Semisch; N. Thomas; M. D. P. Truch; C. Tucker; G. S. Tucker; M. P. Viero; D. Ward-Thompson; D. V. Wiebec

2008-01-01

122

A conceptual design of a large aperture microwave radiometer geostationary platform  

NASA Technical Reports Server (NTRS)

A conceptual design of a Large Aperture Microwave Radiometer (LAMR) Platform has been developed and technology areas essential to the design and on-orbit viability of the platform have been defined. Those technologies that must be developed to the requirement stated here for the LAMR mission to be viable include: advanced radiation resistant solar cells, integrated complex structures, large segmented reflector panels, sub 3 kg/m(exp 2) areal density large antennas, and electric propulsion systems. Technology areas that require further development to enhance the capabilities of the LAMR platform (but are not essential for viability) include: electrical power storage, on-orbit assembly, and on-orbit systems checkout and correction.

Garn, Paul A.; Garrison, James L.; Jasinski, Rachel

1992-01-01

123

Large-aperture sparse array antenna systems of moderate bandwidth for multiple emitter location  

NASA Astrophysics Data System (ADS)

Spatial Linear Prediction Filter (SLPF) antenna systems of large aperture width (in wave-lengths) are described for the superresolution estimation of multiple emitter locations over moderate bandwidths. To accomplish this difficult task with reasonably few degrees-of-freedom (DOF) from the large aperture, the system employs interferometer/sparse array techniques in conjunction with a shaped reference beam which may be steered to the spatial sector of interest. Computer simulations on several multiple source examples have demonstrated that the concept is feasible, provided that true time-delay steering is employed on the shaped reference beam. The optimal estimation system configuration results when time-delay steering is also applied to the interferometer elements, because this focuses the sample covariance matrix and minimizes the DOF required. Even transversal filters may be dispensed with under focused conditions if the bandwidth is moderate. System performance goals included high-resolution with few DOF, fast response/processing time, moderate cost, and ease of frequent calibration.

Gabriel, W. F.

1987-11-01

124

Large-aperture, equal-path interferometer for precision measurements of flat transparent surfaces.  

PubMed

The measurement of flat optical components often presents difficulties because the presence of parallel surfaces generates multiple reflections that confuse conventional laser-based interferometers. These same parts have increasingly demanding surface finish tolerances as technologies improve over time, further complicating the metrology task. Here we describe an interferometric optical system for high-accuracy noncontact evaluation of the form and texture of precision flat surfaces based on an equal-optical-path geometry that uses extended, broadband illumination to reduce the influence of speckle noise, multiple reflections, and coherent artifacts by a factor of 10 when compared to laser-based systems. Combined with a low-distortion, fixed-focus imaging system and 4-Mpixel camera, the 100 mm aperture instrument offers surface height resolutions of 0.1 nm over lateral spatial frequencies extending from 0.01 to 10 cycles/mm. The instrument is vibration resistant for production-line testing of flat optics such as glass hard disks for the data-storage industry and flat-panel-display substrates. PMID:24663410

Deck, Leslie L; de Groot, Peter J; Soobitsky, James A

2014-03-10

125

Laser Power Meter Large, bright, backlit LCD  

E-print Network

Laser Power Meter FEATURES · Large, bright, backlit LCD display · Digital accuracy with analog-like movement for laser tuning · Works with thermopile and optical sensors · Intuitive button-driven user COMPATIBILITY · PowerMax® thermal sensors · Optical sensors FieldMaxII-TO Coherent Laser Measurement and Control

Woodall, Jerry M.

126

On the Potential of Large Ring Lasers  

E-print Network

We describe a new ring laser with area A = 833 m^2 and update performance statistics for several such machines. Anandan & Chaio 1982 judged ring lasers inferior to matter interferometers as possible detectors of gravitational waves. However, we note that geophysically interesting results have been obtained from large ring lasers and that there is still a lot of room for improvements.

G. E. Stedman; R. B. Hurst; K. U. Schreiber

2007-07-10

127

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

128

Extended-field large-aperture interferometer-spectrometer for airglow surveys.  

PubMed

The design of a field-of-view-widened interferometer for airglow survey work is discussed, and some preliminary airglow results are presented. The 4.5-cm aperture optics of the interferometer give a very large throughput gain compared with a conventional slit spectrometer. In addition, by using optical wedge compensators, the field of view is widened to over 5 degrees full angle, resulting in a field-widened throughput gain of approximately 100 compared with a standard Michelson interferometer of the same aperture size. Digital recording is used to achieve sufficient dynamic range and to aid in computation of the fast fourier transforms. A series of airglow spectra of the midlatitude sky in the spectral region from 0.6 micro to 0.9 micro down to a resolution of about 2 A are given for a sunset transition and also at night. Bright features are the vibration-rotation hydroxyl emission bands and the oxygen red lines. Particularly interesting are enhancement of these emissions during twilight and the observation of what may be vibrationally excited O(2) in the lower atmosphere. PMID:20111220

Despain, A M; Baker, D J; Steed, A J; Tohmatsu, T

1971-08-01

129

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

NASA Astrophysics Data System (ADS)

A large aperture blackbody (LABB) with a diameter of 1 m has been successfully constructed for calibrating radiation thermometers 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 long cylindro-conical cavity with a diameter of 1.1 m. Its conical bottom has an apex angle of 120. To achieve good temperature stability and uniformity, the cavity is integrated to a water-bath to which the pressurized water is supplied from a reservoir. To reduce the convection heat loss from the cavity to the ambient, the cavity is purged of the dried air that passes through a coiled tube immersed in the reservoir. For an uncertainty evaluation of the LABB, its temperature stability was measured by using a reference radiation thermometer (RRT) and a platinum resistance thermometer (PRT), and its radiance temperature distributions on the aperture plane were measured by using a thermal camera. Measuring the spectral emissivity of the coating material, the effective emissivity of the blackbody was calculated to be 0.9955 from 1 ?m to 15 ?m. The expanded uncertainty of the radiance temperature scale was evaluated based on the PRT readings, which vary from 0.3 C to 0.5 C ( k = 2) in the temperature range. The temperature scale is validated by comparing with the RRT of which the temperature scale is realized by a multiple fixed-point calibration.

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

2011-08-01

130

Implementation of multilens micro-optical systems with large numerical aperture by stacking of microlenses.  

PubMed

In the field of micro-optics there is a demand for objectives with large numerical aperture (NA). One example is optical storage in which a NA greater than 0.5 is required. For planar microlenses the NA is determined by means of the maximal index difference and the degree of exchange and reaches typical values of 0.13-0.2. Thus stacking is needed to build high NA objectives from planar microlenses. An additional benefit of stacking lenses is the possibility to correct for different types of aberrations. We realized two stacked systems: an array of micro-objectives with a NA of 0.45 from three microlens arrays and a confocal sensor head from four microlens arrays and one pinhole array mask. PMID:18324244

Klug, R; Brenner, K H

1999-12-01

131

Thermal design and performance of the balloon-borne large aperture submillimeter telescope for polarimetry BLASTPol  

NASA Astrophysics Data System (ADS)

We present the thermal model of the Balloon-borne Large-Aperture Submillimeter Telescope for Polarimetry (BLASTPol). This instrument was successfully own in two circumpolar flights from McMurdo, Antarctica in 2010 and 2012. During these two flights, BLASTPol obtained unprecedented information about the magnetic field in molecular clouds through the measurement of the polarized thermal emission of interstellar dust grains. The thermal design of the experiment addresses the stability and control of the payload necessary for this kind of measurement. We describe the thermal modeling of the payload including the sun-shielding strategy. We present the in-flight thermal performance of the instrument and compare the predictions of the model with the temperatures registered during the flight. We describe the difficulties of modeling the thermal behavior of the balloon-borne platform and establish landmarks that can be used in the design of future balloon-borne instruments.

Soler, J. D.; Ade, P. A. R.; Angil, F. E.; Benton, S. J.; Devlin, M. J.; Dober, B.; Fissel, L. M.; Fukui, Y.; Galitzki, N.; Gandilo, N. N.; Klein, J.; Korotkov, A. L.; Matthews, T. G.; Moncelsi, L.; Mroczkowski, A.; Netterfield, C. B.; Novak, G.; Nutter, D.; Pascale, E.; Poidevin, F.; Savini, G.; Scott, D.; Shariff, Jamil A.; Thomas, N. E.; Truch, M. D.; Tucker, C. E.; Tucker, G. S.; Ward-Thompson, D.

2014-07-01

132

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

133

THE BALLOON-BORNE LARGE APERTURE SUBMILLIMETER TELESCOPE (BLAST) 2006: CALIBRATION AND FLIGHT PERFORMANCE  

SciTech Connect

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) operated successfully during a 250 hr flight over Antarctica in 2006 December (BLAST06). As part of the calibration and pointing procedures, the red hypergiant star VY CMa was observed and used as the primary calibrator. Details of the overall BLAST06 calibration procedure are discussed. The 1sigma uncertainty on the absolute calibration is accurate to 9.5%, 8.7%, and 9.2% at the 250, 350, and 500 mum bands, respectively. The errors are highly correlated between bands resulting in much lower errors for the derived shape of the 250-500 mum continuum. The overall pointing error is < 5'' rms for the 36'', 42'', and 60'' beams. The performance of optics and pointing systems is discussed.

Truch, Matthew D. P.; Devlin, Mark J.; Dicker, Simon R.; Klein, Jeff [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Ade, Peter A. R.; Griffin, Matthew; Hargrave, Peter C.; Mauskopf, Philip; Moncelsi, Lorenzo; Pascale, Enzo [Department of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff, CF24 3AA (United Kingdom); Bock, James J. [Jet Propulsion Laboratory, Pasadena, CA 91109-8099 (United States); Chapin, Edward L.; Halpern, Mark; Marsden, Gaelen [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Gundersen, Joshua O. [Department of Physics, University of Miami, 1320 Campo Sano Drive, Coral Gables, FL 33146 (United States); Hughes, David H. [Instituto Nacional de AstrofIsica Optica y Electronica (INAOE), Aptdo. Postal 51 y 72000 Puebla (Mexico); Martin, Peter G. [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Netterfield, C. Barth [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Olmi, Luca [Physics Department, University of Puerto Rico, Rio Piedras Campus, Box 23343, UPR Station, San Juan (Puerto Rico); Patanchon, Guillaume, E-mail: matthew@truch.ne [Universite Paris Diderot, Laboratoire APC, 10 rue Alice Domon et Leonie Duquet 75205 Paris (France)

2009-12-20

134

Thermal design and performance of the balloon-borne large aperture submillimeter telescope for polarimetry BLASTPol  

E-print Network

We present the thermal model of the Balloon-borne Large-Aperture Submillimeter Telescope for Polarimetry (BLASTPol). This instrument was successfully flown in two circumpolar flights from McMurdo, Antarctica in 2010 and 2012. During these two flights, BLASTPol obtained unprecedented information about the magnetic field in molecular clouds through the measurement of the polarized thermal emission of interstellar dust grains. The thermal design of the experiment addresses the stability and control of the payload necessary for this kind of measurement. We describe the thermal modeling of the payload including the sun-shielding strategy. We present the in-flight thermal performance of the instrument and compare the predictions of the model with the temperatures registered during the flight. We describe the difficulties of modeling the thermal behavior of the balloon-borne platform and establish landmarks that can be used in the design of future balloon-borne instruments.

Soler, J D; Angil, F E; Benton, S J; Devlin, M J; Dober, B; Fissel, L M; Fukui, Y; Galitzki, N; Gandilo, N N; Klein, J; Korotkov, A L; Matthews, T G; Moncelsi, L; Mroczkowski, A; Netterfield, C B; Novak, G; Nutter, D; Pascale, E; Poidevin, F; Savini, G; Scott, D; Shariff, J A; Thomas, N E; Truch, M D; Tucker, C E; Tucker, G S; Ward-Thompson, D

2014-01-01

135

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

136

ATLAST-9.2: A Deployable Large Aperture UVOIR Space Telescope  

NASA Technical Reports Server (NTRS)

We present the results of a study of a deployable version of the Advanced Technology Large Aperture Space Telescope (ATLAST) that could be launched on an Evolved Expendable Launch Vehicle (EELV). ATLAST is a concept for a next-generation UVOIR observatory to follow HST and JWST. The observatory retains significant heritage from JWST, thereby taking advantage of technologies and engineering already developed for that mission. At the same time, we have identified several design changes to the JWST architecture, some of which are required due to the demanding wavefront error requirements at visible wavelengths. The optical telescope assembly has a segmented 9.2-meter aperture and consists of 36 hexagonal glass mirrors, each of which is I.3l5m in size (flat-to-flat). The telescope can be folded to fit in the 6.5m fairing on the planned upgrade to the Delta-IV heavy launch vehicle. Near-real time wavefront sensing and control is performed on-board the telescope using stars in the field of view to deliver diffraction limited imaging performance at 500nm wavelength. The optical design of the telescope provides an 8x20 arcmin FOV in which 4-5 instruments can be accommodated, plus fine guidance and wavefront sensors. Unlike JWST, the OTA sits at the end of a multi-gimbaled arm, allowing pitch and roll motion, and is isolated from the sunshield and spacecraft bus by an active isolation system. Our design permits servicing in order to extend the life of the observatory.

Oegerle, William R.; Feinberg, L.; Purves, L.; Hyde, T.; Thronson, H.; Townsend, J.; Postman, M.; Bolcar, M.; Budinoff, J.; Dean, B.; Clampin, N.; Ebbets, D.; Gong, Q.; Gull, T.; Howard, J.; Jones, A.; Lyon, R.; Pasquale, B.; Perrygo, C.; Smith, S.; Thompson, P.; Woodgate, B.

2010-01-01

137

A new large-aperture transportable lidar system for atmospheric measurements is being developed in the  

E-print Network

an array telescope with an equivalent aperture of 1.6 m, and will be housed in a 12 m transportable telescope primary mirrors, to yield an equivalent aperture of 1.6 m. Compared to other telescopes. The observatory is being built from a 12 m shipping container, and will have a retractable roof, a climate

Duck, Thomas J.

138

Large-Aperture Wide-Bandwidth Anti-Reflection-Coated Silicon Lenses for Millimeter Wavelengths  

NASA Technical Reports Server (NTRS)

The increasing scale of cryogenic detector arrays for sub-millimeter and millimeter wavelength astrophysics has led to the need for large aperture, high index of refraction, low loss, cryogenic refracting optics. Silicon with n = 3.4, low loss, and relatively high thermal conductivity is a nearly optimal material for these purposes, but requires an antireflection (AR) coating with broad bandwidth, low loss, low reflectance, and a matched coffecient of thermal expansion. We present an AR coating for curved silicon optics comprised of subwavelength features cut into the lens surface with a custom three axis silicon dicing saw. These features constitute a metamaterial that behaves as a simple dielectric coating. We have fabricated and coated silicon lenses as large as 33.4 cm in diameter with coatings optimized for use between 125-165 GHz. Our design reduces average reflections to a few tenths of a percent for angles of incidence up to 30 deg. with low cross-polarization. We describe the design, tolerance, manufacture, and measurements of these coatings and present measurements of the optical properties of silicon at millimeter wavelengths at cryogenic and room temperatures. This coating and lens fabrication approach is applicable from centimeter to sub-millimeter wavelengths and can be used to fabricate coatings with greater than octave bandwidth.

Datta, R.; Munson, C. D.; Niemack, M. D.; McMahon, J. J.; Britton, J.; Wollack, E. J.; Beall, J.; Devlin, M. J.; Fowler, J.; Gallardo, P.; Hubmayr, J.; Irwin, K.; Newburgh, L.; Nibarger, J. P.; Page, L.; Quijada, M. A.; Schmitt, B. L.; Staggs, S. T.; Thornton, R.; Zhang, L.

2013-01-01

139

Large-aperture Wide-bandwidth Antireflection-coated Silicon Lenses for Millimeter Wavelengths  

NASA Technical Reports Server (NTRS)

The increasing scale of cryogenic detector arrays for submillimeter and millimeter wavelength astrophysics has led to the need for large aperture, high index of refraction, low loss, cryogenic refracting optics. Silicon with n 3.4, low loss, and high thermal conductivity is a nearly optimal material for these purposes but requires an antireflection (AR) coating with broad bandwidth, low loss, low reflectance, and a matched coefficient of thermal expansion. We present an AR coating for curved silicon optics comprised of subwavelength features cut into the lens surface with a custom three-axis silicon dicing saw. These features constitute a metamaterial that behaves as a simple dielectric coating.We have fabricated silicon lenses as large as 33.4 cm in diameter with micromachined layers optimized for use between 125 and 165 GHz. Our design reduces average reflections to a few tenths of a percent for angles of incidence up to 30deg with low cross polarization.We describe the design, tolerance, manufacture, and measurements of these coatings and present measurements of the optical properties of silicon at millimeter wavelengths at cryogenic and room temperatures. This coating and lens fabrication approach is applicable from centimeter to submillimeter wavelengths and can be used to fabricate coatings with greater than octave bandwidth.

Datta, R.; Munson, C. D.; Niemack, M. D.; McMahon, J. J.; Britton, J.; Wollack, Edward J.; Beall, J.; Devlin, M. J.; Fowler, J.; Gallardo, P.; Hubmayr, J.; Irwin, K.; Newburgh, L.; Nibarger, J. P.; Page, L.; Quijada, Manuel A.; Schmitt, B. L.; Staggs, S. T.; Thornton, R.; Zhang, L.

2013-01-01

140

Large-aperture wide-bandwidth antireflection-coated silicon lenses for millimeter wavelengths.  

PubMed

The increasing scale of cryogenic detector arrays for submillimeter and millimeter wavelength astrophysics has led to the need for large aperture, high index of refraction, low loss, cryogenic refracting optics. Silicon with n=3.4, low loss, and high thermal conductivity is a nearly optimal material for these purposes but requires an antireflection (AR) coating with broad bandwidth, low loss, low reflectance, and a matched coefficient of thermal expansion. We present an AR coating for curved silicon optics comprised of subwavelength features cut into the lens surface with a custom three-axis silicon dicing saw. These features constitute a metamaterial that behaves as a simple dielectric coating. We have fabricated silicon lenses as large as 33.4cm in diameter with micromachined layers optimized for use between 125 and 165GHz. Our design reduces average reflections to a few tenths of a percent for angles of incidence up to 30 with low cross polarization. We describe the design, tolerance, manufacture, and measurements of these coatings and present measurements of the optical properties of silicon at millimeter wavelengths at cryogenic and room temperatures. This coating and lens fabrication approach is applicable from centimeter to submillimeter wavelengths and can be used to fabricate coatings with greater than octave bandwidth. PMID:24513939

Datta, R; Munson, C D; Niemack, M D; McMahon, J J; Britton, J; Wollack, E J; Beall, J; Devlin, M J; Fowler, J; Gallardo, P; Hubmayr, J; Irwin, K; Newburgh, L; Nibarger, J P; Page, L; Quijada, M A; Schmitt, B L; Staggs, S T; Thornton, R; Zhang, L

2013-12-20

141

The Balloon-borne Large-Aperture Submillimeter Telescope for Polarization: BLAST-pol  

E-print Network

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a sub-orbital experiment designed to study the process of star formation in local galaxies (including the Milky Way) and in galaxies at cosmological distances. Using a 2-m Cassegrain telescope, BLAST images the sky onto a focal plane, which consists of 270 bolometric detectors split between three arrays, observing simultaneously in 30% wide bands, centered at 250, 350, and 500 microns. The diffraction-limited optical system provides a resolution of 30" at 250 microns. The pointing system enables raster-like scans with a positional accuracy of ~30", reconstructed to better than 5" rms in post-flight analysis. BLAST had two successful flights, from the Arctic in 2005, and from Antarctica in 2006, which provided the first high-resolution and large-area (~0.8-200 deg^2) submillimeter surveys at these wavelengths. As a pathfinder for the SPIRE instrument on Herschel, BLAST shares with the ESA satellite similar focal plane technology and scientific...

Marsden, G; 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; Martin, P G; Martin, T G; Matthews, T G; Mauskopf, P; Moncelsi, L; Netterfield, C B; Novak, G; Pascale, E; Olmi, L; Patanchon, G; Rex, M; Savini, G; Scott, D; Semisch, C; Thomas, N; Truch, M D P; Tucker, C; Tucker, G S; Viero, M P; Ward-Thompson, D; Wiebe, D V

2008-01-01

142

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-Mxico, Chacaltaya-Bolvia, Marcapomacocha-Per, Mrida-Venezuela and Bucaramanga-Colombia.

Rosales, M.

2011-10-01

143

The Balloon-borne Large-Aperture Submillimeter Telescope for Polarization: BLAST-pol  

E-print Network

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a sub-orbital experiment designed to study the process of star formation in local galaxies (including the Milky Way) and in galaxies at cosmological distances. Using a 2-m Cassegrain telescope, BLAST images the sky onto a focal plane, which consists of 270 bolometric detectors split between three arrays, observing simultaneously in 30% wide bands, centered at 250, 350, and 500 microns. The diffraction-limited optical system provides a resolution of 30" at 250 microns. The pointing system enables raster-like scans with a positional accuracy of ~30", reconstructed to better than 5" rms in post-flight analysis. BLAST had two successful flights, from the Arctic in 2005, and from Antarctica in 2006, which provided the first high-resolution and large-area (~0.8-200 deg^2) submillimeter surveys at these wavelengths. As a pathfinder for the SPIRE instrument on Herschel, BLAST shares with the ESA satellite similar focal plane technology and scientific motivation. A third flight in 2009 will see the instrument modified to be polarization-sensitive (BLAST-Pol). With its unprecedented mapping speed and resolution, BLAST-Pol will provide insights into Galactic star-forming nurseries, and give the necessary link between the larger, coarse resolution surveys and the narrow, resolved observations of star-forming structures from space and ground based instruments being commissioned in the next 5 years.

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

2008-05-28

144

The balloon-borne large-aperture submillimeter telescope for polarimetry: BLAST-Pol  

E-print Network

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLAST-Pol) is a suborbital mapping experiment designed to study the role played by magnetic fields in the star formation process. BLAST-Pol is the reconstructed BLAST telescope, with the addition of linear polarization capability. Using a 1.8 m Cassegrain telescope, BLAST-Pol images the sky onto a focal plane that consists of 280 bolometric detectors in three arrays, observing simultaneously at 250, 350, and 500 um. The diffraction-limited optical system provides a resolution of 30'' at 250 um. The polarimeter consists of photolithographic polarizing grids mounted in front of each bolometer/detector array. A rotating 4 K achromatic half-wave plate provides additional polarization modulation. With its unprecedented mapping speed and resolution, BLAST-Pol will produce three-color polarization maps for a large number of molecular clouds. The instrument provides a much needed bridge in spatial coverage between larger-scale, coarse resolutio...

Fissel, Laura M; Angile, Francesco E; Benton, Steven J; Chapin, Edward L; Devlin, Mark J; Gandilo, Natalie N; Gundersen, Joshua O; Hargrave, Peter C; Hughes, David H; Klein, Jeffrey; Korotkov, Andrei L; Marsden, Galen; Matthews, Tristan G; Moncelsi, Lorenzo; Mroczkowski, Tony K; Netterfield, C Barth; Novak, Giles; Olmi, Luca; Pascale, Enzo; Savini, Giorgio; Scott, Douglas; Shariff, Jamil A; Soler, Juan Diego; Thomas, Nicholas E; Truch, Matthew D P; Tucker, Carole E; Tucker, Gregory S; Ward-Thompson, Derek; Wiebe, Donald V

2010-01-01

145

Analysis of mode stability in a concave mirror vertical-cavity surface-emitting laser with an oxide aperture.  

PubMed

We applied the Fox-Li resonator theory to analyze the mode stability of concave mirror surface-emitting lasers. The numerical modeling incorporates the oxide aperture in the simple classical cavity by adding a non-uniform phase shifting layer to the flat mirror side. The calculation shows that there is a modal loss difference between the fundamental mode and the competing modes. The amount of loss difference depends upon cavity length and the thickness of the oxide aperture. In addition to loss difference, modal gain difference plays a key role in discriminating between the fundamental mode and the higher order transverse modes. The modal gain difference heavily depends upon the size of the oxide aperture and the field intensity distribution. To summarize, the geometry of the concave cavity affects the mode profile and the unique field profile of each transverse mode makes a difference in both modal loss and gain. Finally, this leads to a side-mode suppression. PMID:19495278

Ju, Young-Gu

2005-05-16

146

Near-field modulation of laser diode emissions by an aperture probe of near-field optical microscope  

NASA Astrophysics Data System (ADS)

In situ emission profiles of AlGaInP multiple quantum well laser diodes (LDs) observed by a near-field scanning optical microscope (NSOM) probe with an intentionally enlarged aperture shows a single broad elliptic profile, whereas the detected wavelength hops among those of the longitudinal multimodes observed in the far-field. This hopping suggests the near-field coupling between the aperture and the LD cavity, which is proved by the observation of strong modulation of laser intensity by the optical coupling only in the near-field regime. Probes with an intact aperture are found not to couple with the lasing TE 00 mode, but, therefore, couple only with a near-field longitudinal mode. Around the lasing region, emissions detected by an intact aperture are ascribed to amplified spontaneous emissions at wavelengths far from those of the lasing multimode emissions. These near-field modes, with spatial profile different from both the far-field TE and TM modes, are detectable only by the NSOM.

Tomioka, Akihiro; Fujimoto, Atsushi; Kinoshita, Shinji; Susaki, Wataru

2008-04-01

147

Microstrip patch antenna panel for large aperture L-band phased array  

NASA Technical Reports Server (NTRS)

This paper describes the design and development of a large, lightweight antenna panel for an active phased array operating at L-band. The panel was developed under a JPL program of technology development for space based radar. It utilizes dual-stacked patch elements that are interconnected with corporate feed manifold of striplines. This paper focuses on the electromagnetic design and performance of the radiating elements, with emphasis on scan performance, and also addresses mechanical and thermal aspects of the panel. The element in the array environment has a bandwidth of more than 80MHz centered at 1260MHz and is fed so that it can radiate orthogonal linear polarizations. The envisioned phased array, with a nominal aperture of 50m x 2m, is designed to scan +/-45 degrees in azimuth and +/-20 degrees in elevation. The panel of radiating elements has a mass density of 3.9 kg/m2, which represents approximately 50% of the target 8kg/m2 total panel mass density that includes T/R modules and feed manifolds.

Chamberlain, Neil; Amaro, Luis; Oakes, Eric; Hodges, Richard; Spitz, Suzanne; Rosen, Paul A.

2004-01-01

148

Origins of high-frequency scattered waves near PKKP from large aperture seismic array data  

USGS Publications Warehouse

This article identifies the likely origin of 1-Hz scattered waves in the vicinity of PKKP by comparing measurements of slowness and onset time to ray-theoretical predictions. The measurements are obtained from slant stacks of Large Aperture Seismic Array (LASA) data from 36 earthquakes and six explosions in the range 30??-116??. Three types of scattered waves explain the main features seen in the stacks, including: P scattered to PKP near the Earth's surface (P.PKP), PKKP scattered near its core-mantle-boundary (CMB) reflection point (PK.KP), and SKKP scattered near its CMB reflection point (SK.KP). The LASA stacks image the amplitude and slowness variations of the scattered waves with time. They also show where these waves can be detected and where they are free from contaminating arrivals. SK.KP waves rise above the noise approximately 100 sec before the onset time of the main SKKP arrival near 113??. Observations of PK.KP span 30??-100??. However, at distances greater than 50?? they suffer from P.PKP contamination. At distances less than 40?? the PK.KP last for about 280 sec. This is approximately 130 sec longer than the maximum ray-theoretical prediction for waves scattered at the CMB, indicating a possible combination of near-surface scattering and contributions from the overlying mantle.

Earle, P.S.

2002-01-01

149

Study on the method to test large-aperture hyperboloid convex mirror  

NASA Astrophysics Data System (ADS)

There are numerous reflecting optical system designs that call for large-aperture convex surfaces, such as secondary mirror in on-axis three mirror anastigmatic (TMA). Several methods to test high accuracy hyperboloid convex surfaces are introduced separately in this paper. A kind of arrangement is chosen to test a surface with diameter of 420mm, radius of 1371mm, and conic K -2.1229. The CGH compensator for testing is designed, which is made up of illumination lens and hologram test plate with designed residual wavefront aberration less than 0.001? (RMS). The second transmitted method that is equipped with a technical flat surface coating by Ag film in the bottom of surface mirror under test, which form an auto-collimation optical system to eliminate the aberration. The Hindle-Simpson test that requires a larger meniscus lens to compensate the optical aberration, and the designed result of optical test system is less than 0.0016?. Contrasting the CGH compensator and the second transmitted method, the Hindle-Simpson testing method has the advantage of it is easily to manufacture and adjust; meanwhile the test result is stable and has been less affected by the environment. It has been found that the method is rational and reliable, and it can fulfill the requirement of manufacturing and testing process for hyperboloid convex mirrors.

Meng, Xiaohui; Dong, Huiwen; Guo, Wen; Wang, Huijun

2014-08-01

150

8 Meter Advanced Technology Large-Aperture Space Telescope (ATLAST-8m)  

NASA Technical Reports Server (NTRS)

ATLAST-8m (Advanced Technology Large Aperture Space Telescope) is a proposed 8-meter monolithic UV/optical/NIR space observatory (wavelength range 110 to 2500 nm) to be placed in orbit at Sun-Earth L2 by NASA's planned Ares V heavy lift vehicle. Given its very high angular resolution (15 mas @ 500 nm), sensitivity and performance stability, ATLAST-8m is capable of achieving breakthroughs in a broad range of astrophysics including: Is there life elsewhere in the Galaxy? An 8-meter UVOIR observatory has the performance required to detect habitability (H2O, atmospheric column density) and biosignatures (O2, O3, CH4) in terrestrial exoplanet atmospheres, to reveal the underlying physics that drives star formation, and to trace the complex interactions between dark matter, galaxies, and intergalactic medium. The ATLAST Astrophysics Strategic Mission Concept Study developed a detailed point design for an 8-m monolithic observatory including optical design; structural design/analysis including primary mirror support structure, sun shade and secondary mirror support structure; thermal analysis; spacecraft including structure, propulsion, GN&C, avionics, power systems and reaction wheels; mass and power budgets; and system cost. The results of which were submitted by invitation to NRC's 2010 Astronomy & Astrophysics Decadal Survey.

