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1

Enhancement of laser interaction with vacuum for a large angular aperture.  

PubMed

We study the nonlinear interaction of laser light with vacuum for a large angular aperture at electromagnetic field strengths far below the Schwinger limit. The polarization and magnetization in vacuum irradiated by a focused laser beam clearly differ from those in matter. This is due to the dependence on the Lorentz invariant, which results in a ring-shaped radiation distribution in vacuum. The number of the radiated photons increases nonlinearly with increasing angular aperture. PMID:21902393

Monden, Y; Kodama, R

2011-08-12

2

Large-aperture plasma-assisted deposition of inertial confinement fusion laser coatings.  

PubMed

Plasma-assisted electron-beam evaporation leads to changes in the crystallinity, density, and stresses of thin films. A dual-source plasma system provides stress control of large-aperture, high-fluence coatings used in vacuum for substrates 1m in aperture. PMID:21460937

Oliver, James B; Kupinski, Pete; Rigatti, Amy L; Schmid, Ansgar W; Lambropoulos, John C; Papernov, Semyon; Kozlov, Alexei; Spaulding, John; Sadowski, Daniel; Chrzan, Z Roman; Hand, Robert D; Gibson, Desmond R; Brinkley, Ian; Placido, Frank

2011-03-20

3

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

PubMed

We describe the design and performance of large-aperture (>30 cm × 30 cm) optical switches that have demonstrated, for the first time to our knowledge, active switching of a high-energy (>5 kJ) optical pulse in an inertial-confinement fusion laser. These optical switches, which consist of a plasma-electrode Pockels cell (PEPC) and a passive polarizer, permit the design of efficient, multipass laser amplifiers. In a PEPC, plasma discharges on the faces of a thin (1-cm) electro-optic crystal (KDP or KD*P) act as highly conductive and transparent electrodes. These plasma electrodes facilitate rapid (<100 ns) and uniform charging of the crystal to the half-wave voltage and discharging back to 0 V. We discuss the operating principles, design, optical performance, and technical issues of a 32 cm × 32 cm prototype PEPC with both KDP and KD*P crystals, and a 37 cm × 37 cm PEPC with a KDP crystal for the Beamlet laser. This PEPC recently switched a 6-kJ, 3-ns pulse in a four-pass cavity. PMID:21060350

Rhodes, M A; Woods, B; Deyoreo, J J; Roberts, D; Atherton, L J

1995-08-20

4

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

NASA Astrophysics Data System (ADS)

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

Rhodes, Mark A.; Woods, B.; Deyoreo, J. J.; Roberts, D.; Atherton, L. J.

1995-08-01

5

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

6

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

7

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

8

Repetitively pulsed regime of Nd : glass large-aperture laser amplifiers  

SciTech Connect

A repetitively pulsed operation regime of neodymium glass rod laser amplifiers with apertures of 4.5, 6, 8.5, and 10 cm is analysed using experimental data. The limits of an increase in the pulse repetition rates are determined. Universal dependences are obtained, which help finding a compromise between increasing the repetition rate and enhancing the gain for each particular case. In particular, it is shown that an amplifier 4.5-cm in diameter exhibits a five-fold safety factor with respect to a thermo-mechanical breakdown at a repetition rate of 1 pulse min{sup -1} and stored energy of above 100 J. A strong thermally induced birefringence in two such amplifiers is experimentally reduced to a 'cold' level by employing a 90 Degree-Sign optical rotator.

Kuzmin, A A; Khazanov, Efim A; Shaykin, A A [Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod (Russian Federation)

2012-04-30

9

Developing magnetorheological finishing (MRF) technology for the manufacture of large-aperture optics in megajoule class laser systems  

NASA Astrophysics Data System (ADS)

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/cm2 at 1053 nm), visible (>18 J/cm2 at 527 nm), and ultraviolet (>10 J/cm2 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 largeaperture damage resistant optics.

Menapace, Joseph A.

2010-10-01

10

Interferometric Tiling of large-aperture gratings for Petawatt laser systems  

Microsoft Academic Search

A tiled-grating assembly with three large-scale gratings is developed with real-time interferometric tiling control for a petawatt laser system. Tiling-parameters sensitivity and focal-spot degradation are analyzed for a compressor composed of four such assemblies.

J. Qiao; J. H. Kelly; D. Canning; M. J. Guardalben; G. King; J. Price; A. Kalb; R. Jungquist; A. L. Rigatti

2007-01-01

11

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

Microsoft Academic Search

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 cmÃ39 cm and a full-aperture plasma-electrode Pockels cell switch. It has been successfully

Bruno M. Van Wonterghem; John R. Murray; Jack H. Campbell; D. Ralph Speck; Charles E. Barker; Ian C. Smith; Donald F. Browning; William C. Behrendt

1997-01-01

12

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

13

Large aperture diffractive space telescope  

Microsoft Academic Search

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 \\

Hyde; Roderick A

2001-01-01

14

Large aperture diffractive space telescope  

DOEpatents

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

Hyde, Roderick A. (Livermore, CA)

2001-01-01

15

Large-aperture Nd:glass laser amplifiers with high pulse repetition rate.  

PubMed

Nd:glass amplifiers are used in most of the existed petawatt laser facilities. A typical repetition rate of such lasers is 1 shot per 30 minutes or less. Limitations are thermally induced distortions of radiation and tensile stresses in Nd:glass. An increase of the repetition rate is an urgent problem. We have investigated thermally induced depolarization and thermal lens effects in Nd:glass rods up to 10 cm in diameter at a pump pulse repetition period of 3 minutes. It is shown that the rods have a safety factor of at least 5 before thermal stress induced damage would occur, and despite of their size phase and polarization distortions could be compensated. PMID:21934786

Kuzmin, A A; Khazanov, E A; Shaykin, A A

2011-07-18

16

Large Aperture Scintillometer Intercomparison Study  

NASA Astrophysics Data System (ADS)

Two field studies with six large aperture scintillometers (LASs) were performed using horizontal and slant paths. The accuracy of this novel and increasingly popular technique for measuring sensible heat fluxes was quantified by comparing measurements from different instruments over nearly identical transects. Random errors in LAS measurements were small, since correlation coefficients between adjacent measurements were greater than 0.995. However, for an ideal set-up differences in linear regression slopes of up to 21% were observed with typical inter-instrument differences of 6%. Differences of 10% are typical in more realistic measurement scenarios over homogeneous natural vegetation and different transect heights and locations. Inaccuracies in the optics, which affect the effective aperture diameter, are the most likely explanation for the observed differences.

Kleissl, J.; Gomez, J.; Hong, S.-H.; Hendrickx, J. M. H.; Rahn, T.; Defoor, W. L.

2008-07-01

17

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

18

Large aperture Fresnel telescopes/011  

SciTech Connect

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

Hyde, R.A., LLNL

1998-07-16

19

Very Large Aperture Diffractive Space Telescope  

SciTech Connect

A very large (10's of meters) aperture space telescope including two separate spacecraft--an optical primary 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 magnifying glass 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 magnifying glass, 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.

Hyde, Roderick Allen

1998-04-20

20

Large Aperture Electrostatic Dust Detector  

SciTech Connect

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

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

2007-10-09

21

Very Large Aperture Diffractive Space Telescope  

Microsoft Academic Search

A very large (10's of meters) aperture space telescope including two separate spacecraft--an optical primary 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

Hyde; Roderick Allen

1998-01-01

22

Wide-aperture excimer laser system  

SciTech Connect

An excimer laser system having an output aperture diameter of 40 cm and consisting of five lasers, three of which are excited by an electric discharge and the remaining two by an electron beam, is built. The first laser produces a 308-nm radiation with a duration of 200-250 ns, a spectral linewidth of 0.9 cm{sup -1} and the beam divergence close to the diffraction limit. This pulse is amplified in the active media of the other lasers. As a result, radiation with an energy of 5 J, spectral linewidth 0.9 cm{sup -1} and beam divergence 37 {mu}rad is produced at the output of the third laser. The output energy of the entire system amounts to 330 J and the pulse duration is 200-250 ns. (lasers)

Losev, V F; Koval'chuk, B M; Tarasenko, Viktor F; Panchenko, Yu N; Ivanov, N G; Konovalov, I N; Abdullin, E N; Panchenko, Aleksei N; Zorin, V B; Skakun, V S; Gubanov, V P; Stepchenko, A S; Tolkachev, Valerii S [Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk (Russian Federation); Liu, J [Chinese North-West Institute of Nuclear Technologies (China)

2006-01-31

23

Harmonic conversion of large-aperture 1. 05-. mu. m laser beams for inertial-confinement fusion research  

Microsoft Academic Search

To provide high-energy, high-power beams at short wavelengths for inertial-confinement fusion experiments, we routinely convert the 1.05-μm output of the Nova, Nd:phosphate-glass, laser system to its second- or third-harmonic wavelength. We describe the design and performance of the 3 à 3 arrays of potassium dihydrogen phosphate crystal plates used for type-II--type-II phase-matched harmonic conversion of the Nova 0.74-m diameter beams.

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

1992-01-01

24

Comprehensive above-threshold analysis of large-aperture (8-10 ?m) antiresonant reflecting optical waveguide diode lasers  

NASA Astrophysics Data System (ADS)

An above-threshold analysis of 8-10-?m-core antiresonant reflecting optical waveguide (ARROW) lasers is performed, including the carrier-induced index depression, carrier diffusion, and gain spatial hole burning (GSHB). The study is done as a function of the (transverse) optical-mode confinement factor ? and the core width. Just as for index-guided devices, it is found that ARROW devices (i.e., index-antiguided devices) are much less immune to multimoding via GSHB the smaller the value of ?. For the case ?=3%, the high-order mode of most concern reaches the threshold much earlier than for the case ?=1%, due both to gain-profile distortion as well as to distortion of the effective-index profile (in the device core) with increasing drive level. Devices of 8.5-?m-wide cores and ?=1%, are found to stay single-mode to at least 40× threshold, which in turn allows the projection of stable, single-mode operation to 1.2 W output power. In contrast, 10-?m-core devices become multimode at around 10× threshold. Preliminary experimental results from 10-?m-wide core ARROW lasers, with ?=1.5%, are stable, single-mode operation to 300 mW at 10× threshold, in good agreement with the presented study.

Chang, J. C.; Lee, J. J.; Al-Muhanna, A.; Mawst, L. J.; Botez, D.

2002-12-01

25

Large-aperture hybrid photo-detector  

NASA Astrophysics Data System (ADS)

We have developed the first complete large-aperture (13-inch diameter) hybrid photo-detector (HPD). The withstanding voltage problem has been overcome and we were able to attain an HPD operating voltage of +20 kV. Adoption of our newly developed backside illumination avalanche diode (AD) was also critical in successfully countering the additional problem of an increase in AD leakage after the activation process. We observed single photon signal timing jitter of under 450 ps in FWHM, electron transit time of ˜12 ns, and clear pulse height separation up to several photoelectron peaks, all greatly superior to the performance of any conventional large-aperture photomultiplier tubes (PMTs). In addition, our HPD has a much simpler structure than conventional large-aperture PMTs, which simplifies mass production and lowers manufacturing cost. We believe that these attributes position our HPD as the most suitable photo-detector for the next generation mega-ton class water-Cherenkov detector, which is expected to be more than 20× larger than the Super-Kamiokande (SK) detector.

Kawai, Y.; Nakayama, H.; Kusaka, A.; Kakuno, H.; Abe, T.; Iwasaki, M.; Aihara, H.; Tanaka, M.; Shiozawa, M.; Kyushima, H.; Suyama, M.

2007-08-01

26

Progress toward large-aperture membrane mirrors  

NASA Astrophysics Data System (ADS)

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

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

2000-10-01

27

Vacuum aperture isolator for retroreflection from laser-irradiated target  

DOEpatents

The disclosure is directed to a vacuum aperture isolator for retroreflection of a laser-irradiated target. Within a vacuum chamber are disposed a beam focusing element, a disc having an aperture and a recollimating element. The edge of the focused beam impinges on the edge of the aperture to produce a plasma which refracts any retroreflected light from the laser's target.

Benjamin, Robert F. (Los Alamos, NM); Mitchell, Kenneth B. (Los Alamos, NM)

1980-01-01

28

U-turn alternative to the large aperture switch  

SciTech Connect

The primary alternative laser architecture is the U-turn design. The U-turn has significantly different cost and performance risks than the full-aperture switch, which makes it a highly desirable alternative. The U-turn was conceived at LLNL in 1992. A similar concept, the L-turn had already been discovered by the French at CEL-V. Both concepts are based on the multipass glass amplifier design, but the full-aperture Pockels cell and polarizer are replaced with smaller and less expensive optics. Eliminating the large switch and polarizer not only reduces component costs, it also provides options for shortening the laser which, in turn, could reduce the size and cost of the laser building. Efficient use of the amplifier aperture (small vignetting allowance) requires that the U-turn have a long transport spatial filter; however, this is not a disadvantage if a long spatial filter is already required for image relaying to the frequency converter. Given a long spatial filter, the U-turn is potentially more efficient because losses in the switch and polarizer are avoided.

Vann, C.S.

1994-03-09

29

U-turn alternative to the large aperture switch  

NASA Astrophysics Data System (ADS)

The primary alternative laser architecture is the U-turn design. The U-turn has significantly different cost and performance risks than the full-aperture switch, which makes it a highly desirable alternative. The U-turn was conceived at LLNL in 1992. A similar concept, the L-turn, had already been discovered by the French at CEL-V. Both concepts are based on the multipass glass amplifier design, but the full-aperture Pockels cell and polarizer are replaced with smaller and less expensive optics. Eliminating the large switch and polarizer not only reduces component costs, it also provides options for shortening the laser which, in turn, could reduce the size and cost of the laser building. Efficient use of the amplifier aperture (small vignetting allowance) requires that the U-turn have a long transport spatial filter; however, this is not a disadvantage if a long spatial filter is already required for image relaying to the frequency converter. Given a long spatial filter, the U-turn is potentially more efficient because losses in the switch and polarizer are avoided.

Vann, Charles S.

1994-03-01

30

Low-cost Large Aperture Telescopes for Optical Communications  

NASA Technical Reports Server (NTRS)

Low-cost, large-aperture optical receivers are required to form an affordable optical ground receiver network for laser communications. Among the ground receiver station's multiple subsystems, here, we only discuss the ongoing research activities aimed at reducing the cost of the large-size optics on the receiver. Experimental results of two different approaches for fabricating low-cost mirrors of wavefront quality on the order of 100-200X the diffraction limit are described. Laboratory-level effort are underway to improve the surface figure to better than 20X the diffraction limit.

Hemmati, Hamid

2006-01-01

31

Laser beam-quality/aperture-shape scaling relation  

NASA Astrophysics Data System (ADS)

Many high-energy lasers (HELs) have noncircular output apertures. Some are rectangular in shape with or without a central or noncentral (up to 30 percent) obscuration. However, most high-energy laser propagation codes (especially those developed for systems analysis) model the aperture as either an unobscured circle or as a circle with fixed (e.g., 10 percent) obscuration. A beam-quality/aperture-shape scaling relation is presented which can be useful when applying these codes to realistic designs for HELs. The analysis also yields a generalized formula for angular size of the Airy disk and definitions of a characteristic aperture length and aperture quality.

Rockower, E. B.

1986-05-01

32

Laser beam-quality/aperture-shape scaling relation  

SciTech Connect

Many high-energy lasers (HELs) have noncircular output apertures. Some are rectangular in shape with or without a central or noncentral (up to 30%) obscuration. However, most high-energy laser propagation codes (especially those developed for systems analysis) model the aperture as either an unobscured circle or as a circle with fixed (e.g., 10%) obscuration. We present a beam-quality/aperture-shape scaling relation which can be useful when applying these codes to realistic designs for HELs. our analysis also yields a generalized formula for angular size of the Airy disk and definitions of a characteristic aperture length and aperture quality.

Rockower, E.B.

1986-05-01

33

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

34

Large-aperture, polarization-preserving optical circulator  

Microsoft Academic Search

We demonstrate a polarization-preserving optical circulator for large aperture directional beam separation at 1.5 mum. The device utilizes a magnetless latching Faraday rotator to enable large, 11-mm aperture and high-power handling up to 100 W\\/cm2

J. M. Roth; R. Bland; S. Libby

2004-01-01

35

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.; Stéphan, G.

1995-11-01

36

A Semiconductor Laser Model Including Finite Aperture Effects  

Microsoft Academic Search

Lasers consist of a nonlinear gain medium coupled to a resonant cavity. Existing models assume plane wave propagation around the resonant cavity and ignore transverse effects. Due to the small size of semiconductor lasers, transverse effects caused by small aperture size can dominate behavior. This research project is a theoretical study of the transverse effects in the laser cavity. The

Matt Reason; Richard Rolleigh

2000-01-01

37

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

Microsoft Academic Search

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

Joel Askinazi

1997-01-01

38

Feasibility of Very Large Sparse Aperture Deployable Antennas.  

National Technical Information Service (NTIS)

The objective of this research is to explore the technical soundness of a very large, cross-shaped, parabolic, sparse aperture antenna extending 75 m from the bus. Specifically, describing the environment of the satellite, the effect of fabrication error ...

J. C. Heller

2014-01-01

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

Metrology measurements for large-aperture VPH gratings  

NASA Astrophysics Data System (ADS)

The High Efficiency and Resolution Multi Element Spectrograph (HERMES) for the Australian Astronomical Observatory (AAO) uses four large aperture, high angle of incidence volume phase holographic gratings (VPHG) for high resolution `Galactic archaeology' spectroscopy. The large clear aperture, the high diffraction efficiency, the line frequency homogeneity, and mosaic alignment made manufacturing and testing challenging. We developed new metrology systems at the AAO to verify the performance of these VPH gratings. The measured diffraction efficiencies and line frequency of the VPH gratings received so far meet the vendor's provided data. The wavefront quality for the Blue VPH grating is good but the Green and Red VPH gratings need to be post polishing.

Zheng, Jessica R.; Gers, Luke; Heijmans, Jeroen

2013-09-01

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

Large Aperture, Scanning, L-Band SAR  

NASA Technical Reports Server (NTRS)

We have developed the first L-band membrane-based active phased array. The antenna is a 16x16 element patch array with dimensions of 2.3mx2.6m. The array uses membrane-compatible Transmit/Receive (T/R) modules for electronic beam steering. We will discuss the antenna design, the fabrication of this large array, the T/R module development, the signal distribution approach and the measured results of the array

Moussessian, Alina; DelCastillo, Linda; Bach, Vinh; Grando, Maurio; Quijano, Ubaldo; Smith, Phil; Zawadzki, Mark

2011-01-01

43

Synchronized microscanner array for large aperture receiver optics of LIDAR systems  

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

44

Aperture-Guiding in Quasi-Three-Level Lasers.  

National Technical Information Service (NTIS)

Aperture guiding, as opposed to thermal waveguiding, is shown to be the dominant mechanism for cavity mode stabilization in a quasi-three-level Yb:YAG laser in a flat-flat resonator. Excellent agreement is obtained between the experimental and modeled spo...

T. Y. Fan

1994-01-01

45

Operational Aspects of the Main Injector Large Aperture Quadrupole (WQB).  

National Technical Information Service (NTIS)

A two-year Large Aperture Quadrupole (WQB) Project was completed in the summer of 2006 at Fermilab. Nine WQBs were designed, fabricated and bench-tested by the Technical Division. Seven of them were installed in the Main Injector and the other two for spa...

B. Brown D. Capista J. Crisp L. Bartelson W. Chou

2006-01-01

46

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

47

Characterization of localized transverse structures in wide-aperture lasers  

NASA Astrophysics Data System (ADS)

The problem of characterization of spatio-temporal patterns is discussed for the case of wide-aperture lasers with nonlinear losses where variety of such patterns is especially rich. Laser autosolitons (LASs)-localized transverse structures representing “islands of lasing” on a background of the nonlasing mode on the laser aperture-are studied. Existence of stable single LASs which are motionless or moving in the transverse direction with constant linear velocity is shown. Described are also LASs with regular wavefronts, those with screw dislocations (defects) of wavefronts with different topological indices, and those with axially symmetric and asymmetric intensity distributions rotating with constant angular velocity around the LAS center. An approach is given for qualitative and quantitative characterization of a single LAS by its linear and angular velocities and frequency shift, based on a combination of analytical methods and computer simulations. Results of investigations of weak and strong interactions among the LASs are presented.

Rosanov, N. N.; Fedorov, A. V.; Fedorov, S. V.; Khodova, G. V.

48

Generation and Detection of Terahertz Radiation with Large-Aperture Photoconducting Antennas  

NASA Astrophysics Data System (ADS)

Large-aperture photoconducting antennas produce and detect in a phase-sensitive manner optically steerable, directional, ultrashort pulsed electrical transients extending from d. c. to beyond 1 THz in frequency. The coherent nature of the detection technique gives rise to the obtainment of spectral information from a time domain waveform of the radiated electric field. A theory describing the behavior of these antennas excited by femtosecond optical pulses is presented. Experiments performed to study the properties of these devices involve the use of a multikilohertz repetition rate stable train of femtosecond pulses amplified by a dye amplifier pumped by copper vapor laser pulses of a rectified polarization. A receiver based on a large-aperture design is optimized with respect to different photoconductors and dimensions both to be as sensitive and to have the best time resolution as possible. The measured spatial and temporal properties of this radiation are discussed with reference to the model describing it. Saturation of the radiated field generated from a large-aperture transmitter is predicted and observed from antennas incorporating GaAs, InP and radiation damaged silicon-on-sapphire. From the saturation experiments, information about the high-speed response (i.e., the transient carrier mobility in the first few picoseconds after optical excitation) of the photoconductors incorporated in the antenna can be obtained under conditions of high applied electric fields and high optical fluences. A large-aperture photoconducting transmitter is designed to produce terahertz radiation as efficiently as possible. The choice of photoconductor and gap spacing depend on the optical excitation pulse energy and the previously studied transient response of photoconductors used in large -aperture emitters. This large-aperture transmitter produces high-amplitude terahertz radiation that is detected with a high dynamic range of sensitivity. Such radiation can be used in the nonlinear spectroscopy of semiconductors, semiconductor devices and dielectrics and pulsed radar.

Darrow, Justin Thomas

1992-01-01

49

The LAGO (Large Aperture GRB Observatory) in Peru  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

50

Limiting Characteristics of Temporal Contrast for High Aperture CPA Lasers  

NASA Astrophysics Data System (ADS)

We review the impact of major effects taking place in high peak power short pulse CPA lasers, that modify the spectral amplitude and phase of a recompressed pulse and thus produce features that precede the main recompressed pulse. Especially effects associated with clipping of the spectrum, influence of the finite beam aperture on appearance of the pedestal preceding the main pulse (over the dynamic range more than 1010) as well as steepness of the leading front are considered.

Kalashnikov, Mikhail; Andreev, Alexander; Schönnagel, Horst

2010-04-01

51

Scalability of small-aperture selectively oxidized vertical cavity lasers  

SciTech Connect

We analyze the threshold properties of small area selectively oxidized vertical cavity lasers. Agreement for threshold gain versus laser size is found using the experimental intrinsic threshold voltage matched with a gain theory, as compared to a two-dimensional optical cavity simulation. Our analysis indicates the increasing threshold current density of small area lasers arises from both increasing threshold gain and the concomitant increasing leakage current. We further show that the optical loss can be reduced for lasers with areas as small as 0.25 {mu}m{sup 2} while maintaining sufficient transverse optical confinement by displacing the apertures longitudinally away from the cavity and reducing the oxide thickness. {copyright} {ital 1997 American Institute of Physics.}

Choquette, K.D.; Chow, W.W.; Hadley, G.R.; Hou, H.Q.; Geib, K.M. [Center for Compound Semiconductor Technology, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)] [Center for Compound Semiconductor Technology, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

1997-02-01

52

Structure of the optical field of a wide-aperture laser with a saturable filter  

SciTech Connect

Numerical calculations are made of the dynamics of the optical field in a wide-aperture laser with a saturable filter (absorber) inside a Fabry - Perot cavity. Variation of the laser parameters produces a range of spatiotemporal distributions of the radiation field: a steady-state (near-homogeneous) distribution, regular self-waves with small and large amplitudes, self-waves of low regularity, patterns corresponding to pulsed lasing, and those representing a transition from regular to pulsed lasing. The main results of an earlier bifurcation analysis are in almost complete agreement with the results reported in the present paper and can be used to predict and select various regimes of generation of the optical field. An analysis is reported of the influence of the aperture edges and of strong nonlinear effect on the optical field structure. (lasers)

Zaikin, A P; Molevich, N E [Samara Branch of the P.N. Lebedev Physics Institute, Russian Academy of Sciences, Samara (Russian Federation)

1999-11-30

53

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

54

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

55

Autofocus algorithm for synthetic aperture radar imaging with large curvilinear apertures  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

56

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

57

A lattice with no transition and large dynamic aperture  

SciTech Connect

In the case of a one-ring high-energy scheme for an advanced hadron facility, beam losses can be reduced if the ring lattice accomodates the beam from injection to maximum energy without crossing the transition. Since there is no synchrotron booster in such a scheme and the injection energy is relatively low, this requirement implies a negative compaction factor and an imaginary transition energy. This can be achieved by making the horizontal dispersion negative in some regions of the arcs so that the average value taken in the dipoles is globally also negative. Such a modulation of the dispersion may result in an increasing difficulty to obtain a large enough dynamic aperture in the presence of sextupoles. A careful optimization is therefore necessary and the possibility of modifying the linear lattice in order to include the requirements associated with chromaticity adjustments has to be studied. This paper summarizes the work done along this line and based on previous searches for a race track lattice that can be used in a hadron facility main ring. It describes an alternative lattice design, which tends to minimize the effects of the nonlinear aberrations introduced by sextupoles and to achieve a large dynamic aperture, keeping the betatron amplitudes as low as possible. 7 refs., 6 figs., 1 tab.

Guignard, G.

1989-01-01

58

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

59

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

SciTech Connect

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

Zapata, L. E., LLNL

1996-12-17

60

Large-Aperture Membrane Active Phased-Array Antennas  

NASA Technical Reports Server (NTRS)

Large-aperture phased-array microwave antennas supported by membranes are being developed for use in spaceborne interferometric synthetic aperture radar systems. There may also be terrestrial uses for such antennas supported on stationary membranes, large balloons, and blimps. These antennas are expected to have areal mass densities of about 2 kg/sq m, satisfying a need for lightweight alternatives to conventional rigid phased-array antennas, which have typical areal mass densities between 8 and 15 kg/sq m. The differences in areal mass densities translate to substantial differences in total mass in contemplated applications involving aperture areas as large as 400 sq m. A membrane phased-array antenna includes patch antenna elements in a repeating pattern. All previously reported membrane antennas were passive antennas; this is the first active membrane antenna that includes transmitting/receiving (T/R) electronic circuits as integral parts. Other integral parts of the antenna include a network of radio-frequency (RF) feed lines (more specifically, a corporate feed network) and of bias and control lines, all in the form of flexible copper strip conductors on flexible polymeric membranes. Each unit cell of a prototype antenna (see Figure 1) contains a patch antenna element and a compact T/R module that is compatible with flexible membrane circuitry. There are two membrane layers separated by a 12.7-mm air gap. Each membrane layer is made from a commercially available flexible circuit material that, as supplied, comprises a 127-micron-thick polyimide dielectric layer clad on both sides with 17.5-micron-thick copper layers. The copper layers are patterned into RF, bias, and control conductors. The T/R module is located on the back side of the ground plane and is RF-coupled to the patch element via a slot. The T/R module is a hybrid multilayer module assembled and packaged independently and attached to the membrane array. At the time of reporting the information for this article, an 8 16 passive array (not including T/R modules) and a 2 4 active array (including T/R modules) had been demonstrated, and it was planned to fabricate and test larger arrays.