Stahl, H. Philip

2010-01-01

151

Subwavelength grating reflectors in MEMS tunable Fabry-Perot infrared filters with large aperture  

NASA Astrophysics Data System (ADS)

This paper presents a novel tunable infrared filter applying a subwavelength grating that substitutes the distributed Bragg reflectors (DBRs) in tunable Fabry-Perot (FP) filters to reduce cost and fabrication effort. It consists of uniformly arranged disc resonators which are made of 100 nm thick aluminum at a 200 nm Si3N4 membrane carrier that stands freely after fabrication. The dimensions of the subwavelength structures were optimized based on finite difference time domain (FDTD) analysis. The fabrication sequence consists of silicon MEMS technology steps like deposition and patterning of electrodes and of isolation layers, silicon etching, and wafer bonding, and it includes nano imprint lithography for forming the subwavelength structures at wafer level. The samples have an aperture of 2 mm and are mechanically tuned by electrostatic forces with tuning voltages up to 80 V. They show the typical characteristics of FP filters but with high peak transmittance within a remarkably large wavelength range (T < 50% @ 2.5 ?m 6.5 ?m) spanning over 5 interference orders of the optical resonator. The optical performance was measured by Fourier transform infrared spectrometer and compared to the simulation results. It shows a widely good agreement between calculation and measurement.

Kurth, Steffen; Hiller, Karla; Meinig, Marco; Besser, Jan; Seifert, Mario; Ebermann, Martin; Neumann, Norbert; Schlachter, Florian; Gessner, Thomas

2014-02-01

152

Acoustic characterization of high intensity focused ultrasound fields generated from a transmitter with a large aperture  

NASA Astrophysics Data System (ADS)

Prediction and measurement of the acoustic field emitted from a high intensity focused ultrasound (HIFU) is essential for the accurate ultrasonic treatment. In this study, the acoustic field generated from a strongly focused HIFU transmitter was characterized by a combined experiment and simulation method. The spheroidal beam equation (SBE) was utilized to describe the nonlinear sound propagation. The curve of the source pressure amplitude versus voltage excitation was determined by fitting the measured ratio of the second harmonic to the fundamental component of the focal waveform to the simulation result; finally, the acoustic pressure field generated by the strongly focused HIFU transmitter was predicted by using the SBE model. A commercial fiber optic probe hydrophone was utilized to measure the acoustic pressure field generated from a 1.1 MHz HIFU transmitter with a large half aperture angle of 30. The maximum measured peak-to-peak pressure was up to 72 MPa. The validity of this combined approach was confirmed by the comparison between the measured results and the calculated ones. The results indicate that the current approach might be useful to describe the HIFU field. The results also suggest that this method is not valid for low excitations owing to low sensitivity of the second harmonic.

Chen, Tao; Fan, Tingbo; Zhang, Wei; Qiu, Yuanyuan; Tu, Juan; Guo, Xiasheng; Zhang, Dong

2014-03-01

153

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) 2005: Calibration and Targeted Sources  

E-print Network

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) operated successfully during a 100-hour flight from northern Sweden in June 2005 (BLAST05). As part of the calibration and pointing procedures, several compact sources were mapped, including solar system, Galactic, and extragalactic targets, specifically Pallas, CRL 2688, LDN 1014, IRAS 20126+4104, IRAS 21078+5211, IRAS 21307+5049, IRAS 22134+5834, IRAS 23011+6126, K3-50, W 75N, and Mrk 231. One additional source, Arp 220, was observed and used as our primary calibrator. Details of the overall BLAST05 calibration procedure are discussed here. The BLAST observations of each compact source are described, flux densities and spectral energy distributions are reported, and these are compared with previous measurements at other wavelengths. The 250, 350, and 500 um BLAST data can provide useful constraints to the amplitude and slope of the submillimeter continuum, which in turn may be useful for the improved calibration of other submillimeter instruments.

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

2008-03-31

154

Measuring large numerical apertures by imaging the angular distribution of radiation  

E-print Network

for Biological Information Processing 1 Forschungszentrum Jülich 52425 Jülich, Germany j; The importance of numerical aperture and magnification," Biol. Bull. 195, 1-4 (1998). 9. S.W. Hell, H.K. Stelzer

Enderlein, Jörg

155

HI at z 20: The Large Aperture Experiment to Detect the Dark Ages  

NASA Astrophysics Data System (ADS)

When did the first stars form? Did supermassive black holes form at the same time, earlier, or later? One of the great challenges of cosmology today is the study of these first generation objects. The Large Aperture Experiment to Detect the Dark Ages (LEDA) project seeks to detect, in total-power, emission from neutral Hydrogen (21 cm rest wavelength) in the intergalactic medium about 100 million years after the Big Bang (redshifts 20). Detection would deliver the first observational constraints on models of structure formation and the first pockets of star and black holes formation in the Universe. LEDA will develop and integrate by 2013 signal processing instrumentation into the new first station of the Long Wavelength Array (LWA). This comprises a large-N correlator serving all 512 dipole antennas of the LWA1, leveraging a packetized CASPER architecture and combining FPGAs and GPUs for the F and X stages. Iterative calibration and imaging will rely on warped snapshot imaging and be drawn from a GPU-enabled library (cuWARP) that is designed specifically to support wide-field full polarization imaging with fixed dipole arrays. Calibration techniques will include peeling, correction for ionospheric refraction, direction dependent dipole gains, deconvolution via forward modeling, and exploration of pulsar data analysis to improve performance. Accurate calibration and imaging will be crucial requirements for LEDA, necessary to subtract the bright foreground sky and detect the faint neutral Hydrogen signal. From the computational standpoint, LEDA is a O(100) TeraFlop per second challenge that enables a scalable architecture looking toward development of radio arrays requiring power efficient 10 PetaFlop per second performance. Stage two of the Hydrogen Epoch of Reionization Array (HERA2) is one example.

Greenhill, Lincoln J.; Werthimer, D.; Taylor, G.; Ellingson, S.; LEDA Collaboration

2012-05-01

156

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

157

Determining suitability of Large Aperture Scintillometer for validating remote sensing based evapotranspiration maps  

NASA Astrophysics Data System (ADS)

Scintillation method is a relatively new technique for measuring the sensible heat and water fluxes over land surfaces. Path integrating capabilities of scintillometer over heterogeneous landscapes make it a potential tool for comparing the energy fluxes derived from remote sensing based energy balance algorithms. For this reason, scintillometer-derived evapotranspiration (ET) fluxes are being used to evaluate remote sensing based energy balance algorithms for their ability to estimate ET fluxes. However, LAS' (Large Aperture Scintillometer) ability to derive ET fluxes is not thoroughly tested. The objective of this study was to evaluate LAS- and Surface Energy Balance System (SEBS)-derived fluxes against lysimetric data to determine LAS' suitability for validating remote sensing based evapotranspiration (ET) maps. The study was conducted during the Bushland Evapotranspiration and Agricultural Remote sensing EXperiment - 2008 (BEAREX-08) at the USDA-ARS Conservation and Production Research Laboratory (CPRL), Bushland, Texas. SEBS was coded in a GIS environment to retrieve ET fluxes from the high resolution imageries acquired using airborne multispectral sensors. The CPRL has four large weighing lysimeters (3 m long x 3 m wide x 2.4 m deep), each located in the middle of approximately 5 ha fields, arranged in a block pattern. The two lysimeter fields located on the east (NE and SE) were managed under irrigated conditions, and the other two lysimeters on the west (NW and SW) were under dryland management. Each lysimeter field was equipped with an automated weather station that provided measurements for net radiation (Rn), Ts, soil heat flux (Go), Ta, relative humidity, and wind speed. During BEAREX08, the NE and SE fields were planted to cotton on May 21, and the NW and SW dryland lysimeters fields were planted to cotton on June 5. One LAS each was deployed across two large dryland lysimeter fields (NW and SW) and two large irrigated lysimeter fields (NE and SE). The structural parameter of refractive index of air was measured at 1-min interval and averaged at 15-min, and synchronized with weather station. The source area (footprint) of the surface energy fluxes were computed using a footprint model. ET fluxes were derived using LAS-estimated H as a residual from the energy balance equation. Comparison of SEBS- and LAS-derived ET fluxes were made against lysimetric data and performance of each method was discussed to determine the suitability of LAS for evaluating accuracy of remote sensing based ET maps.

Paul, G.; Gowda, P. H.; Howell, T. A.; Basu, S.; Colaizzi, P. D.; Marek, T.

2013-12-01

158

Long-wavelength vertical-cavity surface-emitting lasers with selectively etched thin apertures  

NASA Astrophysics Data System (ADS)

Long-wavelength vertical-cavity surface-emitting lasers (VCSELs) emitting in the 1300--1600nm wavelength window are attractive light sources for short to mid-range optical fiber communications. These devices target low-loss and low-dispersion minima in standard optical fibers and are expected to provide a low-cost alternative to the existing edge-emitting infrastructure. With low-power consumption, on wafer testing; simple packaging, and high fiber-coupling efficiency, VCSELs are ideal transmitters for CWDM, metro, local area, and storage area networks. Recently, much attention has been devoted to a rich variety of approaches to long-wavelength VCSELs. One underlying problem, however, has been the need to match a reliable high-gain active region with high-index-contrast distributed Bragg reflectors (DBRs) over the full 1300--1600nm wavelength range. One solution to this problem is to utilize well-established InAlGaAs active-region technology coupled with AlGaAsSb DBRs. This combination facilitates monolithic all-epitaxial InP-based devices spanning the entire 1300--1600nm wavelength range. Previously, Dr. Shigeru Nakagawa and Dr. Eric Hall have demonstrated long-wavelength VCSELs with Sb-based technology operating at 1550nm. This dissertation demonstrates the first high-performance InP-based VCSELs with Sb-based DBRs operating at 1310nm, thus solidifying Sb-based technology as a wavelength flexible platform for long-wavelength devices. Also developed is a novel and efficient tunnel-junction aperturing technology for generating extremely low-loss optical and electrical confinement. Lastly, it is shown that the benefits from such an aperturing scheme produce marked improvements in device operation versus previously demonstrated Sb-based VCSELs. The devices from this research generated over 1.6mW single-mode continuous-wave (CW) output power at room temperature (>2mW multi-mode), displayed threshold currents down to 1mA, and operated CW up to 90C. Furthermore, world-record CW differential efficiencies (>60%) for long-wavelength VCSELs were obtained, demonstrating the effectiveness of low-loss selectively etched tunnel-junction apertures. High-speed modulation up to 6.0Gb/s was also demonstrated for the first time in Sb-based VCSELs. Error-free operation at 3.125Gb/s was shown up to 60C, with extinction ratios remaining >8dB. These results clearly demonstrate that all-epitaxial InP-based devices with Sb-based DBRs are a viable option for high-performance long-wavelength VCSELs.

Feezell, Daniel F.

159

Assessing Inter-Sensor Variability and Sensible Heat Flux Derivation Accuracy for a Large Aperture Scintillometer  

PubMed Central

The accuracy in determining sensible heat flux (H) of three Kipp and Zonen large aperture scintillometers (LAS) was evaluated with reference to an eddy covariance (EC) system over relatively flat and uniform grassland near Timpas (CO, USA). Other tests have revealed inherent variability between Kipp and Zonen LAS units and bias to overestimate H. Average H fluxes were compared between LAS units and between LAS and EC. Despite good correlation, inter-LAS biases in H were found between 6% and 13% in terms of the linear regression slope. Physical misalignment was observed to result in increased scatter and bias between H solutions of a well-aligned and poorly-aligned LAS unit. Comparison of LAS and EC H showed little bias for one LAS unit, while the other two units overestimated EC H by more than 10%. A detector alignment issue may have caused the inter-LAS variability, supported by the observation in this study of differing power requirements between LAS units. It is possible that the LAS physical misalignment may have caused edge-of-beam signal noise as well as vulnerability to signal noise from wind-induced vibrations, both having an impact on the solution of H. In addition, there were some uncertainties in the solutions of H from the LAS and EC instruments, including lack of energy balance closure with the EC unit. However, the results obtained do not show clear evidence of inherent bias for the Kipp and Zonen LAS to overestimate H as found in other studies. PMID:24473285

Rambikur, Evan H.; Chavez, Jose L.

2014-01-01

160

Thermal Analysis of the Advanced Technology Large Aperture Space Telescope (ATLAST) 8 Meter Primary Mirror  

NASA Technical Reports Server (NTRS)

The Advanced Technology Large Aperture Space Telescope (ATLAST) preliminary design concept consists of an 8 meter diameter monolithic primary mirror enclosed in an insulated, optical tube with stray light baffles and a sunshade. ATLAST will be placed in orbit about the Sun-Earth L2 and will experience constant exposure to the sun. The insulation on the optical tube and sunshade serve to cold bias the telescope which helps to minimize thermal gradients. The primary mirror will be maintained at 280K with an active thermal control system. The geometric model of the primary mirror, optical tube, sun baffles, and sunshade was developed using Thermal Desktop(R) SINDA/FLUINT(R) was used for the thermal analysis and the radiation environment was analyzed using RADCAD(R). A XX node model was executed in order to characterize the static performance and thermal stability of the mirror during maneuvers. This is important because long exposure observations, such as extra-solar terrestrial planet finding and characterization, require a very stable observatory wave front. Steady state thermal analyses served to predict mirror temperatures for several different sun angles. Transient analyses were performed in order to predict thermal time constant of the primary mirror for a 20 degree slew or 30 degree roll maneuver. This paper describes the thermal model and provides details of the geometry, thermo-optical properties, and the environment which influences the thermal performance. All assumptions that were used in the analysis are also documented. Parametric analyses are summarized for design parameters including primary mirror coatings and sunshade configuration. Estimates of mirror heater power requirements are reported. The thermal model demonstrates results for the primary mirror heated from the back side and edges using a heater system with multiple independently controlled zones.

Hornsby, Linda; Stahl, H. Philip; Hopkins, Randall C.

2010-01-01

161

Journal of Atmospheric and Solar-Terrestrial Physics 67 (2005) 11711177 Modelling high-power large-aperture radar meteor trails  

E-print Network

-aperture radar meteor trails Lars P. Dyrud?, Licia Ray, Meers Oppenheim, Sigrid Close, Kelly Denney Center see high-power large-aperture (HPLA) radar observations of meteor phenomena called head echoes and non demonstrating that meteor trails are unstable to growth of Farley­Buneman gradient-drift (FBGD) waves

Oppenheim, Meers

162

In-situ spectral reflectance measurement of off-axis paraboloidal reflector with a large aperture for radiometric calibration  

NASA Astrophysics Data System (ADS)

Off-axis paraboloidal reflector with a large aperture is often used as a collimator in radiometric calibration system in the space environment or a simulator for space carrier. Spectral reflectance measurement of the reflector is an important issue that determines the accuracy of radiometric calibration, especially, for imaging spectrometer. Currently, the reflectance of the reflector is generally measured by the sample contrast method. So, only a small sample of the reflector rather than the whole can be measured. In order to overcome this limitation, a method for in-situ measuring spectral reflectance of off-axis paraboloidal reflector, especially, with a large aperture, is proposed in this paper. First of all, the proposed in-situ measurement approach is designed according to in-situ contrast measurement. Then, the proposed measurement is realized and evaluated in experiment for measuring spectral reflectance of an off-axis paraboloidal reflector with an aperture of 110 mm. Finally, the influence of prodigious temperature fluctuation on the measurement is experimentally investigated and the impact of optical devices and environment on the uncertainty is analyzed. The total experimental uncertainty is obtained as 4.2%. The experimental results proved that the spectral reflectance of the reflector will decrease when the experimental temperature falls from 20 C to -100 C and the decrease degree is different for different wavelength bands.

Zhang, Ying; Zhao, Huijie; Zhou, Pengwei; Li, Chongchong

2014-01-01

163

Design and construction of a large aperture quadrupole electromagnet for ILSE  

SciTech Connect

We are currently constructing a prototype quadrupole electromagnet for the proposed Induction Linac Systems Experiment (ILSE) at LBNL. ILSE will address many physics and engineering issues relevant to the design of a heavy-ion fusion driver accelerator. The pulsed electromagnet has two layers of current windings and will produce a field gradient of 28 T/m, wi a usable aperture of 6 cm. It operates at a repetition rate of 1 Hz, steady-state. In this paper, we discuss how the interaction of various concerns such as maximum dynamic aperture, short lattice period, field quality, iron yoke weight, heat transfer, and voltage standoff have led to our particular design choices. We also present 2- and 3-D numerical calculations concerning field topography and the results of transport simulations of space-charge dominated ion beams with ILSE parameters.

Fawley, W.M.; Vella, M.C.; Peters, C.; Stuart, M.; Faltens, A.

1995-08-01

164

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

165

Optical sparse aperture imaging  

Microsoft Academic Search

The resolution of a conventional diffraction-limited imaging system is proportional to its pupil diameter. A primary goal of sparse aperture imaging is to enhance resolution while minimizing the total light collection area; the latter being desirable, in part, because of the cost of large, monolithic apertures. Performance metrics are defined and used to evaluate several sparse aperture arrays constructed from

Nicholas J. Miller; Matthew P. Dierking; Bradley D. Duncan

2007-01-01

166

Small feature sizes and high aperture ratio organic light-emitting diodes by using laser-patterned polyimide shadow masks  

NASA Astrophysics Data System (ADS)

A shadow mask technique capable of realizing high resolution (>330 pixel-per-inch) and 100% aperture ratio Organic Light-Emitting Diode (OLED) full color displays is demonstrated. The technique utilizes polyimide contact shadow masks, patterned by laser ablation. Red, green, and blue OLEDs with very small feature sizes (<25 ?m) are fabricated side by side on one substrate. OLEDs fabricated via this technique have the same performance as those made by established technology. This technique has a strong potential to achieve high resolution OLED displays via standard vacuum deposition processes even on flexible substrates.

Kajiyama, Yoshitaka; Joseph, Kevin; Kajiyama, Koichi; Kudo, Shuji; Aziz, Hany

2014-02-01

167

Near-Field Modulation of AlGaInP Laser Diode Emissions by an Aperture Probe of Near-Field Optical Microscope  

Microsoft Academic Search

In situ emission profiles of AlGaInP multiple quantum well laser diodes (LD's) observed by a near-field scanning optical microscope (NSOM) aperture probe shows a single broad elliptic profile similar to a far-field observation, whereas the local emission spectrum was different depending where the aperture probe was placed within the emission profile. This observation suggests the existence of a near-field coupling

Yasushi Kamiyama; Akihiro Tomioka; Takahiro Anzai; Kazuhisa Iwamoto; Wataru Susaki

2010-01-01

168

Fine calibration of large-aperture optical scintillometers and an optical estimate of inner scale of turbulence.  

PubMed

Large-aperture optical scintillometers [Ting-i Wang et al., J. Opt. Soc. Am. 68, 334 (1978)] lose their calibration if they are sensitive to portions of the spatial spectrum of temperature fluctuations where (K)(-11/3) fails to hold. The model temperature spectrum having the bump [R. J. Hill, J. Fluid Mech. 88, 541 (1978); R. J. Hill and S. F. Clifford, J. Opt. Soc. Am. 68, 892 (1978)] is used to find conditions under which the scintillometers maintain their calibration. We find that the aperture size D should be at least twenty times the inner scale l(0) if the contribution of the spectral bump is to be ignored. For application in the surface layer, one needs the height above ground of the optical path to be much greater than three times the aperture size if outer-scale effects are to be negligible. It is shown that the inner scale dependence of a scintillometer having D/l(0) approximately 2.0 and the lack of such dependence for a scintillometer having D/l(0) approximately 20.0 can be used to estimate both l(0) and C(2)(n) if the two systems are used simultaneously on the same path. A preliminary experiment was performed in the atmospheric surface layer with scintillometers having aperture sizes of 2.0 cm, 5.0 cm, and 15.0 cm; the results are consistent with the existence of the spectral bump. The inner scale is estimated by comparing data from the 2.0-cm and 15.0-cm systems. Using this inner scale, the C(2)(n) values from the 5.0-cm and 15.0-cm scintillometers are corrected for the spectral bump; the corrected values are in agreement. Other turbulence parameters are not deduced from the l(0) and C(2)(n) estimates because the l(0) values have been found to be insufficiently accurate. PMID:20204039

Hill, R J; Ochs, G R

1978-11-15

169

Near-Field Modulation of AlGaInP Laser Diode Emissions by an Aperture Probe of Near-Field Optical Microscope  

NASA Astrophysics Data System (ADS)

In situ emission profiles of AlGaInP multiple quantum well laser diodes (LD's) observed by a near-field scanning optical microscope (NSOM) aperture probe shows a single broad elliptic profile similar to a far-field observation, whereas the local emission spectrum was different depending where the aperture probe was placed within the emission profile. This observation suggests the existence of a near-field coupling between the aperture and the LD cavity, which might modulate the lasing wavelength among the longitudinal multimodes determined by the LD cavity length.

Kamiyama, Yasushi; Tomioka, Akihiro; Anzai, Takahiro; Iwamoto, Kazuhisa; Susaki, Wataru

2010-01-01

170

Design and construction of a large aperture, quadrupole electromagnet prototype for ILSE  

SciTech Connect

We are currently constructing a prototype quadrupole electromagnet for the proposed Induction Linac Systems Experiment (ILSE) at LBL. ILSE will address many physi and engineering issues relevant to the design of a heavy-ion fusion driver accelerator. The pulsed electromagnet has two layers of current windings and will produce a field gradient exceeding 25 T/m at a repetition rate of 1 Hz steady-state. In this paper, we discuss how the interaction of various concerns such as maximum dynamic aperture, short lattice period, field quality, iron yoke weight, heat transfer, and voltage standoff have led to our particular design choices. We also present 2- and 3-D numerical calculations concerning field topography and the results of transport simulations of space-charge dominated ion beams with ILSE parameters.

Stuart, M.; Faltens, A.; Fawley, W.M.; Peters, C.; Vella, M.C.

1995-04-01

171

Active Optics for a 16-Meter Advanced Technology Large Aperture Space Telescope  

E-print Network

. Continuous low-bandwidth metrology of the optics will be used to preserve image quality during extended observations. Keywords: Wavefront sensing, wavefront control, laser metrology, active optics, segmented mirrors of this opportunity, our group, led by Marc Postman of the STScI and consisting of 66 investigators from NASA

Sirianni, Marco

172

Large field F-? laser scanning system  

NASA Astrophysics Data System (ADS)

A large field laser scanning system is designed for PID imaging system. According to different deflectors, scanning system methods have optical lens scanning system, polygon mirror scanning system, acousto-optic scanning system and holographic scanning method. To realize large field scanning, a polygon mirror is used as scanner, which has high scanning speed, high resolution and contrast, good gamma characteristic and F-? lens system is used as focusing system in type of scanner before lens. F-? lens is special lens with linear scanning characteristic. F-? lens can focus laser beam and make linear scanning. The scanning performance of F-? lens is usually decided by its focusing characteristics. Designed system can scan object in 356mm length and the resolution achieves 35?m. Ball bearing guide screw system is used to realize scanning in Y direction, the scanning length can be set according to request. Thus, the system can make two dimensional scanning. By evaluating performance of optical system, the system focusing characteristics had achieved the diffraction limit in entire field and satisfies the system's requests. Experiment has been carried on to test the F-? optical focusing system. The experimental results show that diameters of focusing facular at all view field are approximately 35?m, which is identical with theoretical parameter and conforms to F-? characteristic.

Shan, Baozhong; Guo, Baoping; Niu, Hanben

2009-05-01

173

An efficient and novel computation method for simulating diffraction patterns from large-scale coded apertures on large-scale focal plane arrays  

NASA Astrophysics Data System (ADS)

A novel and memory efficient method for computing diffraction patterns produced on large-scale focal planes by largescale Coded Apertures at wavelengths where diffraction effects are significant has been developed and tested. The scheme, readily implementable on portable computers, overcomes the memory limitations of present state-of-the-art simulation codes such as Zemax. The method consists of first calculating a set of reference complex field (amplitude and phase) patterns on the focal plane produced by a single (reference) central hole, extending to twice the focal plane array size, with one such pattern for each Line-of-Sight (LOS) direction and wavelength in the scene, and with the pattern amplitude corresponding to the square-root of the spectral irradiance from each such LOS direction in the scene at selected wavelengths. Next the set of reference patterns is transformed to generate pattern sets for other holes. The transformation consists of a translational pattern shift corresponding to each hole's position offset and an electrical phase shift corresponding to each hole's position offset and incoming radiance's direction and wavelength. The set of complex patterns for each direction and wavelength is then summed coherently and squared for each detector to yield a set of power patterns unique for each direction and wavelength. Finally the set of power patterns is summed to produce the full waveband diffraction pattern from the scene. With this tool researchers can now efficiently simulate diffraction patterns produced from scenes by large-scale Coded Apertures onto large-scale focal plane arrays to support the development and optimization of coded aperture masks and image reconstruction algorithms.

Shrekenhamer, Abraham; Gottesman, Stephen R.

2012-10-01

174

Aperture synthesis  

Microsoft Academic Search

The article reviews the principles of aperture synthesis theory, with emphasis on earth rotation aperture synthesis, and the main data processing techniques for aperture synthesis telescope systems. A derivation is given for the formula giving the brightness distribution recorded by a continuum aperture synthesis system which samples the complex autocorrelation function of the electric field. The basic formulas are presented

W. N. Brouw

1975-01-01

175

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

Microsoft Academic Search

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

Wei Hu; Zhenchao Zhang; Daxing Wang

2008-01-01

176

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

177

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry-BLASTPol: performance and results from the 2012 Antarctic flight  

NASA Astrophysics Data System (ADS)

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) is a suborbital mapping experiment, designed to study the role played by magnetic fields in the star formation process. BLASTPol observes polarized light using a total power instrument, photolithographic polarizing grids, and an achromatic half-wave plate to modulate the polarization signal. During its second flight from Antarctica in December 2012, BLASTPol made degree scale maps of linearly polarized dust emission from molecular clouds in three wavebands, centered at 250, 350, and 500 ?m. The instrumental performance was an improvement over the 2010 BLASTPol ight, with decreased systematics resulting in a higher number of confirmed polarization vectors. The resultant dataset allows BLASTPol to trace magnetic fields in star-forming regions at scales ranging from cores to entire molecular cloud complexes.

Galitzki, N.; Ade, P. A. R.; Angil, F. E.; Benton, S. J.; Devlin, M. J.; Dober, B.; Fissel, L. M.; Fukui, Y.; Gandilo, N. N.; Klein, J.; Korotkov, A. L.; Matthews, T. G.; Moncelsi, L.; Netterfield, C. B.; Novak, G.; Nutter, D.; Pascale, E.; Poidevin, F.; Savini, G.; Scott, D.; Shariff, J. A.; Soler, J. D.; Tucker, C. E.; Tucker, G. S.; Ward-Thompson, D.

2014-07-01

178

The Advanced Technology Large Aperture Space Telescope (ATLAST): Science Drivers, Technology Developments, and Synergies with Other Future Facilities  

NASA Technical Reports Server (NTRS)

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers that define the main performance requirements for ATLAST (8 to 16 milliarcsec angular resolution, diffraction limited imaging at 0.5 m wavelength, minimum collecting area of 45 square meters, high sensitivity to light wavelengths from 0.1 m to 2.4 m, high stability in wavefront sensing and control). We will also discuss the synergy between ATLAST and other anticipated future facilities (e.g., TMT, EELT, ALMA) and the priorities for technology development that will enable the construction for a cost that is comparable to current generation observatory-class space missions.

Postman, Marc; Brown, Tom; Sembach, Kenneth; Giavalisco, Mauro; Traub, Wesley; Stapelfeldt, Karl; Calzetti, Daniela; Oegerle, William; Rich, R. Michael; Stahl, H. Phillip; Tumlinson, Jason; Mountain, Matt; Soummer, Remi; Hyde, Tupper

2011-01-01

179

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

180

Multilayer coated grazing incidence condenser for large numerical aperture objective at wavelength of 4.5??nm.  

PubMed

A grazing incidence condenser is developed for objectives with large numerical aperture working in Carbon-window wavelength region (?=4.4-5.0??nm) with the use of a point light source. The condenser is composed of four pieces of toroidal mirrors and a piece of the mirror was fabricated to evaluate the performance of the mirror. The radii of the toroidal mirror are determined by ray-trace calculation, and each radius of the mirror substrate and the roughness of the polished surface were evaluated to satisfy the designed parameter. A Co/C reflection multilayer is also designed to reflect soft x-ray light at 4.5nm wavelength, and the reflection multilayer was deposited on the mirror surface. Measured reflectance of the toroidal mirror with the reflection multilayer is higher than 0.32 at 4.5nm wavelength. PMID:25322392

Ejima, T; Hatano, T; Ohno, K; Fukayama, T; Aihara, S; Yanagihara, M; Tsuru, T

2014-10-10

181

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry-BLASTPol: Performance and results from the 2012 Antarctic flight  

E-print Network

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) is a suborbital mapping experiment, designed to study the role played by magnetic fields in the star formation process. BLASTPol observes polarized light using a total power instrument, photolithographic polarizing grids, and an achromatic half-wave plate to modulate the polarization signal. During its second flight from Antarctica in December 2012, BLASTPol made degree scale maps of linearly polarized dust emission from molecular clouds in three wavebands, centered at 250, 350, and 500 microns. The instrumental performance was an improvement over the 2010 BLASTPol flight, with decreased systematics resulting in a higher number of confirmed polarization vectors. The resultant dataset allows BLASTPol to trace magnetic fields in star-forming regions at scales ranging from cores to entire molecular cloud complexes.

Galitzki, N; Angil, F E; Benton, S J; Devlin, M J; Dober, B; Fissel, L M; Fukui, Y; Gandilo, N N; Klein, J; Korotkov, A L; Matthews, T G; Moncelsi, L; Netterfield, C B; Novak, G; Nutter, D; Pascale, E; Poidevin, F; Savini, G; Scott, D; Shariff, J A; Soler, J D; Tucker, C E; Tucker, G S; Ward-Thompson, D

2014-01-01

182

Reliability of various size oxide aperture VCSELs  

Microsoft Academic Search

This paper presents Honeywell's most recent work on 850 nm oxide aperture vertical cavity surface emitting laser (VCSEL) reliability. The VCSELs studied have a range of aperture diameters from about 5 to 20 ?m and the reliability effect of aperture diameter is of principal interest in this paper. Larger apertures generally exhibit greater reliability. Electrostatic discharge (ESD) sensitivity thresholds of

Bobby M. Hawkins; James K. Guenter; Jim A. Tatum; J. R. Biard

2002-01-01

183

New technologies for the actuation and controls of large aperture lightweight quality mirrors  

NASA Technical Reports Server (NTRS)

This paper presents a set of candidate components: MEMS based large stroke (>100 microns) ultra lightweight (0.01 gm) discrete inch worm actuator technology, and a distributed actuator technology, in the context of a novel lightweight active flexure-hinged substrate concept that uses the nanolaminate face sheet.

Lih, S. S.; Yang, E. H.; Gullapalli, S. N.; Flood, R.