Karasik, Boris; McGrath, William; Leduc, Henry

2009-01-01

61

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

SciTech Connect

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

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

2005-03-01

62

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

63

A large aperture magnification lens for velocity map imaging  

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

64

Concepts for a Large-Aperture, High Dynamic Range Telescope  

NASA Astrophysics Data System (ADS)

This paper summarizes concept studies for a large telescope capable of wide-field imaging and of the highest possible dynamic range for photometry and angular resolution. Point-spread functions (PSFs) and scattered light levels at large offsets are computed and compared for four telescopes of the same light-gathering power but with different pupil functions:1. a reference monolithic mirror telescope with a 17.4 m primary,2. a segmented mirror telescope (SMT) with a hexagonally segmented primary,3. a hexagonal off-axis telescope (HOT) with a distributed aperture made of 6×6.5 m unobstructed circular mirrors that are identical off-axis sections of a parent 20 m mirror, and4. a square off-axis telescope (SOT) whose aperture is made of 4×8 m off-axis mirrors. The characteristics of the PSFs are examined in the diffraction- and seeing-limited regimes, assuming (1) perfect mirror figure and (2) realistic figure errors (edge defects). The implications of field rotation with an altitude-azimuth mounting are discussed in each case. The implementation of adaptive optics (AO) and the properties of AO-compensated PSFs having a Strehl ratio of 0.5, and of coronagraphic imaging, are also discussed for the four configurations. It is shown that, in the seeing-limited regime and as intuitively expected, the optical performance of all four telescopes is comparable. With higher order adaptive optics and for coronagraphic observations, the SOT and HOT are superior to the SMT. This distinction becomes larger with relaxed constraints on mirror edge-polishing requirements. A full optical design is presented for the novel HOT configuration, and optical fabrication issues are briefly addressed. Finally, science programs and possible instrumentation layouts with the HOT are briefly explored for different modes of operation. It appears that the natural ``optical bench'' configuration of the HOT can provide a remarkably versatile and convenient environment for instrument deployment.

Kuhn, J. R.; Moretto, G.; Racine, R.; Roddier, F.; Coulter, R.

2001-12-01

65

BLAST: The Balloon-Borne Large Aperture Submillimeter Telescope  

NASA Technical Reports Server (NTRS)

BLAST is the Balloon-borne Large-Aperture Sub-millimeter Telescope. It will fly from a Long Duration Balloon (LDB) platform from Antarctica. The telescope design incorporates a 2 m primary mirror with large-format bolometer arrays operating at 250, 350 and 500 microns. By providing the first sensitive large-area (10 sq. deg.) sub-mm surveys at these wavelengths, BLAST will address some of the most important galactic and cosmological questions regarding the formation and evolution of stars, galaxies and clusters. Galactic and extragalactic BLAST surveys will: (1) identify large numbers of high-redshift galaxies; (2) measure photometric redshifts, rest-frame FIR luminosities and star formation rates thereby constraining the evolutionary history of the galaxies that produce the FIR and sub-mm background; (3) measure cold pre-stellar sources associated with the earliest stages of star and planet formation; (4) make high-resolution maps of diffuse galactic emission over a wide range of galactic latitudes. In addition to achieving the above scientific goals, the exciting legacy of the BLAST LDB experiment will be a catalogue of 3000-5000 extragalactic sub-mm sources and a 100 sq. deg. sub-mm galactic plane survey. Multi-frequency follow-up observations from SIRTF, ASTRO-F, and Herschel, together with spectroscopic observations and sub-arcsecond imaging from ALMA are essential to understand the physical nature of the BLAST sources.

Devlin, Mark; Ade, Peter; Bock, Jamie; Dicker, Simon; Griffin, Matt; Gunderson, Josh; Halpern, Mark; Hargrave, Peter; Hughes, David; Klein, Jeff

2004-01-01

66

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.

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

2014-04-01

67

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

68

Design considerations for a large aperture high field superconducting dipole  

SciTech Connect

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

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

1989-03-01

69

A proposed large deployable space structures experiment for high power, large aperture missions in MEO  

Microsoft Academic Search

The Air Force Research Laboratory (AFRL) Space Vehicles Directorate has developed the deployable structures experiment (DSX) to research the technologies needed for large space structures and apertures, high-power generation, and survivability in the high radiation environment of a medium earth orbit (MEO). The proposed DSX concept is a combination of four research experiments that coupled together provides DoD with: a)

James Winter; Greg Spanjers; D. Cohen; A. Adler; G. Ginet; B. Dichter; J. Granata; K. Denoyer; T. Murphey; P. Wegner; L. Underwood; P. Hausgen; D. Senft

2004-01-01

70

Research on axial support technology of large aperture primary mirror  

NASA Astrophysics Data System (ADS)

In ground-based optical detection system, when large aperture primary mirror in a different pitch angle detection, the surface shape error of primary mirror is affected by its weight deformation, and the surface shape error of primary mirror is one of the key factors affecting imaging quality. The primary mirror support system, including axial support and radial support, and the axial support is main factor affecting the surface shape error of primary mirror, the position and number of axial support is very important for surface shape error of primary mirror. The support technology of ?1.2m primary mirror was studied detailedly in this paper, the parameterized model of primary mirror was built based on ANSYS, the relationship between the surface shape error of primary mirror and the ratio of its diameter to thickness was analyzed, the axial support was optimized, and the support-ring number, support-ring radius and support point position of axial support were optimum designed. The result of analysis showed that the Root-Mean-Square (RMS) value of the surface shape error of primary mirror was 1.8 nm, when the primary mirror pointed to zenith, met to the design need of the optical system, and the axial support system was verified.

Yao, Hui

2010-05-01

71

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

72

Large field-of-view synthetic aperture holography using rotation stages  

NASA Astrophysics Data System (ADS)

In general, digital holography means a technology to measure an object wave by using a focal plane array (FPA) sensor. Since the limitation of the dimension of the FPA sensor, the field of view obtained by the FPA sensor is usually very narrow. Many methods have been proposed to increase the field of view of measurement. One simple solution is the synthesis of the holograms with small apertures, where each of them is measured by the FPA sensor respectively. If we imagine specific applications such as 360-degree table-top digital holographic display, the large field of view of the object is required to present the three-dimensional contents to the observer who may change his position dynamically. In this paper, we use two-axis rotation stage for acquisition of the object wave with large field of view. In our system, the optics including a laser and a CCD sensor are fixed and the object is mounted on the rotation stage. During the rotation of the object, the holograms are taken sequentially and the object wave over the hemispherical surface in k-space is obtained. The increase of solid angle of the measured hologram means the increase of acquired angular spectrum of interested objects. The resolution of the measurement is closely related with the numerical aperture and the data with fine resolution is expectable. But since it is not easy to match the relative phases of the each hologram, unfortunately the enhancement of the resolution in the reconstructed object wave is negligible.

Kim, Sungmin; Im, Yeonsu; Hahn, Joonku

2014-02-01

73

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

NASA Astrophysics Data System (ADS)

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

Hanes, Stephen A.

2003-03-01

74

Bay of Biscay Coherence Study using Large Aperture Seismic Array.  

National Technical Information Service (NTIS)

The report covers computer processing and analysis of acoustic data obtained with a long aperture seismic receiving array and a mono frequency acoustic source in the Bay of Biscay. Twelve sets of 'signal plus noise' and 'noise only' acoustic data obtained...

W. H. Luehrmann

1973-01-01

75

Synthetic-aperture-radar imaging with a solid-state laser.  

PubMed

We report the operation of an imaging Nd:YAG microchip-laser synthetic-aperture radar, with which we imaged two-dimensional (2-D) models of military targets. The images obtained showed spatial resolution significantly better than the diffraction limit of the real aperture in the along-track dimension. The signal processing is described, and the measurement sensitivity is both predicted and verified. In addition, 2-D images with high resolution in both dimensions were generated by using an asymmetric aperture to match the along-track synthetic-aperture resolution with the across-track diffraction-limited resolution. PMID:21060556

Green, T J; Marcus, S; Colella, B D

1995-10-20

76

Large-aperture refractive lenses for momentum-resolved spectroscopy with hard X-rays  

PubMed Central

One-dimensional kinoform and prism refractive lenses with large aperture and high transmittance at 22?keV have been investigated. A 12.0?µm focus size (full width at half-maximum) and an effective aperture of 0.85?mm, at a focal length of 705?mm and 21.747?keV, were achieved.

Fukui, Hiroshi; Simon, Markus; Nazmov, Vladimir; Mohr, Jurgen; Evans-Lutterodt, Kenneth; Stein, Aaron; Baron, Alfred Q. R.

2013-01-01

77

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

NASA Astrophysics Data System (ADS)

Simple analytical expressions for parameter Strehl of ground-based astronomical telescope: (i) without adaptive correction, (ii) phase correction with use single laser guide star, (iii) phase correction with use multi-guide stars (square matrix system of guide stars with variable number of elements) are obtained. Models of the vertical dependence of the structure parameter of refractive index of the turbulent atmosphere for various sites are used in the calculations. Modal phase correction is considered to large aperture ground-based telescope with multi-guide stars. Wave aberrations presented in the in terms of Zernike polynomials are used to calculate the angular correlation of modal components of phase fluctuations of optical radiation propagating in the turbulent atmosphere. The size of the isoplanatic area in an adaptive optical system is studied. The influence of the model of vertical profile of the structure parameter of atmospheric refractive index fluctuations, the outer scale of atmospheric turbulence, and the size of receiving aperture of a telescopic system are analyzed. Requirements on bandwidth of adaptive optical system for effective correction are formulated.

Bolbasova, Lidia A.; Lukin, Vladimir P.

2009-09-01

78

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

79

Laser alignment of large assemblies  

NASA Technical Reports Server (NTRS)

Electronically leveled laser instrument, incorporating special tiltmeter-controlled laser alignment transit, simplifies alignment of large structure. System operated from single alignment reference tower saves time and costs in assembling of structures.

Cazares, W. S.; Kern, D. D.

1979-01-01

80

Design and fabrication of sub-wavelength annular apertures on fiber tip for femtosecond laser machining  

NASA Astrophysics Data System (ADS)

Adopting optical technique to pursue micromachining must make a compromise between the focal spot sizes the depth of focus. The focal spot size determines the minimum features can be fabricated. On the other hand, the depth of focus influences the ease of alignment in positioning the fabrication light beam. A typical approach to bypass the diffraction limit is to adopt the near-field approach, which has spot size in the range of the optical fiber tip. However, the depth of focus of the emitted light beam will be limited to tens of nanometers in most cases, which posts a difficult challenge to control the distance between the optical fiber tip and the sample to be machined optically. More specifically, problems remained in this machining approach, which include issues such as residue induced by laser ablation tends to deposit near the optical fiber tip and leads to loss of coupling efficiency. We proposed a method based on illuminating femtosecond laser through a sub-wavelength annular aperture on metallic film so as to produce Bessel light beam of sub-wavelength while maintaining large depth of focus first. To further advance the ease of use in one such system, producing sub-wavelength annular aperture on a single mode optical fiber head with sub-wavelength focusing ability is detailed. It is shown that this method can be applied in material machining with an emphasis to produce high aspect ratio structure. Simulations and experimental results are presented in this paper.

Tung, Yen-Chun; Chung, Ming-Han; Sung, I.-Hui; Lee, Chih-Kung

2014-03-01

81

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

82

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

83

Improving 351-nm Damage Performance of Large-Aperture Fused Silica and DKDP Optics  

SciTech Connect

A program to identify and eliminate the causes of UV laser-induced damage and growth in fused silica and DKDP has developed methods to extend optics lifetimes for large-aperture, high-peak-power, UV lasers such as the National Ignition Facility (NIF). Issues included polish-related surface damage initiation and growth on fused silica and DKDP, bulk inclusions in fused silica, pinpoint bulk damage in DKDP, and UV-induced surface degradation in fused silica and DKDP in a vacuum. Approaches included an understanding of the mechanism of the damage, incremental improvements to existing fabrication technology, and feasibility studies of non-traditional fabrication technologies. Status and success of these various approaches are reviewed. Improvements were made in reducing surface damage initiation and eliminating growth for fused silica by improved polishing and post-processing steps, and improved analytical techniques are providing insights into mechanisms of DKDP damage. The NIF final optics hardware has been designed to enable easy retrieval, surface-damage mitigation, and recycling of optics.

Burnham, A K; Hackel, L; Wegner, P; Parham, T; Hrubesh, L; Penetrante, B; Whitman, P; Demos, S; Menapace, J; Runkel, M; Fluss, M; Feit, M; Key, M; Biesiada, T

2002-01-07

84

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

85

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

86

Compensation of beamlet repulsion in a large negative ion source with a multi aperture accelerator  

SciTech Connect

Excess heat loads to accelerator grids limit extension of pulse length in operation of the large negative ion sources with multi aperture accelerator. Part of the heat loads is caused by interception of deflected beamlets due to their space charge repulsion. In this paper, a beamlet steering technique using aperture offset was examined for compensation of the beamlet deflections utilizing a three dimensional beam analysis simulating the D{sup -} negative ion source of JT-60 U. The beamlet deflection was analyzed in detail using fifty beamlets, which were extracted from apertures arranged in a lattice pattern of 10x5. The simulation showed successful compensation of the beamlet deflection by aperture offsets defined according to the thin lens theory. Even if the beam energy was changed, the necessary aperture offset would not be changed maintaining the perveance and a ratio of extraction and acceleration voltage. In JT-60 U, it was shown that the aperture offset of less than 1.0 mm would be enough to compensate the repulsion of all beamlets. When the magnetic field was applied for suppression of co-extracted electrons, necessary aperture offset was estimated to be {+-}0.5 mm for 500 keV D{sup -} ion beam in JT-60 U, in addition to the offset for the space charge repulsion. This result showed good agreements with the previous experimental results and design study of the JT-60 U N-NBI.

Kashiwagi, M.; Inoue, T.; Hanada, M.; Kamada, M.; Taniguchi, M.; Umeda, N.; Watanabe, K. [Japan Atomic Energy Agency, 801-1, Nukoyama, Naka, 311-0193 (Japan); Grisham, L. R. [Princeton University, Plasma Physics Laboratory, Princeton (United States)

2009-03-12

87

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

88

Large aperture deformable mirror with a transferred single-crystal silicon membrane actuated using large-stroke PZT Unimorph Actuators  

NASA Technical Reports Server (NTRS)

We have demonstrated a large aperture (50 mm x 50 mm) continuous membrane deformable mirror (DM) with a large-stroke piezoelectric unimorph actuator array. The DM consists of a continuous, large aperture, silicon membrane 'transferred' in its entirety onto a 20 x 20 piezoelectric unimorph actuator array. A PZT unimorph actuator, 2.5 mm in diameter with optimized PZT/Si thickness and design showed a deflection of 5.7 [m at 20V. An assembled DM showed an operating frequency bandwidth of 30 kHz and influence function of approximately 30%.

Hishinumat, Yoshikazu; Yang, Eui - Hyeok (EH)

2005-01-01

89

First steps in the development of a piston sensor for large aperture space telescopes  

NASA Astrophysics Data System (ADS)

Nowadays spaceborne missions for astronomy or Earth imaging need high resolution observation which implies the development of large aperture telescopes. This can be achieved by multi-aperture telescopes or large segmented telescopes. One of the major issues is the phasing of the sub-apertures or the segments of such telescopes. A cophasing sensor is therefore mandatory to achieve the ultimate resolution of these telescopes. In this framework, Liège Space Center (CSL) concern is the development of a compact cophasing sensor to phase new large lightweight segmented mirrors for future space telescopes. The sensor concept has its origins in new phase retrieval algorithms which have been recently developed. In this paper, we outline the concept and the experimental validation results of our piston sensor breadboard which is currently under development in our laboratory. Finally, future prospects and further developments of our experiment are presented.

Guerri, Géraldine; Roose, Stéphane; Stockman, Yvan; Mazzoli, Alexandra; Surdej, Jean; Defise, Jean-Marc

2010-07-01

90

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

91

Design and Evaluation of Large-Aperture Gallium Fixed-Point Blackbody  

NASA Astrophysics Data System (ADS)

To complement existing water bath blackbodies that now serve as NIST primary standard sources in the temperature range from 15 °C to 75 °C, a gallium fixed-point blackbody has been recently built. The main objectives of the project included creating an extended-area radiation source with a target emissivity of 0.9999 capable of operating either inside a cryo-vacuum chamber or in a standard laboratory environment. A minimum aperture diameter of 45 mm is necessary for the calibration of radiometers with a collimated input geometry or large spot size. This article describes the design and performance evaluation of the gallium fixed-point blackbody, including the calculation and measurements of directional effective emissivity, estimates of uncertainty due to the temperature drop across the interface between the pure metal and radiating surfaces, as well as the radiometrically obtained spatial uniformity of the radiance temperature and the melting plateau stability. Another important test is the measurement of the cavity reflectance, which was achieved by using total integrated scatter measurements at a laser wavelength of 10.6 ?m. The result allows one to predict the performance under the low-background conditions of a cryo-chamber. Finally, results of the spectral radiance comparison with the NIST water-bath blackbody are provided. The experimental results are in good agreement with predicted values and demonstrate the potential of our approach. It is anticipated that, after completion of the characterization, a similar source operating at the water triple point will be constructed.

Khromchenko, V. B.; Mekhontsev, S. N.; Hanssen, L. M.

2009-02-01

92

Subarrays of vivaldi antennas for very large apertures  

Microsoft Academic Search

Truncation effects in small and moderate size arrays of Vivaldi tapered slot antenna elements disrupt the multioctave bandwidth and wide scanning properties that exist for large phased arrays. These truncation effects are evident in small subarrays that are electrically and\\/or physically isolated from neighboring snbarrays. Starting with single elements and with infinite arrays, the truncation effects are explored and shown

Daniel H. Schaubert; A. O. Boryssenko

2004-01-01

93

Principles of an Experimental Large Aperture Seismic Array (Lasa).  

National Technical Information Service (NTIS)

One of the most useful techniques for improving capability to observe small remote seismic events is to connect a large number of seismic sensors distributed in the horizontal plane so as to form an array. This has proved to be of great interest in seismo...

P. E. Green R. A. Frosch C. F. Romney

1965-01-01

94

Wide-aperture solid state laser oscillator distortion dynamic investigation  

Microsoft Academic Search

The results of dynamic thermal lens influence on radiation divergence of high-energy free running mode neodymium glass laser with unstable oscillator are represented. Thermal distortions of active rod influence on temporal changes of output laser radiation are disucssing. The researches of dynamic of thermal lens in neodymium glass GLS-6 (phi) 45 X 300 mm were carried out.

V. V. Kramnik; V. F. Petrov; Anatoly A. Solounin; Valery Y. Khramov

2002-01-01

95

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

NASA Astrophysics Data System (ADS)

An alternative method for measuring the contrast transfer function (CTF) of a pixilated display is proposed that reduces the amount of time required to perform a high sample rate-small aperture luminance scan as outlined in the Video Electronics Standards Association (VESA) standard for measuring the contrast of an n X n grille. The alternative method proposed by the Night Vision Electronic Sensors Directorate (NVESD) Displays group utilizes round sampling apertures and large step sizes to achieve comparable results to the VESA standard method. Theoretical predictions and experimental measurements demonstrated the equivalency between the proposed large aperture method and the VESA standard method with less than 8% maximum variation and an average of 2.4% variation between the two methods over two different input contrasts and 4 different grille frequencies. Experimental results also show a reduction in time to perform the profile scan by as much as 15:1 for the NVESD proposed test method over the VESA standard method.

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

2002-08-01

96

Radiometer design concepts for large aperture microwave radiometer spacecraft  

NASA Technical Reports Server (NTRS)

Concepts involving active and passive microwave systems for soil-moisture monitoring are discussed. It is shown that the first major development efforts should be directed toward the simpler passive design concepts. Subsequently, five passive design concepts for a microwave radiometer spacecraft are outlined and compared. Some common technology needs, such as large space structures and controls, are shown to exist. Also, some peculiar technology needs are identified, such as complicated phasing networks, dielectric lenses, tapered illumination, and reflector-surface irregularity and distortion control techniques. More detailed studies to address these design concepts and assess the associated technology needs are recommended.

Keafer, L. S., Jr.

1981-01-01

97

Fabrication of large aperture kinoform phase plates in fused silica for smoothing focal plane intensity profiles.  

National Technical Information Service (NTIS)

We have fabricated large aperture (40-cm) kinoform phase plates for producing super-Gaussian focal plane intensity profiles. The continuous phase screen, designed using a new iterative procedure, was fabricated in fused silica as a 16-level, one-wave deep...

M. Rushford S. Dixit I. Thomas M. Perry

1996-01-01

98

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

99

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. II. Theoretical Properties and Application to Extremely Large Telescopes  

Microsoft Academic Search

We study the application of Lyot coronagraphy to future Extremely Large Telescopes (ELTs), showing that Apodized Pupil Lyot Coronagraphs enable high-contrast imaging for exoplanet detection and characterization with ELTs. We discuss the properties of the optimal pupil apodizers for this application (generalized prolate spheroidal functions). The case of a circular aperture telescope with a central obstruction is considered in detail,

Rémi Soummer; Laurent Pueyo; André Ferrari; Claude Aime; Anand Sivaramakrishnan; Natalia Yaitskova

2009-01-01

100

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

Microsoft Academic Search

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

Arthur Enneking; Jan Ritter; Rainer Bunger

2003-01-01

101

Thermal analysis of the Advanced Technology Large Aperture Space Telescope (ATLAST) 8-meter primary mirror  

Microsoft Academic Search

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 point and will experience constant exposure to the sun. The insulation on the optical tube and sunshade

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

2010-01-01

102

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

National Technical Information Service (NTIS)

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 astro...

D. Calzetti H. P. Stahl J. Tumlinson K. Sembach K. Stapelfeldt M. Giavalisco M. Mountain M. Postman R. Soummer R. M. Rich T. Brown T. Hyde W. Oegerle W. Traub

2011-01-01

103

Position measurement of the direct drive motor of Large Aperture Telescope  

NASA Astrophysics Data System (ADS)

Along with the development of space and astronomy science, production of large aperture telescope and super large aperture telescope will definitely become the trend. It's one of methods to solve precise drive of large aperture telescope using direct drive technology unified designed of electricity and magnetism structure. A direct drive precise rotary table with diameter of 2.5 meters researched and produced by us is a typical mechanical & electrical integration design. This paper mainly introduces position measurement control system of direct drive motor. In design of this motor, position measurement control system requires having high resolution, and precisely aligning the position of rotor shaft and making measurement, meanwhile transferring position information to position reversing information corresponding to needed motor pole number. This system has chosen high precision metal band coder and absolute type coder, processing information of coders, and has sent 32-bit RISC CPU making software processing, and gained high resolution composite coder. The paper gives relevant laboratory test results at the end, indicating the position measurement can apply to large aperture telescope control system. This project is subsidized by Chinese National Natural Science Funds (10833004).

Li, Ying; Wang, Daxing

2010-07-01

104

Performance predictions for spaceborne, long-lifetime helium dewars containing large-aperture telescopes  

NASA Technical Reports Server (NTRS)

The evolution of design approaches for high-performance superfluid helium dewars containing large-aperture telescopes are discussed. Particular attention is given to thermal-math modeling for the IRAS and the Cosmic Background Explorer (COBE) dewars. Correlation of the recent COBE flight data with the dewar thermal-math model is presented, and apparent predictive deficiencies of the model are discussed.

Hopkins, Richard A.; Nieczkoski, Stephen J.; Volz, Stephen M.

1990-01-01

105

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

NASA Astrophysics Data System (ADS)

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

He, Xin; Zhang, Bin

2011-11-01

106

Large-pore apertures in a series of metal-organic frameworks.  

PubMed

We report a strategy to expand the pore aperture of metal-organic frameworks (MOFs) into a previously unattained size regime (>32 angstroms). Specifically, the systematic expansion of a well-known MOF structure, MOF-74, from its original link of one phenylene ring (I) to two, three, four, five, six, seven, nine, and eleven (II to XI, respectively), afforded an isoreticular series of MOF-74 structures (termed IRMOF-74-I to XI) with pore apertures ranging from 14 to 98 angstroms. All members of this series have noninterpenetrating structures and exhibit robust architectures, as evidenced by their permanent porosity and high thermal stability (up to 300°C). The pore apertures of an oligoethylene glycol-functionalized IRMOF-74-VII and IRMOF-74-IX are large enough for natural proteins to enter the pores. PMID:22628651

Deng, Hexiang; Grunder, Sergio; Cordova, Kyle E; Valente, Cory; Furukawa, Hiroyasu; Hmadeh, Mohamad; Gándara, Felipe; Whalley, Adam C; Liu, Zheng; Asahina, Shunsuke; Kazumori, Hiroyoshi; O'Keeffe, Michael; Terasaki, Osamu; Stoddart, J Fraser; Yaghi, Omar M

2012-05-25

107

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

108

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

109

The application of wavefront coding technology to a large segmented synthetic aperture telescope  

NASA Astrophysics Data System (ADS)

The utilization of a telescope with a large single aperture is limited by the manufacturing technique, cost, volume and weight of a monolithic mirror. In order to solve these problems, the technology of the segmented synthetic aperture was introduced. The primary mirror of a large segmented synthetic aperture telescope consists of several segmented mirrors, whose misalignment errors make the wavefront change drastically and influence the MTF of the optical system badly. The wavefront coding technology (WFC) is an innovative technology that joints the optical design and digital image processing together. By adding a phase mask close to the pupil of an optical system and modulating the wavefront, the WFC system becomes very insensitive to defocus and other aberrations based on defocus. The theoretical analysis of characteristics of the WFC system was done in the form of PSF. The application of WFC to a segmented three mirror anastigmat (TMA) was presented. A space telescope with an effective focal length as 40m, a F number as 10, a field of view as 0.5°x0.05° was designed, whose primary mirror consisted of seven segmented mirrors. The influence of defocus and misalignment errors on the telescope was discussed. The imaging process of the WFC system and following image restoration were simulated. As a result, sharp images were obtained and the large segmented synthetic aperture telescope had looser misalignment tolerance and extended depth of focus.

Feng, Litong; Meng, Junhe; Dun, Xiong; Tao, Yu; Zhu, Lixin; Wu, Xiaojing; Zhang, Zhen; Zhang, Chenzhong; Chen, Xin; Lei, Li; Zhao, Kan

2010-05-01

110

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

111

Multilens array for GEKKO XII glass laser system with circular aperture spherical element lens  

NASA Astrophysics Data System (ADS)

A two-dimensional multi-lens array of 350 mm in diameter with 37 pieces of spherical element lenses is tested for improving the irradiation uniformity of the ICF target. Circular and hexagonal shapes of element lens aperture have been examined. The circular aperture is chosen for eliminating azimuthally asymmetric intensity distribution in the beam pattern. An approximate flat-top intensity distribution has been obtained at the focus of the principal lens. Beam patterns of coherent laser and partially coherent light (PCL) with the random phase plate (RPP) and the multi-lens array (MLA) have been measured at GEKKO XII glass laser system. The irradiation non uniformity of MLA on a spherical target is calculated from the measured beam patterns.

Jitsuno, Takahisa; Nishi, Noriaki; Tsubakimoto, Kouji; Nakatsuka, Masahiro; Nakai, Sadao

1995-12-01

112

Limits of the temporal contrast for CPA lasers with beams of high aperture  

NASA Astrophysics Data System (ADS)

We review the impact of major effects taking place in high peak power short pulse CPA lasers, that modify the spectral amplitude and phase of a recompressed pulse and thus produce features that precede the main recompressed pulse. Especially effects associated with clipping of the spectrum, influence of the finite beam aperture on appearance of the pedestal preceding the main pulse (over the dynamic range more than 1010) as well as steepness of the leading front are considered.

Kalashnikov, Mikhail; Andreev, Alexander; Schönnagel, Horst

2009-10-01

113

Terahertz inverse synthetic aperture radar imaging using self-mixing interferometry with a quantum cascade laser.  

PubMed

We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We demonstrate this by imaging a standard resolution test target, achieving resolution beyond the diffraction limit. PMID:24784063

Lui, H S; Taimre, T; Bertling, K; Lim, Y L; Dean, P; Khanna, S P; Lachab, M; Valavanis, A; Indjin, D; Linfield, E H; Davies, A G; Raki?, A D

2014-05-01

114

Large-aperture chirped volume Bragg grating based fiber CPA system  

NASA Astrophysics Data System (ADS)

A fiber chirped pulse amplification system at 1558nm was demonstrated using a large-aperture volume Bragg grating stretcher and compressor made of Photo-Thermal-Refractive (PTR) glass. Such PTR glass based gratings represent a new type of pulse stretching and compressing devices which are compact, monolithic and optically efficient. Furthermore, since PTR glass technology enables volume gratings with transverse apertures which are large, homogeneous and scalable, it also enables high pulse energies and powers far exceeding those achievable with other existing compact pulse-compression technologies. Additionally, reciprocity of chirped gratings with respect to stretching and compression also enables to address a long-standing problem in CPA system design of stretcher-compressor dispersion mismatch.

Liao, Kai-Hsiu; Cheng, Ming-Yuan; Flecher, Emilie; Smirnov, Vadim I.; Glebov, Leonid B.; Galvanauskas, Almantas

2007-04-01

115

Research on cooling technology for a large-aperture solar telescope's primary mirror  

NASA Astrophysics Data System (ADS)

The surface temperture of Open Large-Aperture Solar Telescope's primary mirror can vulnerablely be warmed too high by exposure to direct sunlight. If its temperature over the external environment is too high, it is likely to decline the mirror seeing. So generally keeping the surface temperture of primary mirror same as the environment's is very important by cooling technology researched. By using Ansys software to analyze a meniscus-shaped aluminum metal primary mirror with a diameter of 2.5m, and thickness of 4.45cm to gain the primary mirror's temperature distribution in order to verify the feasibility of methods of cooling. Furthermore form a more perfect cooling project. Thus it can provide a technical guidance for Large-Aperture primary mirror's development in the future.

Wang, Qingping; Zhang, Haiying

2009-05-01

116

Large-aperture chirped volume Bragg grating based fiber CPA system.  

PubMed

A fiber chirped pulse amplification system at 1558 nm was demonstrated using a large-aperture volume Bragg grating stretcher and compressor made of Photo-Thermal-Refractive (PTR) glass. Such PTR glass based gratings represent a new type of pulse stretching and compressing devices which are compact, monolithic and optically efficient. Furthermore, since PTR glass technology enables volume gratings with transverse apertures which are large, homogeneous and scalable, it also enables high pulse energies and powers far exceeding those achievable with other existing compact pulse-compression technologies. Additionally, reciprocity of chirped gratings with respect to stretching and compression also enables to address a long-standing problem in CPA system design of stretcher-compressor dispersion mismatch. PMID:19532735

Liao, Kai-Hsiu; Cheng, Ming-Yuan; Flecher, Emilie; Smirnov, Vadim I; Glebov, Leonid B; Galvanauskas, Almantas

2007-04-16

117

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

118

LASER FIELDS AND CAVITIES: Periodic self-wave structures in a wide-aperture laser with frequency detuning. II. Distributed model  

NASA Astrophysics Data System (ADS)

A numerical investigation is reported of a distributed model of a wide-aperture laser with frequency detuning. When the detuning is negative, successive changes in the optical field structures occur on increase in the detuning: a near-homogeneous optical field is followed by regular small- and large-amplitude self-waves in the optical field profile, and these are succeeded by structures irregular in space and time. The range of parameters of the laser-active medium, in which quasi-sinusoidal periodic structures can be observed, is found. A comparison is made of the characteristics of these waves with the values obtained on the basis of a bifurcation analysis of this laser system. Similar periodic self-wave profiles of the optical field do not appear when the frequency detuning is positive.

Zaikin, A. P.; Kurguzkin, A. A.; Molevich, N. E.

1999-06-01

119

Fabrication of large aperture kinoform phase plates in fused silica for smoothing focal plane intensity profiles  

SciTech Connect

We have fabricated large aperture (40-cm) kinoform phase plates for producing super-Gaussian focal plane intensity profiles. The continuous phase screen, designed using a new iterative procedure, was fabricated in fused silica as a 16-level, one-wave deep rewrapped phase profile using a lithographic process and wet etching in buffered hydrofluoric acid. The observed far-field contains 94% of the incident energy inside the desired spot.

Rushford, M.; Dixit, S.; Thomas, I.; Perry, M.

1996-04-26

120

Cryogenics for a 5 Tesla Superconducting Solenoid with Large Aperture at DESY  

SciTech Connect

A large aperture superconducting solenoid-magnet with fields up to 5.25 Tesla is being set up as high field test facility at DESY. It is used to measure prototype time projection chambers foreseen as detectors for a future high energy physics collider experiment. The new cryogenic supply of this magnet within the existing HERA cryogenic helium system is described. The cryogenic control, operation and results are outlined.

Gadwinkel, E.; Lierl, H.; Notz, D.; Schaffran, J.; Schoeneburg, B. [Deutsches Elektronen-Synchrotron, DESY, Hamburg, 22607 (Germany); Herzog, H. [Deutsches Elektronen-Synchrotron, DESY, Hamburg, 22607 (Germany); Linde Kryotechnik A.G., plant operation section at DESY, Pfungen, 8422 (Switzerland)

2004-06-23

121

Development of twin aperture dipole magnets for the Large Hadron Collider  

Microsoft Academic Search

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

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

1995-01-01

122

Comparison of full-aperture interferometry to sub-aperture stitched interferometry for a large diameter fast mirror  

NASA Technical Reports Server (NTRS)

The Herschel Space Observatory (formerly known as FIRST) consists of a 3.5 m space telescope. Stitching sub aperture interferograms may offer considerable cost savings during testing of the flight telescope as compared to other techniques. A comparative demonstration is presented of interferogram stitching techniques that enable a composite map of a 3-D surface to be assembled from a sequence of sub-aperture measurements. This paper describes the fundamental procedures for stitching together component data sets and demonstrates such techniques with real data sets.

Catanzaro, B.; Thomas, J.; Cohen, E.

2001-01-01

123

Large eccentric laser angioplasty catheter  

NASA Astrophysics Data System (ADS)

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

Taylor, Kevin D.; Reiser, Christopher

1997-05-01

124

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

125

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

126

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

127

Large Coded Aperture Mask for Spaceflight Hard X-ray Images  

NASA Technical Reports Server (NTRS)

The 2.6 square meter coded aperture mask is a vital part of the Burst Alert Telescope on the Swift mission. A random, but known pattern of more than 50,000 lead tiles, each 5 mm square, was bonded to a large honeycomb panel which projects a shadow on the detector array during a gamma ray burst. A two-year development process was necessary to explore ideas, apply techniques, and finalize procedures to meet the strict requirements for the coded aperture mask. Challenges included finding a honeycomb substrate with minimal gamma ray attenuation, selecting an adhesive with adequate bond strength to hold the tiles in place but soft enough to allow the tiles to expand and contract without distorting the panel under large temperature gradients, and eliminating excess adhesive from all untiled areas. The largest challenge was to find an efficient way to bond the > 50,000 lead tiles to the panel with positional tolerances measured in microns. In order to generate the desired bondline, adhesive was applied and allowed to cure to each tile. The pre-cured tiles were located in a tool to maintain positional accuracy, wet adhesive was applied to the panel, and it was lowered to the tile surface with synchronized actuators. Using this procedure, the entire tile pattern was transferred to the large honeycomb panel in a single bond. The pressure for the bond was achieved by enclosing the entire system in a vacuum bag. Thermal vacuum and acoustic tests validated this approach. This paper discusses the methods, materials, and techniques used to fabricate this very large and unique coded aperture mask for the Swift mission.

Vigneau, Danielle N.; Robinson, David W.

2002-01-01

128

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

129

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

130

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

131

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

NASA Astrophysics Data System (ADS)

VTT has developed Fabry-Pérot 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.

Kantojärvi, Uula; Varpula, Aapo; Antila, Tapani; Holmlund, Christer; Mäkynen, Jussi; Näsilä, Antti; Mannila, Rami; Rissanen, Anna; Antila, Jarkko; Disch, Rolf J.; Waldmann, Torsten A.

2014-03-01

132

System architecture of MMIC-based large aperture arrays for space applications  

NASA Technical Reports Server (NTRS)

The persistent trend to use millimeter-wave frequencies for satellite communications presents the challenge to design large-aperture phased arrays for space applications. These arrays, which comprise 100 to 10,000 elements, are now possible due to the advent of lightwave technology and the availability of monolithic microwave integrated circuits. In this paper, system aspects of optically controlled array design are studied. In particular, two architectures for a 40 GHz array are outlined, and the main system-related issues are examined: power budget, synchronization in frequency and phase, and stochastic effects.

Herczfeld, P. R.; Kam, M.; Kunath, R. R.; Bhasin, K. B.; La Prade, Nick

1987-01-01

133

System architecture of MMIC-based large aperture arrays for space application  

NASA Technical Reports Server (NTRS)

The persistent trend to use millimeter-wave frequencies for satellite communications presents the challenge to design large-aperture phased arrays for space applications. These arrays, which comprise 100 to 10,000 elements, are now possible due to the advent of lightwave technology and the availability of monolithic microwave integrated circuits. In this paper, system aspects of optically controlled array design are studied. In particular, two architectures for a 40 GHz array are outlined, and the main system-related issues are examined: power budget, synchronization in frequency and phase, and stochastic effects.

Herczfeld, P. R.; Kam, M.; Kunath, R. R.; Bhasin, K. B.; Laprade, N.

1987-01-01

134

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

135

Spacecraft Conceptual Design for the 8-Meter Advanced Technology Large Aperture Space Telescope (ATLAST)  

NASA Technical Reports Server (NTRS)

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

Hopkins, Randall C.; Capizzo, Peter; Fincher, Sharon; Hornsby, Linda S.; Jones, David

2010-01-01

136

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

PubMed

Temporal focusing of spatially chirped femtosecond laser pulses overcomes previous limitations for ablating high aspect ratio features with low numerical aperture (NA) beams. Simultaneous spatial and temporal focusing reduces nonlinear interactions, such as self-focusing, prior to the focal plane so that deep (approximately 1 mm) features with parallel sidewalls are ablated at high material removal rates (25 microm(3) per 80 microJ pulse) at 0.04-0.05 NA. This technique is applied to the fabrication of microfluidic devices by ablation through the back surface of thick (6 mm) fused silica substrates. It is also used to ablate bone under aqueous immersion to produce craniotomies. PMID:20721196

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

2010-08-16

137

Large aperture single crystal ZnGeP 2 for high-energy applications  

NASA Astrophysics Data System (ADS)

Zinc germanium phosphide (ZGP), ZnGeP 2, is the non-linear optical crystal of choice for laser frequency conversion in the 2-8 ?m spectral range by virtue of its high non-linear coefficient ( d14=75 pm/V) and thermal conductivity (0.35 W/(cm K)) as well as reductions in near-infrared absorption achieved in crystals grown by the horizontal gradient freeze technique. Recently, the growth of high optical quality, single crystal ZGP boules with dimensions of 27×39×140 mm 3 has been demonstrated. A low-loss (1 0 0)-oriented ZGP sample measuring 30×30×22 mm 3 was fabricated from this boule size. By adjusting the seeding orientation in single crystal boules with dimensions of 17×30×140 mm 3, low-loss ZGP optical parametric oscillator (OPO) samples of 20×20×16 mm 3 have been produced. Previously, typical ZGP OPO samples were 6×6×15 mm 3. Besides allowing for larger aperture samples, the larger ZGP single crystals have the added benefit of lower absorption at both 2 ?m ( ?2 ?m <0.05 cm -1) and 1 ?m ( ?1 ?m ˜1.0 cm -1) than the smaller scale crystals. Improvements to the fabrication and polishing of ZGP samples resulted in an increased laser-induced damage threshold (LIDT). The LIDT of anti-reflection-coated samples at 2.05 ?m and 10 kHz pulse rate frequency was increased to 2 J/cm 2, which was double the previously measured value of 1 J/cm 2. The combination of increased aperture, lower absorption, and improved LIDT of ZGP has resulted in material better suited to high-energy applications.

Zawilski, Kevin T.; Schunemann, Peter G.; Setzler, Scott D.; Pollak, Thomas M.

2008-04-01

138

Aberration analysis for development of a large-aperture reflector by finite element  

NASA Astrophysics Data System (ADS)

The deformation of large- aperture optical mirror is induced by gravity. It is very important to analyze the support structure and format in grounding and testing. By finite element software, a ?620mm mirror is created and its theoretical analysis about three comparative testing programs of vertical support is proposed. Zernike polynomials are used to fit optical surface and separate corresponding aberrations. By reducing the aberrations with great impact on mirror, at the same time, RMS excel 0.025? (?=632.8nm) has been achieved. Experiments of three kinds of support verify that the entirely bound by strip is the best way in all supports. It affords a more scientific and rational support to large-diameter optical mirror reflection. Through research and analysis of support on large-diameter mirror by finite element, it provides a theory of design and guidance for the development and test of reflection mirror in future.

Peng, Yuanjing; Yuan, Lyjun

2009-05-01

139

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

140

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

141

Bragg reflectors for large optical aperture MEMS Fabry-Perot interferometers  

NASA Astrophysics Data System (ADS)

This paper presents the fabrication of large-aperture low-pressure chemical-vapour deposited (LPCVD) Bragg reflectors utilizing low-stress polysilicon (PolySi) and silicon-rich silicon nitride (SiN) ?/4-thin film stacks. These structures can function as the upper mirror in a MEMS FPI device. High aspect-ratio mirror membranes were successfully released for 5 - 10 mm diameter range by sacrificial SiO2 etching in HF vapour. Optical simulations are presented for the Bragg reflector test structures designed for FPIs operating in the NIR range and the properties such as release yield and mechanical stability of the released LPCVD deposited polySi-SiN mirror membranes are compared with similar released atomic layer deposited (ALD) Al2O3-TiO2 ?/4-thin film mirror stacks. The realization of these Bragg reflector structures is the first step in the process integration of large-aperture MEMS FPI for miniature NIR imaging spectrometers, which can be applied to a variety of applications ranging from medical imaging and diagnostics to spaceand environmental monitoring instrumentation.

Rissanen, Anna; Mannila, Rami; Antila, Jarkko

2012-05-01

142

Path-Average Rainfall Estimation From Optical Extinction Measurements Using a Large- Aperture Scintillometer  

NASA Astrophysics Data System (ADS)

We employ a Scintec BLS900 near infrared (880 nm) large aperture boundary layer scintillometer as path average rain gauge. The instrument was installed over a path of 2.4 km in Benin as part of the AMMA CATCH (African Monsoon Multidisciplinary Analysis) intensive observation period during 2006 and 2007. Measurements of the one minute average and variance of the received signal intensity from two transmitter disks of 462 LEDs each, operating at a pulse repetition rate of 5 Hz (i.e. 300 samples per minute), were collected for a few rainfall events that occurred during the dry season and several events during the wet season. Using estimates of the signal base level just before the start of the rain events, the optical extinction coefficient was estimated from the path integrated signal attenuation for each minute. The corresponding one minute path average rain rates were computed using a power law relation between the optical extinction coefficient and rain rate obtained from measurements of raindrop size spectra with an optical spectropluviometer. The estimated rain rates are compared to measurements from nearby rain gauges. Our results demonstrate the potential of optical extinction measurements from large aperture boundary layer scintillometers to obtain estimates of rainfall variability at high temporal resolution for hydrologically relevant spatial scales.

Uijlenhoet, R.; Cohard, J.; Gosset, M.

2008-12-01

143

Development of Large-Aperture, Light-Weight Fresnel Lenses for Gossamer Space Telescopes.  

National Technical Information Service (NTIS)

In order to examine more distant astronomical objects, with higher resolution, future space telescopes require objectives with significantly larger aperture than presently available. NASA has identified a progression in size from the 2.4m aperture objecti...

S. Dixit R. Hyde A. Weisberg J. Early M. Rushford J. Britten

2002-01-01

144

Preliminary Evaluation of Sensible Heat Flux Measurements From a Large Aperture Scintillometer Using Lysimetric Data  

NASA Astrophysics Data System (ADS)

The path integrating capabilities of scintillometers over several kilometers make it a potential tool that can bridge the gap between primary point based observations (lysimeters, Bowen ratio, or eddy covariance) and the demand for large-scale spatially averaged surface fluxes. Further, the spatial scale of sensible heat flux data collected from a scintillometer is comparable to the spatial resolution of satellite images. Therefore, scintillometer data may be useful for validating evapotranspiration maps based on satellite data. Numerous studies have evaluated the measurement accuracy of scintillometers using eddy covariance systems; however, the latter has energy balance closure problems up to 30%. The main objective of this study is to test the Large Aperture Scintillometer (LAS) using lysimetric data. The LAS monitors the sensible heat flux (H) and water vapor flux (LE) is calculated as a residual of the surface energy balance equation by monitoring net radiation (Rn) and soil heat flux (G) (LE=Rn+G-H). A Large Aperture Scintillometer (LAS) was deployed across two lysimeter fields planted with grain sorghum under dryland management conditions. The orientation of LAS was selected to have the path of the LAS perpendicular to the predominant wind direction and to avoid direct sun light on the lenses. The refractive index of air was monitored during the 2007 cropping season at 15-min. intervals, synchronized with weather station and lysimeter measurements. In addition, a net radiometer and three soil heat flux plates were installed near both the receiver and transmitter of the scintillometer as well as on two large monolithic lysimeters. Predicted water vapor fluxes from the scintillometer-net radiometer-heat flux plate setup were compared with lysimeter data. Preliminary results (three months of data) indicate that the LAS is a promising tool for deriving water vapor fluxes. However, further evaluation is needed under a variety of crop/weather conditions to fully assess its capability to accurately estimate spatially distributed water vapor fluxes.

Gowda, P. H.; Howell, T. A.; Scanlon, B. R.; Copeland, K. S.; Bush, K.

2007-12-01

145

Large-mode-area double-clad fibers for pulsed and CW lasers and amplifiers  

Microsoft Academic Search

The advent of double clad fiber technology has made high power lasers and amplifiers possible. However, the scalability of output powers can be limited by amplified spontaneous emission and nonlinear processes such as stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS). These limitations can be overcome by using low numerical apertures (NAs), large-mode areas (LMAs), novel index profiles and

David Machewirth; Victor Khitrov; Upendra Manyam; Kanishka Tankala; Adrian Carter; Jaroslaw Abramczyk; Julia Farroni; Douglas Guertin; Nils Jacobson

2004-01-01

146

Power scaling of cw high power fiber lasers based on large-mode-area fibers  

Microsoft Academic Search

In this paper, we report on a power scaling of stable cw ytterbium-doped high power fiber laser with 170 W output power based on large-mode-area fibers. Single transverse mode output is obtained from a 28 ?m core diameter low-numerical aperture fiber.

J. Limpert; A. Liem; T. Schreiber; H. Zellmer; A. Tunnermann

2003-01-01

147

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

148

Design of large aperture superferric quadrupole magnets for an in-flight fragment separator  

NASA Astrophysics Data System (ADS)

Superferric quadrupole magnets to be used for in-flight fragment separator have been designed. A quadrupole magnet triplet for beam focusing is placed in a cryostat together with superconducting correction coils. To maximize acceptance of rare isotope beams produced by projectile fragmentation, it is essential to use large-aperture quadrupole magnets. The pole tip radius is 17 cm in the current design, and we tried to enlarge the aperture with 3D analysis on magnetic fields. In the front end of the separator, where a target and beam dump are located, we plan to use two sets of quadrupole triplets made of high-Tc superconductor (HTS) operating at 20-50 K considering high radiation heat load. The HTS magnet will use warm iron poles. Both low-Tc and high-Tc superconductors are acquired for test winding, and two kinds of dewar and cryostat are under construction to perform the coil and magnet tests. The magnetic design of superferric quadrupole is mainly discussed.

Zaghloul, Aziz; Kim, Dogyun; Kim, Jangyoul; Kim, Mijung; Kim, Myeongjin; Yun, Chongcheoul; Kim, Jongwon

2014-01-01

149

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

150

A large-aperture space telescope for infrared and submillimeter astronomy  

NASA Technical Reports Server (NTRS)

The Large Aperture Telescope (LAT), which will have a diameter of 10-30 m and will operate in the 2-1000 micron wavelength range, is described. It is noted that the LAT could be carried into orbit with a single launch of the Space Transportation System and semiautomatically deployed as a free flyer with a nominal 10-yr mission duration. Servicing and instrument changes would be made at 2-yr intervals. It is pointed out that the LAT would have to be placed above the earth's atmosphere to avoid both the absorption that occurs through much of the infrared and submillimeter and the turbulence which limits spatial resolution. Important technical considerations for the LAT are discussed; they include the telescope optical form, the primary mirror material, figure control techniques, the deployment techniques, and thermal control. The science objectives and rationale for the LAT are discussed and various hardware techniques and concepts for its implementation are described.

Murphy, J. P.; Kiya, M. K.; Werner, M.; Swanson, P. N.; Kuiper, T. B. H.; Batelaan, P. D.

1980-01-01

151

Advanced Technology Large-Aperture Space Telescope: Science Drivers and Technology Developments  

NASA Technical Reports Server (NTRS)

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8- to 16-m ultraviolet optical near Infrared space observatory for launch in the 2025 to 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-marcsec angular resolution, diffraction limited imaging at 0.5 micron wavelength, minimum collecting area of 45 sq m, high sensitivity to light wavelengths from 0.1 to 2.4 micron, 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 that of current generation observatory-class space missions.

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

2012-01-01

152

Analysis of torque mounting configuration for nonlinear optics with large aperture  

NASA Astrophysics Data System (ADS)

Motivated by the need of decreasing the gravitational distortion and stress of the nonlinear optics with large aperture, as well as increasing the second harmonic generation (SHG) efficiency, a torque mounting configuration was proposed, where the external load brought about the torque to mitigate the distortion and stress. The distortion and stress were calculated by using the Finite Element Method (FEM), and discussed from the view of torque. The effects of the design parameters, namely the external load, loading width, shim plate location and shim plate width, were studied; the changing trends of the distortion and stress with these varying parameters were analyzed. Furthermore, the phase mismatches induced by the distortion and stress were calculated; finally, the SHG efficiency was solved considering the phase mismatch.

Liang, Yingchun; Su, Ruifeng; Liu, Haitao; Lu, Lihua

2014-06-01

153

Horizon: A Proposal for Large Aperture, Active Optics in Geosynchronous Orbit  

NASA Technical Reports Server (NTRS)

In 1999, NASA's New Millennium Program called for proposals to validate new technology in high-earth orbit for the Earth Observing-3 (NMP EO3) mission to fly in 2003. In response, we proposed to test a large aperture, active optics telescope in geosynchronous orbit. This would flight-qualify new technologies for both Earth and Space science: 1) a future instrument with LANDSAT image resolution and radiometric quality watching continuously from geosynchronous station, and 2) the Next Generation Space Telescope (NGST) for deep space imaging. Six enabling technologies were to be flight-qualified: 1) a 3-meter, lightweight segmented primary mirror, 2) mirror actuators and mechanisms, 3) a deformable mirror, 4) coarse phasing techniques, 5) phase retrieval for wavefront control during stellar viewing, and 6) phase diversity for wavefront control during Earth viewing. Three enhancing technologies were to be flight- validated: 1) mirror deployment and latching mechanisms, 2) an advanced microcontroller, and 3) GPS at GEO. In particular, two wavefront sensing algorithms, phase retrieval by JPL and phase diversity by ERIM International, were to sense optical system alignment and focus errors, and to correct them using high-precision mirror mechanisms. Active corrections based on Earth scenes are challenging because phase diversity images must be collected from extended, dynamically changing scenes. In addition, an Earth-facing telescope in GEO orbit is subject to a powerful diurnal thermal and radiometric cycle not experienced by deep-space astronomy. The Horizon proposal was a bare-bones design for a lightweight large-aperture, active optical system that is a practical blend of science requirements, emerging technologies, budget constraints, launch vehicle considerations, orbital mechanics, optical hardware, phase-determination algorithms, communication strategy, computational burdens, and first-rate cooperation among earth and space scientists, engineers and managers. This manuscript presents excerpts from the Horizon proposal's sections that describe the Earth science requirements, the structural -thermal-optical design, the wavefront sensing and control, and the on-orbit validation.

Chesters, Dennis; Jenstrom, Del

2000-01-01

154

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

NASA Astrophysics Data System (ADS)

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. This allowed us to compare H and the direct scintillometer output, the refractive index structure parameter, {Cn2} . Furthermore, spectral analysis was performed on the raw scintillometer signal to investigate the characteristics of the error. Firstly, correlation coefficients ? 0.99 confirm the robustness of the scintillometer method, and secondly we discovered two systematic errors: the low-{Cn2} error and the high-{Cn2} error. The low-{Cn2} error is a non-linear error that is caused by high-frequency noise, and we suspect the error to be caused by the calibration circuit in the receiver. It varies between each K&ZLAS, is significant for H ? 50 W m-2, and we propose a solution to remove this error using the demodulated signal. The high-{Cn2} error identified by us is the systematic error found in previous studies. We suspect this error to be caused by poor focal alignment of the receiver detector and the transmitter light-emitting diode that causes ineffective use of the Fresnel lens in the current Kipp & Zonen design. It varies between each K&ZLAS (35% up to 240%) and can only be removed by comparing with a reference scintillometer in the field.

van Kesteren, B.; Hartogensis, O. K.

2011-03-01

155

Application of image entropy evaluation function for the leveling of large aperture components in auto defects detecting  

NASA Astrophysics Data System (ADS)

In large aperture component's dark-field scattering defects imaging system, the component's size is large and part with a wedge. When the component is in the completely level position, the surface defects image can be clearly acquired by a high magnification microscope. Otherwise, fuzzy defects image would be gained because of defocusing which makes digital identification can't be able to be done. For the problem of leveling large aperture, wedge component, this paper proposes a method that using image information entropy as focusing evaluation function for leveling large aperture components. Firstly, in three different points of component surface acquiring multi-images by the same continuous steps. Then calculating the images' entropy and fitting a curve to it. Based on minimum image information entropy value criterion, the focal plane can be found and each point's defocusingamount of the fist acquisition position can be gained. Relay on the relation model of acquisition points, adjust points and defocusingamount that has been built, each adjust point's adjustment can be got. The component's level position can be achieved by adjusting the adjust points. In the experiment that using a high magnification (of 16) microscope scans over the whole surface of the component with the size of 430mm×430mm. The image microscope is always in the depth of focus which shows that the leveling precision has achieved 20?m. Until now, this method has been successfully used in large aperture component's dark-field scattering defects imaging system.