2003-01-01

184

A Neutral Hydrogen Survey of the Large Magellanic Cloud: Aperture Synthesis and Multibeam Data Combined  

NASA Astrophysics Data System (ADS)

Recent H I surveys of the Large Magellanic Cloud (LMC) with the Australia Telescope Compact Array and the Parkes multibeam receiver have focused, respectively, on the small-scale (<20') structure of the interstellar medium (ISM) and the large-scale (>1) structure of the galaxy. Using a Fourier-plane technique, we have merged both data sets, providing an accurate set of images of the LMC sensitive to structure on scales of 15 pc upward. The spatial dynamic range (2.8 orders of magnitude), velocity resolution (1.649 km s-1), brightness temperature sensitivity (2.4 K), and column density sensitivity (7.21018 cm-2 per 1.649 km s-1 channel) allow for studies of phenomena ranging from the galaxy-wide interaction of the LMC with its close neighbors to the small-scale injection of energy from supernovae and stellar associations into the ISM of the LMC. This paper presents the merged data and size spectrum of H I clouds, which is similar to the typical size spectrum of the holes and shells in the H I distribution. The H I clouds in the LMC have been identified by defining a cloud to be an object composed of all pixels in right ascension, declination, and velocity that are simply connected and that lie above the threshold brightness temperature.

Kim, Sungeun; Staveley-Smith, Lister; Dopita, Michael A.; Sault, Robert J.; Freeman, Kenneth C.; Lee, Youngung; Chu, You-Hua

2003-10-01

185

Multi-Scale Sensible Heat Fluxes in the Suburban Environment from Large-Aperture Scintillometry and Eddy Covariance  

NASA Astrophysics Data System (ADS)

Sensible heat fluxes () are determined using scintillometry and eddy covariance over a suburban area. Two large-aperture scintillometers provide spatially integrated fluxes across path lengths of 2.8 and 5.5 km over Swindon, UK. The shorter scintillometer path spans newly built residential areas and has an approximate source area of 2-4 , whilst the long path extends from the rural outskirts to the town centre and has a source area of around 5-10 . These large-scale heat fluxes are compared with local-scale eddy-covariance measurements. Clear seasonal trends are revealed by the long duration of this dataset and variability in monthly is related to the meteorological conditions. At shorter time scales the response of to solar radiation often gives rise to close agreement between the measurements, but during times of rapidly changing cloud cover spatial differences in the net radiation () coincide with greater differences between heat fluxes. For clear days lags , thus the ratio of to increases throughout the day. In summer the observed energy partitioning is related to the vegetation fraction through use of a footprint model. The results demonstrate the value of scintillometry for integrating surface heterogeneity and offer improved understanding of the influence of anthropogenic materials on surface-atmosphere interactions.

Ward, H. C.; Evans, J. G.; Grimmond, C. S. B.

2014-07-01

186

Sensitivity of large-aperture scintillometer measurements of area-average heat fluxes to uncertainties in topographic heights  

NASA Astrophysics Data System (ADS)

Scintillometer measurements allow for estimations of the refractive index structure parameter Cn2 over large areas in the atmospheric surface layer. Turbulent fluxes of heat and momentum are inferred through coupled sets of equations derived from the Monin-Obukhov similarity hypothesis. One-dimensional sensitivity functions have been produced that relate the sensitivity of heat fluxes to uncertainties in single values of beam height over homogeneous and flat terrain. However, real field sites include variable topography and heterogeneous surfaces. We develop here the first analysis of the sensitivity of scintillometer derived sensible heat fluxes to uncertainties in spatially distributed topographic measurements. For large-aperture scintillometers and independent friction velocity u* measurements, sensitivity is shown to be concentrated in areas near the center of the beam path and where the underlying topography is closest to the beam height. Uncertainty may be greatly reduced by focusing precise topographic measurements in these areas. A new two-dimensional variable terrain sensitivity function is developed for quantitative error analysis. This function is compared with the previous one-dimensional sensitivity function for the same measurement strategy over flat and homogeneous terrain. Additionally, a new method of solution to the set of coupled equations is produced that eliminates computational error. The results are produced using a new methodology for error analysis involving distributed parameters that may be applied in other disciplines.

Gruber, M. A.; Fochesatto, G. J.; Hartogensis, O. K.

2014-01-01

187

Proposal for a feasibility study of very large aperture quadrupole magnets  

SciTech Connect

The authors seek expert assistance in performing a feasibility study for quadrupole magnets with inner radius at least 80 cm, field at that radius of at least 1.5 Tesla, and field integral at that radius of at least 3 Tesla-m. These magnets would be used as the spectrometer magnets in hadron-collider experiments that emphasize relatively low transverse momentum and large angular coverage, such as studies of B physics and of a variety of physics topics in the far-forward direction. The magnets would preferably be superconducting, but conventional construction may be considered as well. Should the magnets be deemed feasible, the authors then seek to initiate an R and D program to construct a prototype.

Bjorken, J.D. [Stanford Linear Accelerator Center, Menlo Park, CA (US); McDonald, K.T. [Princeton Univ., NJ (US). Joseph Henry Labs.

1993-04-01

188

A 16-m Telescope for the Advanced Technology Large Aperture Telescope (ATLAST) Mission  

NASA Astrophysics Data System (ADS)

Future space observatories will require increasingly large telescopes to study the earliest stars and galaxies, as well as faint nearby objects. Technologies now under development will enable telescopes much larger than the 6.5-meter diameter James Webb Space Telescope (JWST) to be developed at comparable costs. Current segmented mirror and deployable optics technology enables the 6.5 meter JWST telescope to be folded for launch in the 5-meter diameter Ariane 5 payload fairing, and deployed autonomously after reaching orbit. Late in the next decade, when the Ares V Cargo Launch Vehicle payload fairing becomes operational, even larger telescope can be placed in orbit. In this paper we present our concept for a 16-meter JWST derivative, chord-fold telescope which could be stowed in the 10-m diameter Ares V fairing, plus a description of the new technologies that enable ATLAST to be developed at an affordable price.

Lillie, Charles F.; Dailey, D. R.; Polidan, R. S.

2010-01-01

189

A large aperture spectrometer at Fermilab to study high mass dimuons  

NASA Astrophysics Data System (ADS)

A large acceptance forward spectrometer located in a unique antiproton enriched beam has been used at Fermi National Accelerator Laboratory by Experiment 537 to study the production of high mass muon pairs. When the beam was operated at a momentum of 125 GeV/ c, it had a flux of 1.5 10 7 particles per second of which 18% were antiprotons. The spectrometer was of closed geometry design and used drift chambers as the tracking elements. Operating over a relatively short period, the experiment accumulated the largest sample of antiproton-induced high mass dimuons of any experiment to date. The contamination of this data by pion-induced dimuons was less than 0.5%.

Anassontzis, E.; Katsanevas, S.; Kostarakis, P.; Kourkoumelis, C.; Markou, A.; Resvanis, L. K.; Voulgaris, G.; Binkley, M.; Cox, B.; Enagonio, J.; Hale, G.; Hojvat, C.; Judd, D.; Kephart, K.; Kephart, R. D.; Malhotra, P. K.; Mazur, P. O.; Murphy, C. T.; Turkot, F.; Wagner, R. L.; Wagoner, D.; Yang, W.; Areti, H.; Conetti, S.; Lebrun, P.; Ryan, D. G.; Ryan, T.; Schappert, W.; Stairs, D. G.; Akerlof, C.; Cui, X.; Kraushaar, P.; Nitz, D.; Thun, R.; Wang, L.; He, Mao; Zhang, Nai-Jian

1986-01-01

190

From Monolithics to Tethers to Freeflyers: The Spectrum of Large Aperture Sensing from Space  

NASA Technical Reports Server (NTRS)

As part of 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 s-pace-based platforms that can permit this data gathering to occur. Observational data gathering is desired at's 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, David; Bauer, Frank (Technical Monitor)

2002-01-01

191

T/R module development for large aperture L-band phased array  

NASA Technical Reports Server (NTRS)

This paper describes a transmit / receive (T/R) module for a large L-band space based radar active phased array being developed at JPL. Electrical performance and construction techniques are described, with emphasis on the former. The T/R modules have a bandwidth of more than 80 MHz centered at 1260MHz and support dual, switched polarizations. Phase and amplitude are controlled by a 6-bit phase shifter and a 6-bit attenuator, respectively. The transmitter power amplifier generates 2.4 W into a nominal 50 ohm load with 36% overall efficiency. The receiver noise figure is 4.4 dB including all front-end losses. The module weighs 32 g and has a footprint of 8 cm x 4.5 cm. Fourteen of these T/R modules were fabricated at the JPL Pick-and-Place Facility and were tested using a computer-controlled measurement facility developed at JPL. Calibrated performance of this set of T/R modules is presented and shows good agreement with design predictions.

Chamberlain, Neil; Andricos, Constantine; Kumley, Kendra; Berkun, Andrew; Hodges, Richard; Spitz, Suzanne

2004-01-01

192

Performance evaluation of large aperture "polished panel" optical receivers based on experimental data  

NASA Astrophysics Data System (ADS)

Recent interest in the development of hybrid RF/Optical communications has led to the installation of a polished-panel optical receiver evaluation assembly on the 34-meter research antenna at Deep-Space Station 13 (DSS-13) at NASA's Goldstone Deep Space Communications Complex1. The test setup consists of a custom aluminum panel polished to optical smoothness, and a large-sensor CCD camera designed to image the point-spread function (PSF) generated by the polished aluminum panel. Extensive data has been obtained via real-time tracking and imaging of planets and stars at DSS-13. Both on-source and off-source data were recorded at various elevations, enabling the development of realistic simulations and analytic models to help determine the performance of future deep-space communications systems operating with on-off keying (OOK) or pulse-position-modulated (PPM) signaling formats, and compared with the ultimate quantum bound on detection performance. Experimentally determined PSFs were scaled to provide realistic signal-distributions across a photon-counting detector array when a pulse is received, and uncoded as well as block-coded performance analyzed and evaluated for a well-known class of block codes.

Vilnrotter, V.

193

Feed system design considerations for large space antenna systems. Part 2: Single aperture with overlapping feeds  

NASA Technical Reports Server (NTRS)

Contiguous multiple beams are used to make use of the set of frequency bands at different beams at different geographical locations and achieve the most efficient use of precious frequency allocation. This is feasible only if the interference among cochannel beams is below some acceptable level, by carrier/interference (C/I) ratio. Individual beam patterns of very low sidelobes, which in turn necessitates narrow feed are required. A physically realizable solution to this problem entails either more than one reflector, more complicated optics, or breaking of each feed into a cluster of smaller elements, some of which would then be shared by adjacent beams. The latter, however, requires a complicated beamforming network (BFN) for the proper feeding of the elements. The feedpacking problem is not unique to reflector antennas and exists in lens type antennas as well. The BFN and associated problems are present in the phased array antennas and on a much larger scale. Poor scan capabilities are associated with reflector systems. The scan properties of offset fed reflector systems can be improved by choosing a very large focal length to parent reflector diameter ((F/Dp) ratio, which requires a longer boom to support the feed. In the case of reflectors with cluster feed arrangements, the scan capability for smaller F/Dp ratios is improved by proper adjustment of cluster element excitations. Such a system seems to be appropriate for up to 10 beamwidths scan. For a larger number of beams, systems with wider scan capabilities, such as phased arrays or phased array/reflector combinations, become more appealing.

Jamnejad, V.

1985-01-01

194

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 m 2 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

195

Spaceborne Microwave Instrument for High Resolution Remote Sensing of the Earth's Surface Using a Large-Aperture Mesh Antenna  

NASA Technical Reports Server (NTRS)

This report describes a two-year study of a large-aperture, lightweight, deployable mesh antenna system for radiometer and radar remote sensing of the Earth from space. The study focused specifically on an instrument to measure ocean salinity and Soil moisture. Measurements of ocean salinity and soil moisture are of critical . importance in improving knowledge and prediction of key ocean and land surface processes, but are not currently obtainable from space. A mission using this instrument would be the first demonstration of deployable mesh antenna technology for remote sensing and could lead to potential applications in other remote sensing disciplines that require high spatial resolution measurements. The study concept features a rotating 6-m-diameter deployable mesh antenna, with radiometer and radar sensors, to measure microwave emission and backscatter from the Earth's surface. The sensors operate at L and S bands, with multiple polarizations and a constant look angle, scanning across a wide swath. The study included detailed analyses of science requirements, reflector and feedhorn design and performance, microwave emissivity measurements of mesh samples, design and test of lightweight radar electronic., launch vehicle accommodations, rotational dynamics simulations, and an analysis of attitude control issues associated with the antenna and spacecraft, The goal of the study was to advance the technology readiness of the overall concept to a level appropriate for an Earth science emission.

Njoku, E.; Wilson, W.; Yueh, S.; Freeland, R.; Helms, R.; Edelstein, W.; Sadowy, G.; Farra, D.; West, R.; Oxnevad, K.

2001-01-01

196

Lupus I Observations from the 2010 Flight of the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry  

E-print Network

The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) was created by adding polarimetric capability to the BLAST experiment that was flown in 2003, 2005, and 2006. BLASTPol inherited BLAST's 1.8 m primary and its Herschel/SPIRE heritage focal plane that allows simultaneous observation at 250, 350, and 500 {\\mu}m. We flew BLASTPol in 2010 and again in 2012. Both were long duration Antarctic flights. Here we present polarimetry of the nearby filamentary dark cloud Lupus I obtained during the 2010 flight. Despite limitations imposed by the effects of a damaged optical component, we were able to clearly detect submillimeter polarization on degree scales. We compare the resulting BLASTPol magnetic field map with a similar map made via optical polarimetry (The optical data were published in 1998 by J. Rizzo and collaborators.). The two maps partially overlap and are reasonably consistent with one another. We compare these magnetic field maps to the orientations of filaments in Lupus I,...

Matthews, Tristan G; Angil, Francesco E; Benton, Steven J; Chapin, Edward L; Chapman, Nicholas L; Devlin, Mark J; Fissel, Laura M; Fukui, Yasuo; Gandilo, Natalie N; Gundersen, Joshua O; Hargrave, Peter C; Klein, Jeffrey; Korotkov, Andrei L; Moncelsi, Lorenzo; Mroczkowski, Tony K; Netterfield, Calvin B; Novak, Giles; Nutter, David; Olmi, Luca; Pascale, Enzo; Poidevin, Frdrick; Savini, Giorgio; Scott, Douglas; Shariff, Jamil A; Soler, Juan Diego; Tachihara, Kengo; Thomas, Nicholas E; Truch, Matthew D P; Tucker, Carole E; Tucker, Gregory S; Ward-Thompson, Derek

2013-01-01

197

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

198

Resolving the Effects of Aperture and Volume Restriction of the Flow by Semi-Porous Barriers Using Large-Eddy Simulations  

NASA Astrophysics Data System (ADS)

The Regional Atmospheric Modelling System (RAMS)-based Forest Large-Eddy Simulation (RAFLES) model is used to simulate the effects of large rectangular prism-shaped semi-porous barriers of varying densities under neutrally buoyant conditions. RAFLES model resolves flows inside and above forested canopies and other semi-porous barriers, and it accounts for barrier-induced drag on the flow and surface flux exchange between the barrier and the air. Unlike most other models, RAFLES model also accounts for the barrier-induced volume and aperture restriction via a modified version of the cut-cell coordinate system. We explicitly tested the effects of the numerical representation of volume restriction, independent of the effects of the drag, by comparing drag-only simulations (where we prescribed neither volume nor aperture restrictions to the flow), restriction-only simulations (where we prescribed no drag), and control simulations where both drag and volume plus aperture restrictions were included. Previous modelling and empirical work have revealed the development of important areas of increased uplift upwind of forward-facing steps, and recirculation zones downwind of backward-facing steps. Our simulations show that representation of the effects of the volume and aperture restriction due to the presence of semi-porous barriers leads to differences in the strengths and locations of increased-updraft and recirculation zones, and the length and strength of impact and adjustment zones when compared to simulation solutions with a drag-only representation. These are mostly driven by differences to the momentum budget of the streamwise wind velocity by resolved turbulence and pressure gradient fields around the front and back edges of the barrier. We propose that volume plus aperture restriction is an important component of the flow system in semi-porous environments such as forests and cities and should be considered by large-eddy simulation (LES).

Chatziefstratiou, Efthalia K.; Velissariou, Vasilia; Bohrer, Gil

2014-09-01

199

Single mode PT symmetric large area lasers  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate single longitudinal mode operation in microring laser using the concept of PT symmetry. A PT-symmetric coupled resonator arrangement can considerably enhance the maximum achievable gain of single mode microring cavity. The method is broadband thus work well for inhomogenously broadened gain mediums. It doesn't rely on any additional component to ensure its mode selective performance, and it is robust with respect to fabrication inaccuracies. This result may pave the way for a novel way of designing integrated laser sources based on PT symmetry.

Hodaei, Hossein; Miri, Mohammad-Ali; Heinrich, Matthias; Christodoulides, Demetrios N.; Khajavikhan, Mercedeh

2014-09-01

200

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; Csar de Oliveira, Antonio

2013-09-01

201

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

202

Hollow Cone Accretion Models for X-ray Pulsars:Rings of Fire, Pencil Beams and Plasma Jets with Large Aperture PCA  

Microsoft Academic Search

We present the first time-dependent, multi-dimensional, radiation hydrodynamical calculations of the plasma flow of super-Eddington accreting neutron stars through hollow cone accretion columns. Applications of hollow cone models for realistic sources will be estimated for detection on the RXTE PCA and for large apertures of order 105 cm2 (10 X PCA). Filled accretion columns are expected when accretion occurs from

R. I. Klein; J. G. Jernigan

2000-01-01

203

Large field F-theta laser scanning system  

Microsoft Academic Search

A large field laser scanning system is designed for PID imaging system. According to different deflectors, scanning system methods have optical lens scanning system, polygon mirror scanning system, acousto-optic scanning system and holographic scanning method. To realize large field scanning, a polygon mirror is used as scanner, which has high scanning speed, high resolution and contrast, good gamma characteristic and

Baozhong Shan; Baoping Guo; Hanben Niu

2009-01-01

204

A new look at Fresnel field computation using the Jacobi-Bessel series. [large aperture antenna design  

NASA Technical Reports Server (NTRS)

Computational procedures that would be useful in finding the Fresnel field from a knowledge of the Jacobi-Bessel expansion of the far field are considered. The range of validity of the Fresnel approximation is carefully examined by comparing it with the exact closed form solution for the uniform circular aperture. Also investigated numerically, and in great detail, is the range of validity (over theta) of the Fresnel small angle (FSA) approximation. For moderate sized apertures as small as 10 wavelengths, it is found that the FSA approximation is very accurate to angles as wide as four or more sidelobes (as seen in the far zone). A very efficient computational method is shown to exist for the radiation integral in the form of a single series expansion that is analytically continuous and convergent for a wide range of observation points in three-dimensional space.

Galindo-Israel, V.; Rahmat-Samii, Y.

1981-01-01

205

Pulsed laser ablation deposition of thin films on large substrates  

Microsoft Academic Search

We have designed and built an ultra-high vacuum chamber which allows thin film deposition on large area (up to 100 mm diameter) flat substrates and on three-dimensional substrates (e.g. 100 mm long, 50 mm diameter cylinders) by the pulsed laser deposition and reactive pulsed laser deposition techniques. Heating of substrates during and after film deposition is possible using either resistive

S. Acquaviva; M. Fernndez; G. Leggieri; A. Luches; M. Martino; A. Perrone

1999-01-01

206

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 30m 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

207

A large-field laser holographic focusing schilieren system  

NASA Technical Reports Server (NTRS)

A large-field laser holographic focusing schlieren system for high-speed flow visualization has been built and evaluated. This system is based on a recently improved large-field focusing schlieren technique and is combined with laser holography methods to record three-dimensional flows. A coordinated experimental and computational study of supersonic flows over wedge, cone, and sphere geometries was conducted to evaluate the capabilities and limitations of the system. The ability of the system to focus on planes normal to its optical axis is demonstrated. The sharpness of focus of the present system was found to be limited. Issues regarding obtaining quantitative measurements of the density gradient are discussed.

Doggett, Glen P.; Chokani, N.

1992-01-01

208

A large-field laser holographic focusing schilieren system  

NASA Astrophysics Data System (ADS)

A large-field laser holographic focusing schlieren system for high-speed flow visualization has been built and evaluated. This system is based on a recently improved large-field focusing schlieren technique and is combined with laser holography methods to record three-dimensional flows. A coordinated experimental and computational study of supersonic flows over wedge, cone, and sphere geometries was conducted to evaluate the capabilities and limitations of the system. The ability of the system to focus on planes normal to its optical axis is demonstrated. The sharpness of focus of the present system was found to be limited. Issues regarding obtaining quantitative measurements of the density gradient are discussed.

Doggett, Glen P.; Chokani, N.

1992-07-01

209

Diagnosing Large Simulations of Laser-Plasma Interaction for NIF ignition targets.  

NASA Astrophysics Data System (ADS)

We have deployed a variety of diagnostics for the pF3d laser-plasma interaction (LPI) simulation code, which includes paraxial wave optics, multi-species hydrodynamics, and models for stimulated scattering. We present a survey of the diagnostics we use to process the data from the simulations and the directions of their development for very large massively-parallel simulations in support of upcoming 96 beam experiments at NIF next year and ignition. Two examples: Now that we can simulate over the entire beam path in the complex interior of an indirect-drive ignition target, we need to be able to form the spatial distribution of the power absorption of the laser and backscattered light. Such post-processing is itself a parallel processing endeavor due to the large number of spatial cells involved. To compare with experimental near-field streak spectra of backscattered and transmitted light, obtained at the ``full aperture backscatter stations'', we form synthetic near field streak spectra. For forensic purposes we can also calculate spectra inside the target, which are experimentally inaccessible.

Langdon, Bruce; Hinkel, Denise; Langer, Steve; Still, Bert; Williams, Ed

2007-11-01

210

Plane-polar Fresnel and far-field computations using the Fresnel-Wilcox and Jacobi-Bessel expansions. [for large aperture antennas  

NASA Technical Reports Server (NTRS)

It is pointed out that the computation of the Fresnel fields for large aperture antennas is significant for many applications. The present investigation is concerned with an approach for the effective utilization of the coefficients of the Jacobi-Bessel series for the far-field to obtain an analytically continuous representation of the antenna field which is valid from the Fresnel region into the far field. Attention is given to exact formulations and closed form solutions, Fresnel and Fresnel small angle approximations, aspects of field expansion, the accuracy of the Fresnel and Fresnel small angle approximations, and the Jacobi-Bessel expansion applied to the Fresnel small angle approximation.

Rahmat-Samii, Y.; Galindo-Israel, V.

1981-01-01

211

Phasing rectangular apertures.  

PubMed

Several techniques have been developed to phase apertures in the context of astronomical telescopes with segmented mirrors. Phasing multiple apertures, however, is important in a wide range of optical applications. The application of primary interest in this paper is the phasing of multiple short pulse laser beams for fast ignition fusion experiments. In this paper analytic expressions are derived for parameters such as the far-field distribution, a line-integrated form of the far-field distribution that could be fit to measured data, enclosed energy or energy-in-a-bucket and center-of-mass that can then be used to phase two rectangular apertures. Experimental data is taken with a MEMS device to simulate the two apertures and comparisons are made between the analytic parameters and those derived from the measurements. Two methods, fitting the measured far-field distribution to the theoretical distribution and measuring the ensquared energy in the far-field, produced overall phase variance between the 100 measurements of less than 0.005 rad(2) or an RMS displacement of less than 12 nm. PMID:19997175

Baker, K L; Homoelle, D; Utterback, E; Jones, S M

2009-10-26

212

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 sufficiently 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 demonstrate the performance of large-scale optics and the beam quality that may be obtained; and to assess the performance of alternative designs of burst systems that increase the neutron output and burst repetition rate. 21 refs., 8 figs., 5 tabs.

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

1989-05-01

213

Surface Change Detection Using Large Footprint Laser Altimetry  

NASA Technical Reports Server (NTRS)

Laser altimeters provide a precise and accurate method for mapping topography at fine horizontal and vertical scales. A laser altimeter provides range by measuring the roundtrip flight time of a short pulse of laser light from the laser altimeter instrument to the target surface. The range is then combined with laser beam pointing knowledge and absolute position knowledge to provide an absolute measurement of the surface topography. Newer generations of laser altimeters measure the range by recording the shape and time of the outgoing and received laser pulses. The shape of the return pulse can also provide unique information about the vertical structure of material such as vegetation within each laser footprint. Distortion of the return pulse is caused by the time-distributed reflections adding together and representing the vertical distribution of surfaces within the footprint. Larger footprints (10 - 100m in diameter) can support numerous target surfaces and thus provide the potential for producing complex return pulses. Interpreting the return pulse from laser altimeters has evolved from simple timing between thresholds, range-walk corrections, constant-fraction discriminators, and multi-stop time interval units to actual recording of the time varying return pulse intensity - the return waveform. Interpreting the waveform can be as simple as digitally thresholding the return pulse, calculating a centroid, to fitting one or more gaussian pulse-shapes to the signal. What we present here is a new technique for using the raw recorded return pulse as a raw observation to detect centimeter-level vertical topographic change using large footprint airborne and spaceborne laser altimetry. We use the correlation of waveforms from coincident footprints as an indication of the similarity in structure of the waveforms from epoch to epoch, and assume that low correlation is an indicator of vertical structure or elevation change. Thus, using vertically and horizontally geolocated waveforms as raw observables (i.e., waveforms tied to a common reference ellipsoid), we assess whether epoch-to-epoch vertical ground motion results in a decrease in the correlation of coincident waveforms over time, and whether this can be used to quantify the magnitude of the deformation. Results of computer models and an example over an area of eroded beachfront will be presented.

Blair, J. Bryan; Hofton, Michelle A.; Smith, David E. (Technical Monitor)

2000-01-01

214

Gallium arsenide-based apertured vertical-cavity surface-emitting lasers and microcavity light emitting diodes  

NASA Astrophysics Data System (ADS)

A new design approach for all all-epitaxial index-guiding VCSEL fabrication with self-aligned current and optical confinement is proposed and demonstrated using MBE regrowth. The epitaxial regrowth approach has significant advantages over oxide confinement due to elimination of strain, aperture size controllability across wafer, and the aperture size controllability from wafer to wafer. A simple microcavity model is used to demonstrate the lateral mode confinement effect obtained by blue-shifting resonance frequency in the lateral regions of cavity, which leads to the new design concept for engineering waveguided VCSELs by modulation of the optical cavity length through MBE regrowth over selectively etched surface structures. The lithographically-defined aperture can be scaled to submicron level---simplifying its post-growth processing and thus making it easier to incorporate additional structural modifications (such as air-gap DBR VCSELs) for improved device performance. Enabling techniques, which include various surface protection and current blocking methods, have been developed in this work for the epitaxial regrowth approach. In-situ low-temperature-grown InAs capping is used to protect the first-step-grown wafer from standard chemical process, and is gently evaporated inside growth chamber before regrowth. Various current blocking structures have been investigated including reversed p-n junction assisted with resistive LT material, buried tunnel junction, and implanted current aperture. Excellent current confinement is achieved, which consequently leads to the first demonstration of GaAs-based air-gap DBR VCSELs and buried tunnel junction (BTJ) VCSELs. A novel fabrication process of air-gap/GaAs DBR mirrors has been realized by selectively removing AlGaAs sacrificial layers. Air-gap/GaAs DBR mirrors have the highest achievable refractive index contrast. This allows Air-gap/GaAs DBR mirrors to achieve desirable features, including a higher reflectivity, wider reflection stopband, lower diffraction loss, and smaller penetration depth than conventional DBR mirrors. An electrically-pumped MBE-regrown 980 nm VCSELs using p-type air-gap DBRs is demonstrated with a low threshold current density of 764 A/cm2 at room temperature under continuous-wave operation. (Abstract shortened by UMI.)

Chen, Hao

215

Laser Pointer System Intuitive Interaction for Large High-Res Displays  

E-print Network

Laser Pointer System Intuitive Interaction for Large High-Res Displays LEDs Accelerometer Vibration Buttons Laser & LEDs Unlike conventional input devices like mouse and keyboard, laser pointers do that are displayed on large high-resolution screens. The laser pointer technology was developed in cooperation

Reiterer, Harald

216

Optical sparse aperture imaging.  

PubMed

The resolution of a conventional diffraction-limited imaging system is proportional to its pupil diameter. A primary goal of sparse aperture imaging is to enhance resolution while minimizing the total light collection area; the latter being desirable, in part, because of the cost of large, monolithic apertures. Performance metrics are defined and used to evaluate several sparse aperture arrays constructed from multiple, identical, circular subapertures. Subaperture piston and/or tilt effects on image quality are also considered. We selected arrays with compact nonredundant autocorrelations first described by Golay. We vary both the number of subapertures and their relative spacings to arrive at an optimized array. We report the results of an experiment in which we synthesized an image from multiple subaperture pupil fields by masking a large lens with a Golay array. For this experiment we imaged a slant edge feature of an ISO12233 resolution target in order to measure the modulation transfer function. We note the contrast reduction inherent in images formed through sparse aperture arrays and demonstrate the use of a Wiener-Helstrom filter to restore contrast in our experimental images. Finally, we describe a method to synthesize images from multiple subaperture focal plane intensity images using a phase retrieval algorithm to obtain estimates of subaperture pupil fields. Experimental results from synthesizing an image of a point object from multiple subaperture images are presented, and weaknesses of the phase retrieval method for this application are discussed. PMID:17694146

Miller, Nicholas J; Dierking, Matthew P; Duncan, Bradley D

2007-08-10

217

Really Large Scale Computer Graphic Projection Using Lasers and Laser Substitutes  

NASA Astrophysics Data System (ADS)

This paper reflects on past laser projects to display vector scanned computer graphic images onto very large and irregular surfaces. Since the availability of microprocessors and high powered visible lasers, very large scale computer graphics projection have become a reality. Due to the independence from a focusing lens, lasers easily project onto distant and irregular surfaces and have been used for amusement parks, theatrical performances, concert performances, industrial trade shows and dance clubs. Lasers have been used to project onto mountains, buildings, 360 globes, clouds of smoke and water. These methods have proven successful in installations at: Epcot Theme Park in Florida; Stone Mountain Park in Georgia; 1984 Olympics in Los Angeles; hundreds of Corporate trade shows and thousands of musical performances. Using new ColorRayTM technology, the use of costly and fragile lasers is no longer necessary. Utilizing fiber optic technology, the functionality of lasers can be duplicated for new and exciting projection possibilities. The use of ColorRayTM technology has enjoyed worldwide recognition in conjunction with Pink Floyd and George Michaels' world wide tours.

Rother, Paul

1989-07-01

218

Versatile large-mode-area femtosecond laser-written Tm:ZBLAN glass chip lasers.  