Cao, Pin; Liu, Dong; Zhao, Peng; Yang, Yong-ying; Wang, Shi-tong

2012-10-01

156

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

157

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

NASA Technical Reports Server (NTRS)

We are developing a micro-machined electrostatically actuated Fabry-Perot tunable filter with a large clear aperture for application in high through-put wide-field imaging spectroscopy and lidar systems. In the first phase of this effort, we are developing key components based on coupled electro-mechanical simulations. In particular, the movable etalon plate design leverages high coating stresses to yield a flat surface in drum-head tension over a large diameter (12.5 mm). In this approach, the cylindrical silicon movable plate is back etched, resulting in an optically coated membrane that is suspended from a thick silicon support ring. Understanding the interaction between the support ring, suspended membrane, and coating is critical to developing surfaces that are flat to within stringent etalon requirements. In this work, we present the simulations used to develop the movable plate, spring suspension system, and electrostatic actuation mechanism. We also present results from tests of fabricated proof of concept components.

Kuhn, Jonathan L.; Barclay, Richard B.; Greenhouse, Matthew A.; Mott, D. Brent; Satyapal, Shobita; Powers, Edward I. (Technical Monitor)

2000-01-01

158

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

NASA Astrophysics Data System (ADS)

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 entire catchment. The objective of this presentation is to assess whether measured sensible heat fluxes from a LAS over a long distance (9.5 km) can be assumed to be valid for a 102.3 km2 heterogeneous catchment. Therefore, a fully process-based water and energy balance model with a spatial resolution of 50 m has been thoroughly calibrated and validated for the Bellebeek catchment in Belgium. A footprint analysis has been performed. It has been found that good estimates of the temporally variable surface roughness parameters are needed in order for the LAS to provide adequate measurements. The modeled H within the footprint has been found to be very similar to the scintillometer observations, and the catchment averaged H. When the scintillometer path is reduced to 1 km, the validity of this statement depends on the location of the scintillometer path.

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

2010-05-01

159

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

National Technical Information Service (NTIS)

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 moi...

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

2001-01-01

160

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

SciTech Connect

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

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

2010-04-06

161

Design studies of large aperture, high-resolution Earth science microwave radiometers compatible with small launch vehicles  

NASA Technical Reports Server (NTRS)

High-spatial-resolution microwave radiometer sensing from space with reasonable swath widths and revisit times favors large aperture systems. However, with traditional precision antenna design, the size and weight requirements for such systems are in conflict with the need to emphasize small launch vehicles. This paper describes tradeoffs between the science requirements, basic operational parameters, and expected sensor performance for selected satellite radiometer concepts utilizing novel lightweight compactly packaged real apertures. Antenna, feed, and radiometer subsystem design and calibration are presented. Preliminary results show that novel lightweight real aperture coupled with state-of-the-art radiometer designs are compatible with small launch systems, and hold promise for high-resolution earth science measurements of sea ice, precipitation, soil moisture, sea surface temperature, and ocean wind speeds.

Schroeder, Lyle C.; Bailey, M. C.; Harrington, Richard F.; Kendall, Bruce M.; Campbell, Thomas G.

1994-01-01

162

Engineering comparison between CCD and the variable aperture methods for measuring the divergence angle of laser beam  

NASA Astrophysics Data System (ADS)

Laser beam divergence angle of laser beams is an important parameter in the laser characterization. There are many methods of beam divergence determination. The most common way is to use a device based on CCD described in the International Standard ISO11146-1 "Test methods for laser beam parameters: Beam widths, divergence angle and beam propagation factor". Moreover, in ISO11146-3 it also presents another alternative method - the variable apertures to measure beam divergence. According to ISO11146, we developed a novel automated laser measurement system with two methods for laser beam characterization, especially for synchronously determining beam divergence. It is also presented for the comparison of two methods measuring beam divergence, while their respective advantages and disadvantages are pointed out in this paper. It has been proved in practice that the auto measurement system based on two methods is an affective and convenient instrument for determining beam divergence.

Xing, Ji-chuan; Song, Yan

2012-10-01

163

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

164

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

165

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

166

A High-Emissivity Blackbody with Large Aperture for Radiometric Calibration at Low-Temperature  

NASA Astrophysics Data System (ADS)

A newly designed high-emissivity cylindrical blackbody source with a large diameter aperture (54 mm), an internal triangular-grooved surface, and concentric grooves on the bottom surface was immersed in a temperature-controlled, stirred-liquid bath. The stirred-liquid bath can be stabilized to better than 0.05°C at temperatures between 30 °C and 70 °C, with traceability to the ITS-90 through a platinum resistance thermometer (PRT) calibrated at the fixed points of indium, gallium, and the water triple point. The temperature uniformity of the blackbody from the bottom to the front of the cavity is better than 0.05 % of the operating temperature (in °C). The heat loss of the cavity is less than 0.03 % of the operating temperature as determined with a radiation thermometer by removing an insulating lid without the gas purge operating. Optical ray tracing with a Monte Carlo method (STEEP 3) indicated that the effective emissivity of this blackbody cavity is very close to unity. The size-of-source effect (SSE) of the radiation thermometer and the effective emissivity of the blackbody were considered in evaluating the uncertainty of the blackbody. The blackbody uncertainty budget and performance are described in this paper.

Ko, Hsin-Yi; Wen, Bor-Jiunn; Tsa, Shu-Fei; Li, Guo-Wei

2009-02-01

167

Dynamic characteristics analysis of a large-aperture rotating prism with adjustable radial support.  

PubMed

Support elements as key components in performing the opto-mechanical function have been an important topic for optical system development. Focusing on a rotation prism with a large aperture and asymmetric loading, a radial multi-segment support is developed to solve the dynamic mounting issue. In order to explore the actual surface deformations over the full rotation, a novel dynamic analysis method to extract the transient load spectrum is established to access the surface deformations, including dynamic load extraction to connect varying loads with corresponding rotation positions, typical position analysis to obtain maximum deformation values, and vibration analysis. The results show that a maximum peak-to-valley value on the plane side reaches 103.16 nm when the prism rotates to 159.84°, and that of the wedge side is 74.38 nm when the prism rotates to 213.84°, both of which are less than ?/4 (?=632.8 nm). However, when excited by the external loads with response frequency, the surface deformations become more serious. Because the dynamic characteristics obtained can reflect the actual usage situation, the proposed method is preferable for system development. PMID:24787184

Li, Anhu; Wang, Wei; Bian, Yongming; Liu, Liren

2014-04-01

168

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

169

Large-aperture BVRJK photometry of rich Abell clusters - Constraints on dark matter  

SciTech Connect

This paper presents results of large (arcmin), single-aperture JK photometry and CCD BVR photometry on and near the centers of distant (Z between values of 0.14 and 0.20), rich Abell clusters. The colors of the integrated light of the cores of these clusters are consistent with those of nearby E and S0 galaxies. The absence of anomalous infrared emission provides the strongest constraint to date on the possible stellar make-up of the dark matter in clusters of galaxies, requiring K band (2.2 microns) mass-to-light ratios of the dark matter of (M/L)K not less than 400h. Indeed, no more than 5/h percent of the dark mass can be made of objects with mass greater than 0.1 solar mass. Although these results do not require a contribution of nonbaryonic matter, they provide some constraints on the mass function for baryonic objects which might compose the dark matter. These conclusions do not depend on the detailed distribution of the dark matter in the clusters. 35 refs.

Uson, J.M.; Boughn, S.P. (National Radio Astronomy Observatory, Socorro, NM (USA) Haverford College, PA (USA))

1991-03-01

170

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.

Rambikur, Evan H.; Chavez, Jose L.

2014-01-01

171

Test results of a single aperture 10 tesla dipole model magnet for the Large Hadron Collider  

Microsoft Academic Search

A single aperture dipole magnet has been developed with a design magnetic field of 10 tesla by using Nb-Ti\\/Cu conductor to be operated at 1.8 K in pressurized super fluid helium, The magnet features double shell coil design by using high keystone Rutherford cable and compact non-magnetic steel collars to be adaptable in split\\/symmetric coil\\/collar design for twin aperture dipoles.

Akira Yamamoto; Takakazu Shintomi; Nobuhiro Kimura; Yoshikuni Doi; Tomiyoshi Haruyama; Norio Higashi; Hiromi Hirabayashi; Hiroshi Kawamata; Seog-Whan Kim; Takamitsu M. Kobayashi; Yasuhiro Makida; Toru Ogitsu; Norihito Ohuchi; Ken-ichi Tanaka; Akio Terashima; Kiyosumi Tsuchiya; Hiroshi Yamaoka; Giorgio Brianti; Daniel Leroy; Romeo Perin; Shoichi Mizumaki; Shuichi Kato

1996-01-01

172

Imaging the midcontinent rift beneath Lake Superior using large aperture seismic data  

SciTech Connect

The authors present a detailed velocity model across the 1.1 billion year old Midcontinent Rift System (MRS) in central Lake Superior. The model was derived primarily from onshore-offshore large-aperture seismic and gravity data. High velocities obtained within a highly reflective half-graben that was imaged on coincident seismic reflection data demonstrate the dominantly magic composition of the graben fill and constrain its total thickness to be at least 30 km. Strong wide-angle reflections are observed from the lower crust and Moho, indicating that the crust is thickest (55-60 km) beneath the axis of the graben. The total crustal thickness decreases rapidly to about 40 km beneath the south shore of the lake and decreases more gradually to the north. Above the Moho is a high-velocity lower crust interpreted to result from syn-rift basaltic intrusion into and/or underplating beneath the Archean lower crust. The lower crust is thickest beneath the axis of the main rift half-graben. A second region of thick lower crust is found approximately 100 km north of the axis of the rift beneath a smaller half graben that is interpreted to reflect an earlier stage of rifting. The crustal model presented here resembles recent models of some passive continental margins and is in marked contrast to many models of both active and extinct Phanerozoic continental rift zones. It demonstrates that the Moho is a dynamic feature, since the pre-rift Moho is probably within or above the high-velocity lower crust, whereas the post-rift Moho is defined as the base of this layer. In the absence of major tectonic activity, however, the Moho is very stable, since the large, abrupt variations in crustal thickness beneath the MRS have been preserved for at least a billion years.

Trehu, A.; Shay, J. (Oregon State Univ., Corvallis (United States)); Morel-a-l'Huissier, P.; Milkereit, B. (Geological Survey of Canada, Ottawa, Ontario (Canada)); Meyer, R.; Jefferson, T.; Shih, X.R. (Univ. of Wisconsin, Madison (United States)); Karl, J. (Univ. of Saskatchewan, Saskatoon (Canada)); Mereu, R.; Epili, D. (Univ. of Wisconsin, Oshkosh (United States)); Sexton, J.; Wendling, S. (Univ. of Western Ontario, London (Canada)); Hajnal, Z.; Chan, W.K. (Southern Illinois Univ., Carbondale (United States)); Hutchison, D. (Geological Survey, Woods Hole, MA (United States))

1991-04-01

173

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

174

Solar neutrino detection utilizing a variant of a coded aperture on a large scale (HERON)  

NASA Astrophysics Data System (ADS)

A neutrino-electron scattering occuring in liquid 4 He results in an energetic electron that deposits its energy into the liquid through various mechanics. Some of this energy deposition is released in the form of detectable signals, among which is the scintillation signals: photons in the extreme ultraviolet range. The isotropic scintillation signal can be detected and analysed to reconstruct the energy and position of the original electron in the neutrino scattering, which provides information regarding the energy spectrum of the neutrino flux itself. In one proposed version of a neutrino detector, the scintillation signals are observed using ~2000 sensors capable of detecting individual 16 eV photons. Each of these sensor is a calorimeter in the shape of a thin metallic film deposited on a large wafer. The wafers are arranged in two parallel planes above the liquid body, forming a coded-aperture imaging array. Large numbers of Monte Carlo events are generated with various sets of design parameters of the system, and the systematic and statistical behavior is studied to decide the optimal design and its accuracy in determining solar neutrino fluxes. This method of detecting scintillation signals is intended to be used in HERON, a proposed detector for low energy solar neutrinos-- pp and 7 Be neutrinos from the Sun. The study shows that, at temperatures below 40 mK, with ~40 ton-year worth of fiducial events from the 4 He body, the pp and 7 Be solar neutrino fluxes can be determined with a combined systematic and statistical error of < 1.5% for total flux, and separately < 1.7% for pp and < 3.5% for 7 Be.

Huang, Yun-Hu

2007-08-01

175

Imaging the midcontinent rift beneath Lake Superior using large aperture seismic data  

NASA Astrophysics Data System (ADS)

We present a detailed velocity model across the 1.1 billion year old Midcontinent Rift System (MRS) in central Lake Superior. The model was derived primarily from onshore-offshore large-aperture seismic and gravity data. High velocities obtained within a highly reflective half-graben that was imaged on coincident seismic reflection data demonstrate the dominantly mafic composition of the graben fill and constrain its total thickness to be at least 30km. Strong wide-angle reflections are observed from the lower crust and Moho, indicating that the crust is thickest (55-60km) beneath the axis of the graben. The total crustal thickness decreases rapidly to about 40 km beneath the south shore of the lake and decreases more gradually to the north. Above the Moho is a high-velocity lower crust interpreted to result from syn-rift basaltic intrusion into and/or underplating beneath the Archean lower crust. The lower crust is thickest beneath the axis of the main rift half-graben. A second region of thick lower crust is found approximately 100km north of the axis of the rift beneath a smaller half graben that is interpreted to reflect an earlier stage of rifting. The crustal model presented here resembles recent models of some passive continental margins and is in marked contrast to many models of both active and extinct Phanerozoic continental rift zones. It demonstrates that the Moho is a dynamic feature, since the pre-rift Moho is probably within or above the high-velocity lower crust, whereas the post-rift Moho is defined as the base of this layer. In the absence of major tectonic activity, however, the Moho is very stable, since the large, abrupt variations in crustal thickness beneath the MRS have been preserved for at least a billion years.

Tréhu, A.; Morel-à-l'Huissier, P.; Meyer, R.; Hajnal, Z.; Karl, J.; Mereu, R.; Sexton, J.; Shay, J.; Chan, W.-K.; Epili, D.; Jefferson, T.; Shih, X.-R.; Wendling, S.; Milkereit, B.; Green, A.; Hutchinson, D.

1991-04-01

176

Speckle random pattern laser: Self-formation of looped lasing paths and dynamic effects in a wide-aperture thin-slice solid-state laser  

Microsoft Academic Search

We observed self-formation of looped random lasing paths in a laser-diode-pumped wide-aperture thin-slice solid-state laser with imperfect reflective end surfaces. Observed lasing patterns, resulting from random scatterers on the surfaces, showed transverse intensity distributions possessing exponential spatial autocorrelation functions. It is shown that such a speckle type of lasing pattern formation takes place when the pump position is tuned such

Kenju Otsuka; Yoshihiko Miyasaka; Kana Nemoto

2007-01-01

177

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

SciTech Connect

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

McCarville, T; Soufli, R; Pivovaroff, M

2011-03-02

178

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

179

Full-aperture tilt measurement technique with a laser guide star  

NASA Astrophysics Data System (ADS)

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

Belen'kii, Mikhail S.

1995-06-01

180

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

181

Surface accuracy analysis and mathematical modeling of deployable large aperture elastic antenna reflectors  

NASA Astrophysics Data System (ADS)

One class of deployable large aperture antenna consists of thin light-weight parabolic reflectors. A reflector of this type is a deployable structure that consists of an inflatable elastic membrane that is supported about its perimeter by a set of elastic tendons and is subjected to a constant hydrostatic pressure. A design may not hold the parabolic shape to within a desired tolerance due to an elastic deformation of the surface, particularly near the rim. We can compute the equilibrium configuration of the reflector system using an optimization-based solution procedure that calculates the total system energy and determines a configuration of minimum energy. Analysis of the equilibrium configuration reveals the behavior of the reflector shape under various loading conditions. The pressure, film strain energy, tendon strain energy, and gravitational energy are all considered in this analysis. The surface accuracy of the antenna reflector is measured by an RMS calculation while the reflector phase error component of the efficiency is determined by computing the power density at boresight. Our error computation methods are tailored for the faceted surface of our model and they are more accurate for this particular problem than the commonly applied Ruze Equation. Previous analytical work on parabolic antennas focused on axisymmetric geometries and loads. Symmetric equilibria are not assumed in our analysis. In addition, this dissertation contains two principle original findings: (1) the typical supporting tendon system tends to flatten a parabolic reflector near its edge. We find that surface accuracy can be significantly improved by fixing the edge of the inflated reflector to a rigid structure; (2) for large membranes assembled from flat sheets of thin material, we demonstrate that the surface accuracy of the resulting inflated membrane reflector can be improved by altering the cutting pattern of the flat components. Our findings demonstrate that the proper choice of design parameters can increase the performance of inflatable antennas, opening up new antenna applications where higher resolution and greater sensitivity are desired. These include space applications involving high data rates and high bandwidths, such as lunar surface wireless local networks and orbiting relay satellites. A light-weight inflatable antenna is also an ideal component in aerostat, airship and free balloon systems that supports communication, surveillance and remote sensing applications.

Coleman, Michael J.

182

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

SciTech Connect

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

Tatchyn, Roman; /SLAC

2011-08-12

183

Properties of a matched halide glass pair for the fabrication of large numerical aperture core-cladding preform structures  

Microsoft Academic Search

A large numerical aperture core-cladding structure is required for drawing single-mode fibers for the fabrication of Pr-doped 1.3 ?m optical fibre amplifiers. Geometrical restrictions on fibres and hence on preforms are important for confining the optical pump power into a small core volume (3–5 ?m diameter) in order to promote efficient amplification at 1.3 ?m. Cadmium mixed halide glasses exhibiting

Animesh Jha; Sophie Jordery; Mira Naftaly

1995-01-01

184

Processing of multi-aperture SAR to produce fine-resolution images of arbitrarily large extent  

Microsoft Academic Search

The spatial extent that can be accurately imaged by a synthetic aperture radar (SAR) is unfortunately limited. This restriction results from the fact that the number of independent pixel estimates produced by a SAR is constrained by the number of independent measurements that it collects. The solution is to increase the number of independent sensor measurements, without modifying sensor resolution.

James M. Stiles; Nathan Goodman

2001-01-01

185

Origins of High-frequency Scattered Waves Near PKKP From Large Aperture Seismic Array Data  

NASA Astrophysics Data System (ADS)

Observations of high--frequency ( ~1 Hz) teleseismic scattered waves provide constraints for modelling fine--scale ( ~10 km) core--mantle boundary (CMB) topography and fine--scale mantle heterogeneity. The majority of previous modelling relied on precursors to PKPdf, but here we present an underutilized data set that will aid future research into Earth's fine--scale structure: scattered waves in the vicinity of PKKP. The data set consists of slant stacks generated from Large Aperture Seismic Array (LASA) data from 36 earthquakes and 6 explosions in the range 30o to 129o. Although precursors to PKKP have been studied, we examine stacks in a larger time--distance window and find that waves previously associated with scattering along the PKKP raypath actually originate from near surface scattering of PKP to P (PKP.P). In addition to these near surface contributions, three types of waves scattered at the CMB or in the overlying mantle explain the observed slownesses and onset times, including: forward scattering of PKKP between its P and KKP legs (P.KKP and PKK.P), back scattering of PKKP between its PK and KP legs (PK.KP), and similarly back scattering of SKKP energy between its SK and KP legs (SK.KP). The LASA stacks show where and when these waves are detected and where they are contaminated by the surface--scattered P.PKP. In addition, the stacks image the scattered waves' amplitude and slowness variations with time. P.KKP waves are observed near 128o (just beyond the PKKP ``b'' caustic) and last ~100 s. Close to 113o, SK.KP waves rise above the noise ~100 s before onset time of the main SKKP arrival. Observations of PK.KP span 30o to 100o. However, at distances greater than 50o they suffer from P.PKP contamination. At distances less than 50o PK.KP last for ~300 s. This is ~150 s longer than the maximum ray-theoretical prediction for waves scattered at the CMB, indicating possible contributions from the overlying mantle.

Earle, P. S.; Vidale, J. E.

2001-05-01

186

52 mJ narrow-bandwidth degenerated optical parametric system with a large-aperture periodically poled MgO:LiNbO3 device  

NASA Astrophysics Data System (ADS)

We have demonstrated efficient, high-energy, narrow-spectral-bandwidth 2.128 ?m pulse generation by use of periodically poled MgO:LiNbO3 devices with a 36 mm length and a 5 mm×5 mm large aperture. A free-running degenerated optical parametric oscillator (OPO) pumped with a Q-switched 1.064 ?m Nd:YAG laser exhibits a high slope efficiency of 75% and an optical-to-optical conversion efficiency of 70% with a broad spectral bandwidth (>100 nm). In a configuration with a spectrally narrowed master oscillator followed by a power amplifier, we have achieved an output pulse energy of 52 mJ with a spectral bandwidth of less than 2 nm at the degeneracy point. The total optical-to-optical conversion efficiency of the system reached 50%.

Saikawa, J.; Fujii, M.; Ishizuki, H.; Taira, T.

2006-11-01

187

Generation of 1.5 microJ single-cycle terahertz pulses by optical rectification from a large aperture ZnTe crystal.  

PubMed

We demonstrate the generation muJ-level, single-cycle terahertz pulses by optical rectification from a large-aperture ZnTe single crystal wafer. Energies up to 1.5 muJ per pulse and a spectral range extending to 3 THz were obtained using a 100 Hz Ti:sapphire laser source and a 75-mmdiameter, 0.5-mm-thick, (110) ZnTe crystal, corresponding to an average power of 150 muW and an energy conversion efficiency of 3.1 x 10(-5). We also demonstrate real-time imaging of the focused terahertz beam using a pyroelectric infrared camera. PMID:19550589

Blanchard, F; Razzari, L; Bandulet, H C; Sharma, G; Morandotti, R; Kieffer, J C; Ozaki, T; Reid, M; Tiedje, H F; Haugen, H K; Hegmann, F A

2007-10-01

188

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

189

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

190

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

191

Two-dimensional laser collision-induced fluorescence measurements of plasma properties near an RF plasma cathode extraction aperture  

NASA Astrophysics Data System (ADS)

A dense plasma structure was observed to form near the extraction aperture of a helium RF plasma cathode. Laser collision-induced fluorescence was used to generate two-dimensional spatial maps of the electron density and the effective electron temperature within the structure over a range of operating conditions. The aperture plasma reached densities nearly an order of magnitude higher than the surrounding bulk plasma. The sharp spatial change in density at the plasma structure boundary suggests the presence of a double layer sheath. Higher temperature electrons were also observed at the periphery of the plasma structure. Variations in the observed plasma structure with extracted electron current were found to be consistent with reported low pressure anode spot behavior. Measurements of plasma density within and at the boundary of the structure, and the dependence of these on the current extracted across the external gap, are compared with calculations and discussed.

Weatherford, B. R.; Barnat, E. V.; Foster, J. E.

2012-10-01

192

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

SciTech Connect

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

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

1989-04-01

193

Wave field processing of data from a large-aperture seismic experiment in southwestern Oklahoma  

NASA Astrophysics Data System (ADS)

Data from a wide-aperture survey performed in January 1985 in southwestern Oklahoma have been processed using prestack imaging, and the images are interpreted to reveal a new picture of the crustal structure in the Wichita Uplift and the Anadarko Basin. As the data were in recording apertures of approximately 90 km, it was necessary to develop new processing concepts and software. A complete new imaging system, based on common source gathers, was conceived, implemented, tested, and applied to these data. The heart of the system consists of velocity estimation by slant stacking, and acoustic prestack reverse time, finite difference migration. The migration produces reflectivity images in regions of 50 km × 100 km, has no dip restrictions, and operates in an arbitrarily complicated two-dimensional velocity distribution. For comparison the data were also processed using standard common midpoint processing, but this is a less valid approach for wide-aperture data. The main ambiguities and limitations in processing and interpretation are a consequence of the small number of shots. Processing and interpretation of the data provide a new picture of the subsurface structure of southwestern Oklahoma. The environment is clearly compressive with thrust faulting as the main accommodating mechanism in the upper and central crust. Beneath a possible detachment zone at ?30 km depth the lower crust has responded to the compression by thickening by ?50%. The Moho is interpreted to be ?45 km in depth beneath the thrust zone, shallowing to ?40 km beneath the Wichita Uplift and the Anadarko Basin.

Chang, Wen-Fong; McMechan, George A.; Keller, G. Randy

1989-02-01

194

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

NASA Technical Reports Server (NTRS)

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

Greenhouse, Matt; Mott, Brent; Powell, Dan; Barclay, Rich; Hsieh, Wen-Ting

2002-01-01

195

A Large Sparse Aperture Densified Pupil Hypertelescope Concept for Ground Based Detection of Extra-Solar Earth-Like Planets  

NASA Technical Reports Server (NTRS)

A concept is presented for a large (10 - 30 meter) sparse aperture hyper telescope to image extrasolar earth-like planets from the ground in the presence of atmospheric seeing. The telescope achieves high dynamic range very close to bright stellar sources with good image quality using pupil densification techniques. Active correction of the perturbed wavefront is simplified by using 36 small flat mirrors arranged in a parabolic steerable array structure, eliminating the need for large delat lines and operating at near-infrared (1 - 3 Micron) wavelengths with flats comparable in size to the seeing cells.

Gezari, D.; Lyon, R.; Woodruff, R.; Labeyrie, A.; Oegerle, William (Technical Monitor)

2002-01-01

196

Synthetic aperture compression scheme for multi-petawatt high energy laser  

Microsoft Academic Search

An original synthetic aperture compressor scheme is proposed for multi-kilojoule petawatt beam. This scheme uses two compressor stages with multi-dielectric gratings allowing suppressing the mosaic of gratings. The main technical issues are detailed.

N. Blanchot; A. Cotel; C. Le Blanc; G. Marre; S. Montant; J. Néauport; C. Rouyer; C. Sauteret; L. Videau

2006-01-01

197

Multilens array for GEKKO XII glass laser system with circular aperture spherical element lens  

Microsoft Academic Search

A two-dimensional multi-lens array of 350 mm in diameter with 37 pieces of spherical element lenses is tested for improving the irradiation uniformity of the ICF target. Circular and hexagonal shapes of element lens aperture have been examined. The circular aperture is chosen for eliminating azimuthally asymmetric intensity distribution in the beam pattern. An approximate flat-top intensity distribution has been

Takahisa Jitsuno; N. Nishi; K. Tsubakimoto; Masahiro Nakatsuka; Sadao Nakai

1995-01-01

198

Numerical aperture limits on efficient ball lens coupling of laser diodes to single-mode fibers with defocus to balance spherical aberration  

Microsoft Academic Search

The potential capabilities and limitations of single ball lenses for coupling laser diode radiation to single-mode optical fibers have been analyzed; parameters important to optical communications were specifically considered. These parameters included coupling efficiency, effective numerical apertures, lens radius, lens refractive index, wavelength, magnification in imaging the laser diode on the fiber, and defocus to counterbalance spherical aberration of the

R. Gale Wilson

1994-01-01

199

Speckle random pattern laser: Self-formation of looped lasing paths and dynamic effects in a wide-aperture thin-slice solid-state laser  

SciTech Connect

We observed self-formation of looped random lasing paths in a laser-diode-pumped wide-aperture thin-slice solid-state laser with imperfect reflective end surfaces. Observed lasing patterns, resulting from random scatterers on the surfaces, showed transverse intensity distributions possessing exponential spatial autocorrelation functions. It is shown that such a speckle type of lasing pattern formation takes place when the pump position is tuned such that the surface irregularity possesses an exponential autocorrelation function whose delay length is smaller than the lasing beam diameter.

Otsuka, Kenju; Miyasaka, Yoshihiko [Department of Human and Information Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292 (Japan); Nemoto, Kana [Department of Physics, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292 (Japan)

2007-06-15

200

Optical Design for the Optimum Solid Immersion Lens with High Numerical Aperture and Large Tolerance  

NASA Astrophysics Data System (ADS)

Super hemispherical solid immersion lens system becomes a matter of interest due to its high numerical aperture (NA) gain. However, because of the instability of the aplanatic condition, even small amount of alignment error can easily lower the optical performance. To overcome the instability while maintaining high NA gain, we suggest an optimum solid immersion lens (opti-SIL) system which combines the advantages of both super hemispherical SIL (hyper-SIL) and hemispherical SIL (hemi-SIL). Exemplary designs and simulation results of the tolerance analysis show that opti-SIL system has much higher tolerances to various performance-lowering factors than hyper-SIL, even with relatively small NA resignation.

Choi, Narak; Shim, Seongbo; Milster, Tom D.; Kim, Jaisoon

2007-06-01

201

Periodic self-wave structures in a wide-aperture laser with frequency detuning. I. Bifurcation analysis  

SciTech Connect

A theoretical investigation is reported of the stability of a homogeneous transverse distribution of lasing in a wide-aperture Fabry - Perot cavity. It is shown that when the detuning of the lasing frequency from the centre of the gain line of the active medium is negative, the conditions may be favourable for the Andronov - Hopf bifurcation. This leads to the appearance of periodic transverse wave structures. The main parameters of these waves (velocity, period, amplitude, growth increment) are found. It is also shown that a transition of a periodic wave pattern into a chaotic one is possible with increase in the wave amplitude. (laser fields and cavities)

Zaikin, A P; Molevich, N E [Samara Branch of the P.N. Lebedev Physics Institute, Russian Academy of Sciences, Samara (Russian Federation); Kurguzkin, A A [S.P. Korolev Samara State Aerospace University, Samara (Russian Federation)

1999-06-30

202

Diffraction-limited emission from a diode laser array in an apertured graded-index lens external cavity  

NASA Astrophysics Data System (ADS)

A gain-guided coupled-stripe GaAs/GaAlAs diode laser array in an external cavity configuration consisting of a graded refractive index lens and a 25-micron stripe apertured mirror was studied. Output power of almost 500 mW was obtained from the cavity under pulsed operation. A centered, single-lobed far-field radiation pattern which did not steer with the drive current was observed up to 4.1I(th). At 2I(th) approximately 94 percent of the 102-mW output power is contained in the 0.8 deg full width half-maximum central lobe.

Chang-Hasnain, C.; Welch, D. F.; Scifres, D. R.; Whinnery, J. R.; Dienes, A.

1986-09-01

203

Highly temperature-stable modulation characteristics of multioxide-aperture high-speed 980 nm vertical cavity surface emitting lasers  

NASA Astrophysics Data System (ADS)

We present multioxide-aperture 980 nm-range vertical cavity surface emitting lasers (VCSELs) with highly temperature stable modulation characteristics operating error-free at 25 Gbit/s at 25 and 85 °C. We perform small signal modulation experiments and extract the fundamental physical parameters including relaxation resonance frequency, damping factor, parasitic cut-off frequency, D-factor, and K-factor, leading to identification of thermal processes and damping as the main factors that presently limit high speed device operation. We obtain very temperature-insensitive bandwidths around 13-15 GHz. Presented results clearly demonstrate the suitability of our VCSELs for practical and reliable optical data transmission systems.

Mutig, A.; Lott, J. A.; Blokhin, S. A.; Wolf, P.; Moser, P.; Hofmann, W.; Nadtochiy, A. M.; Payusov, A.; Bimberg, D.

2010-10-01

204

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

SciTech Connect

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

Ditmire, T.; Perry, M.D.

1995-01-01

205

[Delivery of megawatts high energy laser pulse with large core diameter silica fiber and its application in dual-wavelength laser-ablation laser-induced breakdown spectroscopy].  

PubMed

To resolve the contradiction between spatial resolution and analysis sensitivity in single pulse laser-induced breakdown spectroscopy (LIBS), a study on dual-wavelength laser-ablation laser-induced breakdown spectroscopy (LA-LIBS) was carried out by using one Nd : YAG laser which was capable of two laser beam outputs with different wavelengths, where, the second harmonic output, 532 nm laser beam, was used as laser-ablation source, and the fundamental output, 1064 nm laser beam, was delivered with a large core diameter silica fiber to realize nanoseconds time-delay and then used to breakdown the ablated samples. Two laser beams were orthogonally arranged to realize element analysis with high spatial resolution and high sensitivity. Some key techniques on the coupling of 1064 nm laser beam into fiber, the collimation of laser at the fiber end and re-focusing of the laser beam were studied. The energy delivery capabilities of four fibers of different types were studied and the maximum values were determined experimentally. A Q-switched laser pulse with 15 mJ pulse energy was successfully delivered by selecting a 50 meter long silica fiber with 800 microm core diameter and 0. 39 numerical aperture. And 250 ns time-delay was realized. A copper alloy was analyzed by spectra with current established LA-LIBS system and the possibility of realizing dual-wavelength LA-LIBS analysis based on one Nd : YAG laser was demonstrated experimentally. In this technique, only one Nd: YAG laser was required to carry out spectral analysis. It has a few advantages, such as simple equipment structure, and being convenient to miniaturize the whole system etc. This dual-wavelength LA-LIBS technique was suitable for in-situ elements microanalysis for different samples with both high spatial resolution and high sensitivity. PMID:24611409

Zhou, Qi; Peng, Fei-Fei; Li, Run-Hua; Chen, Yu-Qi; Yang, Xue-Jiao

2013-12-01

206

Numerical comparison of thermal damage threshold from pulsed and scanning laser in a measurement aperture  

NASA Astrophysics Data System (ADS)

Optical radiation hazards of scanning light sources are often evaluated using pulsed light source criteria, with the relevant pulse parameter equivalent to the scanning light source determined by the energy delivered through a measurement aperture. This study utilizes a numerical analysis based upon the melanin granule model to compare the thermal effects of scanning and pulsed light sources through a measurement aperture in the pigmented retinal layer. The numerical analysis calculates the thermal contribution of individual melanin granules with varying temporal sequence, and finds that temperature changes and thermal damage thresholds for the two different types of light sources were not equal.

Kim, Do-Hyun

2012-02-01

207

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

208

Optical design and testing of a fast, large aperture, infrared space telescope  

NASA Technical Reports Server (NTRS)

An optical design study for a next generation infrared space telescope has been performed. The concept is that of a passively cooled telescope of minimum aperture 2.5 m with an F/1.2 primary and wavelength coverage from 2 to as least 40 microns, and possibly to 100 microns. Compactness, low thermal emission from the optics and structure, diffraction limited imaging at 2 microns, and sensitivity to misalignment aberrations and manufacturing errors were the main considerations for this study. Ray tracing results are presented showing the characteristics of the various designs considered. A preliminary investigation of stray light properties is also given. Special emphasis has been placed on the testing of such a fast primary, and optical systems using a lateral shearing interferometer are described for testing both the primary and the primary/secondary combination.

Humphries, C. M.; Nevo, Y.; Ettedgui-Atad, E.; Harris, J. W.

1992-01-01

209

11 nm hard X-ray focus from a large-aperture multilayer Laue lens  

NASA Astrophysics Data System (ADS)

The focusing performance of a multilayer Laue lens (MLL) with 43.4 ?m aperture, 4 nm finest zone width and 4.2 mm focal length at 12 keV was characterized with X-rays using ptychography method. The reconstructed probe shows a full-width-at-half-maximum (FWHM) peak size of 11.2 nm. The obtained X-ray wavefront shows excellent agreement with the dynamical calculations, exhibiting aberrations less than 0.3 wave period, which ensures the MLL capable of producing a diffraction-limited focus while offering a sufficient working distance. This achievement opens up opportunities of incorporating a variety of in-situ experiments into ultra high-resolution X-ray microscopy studies.

Huang, Xiaojing; Yan, Hanfei; Nazaretski, Evgeny; Conley, Raymond; Bouet, Nathalie; Zhou, Juan; Lauer, Kenneth; Li, Li; Eom, Daejin; Legnini, Daniel; Harder, Ross; Robinson, Ian K.; Chu, Yong S.

2013-12-01

210

Laser ablation of silicon using a Bessel-like beam generated by a subwavelength annular aperture structure.  

PubMed

Using a femtosecond laser incident to an oxide-metal-oxide film engraved with a subwavelength annular aperture (SAA) structure, we generated a Bessel-like beam to ablate silicon. Experimental results show that the silicon can be ablated with a 0.05 J/cm(2) input ablation threshold at 120 fs pulse duration. We obtained a surface hole possessing a diameter less than 1 ?m. Optical performance, including depth-of-focus and focal spot of the SAA structure, were simulated using finite-different time-domain calculations. We found that a far-field laser beam propagating through a SAA structure possesses a submicrometer focal spot and high focus intensity. Our method can be easily adopted for surface machining in microfabrication applications. PMID:22192990

Yu, Yuh-Yan; Chang, Chin-Kai; Lai, Ming-Wei; Huang, Long-Sun; Lee, Chih-Kung

2011-12-01

211

Status and future of laser scanning, synthetic aperture radar and hyperspectral remote sensing data for forest biomass assessment  

NASA Astrophysics Data System (ADS)

This is a review of the latest developments in different fields of remote sensing for forest biomass mapping. The main fields of research within the last decade have focused on the use of small footprint airborne laser scanning systems, polarimetric synthetic radar interferometry and hyperspectral data. Parallel developments in the field of digital airborne camera systems, digital photogrammetry and very high resolution multispectral data have taken place and have also proven themselves suitable for forest mapping issues. Forest mapping is a wide field and a variety of forest parameters can be mapped or modelled based on remote sensing information alone or combined with field data. The most common information required about a forest is related to its wood production and environmental aspects. In this paper, we will focus on the potential of advanced remote sensing techniques to assess forest biomass. This information is especially required by the REDD (reducing of emission from avoided deforestation and degradation) process. For this reason, new types of remote sensing data such as fullwave laser scanning data, polarimetric radar interferometry (polarimetric systhetic aperture interferometry, PolInSAR) and hyperspectral data are the focus of the research. In recent times, a few state-of-the-art articles in the field of airborne laser scanning for forest applications have been published. The current paper will provide a state-of-the-art review of remote sensing with a particular focus on biomass estimation, including new findings with fullwave airborne laser scanning, hyperspectral and polarimetric synthetic aperture radar interferometry. A synthesis of the actual findings and an outline of future developments will be presented.

Koch, Barbara

2010-11-01

212

Dynamics of radiation from a wide-aperture laser under conditions of coherent interaction of the radiation with a medium  

SciTech Connect

The dynamics of the radiation from a wide-aperture laser is investigated taking account of the finite response time of the polarisation of the active medium. This radiation is described by the Maxwell - Bloch equations, which are simplified for the case of fast relaxation of the polarisation. The methods of a qualitative theory of nonlinear dynamics systems are used to find the conditions for instability of the steady-state homogeneous laser radiation field in a Fabry - Perot cavity. It is shown that, as a rule, the system becomes unstable via an Andronov - Hopf bifurcation and the transverse profile of the optical field is modulated by a travelling self-wave. The main parameters of these self-waves are determined and their growth increment is found. It is shown that each of the roots of the characteristic equation of the system can be used to estimate the stability range of the self-wave solutions. The laser equations are also solved numerically and the results obtained are in good agreement with the conclusions of the qualitative theory. The numerical results predict harmonic and quasi-harmonic self-waves (with multiplication of their period) and also behaviour resembling chaos. (lasers)

Zaikin, A P [Samara Branch of the P.N. Lebedev Physics Institute, Russian Academy of Sciences, Samara (Russian Federation)

1999-11-30

213

Laser velocimeter for large wind tunnels  

NASA Technical Reports Server (NTRS)

The measurement of velocity in large wind tunnels is normally performed using mechanical probes. This practice can entail considerable complexity in connection with the structure often required for probe support. The use of laser velocimetry for the flowfield measurements in large wind tunnels is, therefore, far more desirable since it can be implemented with minimal mechanical complexity and with minimal modifications to the test section structure. A description is provided of a velocimeter which is intended for use in investigations which include V/STOL vehicle flowfield mapping for location and sizing of wakes and plumes, wing-loading distribution determination without the need for pressure taps, the aerodynamics of high-lift airfoils as well as rotating rotor blades, and vehicle wake studies. Use is made of a single-color dual-beam backscatter system which is capable of sensing two orthogonal components of velocity.

Reinath, M. S.

1982-01-01

214

Lower bound on the critical energy for the onset of chaos and the chaotic dynamical aperture of large accelerators  

SciTech Connect

A generic nonintegrable Hamiltonian system is characterized by a critical energy above which chaotic motion sets in. A general method of finding a lower bound to this critical energy that does not require a solution of the equations of motion is discussed. Below the critical energy, the motion is regular everywhere on the energy surface and no instabilities can develop. The method is applied to a practical situation encountered in modern large accelerators, where the transverse motion of the particles in an arrangement of quadrupole, sextupole, and octupole magnetic elements may become chaotic. The chaotic dynamical aperture of the beam is calculated as a function of a dimensionless strength parameter. The estimated critical energy is compared with that obtained from detailed studies of the Poincare sections of the above system at various energies.

Guersey, Y. (Department of Natural Sciences, Baruch College of The City University of New York, 17 Lexington Avenue, New York 10010 (United States)); Alhassid, Y. (Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Conneticut 06511 (United States) Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06511 (United States))

1992-02-15

215

Development of a mirror backed volume phase grating with potential for large aperture and high damage threshold  

NASA Astrophysics Data System (ADS)

The present paper proposes a new grating concept by which a volume phase grating is placed on top of a dielectric mirror stack. Instead of using a multilayer dielectric grating, wherein the uppermost layer of a thin film mirror is etched to create the desired binary phase grating we suggest to have an upper grating layer of a lower density gelatin-based volume phase grating in either sol-gel or dichromated gelatin. The key benefit is the elimination of the etching step which is the limiting factor in the production of large aperture gratings. We have investigated designs for s- and p-polarization as well as the necessary chemistry that is needed to achieve the required index modulations. Damage testing on dichromated gelatin and aerogel was performed and diffraction efficiencies for various prototypes were measured.

Rambo, Patrick; Schwarz, Jens; Smith, Ian

2006-04-01

216

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

217

1030nm Yb-fiber-MOPA-based, multi-aperture high power, high energy uplink laser beacon for deep space communication  

NASA Astrophysics Data System (ADS)

A Yb LMA fiber amplifier based laser transmitter capable of operating with high average power and high energy (~500W, 1mJ) is presented. The prototype, all-fiber, high TRL level laser transmitter is designed to meet all the single aperture requirements of an eight aperture deep space laser beacon system. The high speed FPGA controlled transmitter supports a directly modulated DFB laser and two acousto-optic modulators which are used to implement an open loop pattern dependent -pulse pre-shaping algorithm. Ultra-fast high power diode drivers are used for generating outer nested PPM modulation with Binary PPM (67usec, 33mJ pulses) and for implementing <1usec loss of signal (LOS) protection. Optical performance to be presented will include diffraction limited (M2~1.2) nested PPM optical outputs with >300W average and 9kW peak power with >70% o-o efficiency for the final power stage.

Engin, Doruk; Burton, John; Darab, Ibraheem; Kimpel, Frank; Mathason, Brian; Gupta, Shantanu

2014-03-01

218

Carrier Lifetime in Oxide Confined Vertical Cavity Surface Emitting Lasers  

SciTech Connect

The carrier lifetime in vertical cavity surface emitting lasers is determined for various oxide aperture sizes using turn-on delay measurements. The lifetime is relatively constant for large devices, but decreases for aperture sizes below 9 x 9 µm.

Allerman, A.A.; Choquette, K.D.; Fischer, A.J.; Geib, K.M.

1999-05-26

219

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

SciTech Connect

In ICF, the understanding of laser plasma scattering processes is essential for laser target coupling and in controlling the symmetry of indirect drive implosions. The existing Nova Full Aperture Backscatter Station (FABS) has been useful in understanding laser plasma instabilities occurring in hohlraums by measuring the quantity, spectral distribution and near-field spatial distributions of Brillouin and more recently Raman backscatter. Equally important is an understanding of the farfield spatial intensity distribution which provides information on density, temperature and velocity gradient distributions, and which affect capsule implosion symmetry in hohlraums. Such information could potentially help in understanding processes such as filamentation and saturation mechanism. This paper describes a broad-band, color-corrected far-field imager and associated diagnostics capable of imaging the source of scattered light to better than 25 {micro}m resolution. The imager can either image Brillouin or Raman backscatter through the Nova beam 7 focusing lens or be used like a microscope to image side scatter from other beams.

Wilke, M.D.; Fernandez, J.C.; Berggren, R.R.; Montgomery, D.; Faulkner, J.; Looney, L.; Jimerson, J. [Los Alamos National Lab., NM (United States); Horton, R.F. [SAIC, Albuquerque, NM (United States)

1996-06-01

220

A TEM00 Mode Lamp-Pumped Nd:YAG Laser Operated at 1318.8 nm in the Absence of Intracavity Etalons and Additional Apertures  

Microsoft Academic Search

We present a lamp-pumped high-efficiency continuous-wave (cw) TEM00 mode Nd:YAG laser operated at the 1318.8 nm single line in the absence of intracavity etalons and additional apertures. A 15 W laser with beam quality M2<2 has been achieved, which is, to our knowledge, the highest power in the cw TEM00 mode at 1318.8 nm within China. From the experimental results

Wen-Xiong Lin; Jian-Hong Huang; Shou-Qun Lin

2002-01-01

221

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

222

Demonstration of synthetic aperture imaging ladar  

Microsoft Academic Search

The spatial resolution of a conventional imaging LADAR system is constrained by the diffraction limit of the telescope aperture. The purpose of this work is to investigate Synthetic Aperture Imaging LADAR (SAIL), which employs aperture synthesis with coherent laser radar to overcome the diffraction limit and achieve fine-resolution, long range, two-dimensional imaging with modest aperture diameters. This paper details our

W. Buell; N. Marechal; J. Buck; R. Dickinson; D. Kozlowski; T. Wright; S. Beck

2005-01-01

223

Comparison of fiber optic and space feed for large aperture phased array antennas  

NASA Astrophysics Data System (ADS)

Two technologies which are potential candidates for distributing control and intelligence information in large phased array antennas, are space feeding and fiber optic corporate feeding. A comparison of the two technologies is presented in both qualitative and quantitative form. The comparison is embodied in the hypothetical cases of a V-band and an L-band spaceborne imaging radar. Size, weight, power and performance impacts of the two feeding methods are contrasted.

Jespersen, Nils V.; Herczfeld, Peter R.

1987-01-01

224

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

225

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

NASA Astrophysics Data System (ADS)

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 ?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, and we find that the dominant filament in the cloud is approximately perpendicular to the large-scale field, while secondary filaments appear to run parallel to the magnetic fields in their vicinities. This is similar to what is observed in Serpens South via near-IR polarimetry, and consistent with what is seen in MHD simulations by F. Nakamura and Z. Li.

Matthews, Tristan G.; Ade, Peter A. R.; Angilè, 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, Frédérick; 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

2014-04-01

226

Deposition of high quality YBa2Cu3O(7-delta) thin films over large areas by pulsed laser ablation with substrate scanning  

NASA Technical Reports Server (NTRS)

The paper describes thin films deposited in a system where substrates are scanned over areas up to 3.5 x 3.5 cm through the stationary plume of an ablated material defined by an aperture. These YBCO films are deposited on LaAlO3 and SrTiO3 substrates with the thickness of 90 and 160 nm. Attention is focused on the main features of the deposition system: line focusing of the laser beam on the target; an aperture defining the area of the plume; computerized stepper motor-driven X-Y stage translating the heated sampler holder behind the plume-defining aperture in programmed patterns; and substrate mounting block with uniform heating at high temperatures over large areas. It is noted that the high degree of uniformity of the properties in each film batch illustrates that the technique of pulsed laser deposition can be applied to produce large YBCO films of high quality.

Davis, M. F.; Wosik, J.; Forster, K.; Deshmukh, S. C.; Rampersad, H. R.

1991-01-01

227

Laser induced photoreceptor damage and recovery in the high numerical aperture eye of the garter snake.  

PubMed

The garter snake provides a unique model for in-vivo imaging of photoreceptor damage induced by laser retinal exposure. Laser thermal/mechanical retinal injury induced alterations in photoreceptor structure and leukocyte cellular behavior. Photoreceptors turned white, lost mode structure, and swelled; leukocyte activity was observed in the vicinity of photoreceptor cells. Non-thermal alterations were identified with a bio-tag for oxidative stress. Mechanisms of photoreceptor recovery and replacement were observed and evaluated for active cytoskeletal systems by using an anti-actin tag that could detect the presence of active cytoskeletal systems resident in photoreceptors as well as other retinal systems. PMID:18252238

Zwick, H; Edsall, P; Stuck, B E; Wood, E; Elliott, R; Cheramie, R; Hacker, H

2008-02-01

228

Cleaning of large area by excimer laser ablation  

Microsoft Academic Search

Surface removal technologies are being challenged from environmental and economic perspectives. This paper is concerned with laser ablation applied to large surface cleaning with an automatized excimer laser unit. The study focused on metallic surfaces that are oxidized and are representative of contaminated surfaces with radionuclides in a context of nuclear power plant maintenance. The whole system is described: laser,

Marc L. Sentis; Philippe C. Delaporte; Vladimir I. Marine; Olivier Uteza

2000-01-01

229

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

230

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

231

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.

232

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

233

Application of research for metal primary mirror of large-aperture infrared solar telescope  

NASA Astrophysics Data System (ADS)

Metal is an early telescope mirror material, it was later replaced by glass which has lower thermal expansion coefficient. However, for observing the sun, these glass materials in the primary mirror are affected by the sun's intense radiation, its temperature rises rapidly, but which conducts heat slowly. The temperature difference between mirror and ambient air is so large that causing the air turbulence which has affected the observation precision. While the metal material has better thermal conductivity characteristics, it can greatly improve the problems caused by air turbulence. This paper analyzes the characteristics of the various mirror materials, and then makes a rust-proof aluminum alloy 5A05 as the mirror substrate material. For the major deficiencies of the soft aluminum surface which is not suitable for polishing, this paper presents a method of electroless nickel plating to improve its surface properties. After the mirror go through a thermal shock, the upper and lower levels of metal CTE don't match with each other, which leads to mirror deformation and warping. The bimetallic effect has been illustrated by the theory of beam element and give a result of elementary approximated. The analysis shows that the displacement deformation of the upper and lower layers of metal which is caused by thermal shock is smaller when the CTE is closer. In the experiments, a spherical aluminum mirrors with the substrate of 5A05 aluminum alloy, diameter of 110mm, the radius of curvature of 258.672mm is manufactured in classical technique. And it ultimately achieves optical mirror-polished precision. Besides, the long-term thermal stability experimental study of the aluminum mirrors proved that Al-infrared solar telescope primary mirror meets the needs of the long-term observation during use.

Meng, Xiaohui; Zhang, Haiying; Li, Xinnan

2010-05-01

234

Cleaning of large area by excimer laser ablation  

NASA Astrophysics Data System (ADS)

Surface removal technologies are being challenged from environmental and economic perspectives. This paper is concerned with laser ablation applied to large surface cleaning with an automatized excimer laser unit. The study focused on metallic surfaces that are oxidized and are representative of contaminated surfaces with radionuclides in a context of nuclear power plant maintenance. The whole system is described: laser, beam deliver, particle collection cell, real time control of cleaning processes. Results concerning surface laser interaction and substrate modifications are presented.

Sentis, Marc L.; Delaporte, Philippe C.; Marine, Vladimir I.; Uteza, Olivier

2000-01-01

235

OpTIIX: An ISS-Based Testbed Paving the Roadmap Toward a Next Generation Large Aperture UV/Optical Space Telescope  

NASA Technical Reports Server (NTRS)

The next generation large aperture UV/Optical space telescope will need a diameter substantially larger than even that of JWST in order to address some of the most compelling unanswered scientific quests. These quests include understanding the earliest phases of the Universe and detecting life on exo-planets by studying spectra of their atmospheres. Such 8-16 meter telescopes face severe challenges in terms of cost and complexity and are unlikely to be affordable unless a new paradigm is adopted for their design and construction. The conventional approach is to use monolithic or preassembled segmented mirrors requiring complicated and risky deployments and relying on future heavy-lift vehicles, large fairings and complex geometry. The new paradigm is to launch component modules on relatively small vehicles and then perform in-orbit robotic assembly of those modules. The Optical Testbed and Integration on ISS eXperiment (OpTIIX) is designed to demonstrate, at low cost by leveraging the infrastructure provided by ISS, telescope assembly technologies and end-to-end optical system technologies. The use of ISS as a testbed permits the concentration of resources on reducing the technical risks associated with robotically integrating the components. These include laser metrology and wavefront sensing and control (WFS&C) systems, an imaging instrument, lightweight, low-cost deformable primary mirror segments and the secondary mirror. These elements are then aligned to a diffraction-limited optical system in space. The capability to assemble the optical system and remove and replace components via the existing ISS robotic systems like the Special Purpose Dexterous Manipulator (SPDM), or by the ISS flight crew, allows for future experimentation, as well as repair.

Carpenter, Kenneth G.; Etemad, Shar; Seery, Bernard D.; Thronson, Harley; Burdick, Gary M.; Coulter, Dan; Goullioud, Renaud; Green, Joseph J.; Liu, Fengchuan; Ess, Kim; Postman, Marc; Sparks, Williams

2012-01-01

236

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

237

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

Microsoft Academic Search

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

Daniel F. Feezell

2005-01-01

238

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

SciTech Connect

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

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

2007-01-25

239

Advancements in adaptive optics technology: micro deformable mirrors and laser guidestars for the next generation of extremely large telescopes  

NASA Astrophysics Data System (ADS)

Micro-electro mechanical devices (MEMS) deformable mirrors offer a compact and affordable path to complex next generation AO instruments on large telescopes. In this talk we discuss our plans and experimental progress on MEMS-based AO systems: the high-contrast Gemini Planet Imager, the ShaneAO laser guidestar system, and the proposed Keck Next Generation AO system. Each of these instruments employs unique advantages of micro-mirrors including a large actuator count in a small space and go-to open-loop controllability. Large aperture telescopes present a challenging wide-field optical design problem however, a topic we will address with proposed MEMS solutions. We also discuss the advances in laser guidestar technology for AO, highlighting the need for brighter guidestars as we increase the sampling density for higher Strehl systems. We discuss our modeling of the sodium laser interaction and exploration of pulse and spectral format for maximum return from the sodium layer.