PubMed

We report performance characteristics of a thulium doped ZBLAN waveguide laser that supports the largest fundamental modes reported in a rare-earth doped planar waveguide laser (to the best of our knowledge). The high mode quality of waveguides up to 45 um diameter (~1075 ?m(2) mode-field area) is validated by a measured beam quality of M(2)~1.1 0.1. Benefits of these large mode-areas are demonstrated by achieving 1.9 kW peak-power output Q-switched pulses. The 1.89 ?m free-running cw laser produces 205 mW and achieves a 67% internal slope efficiency corresponding to a quantum efficiency of 161%. The 9 mm long planar chip developed for concept demonstration is rapidly fabricated by single-step optical processing, contains 15 depressed-cladding waveguides, and can operate in semi-monolithic or external cavity laser configurations. PMID:23262700

Lancaster, D G; Gross, S; Fuerbach, A; Heidepriem, H Ebendorff; Monro, T M; Withford, M J

2012-12-01

219

Early laser operations at the Large Binocular Telescope Observatory  

NASA Astrophysics Data System (ADS)

ARGOS is the GLAO (Ground-Layer Adaptive Optics) Rayleigh-based LGS (Laser Guide Star) facility for the Large Binocular Telescope Observatory (LBTO). It is dedicated for observations with LUCI1 and LUCI2, LBTO's pair of NIR imagers and multi-object spectrographs. The system projects three laser beams from the back of each of the two secondary mirror units, which create two constellations circumscribed on circles of 2 arcmin radius with 120 degree spacing. Each of the six Nd:YAG lasers provides a beam of green (532nm) pulses at a rate of 10kHz with a power of 14W to 18W. We achieved first on-sky propagation on the night of November 5, 2013, and commissioning of the full system will take place during 2014. We present the initial results of laser operations at the observatory, including safety procedures and the required coordination with external agencies (FAA, Space Command, and Military Airspace Manager). We also describe our operational procedures and report on our experiences with aircraft spotters. Future plans for safer and more efficient aircraft monitoring and detection are discussed.

Rahmer, Gustavo; Lefebvre, Michael; Christou, Julian; Raab, Walfried; Rabien, Sebastian; Ziegleder, Julian; Borelli, Jos L.; Gssler, Wolfgang

2014-08-01

220

Large-aperture germanium detector package for picosecond photon counting in the 0.5-1.6-microm range.  

PubMed

We report the design, construction, and parameters of a detector package based on a germanium avalanche photodiode operated in the Geiger mode cooled to 77 K. The new design of the active quenching circuit, proper diode structure, and cryogenic cooling setup permitted us to increase the detector's active area to 0.1-mm diameter while maintaining an acceptable dark-count rate, timing resolution, and photon-counting sensitivity at 1.54 microm. The active-area size and the compact design of the detector package permitted its application in satellite laser ranging at 0.532- and 1.543-microm wavelengths, yielding subcentimeter ranging precision. PMID:19876357

Prochazka, I; Hamal, K; Greene, B; Kunimori, H

1996-09-01

221

Large Field of View, Modular, Stabilized, Adaptive-Optics-Based Scanning Laser Ophthalmoscope  

PubMed Central

We describe the design and performance of an adaptive optics retinal imager that is optimized for use during dynamic correction for eye movements. The system incorporates a retinal tracker and stabilizer, a wide field line scan Scanning Laser Ophthalmocsope (SLO), and a high resolution MEMS based adaptive optics SLO. The detection system incorporates selection and positioning of confocal apertures, allowing measurement of images arising from different portions of the double pass retinal point spread function (psf). System performance was excellent. The adaptive optics increased the brightness and contrast for small confocal apertures by more than 2x, and decreased the brightness of images obtained with displaced apertures, confirming the ability of the adaptive optics system to improve the pointspread function. The retinal image was stabilized to within 18 microns 90% of the time. Stabilization was sufficient for cross-correlation techniques to automatically align the images. PMID:17429477

Burns, Stephen A.; Tumbar, Remy; Elsner, Ann E.; Ferguson, Daniel; Hammer, Daniel X.

2007-01-01

222

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

223

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

224

On tidal tilt corrections to large ring laser gyroscope observations  

NASA Astrophysics Data System (ADS)

With the fast development of the large ring laser gyroscope (RLG) technology in the last decades, promising applications in geophysics and geodesy (e.g. observations of high-frequency variations of Earth's rotation, Earth's tide tilt and seismic waves) have been realized by various groups with currently running large RLGs. In this letter, we point out that in a large number of previous tilt correction models a significant term is missing. This term is related with the Shida number l2 (called l2-term in the following) and has a contribution, which is comparable with that from high-frequency Earth rotation variations due to ocean tides, to the Sagnac frequency record of RLGs. This term has to be removed (as part of the tilt correction) from the raw data so that RLGs can efficiently be employed as Earth's rotation detectors.

Tian, Wei

2014-01-01

225

Synthetic aperture confocal imaging  

Microsoft Academic Search

Confocal microscopy is a family of imaging techniques that employ focused patterned illumination and synchronized imaging to create cross-sectional views of 3D biological specimens. In this paper, we adapt confocal imaging to large-scale scenes by replacing the optical apertures used in microscopy with arrays of real or virtual video projectors and cameras. Our prototype implementation uses a video projector, a

Marc Levoy; Billy Chen; Vaibhav Vaish; Mark Horowitz; Ian McDowall; Mark T. Bolas

2004-01-01

226

Multi-laser-guided adaptive optics for the Large Binocular Telescope  

NASA Astrophysics Data System (ADS)

We describe the conceptual design of an advanced laser guide star facility (LGSF) for the Large Binocular Telescope (LBT), to be built in collaboration with the LBT's international partners. The highest priority goal for the facility is the correction of ground-layer turbulence, providing partial seeing compensation in the near IR bands over a 4' field. In the H band, GLAO is projected to improve the median seeing from 0.55" to 0.2". The new facility will build on the LBT's natural guide star AO system, integrated into the telescope with correction by adaptive secondary mirrors, and will draw on Arizona's experience in the construction of the first multi-laser adaptive optics (AO) system at the 6.5 m MMT. The LGSF will use four Rayleigh beacons at 532 nm, projected to an altitude of 25 km, on each of the two 8.4 m component telescopes. Initial use of the system for ground layer correction will deliver image quality well matched to the LBT's two LUCIFER near IR instruments. They will be used for direct imaging over a 4'4' field and will offer a unique capability in high resolution multi-object spectroscopy. The LGSF is designed to include long-term upgrade paths. Coherent imaging at the combined focus of the two apertures will be exploited by the LBT Interferometer in the thermal IR. Using the same launch optics, an axial sodium or Rayleigh beacon can be added to each constellation, for tomographic wavefront reconstruction and diffraction limited imaging over the usual isoplanatic patch. In the longer term, a second DM conjugated to high altitude is foreseen for the LBT's LINC-NIRVANA instrument, which would extend the coherent diffraction-limited field to an arcminute in diameter with multi-conjugate AO.

Lloyd-Hart, M.; Angel, R.; Green, R.; Stalcup, T.; Milton, N. M.; Powell, K.

2007-09-01

227

Large-aperture automatic focimeter for the measurement of optical power and other optical characteristics of ophthalmic lenses  

NASA Astrophysics Data System (ADS)

We propose an optical apparatus enabling the measurement of spherical power, cylindrical power, and optical center coordinates of ophthalmic lenses. The main advantage of this new focimeter is to provide a full bidimensional mapping of the characteristics of ophthalmic glasses. This is made possible thanks to the use of a large-area and high-resolution position-sensitive detector. We describe the measurement principle and present some typical mappings, particularly for progressive lenses. We then discuss the advantages in terms of speed and versatility of such a focimeter for the measurement of complex lens mappings.

Gnanvo, Kondo; Wu, Zong Yan; de La Tocnaye, Jean-Louis De Bougrenet; Liu, Liren

2002-10-01

228

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

229

Zero Focal Shift in High Numerical Aperture Focusing of a Gaussian Laser Beam through Multiple Dielectric Interfaces  

E-print Network

In this paper, focal shift of a Guassian laser beam tightly focused through several planar dielectric interfaces is discussed. It is shown that the focal shift and focus point can be changed by variation of refractive index mismatch and this shift could be positive or negative, and it is proportional to refractive index mismatch between coverglass and immersion medium. It is shown also that for every immersion medium(coverglass), focal shift could be removed for a continuous range of depths by choosing a coverglass (immersion medium) with appropriate refractive index.

Mahmoudi, Ali

2014-01-01

230

Multi-static synthetic aperture radar and inverse scattering  

Microsoft Academic Search

Abstract In this paper synthetic aperture radar is analyzed from an inverse scattering perspective. It is shown that the classical point scattering model can be generalized to a dipole scattering model. The dipole scattering model reduces to the point scattering model for small aperture angles. For large aperture angles or multiple illumination apertures the dipole model gives an anisotropic reflectivity

Mats Gustafsson

2003-01-01

231

Functional derivatives applied to error propagation of uncertainties in topography to large-aperture scintillometer-derived heat fluxes  

NASA Astrophysics Data System (ADS)

Scintillometer measurements allow for estimations of the refractive index structure parameter Cn2 over large areas in the atmospheric surface layer. Turbulent fluxes of heat and momentum are inferred through coupled sets of equations derived from the Monin-Obukhov similarity hypothesis. One-dimensional sensitivity functions have been produced that relate the sensitivity of heat fluxes to uncertainties in single values of beam height over flat terrain. However, real field sites include variable topography. We develop here, using functional derivatives, the first analysis of the sensitivity of scintillometer-derived sensible heat fluxes to uncertainties in spatially distributed topographic measurements. Sensitivity is shown to be concentrated in areas near the center of the beam path and where the underlying topography is closest to the beam height. Relative uncertainty contributions to the sensible heat flux from uncertainties in topography can reach 20% of the heat flux in some cases. Uncertainty may be greatly reduced by focusing accurate topographic measurements in these specific areas. A new two-dimensional variable terrain sensitivity function is developed for quantitative error analysis. This function is compared with the previous one-dimensional sensitivity function for the same measurement strategy over flat terrain. Additionally, a new method of solution to the set of coupled equations is produced that eliminates computational error.

Gruber, M. A.; Fochesatto, G. J.; Hartogensis, O. K.; Lysy, M.

2014-07-01

232

Simulation of synthetic aperture imaging ladar (SAIL) for three-dimensional target model  

Microsoft Academic Search

In conventional imaging laser radar, the resolution of target is constrained by the diffraction-limited, which includes the beamwidth of the laser in the target plane and the telescope's aperture. Synthetic aperture imaging Ladar (SAIL) is an imaging technique which employs aperture synthesis with coherent laser radar, the resolution is determined by the total frequency spread of the source and is

Ning Yi; Zhen-Sen Wu

2010-01-01

233

Imaging Laser Altimetry in the Amazon: Mapping Large Areas of Topography, Vegetation Height and Structure, and Biomass  

NASA Technical Reports Server (NTRS)

A flight mission of NASA GSFC's Laser Vegetation Imaging Sensor (LVIS) is planned for June-August 2003 in the Amazon region of Brazil. The goal of this flight mission is to map the vegetation height and structure and ground topography of a large area of the Amazon. This data will be used to produce maps of true ground topography, vegetation height, and estimated above-ground biomass and for comparison with and potential calibration of Synthetic Aperture Radar (SAR) data. Approximately 15,000 sq. km covering various regions of the Amazon will be mapped. The LVIS sensor has the unique ability to accurately sense the ground topography beneath even the densest of forest canopies. This is achieved by using a high signal-to-noise laser altimeter to detect the very weak reflection from the ground that is available only through small gaps in between leaves and between tree canopies. Often the amount of ground signal is 1% or less of the total returned echo. Once the ground elevation is identified, that is used as the reference surface from which we measure the vertical height and structure of the vegetation. Test data over tropical forests have shown excellent correlation between LVIS measurements and biomass, basal area, stem density, ground topography, and canopy height. Examples of laser altimetry data over forests and the relationships to biophysical parameters will be shown. Also, recent advances in the LVIS instrument will be discussed.

Blair, J. Bryan; Nelson, B.; dosSantos, J.; Valeriano, D.; Houghton, R.; Hofton, M.; Lutchke, S.; Sun, Q.

2002-01-01

234

A laser tomography test bed for extremely large telescopes  

NASA Astrophysics Data System (ADS)

The Advanced Instrumentation and Technology Center at the Australian National University is building a Laser Tomography Adaptive Optics Test Bed for Extremely Large Telescopes. The optical test bench is using three Laser Guide Stars (LGS) propagating through three phase screens. The LGS wavefronts are sampled with a 16 16 Shack-Hartmann wavefront sensor (SH-WFS). Cone effect, spot elongation and Sodium layer density fluctuations are reproduced on the bench. Two Natural Guide Stars (NGS), on-axis and off-axis, are also added to the bench. The wavefront of the on-axis NGS is corrected with a DM located in the optical path of both the LGSs and the on-axis NGS. The DM commands are derived from the tomographic estimate of the on-axis NGS wavefront using the measurements of the 3 LGS WFSs. The off-axis NGS wavefront is sampled with a 6 6 SH-WFS and is emulating tip-tilt, focus and truth sensing. A DM located in front of the off-axis NGS WFS is correcting the off-axis NGS wavefront. The commands of this DM are also derived from the tomographic reconstructor. In the paper, the design of the LTAO test bed is presented.

Conan, R.; Piatrou, P.; Rigaut, F.; Uhlendorf, K.

2014-08-01

235

Large-aperture approximation for not-so-large apertures  

E-print Network

angles, the LAA consistently underestimates the time-averaged Strehl ratio, so the LAA should be used of the optical wavefronts. A different approximation for computing time-averaged Strehl ratios is proposed

Gordeyev, Stanislav

236

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

237

Lasers for coherent optical satellite links with large dynamics.  

PubMed

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) while 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. PMID:24216589

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

2013-10-20

238

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) 2005: A 4 sq. deg Galactic Plane Survey in Vulpecula (l=59)  

E-print Network

We present the first results from a new 250, 350, and 500 micron Galactic Plane survey taken with the Balloon-borne Large-Aperture Submillimeter Telescope (BLAST) in 2005. This survey's primary goal is to identify and characterize high-mass proto-stellar objects (HMPOs). The region studied here covers 4 sq. deg near the open cluster NGC 6823 in the constellation Vulpecula (l=59). We find 60 compact sources (0) velocities combined with a variety of other velocity and morphological data in the literature. In total, 49 sources are associated with a molecular cloud complex encompassing NGC 6823 (distance ~2.3kpc), 10 objects with the Perseus Arm (~8.5kpc) and one object is probably in the outer Galaxy (~14kpc). Near NGC 6823, the inferred luminosities and masses of BLAST sources span ~40-10^4 L_\\odot, and ~15-700 M_\\odot, respectively. The mass spectrum is compatible with molecular gas masses in other high-mass star forming regions. Several luminous sources appear to be Ultra Compact HII regions powered by early B stars. However, many of the objects are cool, massive gravitationally-bound clumps with no obvious internal radiation from a protostar, and hence excellent HMPO candidates.

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

2007-11-21

239

Numerical aperture dependence of damage and supercontinuum generation from femtosecond  

E-print Network

Numerical aperture dependence of damage and supercontinuum generation from femtosecond laser pulses laser pulses with transpar- ent dielectrics: supercontinuum generation and multiphoton-induced bulk damage. We measured the threshold energy for supercontinuum generation and bulk damage in fused silica

Schaffer, Chris B.

240

Effects of including a diffraction term into Rigrod theory for a continuous-wave laser  

E-print Network

-gain lasers with large mirror scattering losses [9]. The electrically driven oxygen­iodine laser (Elec- tricEffects of including a diffraction term into Rigrod theory for a continuous-wave laser David L-gain continuous-wave lasers are often subject to having intracavity apertures that create diffractive losses

Carroll, David L.

241

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

Microsoft Academic Search

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

W. E. Stocum

1992-01-01

242

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

243

Effect of the degree of preionisation of a gas on the homogeneity of a volume discharge and generation of radiation in a wide-aperture XeCl-laser  

SciTech Connect

The results of investigation of an electric discharge XeCl laser with active region apertures 8 x 11, 10 x 15, and 15 x 15 cm are presented. The preionisation of the Ne - Xe - HCl working mixture was performed by soft X-rays and a low-current electron beam, which provided the initial concentration n{sub 0} of electrons in the gas from 10{sup 6} to 2 x 10{sup 13} cm{sup -3}. For n{sub 0} < 10{sup 12} cm{sup -3}, the homogeneity of the initial electron concentration and of an electric field in the discharge gap have a considerable effect on the homogeneity of the volume discharge and output characteristics of the laser. For n{sub 0} {>=} 10{sup 12} cm{sup -3}, a homogeneous volume discharge is ignited and is stable if the inhomogeneity of the electric field in the discharge gap does not exceed 10%. A storage capacitor charged to double the voltage of the quasi-stationary discharge operation is sufficient for discharge formation. It is shown that an improvement of the volume discharge homogeneity and a decrease in the size of the discharge chamber make it possible to increase the efficiency of a wide-aperture XeCl laser. (active media. lasers)

Konovalov, I N; Koval', N N; Suslov, A I [Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk (Russian Federation)

2002-08-31

244

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

2011-12-01

245

Laser-cooling brings large object near absolute zero  

NSDL National Science Digital Library

This page showcases research conducted at MIT on the laser-cooling of macroscopic materials, in order to observe quantum effects. The material--a dime-sized mirror--was suspended with laser beams and cooled to temperatures near 0.8 degrees Kelvin. The site also provides images of the experimental apparatus and the researchers.

2007-06-22

246

Laser-cooling Brings Large Object Near Absolute Zero  

NSDL National Science Digital Library

This page showcases research conducted at Massachusetts Institute of Technology on the laser-cooling of macroscopic materials, in order to observe quantum effects. The material--a dime-sized mirror--was suspended with laser beams and cooled to temperatures near 0.8 degrees Kelvin. The site also provides images of the experimental apparatus and the researchers.

Trafton, Anne

2009-12-09

247

Aperture undersampling using compressive sensing for synthetic aperture stripmap imaging  

NASA Astrophysics Data System (ADS)

Synthetic aperture imaging is a high-resolution imaging technique employed in radar and sonar applications, which construct a large aperture by constantly transmitting pulses while moving along a scene of interest. In order to avoid azimuth image ambiguities, spatial sampling requirements have to be fulfilled along the aperture trajectory. The latter, however, limits the maximum speed and, therefore, the coverage rate of the imaging system. This paper addresses the emerging field of compressive sensing for stripmap synthetic aperture imaging using transceiver as well as single-transmitter and multi-receiver systems so as to overcome the spatial Nyquist criterion. As a consequence, future imaging systems will be able to significantly reduce their mission time due to an increase in coverage rate. We demonstrate the capability of our proposed compressive sensing approach to at least double the maximum sensor speed based on synthetic data and real data examples. Simultaneously, azimuth image ambiguities are successfully suppressed. The real acoustical measurements are obtained by a small-scale ultrasonic synthetic aperture laboratory system.

Leier, Stefan; Zoubir, Abdelhak M.

2014-12-01

248

Solar Central Receiver with an Irising Aperture  

E-print Network

. If the aperture is small, it will be inefficient for periods when the solar isolation is inclined due to spillage. However, if the aperture is large, it will be inefficient for periods when the solar isolation is normal, due to excess heat radiation and convection...

Galal, T.; Kulaib, A. M.; Abuzaid, M.

2010-01-01

249

Optoacoustic imaging with synthetic aperture focusing and coherence weighting.  

PubMed

Optoacoustic imaging takes advantage of high optical contrast and low acoustic scattering and has found several biomedical applications. In the common backward mode a laser beam illuminates the image object, and an acoustic transducer located on the same side as the laser beam detects the optoacoustic signal produced by thermoelastic effects. A cross-sectional image is formed by laterally scanning the laser beam and the transducer. Although the laser beam width is generally narrow to provide good lateral resolution, strong optical scattering in tissue broadens the optical illumination pattern and thus degrades the lateral resolution. To solve this problem, a combination of the synthetic aperture focusing technique with coherence weighting is proposed. This method synthesizes a large aperture by summing properly delayed signals received at different positions. The focusing quality is further improved by using the signal coherence as an image quality index. A phantom comprising hair threads in a 1% milk solution was imaged with an optoacoustic imaging system. The results show that the proposed technique improved lateral resolution by 400-800% and the signal-to-noise ratio by 7-23 dB over conventional techniques. PMID:15584276

Liao, C K; Li, M L; Li, P C

2004-11-01

250

Aperture masking behind AO systems  

NASA Astrophysics Data System (ADS)

Sparse Aperture-Mask Interferometry (SAM or NRM) behind Adaptive Optics (AO) has now come of age, with more than a dozen astronomy papers published from several 5-10m class telescopes around the world. I will describe the reasons behind its success in achieving relatively high contrasts ( 1000:1 at lambda/ D) and repeatable binary astronomy at the diffraction limit, even when used behind laser-guide star adaptive optics. Placed within the context of AO calibration, the information in an image can be split into pupil-plane phase, Fourier amplitude and closure-phase. It is the closure-phase observable, or its generalisation to Kernel phase, that is immune to pupil-plane phase errors at first and second-order and has been the reason for the technique's success. I will outline the limitations of the technique and the prospects for aperture-masking and related techniques in the future.

Ireland, Michael J.

2012-07-01

251

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

2013-01-01

252

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

253

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

254

Large core single-mode chirally-coupled-core fibers for high power fiber lasers  

Microsoft Academic Search

Novel chirally-coupled-core (CCC) fibers enabled large-core laser systems operating robustly-singlemode, independently of fiber excitation, splicing and coiling conditions. A variety of high power continuous-wave, nanosecond-pulse and femtosecond-pulse fiber-laser systems have been demonstrated using CCC fibers.

Xiuquan Ma; Cheng Zhu; Matthew Rever; Shenghong Huang

2009-01-01

255

80-W green KTP laser used in photoselective laser vaporization of the prostrate by frequency doubling of Yb 3+ -doped large-mode area fiber laser  

NASA Astrophysics Data System (ADS)

Photoselective laser vaporization of the prostate (PVP) is the most promising method for the treatment of benign prostatic hyperplasia (BPH), but KTP lasers used in PVP with lamp-pumped are low efficient .To increase the efficiency , we develop a 80-W, 400kHz, linearly polarized green laser based on a frequency-doubled fiber laser. A polarization-maintaining large-mode area (LMA) fiber amplifier generate polarized 1064nm fundamental wave by amplifying the seed signal from a composite Cr 4+:YAG-Nd 3+:YAG crystal fiber laser. The fundamental wave is injected into a KTP crystal with confined temperature management to achieve second harmonic generation (SHG). The overall electrical efficiency to the green portion of the spectrum is 10%.80-W maintenance-free long-lifetime KTP laser obtained can well satisfy the need of PVP.

Xia, Hongxing; Li, Zhengjia

2007-05-01

256

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.

257

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

258

Synthetic-aperture optical imaging system using digital phase conjugation  

Microsoft Academic Search

A basic experiment which examines an image reconstruction algorithm is reported. In this experiment, the object-wave field data are collected by irradiating He-Ne laser light from each point on the aperture, superposing the reflected wave with the reference wave on the other aperture, and then detecting the resulting fringe pattern with a CCD array sensor. Next, the array data are

O. Ikeda

1991-01-01

259

Optical synthetic aperture imaging with spatial heterodyne interferometry  

Microsoft Academic Search

Experimental demonstrations of optical synthetic aperture imaging using spatial heterodyne interferometry have been achieved at the Lockheed Martin Advanced Technology Center in Palo Alto, CA. In laboratory experiments, a reflective binary star scene and an Air Force resolution bar target were illuminated and imaged by a 532 nm laser and an afocal telescope. The real aperture diffraction limit in the

Mel S. Ni; J. Wes Irwin

2009-01-01

260

Modelling of a reflective waveplate for high-power lasers  

NASA Astrophysics Data System (ADS)

The polarization state of a laser has a huge bearing on the physics of laser-plasma interactions and it is often desirable to change between linear and circular. For short pulse high power lasers large beam apertures are necessary for transportation. However, in these extreme conditions transmissive birefringent polarization optics become impractical due to their delicacy and their dispersion of the laser bandwidth which will increase the pulse length, which along with large B-integrals, which arises from the transmission of the high-power beams through optics, can be detrimental to the intensity of the laser. It is therefore necessary to consider reflective optics in order to change the polarization. Modelling has been performed at the Central Laser Facility on a design of a large aperture broadband reflective waveplate suitable for short pulse laser systems.

Heathcote, Robert I.; Buck, Samuel; Clarke, Robert J.; Green, James S.

2014-09-01

261

A new efficient laser angle metrology system for maintaining the large radio telescope active reflecting antenna  

NASA Astrophysics Data System (ADS)

Radio telescopes with much more larger aperture collect much more signals and therefore sought after by astronomers. The primary reflecting antenna is traditionally segmented and perfectly optically aligned at the central altitude among the whole observation sky area for minimizing the gravitational deformation during operation and passively open-loop maintained at any other altitude. A new laser segmentation sensing and maintaining method based on normal deflection angle measurement is proposed in this paper. After the introduction of the theory, the method is simulated and tested on a special prototype of radio panel segmentation system. It provides real-time monitoring and measurement of the global segmentation status of all panels and is proved to be a high accurate, high efficient and low cost method. Finally several conclusions are reached.

Zhang, Yong; Yang, Dehua; Li, Yeping; Zhou, Guohua; Li, Aihua; Li, Guoping; Zhang, Zhenchao

2010-07-01

262

Variable-aperture screen  

DOEpatents

Apparatus for separating material into first and second portions according to size including a plurality of shafts, a plurality of spaced disks radiating outwardly from each of the shafts to define apertures and linkage interconnecting the shafts for moving the shafts toward or away from one another to vary the size of the apertures while the apparatus is performing the separating function.

Savage, George M. (Richmond, CA)

1991-01-01

263

Low emittance lattice cell withlarge dynamic aperture  

E-print Network

Compact low emittance lattice cell providing large dynamic aperture is essentual for development of extremely low (pm range) emittance storage rings. As it is well known, a pair of identical sextupoles connected by a minus-identy matrix transformer in ideal case of kick-like magnets provides infinite dynamic aperture. Though the finite sextupole length degrades the aperture, it is still large enough, and in this report we discuss development of the low emittance lattice cell providing the -I condition for both horizontal and vertical chromatic sextupoles. Such cell can be used as a module for lattices of different emittance and length. As an example we develop a 3 GeV 10 pm emittance storage ring and study its transverse dynamic aperture.

Bogomyagkov, A; Piminov, P

2014-01-01

264

Power amplification of a phased array steered laser beam  

Microsoft Academic Search

Steering a laser beam by an optical phased array provides non-mechanical beam steering, high angular resolution with large apertures. It is therefore considered in several applications such as laser communication and power transmission links between moving objects. However, in many devices the incident power density is limited and the fill factor leads to a high loss of light. These two

C. A. Schfer; O. Matoba; N. Kaya

2008-01-01

265

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

266

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

2013-10-01

267

Self-similar erbium-doped fiber laser with large normal dispersion  

PubMed Central

We report a large normal dispersion erbium-doped fiber laser with self-similar pulse evolution in the gain fiber. The cavity is stabilized by the local nonlinear attractor in the gain fiber through the use of a narrow filter. Experimental results are accounted for by numerical simulations. This laser produces 3.5 nJ pulses, which can be dechirped to 70 fs with an external grating pair. PMID:24562267

Liu, Hui; Liu, Zhanwei; Lamb, Erin S.; Wise, Frank

2014-01-01

268

Femtosecond laser-induced asymmetric large scale waves on gold surfaces  

SciTech Connect

With femtosecond (fs) pulse irradiation, we investigate the morphological evolution of a unique type of fs laser-induced periodic surface structure, called nanostructure-covered large scale waves (NC-LSWs), covered by iterating stripe patterns of nanostructures and microstructures with a period of tens of microns. By monitoring the morphological profile of NC-LSWs following fs laser heating of Au, we show that the NC-LSWs are highly asymmetrically formed and propagate on a gold surface. We believe that the selective laser ablation of Au surface and the subsequent mass transfer of liquid Au following nonuniform energy deposition result in the asymmetric NC-LSW propagation on metals.

Yong Hwang, Taek; Guo, Chunlei [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States)

2012-07-09

269

Waveguide grating mirror for large-area semiconductor lasers  

Microsoft Academic Search

We have fabricated and tested a waveguide grating mirror that uses anomalous ref lection of light associ- ated with excitation of waveguide modes. Sharp features are observed in the ref lection spectra in both the wavelength and the angular domains. We confirm experimentally that, when the waveguide grating mirror is placed a short distance in front of a large-area semiconductor

Ivan Avrutsky; Rabi Rabady

2001-01-01

270

Laser lithographic approach to micro-optical freeform elements with extremely large sag heights.  

PubMed

Artificial compound eye cameras are an attractive approach to generate imaging systems of maximum miniaturization. Their thickness can be reduced by a factor of two in comparison to miniaturized single aperture cameras with the same pixel size and resolution. The imaging performance of these systems can be improved significantly by the use of micro-optical refractive freeform arrays (RFFA). Due to the complexity of these non-symmetric surface profiles with sag heights larger than 50 m in combination with extreme profile accuracies better than ?/14 (rms), there is no dedicated fabrication technology currently available. In the presented research, significant improvements in the fabrication of these elements with laser lithography were reached. Therefore, a laser lithographic process based on several coating steps in combination with a multiple exposure strategy was developed that is suitable for the fabrication of arbitrary freeform structures with sag heights up to 60 m. In order to minimize surface deviations caused by unavoidable process nonlinearities, a compensation strategy based on an empirical process model is used. The achievable accuracy of the proposed method and its limitations were investigated by fabricating a spherical micro lens array for demonstration. The fabricated elements possess a shape deviation of less than 1.3 m (rms) and can be used as master structures for a subsequent replication process in order to realize a cost efficient mass production of artificial compound eye optics on wafer level. PMID:22418233

Dunkel, Jens; Wippermann, Frank; Brckner, Andreas; Bruer, Andreas; Tnnermann, Andreas

2012-02-13

271

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

272

Large area laser surface treatment of aluminium alloys for pitting corrosion protection  

NASA Astrophysics Data System (ADS)

Laser surface treatment has been recognised as a useful method for corrosion protection of surfaces as a result of improved microstructure/phase formation and compositions. In large area applications, overlapping of individual tracks corresponding to the width of the laser beam is often necessary. This involves re-melting and re-heating of a portion of the previous track and results in microstructural changes, such as precipitate coarsening and microsegregation, which may influence localised corrosion at the overlapped regions. The purpose of this work is to investigate the influence of overlapped regions on corrosion behaviour of laser-melted aluminium 2014-T6 alloy. Laser melting was carried out using a 3 kW CW Nd:YAG laser with a line beam profile. The microstructures of the central part and the overlapped region of the melt pool were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Pitting corrosion resistance was evaluated using potentiodynamic anodic polarisation in 1 M NaCl solution. The work revealed enhancement of the pitting potential by 170 mV compared with that of the untreated alloy, similar to that achieved by laser surface melting with a CO 2 laser in a Gaussian mode. The line beam profile results in elimination of the planar front zones at the treated surface, but this benefit was offset by a coarser microstructure.

Chong, P. H.; Liu, Z.; Skeldon, P.; Thompson, G. E.

2003-03-01

273

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

SciTech Connect

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. In this report we present our successful demonstration of spark formation using fiber delivery made possible though the use of novel coated hollow fibers. We present results of (high power) experimental characterizations of light propagation using hollow fibers using both a high power research grade laser as well as a more compact laser. Finally, we present initial designs of the system we are developing for future on-engine testing using the hollow fibers.

Azer Yalin; Morgan Defoort; Bryan Willson

2005-01-01

274

Annular Apertures Focused In The Fresnel Region  

NASA Astrophysics Data System (ADS)

This paper investigates the Fresnel diffraction of a monochromatic light beam due to annular square and circular apertures, when the system is focused in the Fresnel region. Perspective plots of the intensity distribution diagrams for modified Fresnel number(FMOD)=1, 2, . . . ; Lense focusing factor(FLNS)=1 and obstruction ratio(EPS)=0.01 are generated with IBM-370/168 computer. A comparison is done with the correspon-ding diagrams for unobstructed apertures. The results indicates that the central obstruction ratio(EPS=0.01) yields a systematic change in the shape of the intensity pattern over the image radius of a circular aperture. On the other hand the shape of the diffraction pattern remains unchanged for the square and the annular square apertures. It appears that the ring pattern generated with the annular circular aperture for FMOD=1, FLNS=1 and EPS=0.01 can effectively be used to drill good quality holes by using high power laser beam.

Kathuria, Y. P.; Herziger, G.

1981-12-01

275

Large-Scale Production of Single-Walled Carbon Nanotubes Using Ultrafast Pulses from a Free Electron Laser  

Microsoft Academic Search

We report the first use of ultrafast (subpicosecond) laser pulses for large-scale production of single wall carbon nanotubes (SWNT's) by the pulsed laser vaporization (PLV) technique. Very high production rates were achieved; using only 20% of the nominal average power of the 1 kW Jefferson Lab free electron laser (Jlab FEL), carbon soots rich in high quality bundles of SWNT's

P. C. Eklund; B. K. Pradhan; U. J. Kim; Q. Xiong; J. E. Fischer; A. D. Friedman; B. C. Holloway; M. W. Smith

2002-01-01

276

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 35mm 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

2012-03-01

277

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

278

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

279

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

280

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 3107 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

281

Polarisation splitting of laser beams by large angles with minimal reflection losses  

SciTech Connect

New crystal anisotropic prisms for splitting orthogonally polarised components of laser radiation by large angles with minimal reflection losses caused by the Brewster refraction and total internal reflection of polarised waves from the crystal-air interface are considered and the method for their calculation is described. It is shown that, by assembling glue-free combinations of two or three prisms, thermally stable beamsplitters can be fabricated, which are free from the beam astigmatism and the wave dispersion of the output angles of the beams. The parameters and properties of new beamsplitters are presented in a convenient form in figures and tables. (laser applications and other topics in quantum electronics)

Davydov, B L [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Fryazino, Moscow Region (Russian Federation)

2006-05-31

282

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.; Nemes, G.; Baldwin, C.

2011-07-25

283

Arbitrary-speed quantum gates within large ion crystals through minimum control of laser beams  

E-print Network

We propose a scheme to implement arbitrary-speed quantum entangling gates on two trapped ions immersed in a large linear crystal of ions, with minimal control of laser beams. For gate speeds slower than the oscillation frequencies in the trap, a single appropriately-detuned laser pulse is sufficient for high-fidelity gates. For gate speeds comparable to or faster than the local ion oscillation frequency, we discover a five-pulse protocol that exploits only the local phonon modes. This points to a method for efficiently scaling the ion trap quantum computer without shuttling ions.

Shi-Liang Zhu; C. Monroe; L. -M. Duan

2005-08-03

284

Sequential nonadiabatic excitation of large molecules and ions driven by strong laser fields Alexei N. Markevitch,1  

E-print Network

, continues with small diatomic molecules, and culminates in large polyatomic molecules that are the subjectSequential nonadiabatic excitation of large molecules and ions driven by strong laser fields Alexei to dissociative ionization of polyatomic molecules in strong laser fields are investigated experimentally

Schlegel, H. Bernhard

285

Solar filter for the Mars laser communication demonstration optical receiver  

Microsoft Academic Search

To maximize the cost-effectiveness of the Mars Laser Communication Demonstration (MLCD), the project is pursuing the use of ground-based astronomical telescopes as large-aperture optical receiving antennae. To facilitate communication as the spacecraft approaches solar conjunction, a large membrane filter is being considered to reject approximately 95% of the sun\\

Brian G. Patrick; Paul Gierow; David Sheikh; W. Tom Roberts

2004-01-01

286

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

287

A feasibility study into the screening and imaging of hand luggage for threat items at 35 GHz using an active large aperture (1.6 m) security screening imager  

NASA Astrophysics Data System (ADS)

The feasibility of screening hand luggage for concealed threat items such as Person-Borne Improvised Explosive Devices (PBIED's) both metallic and non-metallic, together with handguns and at millimetre wavelengths is investigated. Previous studies by the authors and others indicate that hand baggage material and fabric is much more transmissive and has less scattering at lower millimetre wave frequencies and the ability to use K-band active imaging with high spatial resolution presents an opportunity to image and hence recognise concealed threats. For this feasibility study, a 1.6 m aperture, 35 GHz security screening imaging system with a spatial resolution of 2.5 cm and a depth of field of around 5 cm is employed, using spatially incoherent illuminating panels to enhance image contrast. In this study, realistic scenarios using backpacks containing a realistic range of threat and non-threat items are scanned, both carried and standalone. This range of items contains large vessels suitable for containing simulated home-made PBIED's and handguns. The comprehensive list of non-threat items includes laptops, bottles, clothing and power supplies. For this study, the range at which imaging data at standoff distances can be acquired is confined to that of the particular system in use, although parameters such as illumination and integration time are optimised. However, techniques for extrapolating towards effective standoff distances using aperture synthesis imagers are discussed. The transmission loss through fabrics and clothing that may form, or be contained in baggage, are reported over range of frequencies ranging from 26 to 110 GHz.

Bowring, Nicholas J.; O'Reilly, Dean; Salmon, Neil A.; Andrews, David A.; Rezgui, Nacer-Ddine; Harmer, Stuart W.

2013-10-01

288

Crystal growth and application of large size YCOB crystal for high power laser  

NASA Astrophysics Data System (ADS)

Yttrium calcium oxyborate YCa4O(BO3)3 (YCOB) is a novel non-linear optical crystal possessing good thermal, mechanical and nonlinear optical properties. It is regards the important candidate frequency conversion material for the high-average power laser system. In this work, we described our effort to achieve the successful growth of large size YCOB single crystals, and the crystal quality of large size YCOB crystal grown by the Bridgman method. The OPCPA application of YCOB element was also introduced simply. The results confirmed that Bridgman technology can be used for the growth of large size YCOB crystal as an alternative to Czochralski method.

Wu, Anhua; Xu, Jun; Zheng, Yanqing; Liang, Xiaoyan

2014-10-01

289

Simulating Extremely Large-Scale Laser-Plasma Interactions of NIF Experiments  

NASA Astrophysics Data System (ADS)

National Ignition Facility (NIF) laser beams will propagate through several mm of plasma between where they enter the hohlraum and where they deposit their energy near the hohlraum wall. Patch simulations, which propagate a small cross-section of the laser beam through the plasma to the wall, demonstrate beam propagation with acceptable levels of laser scatter and spray for 2010 ignition targets. However, these simulations must be normalized to whole beam simulations (C.H. Still et al., this meeting). Such simulations are extremely large calculations, requiring thousands of CPUs on the world's most advanced parallel computers, such as ASC Purple and Blue Gene/L. Simulations of this scale introduce a number of difficulties, including diagnosis. We will show results from these simulations, demonstrating the ability to run effectively on thousands of processors. We will briefly discuss the technologies that enable these calculations and the diagnostics we use to understand them.

Langer, Steven H.; Berger, Richard L.; Divol, Laurent M.; Dorr, Milo R.; Hinkel, Denise E.; Hittinger, Jeffrey A. F.; Langdon, A. Bruce; Still, Charles H.; Williams, Edward A.

2006-10-01

290

Preparation of large-area high-quality YBCO thin films by pulsed laser deposition with Si heater and composite scanning of laser and target  

Microsoft Academic Search

We report on the successful preparation of large-area high-quality YBa2Cu3O7 superconducting thin films by pulsed excimer laser ablation with a Si heater and composite scanning of laser beam and target. The Si heater, composite scanning of laser beam and target, and experiment results are described. The temperature variation of the Si heater was 2 area of 9001000 C. Films were

H. B. Lu; S. F. Xu; Y. J. Tian; D. F. Cui; Z. H. Chen; Y. Z. Zhang; L. Li; G. Z. Yang

1993-01-01

291

Preliminary Report On Combined Surgical- And Laser-Treatment Of Large Hemangiomas And Tattoos  

NASA Astrophysics Data System (ADS)

As most hemangiomas and tattoos require many sessions to be cured completely by argon-laser or conventional therapy I developed a new combined surgical and laser-therapy method for large hemangiomas and tattoos. This is a three step method. First: The skin lesion is treated by argon-laser with the point by point method, developed by ourself. Second: Under local or general anaesthesia a) the hemangioma is partially excised and undermined letting only the skin which is already treated by argon-laser-beams. Than the hemangioma is exstirpated in toto, the wound closed by running intradermal sutures and a pressure bandage applied, b) the tattoo is abraded as deep as possible, draped by lyofoam. Then a pressure bandage is applied. Third: The hemangioma as well as the tattoo are treated by argon-laser-beams after the operation. This method is safe and effective, gives good results, minimal scars in the case of hemangiomas and tattoos. In this paper the method is described and some cases are illustrated by pre- and postoperational photographs.

Ginsbach, G.

1981-05-01

292

Development of a large-screen high-definition laser video projection system  

NASA Astrophysics Data System (ADS)

A prototype laser video projector which uses electronic, optical, and mechanical means to project a television picture is described. With the primary goal of commercial viability, the price/performance ratio of the chosen means is critical. The fundamental requirement has been to achieve high brightness, high definition images of at least movie-theater size, at a cost comparable with other existing large-screen video projection technologies, while having the opportunity of developing and exploiting the unique properties of the laser projected image, such as its infinite depth-of-field. Two argon lasers are used in combination with a dye laser to achieve a range of colors which, despite not being identical to those of a CRT, prove to be subjectively acceptable. Acousto-optic modulation in combination with a rotary polygon scanner, digital video line stores, novel specialized electro-optics, and a galvanometric frame scanner form the basis of the projection technique achieving a 30 MHz video bandwidth, high- definition scan rates (1125/60 and 1250/50), high contrast ratio, and good optical efficiency. Auditorium projection of HDTV pictures wider than 20 meters are possible. Applications including 360 degree(s) projection and 3-D video provide further scope for exploitation of the HD laser video projector.

Clynick, Tony J.

1991-08-01

293

Multiple aperture window and seeker concepts for endo KEW applications  

NASA Astrophysics Data System (ADS)

Hypersonic interceptors performing endoatmospheric hit-to-kill missions require very high seeker angle measurement accuracies in very severe aero-thermal environments. Wall jet window/aperture cooling usually leads to significant aero-optic degradation in seeker and hence interceptor performance. This paper describes window/aperture concepts that have the potential of eliminating or significantly reducing the need for coolant injection, together with a multiple aperture sensor concept that can provide a high angle measurement accuracy and a large field of regard, with a small aperture size.

Shui, V. H.; Reeves, B. L.; Thyson, N. A.; Mueffelmann, W. H.; Werner, J. S.; Jones, G.

1992-05-01

294

Multiple aperture window and seeker concepts for endo KEW applications  

SciTech Connect

Hypersonic interceptors performing endoatmospheric hit-to-kill missions require very high seeker angle measurement accuracies in very severe aero-thermal environments. Wall jet window/aperture cooling usually leads to significant aero-optic degradation in seeker and hence interceptor performance. This paper describes window/aperture concepts that have the potential of eliminating or significantly reducing the need for coolant injection, together with a multiple aperture sensor concept that can provide a high angle measurement accuracy and a large field of regard, with a small aperture size. 15 refs.

Shui, V.H.; Reeves, B.L.; Thyson, N.A.; Mueffelmann, W.H.; Werner, J.S.; Jones, G. (Textron Defense Systems, Wilmington, MA (United States) Loral Infrared and Imaging Systems, Lexington, MA (United States) U.S. Army, Strategic Defense Command, Huntsville, AL (United States))

1992-05-01

295

Efficient Utilization Of Aperture And Detector By Optimal Coding  

NASA Astrophysics Data System (ADS)

Performance for several apertures is presented for a number of Rayleigh discrimination tasks with signal and background exactly specified. Performance is defined as the squared signal-to-noise ratio of an ideal observer determined from statistical decision theory. The conclusions of Wagner, Brown, and Metz (1981) are shown to hold for different source-pair orientations and some other well-known (but non-ideal) figures of merit. When the background is assumed to be a known constant, and the source width and separation are also known, the performance of a simple open aperture increases as the aperture is enlarged. For a known source width a complex aperture can be designed which will give performance superior to a large open aperture for these simple discrimination tasks. For any of these apertures to be clinically relevant, performance comparisons over a wider range of clinically realistic tasks, including signal and object variability, must be considered.

Myers, Kyle J.; Wagner, Robert F.; Brown, David G.; Barrett, Harrison H.

1989-05-01

296

Laser guide star wavefront sensing for ground-layer adaptive optics on extremely large telescopes.  

PubMed

We propose ground-layer adaptive optics (GLAO) to improve the seeing on the 42?m European Extremely Large Telescope. Shack-Hartmann wavefront sensors (WFSs) with laser guide stars (LGSs) will experience significant spot elongation due to off-axis observation. This spot elongation influences the design of the laser launch location, laser power, WFS detector, and centroiding algorithm for LGS GLAO on an extremely large telescope. We show, using end-to-end numerical simulations, that with a noise-weighted matrix-vector-multiply reconstructor, the performance in terms of 50% ensquared energy (EE) of the side and central launch of the lasers is equivalent, the matched filter and weighted center of gravity centroiding algorithms are the most promising, and approximately 1010 undersampled pixels are optimal. Significant improvement in the 50% EE can be observed with a few tens of photons/subaperture/frame, and no significant gain is seen by adding more than 200 photons/subaperture/frame. The LGS GLAO is not particularly sensitive to the sodium profile present in the mesosphere nor to a short-timescale (less than 100?s) evolution of the sodium profile. The performance of LGS GLAO is, however, sensitive to the atmospheric turbulence profile. PMID:21283238

Clare, Richard M; Le Louarn, Miska; Bchet, Clementine

2011-02-01

297

Ballistic effusion of normal liquid 3 He through nanoscale apertures  

E-print Network

Ballistic effusion of normal liquid 3 He through nanoscale apertures A. Marchenkov, R. W. Simmonds is decreased we observe the crossover from viscous flow to ballistic effusion transport by quasiparticles. In this ballistic regime the quasiparticle mean free path is large compared to both the aperture diameter

Packard, Richard E.

298

Exploiting multi-scale parallelism for large scale numerical modelling of laser wakefield accelerators  

E-print Network

A new generation of laser wakefield accelerators, supported by the extreme accelerating fields generated in the interaction of PW-Class lasers and underdense targets, promises the production of high quality electron beams in short distances for multiple applications. Achieving this goal will rely heavily on numerical modeling for further understanding of the underlying physics and identification of optimal regimes, but large scale modeling of these scenarios is computationally heavy and requires efficient use of state-of-the-art Petascale supercomputing systems. We discuss the main difficulties involved in running these simulations and the new developments implemented in the OSIRIS framework to address these issues, ranging from multi-dimensional dynamic load balancing and hybrid distributed / shared memory parallelism to the vectorization of the PIC algorithm. We present the results of the OASCR Joule Metric program on the issue of large scale modeling of LWFA, demonstrating speedups of over 1 order of magni...

Fonseca, Ricardo A; Fiza, Frederico; Davidson, Asher; Tsung, Frank S; Mori, Warren B; Silva, Lus O

2013-01-01

299

Propagation of apertured Bessel beams  

NASA Astrophysics Data System (ADS)

The propagation features of several apertured Bessel beams are numerically calculated. The calculations show that the relations of axial intensity versus propagation distance are similar to the radial distribution of the aperture functions, which may be helpful in choosing the proper aperture functions in experiments.

Jiang, Zhiping; Lu, Qisheng; Liu, Zejin

1995-11-01

300

Ship signatures in synthetic aperture radar imagery  

Microsoft Academic Search

Ship signatures in synthetic aperture radar (SAR) imagery have been matched to Automatic Identification System (AIS) data to yield a large database of known ships for ship signature analysis. This paper focuses on ship radar cross section and ship length derived from the ship signature length. Cross- polarization is an attractive option for ship detection.

Paris W. Vachon; Ryan A. English; John Wolfe

2007-01-01

301

A 103 W erbiumytterbium co-doped large-core fiber laser  

Microsoft Academic Search

We report a highly efficient cladding-pumped erbiumytterbium co-doped large-core fiber laser, generating up to 103 W of continuous-wave output power at 1.57 ?m with a beam quality (M2) of 2.0. The overall slope efficiency was 30% (40% at low powers) with respect to the launched pump power. A roll-off in output power was observed at higher powers caused by the

J. K Sahu; Y Jeong; D. J Richardson; J Nilsson

2003-01-01

302

Aperture center energy showcase  

SciTech Connect

Sandia and Forest City have established a Cooperative Research and Development Agreement (CRADA), and the partnership provides a unique opportunity to take technology research and development from demonstration to application in a sustainable community. A project under that CRADA, Aperture Center Energy Showcase, offers a means to develop exhibits and demonstrations that present feedback to community members, Sandia customers, and visitors. The technologies included in the showcase focus on renewable energy and its efficiency, and resilience. These technologies are generally scalable, and provide secure, efficient solutions to energy production, delivery, and usage. In addition to establishing an Energy Showcase, support offices and conference capabilities that facilitate research, collaboration, and demonstration were created. The Aperture Center project focuses on establishing a location that provides outreach, awareness, and demonstration of research findings, emerging technologies, and project developments to Sandia customers, visitors, and Mesa del Sol community members.

Torres, J. J.

2012-03-01

303

Integrated electrochromic aperture diaphragm  

NASA Astrophysics Data System (ADS)

In the last years, the triumphal march of handheld electronics with integrated cameras has opened amazing fields for small high performing optical systems. For this purpose miniaturized iris apertures are of practical importance because they are essential to control both the dynamic range of the imaging system and the depth of focus. Therefore, we invented a micro optical iris based on an electrochromic (EC) material. This material changes its absorption in response to an applied voltage. A coaxial arrangement of annular rings of the EC material is used to establish an iris aperture without need of any mechanical moving parts. The advantages of this device do not only arise from the space-saving design with a thickness of the device layer of 50?m. But it also benefits from low power consumption. In fact, its transmission state is stable in an open circuit, phrased memory effect. Only changes of the absorption require a voltage of up to 2 V. In contrast to mechanical iris apertures the absorption may be controlled on an analog scale offering the opportunity for apodization. These properties make our device the ideal candidate for battery powered and space-saving systems. We present optical measurements concerning control of the transmitted intensity and depth of focus, and studies dealing with switching times, light scattering, and stability. While the EC polymer used in this study still has limitations concerning color and contrast, the presented device features all functions of an iris aperture. In contrast to conventional devices it offers some special features. Owing to the variable chemistry of the EC material, its spectral response may be adjusted to certain applications like color filtering in different spectral regimes (UV, optical range, infrared). Furthermore, all segments may be switched individually to establish functions like spatial Fourier filtering or lateral tunable intensity filters.

Deutschmann, T.; Oesterschulze, E.

2014-05-01

304

Aperture effects in squid jet propulsion.  

PubMed

Squid are the largest jet propellers in nature as adults, but as paralarvae they are some of the smallest, faced with the inherent inefficiency of jet propulsion at a low Reynolds number. In this study we describe the behavior and kinematics of locomotion in 1 mm paralarvae of Dosidicus gigas, the smallest squid yet studied. They swim with hop-and-sink behavior and can engage in fast jets by reducing the size of the mantle aperture during the contraction phase of a jetting cycle. We go on to explore the general effects of a variable mantle and funnel aperture in a theoretical model of jet propulsion scaled from the smallest (1 mm mantle length) to the largest (3 m) squid. Aperture reduction during mantle contraction increases propulsive efficiency at all squid sizes, although 1 mm squid still suffer from low efficiency (20%) because of a limited speed of contraction. Efficiency increases to a peak of 40% for 1 cm squid, then slowly declines. Squid larger than 6 cm must either reduce contraction speed or increase aperture size to maintain stress within maximal muscle tolerance. Ecological pressure to maintain maximum velocity may lead them to increase aperture size, which reduces efficiency. This effect might be ameliorated by nonaxial flow during the refill phase of the cycle. Our model's predictions highlight areas for future empirical work, and emphasize the existence of complex behavioral options for maximizing efficiency at both very small and large sizes. PMID:24501132

Staaf, Danna J; Gilly, William F; Denny, Mark W

2014-05-01

305

Class of near-perfect coded apertures  

NASA Technical Reports Server (NTRS)

Coded aperture imaging of gamma ray sources has long promised an improvement in the sensitivity of various detector systems. The promise has remained largely unfulfilled, however, for either one of two reasons. First, the encoding/decoding method produces artifacts, which even in the absence of quantum noise, restrict the quality of the reconstructed image. This is true of most correlation-type methods. Second, if the decoding procedure is of the deconvolution variety, small terms in the transfer function of the aperture can lead to excessive noise in the reconstructed image. It is proposed to circumvent both of these problems by use of a uniformly redundant array (URA) as the coded aperture in conjunction with a special correlation decoding method.

Cannon, T. M.; Fenimore, E. E.

1977-01-01

306

On choosing an aperture  

SciTech Connect

The most difficult part of choosing an aperture is choosing the right method of choosing, after that the choice simply requires work. We must find just which important of a good ring, of the type we are designing, makes the severest demand on field quality and hence specifies the largest aperture. For electron rings, beam loss at many sigma makes the greatest demand because of the total dominance of synchrotron radiation. Proton rings and particularly superconducting proton rings are not similar to electron rings. The Fermilab experience with the Doubler and with the Main Ring shows very clearly that workability'' is the dominant virtue. An aperture decision based solely on beam loss from a modest beam size will not produce a good superconducting proton ring; a decision based on workability will. Workability is the property that the Main Ring lacks. The Doubler on the other hand has excellent workability, in spite of the more complex operation necessary for superconducting rings --- for example correction elements must ramp to full field and generally will require different relative settings for injection, acceleration, and flat-top. Our problem is to express this quality concept in a numeric form.

Collins, T.L. (Fermi National Accelerator Lab., Batavia, IL (USA))

1985-04-01

307

Aperture excited dielectric antennas  

NASA Technical Reports Server (NTRS)

The results of a comprehensive experimental and theoretical study of the effect of placing dielectric objects over the aperture of waveguide antennas are presented. Experimental measurements of the radiation patterns, gain, impedance, near-field amplitude, and pattern and impedance coupling between pairs of antennas are given for various Plexiglas shapes, including the sphere and the cube, excited by rectangular, circular, and square waveguide feed apertures. The waveguide excitation of a dielectric sphere is modeled using the Huygens' source, and expressions for the resulting electric fields, directivity, and efficiency are derived. Calculations using this model show good overall agreement with experimental patterns and directivity measurements. The waveguide under an infinite dielectric slab is used as an impedance model. Calculations using this model agree qualitatively with the measured impedance data. It is concluded that dielectric loaded antennas such as the waveguide excited sphere, cube, or sphere-cylinder can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of 2 wavelengths or less. It is also shown that for certain configurations coupling between two antennas of this type is less than that for the same antennas without dielectric loading.

Crosswell, W. F.; Chatterjee, J. S.; Mason, V. B.; Tai, C. T.

1974-01-01

308

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

309

DFB laser based on single mode large effective area heavy concentration EDF.  

PubMed

A ? phase shifted distributed feedback (DFB) laser based on single mode large effective area heavy concentration erbium-doped fiber (EDF) has been demonstrated. The homemade EDF was fabricated by the modified chemical-vapor deposition (MCVD) technique, and the 13cm long ? phase shifted fiber grating was written in the intracore of the EDF. The erbium-doped concentration is 4.19 10(25) ions/m(3), the mode field diameter of the fiber is 12.2801 um at 1550 nm, the absorption coefficients of the fiber are 34.534 dB/m at 980 nm and 84.253 dB/m at 1530 nm. The threshold of the DFB laser is 66 mW, and the measured maximum output power is 43.5 mW at 450 mW pump power that corresponding to the slope efficiency of 11.5%. The signal-to-noise ratio (SNR) of the operating laser at 200 mW input power is 55 dB, and the DFB laser has a Lorentz linewidth of 9.8 kHz at the same input pump power. PMID:23188334

Li, Qi; Yan, Fengping; Peng, Wanjing; Feng, Ting; Feng, Suchun; Tan, Siyu; Liu, Peng; Ren, Wenhua

2012-10-01

310

Observations of large-scale fluid transport by laser-guided plankton aggregationsa)  

NASA Astrophysics Data System (ADS)

Diel vertical migration of plankton has been proposed to affect global ocean circulation to a degree comparable to winds and tides. This biomixing process has never been directly observed, however, due to the inability to predict its occurrence in situ or to reproduce it in a laboratory setting. Furthermore, it has been argued that the energy imparted to the ocean by plankton migrations occurs at the scale of individual organisms, which is too small to impact ocean mixing. We describe the development of a multi-laser guidance system that leverages the phototactic abilities of plankton to achieve controllable vertical migrations concurrently with laser velocimetry of the surrounding flow. Measurements in unstratified fluid show that the hydrodynamic interactions between neighboring swimmers establish an alternate energy transfer route from the small scales of individually migrating plankton to significantly larger scales. Observations of laser-induced vertical migrations of Artemia salina reveal the appearance of a downward jet, which triggers a Kelvin-Helmholtz instability that results in the generation of eddy-like structures with characteristic length scales much larger than the organisms. The measured energy spectrum is consistent with these findings and indicates energy input at large scales, despite the small individual size of the organisms. These results motivate the study of biomixing in the presence of stratification to assess the contribution of migrating zooplankton to local and global ocean dynamics. The laser control methodology developed here enables systematic study of the relevant processes.

Wilhelmus, Monica M.; Dabiri, John O.

2014-10-01

311

Tracking Studies to Determine the Required Wiggler Aperture forthe ILC Damping Rings  

SciTech Connect

The injection efficiency of an ILC damping ring is closely tied to its acceptance. To maximize both, one wants a physical aperture as large as possible in the wiggler magnets, as these are likely to be the limiting physical apertures in the ring. On the other hand, a small aperture in the wiggler magnets is needed to achieve the required field profile, a high magnetic field that is very linear over the whole physical aperture of the magnet. Tracking studies were done for all proposed ILC damping ring lattices to determine their required physical apertures. Although a half-aperture of 8 or 10mm had been proposed, our studies showed that, for most lattices, a 16mm half-aperture is required. For some lattices a 12mm half aperture might suffice. We present here the results of our studies, which led to adopting a 16mm half-aperture in the current ILC damping ring baseline design.

Reichel, I.; Wolski, A.

2006-06-21

312

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

313

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

2012-03-01

314

Asymmetric dihedral angle offsets for large-size lunar laser ranging retroreflectors  

NASA Astrophysics Data System (ADS)

The distribution of two-dimensional velocity aberration is off-centered by 5 to 6 microradians in lunar laser ranging, due to the stable measurement geometry in the motion of the Earth and the Moon. The optical responses of hollow-type retroreflectors are investigated through numerical simulations, especially focusing on large-size, single-reflector targets that can ultimately minimize the systematic error in future lunar laser ranging. An asymmetric dihedral angle offset, i.e. setting unequal angles between the three back faces, is found to be effective for retroreflectors that are larger than 100 mm in diameter. Our numerical simulation results reveal that the optimized return energy increases approximately 3.5 times more than symmetric dihedral angle cases, and the optimized dihedral angle offsets are 0.65-0.8 arcseconds for one angle, and zeroes for the other two angles.

Otsubo, T.; Kunimori, H.; Noda, H.; Hanada, H.; Araki, H.; Katayama, M.

2011-08-01

315

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

316

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

317

Vertical emitting aperture nanoantennas.  

PubMed

Herein we propose, theoretically investigate, and numerically demonstrate a compact design for a vertical emitter at a wavelength of 1.5 ?m based on nanophotonic aperture antennas coupled to a dielectric waveguide. The structure utilizes a plasmonic antenna placed above a Si3N4 waveguide with a ground plane for breaking the up-down symmetry and increasing the emission efficiency. Three-dimensional (3-D) finite-difference time-domain (FDTD) simulations reveal that up to 60% vertical emission efficiency is possible in a structure only four wavelengths long with a 3 dB bandwidth of over 300 nm. PMID:22555702

Yaacobi, Ami; Timurdogan, Erman; Watts, Michael R

2012-05-01

318

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

319

Large Aperture Systems: 2000-2004  

NASA Technical Reports Server (NTRS)

This custom bibliography from the NASA Scientific and Technical Information Program lists a sampling of records found in the NASA Aeronautics and Space Database. The scope of this topic includes technologies for next generation astronomical telescopes and detectors. This area of focus is one of the enabling technologies as defined by NASA s Report of the President s Commission on Implementation of United States Space Exploration Policy, published in June 2004.

2004-01-01

320

Large-aperture radiant solar energy concentrators  

Microsoft Academic Search

The relation between the maximum concentration factor and the number and form of facets of a paraboloid mirror used for solar energy concentration is analyzed. The three-step approach begins by describing, in terms of differential geometry, the ray deflections associated with a facet system approximating an ideal paraboloid reflector. Then the formation of the receiver irradiation field is represented by

I. V. Baum

1978-01-01

321

Large Aperture Multiplexed Diffractive Lidar Optics  

NASA Technical Reports Server (NTRS)

We have delivered only 2 or 3 UV Holographic Optical Elements (HOEs) thus far and have fallen short of the intended goal in size and in dual wavelength function. Looking back, it has been fortuitous that we even made anything work in the UV region. It was our good fortune to discover that the material we work with daily was adequate for use at 355 nm, if well rinsed during processing. If we had stuck to our original plan of etching in small pieces of fused silica, we would still be trying to make the first small section in our ion mill, which is not yet operational. The original plan was far too ambitious and would take another 2 years to complete beginning where we left off this time. In order to make a HOE for the IR as well as the UV we will likely have to learn to sensitize some film to the 1064 line and we have obtained sensitizer that is reported to work in that region already. That work would also take an additional year to complete.

Rallison, Richard D.; Schwemmer, Geary K. (Technical Monitor)

1999-01-01

322

Assembly of a large modular optical telescope (ALMOST)  

E-print Network

Future space telescope programs need to assess in-space robotic assembly of large apertures at GEO and ESL2 to support ever increasing aperture sizes. Since such large apertures will not fit within a fairing, they must ...