Gavel, Donald; Kupke, Renate; Thomas, Sandrine; Morzinski, Katie; Norton, Andrew; Rampy, Rachel

2011-09-01

240

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

SciTech Connect

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

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

1999-11-01

241

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

242

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

2014-04-01

243

A comparison of eddy-covariance and large aperture scintillometer measurements with respect to the energy balance closure problem  

NASA Astrophysics Data System (ADS)

We analyzed the seasonal variations of energy balance components over three different surfaces: irrigated cropland (Yingke, YK), alpine meadow (A'rou, AR), and spruce forest (Guantan, GT). The energy balance components were measured using eddy covariance (EC) systems and a large aperture scintillometer (LAS) in the Heihe River Basin, China, in 2008 and 2009. We also determined the source areas of the EC and LAS measurements with a footprint model for each site and discussed the differences between the sensible heat fluxes measured with EC and LAS at AR. The results show that the main EC source areas were within a radius of 250 m at all of the sites. The main source area for the LAS (with a path length of 2390 m) stretched along a path line approximately 2000 m long and 700 m wide. The surface characteristics in the source areas changed with the season at each site, and there were characteristic seasonal variations in the energy balance components at all of the sites. The sensible heat flux was the main term of the energy budget during the dormant season. During the growing season, however, the latent heat flux dominated the energy budget, and an obvious "oasis effect" was observed at YK. The sensible heat fluxes measured by LAS at AR were larger than those measured by EC at the same site. This difference seems to be caused by the so-called energy imbalance phenomenon, the heterogeneity of the underlying surfaces, and the difference between the source areas of the LAS and EC measurements.

Liu, S. M.; Xu, Z. W.; Wang, W. Z.; Jia, Z. Z.; Zhu, M. J.; Bai, J.; Wang, J. M.

2011-04-01

244

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

245

Design and prototype tests of a large-aperture 37-53 MHz ferrite-tuned booster synchrotron cavity  

SciTech Connect

The Booster synchrotron at Fermilab employs eighteen 37-53 MHz ferrite-tuned double-gap coaxial radiofrequency cavities for acceleration of protons from 400 MeV to 8 GeV. The cavities have an aperture of 2.25 inches and operate at 55 kV per cavity. Future high duty factor operation of the Booster will be problematic due to unavoidable beam loss at the cavities resulting in excessive activation. The power amplifiers, high maintenance items, are mounted directly to the cavities in the tunnel. A proposed replacement for the Booster, the Proton Driver, will utilize the Booster radiofrequency cavities and requires not only a larger aperture, but also higher voltage. A research and development program is underway at Fermilab to modify the Booster cavities to provide a 5-inch aperture and a 20% voltage increase. A prototype has been constructed and high power tests have bee completed. The cavity design and test results is presented.

Mark S. Champion et al.

2001-07-12

246

Large volume multiple-path nuclear pumped laser  

NASA Technical Reports Server (NTRS)

Large volumes of gas are excited by using internal high reflectance mirrors that are arranged so that the optical path crosses back and forth through the excited gaseous medium. By adjusting the external dielectric mirrors of the laser, the number of paths through the laser cavity can be varied. Output powers were obtained that are substantially higher than the output powers of previous nuclear laser systems.

Hohl, F.; Deyoung, R. J. (inventors)

1981-01-01

247

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

SciTech Connect

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

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

2006-06-01

248

Large-Aperture [O I] 6300 A Photometry of Comet Hale-Bopp: Implications for the Photochemistry of OH  

NASA Technical Reports Server (NTRS)

Large-aperture photometric observations of comet Hale-Bopp (C/1995 O1) in the forbidden red line of neutral oxygen ([O I] 6300 angstroms) with the 150 mm dual-etalon Fabry-Perot spectrometer that comprises the Wisconsin H-alpha Mapper and a 50 mm dual-etalon Fabry-Perot spectrometer at the McMath-Pierce main telescope from 1997 late February to mid April yield a total metastable O((sup 1)D) production rate of (2.3-5.9) x 10(exp 30)/s. Applying the standard H2O and OH photodissociation branching ratios, we derive a water production rate, Q(H2O), of (2.6-6.1) x 10(exp 31)/s, which disagrees with Q(H2O = 1x10(exp 31)/s determined by independent H2O, OH, and H measurements. Furthermore, our own [O I] 6300 observations of the inner coma (< 30,000 km) using the 3.5 m Wisconsin-Indiana-Yale-NOAO telescope Hydra and Densepak multi-object spectrographs yield Q(H2O) = 1 x 10(exp 31)/s. Using our [O I] 6300 data, which cover spatial scales ranging from 2,000 to 1x10(exp 6) km, and a complementary set of wide-field ground-based OH images, we can constrain the sources of the apparent excess O((sup 1)D) emission to the outer coma, where photodissociation of OH is assumed to be the dominant O((sup 1)D) production mechanism. From production rates of other oxygen-bearing volatiles (e.g., CO and CO2), we can account for at most 30% of the observed excess O((sup 1)D) emission. Since even less O((sup 1)D) should be coming from other sources (e.g., electron excitation of neutral O and distributed nonnuclear sources of H2O), we hypothesize that the bulk of the excess O((sup 1)D) is likely coming from photodissociating OH. Using the experimental OH photo-dissociation cross section of Nee and Lee at Ly-alpha as a guide in modifying the theoretical OH cross sections of van Dishoeck and Dalgarno, we can account for approximately 60% of the observed O((sup 1)D) excess without requiring major modifications to the other OH branching ratios or the total OH photodissociation lifetime.

Morgenthaler, Jeffrey P.; Harris, Walter M.; Scherb, Frank; Anderson, Christopher M.; Oliversen, Ronald J.; Doane, Nathaniel E.; Combi, Michael R.; Marconi, Maximus L.; Smyth, William H.

2001-01-01

249

Estimating Evapotranspiration over Heterogeneously Vegetated Surfaces using Large Aperture Scintillometer, LiDAR, and Airborne Multispectral Imagery  

NASA Astrophysics Data System (ADS)

Estimates of evapotranspiration (ET) over heterogeneous areas is challenging especially in water-limited sparsely vegetated environments. New techniques such as airborne full-waveform LiDAR (Light Detection and Ranging) and high resolution multispectral and thermal imagery can provide enough detail of sparse canopies to improve energy balance model estimations as well as footprint analysis of scintillometer data. The objectives of this study were to estimate ET over such areas and develop methodologies for the use of these airborne data technologies. Because of the associated heterogeneity, this study was conducted over the Cibola National wildlife refuge, southern California on an area dominated with tamarisk (salt cedar) forest (90%) interspersed with arrowweed and bare soil (10%). A set of two large aperture scintillometers (LASs) were deployed over the area to provide estimates of sensible heat flux (HLAS). The LASs were distributed over the area in a way that allowed capturing different surface spatial heterogeneity. Bowen ratio systems were used to provide hydrometeorological variables and surface energy balance fluxes (SEBF) (i.e. Rn, G, H, and LE) measurements. Scintillometer-based estimates of HLAS were improved by considering the effect of the corresponding 3D footprint and the associated displacement height (d) and the roughness length (z0) following Geli et al. (2011). The LiDAR data were acquired using the LASSI Lidar developed at Utah State University (USU). The data was used to obtain 1-m spatial resolution DEM's and vegetation canopy height to improve the HLAS estimates. The BR measurements of Rn and G were combined with LAS estimates, HLAS, to provide estimates of LELASas a residual of the energy balance equation. A thermal remote sensing model namely the two source energy balance (TSEB) of Norman et al. (1995) was applied to provide spatial estimates of SEBF. Four airborne images at 1-4 meter spatial resolution acquired using the USU airborne multispectral system during the 2007-2008 growing season were used. Estimates of LETSEB and HTSEB were compared with those derived based on LAS, HLAS and LELAS, and with those based on BR, HBR and LEBR. The comparison was performed by integrating the spatially estimated fluxes using the BR and the LAS 3D footprint weights.

Geli, H. M.; Neale, C. M.; Pack, R. T.; Watts, D. R.; Osterberg, J.

2011-12-01

250

Evolution of ultrashort laser pulse in large amplitude plasma waves  

SciTech Connect

The propagation and evolution of an ultrashort laser pulse in a large amplitude plasma wave are investigated based on the photon kinetic theory. The photon number distribution function for a laser pulse in the phase space is analytically obtained by solving the photon kinetic equation in the background plasma wave. And then, the behavior of the laser pulse can be described by combining the single photon dynamics and the photon number distribution function. The evolutions of the photon number density in the coordinate and frequency domain space are discussed, and broadening or compressing of the laser pulse is also displayed in this paper. In particular, the frequency shift of the entire laser pulse is analyzed, which reflects a way of energy transformation between the laser pulse and the plasma wave.

Bu Zhigang [Department of Physics, Shanghai University, Shanghai 200444 (China); Ji Peiyong [Department of Physics, Shanghai University, Shanghai 200444 (China); The Shanghai Key Lab of Astrophysics, Shanghai 200234 (China)

2012-11-15

251

Differential Optical Synthetic Aperture Radar  

DOEpatents

A new differential technique for forming optical images using a synthetic aperture is introduced. This differential technique utilizes a single aperture to obtain unique (N) phases that can be processed to produce a synthetic aperture image at points along a trajectory. This is accomplished by dividing the aperture into two equal "subapertures", each having a width that is less than the actual aperture, along the direction of flight. As the platform flies along a given trajectory, a source illuminates objects and the two subapertures are configured to collect return signals. The techniques of the invention is designed to cancel common-mode errors, trajectory deviations from a straight line, and laser phase noise to provide the set of resultant (N) phases that can produce an image having a spatial resolution corresponding to a synthetic aperture.

Stappaerts, Eddy A. (San Ramon, CA)

2005-04-12

252

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

253

Laser processing system development of large area and high precision  

NASA Astrophysics Data System (ADS)

As industry of PCB (Printed Circuit Board) and display growing, this industry requires an increasingly high-precision quality so current cutting process in industry is preferred laser machining than mechanical machining. Now, laser machining is used almost "step and repeat" method in large area, but this method has a problem such as cutting quality in the continuity of edge parts, cutting speed and low productivity. To solve these problems in large area, on-the-fly (stagescanner synchronized system) is gradually increasing. On-the-fly technology is able to process large area with high speed because of stage-scanner synchronized moving. We designed laser-based high precision system with on-the-fly. In this system, we used UV nano-second pulse laser, power controller and scanner with telecentric f-theta lens. The power controller is consisted of HWP(Half Wave Plate), thin film plate polarizer, photo diode, micro step motor and control board. Laser power is possible to monitor real-time and adjust precision power by using power controller. Using this machine, we tested cutting of large area coverlay and sheet type large area PCB by applying on-the-fly. As a result, our developed machine is possible to process large area without the problem of the continuity of edge parts and by high cutting speed than competitor about coverlay.

Park, Hyeongchan; Ryu, Kwanghyun; Hwang, Taesang

2013-03-01

254

AUTOMATED OBJECT IDENTIFICATION AND ATTRIBUTE ACQUISITION SYSTEM HAVING A MULTI-COMPARTMENT HOUSING WITH OPTICALLY-ISOLATED LIGHT TRANSMISSION APERTURES FOR OPERATION OF A PLANAR LASER ILLUMINATION AND IMAGING (PLIIM) BASED LINEAR IMAGING SUBSYSTEM AND A LASER-BASE  

US Patent & Trademark Office Database

An automated object identification and attribute acquisition system comprising a planar light illumination and imaging subsystem (PLIIM) based linear imaging subsystem, and a laser-based object profiling subsystem integrated within a multi-compartment system housing. The system housing has a substantially unitary construction and includes a first optically-isolated compartment formed in its upper deck portion for containing the PLIIM based linear imaging subsystem and associated components therewithin. The system housing also includes a second optically-isolated compartment formed in its lower deck portion, disposed below the first optically-isolated compartment; for containing the laser-based object profiling subsystem and associated components therewithin. First and second light transmission apertures are formed in the first optically-isolated compartment, for enabling the transmission of a planar laser illumination beam (PLIB) from the PLIIM based linear imaging sybsystem, and towards the object to be illuminated. A third light transmission aperture is formed in the first optically-isolated compartment, and spatially aligned with the first and second light transmission apertures, for enabling the field of view (FOV) of a linear image detection array provided in the PLIIM-based linear imaging subsystem, to project from the linear image detection array towards the illuminated object to be imaged. A fourth light transmission aperture is formed in the second optically-isolated compartment, and spatially distanced from the first optically-isolated compartment, for enabling the transmission of one or more laser scanning beams from the laser-based object profiling subsystem, towards the object being illuminated and imaged. By virtue of the present invention, it is now possible to automatically identify a moving object such as a package moving along a conveyor belt structure, and acquire geometrical and surface attributes thereof, using a single integrated device of substantially unitary construction, thereby simplifying system installation, set-up and maintenance in diverse field of operation

2006-01-24

255

Scale-factor corrections in large ring lasers  

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

256

Pulsed RGB lasers for large-screen video displays  

NASA Astrophysics Data System (ADS)

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

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

1997-01-01

257

Large Signal Resonance and Laser Dilatometer Methods  

NASA Astrophysics Data System (ADS)

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

Wolff, A.

258

A study program on large aperture electronic scanning phased array antennas for the shuttle imaging microwave system  

NASA Technical Reports Server (NTRS)

Fundamental phased array theory and performance parameters are discussed in terms of their application to microwave radiometry, and four scanning phased arrays representing current examples of state-of-the-art phased array technology are evaluated for potential use as components of the multispectral antenna system for the space shuttle imaging microwave system (SIMS). A discussion of problem areas, both in performance and fabrication is included, with extrapolations of performance characteristics for phased array antennas of increased sizes up to 20 m by 20 m. The possibility of interlacing two or more phased arrays to achieve a multifrequency aperture is considered, and, finally, a specific antenna system is recommended for use with SIMS.

1974-01-01

259

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

NASA Astrophysics Data System (ADS)

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

Isham, John D.

260

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

261

Update of Laser Mégajoule large optics wavefront performance requirements  

NASA Astrophysics Data System (ADS)

The Laser Mégajoule (LMJ) facility has about 40 large optics per beam. For 22 bundles with 8 beams per bundle, it will contain about 7.000 optical components. First experiments are scheduled at the end of 2014. LMJ components are now being delivered. Therefore, a set of acceptance criteria is needed when the optical components are exceeding the specifications. This set of rules is critical even for a small non-conformance ratio. This paper emphasizes the methodology applied to check or re-evaluate the wavefront requirements of LMJ large optics. First we remind how LMJ large component optical specifications are expressed and we describe their corresponding impacts on the laser chain. Depending on the location of the component in the laser chain, we explain the criteria on the laser performance considered in our impact analyses. Then, we give a review of the studied propagation issues. The performance analyses are mainly based on numerical simulations with Miró propagation simulation software. Analytical representations for the wavefront allow to study the propagation downstream local surface or bulk defects and also the propagation of a residual periodic aberration along the laser chain. Generation of random phase maps is also used a lot to study the propagation of component wavefront/surface errors, either with uniform distribution and controlled rms value on specific spatial bands, or following a specific wavefront/surface Power Spectral Distribution (PSD).

Mainguy, Stéphane; Airiau, Jean-Philippe; Bart, Thierry; Beau, Vincent; Bordenave, Edouard; Bouillet, Stéphane; Chappuis, Christian; Chico, Sandrine; Cormont, Philippe; Darbois, Nathalie; Daurios, Jérome; Denis, Vincent; Eupherte, Laure; Ferriou-Darbois, Nathalie; Fontaine, Servane; Gaborit, Gaël.; Grosset-Grange, Claire; Journot, Eric; Lamaignère, Laurent; Lanternier, Thomas; Lavastre, Eric; Leymarié, Christophe; Lompré, Louis-André; Mangeant, Mélanie; Maunier, Cédric; Néauport, Jérome; Perrot-Minnot, Etienne; Razé, Gérard; Reyné, Stéphane; Rouyer, Claude; Sajer, Jean-Michel; Seznec, Stéphane; Taroux, Daniel; Vermersch, Sébastien; Le Déroff, Laurent

2013-02-01

262

Large-Angle Deflection Technique for Laser Display.  

National Technical Information Service (NTIS)

This report describes the continuing effort on a large angle of deflection technique for producing a 945 line T.V. raster scan in an experimental laser display. It was determined that 23 KC is the approximate limiting frequency for reliable operation of a...

C. E. Baker G. R. Fournier

1966-01-01

263

Nuclear-pumped lasers for large-scale applications  

SciTech Connect

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

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

1988-01-01

264

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

265

A bright, pulsed, guide star laser for very large telescopes  

NASA Astrophysics Data System (ADS)

We demonstrate for the first time the practical feasibility of a new sodium guide star laser with a pulsed burst output of sufficient energy at 589nm to be useful for current applications and readily scalable to meet future requirements. We describe complete experimental design verification results of the pulse burst laser concept, optimized to eliminate guide-star elongation issues and to meet all requirements for Multi Conjugate Adaptive Optics (MCAO) for future extremely large ground-based telescopes (ELTs). It makes use of sum frequency generation (SFG) of two, Q-switched, injection mode-locked, wavelength stabilized Nd:YAG lasers, producing a macro-micro, pulse-burst output which is optimized in power and bandwidth to maximize the fluorescence from the high altitude sodium layer.

Munch, Jesper; Hamilton, Murray; Hosken, David; Simakov, Nikita; Veitch, Peter

2010-07-01

266

Invited review article: Large ring lasers for rotation sensing.  

PubMed

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

Schreiber, Karl Ulrich; Wells, Jon-Paul R

2013-04-01

267

Large Ring Laser Gyroscopes for Geo-physical Measurements  

NASA Astrophysics Data System (ADS)

Researchers at the University of Canterbury in Christchurch, New Zealand, the Technical University of Munich in Munich, Germany, and Hendrix College in Conway, Arkansas are engaged in a collaboration using large ring laser gyroscopes to measure geophysical phenomena. This presentation will focus on the contributions of Hendrix College to this collaboration. In an active ring laser gyroscope, coherent waves of light are propagated simultaneously around the laser cavity in both a clockwise and counterclockwise direction. A relatively small amount of light from each of the bi-directional waves is transmitted through the dielectric mirror. At one of the mirrors, the transmitted portions of the bi-directional waves are collimated and combined on a detector. If the laser cavity is rotating, the time for light to complete a path around the cavity depends on its direction of propagation. This difference in transit time creates a beat frequency proportional to the rotation rate. Geophysical effects are observed when they perturb the ring laser and modulate the beat frequency.

Coats, Julie

2005-03-01

268

Measuring large amplitudes of mechanical vibrations with laser interferometers  

NASA Astrophysics Data System (ADS)

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

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

1984-09-01

269

Large aperture PPMgLN based high-power optical parametric oscillator at 3.8 µm pumped by a nanosecond linearly polarized fiber MOPA.  

PubMed

We report a large aperture PPMgLN based OPO generating 21W of average output power at a slope efficiency of 45%. The OPO is pumped with the output from a polarization maintaining Ytterbium doped fiber MOPA operating at 1060nm producing 20ns pulses at a repetition rate of 100kHz and an average output power of 58W (after the isolators). A maximum of 5.5W of optical power was recorded at the idler wavelength of 3.82µm without thermal roll-off. The pulse rise/fall time plays a significant role in the OPO conversion efficiency and that further enhancements in the efficiency should be possible using pulses with faster rise and fall times. PMID:22772196

Lin, Dejiao; Alam, Shaif-ul; Shen, Yonghang; Chen, Tao; Wu, Bo; Richardson, David J

2012-07-01

270

Physical stability and aerosol properties of liposomes delivered using an air-jet nebulizer and a novel micropump device with large mesh apertures.  

PubMed

The aerosol properties of liposomes and their physical stability to aerosolization were evaluated using an air-jet nebulizer (Pari LC Plus) and a customized large aperture vibrating-mesh nebulizer (Aeroneb Pro-8microm). Soya phosphatidylcholine: cholesterol (1:1 mole ratio) multilamellar liposomes (MLVs) entrapping salbutamol sulfate were nebulized directly, or after being reduced in size by extrusion through 1 or 0.4microm polycarbonate membrane filters. MLVs were very unstable to jet nebulization and stability was not markedly enhanced when vesicles were extruded before nebulization, such that drug losses from delivered liposomes using the Pari nebulizer were up to 88% (i.e. only 12% retained in liposomes). The Aeroneb Pro-8microm nebulizer was less disruptive to liposomes, completed nebulization in a much shorter time, and produced greater mass output rate than the Pari nebulizer. However, aerosol droplets were larger, total drug and mass outputs were lower and aerosolization performance was dependent on formulation. Vibrating-mesh nebulization was less disruptive to liposomes extruded through the 1microm membranes compared with the non-extruded MLVs, so that the retained entrapment of the drug in the nebulized vesicles was 56% and 37%, respectively. However, extrusion of liposomes to 0.4microm resulted in reduced stability of liposomes to vibrating-mesh nebulization (retained entrapment=41%) which was attributed to the reduced liposome lamellarity and subsequent reduced resistance to nebulization-induced shearing. This study has shown that vibrating-mesh nebulization using the customized large aperture mesh nebulizer (Aeroneb Pro-8microm) had a less disruptive effect on liposomes and produced a higher output rate compared with the Pari LC Plus air-jet nebulizer. On the other hand, the air-jet nebulizer produced higher total mass and drug outputs and smaller aerosol droplets. PMID:17123757

Elhissi, A M A; Faizi, M; Naji, W F; Gill, H S; Taylor, K M G

2007-04-01

271

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.

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

2007-01-01

272

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

273

Planarization of amorphous silicon thin film transistors for high-aperture-ratio and large-area active-matrix liquid crystal displays  

NASA Astrophysics Data System (ADS)

The reduction of the backlight power consumption and the improvement of the display image uniformity for future large-area and high-resolution active-matrix liquid- crystal displays (AM-LCDs) are very important. One possible method to achieve the former goal is to increase the pixel electrode aperture-ratio. This can be realized by overlapping the pixel electrode with both gate/data buslines. While for the latter, reduction of the RC-delay by using a low resistance gate metal line is the key. Both of these approaches can be realized by using planarization technology. In this dissertation, the planarization technology based on low dielectric constant organic polymer, benzocyclobutene (BCB), is demonstrated, and this technology has been successfully applied to hydrogenated amorphous-silicon (a-Si:H) thin-film transistor (TFT) arrays and thick metal gate buslines/electrodes. Through the planarization technology, a high-aperture-ratio (HAR) pixel electrode structure has been fabricated. The parasitic capacitance and crosstalk issues in the HAR pixel electrode have been studied through interconnect analysis and circuit simulation. The impact of the parasitic capacitance on display performances, such as feedthrough voltage, vertical crosstalk, pixel electrode aperture-ratio, pixel charging behavior, and gate busline RC-delay issues, has been thoroughly discussed. Some key issues during the process integration of the HAR pixel electrode structure have been addressed. These include the BCB contact via formation, the patterning of the ITO pixel electrodes on BCB layer, the selection of Ar plasma treatment conditions for BCB surface, and the optical transmittance evaluation of the ITO/BCB double-layer structure. In addition, the BCB passivation effects on back-channel etched type a-Si:H TFTs have been investigated. It is found that there is no degradation in the TFT electrical performance and reliability after the BCB passivation. Finally, the planarization technology is applied to a- Si:H TFTs incorporating a very thick Cr gate electrode and a Cu gate electrode. It is found that the gate- planarized (GP) TFTs have an electrical performance comparable to the conventional TFTs without gate planarization. However, an abnormal behavior, hole injection into the nitride/BCB double-layer gate insulator at a high positive voltage stress, was found for the GP-TFTs.

Lan, Je-Hsiung

274

Large amplitude electromagnetic solitons in intense laser plasma interaction  

NASA Astrophysics Data System (ADS)

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

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

2006-09-01

275

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

Microsoft Academic Search

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~1014 - 1015 W now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a prism stretcher with negative

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

2007-01-01

276

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

Microsoft Academic Search

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~1014 - 1015 W being now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by a solid state laser system, first going through a prism stretcher

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

2007-01-01

277

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

Microsoft Academic Search

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~1014 - 1015 W now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a prism stretcher with negative

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

2007-01-01

278

Switched fragmented aperture antennas  

Microsoft Academic Search

This paper introduces a reconfigurable aperture concept derived from fragmented aperture design where the configuration of the fragmented aperture may be switched by the user to obtain different functionalities. A fragmented aperture antenna is a patchwork of discrete conducting and dielectric units distributed over the specified aperture. The arrangement of the units is determined using an efficient, multistage procedure that

James C. Maloney; Morris P. Kesler; Lisa M. Lust; Lon N. Pringle; T. Lynn Fountain; Paul H. Harms; Glenn S. Smith

2000-01-01

279

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

280

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

281

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

282

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

NASA Astrophysics Data System (ADS)

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~10 14 - 10 15 W now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)laser excited by VUV radiation of an e-beam pumped Xe II lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(CA) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High- Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm 3, e-beam pulse duration ~ 100- 200 ns. A possibility of using Kr IIF as an active medium with saturation energy 0.2 J/cm2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing ~50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute. Preliminary experiments on amplification of UV femtosecond pulses were carried out with electric discharge KrF laser amplifier.

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

2007-08-01

283

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

NASA Astrophysics Data System (ADS)

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~10 14 - 10 15 W now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)-laser excited by VUV radiation of an e-beam pumped Xe II lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(CA) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High- Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm 3, e-beam pulse duration ~ 100- 200 ns. A possibility of using Kr IIF as an active medium with saturation energy 0.2 J/cm2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing ~50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute. Preliminary

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

2007-03-01

284

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

NASA Astrophysics Data System (ADS)

The multi-stage hybrid laser system producing ultrashort pulses of radiation with peak power ~10 14 - 10 15 W being now under developing at the Lebedev Physical Institute of the Russian Academy of Sciences is discussed. The distinctive feature of the laser system is direct amplification of ultrashort pulses produced by a solid state laser system, first going through a prism stretcher with negative dispersion, in gas active medium without using a rather expensive and complicated grating compressor of laser pulses. Two hybrid schemes are being developed now based on the amplification of femtosecond pulses of the third harmonic of Ti:Sapphire laser at the wavelength 248 nm in the active medium of KrF laser amplifier, and on the amplification of the second harmonic of Ti:Sa laser at the wavelength 480 nm in the active medium of photochemical XeF(C-A)-laser excited by VUV radiation of an e-beam pumped Xe II lamp. The final stage of the laser system is supposed to be an e-beam pumped facility with a laser chamber of 60 cm in diameter and 200 cm long in the case of KrF laser, and with another laser chamber of 30-40 cm in diameter put into the former one in the case of XeF(C-A) laser. The parameters of such e-beam facility are close to those of previously developed at the Institute of High-Current Electronics: electron energy ~600 keV, specific input power ~ 300-500 kW/cm 3, e-beam pulse duration ~ 100-200 ns. A possibility of using Kr IIF as an active medium with saturation energy 0.2 J/cm2 for amplification of ultrashort laser pulses is also under consideration. There was theoretically demonstrated that the energy of a laser pulse at the exit of the final stage of the laser system could come up to ~ 17 J with pulse duration ~50 fs in the case of KrF laser, and ~75 J with pulse duration of 25 fs in the case of XeF laser. Two Ti:Sa laser systems producing 50 fs pulses with energy ~0.5 mJ at the wavelength 248 nm and ~5 mJ at the wavelength 480 nm have been already developed and are being now installed at the Lebedev Institute.