Mohan, Swati

323

Exploiting multi-scale parallelism for large scale numerical modelling of laser wakefield accelerators  

NASA Astrophysics Data System (ADS)

A new generation of laser wakefield accelerators (LWFA), supported by the extreme accelerating fields generated in the interaction of PW-Class lasers and underdense targets, promises the production of high quality electron beams in short distances for multiple applications. Achieving this goal will rely heavily on numerical modelling to further understand the underlying physics and identify optimal regimes, but large scale modelling of these scenarios is computationally heavy and requires the efficient use of state-of-the-art petascale supercomputing systems. We discuss the main difficulties involved in running these simulations and the new developments implemented in the OSIRIS framework to address these issues, ranging from multi-dimensional dynamic load balancing and hybrid distributed/shared memory parallelism to the vectorization of the PIC algorithm. We present the results of the OASCR Joule Metric program on the issue of large scale modelling of LWFA, demonstrating speedups of over 1 order of magnitude on the same hardware. Finally, scalability to over ?106 cores and sustained performance over ?2 P Flops is demonstrated, opening the way for large scale modelling of LWFA scenarios.

Fonseca, R. A.; Vieira, J.; Fiuza, F.; Davidson, A.; Tsung, F. S.; Mori, W. B.; Silva, L. O.

2013-12-01

324

Complex aperture networks  

NASA Astrophysics Data System (ADS)

A complex network approach is proposed for studying the shear behavior of a rough rock joint. Similarities between aperture profiles are established, and a functional complex network-in each shear displacement-is constructed in two directions: parallel and perpendicular to the shear direction. We find that the growth of the clustering coefficient and that of the number of edges are approximately scaled with the development of shear strength and hydraulic conductivity, which could possibly be utilized to estimate and formulate a friction law and the evolution of shear distribution over asperities. Moreover, the frictional interface is mapped in the global-local parameter space of the corresponding functional friction network, showing the evolution path and, eventually, the residual stage. Furthermore, we show that with respect to shear direction, parallel aperture patches are more adaptable to environmental stimuli than perpendicular profiles. We characterize the pure-contact profiles using the same approach. Unlike the first case, the later networks show a growing trend while in the residual stage; a saturation of links is encoded in contact networks.

Ghaffari, H. O.; Sharifzadeh, M.; Young, R. Paul

2013-02-01

325

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

326

Fabrication and alignment of large sapphire microlenses for use in electrically-injected GaN-based vertical-cavity laser applications  

NASA Astrophysics Data System (ADS)

We have fabricated large sapphire microlenses for use in electrically-injected GaN-based vertical-cavity surface-emitting laser (VCSEL) applications. Thermally reflown photoresist microlenses are used as sacrificial masks for a BCl3/Cl2-based dry etch of sapphire. Sapphire microlenses with base diameters ranging from 10-250 ?m and radii of curvature (ROC) ranging from 50-2000 ?m are created by varying the initial thickness and diameter of the photoresist mask. Typical rms surface roughnesses of 1.5 over 5.0 ?m x 5.0 ?m scan areas are achieved by utilizing specialized post-etch cleaning techniques. By coating the sapphire microlenses with dielectric distributed Bragg reflectors (DBRs) and aligning them to current apertures on InGaN-based devices on the opposite side of the sapphire wafer, we have demonstrated a viable technique for making high-reflectivity concave micromirrors for use in electrically-injected GaN-based VCSELs.

Farrell, Robert; Feezell, Daniel; Ishida, Masahiro; Newman, Scott; Cohen, Daniel; Nakamura, Shuji

2007-03-01

327

A laser tracker active optics system for the Large Binocular Telescope  

NASA Astrophysics Data System (ADS)

The Large Binocular Telescope consists of two 8.4m telescopes on a common mount. Its current active optics system uses measured mechanical deflections of its optics to compensate for misalignment due to changes in telescope elevation angle and analysis of stellar images to calculate compensating optic displacements. The process is iterated until the inferred wavefront is within tolerance. Due to the asymmetry of the distribution of thermal mass of the telescope structure, thermal gradients during the night cause the current active optics alignment system to require extra iterations to achieve alignment. A system is proposed which uses a laser tracker to measure optic misalignment resulting from the additional thermal influence. This provides a single measurement of relative optic misalignment and reduces the number of iterations required to achieve collimation. A single laser tracker location can be used to measure the rigid body locations of the primary mirror, secondary mirror, prime focus camera, and flat tertiary mirror for both telescopes. A set of reference points on the telescope structure provides a common coordinate system for measurements of optic locations on each side and to assist with binocular copointing. The laser tracker measures the displacement of the optics relative to their locations measured when the telescope is in collimation. Practical considerations integrating the system with the telescope will be discussed, as well as its expected performance.

Dettmann, Lee; Ashby, Dave; Hill, John M.; Chatila, Amjad

2014-07-01

328

Large-area laser nano-texturing with user-defined patterns  

NASA Astrophysics Data System (ADS)

Writing nano-sized features less than the diffraction limit of the lasers efficiently over a large area requires special technology development. This paper reports the use of a self-assembled particle lens array with near-field enhancement effect to write millions of nano-sized user-defined features, e.g. English letters, lines, curves, simultaneously by angular beam scanning. About a 5 mm 5 mm area can be written with a single shot of a laser beam or few scans for up to 100 million identical features of nano or sub-micro scales. With the help of certain environmental conditions, such as the use of a suitable chemical solution in conjunction with the particle lens array, the characteristic of the features produced can be further controlled, including the generation of reversed (e.g. pits become hills and grooves become walls) features of laser-written patterns. The technical challenges, experimental findings and theoretical analysis/simulation are presented.

Li, L.; Guo, W.; Wang, Z. B.; Liu, Z.; Whitehead, D.; Luk'yanchuk, B.

2009-05-01

329

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

330

Laser-driven, magnetized quasi-perpendicular collisionless shocks on the Large Plasma Devicea)  

NASA Astrophysics Data System (ADS)

The interaction of a laser-driven super-Alfvnic magnetic piston with a large, preformed magnetized ambient plasma has been studied by utilizing a unique experimental platform that couples the Raptor kJ-class laser system [Niemann et al., J. Instrum. 7, P03010 (2012)] to the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles. This platform provides experimental conditions of relevance to space and astrophysical magnetic collisionless shocks and, in particular, allows a detailed study of the microphysics of shock formation, including piston-ambient ion collisionless coupling. An overview of the platform and its capabilities is given, and recent experimental results on the coupling of energy between piston and ambient ions and the formation of collisionless shocks are presented and compared to theoretical and computational work. In particular, a magnetosonic pulse consistent with a low-Mach number collisionless shock is observed in a quasi-perpendicular geometry in both experiments and simulations.

Schaeffer, D. B.; Everson, E. T.; Bondarenko, A. S.; Clark, S. E.; Constantin, C. G.; Vincena, S.; Van Compernolle, B.; Tripathi, S. K. P.; Winske, D.; Gekelman, W.; Niemann, C.

2014-05-01

331

Large format imaging detectors for x-ray free-electron-lasers  

NASA Astrophysics Data System (ADS)

New generation synchrotron light sources, the X-ray free electron lasers, require a two dimensional focal plane instrumentation to perform X-ray imaging from below 100eV up to 25keV. The instruments have to face the accelerator bunch structure and energy bandwidth which is different for existing (FLASH, Hamburg and LCLS, Menlo Park) and future photon sources (SACLA, Harima and XFEL, Hamburg). Within the frame of the Center for Free Electron Laser Science (CFEL), a joint effort of the Max-Planck Society, DESY and the University of Hamburg, the MPI semiconductor laboratory developed, produced and operated large area X-ray CCD detectors with a format of nearly 60cm2 image area. They show outstanding characteristics: a high readout speed due to a complete parallel signal processing, high and homogeneous quantum efficiency, low signal noise, radiation hardness and a high pixel charge handling capacitance. We will present measurement results which demonstrate the X-ray spectroscopic and imaging capabilities of the fabricated devices. We will also report on the concept and the anticipated properties of the full, large scale system. The implementation of the detector into an experimental chamber to perform measurements e.g. of macromolecules in order to determine their structure at atomic resolutions will be shown.

Hartmann, Robert; Epp, Sascha; Gorke, Hubert; Hartmann, Andreas; Hauser, Gnther; Herrmann, Sven; Holl, Peter; Kimmel, Nils; Meidinger, Norbert; Reich, Christian; Rolles, Daniel; Soltau, Heike; Strder, Lothar; Ullrich, Joachim; Weidenspointner, Georg

2011-06-01

332

Superresolving masks for incoherent high-numerical-aperture scanning  

E-print Network

Received January 27, 1998; accepted May 4, 1998 A singular-value-decomposition analysis of the imaging kernel for three-dimensional fluorescent laser scan- ning microscopy at a high numerical aperture (NA) is presented. The design and superresolving performance of image-plane binary optical masks are then derived

Bertero, Mario

333

Phase calibration for synthetic aperture imaging  

Microsoft Academic Search

High-resolution imaging can be achieved by optical aperture synthesis. Using a sparse array of smaller aperture, one can synthesize an aperture with the resolution of the equivalent filled aperture while reducing the size and weight of system. The environment and vibration factors of synthetic aperture arrays lead to errors in phase measurement and cause a severe degradation in the image

Changwei Wang; Yuesong Jiang; Yuntao He; Li Liu

2008-01-01

334

High rate, large area laser-assisted chemical vapor deposition of nickel from nickel carbonyl  

NASA Astrophysics Data System (ADS)

High-power diode lasers (HPDL) are being increasingly used in industrial applications. Deposition of nickel from nickel carbonyl (Ni(CO)4 ) precursor by laser-induced chemical vapor deposition (CVD) was studied with emphasis on achieving high deposition rates. An HPDL system was used to provide a novel energy source facilitating a simple and compact design of the energy delivery system. Nickel deposits on complex, 3-dimensional polyurethane foam substrates were prepared and characterized. The resulting "nickel foam" represents a novel material of high porosity (>95% by volume) finding uses, among others, in the production of rechargeable battery and fuel cell electrodes and as a specialty high-temperature filtration medium. Deposition rates up to 19 mum/min were achieved by optimizing the gas precursor flow pattern and energy delivery to the substrate surface using a 480W diode laser. Factors affecting the transition from purely heterogeneous decomposition to a combined hetero- and homogeneous decomposition of nickel carbonyl were studied. High quality, uniform 3-D deposits produced at a rate more than ten times higher than in commercial processes were obtained by careful balance of mass transport (gas flow) and energy delivery (laser power). Cross-flow of the gases through the porous substrate was found to be essential in facilitating mass transport and for obtaining uniform deposits at high rates. When controlling the process in a transient regime (near the onset of homogenous decomposition), unique morphology features formed as part of the deposits, including textured surface with pyramid-shape crystallites, spherical and non-spherical particles and filaments. Operating the laser in a pulsed mode produced smooth, nano-crystalline deposits with sub-100 nm grains. The effect of H2S, a commonly used additive in nickel carbonyl CVD, was studied using both polyurethane and nickel foam substrates. H2S was shown to improve the substrate coverage and deposit uniformity in tests with polyurethane substrate, however, it was found to have no effect in improving the overall deposition rate compared to H2S-free deposition process. Deposition on other selected substrates, such as ultra-fine polymer foam, carbon nanofoam and multi-wall carbon nanotubes, was demonstrated. The HPDL system shows good promise for large-scale industrial application as the cost of HPDL energy continues to decrease.

Paserin, Vlad

335

A self pulsed laser ranging system under development at 'JPL'. [for onboard measurement of large space deployable reflector surface distortions  

NASA Technical Reports Server (NTRS)

The performance of large space deployable antenna reflectors to be used for broad-based communications systems is largely dependent on the accuracy with which the surface figure can be constructed and maintained. The paper examines various surface distortion tolerance and measurement requirements for various classes of communication antennas. Several surface measuring methods are described including a self-pulsed laser ranging system.

Berdahl, M.

1979-01-01

336

Dynamic Aperture Measurements at the Advanced Light Source  

SciTech Connect

A large dynamic aperture for a storage ring is of importance for long lifetimes and a high injection efficiency. Measurements of the dynamic aperture of the third generation synchrotron light source Advanced Light Source (ALS) using beam excitation with kicker magnets are presented. The experiments were done for various accelerator conditions, allowing us to investigate the influence of different working points, chromaticities, insertion devices, etc.. The results are compared both with tracking calculations and a simple model for the dynamic aperture yielding good agreements. This gives us confidence in the predictability of the nonlinear accelerator model. This is especially important for future ALS upgrades as well as new storage ring designs.

Decking, W.; Robin, D.

1999-03-12

337

Versatile method for achieving 1% speckle contrast in large-venue laser projection displays using a stationary multimode optical fiber.  

PubMed

We propose a method based on quantitative theoretical analysis for achieving speckle contrast of 1% or less in images created by a full-frame laser projection display system. The method employs a stationary multimode optical fiber to achieve the effect of using a rapidly moving diffuser, but without moving the fiber or any other system component. When a suitably large projector lens is used, low-speckle illumination light delivered through the fiber acts in conjunction with wavelength diversity at the projection screen to achieve speckle contrast of 1% in viewed images. We describe in detail how the proposed method might be used with most types of high-power visible lasers being considered for large-venue displays. When used with visible laser diodes, the method may also be suitable for use in laser-based television. PMID:22565751

Manni, Jeffrey G; Goodman, Joseph W

2012-05-01

338

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

339

Simulation of high power-aperture Rayleigh lidar for upper atmospheric studies  

NASA Astrophysics Data System (ADS)

The objective of this research effort is to investigate the use of a high power-aperture Rayleigh lidar to measure neutral density and temperature in the upper atmosphere, into the lower thermosphere (>100 km). The scientific interest with this system is to obtain measurements of atmospheric tides, planetary and gravity wave amplitudes and phase in the lower thermosphere. Measurement of waves into the lower thermosphere is accomplished using Rayleigh lidar methods with high power-aperture (PA) products using new technology lasers and large collecting apertures, resulting in PA of 50-700 W m2. This paper describes the simulation of high PA Rayleigh lidar systems and estimates their capability to measure gravity waves and tides in the mesosphere and lower thermosphere. Both traditional backscatter and bistatic (imaging) methods are simulated. Simulations show that substantive measurements can be achieved for characterizing gravity waves at altitudes >90 km and atmospheric tides at altitudes >100 km for this lidar system. Measurements of density and temperature to 10% precision are possible up to 120 km.

Westerhoff, John; Swenson, Gary R.

2014-01-01

340

High-efficiency high-power solid-state CW visible lasers for large-format-display applications  

Microsoft Academic Search

High-efficiency (5%-10% wall-plug efficiency) high-power continuous-wave (CW) visible lasers have been developed for large-format-display applications (e.g., planetariums, visualization centers, etc.). Using an approach pioneered by Evans & Sutherland (E&S), a fiber based master-oscillator-power-amplifier (MOPA) architecture is employed to generate high power near-infrared (NIR) tunable lasers that are then converted to visible wavelengths in external enhancement nonlinear ring cavities. Depending on

Tatyana A. Chernysheva; Dennis F. Elkins; Jesse P. Anderegg; Forrest L. Williams

2009-01-01

341

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

342

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

NASA Technical Reports Server (NTRS)

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.

1982-01-01

343

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

344

FRET Imaging by Laser Scanning Cytometry on Large Populations of Adherent Cells.  

PubMed

The application of FRET (fluorescence resonance energy transfer) sensors for monitoring protein-protein interactions under vital conditions is attracting increasing attention in molecular and cell biology. Laser-scanning cytometry (LSC), a slide-based sister procedure to flow cytometry, provides an opportunity to analyze large populations of adherent cells or 2-D solid tissues in their undisturbed physiological settings. Here we provide an LSC-based three-laser protocol for high-throughput ratiometric FRET measurements utilizing cyan and yellow fluorescent proteins as a FRET pair. Membrane labeling with Cy5 dye is used for cell identification and contouring. Pixel-by-pixel and single-cell FRET efficiencies are calculated to estimate the extent of the molecular interactions and their distribution in the cell populations examined. We also present a non-high-throughput donor photobleaching FRET application, for obtaining the required instrument parameters for ratiometric FRET. In the biological model presented, HeLa cells are transfected with the ECFP- or EYFP-tagged Fos and Jun nuclear proteins, which heterodimerize to form active AP1 transcription factor. Curr. Protoc. Cytom. 70:2.23.1-2.23.29. 2014 by John Wiley & Sons, Inc. PMID:25271960

Doan-Xuan, Quang-Minh; Szalki, Nikoletta; Tth, Katalin; Szll?si, Jnos; Bacso, Zsolt; Vmosi, Gyrgy

2014-01-01

345

Tunable fiber laser using fiber Bragg gratings integrated carbon fiber composite with large tuning range  

NASA Astrophysics Data System (ADS)

A wide-tuning range linear cavity C+L band tunable fiber laser is proposed in this paper. By using 3-point bending device to facilitate wavelength tuning of fiber Bragg gratings (FBGs), a scheme with two parallel strain-tunable FBGs (TFBGs) is demonstrated in L band operation. A large tuning range of over 22.5 nm with 0.1 nm precise resolution for each TFBG is obtained. The overlapping tuning range for two TFBGs is from 1564 to 1600.5 nm with 2 dB power variation. Using 10 M Erbium-doped fiber (EDF) and 100 mW pumping power, the stable lasing output power is measured at 1582.0 nm with threshold pump power and side mode suppression ratio (SMSR) of 10 mW and 50 dB, respectively. And the measured slope efficiency is 11.5% corresponding to quantum efficiency of 12.3%.

Liaw, Shien-Kuei; Shin, Chow-Shing; Wu, Wen-Fang

2014-12-01

346

Investigations of large x-ray optics for free electron lasers  

NASA Astrophysics Data System (ADS)

A free electron laser (FEL) is being set up at DESY (Deutsches Elektronen Synchrotron, Hamburg, Germany). In the current XUV range of the FEL, total-reflection X-ray mirrors are needed for beam guidance, beam alignment, and monochromatisation. Such X-ray optics are used at a grazing incidence angle of about 2 thus a maximum length of about 500 mm is required. Due to the working range of the FEL (50 - 200 eV), carbon has been selected as a suitable material with an absorption edge at 284 eV. The amorphous carbon coatings were manufactured by magnetron sputtering in a special UHV system for large deposition at GKSS research centre (Geesthacht, Germany). The variation in film thickness over the whole length has been investigated by X-ray reflectometry (XRR). Good uniformity (better than 2 %) and low roughness (< 0.5 nm) have been observed.

Stormer, Michael; Liard-Cloup, Audrey; Felten, Frank; Jacobi, Sandra; Steeg, Barbara; Feldhaus, Josef; Bormann, Rudiger

2004-10-01

347

Large-Scale Hollow Retroreflectors for Lunar Laser Ranging at Goddard Space Flight Center  

NASA Technical Reports Server (NTRS)

Laser ranging to the retroreflector arrays placed on the lunar surface by the Apollo astronauts and the Soviet Luna missions have dramatically increased our understanding of gravitational physics along with Earth and Moon geophysics, geodesy, and dynamics. Although the precision of the range measurements has historically been limited by the ground station capabilities, advances in the APOLLO instrument at the Apache Point facility in New Mexico is beginning to be limited by errors associated with the lunar arrays. We report here on efforts at Goddard Space Flight Center to develop the next generation of lunar retroreflectors. We will describe a new facility that is being used to design, assemble, and test large-scale hollow retroreflectors. We will also describe results from investigations into various bonding techniques used to assemble the open comer cubes and mirror coatings that have dust mitigation properties.

Preston, Alix

2012-01-01

348

DAVINCI: Dilute Aperture VIsible Nulling Coronagraphic Imager  

NASA Technical Reports Server (NTRS)

This slide presentation gives an overview of DAVINCI (Dilute Aperture VIsible Nulling Coronagraphic Imager). The presentation also includes information about dilute aperture coronagraph, and lyot efficiency.

Shao, Michael; Levine, B. M.; Vasisht, G.; Lane, B. F.; Woodruff, R.; Vasudevan, G.; Samuele, R.; Lloyd, C. A.; Clampin, M.; Lyon, R.; Guyon, O.

2008-01-01

349

The Historical Growth of Telescope Aperture  

NASA Astrophysics Data System (ADS)

This paper analyzes a compilation of aperture diameters D and commissioning dates t for 177 optical telescopes, including those that have been among the largest of their time. We offer the following findings, and draw the following inferences, about aperture growth D(t) over four centuries: 1. From the days of Galileo to the present, telescope diameters have steadily grown, with a doubling time t2 of nearly 50 yr. 2. Beginning in 1730, major refractors' apertures followed a strictly exponential curve of growth, with t2=45 yr, before stopping with the Yerkes 40 inch (1.02 m) in 1897. 3. Over the last 300 yr, the very largest ``frontier'' reflectors have defined a sharp and distinct upper boundary to the D(t) distribution, with t2=48 yr and D1900=2.3 m. This exponential growth is taken to have been imposed strictly by the rate at which telescope technology has progressed. 4. Data for second-tier ``large'' reflectors yield D1900=1.0 m and t2=47 yr until 1950 and suggest an exponential decrease of the doubling time afterwards, e-folding in ~70 yr and leading to t2=20 yr in 2000. This may be the result of a gradual relief, through increased collaboration, of constraints that prevented the limits of technology from being reached. 5. The curves of growth for large and for frontier reflectors cross in ~2010. Whether the aperture growth in the 21st century is limited by demographics-collaborations-or by technology remains to be seen. 6. During the 20th century, commissioning of large telescopes tended to occur in bursts at ~35 yr intervals. 7. Giant telescopes with serious shortcomings were not uncommon before 1850. These typically had twice the aperture of their more productive contemporaries. 8. The completion of the current burst of ambitiously large 20-100 m telescope projects with the scheduled launch of the James Webb Space Telescope in the 2010s would constitute a dramatic break with 4 centuries of historical evolution.

Racine, Ren

2004-01-01

350

Evaluation of a laser scanner for large volume coordinate metrology: a comparison of results before and after factory calibration  

NASA Astrophysics Data System (ADS)

Large volume laser scanners are increasingly being used for a variety of dimensional metrology applications. Methods to evaluate the performance of these scanners are still under development and there are currently no documentary standards available. This paper describes the results of extensive ranging and volumetric performance tests conducted on a large volume laser scanner. The results demonstrated small but clear systematic errors that are explained in the context of a geometric error model for the instrument. The instrument was subsequently returned to the manufacturer for factory calibration. The ranging and volumetric tests were performed again and the results are compared against those obtained prior to the factory calibration.

Ferrucci, M.; Muralikrishnan, B.; Sawyer, D.; Phillips, S.; Petrov, P.; Yakovlev, Y.; Astrelin, A.; Milligan, S.; Palmateer, J.

2014-10-01

351

Gradient polymer-disposed liquid crystal single layer of large nematic droplets for modulation of laser light.  

PubMed

The light modulating ability of gradient polymer-disposed liquid crystal (PDLC) single layer of large droplets formed by nematic E7 in UV-cured polymer NOA65 is studied. Operating at relatively low voltages, such PDLC film with a of thickness 10-25??m and droplet size up to 50??m exhibits a good contrast ratio and is capable of producing a large phase shift for the propagating coherent light. For a linearly polarized He-Ne laser (?=633?nm), an electrically commanded phase shift as large as ?/2 can be obtained by the large-droplet region of the film. The electrically produced phase shift and its spatial profile controlled by the thickness of the gradient PDLC single layers of large nematic droplets can be useful for tunable spatial light modulators and other devices for active control of laser light. PMID:21629309

Hadjichristov, Georgi B; Marinov, Yordan G; Petrov, Alexander G

2011-06-01

352

UAVSAR Phased Array Aperture  

NASA Technical Reports Server (NTRS)

This paper describes the development of a patch antenna array for an L-band repeat-pass interferometric synthetic aperture radar (InSAR) instrument that is to be flown on an unmanned aerial vehicle (UAV). The antenna operates at a center frequency of 1.2575 GHz and with a bandwidth of 80 MHz, consistent with a number of radar instruments that JPL has previously flown. The antenna is designed to radiate orthogonal linear polarizations in order to facilitate fully-polarimetric measurements. Beam-pointing requirements for repeat-pass SAR interferometry necessitate electronic scanning in azimuth over a range of -20degrees in order to compensate for aircraft yaw. Beam-steering is accomplished by transmit/receive (T/R) modules and a beamforming network implemented in a stripline circuit board. This paper, while providing an overview of phased array architecture, focuses on the electromagnetic design of the antenna tiles and associated interconnects. An important aspect of the design of this antenna is that it has an amplitude taper of 10dB in the elevation direction. This is to reduce multipath reflections from the wing that would otherwise be detrimental to interferometric radar measurements. This taper is provided by coupling networks in the interconnect circuits as opposed to attenuating the output of the T/R modules. Details are given of material choices and fabrication techniques that meet the demanding environmental conditions that the antenna must operate in. Predicted array performance is reported in terms of co-polarized and crosspolarized far-field antenna patterns, and also in terms of active reflection coefficient.

Chamberlain, Neil; Zawadzki, Mark; Sadowy, Greg; Oakes, Eric; Brown, Kyle; Hodges, Richard

2009-01-01

353

Treatment strategies for large oral venous malformations using intralesional laser photocoagulation.  

PubMed

We report two treatment strategies using intralesional laser photocoagulation (ILP) for large venous malformations (VMs) in the oral cavity. ILP is considered to be an effective technique for massive vascular lesion. The satisfactory results could have been obtained, since we started ILP for the treatment of large VMs. Recently, to improve the safety, reliability, and effectiveness of the treatment, we developed modifications of ILP that include a combination of ILP and transmucosal irradiation; and compartmentalization and serial step irradiation. In the former, ILP is performed for a deep layer lesion and transmucosal irradiation with multiple spots fashioned using a single pulse is added for the superficial layer in the same session, to increase the efficacy of regression. In the latter, the lesion is divided by virtual compartment and each area will be sequentially treated by ILP. The irradiated area and total energy in a session should be limited to avoid severe reactions and excessive thermal destruction of surrounding tissue. All treatment outcomes by each technique were satisfactory without serious complications, such as deep ulcer formation, bleeding, or severe swelling developing obstruction. Both treatment strategies improve the safety, reliability, and effectiveness of ILP and make the method less traumatic for patients. PMID:23893092

Miyazaki, Hidetaka; Romeo, Umberto; Ohshiro, Takafumi; Kudo, Toshifumi; Makiguchi, Takaya; Kawachi, Naoko; Ogawa, Masaru; Inoue, Yoshinori; Yokoo, Satoshi

2014-11-01

354

[Study on large-scale regional laser detection methods for water vapor concentration].  

PubMed

Water vapor is an important meteorological parameter in the atmosphere, TDLAS direct absorption technology combined with open-path monitoring was used in order to achieve large-scale regional atmospheric water vapor concentration detection with high sensitivity, high accuracy and fast response, and to correct the remote sensing data. The large-scale regional laser detection system for water vapor was designed and the absorption line of water vapor molecules near 1.27 microm was chosen as the goal line. The system performance was verified in conjunction with a multiple reflection cell, that the system limit sensitivity was 14.803 mmol.mol-1 in optical path of 40 m. The continuous field experiment in 1,420 m optical path at the Yucheng Integrated Experimental Station, CAS was completed with this system which worked stably. Then the measured data was compared with the data of a gas analyzer LI-7500 in eddy correlation observation system at the same site, and the data consistency was good. A new method for water vapor concentration monitoring in the complex field of non-uniform underlying surface was provided. PMID:23705417

He, Ying; Zhang, Yu-Jun; Wang, Li-Ming; You, Kun; Zhou, Yi; Sun, Xiao-Min; Liu, Zhen-Min

2013-03-01

355

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

NASA Astrophysics Data System (ADS)

We develop a digital direct writing method for ZnO NW micro-patterned growth on a large scale by selective laser decomposition of zinc acetate. For ZnO NW growth, by replacing the bulk heating with the scanning focused laser as a fully digital local heat source, zinc acetate crystallites can be selectively activated as a ZnO seed pattern to grow ZnO nanowires locally on a larger area. Together with the selective laser sintering process of metal nanoparticles, more than 10 000 UV sensors have been demonstrated on a 4 cm 4 cm glass substrate to develop all-solution processible, all-laser mask-less digital fabrication of electronic devices including active layer and metal electrodes without any conventional vacuum deposition, photolithographic process, premade mask, high temperature and vacuum environment.We develop a digital direct writing method for ZnO NW micro-patterned growth on a large scale by selective laser decomposition of zinc acetate. For ZnO NW growth, by replacing the bulk heating with the scanning focused laser as a fully digital local heat source, zinc acetate crystallites can be selectively activated as a ZnO seed pattern to grow ZnO nanowires locally on a larger area. Together with the selective laser sintering process of metal nanoparticles, more than 10 000 UV sensors have been demonstrated on a 4 cm 4 cm glass substrate to develop all-solution processible, all-laser mask-less digital fabrication of electronic devices including active layer and metal electrodes without any conventional vacuum deposition, photolithographic process, premade mask, high temperature and vacuum environment. Electronic supplementary information available. See DOI: 10.1039/c3nr34346d

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

2013-04-01

356

A new method for grating lobe reduction for 3D synthetic aperture imaging with ultrasound computer tomography  

Microsoft Academic Search

Our 3D Ultrasound Computer Tomograph for breast imaging uses unfocused transducers grouped on a large non-planar aperture and synthetic aperture focusing in 3D. Technical feasibility limits the number of transducer positions to a sparse aperture, causing artifacts due to grating lobe effects in the resulting images. To suppress the artifacts, a median filter is applied to special pressure distributions, which

N. V. Ruiter; R. Dapp; M. Zapf; H. Gemmeke

2010-01-01

357

Super-Resolution in a Synthetic Aperture Imaging System  

Microsoft Academic Search

Large telescopes have reached a limit of practical realization, restricted by the high costs of manufacturing large and precise optics. To overcome these limitations, images can be collected from a strip aperture which rotates to synthesize a circular one. Variations of a Poisson maximum a priori (PMAP) algorithm are applied to the collection of frames to reconstruct and super-resolve the

J. J. Green; Bobby R. Hunt

1997-01-01

358

Principles and applications of unconventional laser imaging  

Microsoft Academic Search

The intent of this paper is to introduce sampled-aperture, coherent, laser imaging techniques for application to diverse technical and commercial problems that can benefit from the unique advantages of laser imaging. A brief overview is presented of the principles underlying sampled-aperture laser techniques and several example techniques are described along with a discussion of their attributes. Six potential applications are

David G. Voelz

1995-01-01

359

COMPONENTS OF LASER SYSTEMS AND PROCESSES OCCURRING IN THEM: Fast-response system for stabilization of the axis of the angular distribution of laser radiation  

NASA Astrophysics Data System (ADS)

A fast-acting system for stabilization of the axis of the angular distribution of radiation from a continuous-flow CO2 laser is considered. The results of a simulation experiment are reported: they show that it is possible to suppress, by 24-28 dB, fluctuations of the position of the axis in the spectral range 0-20 Hz. This makes the proposed system a promising method for large-aperture laser beams.

Vinogradov, E. G.; Glebova, S. N.; Pavlov, N. V.; Razhenkov, E. T.

1988-09-01

360

Large-Scale Production of Carbon Nanotubes Using the Jefferson Lab Free Electron Laser  

NASA Technical Reports Server (NTRS)

We report on our interdisciplinary program to use the Free Electron Laser (FEL) at the Thomas Jefferson National Accelerator Facility (J-Lab) for high-volume pulsed laser vaporization synthesis of carbon nanotubes. Based in part on the funding of from this project, a novel nanotube production system was designed, tested, and patented. Using this new system nanotube production rates over 100 times faster than conventional laser systems were achieved. Analysis of the material produced shows that it is of as high a quality as the standard laser-based materials.

Holloway, Brian C.

2003-01-01

361

Large scale Tesla coil guided discharges initiated by femtosecond laser filamentation in air  

NASA Astrophysics Data System (ADS)

The guiding of meter scale electric discharges produced in air by a Tesla coil is realized in laboratory using a focused terawatt laser pulse undergoing filamentation. The influence of the focus position, the laser arrival time, or the gap length is studied to determine the best conditions for efficient laser guiding. Discharge parameters such as delay, jitter, and resistance are characterized. An increase of the discharge length by a factor 5 has been achieved with the laser filaments, corresponding to a mean breakdown field of 2 kV/cm for a 1.8 m gap length. Consecutive guided discharges at a repetition rate of 10 Hz are also reported.

Arantchouk, L.; Point, G.; Brelet, Y.; Prade, B.; Carbonnel, J.; Andr, Y.-B.; Mysyrowicz, A.; Houard, A.

2014-07-01

362

Near-term feasibility demonstration of laser power beaming  

SciTech Connect

A mission to recharge batteries of satellites in geostationary orbits (geosats) may be a commercially viable application which could be achieved with laser systems somewhat larger than present state-of-the-art. The lifetime of batteries on geosats is limited by repetitive discharge cycles which occur when the satellites are eclipsed by the earth during the spring and fall equinoxes. By coupling high power lasers with modern, large aperture telescopes and laser guide star adaptive optics systems, present day communications satellites could be targeted. It is important that a near term demonstration of laser power beaming be accomplished using lasers in the kilowatt range so that issues associated with high average power be addressed. The Laser Guide Star Facility at LLNL has all the necessary subsystems needed for such a near term demonstration, including high power lasers for both the power beam and guide star, beam directors and satellite tracking system.

Friedman, H.W.

1994-01-01

363

Very high numerical aperture light transmitting device  

DOEpatents

A new light-transmitting device using a SCIN glass core and a novel calcium sodium cladding has been developed. The very high index of refraction, radiation hardness, similar solubility for rare earths and similar melt and viscosity characteristics of core and cladding materials makes them attractive for several applications such as high-numerical-aperture optical fibers and specialty lenses. Optical fibers up to 60 m in length have been drawn, and several simple lenses have been designed, ground, and polished. Preliminary results on the ability to directly cast optical components of lead-indium phosphate glass are also discussed as well as the suitability of these glasses as a host medium for rare-earth ion lasers and amplifiers.

Allison, Stephen W. (Knoxville, TN); Boatner, Lynn A. (Oak Ridge, TN); Sales, Brian C. (Knoxville, TN)

1998-01-01

364

Evidence for whole-beam self-focusing of induced spatially incoherent laser light in large underdense plasma  

SciTech Connect

The propagation of an intense electromagnetic pulse in a large underdense plasma has been investigated using spatially and temporally incoherent laser light. Spatial incoherence was obtained using the induced spatial incoherence (ISI) technique. The first observation of the occurrence of thermal whole-beam self-focusing with ISI laser light is presented. Thermal imaging with a multiframe x-ray camera (140 ps gate time) was used to record the propagation characteristics of the interaction beam through the plasma. A direct measurement of the self-focusing growth length has been made.

Afshar-rad, T.; Gizzi, L.A.; Desselberger, M.; Khattak, F.; Willi, O. (The Blackett Laboratory, Imperial College of Science and Technology, Prince Consort Road, London SW7 2BZ (United Kingdom)); Giulietti, A. (Istituto di Fisica Atomica e Molecolare, Piza (Italy))

1992-02-17

365

Separation of the electron and proton cosmic-ray components by means of a calorimeter in the PAMELA satellite-borne experiment for the case of particle detection within a large aperture  

SciTech Connect

The PAMELA satellite-borne experiment is designed to study cosmic rays over a broad energy range. The apparatus has been in near-Earth cosmic space from June 2006 to the present time. It is equipped with a magnetic spectrometer for determining the sign of the particle charge and rigidity. In solving some problems, however, information from the magnetic spectrometer becomes inaccessible, so that it is necessary to employ a calorimeter to separate the electron and nuclear cosmic-ray components. A procedure for separating these components for particles arriving off the magnetic-spectrometer aperture is considered.

Karelin, A. V., E-mail: karelin@hotbox.ru; Borisov, S. V.; Voronov, S. A.; Malakhov, V. V. [National Research Nuclear University MEPhI (Russian Federation)

2013-06-15

366

Metamaterial apertures for computational imaging.  

PubMed

By leveraging metamaterials and compressive imaging, a low-profile aperture capable of microwave imaging without lenses, moving parts, or phase shifters is demonstrated. This designer aperture allows image compression to be performed on the physical hardware layer rather than in the postprocessing stage, thus averting the detector, storage, and transmission costs associated with full diffraction-limited sampling of a scene. A guided-wave metamaterial aperture is used to perform compressive image reconstruction at 10 frames per second of two-dimensional (range and angle) sparse still and video scenes at K-band (18 to 26 gigahertz) frequencies, using frequency diversity to avoid mechanical scanning. Image acquisition is accomplished with a 40:1 compression ratio. PMID:23329043

Hunt, John; Driscoll, Tom; Mrozack, Alex; Lipworth, Guy; Reynolds, Matthew; Brady, David; Smith, David R

2013-01-18

367

Metamaterial Apertures for Computational Imaging  

NASA Astrophysics Data System (ADS)

By leveraging metamaterials and compressive imaging, a low-profile aperture capable of microwave imaging without lenses, moving parts, or phase shifters is demonstrated. This designer aperture allows image compression to be performed on the physical hardware layer rather than in the postprocessing stage, thus averting the detector, storage, and transmission costs associated with full diffraction-limited sampling of a scene. A guided-wave metamaterial aperture is used to perform compressive image reconstruction at 10 frames per second of two-dimensional (range and angle) sparse still and video scenes at K-band (18 to 26 gigahertz) frequencies, using frequency diversity to avoid mechanical scanning. Image acquisition is accomplished with a 40:1 compression ratio.

Hunt, John; Driscoll, Tom; Mrozack, Alex; Lipworth, Guy; Reynolds, Matthew; Brady, David; Smith, David R.

2013-01-01

368

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

369

Large spectral tuning of a waterglycerol microdroplet by a focused laser: characterization and modeling  

E-print Network

infrared laser is studied both experimentally by optical spectroscopy and computationally using a lumped of water; hence its size is reduced. When the infrared laser is switched off, the temperature of a water­glycerol microdroplet standing on a superhydrophobic surface by local heating with a focused

Muradoglu, Metin

370

Stimulated forward Raman scattering in large scale-length laser-produced plasmas  

NASA Astrophysics Data System (ADS)

A forward stimulated Raman scattering (FSRS) diagnostic was developed for the 60 beam Omega laser facility to investigate the propagation of an intense ( ~ 8 1014 W/cm2), frequency doubled Nd:glass laser beam ( <= 360 J, 527 nm, 1 ns) through a mm-scale laser-produced plasma. Forward scattered light was measured with spectral, and temporal resolution using a streaked spectrometer and an absolutely calibrated photo-multiplier. We present a detailed description of the instrument, the calibration methods, as well as the first forward Raman scattering measurements from hot ( ~ 2 keV), dense (5.5 1020 cm-3) laser-produced plasmas. These results are of interest to laser-driven inertial fusion at the National Ignition Facility where larger plasma scales could potentially lead to higher FSRS gains. In addition, simultaneous measurements of stimulated forward and backward scattered light present an unambiguous method for determining plasma density and temperature.

Niemann, C.; Berger, R. L.; Divol, L.; Kirkwood, R. K.; Moody, J. D.; Sorce, C. M.; Glenzer, S. H.

2011-10-01

371

Optical properties of plastically bent large-diameter sapphire fiber tips for laser tissue ablations  

NASA Astrophysics Data System (ADS)

Aiming to facilitate laser surgery applications, six 0.75mm- diameter 90mm-length sapphire fiber tips were plastically bent by means of CO2 lasers with bending radii from 1.7mm to 3.6mm and bending angles of 15-120 degree(s). The average bending loss caused by the bending process of the tips is about 0.03dB with the minimum loss less than 0.02dB, the damage thresholds of these tips are higher than 160MW/cm2 for Nd:YAG laser pulses at 1.06micrometers and 2MW/cm2 for CuBr laser pulses at 510.6nm. Satisfactory optical properties of these sapphire fiber tips show that they are promising for use in laser surgery applications such as tissue ablations. 16

Tong, Limin

2000-10-01

372

Polarization and angular effects of femtosecond laser-induced nanostructure-covered large scale waves on metals  

SciTech Connect

In this paper, we find that nanostructure-covered large scale waves (NC-LSWs) can be produced on metals using both s- and p-polarized femtosecond laser pulses. We show that the period of NC-LSWs can be controlled by laser fluence, the number of irradiating pulses, and the incident beam angle. By modeling angular dependence of NC-LSW period induced by s-polarized light, we reveal that inhomogeneous energy deposition plays an important role in the formation of NC-LSWs. This allows us to establish a three-step model for NC-LSW formation, the formation of laser-induced surface unevenness, inhomogeneous energy deposition due to the interference of the incident light with the scattered light, and nonuniform energy deposition due to shielding by LSWs.

Hwang, Taek Yong; Guo Chunlei [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States)

2011-10-01

373

Hard X-ray generation and plasma filament formation under interaction of femtosecond laser pulses with large molecular clusters  

NASA Astrophysics Data System (ADS)

We have demonstrated that the efficiency of hard X-ray generation (with energy 2 - 4 keV) from the femtosecond laser excitation (intensity I 1016 W/cm2, pulse energy E 5 mJ) of large molecular clusters (SF6, CF3I) can reach 10-6 (with yield 109 photons/J). It was shown that at maximal X-ray yield, the plasma filament is essentially non-uniform and has a multifocal structure. It was observed that the amplitude of the central and trailing spectral components of the chirped laser pulse decreases after its interaction with the cluster target as a result of efficient laser energy absorption under self-focusing conditions.

Gordienko, Vyacheslav M.; Dzhidzhoev, Murat S.; Zhvaniya, Irina A.; Platonenko, Viktor T.; Trubnikov, Dmitriy N.; Fedorov, Denis O.

2013-03-01

374

Experimental study of population inversion in the shock-pumped iodine laser  

Microsoft Academic Search

Shock wave radiation allows us to pump quite large volumes and, therefore, to obtain iodine laser beams with high energy and power. In particular, previously we carried out experiments on the shock-pumped iodine laser with a beam aperture up to 1.2 m. Radiation energy up to 6 kJ in a single beam with a pulse duration of 3 - 5

S. N. Pevny; V. A. Eroshenko; Stanislav M. Kulikov; Gennadi A. Kirillov; Gennadiy G. Kochemasov; Sergey P. Smyshlyaev; Stanislav A. Sukharev

1993-01-01

375

Fundamental Studies of Ignition Process in Large Natural Gas Engines Using Laser Spark Ignition  

SciTech Connect

Past research has shown that laser ignition provides a potential means to reduce emissions and improve engine efficiency of gas-fired engines to meet longer-term DOE ARES (Advanced Reciprocating Engine Systems) targets. Despite the potential advantages of laser ignition, the technology is not seeing practical or commercial use. A major impediment in this regard has been the 'open-path' beam delivery used in much of the past research. This mode of delivery is not considered industrially practical owing to safety factors, as well as susceptibility to vibrations, thermal effects etc. The overall goal of our project has been to develop technologies and approaches for practical laser ignition systems. To this end, we are pursuing fiber optically coupled laser ignition system and multiplexing methods for multiple cylinder engine operation. This report summarizes our progress in this regard. A partial summary of our progress includes: development of a figure of merit to guide fiber selection, identification of hollow-core fibers as a potential means of fiber delivery, demonstration of bench-top sparking through hollow-core fibers, single-cylinder engine operation with fiber delivered laser ignition, demonstration of bench-top multiplexing, dual-cylinder engine operation via multiplexed fiber delivered laser ignition, and sparking with fiber lasers. To the best of our knowledge, each of these accomplishments was a first.

Azer Yalin; Bryan Willson

2008-06-30

376

PULSE: The Palomar Ultraviolet Laser for the Study of Exoplanets  

E-print Network

The Palomar Ultraviolet Laser for the Study of Exoplanets (PULSE) will dramatically expand the science reach of PALM-3000, the facility high-contrast extreme adaptive optics system on the 5-meter Hale Telescope. By using an ultraviolet laser to measure the dominant high spatial and temporal order turbulence near the telescope aperture, one can increase the limiting natural guide star magnitude for exquisite correction from mV Strehl ratios from any large telescope laser adaptive optics system, PULSE uniquely enables spectroscopy of low-mass and more distant young exoplanet systems, essential to formulating a complete picture of exoplanet populations.

Baranec, Christoph; Burruss, Rick S; Bowler, Brendan P; van Dam, Marcos; Riddle, Reed; Shelton, J Christopher; Truong, Tuan; Roberts, Jennifer; Milburn, Jennifer; Tesch, Jonathan

2014-01-01

377

Large Signal Circuit Model of Two-Section Gain Lever Quantum Dot Laser  

NASA Astrophysics Data System (ADS)

An equivalent circuit model for the design and analysis of two-section gain lever quantum dot (QD) laser is presented. This model is based on the three level rate equations with two independent carrier populations and a single longitudinal optical mode. By using the presented model, the effect of gain lever on QD laser performances is investigated. The results of simulation show that the main characteristics of laser such as threshold current, transient response, output power and modulation response are affected by differential gain ratios between the two-sections.

Ashkan, Horri; Seyedeh Zahra, Mirmoeini; Rahim, Faez

2012-11-01

378

INTERACTION OF LASER RADIATION WITH MATTER: Large-scale structures produced on metal surfaces by multiple laser pulses  

NASA Astrophysics Data System (ADS)

A mathematical model is constructed to describe the formation of inhomogeneous surface structures 10-50 ?m in height on metal surfaces exposed to repetitive laser pulses with the following parameters: pulse duration of ~20 ns, pulse repetition rate of ~10 kHz, pulse intensity in the range 107108 W cm-2 and beam diameter from 50 to 100 ?m. The model takes into account melting of the metal and melt flow over a distorted surface. The surface profile amplitude evaluated in the model agrees with experimental data.

Kirichenko, N. A.

2009-05-01

379

High Contrast Imaging with an Arbitrary Aperture: Active Correction of Aperture Discontinuities  

E-print Network

We present a new method to achieve high-contrast images using segmented and/or on-axis telescopes. Our approach relies on using two sequential Deformable Mirrors to compensate for the large amplitude excursions in the telescope aperture due to secondary support structures and/or segment gaps. In this configuration the parameter landscape of Deformable Mirror Surfaces that yield high contrast Point Spread Functions is not linear, and non-linear methods are needed to find the true minimum in the optimization topology. We solve the highly non-linear Monge-Ampere equation that is the fundamental equation describing the physics of phase induced amplitude modulation. We determine the optimum configuration for our two sequential Deformable Mirror system and show that high-throughput and high contrast solutions can be achieved using realistic surface deformations that are accessible using existing technologies. We name this process Active Compensation of Aperture Discontinuities (ACAD). We show that for geometries si...

Pueyo, Laurent

2012-01-01

380

Aperture coupled, differentially fed DRAs  

Microsoft Academic Search

Antennas with differential signaling is of interest due to their inherent common mode noise rejection ability and their compatibility with existing differential circuits. To our knowledge, very little works have been done to exploit these intrinsic benefits in DRA structures. In this paper, a simple differential scheme based on the aperture coupling technique is shown to be suitable for coupling

Lee Ee; Michael Ong

2009-01-01

381

Dynamic aperture measurement on Aladdin  

SciTech Connect

The sextupole-induced non-linear transverse beam dynamics in the synchrotron radiation storage ring Aladdin is studied. Specifically, the dynamic aperture is measured as function of the sextupole strength. The results agree reasonably well with computer simulations. 1 ref., 8 figs., 1 tab.

Bridges, J.; Cho, Y.; Chou, W.; Crosbie, E.; Kramer, S.; Kustom, R.; Voss, D.; Teng, L.; Kleman, K.; Otte, R.; Trzeciak, W.; Symon, K. (Argonne National Lab., IL (USA); Wisconsin Univ., Stoughton, WI (USA). Synchrotron Radiation Center; Wisconsin Univ., Madison, WI (USA). Dept. of Physics)

1989-01-01

382

Rapid adaptive optical recovery of optimal resolution over large volumes.  

PubMed

Using a descanned, laser-induced guide star and direct wavefront sensing, we demonstrate adaptive correction of complex optical aberrations at high numerical aperture (NA) and a 14-ms update rate. This correction permits us to compensate for the rapid spatial variation in aberration often encountered in biological specimens and to recover diffraction-limited imaging over large volumes (>240 mm per side). We applied this to image fine neuronal processes and subcellular dynamics within the zebrafish brain. PMID:24727653

Wang, Kai; Milkie, Daniel E; Saxena, Ankur; Engerer, Peter; Misgeld, Thomas; Bronner, Marianne E; Mumm, Jeff; Betzig, Eric

2014-06-01

383

Large area mapping of non-metallic inclusions in stainless steel by an automated system based on laser ablation  

NASA Astrophysics Data System (ADS)

Large area compositional mapping (>6 mm 2) using a fast and automated system based on laser-induced plasma spectrometry is presented. The second harmonic of a flat top Nd:YAG laser beam was used to generate a microline plasma on the sample surface. The emitted light from the microline plasma was imaged onto the entrance slit of an imaging spectrograph and was detected by an intensified charge-coupled device to generate a spatially and spectrally resolved data set. Individual LIPS images, each measuring roughly 25002500 ?m with spatial resolution of 50 ?m between adjacent craters and 4.8 ?m along the microline are presented. These large area maps were acquired in less than 1 min. Steel samples containing MnS and TiN inclusions were chosen as the most adequate for this study. The results are presented for the characterization of inclusionary material in stainless steel products in terms of morphology, distribution and abundance.

Cabaln, L. M.; Mateo, M. P.; Laserna, J. J.

2004-04-01

384

Theoretical study of a large-scale chemically pumped pulsed iodine laser amplifier  

Microsoft Academic Search

The feasibility of a 100 kJ class chemically pumped iodine laser amplifier is studied by numerical calculations of the Maxwell-Bloch equations. The idea is based on a chemical iodine pulse laser utilizing a porous-pipe, high-pressure singlet oxygen generator. It is shown that at the high singlet oxygen pressure conditions, the energy transfer reaction from singlet oxygen to ground state iodine

Masamori Endo; K. Kodama; Y. Handa; Taro Uchiyama

1993-01-01

385

Asymptotic theory of a large fiber-laser array passive phase locking.  

PubMed

Coherent laser beam combining is a potentially attractive way to increase the combined beam brightness beyond the technological limits to single-mode fiber lasers. Passive phase locking (PPL) does not need external management and leads to strong simplification of the system. A specific feature of fiber amplifiers and lasers is that they possess optical path differences of the magnitude of many wavelengths. The involved problem in the PPL approach is to specify an ultimate limit to the phase-locked laser-array size. Earlier studies confirm the stabilizing role of gain saturation on beam-combining efficiency. The purpose of our study is to decipher the desired effect of nonlinearity on the combining efficiency in two architectures of a globally coupled fiber-laser array: (I)an array of amplifiers in ring resonator configuration with spatially filtered feedback; (II)an array of lasers also with external feedback. The external-cavity feedback in both systems results in global coupling, i.e., each element is coherently coupled to all the others. A semi-analytical approach based on the probability theory is developed to calculate the probability density for the efficiency as a function of system parameters in both ensembles. Comparison between (I) and (II) arrays indicates that the II-type arrays demonstrate better characteristics while scaling the array size. PMID:25402934

Napartovich, Anatoly P; Elkin, Nikolay N; Vysotsky, Dmitry V

2014-11-01

386

Vacuum isostatic micro/macro molding of PTFE materials for laser beam shaping in environmental applications: large scale UV laser water purification  

NASA Astrophysics Data System (ADS)

Accessibility to fresh clean water has determined the location and survival of civilizations throughout the ages [1]. The tangible economic value of water is demonstrated by industry's need for water in fields such as semiconductor, food and pharmaceutical manufacturing. Economic stability for all sectors of industry depends on access to reliable volumes of good quality water. As can be seen on television a nation's economy is seriously affected by water shortages through drought or mismanagement and as such those water resources must therefore be managed both for the public interest and the economic future. For over 50 years ultraviolet water purification has been the mainstay technology for water treatment, killing potential microbiological agents in water for leisure activities such as swimming pools to large scale waste water treatment facilities where the UV light photo-oxidizes various pollutants and contaminants. Well tailored to the task, UV provides a cost effective way to reduce the use of chemicals in sanitization and anti-biological applications. Predominantly based on low pressure Hg UV discharge lamps, the system is plagued with lifetime issues (~1 year normal operation), the last ten years has shown that the technology continues to advance and larger scale systems are turning to more advanced lamp designs and evaluating solidstate UV light sources and more powerful laser sources. One of the issues facing the treatment of water with UV lasers is an appropriate means of delivering laser light efficiently over larger volumes or cross sections of water. This paper examines the potential advantages of laser beam shaping components made from isostatically micro molding microstructured PTFE materials for integration into large scale water purification and sterilization systems, for both lamps and laser sources. Applying a unique patented fabrication method engineers can form micro and macro scale diffractive, holographic and faceted reflective structures into fused and semi-fused PTFE materials and compounds for use in UV Reactors. The materials unique attributes provide an unusual but effective hybrid element, by combining Lambertian diffusion and spectral reflective attributes. This paper will provide examples of the applications where this technology could be applied and typical constructions. An overview of UV sources commonly used in water treatment, including high power UV lasers and solid state UV light sources will be discussed. The paper will summarize how beam shaping elements produced in PTFE materials would provide further benefits to the emerging water disinfection or treatment market.

Lizotte, Todd; Ohar, Orest

2009-08-01

387

Development of the Synthetic Aperture Radiometer ESTAR and the Next Generation  

NASA Technical Reports Server (NTRS)

ESTAR is a research instrument built to develop the technology of aperture synthesis for passive remote sensing of Earth from space. Aperture synthesis is an interferometric technology that addresses the problem of putting large antenna apertures in space to achieve the spatial resolution needed for remote sensing at long wavelengths ESTAR was a first step (synthesis only across track and only at horizontal polarization). The development has progressed to a new generation instrument that is dual polarized and does aperture synthesis in two dimensions. Among the plans for the future is technology to combine active and passive remote sensing.

LeVine, David M.; Haken, Michael; Swift, Calvin T.

2004-01-01

388

High numerical aperture tabletop soft x-ray diffraction microscopy with 70-nm resolution  

PubMed Central

Light microscopy has greatly advanced our understanding of nature. The achievable resolution, however, is limited by optical wavelengths to ?200 nm. By using imaging and labeling technologies, resolutions beyond the diffraction limit can be achieved for specialized specimens with techniques such as near-field scanning optical microscopy, stimulated emission depletion microscopy, and photoactivated localization microscopy. Here, we report a versatile soft x-ray diffraction microscope with 70- to 90-nm resolution by using two different tabletop coherent soft x-ray sourcesa soft x-ray laser and a high-harmonic source. We also use field curvature correction that allows high numerical aperture imaging and near-diffraction-limited resolution of 1.5?. A tabletop soft x-ray diffraction microscope should find broad applications in biology, nanoscience, and materials science because of its simple optical design, high resolution, large depth of field, 3D imaging capability, scalability to shorter wavelengths, and ultrafast temporal resolution. PMID:18162534

Sandberg, Richard L.; Song, Changyong; Wachulak, Przemyslaw W.; Raymondson, Daisy A.; Paul, Ariel; Amirbekian, Bagrat; Lee, Edwin; Sakdinawat, Anne E.; La-O-Vorakiat, Chan; Marconi, Mario C.; Menoni, Carmen S.; Murnane, Margaret M.; Rocca, Jorge J.; Kapteyn, Henry C.; Miao, Jianwei

2008-01-01

389

Laser conditioning methods fo hafnia silica multiplayer mirrors  

SciTech Connect

Large aperture multilayer hafnia silica high reflector coatings at 1064 nm, deposited by reactive electron-beam deposition, were prepared to examine different laser conditioning methods for manufacturing high fluence optics in the National Ignition Facility. Laser conditioning is a process where the damage threshold of the coating is increased or the damage that is created is minimized so that it does not grow upon further irradiation. Two laser conditioning methods were examined for coatings deposited from only oxide starting materials. Off-line laser conditioning consists of raster scanning a mirror past a 1 mm diameter Gaussian beam over the entire clear aperture; a process that takes approximately 24 hours per scan. On-line laser conditioning consisted of a large aperture 300 mm x 300 mm beam from the Beamlet laser that irradiated the entire full clear aperture of a series of mirrors; a process that was limited by a 2-4 hour shot rate. In both cases a six-step process was used with the mirror first irradiated at a low fluence, then successively higher fluences increased in equal increments up to the peak laser operating fluence. Mirrors that were only partially laser conditioned damaged catastrophically while fully conditioned mirrors survived fluences exceeding the safe operating Beamlet fluence. An alternative off-line laser conditioning method was examined for coatings deposited from hafnia or metallic hafnium sources. Single-step laser conditioning consists of off-line raster scanning an optic at the peak operating fluence, thus decreasing the laser conditioning cost by reducing the number of scans and required laser conditioning stations to process all the mirrors for the National Ignition Facility. Between pulses the optic is stepped approximately one fourth of the l/e* Gaussian beam diameter so each area of the coating is irradiated by different segments of the beam starting at a low fluence at the outer edge of the beam diameter and increasing to the peak fluence in the center of the beam. The one-step conditioning results appear positive, but the influence of the coating improvements due to the metallic hafnium process on laser conditioning is undefined.

Stolz, C.J.; Sheehan, L.M.; Maricle, S.M. Schwartz, S.; Kozlowski, M.R.; Jennings, R.T.; Hue, J.

1998-01-06

390

Effects of activity pattern on eye size and orbital aperture size in primates  

Microsoft Academic Search

Among primates, nocturnal species exhibit relatively larger orbital apertures than diurnal species. Most researchers have considered this disparity in orbital aperture size to reflect differences in eye size, with nocturnal primates having relatively large eyes in order to maximize visual sensitivity. Presumed changes in eye size due to shifts in activity pattern are an integral part of theoretical explanations for

E. Christopher Kirk

2006-01-01

391

Practical applications of synthetic aperture imaging  

Microsoft Academic Search

Synthetic aperture imaging has been a focus of research for almost 3 decades. The research carried out at the Center for Fast Ultrasound Imaging has demonstrated that synthetic aperture focusing not only can be used in-vivo, but that it also yields superior B-mode and blood flow images. In the last years synthetic aperture focusing has moved from the lab to

Svetoslav Ivanov Nikolov; Jacob Kortbek; Jorgen Arendt Jensen

2010-01-01

392

Optimized algorithm for synthetic aperture imaging  

Microsoft Academic Search

We present a novel synthetic aperture imaging algorithm based on concepts used in synthetic aperture radar (SAR) and sonar (SAS). The algorithm, based on a convolution model of the imaging system developed in the frequency domain, accounts for the beam-pattern of the finite sized transducer used in the synthetic aperture. A 2D Fourier transform is used for the calculation of

T. Stepinski; F. Lingvall

2004-01-01

393

Imagery of ocean waves by synthetic aperture radar  

Microsoft Academic Search

We consider the image structure of ocean waves produced by a synthetic aperture radar (SAR). The theory takes account of the spatial and temporal dependence of small scale capillary waves and large scale waves. Detailed discussions are given to the imaging process in which both amplitude modulation and velocity bunching contribute to the final images. Discussions are also presented on

K. Ouchi

1982-01-01

394

Support Vector Machines For Synthetic Aperture Radar Automatic Target Recognition  

Microsoft Academic Search

: Algorithms that produce classifiers with large margins, such as support vector machines (SVMs), AdaBoost, etc. are receiving more and more attention in the literature. This paper presents a real application of SVMs for synthetic aperture radar automatic target recognition (SAR\\/ATR) and compares the result with conventional classifiers. The SVMs are tested for classification both in closed and open sets

Qun Zhao; Jose C. Principe

395

Large Scale Laser Two-Photon Polymerization Structuring for Fabrication of Artificial Polymeric Scaffolds for Regenerative Medicine  

NASA Astrophysics Data System (ADS)

We present a femtosecond Laser Two-Photon Polymerization (LTPP) system of large scale three-dimensional structuring for applications in tissue engineering. The direct laser writing system enables fabrication of artificial polymeric scaffolds over a large area (up to cm in lateral size) with sub-micrometer resolution which could find practical applications in biomedicine and surgery. Yb:KGW femtosecond laser oscillator (Pharos, Light Conversion. Co. Ltd.) is used as an irradiation source (75 fs, 515 nm (frequency doubled), 80 MHz). The sample is mounted on wide range linear motor driven stages having 10 nm sample positioning resolution (XY-ALS130-100, Z-ALS130-50, Aerotech, Inc.). These stages guarantee an overall travelling range of 100 mm into X and Y directions and 50 mm in Z direction and support the linear scanning speed up to 300 mm/s. By moving the sample three-dimensionally the position of laser focus in the photopolymer is changed and one is able to write complex 3D (three-dimensional) structures. An illumination system and CMOS camera enables online process monitoring. Control of all equipment is automated via custom made computer software ``3D-Poli'' specially designed for LTPP applications. Structures can be imported from computer aided design STereoLihography (stl) files or programmed directly. It can be used for rapid LTPP structuring in various photopolymers (SZ2080, AKRE19, PEG-DA-258) which are known to be suitable for bio-applications. Microstructured scaffolds can be produced on different substrates like glass, plastic and metal. In this paper, we present microfabricated polymeric scaffolds over a large area and growing of adult rabbit myogenic stem cells on them. Obtained results show the polymeric scaffolds to be applicable for cell growth practice. It exhibit potential to use it for artificial pericardium in the experimental model in the future.

Malinauskas, M.; Purlys, V.; ukauskas, A.; Rutkauskas, M.; Danilevi?ius, P.; Paipulas, D.; Bi?kauskait?, G.; Bukelskis, L.; Baltriukien?, D.; irmenis, R.; Gaidukevi?iut?, A.; Bukelskien?, V.; Gadonas, R.; Sirvydis, V.; Piskarskas, A.