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

2007-05-01

285

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

286

Precision large field scanning system for high numerical aperture lenses and application to femtosecond micromachining of ophthalmic materials  

NASA Astrophysics Data System (ADS)

A precision, large stroke (nearly 1 cm) scanning system was designed, built, and calibrated for micromachining of ophthalmic materials including hydrogels and cornea (excised and in vivo). This system comprises a flexure stage with an attached objective on stacked vertical and horizontal translation stages. This paper outlines the design process leading to our most current version including the specifications that were used in the design and the drawbacks of other methods that were previously used. Initial measurements of the current version are also given. The current flexure was measured to have a 27 Hz natural frequency with no load.

Brooks, D. R.; Brown, N. S.; Savage, D. E.; Wang, C.; Knox, W. H.; Ellis, J. D.

2014-06-01

287

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

288

Distributed aperture design for low profile Earth station antennas  

Microsoft Academic Search

The objective of this paper is to develop a distributed aperture antenna, which has the same performance as a single large aperture antenna, but has lower profile. The distributed aperture will have a simpler mechanical design, lower cost, lower power electronics, graceful performance degradation and overall higher reliability. This paper presents a design that forms an antenna aperture from distributed

A. I. Zaghloui; O. Kilic; L. Q. Sun; M. Lieberman

1999-01-01

289

LASER FIELDS AND CAVITIES: Periodic self-wave structures in a wide-aperture laser with frequency detuning. I. Bifurcation analysis  

NASA Astrophysics Data System (ADS)

A theoretical investigation is reported of the stability of a homogeneous transverse distribution of lasing in a wide-aperture Fabry — Perot cavity. It is shown that when the detuning of the lasing frequency from the centre of the gain line of the active medium is negative, the conditions may be favourable for the Andronov — Hopf bifurcation. This leads to the appearance of periodic transverse wave structures. The main parameters of these waves (velocity, period, amplitude, growth increment) are found. It is also shown that a transition of a periodic wave pattern into a chaotic one is possible with increase in the wave amplitude.

Zaikin, A. P.; Kurguzkin, A. A.; Molevich, N. E.

1999-06-01

290

Numerical modeling of the spatial and spectro-temporal behavior of wide-aperture unstable resonator semiconductor lasers  

Microsoft Academic Search

We propose a numerical model adapted to the analysis of the (sub)picosecond dynamics of broad area semiconductor optical systems with a simultaneous description of the 2-D spatial and spectral behaviors. The model combines the advantages of the beam propagation method and time-domain method and treats the 2-D spatial inhomogeneities of the laser structure as well as the gain nonlinearities, the

A. V. Chelnokov; J.-M. Lourtioz; P. Gavrilovic

1995-01-01

291

Single-beam trapping using laser beams focused by low and high numerical apertures: angular spectrum approach  

NASA Astrophysics Data System (ADS)

Single beam optical tweezers hold particles behind the focal plane due to the highly focused laser beam. However, even moderately focused beams may stably con ne particles of high refractive index contrast and sizes up to half wavelength. This is caused by the fact that the light structure near focus is complex even for such moderately focused beams. The intensity pro le consists of several axial oscillations as well as off-axis lobes or rings which enhance trapping. Moreover, side lobes provide another multiple trapping sites for small sized particles. The properties of these traps will be analyzed theoretically by means of Generalized Lorenz-Mie Scattering theory.

Siler, Martin; Brzobohaty, Oto; Jakl, Petr; Karasek, Vitezslav; Zemanek, Pavel

2014-02-01

292

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

Microsoft Academic Search

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

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

1996-01-01

293

Large area single and multi-core photonic crystal fiber amplifiers and lasers  

Microsoft Academic Search

We use a combination of finite element modal analysis and laser modeling to design high power, large core area, single transverse mode and phase-locked multi-core photonic crystal fiber amplifiers and lasers.

A. Mafi; J. V. Moloney

2003-01-01

294

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

295

The vector behavior of aberrations in high numerical aperture (0.9 < NA < 3.1) laser focusing systems  

NASA Astrophysics Data System (ADS)

This dissertation investigates vector behavior of aberrations for high numerical aperture optical systems using a solid immersion lens (SIL). In order to analyze the system, this dissertation introduces the illumination system transfer function (ISTF), which is a map in the space of the exit pupil that shows reflection and transmission properties of individual plane waves that are emitted from corresponding points in the exit pupil. A vector analysis using ISTF presents the role of propagating and evanescent energy in the SIL systems, where the boundary between the them is defined by total internal reflection. The behavior of third-order aberrations such as coma and astigmatism, are dramatically affected by polarization in high NA systems. The irradiance distribution exhibits significantly different characteristics, depending on how coma or astigmatism is aligned with the incident linear polarized light. Vector effects including diffraction, polarization, and aberration, are used to analyze tolerances along with a comparison to geometrical optics. Apodization in amplitude and phase of the angular spectrum is generated in high NA focusing systems due to the difference in vector transmission and reflection for each plane wave. The size of the incident gaussian beam is effectively reduced at the exit pupil by the amplitude apodization and causes a spot size increase in image space. The apodization in phase is called gap-induced aberration due to its dependence on the air gap. The gap- induced aberration does not come from lens surface imperfection, and it exhibits multiple orders of spherical aberration and astigmatism. The apodization in amplitude and phase is well characterized by separable supergaussian functions, where each function depends on the refractive index of the SIL n SIL and the air gap height h. The best defocus, based on characteristics of gap-induced aberration, is suggested to be a good compensator only for low nSIL and h. The system performance, as represented by Strehl ratio and spot width, is characterized as a function of nSIL and h before and after defocus. C vector formalism is developed based on the common-mode and different-mode transmission coefficients between p and s polarization. Experiments to confirm the apodization are summarized and compared with simulation.

Jo, Sseunhyeun

296

Laser conditioning methods for hafnia silica multiplayer mirrors.  

National Technical Information Service (NTIS)

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 Facili...

C. J. Stolz L. M. Sheehan S. M. Maricle M. R. Kozlowski R. T. Jennings

1998-01-01

297

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, André; Wolf, Peter

2013-10-20

298

Microstructured phosphate glass fiber lasers with large mode areas  

Microsoft Academic Search

We report fabrication and testing of the first phosphate glass microstructured fiber lasers. From cladding-pumped, 11 cm long fiber lasers of 430 ?m2 core area we obtain 3 W CW output with good beam quality.

L. Li; A. Schfilzgen; V. L. Ternyanko; T. Qiu; A. Mafi; J. V. Moloney; N. Peyghambarian

2005-01-01

299

On the relationship between small and large signal modulation capabilities in highly nonlinear quantum dot lasers  

NASA Astrophysics Data System (ADS)

The small signal modulation response of semiconductor lasers is commonly used to predict large signal modulation capabilities. Recent experiments suggest that this prediction may fail in some quantum dot (QD) lasers. We present a model supported by experiments, which shows that when the small signal modulation response is limited by gain compression and the gain is large, the laser can be modulated at very high bit rates. This effect is inherent to dynamics governing all semiconductor lasers but the conditions needed for high bit rate modulation in the presence of narrow small signal bandwidths are only obtainable in QD lasers.

Gready, D.; Eisenstein, G.; Gioannini, M.; Montrosset, I.; Arsenijevic, D.; Schmeckebier, H.; Stubenrauch, M.; Bimberg, D.

2013-03-01

300

Plasma Electrode Pockels Cells for the Beamlet and NIF lasers  

Microsoft Academic Search

We describe Plasma Electrode Pockels Cells (PEPC) for the Beamlet laser and the proposed National Ignition Facility (NIF) laser. These PEPC's, together with passive polarizers, function as large aperture (greater than 35 x 35 sq cm) optical switches enabling the design of high-energy (greater than 5 kJ), multipass laser amplifiers. In a PEPC, plasma discharges form on both sides of

M. A. Rhodes; B. Woods; J. Deyoreo; J. Atherton

1994-01-01

301

Laser cooling of stored relativistic ion beams with large momentum spreads using a laser system with a wide scanning range  

NASA Astrophysics Data System (ADS)

New results on laser cooling of stored, bunched, relativistic ion beams are presented. For the first time it has been possible to cool an ion beam with large momentum spread without initial electron cooling or scanning of the bunching frequency by using a single cw laser system.

Wen, Weiqiang; Winters, Danyal; Beck, Tobias; Rein, Benjamin; Walther, Thomas; Tichelmann, Sascha; Birkl, Gerhard; Sanchez-Alarcon, Rodolfo; Ullmann, Johannes; Lochmann, Matthias; Nörtershäuser, Wilfried; Clark, Colin; Kozhuharov, Christopher; Kühl, Thomas; Sanjari, Shahab; Litvinov, Yuri; Giacomini, Tino; Steck, Markus; Dimopoulou, Christina; Nolden, Fritz; Stöhlker, Thomas; Yang, Jie; Zhang, Dacheng; Ma, Xinwen; Seltmann, Michael; Siebold, Matthias; Schramm, Ulrich; Bussmann, Michael

2014-04-01

302

Pulsed chemical HF laser with a large discharge gap  

SciTech Connect

The characteristics of the radiation emitted by an electric-discharge pulsed chemical HF laser with a discharge gap of 10 cm are studied. The discharge was stabilised by a semiconducting ferroelectric ceramic layer deposited on plane metal electrodes. The specific energy and technical efficiency were 3 J L{sup -1} and 3.4%, respectively, for a laser operating on a nonchain reaction in SF{sub 6}-H{sub 2} mixture and 25 J L{sup -1} and 26%, respectively, for a laser operating on a chain reaction in F{sub 2}-O{sub 2}-SF{sub 6}-H{sub 2} mixture. (lasers)

Azarov, M A; Klimuk, Evgenii A; Kutumov, Konstantin A; Troshchinenko, G A [Russian Science Centre 'Applied Chemistry', St Petersburg (Russian Federation); Lacour, Bernard M [Laboratoire de Physique des Gaz et des Plasmas, Universite Paris-Sud, Orsay (France)

2004-11-30

303

Transmission of information from large groups of sensors using synthetic aperture radar and modulated reradiation, and, Quasi-regular LDPC code design for QAM constellations  

Microsoft Academic Search

This thesis consists of two parts. In the first part, we develop a remote data collection system to extract information from a number of passive sensors. Active transmitters on sensors, being inherently energy expensive, pose a bottleneck to long battery life. We propose modulated reradiation of radar illumination by sensor nodes as a means to transmit information. A Synthetic Aperture

Srinivas V. Vanjari

2006-01-01

304

Longwave infrared (LWIR) coded aperture dispersive spectrometer.  

PubMed

We describe a static aperture-coded, dispersive longwave infrared (LWIR) spectrometer that uses a microbolometer array at the detector plane. The two-dimensional aperture code is based on a row-doubled Hadamard mask with transmissive and opaque openings. The independent column code nature of the matrix makes for a mathematically well-defined pattern that spatially and spectrally maps the source information to the detector plane. Post-processing techniques on the data provide spectral estimates of the source. Comparative experimental results between a slit and coded aperture for emission spectroscopy from a CO(2) laser are demonstrated. PMID:19532832

Fernandez, C; Guenther, B D; Gehm, M E; Brady, D J; Sullivan, M E

2007-04-30

305

Chiral slab polarization transformer for aperture antennas  

Microsoft Academic Search

The cross polarization of large aperture antennas can be eliminated by a chiral slab transformer in front of the aperture to obtain a more efficient field pattern. The inhomogeneous chirality distribution required can easily be achieved by using a mixture of right- and left-hand helices so that the total density of the helices is constant inside the slab. Reflection from

Ari J. Viitanen; Ismo V. Lindell

1998-01-01

306

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

307

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

NASA Astrophysics Data System (ADS)

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

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

2008-01-01

308

High efficiency, 40 W cw Nd: YLF laser with large TEM00 mode  

Microsoft Academic Search

A TEM00 polarized beam of 40 W at 1047 nm and 35 W at 1053 nm has been extracted from a Nd: YLF rod of large cross-section (6.35 mm diameter). By an appropriate resonator design, which uses the rod as mode selecting aperture, the highest efficiency so far reported for TEM00 operation at this power level has been obtained. The

Giulio Cerullo; Sandro de Silvestri; Vittorio Magni

1992-01-01

309

Aberration beam shaping in laser cutting with large aspect ratios  

NASA Astrophysics Data System (ADS)

The reasons of occurrence of the primary aberrations in optical systems for high-power-technology lasers have been analyzed. The laser intensity profile transformation in presence of a primary aberration of the both signs has been studied. A number of the optical systems with completely the same optical parameters except uncorrected primary aberration has been designed. The influence of laser intensity profile produced by these systems on the quality of midpenetrating laser cutting has been examined. It has been found that good quality cuts may be obtained for every shape of the laser intensity distribution. However, the more the scale of an uncorrected aberration is the more accurate the focal point position has to be maintained.

Yurevich, V. I.; Gorny, S. G.; Polyakov, I. V.; Afonyushkin, A. A.

2014-02-01

310

Precision modeling of grid fields and beam dynamics in a large-aperture accelerator for an electroionization laser  

NASA Astrophysics Data System (ADS)

The accelerator considered is a planar tetrode-type system. It contains a grid of lengthy glowers emitting beamlets, which cover an anode exit window of 6600 cm 2 in area. Key parameters of the system, i.e. maximal extracted current, continuous service life and reliability, depend directly on the physical properties of the exit window foil, as well as non-uniformity in density of the accelerated beam. Adequate computer simulation is necessary in designing the latter. In this paper, careful modeling of electrostatic fields, which are highly nonlinear near the grid rods of small diameter, has been performed using the boundary collocation method. Stray magnetic cathode fields were found analytically. Electron ray tracing in these fields provided useful information on abnormal local heating of the foil due to aberrations in the beamlets.

Zuev, Yuri V.

2006-03-01

311

Large-aperture fast multilevel Fresnel zone lenses in glass and ultrathin polymer films for visible and near-infrared imaging applications.  

PubMed

The ability to fabricate 4-level diffractive structures with 1 µm critical dimensions has been demonstrated for the creation of fast (?f/3.1 at 633 nm) Fresnel zone lenses (FZLs) with >60% diffraction efficiency into the -1 focusing order and nearly complete suppression of 0 and +1 orders. This is done using tooling capable of producing optics with 800 mm apertures. A 4-level grating fabricated in glass at 300 mm aperture is shown to have <15??nm rms holographic phase error. Glass FZLs have also been used as mandrels for casting zero-thermal-expansion, 20 µm thick polymer films created with the 4-level structure as a route to mass replication of efficient diffractive membranes for ultralight segmented space-based telescope applications. PMID:24787399

Britten, Jerald A; Dixit, Shamusundar N; DeBruyckere, Michael; Steadfast, Daniel; Hackett, James; Farmer, Brandon; Poe, Garrett; Patrick, Brian; Atcheson, Paul D; Domber, Jeanette L; Seltzer, Aaron

2014-04-10

312

Measurement system for large size laser beam intensity distribution based on CCD diffuse transmission imaging  

NASA Astrophysics Data System (ADS)

We designed a measurement system to measure large size laser beam intensity distribution based on CCD diffuse transmission imaging. The measurement principle is presented. The configuration of the system is introduced. An emphasis is placed on the design of diffuse transmission target. The methods of spot geometry distortion correction and intensity distortion correction are described in detail. After laser spot correction, we can get the real laser beam intensity profile. The test results are given, which validate the correctness of the method. The paper provides a new way to measure quantitatively the profile of large size laser beam with high accuracy.

Pang, Miao; Rong, Jian; Yuan, Xuewen; Gao, Xueyan; Zhou, Shan

2013-12-01

313

PM double-clad fibers for high-power lasers and amplifiers  

Microsoft Academic Search

Fibers for high-power laser and amplifier applications require large claddings with high numerical apertures for efficiently coupling pump energy. In addition, such fibers should have high rare-earth dopant concentrations in relatively large cores, with low numerical apertures, to reduce non-linearities. Furthermore, polarization maintaining double-clad fibers (PM-DCF) are needed for coherently combining the outputs of several lasers\\/amplifiers to achieve output powers

Kanishka Tankala; Adrian Carter; David P. Machewirth; Julia Farroni; Jaroslaw Abramczyk; Upendra H. Manyam

2003-01-01

314

LASS (Larger Aperture Superconducting Solenoid) Spectrometer.  

National Technical Information Service (NTIS)

LASS is the acronym for the Large Aperture Superconducting Solenoid spectrometer which is located in an rf-separated hadron beam at the Stanford Linear Accelerator Center. This spectrometer was constructed in order to perform high statistics studies of mu...

D. Aston N. Awaji B. Barnett T. Bienz R. Bierce

1986-01-01

315

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

316

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

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

317

Future trends for large-area pulsed laser deposition  

Microsoft Academic Search

Over the past decade Pulsed Laser Deposition (PLD) has become a routine laboratory tool with which to grow a wide variety of complex chemical compounds. A recent review of the literature has shown that over 275 different compounds have been deposited with this unique Physical Vapor Deposition (PVD) process [1]. Also, recent reports have shown that this process can be

J. A. Greer; M. D. Tabat; C. Lu

1997-01-01

318

Future trends for large-area pulsed laser deposition  

Microsoft Academic Search

Over the past decade Pulsed Laser Deposition (PLD) has become a routine laboratory tool with which to grow a wide variety of complex chemical compounds. A recent review of the literature has shown that over 275 different compounds have been deposited with this unique Physical Vapor Deposition (PVD) process. Also, recent reports have shown that this process can be used

J. A. Greer; M. D. Tabat; C. Lu

1997-01-01

319

Large-eddy simulation and laser diagnostic measurements of mixing in a coaxial jet mixer  

Microsoft Academic Search

Numerical and experimental investigation of the turbulent mixing in a coaxial jet mixer is presented. Laser doppler velocimetry (LDV) and planar laser induced fluorescence (PLIF) were applied for measurements of velocity and scalar fields and their fluctuations. Numerical simulations were performed using large-eddy simulation and RANS with different closure models. These results are used for validation of numerical models and

Egon Hassel; Steffen Jahnke; Nikolai Kornev; Igor Tkatchenko; Valery Zhdanov

2006-01-01

320

High-Average-Power Room-Temperature Large Optical Cavity (LOC) Lasers.  

National Technical Information Service (NTIS)

This report concerns the results of a one-year research program aimed at the study and development of laser structures suitable for high-power, high-duty cycle operation at room temperature. Of the laser structures which can be used, the large optical cav...

H. Kressel H. F. Lockwood H. S. Sommers M. Ettenberg

1972-01-01

321

Short-length microstructured phosphate glass fiber lasers with large mode areas  

Microsoft Academic Search

We report fabrication and testing of the first phosphate glass microstructured fiber lasers with large Er-Yb-codoped cores. For an 11-cm-long cladding-pumped fiber laser, more than 3 W of continuous wave output power is demonstrated, and near single-mode beam quality is obtained for an active core area larger than 400 mum.

L. Li; Axel Schülzgen; V. L. Temyanko; T. Qiu; M. M. Morrell; Q. Wang; A. Mafi; J. V. Moloney; Nasser Peyghambarian

2005-01-01

322

Gain-guided solitons in dispersion-managed fiber lasers with large net cavity dispersion.  

PubMed

Gain-guided solitons are experimentally observed in dispersion-managed fiber lasers with large net positive group-velocity dispersion. It is shown that formation of the soliton is a robust feature of the lasers. Numerical simulations also confirmed the experimental results. PMID:17001365

Zhao, L M; Tang, D Y; Cheng, T H; Lu, C

2006-10-15

323

Systematic design and analysis of laser-guide-star adaptive-optics systems for large telescopes  

Microsoft Academic Search

The authors discuss the design of laser-guided adaptive-optics systems for the large, 8-10-m-class telescopes. Through proper choice of system components and optimized system design, the laser power that is needed at the astronomical site can be kept to a minimum. 37 refs., 9 figs., 3 tabs.

D. T. Gavel; J. R. Morris; R. G. Vernon

1994-01-01

324

Ronchi-like laser interferometer for large spectral region-from extreme UV to far infrared  

Microsoft Academic Search

Proposed interferometer is a combination of well known Ronchi optical tester and a special designed laser interferometer for large spectral region: from extreme ultraviolet to far infrared. This apparatus consists of the coherent point light source (it is possible also to use parallel coherent point light beam, for example of laser), two off-axis mirrors, forming two point sources of light,

G. M. Popov; E. G. Popov

2003-01-01

325

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

326

Single-row laser beam with energy strengthened ends for continuous scanning laser surface hardening of large metal components  

NASA Astrophysics Data System (ADS)

For laser surface hardening of metal components with large superficies, a binary grating is proposed to generate single-row laser beam with proportional-intensity diffractive orders. To obtain a uniform hardened band distribution and improve the wear resistance of the sample surface, the binary grating is designed to produce single-row laser beam with energy strengthened at the two ends. The profile of the laser beam spot was designed to be strip with high length-width ratio to improve the machining efficiency of the hardening of large surfaces. A new advantage is suggested to obtain proportional intensity spots with evenness. The design results show that the diffractive efficiency of the binary grating is more than 70%, and the uniformity is less than 3%. The surface profile of the grating fabricated was measured, which shows that the fabrication error is less than 2%. The application of the binary grating in the laser surface hardening of metal components with large superficies is experimentally investigated, and the results show that the hardness distribution of the modified layer is more uniform than that hardened by Gaussian laser beam or array spots with equal intensity distribution.

Li, ShaoXia; Yu, Gang; Zhang, JingChuan; Tan, QiaoFeng; Xu, NingHan; Sun, PeiPei; Zheng, CaiYun

2013-06-01

327

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.

328

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

SciTech Connect

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 1 100 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.

1992-12-31

329

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

SciTech Connect

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 1 100 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.

1992-01-01

330

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

331

Measurements of aperture averaging on bit-error-rate  

Microsoft Academic Search

We report on measurements made at the Shuttle Landing Facility (SLF) runway at Kennedy Space Center of receiver aperture averaging effects on a propagating optical Gaussian beam wave over a propagation path of 1,000 m. A commercially available instrument with both transmit and receive apertures was used to transmit a modulated laser beam operating at 1550 nm through a transmit

Gary L. Bastin; Larry C. Andrews; Ronald L. Phillips; Richard A. Nelson; Bobby A. Ferrell; Michael R. Borbath; Darren J. Galus; Peter G. Chin; William G. Harris; Jose A. Marin; Geoffrey L. Burdge; David Wayne; Robert Pescatore

2005-01-01

332

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

333

Continuous Earth Rotation Monitoring with the large Ring Laser G  

NASA Astrophysics Data System (ADS)

Over the last decade, ring lasers have found their way back into the research laboratories. By scaling them up in size, they have gained several orders of magnitude over their commercial counterparts, both in sensitivity and stability. Unlike the established space geodetic techniques SLR/LLR and VLBI, ring lasers can be operated autonomous and continuously. Furthermore laser gyros reach a resolution of 1 pico-rad/s already after an integration time of less than 2 hours. This opens the door for the research of high frequency variations in Earth rotation. Over the last year we have improved the sensor sensitivity by as much as a factor of 3 in order to reach the shot noise limit at 2.1x10-11 rad/s/sqrt(Hz). So the regime of ??/? ? 10-9 of Earth rotation becomes accessible to a local rotation sensor. Recent efforts concentrate on the reduction of scale factor instability by controlling the drift induced by atmospheric pressure variations and the corresponding temperature changes from adiabatic expansion and compression of the local air as well as a new approach to the modeling of the behavior of the sensor location. This talk outlines recent progress in Sagnac interferometry.

Schreiber, K. U.; Klügel, T.; Wells, J. P.; Holdaway, J.; Gebauer, A.

2010-12-01

334

Underwater laser imaging system with large field of view  

NASA Astrophysics Data System (ADS)

Two years ago we designed, built, and tested a ROV mounted range-gated imaging system. Given that the target covers at least one pixel at the maximum range of interest the model predicts that for the same laser power and under the condition where the field of illumination is matched to the field of view there is no performance penalty in increasing the field of view. In order to test this result we have built and deployed a second generation underwater imaging system whose field of view and field of illumination are matched and continuously variable from 60 mr to 600 mr in water. The laser source was also upgraded in power by a factor of 10 to a water cooled, 2-kHz, 400 mw doubled Nd:YLF laser. The light is collected by a 7-cm diameter zoom lens. The detector is a gated image intensifier with a 7-ns gate and a gain which is continuously variable from 500 to 1,000,000. An on-board image processor has been added to the system. It allows us to frame integrate in real-time and thus further improve system performance.

Fournier, Georges R.; Bonnier, Deni; Forand, J. Luc

1994-10-01

335

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

PubMed

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

Deng, Chun; Ki, Hyungson

2013-10-21

336

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

337

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

SciTech Connect

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

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

2011-02-01

338

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

339

Overview of recent advances in excimer laser technology at Los Alamos  

SciTech Connect

From among the areas of excimer laser development at Los Alamos two are selected for further discussion: ultra-high brightness excimer laser systems and discharge-pumped XeF(C..-->..A) lasers operating in the blue-green portion of the spectrum. Two different high brightness systems are described. One is based on small-aperture KrF amplifiers, while the other is based on a large-aperture XeCl amplifier. The XeF(C..-->..A) laser is tunable from 435 to 525 nm, and may one day become a viable alternative to pulsed dye lasers for many applications. 14 refs., 4 figs.

Bigio, I.J.; Sze, R.C.; Taylor, A.J.; Gibson, R.B.

1988-01-01

340

Quad aperture RF definition  

NASA Technical Reports Server (NTRS)

A single STS package 118 m diameter hoop/column antenna is capable of providing service for appr. 250,000 mobile users. The selected quad aperture configuration is able to provide at least 25 db C/I without cable blockage, column scatter, coupling between quad apertures, and tolerance effects. A feed can be designed which uses single polarized radiating elements while the overall system employs dual polarization. The quad aperture concept can eliminate the use of diplexers and their associated losses. The critical technology issues in the RF area include the design of the radiating elements, BFN, monolithic power amplifiers and receiver front end, tolerance control and packaging of the feed.

Foldes, P.

1982-01-01

341

Sub-Aperture Interferometers  

NASA Technical Reports Server (NTRS)

Sub-aperture interferometers -- also called wavefront-split interferometers -- have been developed for simultaneously measuring displacements of multiple targets. The terms "sub-aperture" and "wavefront-split" signify that the original measurement light beam in an interferometer is split into multiple sub-beams derived from non-overlapping portions of the original measurement-beam aperture. Each measurement sub-beam is aimed at a retroreflector mounted on one of the targets. The splitting of the measurement beam is accomplished by use of truncated mirrors and masks, as shown in the example below

Zhao, Feng

2010-01-01

342

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

343

Permeability of self-affine aperture fields.  

PubMed

We introduce a model that allows for the prediction of the permeability of self-affine rough channels (one-dimensional fracture) and two-dimensional fractures over a wide range of apertures. In the lubrication approximation, the permeability shows three different scaling regimes. For fractures with a large mean aperture or an aperture small enough to the permeability being close to disappearing, the permeability scales as the cube of the aperture when the zero level of the aperture is set to coincide with the disappearance of the permeability. Between these two regimes, there is a third regime where the scaling is due to the self-affine roughness. For rough channels, the exponent is found to be 3-1/H, where H is the Hurst exponent. For two-dimensional fractures, it is necessary to introduce an equivalent aperture b(c) to make the scaling regime apparent. b(c) is defined as the hydraulic aperture of the most restrictive barrier crossing the fracture normal to the flow direction. This regime is characterized by an exponent higher than that for the one-dimensional case: it is 2.25 for H=0.8 and 2.16 for H=0.3. PMID:21230346

Talon, Laurent; Auradou, Harold; Hansen, Alex

2010-10-01

344

Large mode area waveguides with polarization functions by volume ultrafast laser photoinscription of fused silica.  