2010-11-01

396

Highly reproducible large-area and double-sided pulsed laser deposition of HTSC YBCO:Ag thin films for microwave applications  

Microsoft Academic Search

Large-area pulsed laser deposition (PLD) producing high-quality YBa2Cu3O7-x (YBCO) thin films on both sides of R-plane sapphire substrates with CeO2 buffer layer is used routinely to optimize planar microwave stripline filters for satellite and mobile communication systems. A relatively simple PLD arrangement with fixed laser plume and rotating substrate, with an offset between the laser plume and the center of

M. Lorenz; H. Hochmuth; D. Natusch; K. Kreher

1999-01-01

397

ESTAR - A synthetic aperture microwave radiometer for measuring soil moisture  

NASA Technical Reports Server (NTRS)

The measurement of soil moisture from space requires putting relatively large microwave antennas in orbit. Aperture synthesis, an interferometric technique for reducing the antenna aperture needed in space, offers the potential for a practical means of meeting these requirements. An aircraft prototype, electronically steered thinned array L-band radiometer (ESTAR), has been built to develop this concept and to demonstrate its suitability for the measurement of soil moisture. Recent flights over the Walnut Gulch Watershed in Arizona show good agreement with ground truth and with measurements with the Pushbroom Microwave Radiometer (PBMR).

Le Vine, D. M.; Griffis, A.; Swift, C. T.; Jackson, T. J.

1992-01-01

398

Laser Metrology Sensing and Control for Large Segmented-Mirror Telescopes  

NASA Technical Reports Server (NTRS)

Described an optical hexapod metrology concept: a) Can work together with edge sensors; b) Can measure M1 - M2 distance and M1 global curvature. Swept-frequency laser metrology system: a) Absolute optical path length measurement (approx.1 micron); b) Relative optical path length measurement (approx.nm) Air turbulence is a concern for ground-based telescopes and needs further study.

Zhao, Feng; Rao, Shanti; Ksendzov, Alex; Kadogawa, Hiroshi

2006-01-01

399

Three-dimensional large-scale microfluidic integration by laser ablation of interlayer connections.  

PubMed

Multilayer Soft Lithography (MSL) is a robust and mature fabrication technique for the rapid prototyping of microfluidic circuits having thousands of integrated valves. Despite the success and wide application of this method, it is fundamentally a planar fabrication technique which imposes serious design constraints on channel routing, feature density, and fluid handling complexity. We present here methods and related instrumentation to remove these limitations by combining the advantages of MSL processing with laser micromachining using a CO(2) laser ablation system. This system is applied to both the dense integration of layer-layer interconnects and the direct writing of microchannels. Real-time image recognition and computer control allow for robust wafer-scale registration of laser ablation features with moulded channel structures. Ablation rates of up to 8 Hz are achieved with positional accuracy of approximately 20 microm independent of mechanical distortions in the elastomer substrate. We demonstrate these capabilities in the design and fabrication of a production scale multi-laminate micromixer that achieves sub-millisecond mixing of two streams at flow rates up to 1 mL min(-1). The marriage of laser micromachining with MSL-based valve integration allows for high-yield fabrication of topologically complex microfluidic circuits having thousands of layer-layer interconnects and integrated valves. PMID:20539896

Huft, Jens; Da Costa, Daniel J; Walker, David; Hansen, Carl L

2010-09-21

400

In-situ optical breakdown: studies for a large CO/sub 2/ laser amplifier  

SciTech Connect

We study optical breakdown from target reflected optical pulses in the Gemini laser system. We measure the retropulse fluence (or illuminance) leaving the amplifier in terms of the energy entering the breakdown region and find qualitative agreement but no quantitative agreement with theory. Particulates were observed on nucleopore filters through which gas samples were drawn.

Elliott, C.J.; Bjurstrom, R.G.; Carpenter, J.P.; Coffelt, E.L.; Hayden, J.J.; Hebron, D.E.; McLeod, J.; Romero, V.

1981-01-01

401

Aperture effects on spectroscopic galaxy activity classification  

NASA Astrophysics Data System (ADS)

Activity classification of galaxies based on long-slit and fibre spectroscopy can be strongly influenced by aperture effects. Here, we investigate how activity classification for 14 nearby galaxies depends on the proportion of the host galaxy's light that is included in the aperture. We use both observed long-slit spectra and simulated elliptical-aperture spectra of different sizes. The degree of change varies with galaxy morphology and nuclear activity type. Starlight removal techniques can mitigate but not remove the effect of host galaxy contamination in the nuclear aperture. Galaxies with extranuclear star formation can show higher [O III] ?5007/H? ratios with increasing aperture, in contrast to the naive expectation that integrated light will only dilute the nuclear emission lines. We calculate the mean dispersion for the diagnostic line ratios used in the standard BPT diagrams with respect to the central aperture of spectral extraction to obtain an estimate of the uncertainties resulting from aperture effects.

Maragkoudakis, A.; Zezas, A.; Ashby, M. L. N.; Willner, S. P.

2014-07-01

402

Transmission of Megawatt Relativistic Electron Beams Through Millimeter Apertures  

E-print Network

High power, relativistic electron beams from energy recovery linacs have great potential to realize new experimental paradigms for pioneering innovation in fundamental and applied research. A major design consideration for this new generation of experimental capabilities is the understanding of the halo associated with these bright, intense beams. In this Letter, we report on measurements performed using the 100 MeV, 430 kWatt CW electron beam from the energy recovery linac at the Jefferson Laboratory's Free Electron Laser facility as it traversed a set of small apertures in a 127 mm long aluminum block. Thermal measurements of the block together with neutron measurements near the beam-target interaction point yielded a consistent understanding of the beam losses. These were determined to be 3 ppm through a 2 mm diameter aperture and were maintained during a 7 hour continuous run.

R. Alarcon; S. Balascuta; S. V. Benson; W. Bertozzi; J. R. Boyce; R. Cowan; D. Douglas; P. Evtushenko; P. Fisher; E. Ihloff; N. Kalantarians; A. Kelleher; R. Legg; R. G. Milner; G. R. Neil; L. Ou; B. Schmookler; C. Tennant; C. Tschalaer; G. P. Williams; S. Zhang

2013-05-01

403

Transmission of Megawatt Relativistic Electron Beams Through Millimeter Apertures  

SciTech Connect

High power, relativistic electron beams from energy recovery linacs have great potential to realize new experimental paradigms for pioneering research in fundamental and applied research. A major design consideration for these new generation of experimental capabilities is the understanding of the halo associated with these bright, intense beams. In this Letter, we report on measurements performed using the 100 MeV, 430 kWatt CW electron beam from the energy recovery linac at the Jeff#11;erson Laboratory's Free Electron Laser facility as it traversed a set of small apertures in a 127 mm long aluminum block. Thermal measurements of the block together with neutron measurements near the beam-target interaction point yielded a consistent understanding of the beam losses. These were determined to be 3 ppm through a 2 mm diameter aperture and were maintained during a 7 hour continuous run.

Arizona State University; Arizona State University; JLAB; MIT; College of William and Mary, JLAB; MIT; JLAB; JLAB; MIT; MIT; Hampton University; MIT; JLAB; MIT; JLAB; MIT; MIT; JLAB; MIT; JLAB; JLAB

2013-10-01

404

The Opals Data Manager - Efficient Data Management for Processing Large Airborne Laser Scanning Projects  

NASA Astrophysics Data System (ADS)

The fast measurement rate of today's Airborne Laser Scanners results in billions of points for single ALS projects. Efficient algorithms and data management methods are, therefore, a precondition for successful project handling. The software package OPALS (Orientation and Processing of Airborne Laser Scanning data) was especially designed to meet those criteria. Central core of the package is the OPALS Data Manager (ODM). It provides both, fast spatial access to huge point clouds, as well as a flexible attribute schema to store additional point related quantities. Concepts of the spatial data organization and implementation details about the attribute handling are presented. Additionally, design rationales of the ODM, its file format and the system performance are described.

Otepka, J.; Mandlburger, G.; Karel, W.

2012-07-01

405

Laser-produced plasma with large amplitude density modulation of controllable wavelength  

SciTech Connect

A 6 nsec 10{sup 10} W/cm{sup 2} ruby laser pulse irradiates a grating with spacing in the 6--35 {mu}m range. The expansion of the plasma above the surface is observed using interferometry and shadowgraphy. The plasma is found to be modulated with {ital {tilde n}}/{ital n} up to 8%. Such a plasma can be used to accelerate charged particles.

Laberge, M.; Meyer, J. (Department of Physics, University of British Columbia, Vancouver, BC (Canada))

1990-11-01

406

Growth and characterization of large Nd,Cr:GSGG crystals for high-average-power slab lasers  

NASA Astrophysics Data System (ADS)

Nd,Cr:GSGG crystal boules up to 13 cm in diameter and 20.5 cm long have been grown by the Czochralski method. Several problems with Nd,Cr:GSGG growth were identified, and solved separately but not all at once; these problems included spiral boule growth, 1-micron absorption loss, iridium on the melt surface, iridium inclusions, boule cracking, dislocation, and fine scattering (smoke). In the grown crystals parameters relevant to their eventual use as gain elements for large slab lasers were measured including optical homogeneity, birefringence, absorption loss at 1 micron, scattering loss, and iridium inclusions. The optical homogeneity of the boules is good, except for a radial gradient in refractive index of about 10 to the -5th/cm. The birefringence is low (less than 3 nm/cm) in slabs cut from the boules. Scattering losses in the boules range from 0.01 to 0.08/cm. This absorption has been reduced to less than 0.0025/cm in small samples using reducing heat treatments, but appropriate treatment conditions for full-scale slabs have yet to be determined. Low iridium inclusion densities, less than 0.01/cm, have been demonstrated in isolated boules; at this inclusion density, large-gain elements which are entirely inclusion-free should be possible. Additional development is required to grow large crystals with the desired quality for laser operation.

Stokowski, S. E.; Randles, M. H.; Morris, R. C.

1988-06-01

407

Matrix shaped pulsed laser deposition: New approach to large area and homogeneous deposition  

NASA Astrophysics Data System (ADS)

Pulsed laser deposition (PLD) is one of the well-established physical vapor deposition methods used for synthesis of ultra-thin layers. Especially PLD is suitable for the preparation of thin films of complex alloys and ceramics where the conservation of the stoichiometry is critical. Beside several advantages of PLD, inhomogeneity in thickness limits use of PLD in some applications. There are several approaches such as rotation of the substrate or scanning of the laser beam over the target to achieve homogenous layers. On the other hand movement and transition create further complexity in process parameters. Here we present a new approach which we call Matrix Shaped PLD to control the thickness and homogeneity of deposited layers precisely. This new approach is based on shaping of the incoming laser beam by a microlens array and a Fourier lens. The beam is split into much smaller multi-beam array over the target and this leads to a homogenous plasma formation. The uniform intensity distribution over the target yields a very uniform deposit on the substrate. This approach is used to deposit carbide and oxide thin films for biomedical applications. As a case study coating of a stent which has a complex geometry is presented briefly.

Akkan, C. K.; May, A.; Hammadeh, M.; Abdul-Khaliq, H.; Aktas, O. C.

2014-05-01

408

Lunar Laser Ranging Experiment for Japanese SELENE-2 landing mission  

NASA Astrophysics Data System (ADS)

We present the development status of the Lunar Laser Ranging experiment proposed to Japanese SELENE-2 lunar landing mission. The Lunar Laser Ranging measures the distance between laser link stations on the Earth and retroreflectors on the Moon, by detecting the time of flight of photons of high-powered laser emitted from the ground station. Since the Earth-Moon distance contains information of lunar orbit, lunar solid tides, and lunar orientation and rotation, we can estimate the inner structure of the Moon through orientation, rotation and tide. Retroreflectors put by the Apollo and Luna missions in 1970's are arrays of many small Corner Cube Prisms (CCP). Because of the tilt of these arrays from the Earth direction due to the optical libration, the returned laser pulse is broaden, causing the main range error of more than 1.5 cm ([1]). Therefore retroreflectors with larger single aperture are necessary for more accurate ranging, and we propose a large single retroreflector of hollow-type with 15 cm aperture. Larger aperture up to 20 cm might be favorable if more mass is permitted for payloads. To cancel the velocity aberration, a large, single aperture retroreflector needs small amount of offset angle between the reflecting planes to spoil the return beam pattern. This angle offset, called Dihedral Angle Offset (DAO) must be optimized to be less than 1 second of arc with 0.1 seconds of arc accuracy to accumulate more photons [2, 3]. The realization of such small DAO is challenging with current technology, therefore the development of fabrication method is important. As for the mirror material, some ceramic products (ZPF: Zero-expansion Pore-free ceramics or SiC: silicon carbide) are under consideration in terms of weight, hardness and handling. The thermal quality of the material can be evaluated by both the thermal conductivity and the coefficient of thermal expansion. The method to fasten three planes each other with precise DAO must be developed.

Noda, H.; Kunimori, H.; Araki, H.; Fuse, T.; Hanada, H.; Katayama, M.; Otsubo, T.; Sasaki, S.; Tazawa, S.; Tsuruta, S.; Funazaki, K.; Taniguchi, H.; Murata, K.

2012-04-01

409

Analysis of synthetic aperture radar imagery  

NASA Technical Reports Server (NTRS)

Some problems faced in applications of radar measurements in hydrology are: (1) adequate calibration of the radar systems and direct digital data will be required in order that repeatable data can be acquired for hydrologic applications; (2) quantitative hydrologic research on a large scale will be prohibitive with aircraft mounted synthetic aperture radar systems due to the system geometry; (3) spacecraft platforms appear to be the best platforms for radar systems when conducting research over watersheds larger than a few square kilometers; (4) experimental radar systems should be designed to avoid use of radomes; and (5) cross polarized X and L band data seem to discriminate between good and poor hydrologic cover better than like polarized data.

Blanchard, B. J.

1977-01-01

410

Use of Zernike polynomials and interferometry in the optical design and assembly of large carbon-dioxide laser systems  

SciTech Connect

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 of experimentally produced interferograms of the components. A Fast Fourier Transform code then propagates the complex amplitude and phase of the beam through the whole system and computes the optical parameters of interest. The analysis scheme is illustrated through examples of the Gigawatt, Gemini, and Helios systems. A possible way of using the Zernike polynomials in optical design problems of this type is discussed. Comparisons between the computed values and experimentally obtained results are made and it is concluded that this appears to be a valid approach. As this is a review article, some previously published results are also used where relevant.

Viswanathan, V.K.

1981-01-01

411

GV /m Single-Cycle Terahertz Fields from a Laser-Driven Large-Size Partitioned Organic Crystal  

NASA Astrophysics Data System (ADS)

We report on compact and efficient laser-based THz generation in the terahertz frequency gap (1-10 THz). The radiation is generated by optical rectification of a midinfrared laser in a large-size, partitioned nonlinear organic crystal assembly. This enables up-scaling of presently field-limited tabletop THz sources to GV /m electric and several tesla magnetic field at millijoule pulse energy. In agreement with simulations, the THz beam properties at focus are shown to be not deteriorated by the discontinuity of the emitter surface. The high laser-to-THz energy conversion efficiency exceeds the Manley-Rowe limit and is explained by a cascaded ?(2) process in the organic crystals accompanied by a significant redshift of the pump spectrum. The scheme provides a compact, tabletop THz source for single-cycle transients at field strength equivalent or even higher to linear accelerator and FEL-based THz sources. This opens an avenue toward novel nonlinear THz applications.

Vicario, Carlo; Monoszlai, Balazs; Hauri, Christoph P.

2014-05-01

412

Synthetic aperture interferometry: error analysis.  

PubMed

Synthetic aperture interferometry (SAI) is a novel way of testing aspherics and has a potential for in-process measurement of aspherics [Appl. Opt. 42, 701 (2003)]. A method to measure steep aspherics using the SAI technique has been previously reported [Appl. Opt. 47, 1705 (2008)]. Here we investigate the computation of surface form using the SAI technique in different configurations and discuss the computational errors. A two-pass measurement strategy is proposed to reduce the computational errors, and a detailed investigation is carried out to determine the effect of alignment errors on the measurement process. PMID:20648161

Biswas, Amiya; Coupland, Jeremy

2010-07-10

413

Reconstruction of coded aperture images  

NASA Technical Reports Server (NTRS)

Balanced correlation method and the Maximum Entropy Method (MEM) were implemented to reconstruct a laboratory X-ray source as imaged by a Uniformly Redundant Array (URA) system. Although the MEM method has advantages over the balanced correlation method, it is computationally time consuming because of the iterative nature of its solution. Massively Parallel Processing, with its parallel array structure is ideally suited for such computations. These preliminary results indicate that it is possible to use the MEM method in future coded-aperture experiments with the help of the MPP.

Bielefeld, Michael J.; Yin, Lo I.

1987-01-01

414

Ionospheric effects on synthetic aperture radar at VHF  

SciTech Connect

Synthetic aperture radars (SAR) operated from airplanes have been used at VHF because of their enhanced foliage and ground penetration compared to radars operated at UHF. A satellite-borne VHF SAR would have considerable utility but in order to operate with high resolution it would have to use both a large relative bandwidth and a large aperture. The presence of the ionosphere in the propagation path of the radar will cause a deterioration of the imaging because of dispersion over the bandwidth and group path changes in the imaged area over the collection aperture. In this paper we present calculations of the effects of a deterministic ionosphere on SAR imaging for a radar operated with a 100 MHz bandwidth centered at 250 MHz and over an angular aperture of 23{degrees}. The ionosphere induces a point spread function with an approximate half-width of 150 m in the slant-range direction and of 25 m in the cross-range direction compared to the nominal resolution of 1.5 m in both directions.

Fitzgerald, T.J.

1997-02-01

415

Production of extended plasma channels in atmospheric air by amplitude-modulated UV radiation of GARPUN-MTW Ti : sapphire-KrF laser. Part 1. Regenerative amplification of subpicosecond pulses in a wide-aperture electron beam pumped KrF amplifier  

SciTech Connect

Regenerative amplification of single and multiple ultrashort subpicosecond UV pulses in a wide-aperture KrF amplifier with an unstable confocal resonator was investigated on the GARPUN-MTW hybrid laser system. Amplitude-modulated 100-ns long UV radiation pulses with an energy of several tens of joules were obtained at the output of the system. The pulses were a combination of a quasi-stationary oscillation pulse and a train of amplified ultrashort pulses (USPs) with a peak power of 0.2-0.3 TW, which exceeded the power of free-running lasing pulse by three orders of magnitude. The population inversion recovery time in the active KrF laser medium was estimated: {tau}{sub c} {<=} 2.0 ns. Trains of USPs spaced at an interval {Delta}t Almost-Equal-To {tau}{sub c} were shown to exhibit the highest amplification efficiency. The production of amplitude-modulated UV pulses opens up the way to the production and maintenance of extended plasma channels in atmospheric air. (extreme light fields and their applications)

Zvorykin, V D; Ionin, Andrei A; Levchenko, A O; Mesyats, Gennadii A; Seleznev, L V; Sinitsyn, D V; Smetanin, Igor V; Sunchugasheva, E S; Ustinovskii, N N; Shutov, A V [P N Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2013-04-30

416

Production of extended plasma channels in atmospheric air by amplitude-modulated UV radiation of GARPUN-MTW Ti : sapphireKrF laser. Part 1. Regenerative amplification of subpicosecond pulses in a wide-aperture electron beam pumped KrF amplifier  

NASA Astrophysics Data System (ADS)

Regenerative amplification of single and multiple ultrashort subpicosecond UV pulses in a wide-aperture KrF amplifier with an unstable confocal resonator was investigated on the GARPUN-MTW hybrid laser system. Amplitude-modulated 100-ns long UV radiation pulses with an energy of several tens of joules were obtained at the output of the system. The pulses were a combination of a quasi-stationary oscillation pulse and a train of amplified ultrashort pulses (USPs) with a peak power of 0.2-0.3 TW, which exceeded the power of free-running lasing pulse by three orders of magnitude. The population inversion recovery time in the active KrF laser medium was estimated: ?c <= 2.0 ns. Trains of USPs spaced at an interval ?t ? ?c were shown to exhibit the highest amplification efficiency. The production of amplitude-modulated UV pulses opens up the way to the production and maintenance of extended plasma channels in atmospheric air.

Zvorykin, V. D.; Ionin, Andrei A.; Levchenko, A. O.; Mesyats, Gennadii A.; Seleznev, L. V.; Sinitsyn, D. V.; Smetanin, Igor V.; Sunchugasheva, E. S.; Ustinovskii, N. N.; Shutov, A. V.

2013-04-01

417

Hypersonic gasdynamic laser system  

SciTech Connect

This patent describes a visible, or near to mid infra-red, hypersonic gas dynamic laser system. It comprises: a hypersonic vehicle for carrying the hypersonic gas dynamic laser system, and also providing high energy ram air for thermodynamic excitation and supply of the laser gas; a laser cavity defined within the hypersonic vehicle and having a laser cavity inlet for the laser cavity formed by an opening in the hypersonic vehicle, such that ram air directed through the laser cavity opening supports gas dynamic lasing operations at wavelengths less than 10.6{mu} meters in the laser cavity; and an optical train for collecting the laser radiation from the laser cavity and directing it as a substantially collimated laser beam to an output aperture defined by an opening in the hypersonic vehicle to allow the laser beam to be directed against a target.

Foreman, K.M.; Maciulaitis, A.

1990-05-22

418

Laser amplifier based on a neodymium glass rod 150 mm in diameter  

NASA Astrophysics Data System (ADS)

A unique large-aperture neodymium glass rod amplifier is experimentally studied. The small-signal gain distribution is measured at different pump energies. The aperture-averaged gain is found to be 2.3. The stored energy (500 J), the maximum possible pump pulse repetition rate, and the depolarisation in a single pulse and in a series of pulses with a repetition rate of one pulse per five minutes are calculated based on the investigations performed. It is shown that the use of this amplifier at the exit of the existing laser can increase the output pulse energy from 300 to 600 J.

Shaykin, A. A.; Fokin, A. P.; Soloviev, A. A.; Kuzmin, A. A.; Shaikin, I. A.; Burdonov, K. F.; Charukhchev, A. V.; Khazanov, E. A.

2014-05-01

419

Dynamically variable spot size laser system  

NASA Technical Reports Server (NTRS)

A Dynamically Variable Spot Size (DVSS) laser system for bonding metal components includes an elongated housing containing a light entry aperture coupled to a laser beam transmission cable and a light exit aperture. A plurality of lenses contained within the housing focus a laser beam from the light entry aperture through the light exit aperture. The lenses may be dynamically adjusted to vary the spot size of the laser. A plurality of interoperable safety devices, including a manually depressible interlock switch, an internal proximity sensor, a remotely operated potentiometer, a remotely activated toggle and a power supply interlock, prevent activation of the laser and DVSS laser system if each safety device does not provide a closed circuit. The remotely operated potentiometer also provides continuous variability in laser energy output.

Gradl, Paul R. (Inventor); Hurst, John F. (Inventor); Middleton, James R. (Inventor)

2012-01-01

420

Synthetic aperture sonar image statistics  

NASA Astrophysics Data System (ADS)

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 formation process provides a unique opportunity to improve our understanding of system and environment interactions, which is essential for accurate performance prediction. This research focused on the impact of multipath contamination and the impact of resolution on image statistics, accomplished through analyses of data collected during at-sea experiments, analytical modeling, and development of numerical simulations. Multipath contamination was shown to have an appreciable impact on image statistics at ranges greater than the water depth and when the levels of the contributing multipath are within 10 dB of the direct path, reducing the image amplitude distribution tails while also degrading image clarity. Image statistics were shown to depend strongly upon both system resolution and orientation to seafloor features such as sand ripples. This work contributes to improving detection systems by aiding understanding of the influences of background (i.e. non-target) image statistics.

Johnson, Shawn F.

421

Digital holographic interferometry with CO2 lasers and diffuse illumination applied to large space reflector metrology [Invited].  

PubMed

Digital holographic interferometry in the long-wave infrared domain has been developed by combining a CO(2) laser and a microbolometer array. The long wavelength allows large deformation measurements, which are of interest in the case of large space reflectors undergoing thermal changes when in orbit. We review holography at such wavelengths and present some specific aspects related to this spectral range on our measurements. For the design of our digital holographic interferometer, we studied the possibility of illuminating specular objects by a reflective diffuser. We discuss the development of the interferometer and the results obtained on a representative space reflector, first in the laboratory and then during vacuum cryogenic test. PMID:23292383

Georges, Marc P; Vandenrijt, Jean-Franois; Thizy, Cdric; Stockman, Yvan; Queeckers, Patrick; Dubois, Frank; Doyle, Dominic

2013-01-01

422

Large Ti-doped sapphire bulk crystal for high power laser applications  

NASA Astrophysics Data System (ADS)

Large Ti-doped sapphire single crystals have been successfully grown by Kyroupolos technique for optical amplification. Without post growth annealing, the absorption and emission spectra do not show any presence of unwanted impurities. The obtained results indicate the possibilities to get crystals with homogeneous Ti3+ ion concentrations in large sections using this growth technique.

Alombert-Goget, G.; Lebbou, K.; Barthalay, N.; Legal, H.; Chriaux, G.

2014-10-01

423

Scaling Fiber Lasers to Large Mode Area: An Investigation of Passive Mode-Locking Using a Multi-Mode Fiber  

PubMed Central

The mode-locking of dissipative soliton fiber lasers using large mode area fiber supporting multiple transverse modes is studied experimentally and theoretically. The averaged mode-locking dynamics in a multi-mode fiber are studied using a distributed model. The co-propagation of multiple transverse modes is governed by a system of coupled GinzburgLandau equations. Simulations show that stable and robust mode-locked pulses can be produced. However, the mode-locking can be destabilized by excessive higher-order mode content. Experiments using large core step-index fiber, photonic crystal fiber, and chirally-coupled core fiber show that mode-locking can be significantly disturbed in the presence of higher-order modes, resulting in lower maximum single-pulse energies. In practice, spatial mode content must be carefully controlled to achieve full pulse energy scaling. This paper demonstrates that mode-locking performance is very sensitive to the presence of multiple waveguide modes when compared to systems such as amplifiers and continuous-wave lasers. PMID:21731106

Ding, Edwin; Lefrancois, Simon; Kutz, Jose Nathan; Wise, Frank W.

2011-01-01

424

Wavefront sensor for the Large Binocular Telescope laser guide star facility  

NASA Astrophysics Data System (ADS)

A laser guide star facility is currently being planned for the LBT. The first step of the program aims at the implementation of a ground layer adaptive optics (GLAO) system tailored on the wide-field imager / multi-object spectrograph LUCIFER having a 4x4' FoV. The current design is based on multiple Rayleigh guide stars arranged in a 2-5 arcmin angular radius constellation. A future update path toward small-field diffraction limited performances is foreseen using a hybrid system of sodium and Rayleigh beacons promising lower power requirements for the sodium laser. In this paper we present the estimated performances for both the GLAO and the hybrid implementations and we introduce the wavefront sensors opto-mechanical design . Simulations of the GLAO system show an expected gain in FWHM and encircled energy of 1.5-3 (depending on atmospheric turbulence profiles) with a FWHM variation over LUCIFER FoV below 10% and point out the role of such a GLAO system as PSF stabilizer both over the FoV and with respect to seeing temporal variations. Results of simulations for the hybrid configurations will be presented.

Busoni, L.; Esposito, S.; Rabien, S.; Haug, M.; Ziegleder, J.; Hlzl, G.

2008-07-01

425

Laser beam shaping techniques  

SciTech Connect

Industrial, military, medical, and research and development applications of lasers frequently require a beam with a specified irradiance distribution in some plane. A common requirement is a laser profile that is uniform over some cross-section. Such applications include laser/material processing, laser material interaction studies, fiber injection systems, optical data image processing, lithography, medical applications, and military applications. Laser beam shaping techniques can be divided into three areas: apertured beams, field mappers, and multi-aperture beam integrators. An uncertainty relation exists for laser beam shaping that puts constraints on system design. In this paper the authors review the basics of laser beam shaping and present applications and limitations of various techniques.

DICKEY,FRED M.; WEICHMAN,LOUIS S.; SHAGAM,RICHARD N.

2000-03-16

426

4D Light Field Imaging System Using Programmable Aperture  

NASA Technical Reports Server (NTRS)

Complete depth information can be extracted from analyzing all angles of light rays emanated from a source. However, this angular information is lost in a typical 2D imaging system. In order to record this information, a standard stereo imaging system uses two cameras to obtain information from two view angles. Sometimes, more cameras are used to obtain information from more angles. However, a 4D light field imaging technique can achieve this multiple-camera effect through a single-lens camera. Two methods are available for this: one using a microlens array, and the other using a moving aperture. The moving-aperture method can obtain more complete stereo information. The existing literature suggests a modified liquid crystal panel [LC (liquid crystal) panel, similar to ones commonly used in the display industry] to achieve a moving aperture. However, LC panels cannot withstand harsh environments and are not qualified for spaceflight. In this regard, different hardware is proposed for the moving aperture. A digital micromirror device (DMD) will replace the liquid crystal. This will be qualified for harsh environments for the 4D light field imaging. This will enable an imager to record near-complete stereo information. The approach to building a proof-ofconcept is using existing, or slightly modified, off-the-shelf components. An SLR (single-lens reflex) lens system, which typically has a large aperture for fast imaging, will be modified. The lens system will be arranged so that DMD can be integrated. The shape of aperture will be programmed for single-viewpoint imaging, multiple-viewpoint imaging, and coded aperture imaging. The novelty lies in using a DMD instead of a LC panel to move the apertures for 4D light field imaging. The DMD uses reflecting mirrors, so any light transmission lost (which would be expected from the LC panel) will be minimal. Also, the MEMS-based DMD can withstand higher temperature and pressure fluctuation than a LC panel can. Robotics need near complete stereo images for their autonomous navigation, manipulation, and depth approximation. The imaging system can provide visual feedback

Bae, Youngsam

2012-01-01

427

High-contrast Imaging with an Arbitrary Aperture: Active Compensation of Aperture Discontinuities  

NASA Astrophysics Data System (ADS)

We present a new method to achieve high-contrast images using segmented and/or on-axis telescopes. Our approach relies on using two sequential deformable mirrors (DMs) to compensate for the large amplitude excursions in the telescope aperture due to secondary support structures and/or segment gaps. In this configuration the parameter landscape of DM surfaces that yield high-contrast point-spread functions is not linear, and nonlinear methods are needed to find the true minimum in the optimization topology. We solve the highly nonlinear Monge-Ampere equation that is the fundamental equation describing the physics of phase-induced amplitude modulation. We determine the optimum configuration for our two sequential DM system and show that high-throughput and high-contrast solutions can be achieved using realistic surface deformations that are accessible using existing technologies. We name this process Active Compensation of Aperture Discontinuities (ACAD). We show that for geometries similar to the James Webb Space Telescope, ACAD can attain at least 10-7 in contrast and an order