PubMed

We present optical designs allowing large mode area light guiding by ultrafast laser photoinscription of bulk fused silica. If usual concepts are based on large core and depressed cladding, evanescently coupled multicore waveguides with coherent mode superposition can be effective solutions, where the introduction of nanostructured defects determines additional polarization functions. PMID:23722791

Cheng, G; D'Amico, C; Liu, X; Stoian, R

2013-06-01

345

Broadband synthetic aperture geoacoustic inversion.  

PubMed

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

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

2013-07-01

346

Demonstration of synthetic aperture imaging ladar  

NASA Astrophysics Data System (ADS)

The spatial resolution of a conventional imaging LADAR system is constrained by the diffraction limit of the telescope aperture. The purpose of this work is to investigate Synthetic Aperture Imaging LADAR (SAIL), which employs aperture synthesis with coherent laser radar to overcome the diffraction limit and achieve fine-resolution, long range, two-dimensional imaging with modest aperture diameters. This paper details our laboratory-scale SAIL testbed, digital signal processing techniques, and image results. A number of fine-resolution, well-focused SAIL images are shown including both retro-reflecting and diffuse scattering targets. A general digital signal processing solution to the laser waveform instability problem is described and demonstrated, involving both new algorithms and hardware elements. These algorithms are primarily data-driven, without a priori knowledge of waveform and sensor position, representing a crucial step in developing a robust imaging system. These techniques perform well on waveform errors, but not on external phase errors such as turbulence or vibration. As a first step towards mitigating phase errors of this type, we have developed a balanced, quadrature phase, laser vibrometer to work in conjunction with our SAIL system to measure and compensate for relative line of sight motion between the target and transceiver. We describe this system and present a comparison of the vibrometer-measured phase error with the phase error inferred from the SAIL data.

Buell, W.; Marechal, N.; Buck, J.; Dickinson, R.; Kozlowski, D.; Wright, T.; Beck, S.

2005-05-01

347

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

PubMed

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

2014-02-15

348

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

SciTech Connect

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

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

1999-02-01

349

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.

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

2014-01-01

350

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

351

Multispectral laser-induced fluorescence imaging system for large biological samples  

Microsoft Academic Search

A laser-induced fluorescence imaging system developed to capture multispectral fluorescence emission images simultaneously from a relatively large target object is described. With an expanded, 355-nm Nd:YAG laser as the excitation source, the system captures fluorescence emission images in the blue, green, red, and far-red regions of the spectrum centered at 450, 550, 678, and 730 nm, respectively, from a 30-cm-diameter

Moon S. Kim; Alan M. Lefcourt; Yud-Ren Chen

2003-01-01

352

Cleaved-coupled-cavity lasers with large cavity length ratios for enhanced stability  

SciTech Connect

The fabrication and operation of the first cleaved-coupled-cavity (C/sup 3/) semiconductor lasers with large cavity length ratios are described. The internal cleaved facet is precisely positioned by photochemically etching a groove through most of the wafer. Single longitudinal mode operation is obtained over a temperature range of 21 /sup 0/C and over a current range of threshold to greater than four times threshold. Sidemode suppression of 100:1 was measured when the laser was modulated at 350 MHz with an extinction ratio greater than 10:1. These results are experimentally and theoretically compared to approximately equal length C/sup 3/ lasers.

Bowers, J.E.; Bjorkholm, J.E.; Burrus, C.A.; Coldren, L.A.; Hemenway, B.R.; Wilt, D.P.

1984-05-01

353

Investigation of standing wave formation in a human skull for a clinical prototype of a large-aperture, transcranial MR-guided Focused Ultrasound (MRgFUS) phased array: An experimental and simulation study  

PubMed Central

Standing wave formation in an ex vivo human skull was investigated using a clinical prototype of a 30 cm diameter with 15 cm radius of curvature, low frequency (230 kHz), hemispherical transcranial Magnetic Resonance guided Focused Ultrasound (MRgFUS) phased-array. Experimental and simulation studies were conducted with changing aperture size and f-number configurations of the phased array, and qualitatively and quantitatively examined the acoustic pressure variation at the focus due to standing waves. The results demonstrated that the nodes and anti-nodes of standing wave produced by the small aperture array were clearly seen at approximately every 3 mm. The effect of the standing wave became more pronounced as the focus was moved closer to skull base. However, a sharp focus was seen for the full array, and there was no such standing wave pattern in the acoustic plane or near the skull base. This study showed that the fluctuation pressure amplitude would be greatly reduced by using a large-scale, hemispherical phased array with a low f-number.

Song, Junho; Pulkkinen, Aki; Huang, Yuexi; Hynynen, Kullervo

2014-01-01

354

Micro-scanning mirrors for high-power laser applications in laser surgery  

NASA Astrophysics Data System (ADS)

We present two novel micro scanning mirrors with large aperture and HR dielectric coatings suitable for high power laser applications in a miniaturized laser-surgical instrument for neurosurgery to cut skull tissue. An electrostatic driven 2D-raster scanning mirror with 5x7.1mm aperture is used for dynamic steering of a ps-laser beam of the laser cutting process. A second magnetic 2D-beam steering mirror enables a static beam correction of a hand guided laser instrument. Optimizations of a magnetic gimbal micro mirror with 6 mm x 8 mm mirror plate are presented; here static deflections of 3° were reached. Both MEMS devices were successfully tested with a high power ps-laser at 532nm up to 20W average laser power.

Sandner, Thilo; Kimme, Simon; Grasshoff, Thomas; Todt, Ulrich; Graf, Alexander; Tulea, Cristian; Lenenbach, Achim; Schenk, Harald

2014-03-01

355

Variable-aperture screen  

DOEpatents

Apparatus is described 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. 10 figures.

Savage, G.M.

1991-10-29

356

Polarization coded aperture.  

PubMed

Two examples are presented to illustrate the advantages of polarization coded apertures, in which the incoming light will rotate its polarization at a portion of an aperture. In the first example the depth of field of a diffraction limited lens is increased without sacrificing the light throughput; in the second example the axial focal intensity of a pixelated Fresnel zone plate is increased by 100%. Both examples work for linearly polarized or unpolarized illumination. PMID:19516844

Chi, Wanli; Chu, Kaiqin; George, Nicholas

2006-07-24

357

Large angle and high linearity two-dimensional laser scanner based on voice coil actuators  

NASA Astrophysics Data System (ADS)

A large angle and high linearity two-dimensional laser scanner with an in-house ingenious deflection angle detecting system is developed based on voice coil actuators direct driving mechanism. The specially designed voice coil actuators make the steering mirror moving at a sufficiently large angle. Frequency sweep method based on virtual instruments is employed to achieve the natural frequency of the laser scanner. The response shows that the performance of the laser scanner is limited by the mechanical resonances. The closed-loop controller based on mathematical model is used to reduce the oscillation of the laser scanner at resonance frequency. To design a qualified controller, the model of the laser scanner is set up. The transfer function of the model is identified with MATLAB according to the tested data. After introducing of the controller, the nonlinearity decreases from 13.75% to 2.67% at 50 Hz. The laser scanner also has other advantages such as large deflection mirror, small mechanical structure, and high scanning speed.

Wu, Xin; Chen, Sihai; Chen, Wei; Yang, Minghui; Fu, Wen

2011-10-01

358

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 µm 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 µm. 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 µm (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; Brückner, Andreas; Bräuer, Andreas; Tünnermann, Andreas

2012-02-13

359

Large growth Rayleigh-Taylor experiments using shaped laser pulses  

Microsoft Academic Search

Larege growth Rayleigh-Taylor (RT) experiments have been conducted by pulse-shaped radiative acceleration of planar fluorosilicone foils with 50-μm wavelength initial surface perturbations. Foils with large-amplitude initial perturbation quickly enter the nonlinear RT regime, and show little growth. Foils with very-small-amplitude initial perturbations grow exponentially for longer, and show much larger growth factors. From comparisons with two-dimensional computer simulations, we deduce

B. A. Remington; S. W. Haan; S. G. Glendinning; J. D. Kilkenny; D. H. Munro; R. J. Wallace

1991-01-01

360

Desorption of large organic molecules by laser-induced plasmon excitation  

SciTech Connect

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

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

1991-01-01

361

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

362

Shock wave absorber having apertured plate  

DOEpatents

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

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

1983-08-26

363

Transmission of information from large groups of sensors using synthetic aperture radar and modulated reradiation, and, Quasi-regular LDPC code design for QAM constellations  

NASA Astrophysics Data System (ADS)

This thesis consists of two parts. In the first part, we develop a remote data collection system to extract information from a number of passive sensors. Active transmitters on sensors, being inherently energy expensive, pose a bottleneck to long battery life. We propose modulated reradiation of radar illumination by sensor nodes as a means to transmit information. A Synthetic Aperture processing technique is developed to decode the transmitted information and simultaneously obtain a geographic map of the sensor locations. Modulated re-radiation be achieved by switching a load on the sensor antenna. Load modulation consumes negligible power compared to an active transmitter, thus reducing the overall power consumption of the sensor. To eliminate the clutter interference in the imaging process due to the presence of unwanted targets, a nonlinear antenna load is used and the reradiated harmonics are processed. In the second part, we develop an LDPC coded modulation scheme for bandwidthefficient data transmission using QAM modulation. The underlying LDPC code is a rate 1/2 quasi-regular code having a low check degree of 5. The code is designed to offer different levels of protection to each bit position in the modulation symbol. Edges attached to different bit positions are treated differently and constraints are imposed on the check node connections to maximize the reliability of the outgoing messages from the check nodes. With a suitable choice of the constellation labeling and by using iterative demodulation, the code is shown to provide excellent performance on an AWGN channel at reasonably short block lengths.

Vanjari, Srinivas V.

364

Multiple instrument distributed aperture sensor (MIDAS) for remote sensing  

NASA Astrophysics Data System (ADS)

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

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

2004-11-01

365

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

NASA Astrophysics Data System (ADS)

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

Helm, P. Johannes

2012-02-01

366

Excitation of a large amplitude plasma wave by a short laser pulse  

NASA Astrophysics Data System (ADS)

The laser wake-field accelerator (LWFA) originally proposed by Tajima and Dawson (1979) is a plasma-based accelerator which employs the large-amplitude wave excited by a laser pulse propagating through the plasma. A discussion is presented of recent results on the excitation of a large amplitude plasma wave by a single electromagnetic packet which are relevant to the LWFA scheme, giving attention to both the weak-pump, weakly-relativistic limit and the fully relativistic regime. An efficient wake-beat excitation mechanism is suggested for the case of ultrashort high intensity pulses.

de Angelis, U.

1990-01-01

367

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

368

Filled aperture concepts for the Terrestrial Planet Finder  

NASA Astrophysics Data System (ADS)

Filled aperture telescopes can deliver a real, high Strehl image which is well suited for discrimination of faint planets in the vicinity of bright stars and against an extended exo-zodiacal light. A filled aperture offers a rich variety of PSF control and diffraction suppression techniques. Filled apertures are under consideration for a wide spectral range, including visible and thermal-IR, each of which offers a significant selection of biomarker molecular bands. A filled aperture visible TPF may be simpler in several respects than a thermal-IR nuller. The required aperture size (or baseline) is much smaller, and no cryogenic systems are required. A filled aperture TPF would look and act like a normal telescope - vendors and users alike would be comfortable with its design and operation. Filled aperture telescopes pose significant challenges in production of large primary mirrors, and in very stringent wavefront requirements. Stability of the wavefront control, and hence of the PSF, is a major issue for filled aperture systems. Several groups have concluded that these and other issues can be resolved, and that filled aperture options are competitive for a TPF precursor and/or for the full TPF mission. Ball, Boeing-SVS and TRW have recently returned architecture reviews on filled aperture TPF concepts. In this paper, I will review some of the major considerations underlying these filled aperture concepts, and suggest key issues in a TPF Buyers Guide.

Ridgway, Stephen T.

2003-02-01

369

Synthetic Aperture Techniques for Sonar Systems  

Microsoft Academic Search

about this segment is still very far away from that of the land segment. Synthetic aperture is a technique that enables high resolution through the coherent processing of consecutive displaced echo data. Instead of using one static large array of transducers, it uses the along-track displacement of the sensors to synthesize a large virtual array. The resolution thus obtained is

Sérgio Rui Silva; Sérgio Cunha; Aníbal Matos; Nuno Cruz

2009-01-01

370

Numerical Aperture Limits on Efficient Ball Lens Coupling of Laser Diodes to Single-Mode Fibers with Defocus to Balance Spherical Aberration.  

National Technical Information Service (NTIS)

The potential capabilities and limitations of single ball lenses for coupling laser diode radiation to single-mode optical fibers have been analyzed; parameters important to optical communications were specifically considered. These parameters included co...

R. G. Wilson

1994-01-01

371

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

372

Confocal coded aperture imaging  

DOEpatents

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

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

2001-01-01

373

Cleaved-coupled-cavity lasers with large cavity length ratios for enhanced stability  

Microsoft Academic Search

The fabrication and operation of the first cleaved-coupled-cavity (C3) semiconductor lasers with large cavity length ratios are described. The internal cleaved facet is precisely positioned by photochemically etching a groove through most of the wafer. Single longitudinal mode operation is obtained over a temperature range of 21 °C and over a current range of threshold to greater than four times

J. E. Bowers; J. E. Bjorkholm; C. A. Burrus; L. A. Coldren; B. R. Hemenway; D. P. Wilt

1984-01-01

374

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

National Technical Information Service (NTIS)

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 r...

W. E. Stocum

1992-01-01

375

Large and small-signal dynamic behavior of high-speed dual-polarization quantum-well semiconductor lasers  

Microsoft Academic Search

The transmission-line laser model is modified to model both transverse-electric (TE) and transverse-magnetic (TM) modes so that it is applicable to quantum-well (QW) dual-polarization lasers and polarization-insensitive semiconductor optical amplifiers (SOAs). The effects of carrier transport are also included in the model. The resulting dual-polarization transmission-line laser model is used to study large- and small-signal dynamic behavior of dual-polarization lasers.

Linh V. T. Nguyen; Arthur J. Lowery; Dalma Novak

1997-01-01

376

High-power picosecond laser with 400W average power for large scale applications  

NASA Astrophysics Data System (ADS)

Laser processing is generally known for low thermal influence, precise energy processing and the possibility to ablate every type of material independent on hardness and vaporisation temperature. The use of ultra-short pulsed lasers offers new possibilities in the manufacturing of high end products with extra high processing qualities. For achieving a sufficient and economical processing speed, high average power is needed. To scale the power for industrial uses the picosecond laser system has been developed, which consists of a seeder, a preamplifier and an end amplifier. With the oscillator/amplifier system more than 400W average power and maximum pulse energy 1mJ was obtained. For study of high speed processing of large embossing metal roller two different ps laser systems have been integrated into a cylinder engraving machine. One of the ps lasers has an average power of 80W while the other has 300W. With this high power ps laser fluencies of up to 30 J/cm2 at pulse repetition rates in the multi MHz range have been achieved. Different materials (Cu, Ni, Al, steel) have been explored for parameters like ablation rate per pulse, ablation geometry, surface roughness, influence of pulse overlap and number of loops. An enhanced ablation quality and an effective ablation rate of 4mm3/min have been achieved by using different scanning systems and an optimized processing strategy. The max. achieved volume rate is 20mm3/min.

Du, Keming; Brüning, Stephan; Gillner, Arnold

2012-02-01

377

Optofluidic laser for dual-mode sensitive biomolecular detection with a large dynamic range  

NASA Astrophysics Data System (ADS)

Enzyme-linked immunosorbent assay (ELISA) is a powerful method for biomolecular analysis. The traditional ELISA employing light intensity as the sensing signal often encounters large background arising from non-specific bindings, material autofluorescence and leakage of excitation light, which deteriorates its detection limit and dynamic range. Here we develop the optofluidic laser-based ELISA, where ELISA occurs inside a laser cavity. The laser onset time is used as the sensing signal, which is inversely proportional to the enzyme concentration and hence the analyte concentration inside the cavity. We first elucidate the principle of the optofluidic laser-based ELISA, and then characterize the optofluidic laser performance. Finally, we present the dual-mode detection of interleukin-6 using commercial ELISA kits, where the sensing signals are simultaneously obtained by the traditional and the optofluidic laser-based ELISA, showing a detection limit of 1?fg?ml?1 (38?aM) and a dynamic range of 6 orders of magnitude.

Wu, Xiang; Oo, Maung Kyaw Khaing; Reddy, Karthik; Chen, Qiushu; Sun, Yuze; Fan, Xudong

2014-04-01

378

LLNL medical and industrial laser isotope separation: large volume, low cost production through advanced laser technologies  

SciTech Connect

The goal of this LDRD project was to demonstrate the technical and economical feasibility of applying laser isotope separation technology to the commercial enrichment (>lkg/y) of stable isotopes. A successful demonstration would well position the laboratory to make a credible case for the creation of an ongoing medical and industrial isotope production and development program at LLNL. Such a program would establish LLNL as a center for advanced medical isotope production, successfully leveraging previous LLNL Research and Development hardware, facilities, and knowledge.

Comaskey, B.; Scheibner, K. F.; Shaw, M.; Wilder, J.

1998-09-02

379

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

380

Measurements of Aperture Averaging on Bit-Error-Rate  

NASA Technical Reports Server (NTRS)

We report on measurements made at the Shuttle Landing Facility (SLF) runway at Kennedy Space Center of receiver aperture averaging effects on a propagating optical Gaussian beam wave over a propagation path of 1,000 in. A commercially available instrument with both transmit and receive apertures was used to transmit a modulated laser beam operating at 1550 nm through a transmit aperture of 2.54 cm. An identical model of the same instrument was used as a receiver with a single aperture that was varied in size up to 20 cm to measure the effect of receiver aperture averaging on Bit Error Rate. Simultaneous measurements were also made with a scintillometer instrument and local weather station instruments to characterize atmospheric conditions along the propagation path during the experiments.

Bastin, Gary L.; Andrews, Larry C.; Phillips, Ronald L.; Nelson, Richard A.; Ferrell, Bobby A.; Borbath, Michael R.; Galus, Darren J.; Chin, Peter G.; Harris, William G.; Marin, Jose A.; Burdge, Geoffrey L.; Wayne, David; Pescatore, Robert

2005-01-01

381

Measurements of aperture averaging on bit-error-rate  

NASA Astrophysics Data System (ADS)

We report on measurements made at the Shuttle Landing Facility (SLF) runway at Kennedy Space Center of receiver aperture averaging effects on a propagating optical Gaussian beam wave over a propagation path of 1,000 m. A commercially available instrument with both transmit and receive apertures was used to transmit a modulated laser beam operating at 1550 nm through a transmit aperture of 2.54 cm. An identical model of the same instrument was used as a receiver with a single aperture that was varied in size up to 20 cm to measure the effect of receiver aperture averaging on Bit Error Rate. Simultaneous measurements were also made with a scintillometer instrument and local weather station instruments to characterize atmospheric conditions along the propagation path during the experiments.

Bastin, Gary L.; Andrews, Larry C.; Phillips, Ronald L.; Nelson, Richard A.; Ferrell, Bobby A.; Borbath, Michael R.; Galus, Darren J.; Chin, Peter G.; Harris, William G.; Marin, Jose A.; Burdge, Geoffrey L.; Wayne, David; Pescatore, Robert

2005-08-01

382

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

383

Large area single-mode parity-time-symmetric laser amplifiers.  

PubMed

By exploiting recent developments associated with parity-time (PT) symmetry in optics, we here propose a new avenue in realizing single-mode large area laser amplifiers. This can be accomplished by utilizing the abrupt symmetry breaking transition that allows the fundamental mode to experience gain while keeping all the higher order modes neutral. Such PT-symmetric structures can be realized by judiciously coupling two multimode waveguides, one exhibiting gain while the other exhibits an equal amount of loss. Pertinent examples are provided for both semiconductor and fiber laser amplifiers. PMID:22378386

Miri, Mohammad-Ali; LiKamWa, Patrik; Christodoulides, Demetrios N

2012-03-01

384

Large-area conditioning of optics for high-power laser systems  

NASA Astrophysics Data System (ADS)

In order to reach the high fluence goals of the Beamlet laser at Lawrence Livermore National Laboratory (LLNL), the polarizers in the system must be laser conditioned to increase their damage thresholds. Research has shown that by using a six-step raster conditioning program, the damage thresholds of the HfO2/SiO2 multilayer polarizer coatings can be increased to meet the Beamlet 3-ns design goal of 8 J/cm(exp 2). Because of the large size of the polarizers (73 cm by 37 cm by 9 cm), a large-area conditioning facility was constructed capable of rastering a one-meter optic, weighing as much as 400 pounds, at any specified use angle. A large translational stage moves the optic in a raster pattern through a stationary, 10-Hz rep-rated, 1064-nm beam with 10-ns pulses. A scatter measurement diagnostic allows on-the-fly evaluation of laser induced damage and logs the coordinates of the damage. Laser energy is measured pulse-to-pulse in order to ensure stability during a scan. A small amount of minor coating damage does occur during the process, but the damage does not grow upon further irradiation. This damage causes only a small increase in total scatter compared to that due to the preexisting defects, and would not influence the system performance.

Sheehan, L. M.; Kozlowski, M. R.; Rainer, F.; Staggs, M. C.

1993-12-01

385

Large-area conditioning of optics for high-power laser systems  

SciTech Connect

In order to reach the high fluence goals of the Beamlet laser at Lawrence Livermore National Laboratory (LLNL), the polarizers in the system must be laser conditioned to increase their damage thresholds. Research has shown that by using a six-step raster-conditioning program, the damage thresholds of the HfO{sub 2}/SiO{sub 2} multilayer polarizer coatings can be increased to meet the Beamlet 3-ns design goal of 8 J/cm{sub 2}. Because of the large size of the polarizers (73 cm {times} 37 cm {times} 9 cm), a large-area conditioning facility was constructed capable of rastering a one-meter optic, weighing as much as 400 pounds, at any specified use angle. A large translational stage moves the optic in a raster pattern through a stationary, 10-Hz rep-rated, 1064-nm beam with 10-ns pulses. A scatter measurement diagnostic allows on-the-fly evaluation of laser-induced damage and logs the coordinates of the damage. Laser energy is measured pulse-to-pulse in order to ensure stability during a scan. A small amount of minor coating damage does occur during the process, but the damage does not grow upon further irradiation. This damage causes only a small increase in total scatter compared to that due to the preexisting defects, and would not influence the system performance.

Sheehan, L.M.; Kozlowski, M.R.; Rainer, F.; Staggs, M.C.

1993-12-21

386

Large-area electron beam diode modeling for KrF Laser IFE  

NASA Astrophysics Data System (ADS)

The KrF Laser Inertial Fusion Energy (IFE) scheme focuses ˜ 60 individually generated 58 kJ laser pulses symmetrically onto a high yield fusion target. The lasers are pumped by large-area electron beam diodes, the technology for which is presently being developed on the Electra^1 and Nike^2 facilities at the Naval Research Laboratory in Washington, DC. An IFE-level diode design is examined via large-scale numerical simulations using the particle-in-cell code LSP. The simulations include detailed geometric representations of the cathode, foils, and support structures (the hibachi) as well as gas transport models. This integrated modeling procedure has been successfully benchmarked against recent Electra large-area diode experiments^3. The simulations provide estimates of the electron beam energy deposited in the gas, foils, and hibachi. The estimates of energy deposition in the laser gas from the simulations will be integrated with existing system designs. [1] J. D. Sethian, et al., IEEE Trans. Plasma Sci. 28, 1333 (2000). [2] J. D. Sethian, et al., Rev. Sci. Instrum. 68, 2357 (1997). [3] D. V. Rose, et al., submitted to J. Appl. Phys. (2003).

Rose, D. V.; Welch, D. R.; Sethian, J. D.; Guiliani, J. L.; Hegeler, F.; Swanekamp, S. B.

2003-10-01

387

Management of large prostatic adenoma: Lasers versus bipolar transurethral resection of prostate  

PubMed Central

Transurethral resection of prostate (TURP) has long been the most commonly performed surgical procedure for the management of benign prostate enlargement (BPE), but has several associated limitations. Over the years, laser techniques have developed as major contenders as alternative therapies for BPE. However, simultaneously, TURP has also flourished and with relatively recent development of resection in saline (bipolar TURP), the tussle between laser techniques and TURP has further gained momentum. A systematic search was performed on Medline using the various Medical subject headings related to the surgical management of BPE including TURP, bipolar, lasers, holmium laser enucleation of prostate (HoLEP), photo-selective vaporization of prostate (PVP), etc., All articles types including meta-analysis randomized controlled trials, review articles, guidelines from various urological associations, single center studies from 2002 onward were considered for review. Bipolar TURP, HoLEP, and PVP provide equivalent outcomes for large prostate adenoma (<60 g). For extremely large glands (<150 g), HoLEP is a very efficacious endoscopic alternative to open prostatectomy and has proven long-term results over more than a decade. Bipolar TURP and PVP are attractive with a minimal learning curves and equivalent short term durability. Surgical management of large prostate should be individualized based upon patient's comorbidities and surgeon's expertise.

Gupta, Narmada P; Nayyar, Rishi

2013-01-01

388

Excitation, Fragmentation and Control of Large Finite Systems: C60 in Moderately Strong Laser Fields  

NASA Astrophysics Data System (ADS)

Recent progress in the understanding of the primary excitation mechanisms of the C60 fullerene in intense laser pulses is reported. By analyzing mass spectra as a function of pulse duration, laser intensity and time delay between pump- and probe pulse insight into fundamental photoinduced processes such as ionization and fragmentation is obtained. Using ultrashort sub-10fs pulses excitation times are addressed which lie well below the characteristic time scales for electron-electron and electron-phonon coupling. The measured saturation intensities of multiply charged parent ions indicate that for higher charge states the well known C60 giant plasmon resonance is involved in creating ions and a significant amount of large fragments through a non-adiabatic multi-electron dynamics. To enhance the formation of large fragments femtosecond laser pulses tailored with closed-loop, optimal control feedback were used. A characteristic pulse sequence excites oscillations in C60 with large amplitude by coherent heating of nuclear motion. Again, the experimental findings can be understood by a laser-induced multi-electron excitation via the electronically excited resonance followed by efficient coupling to the radial symmetric breathing vibration of C60.

Laarmann, Tim; Schulz, Claus Peter; Hertel, Ingolf Volker

389

High temperature thermal behaviour modeling of large-scale fused silica optics for laser facility  

NASA Astrophysics Data System (ADS)

High temperature annealing is often used for the stress control of optical materials. However, weight and viscosity at high temperature may destroy the surface morphology, especially for the large-scale, thin and heavy optics used for large laser facilities. It is necessary to understand the thermal behaviour and design proper support systems for large-scale optics at high temperature. In this work, three support systems for fused silica optics are designed and simulated with the finite element method. After the analysis of the thermal behaviours of different support systems, some advantages and disadvantages can be revealed. The results show that the support with the optical surface vertical is optimal because both pollution and deformation of optics could be well controlled during annealing at high temperature. Annealing process of the optics irradiated by CO2 laser is also simulated. It can be concluded that high temperature annealing can effectively reduce the residual stress. However, the effects of annealing on surface morphology of the optics are complex. Annealing creep is closely related to the residual stress and strain distribution. In the region with large residual stress, the creep is too large and probably increases the deformation gradient which may affect the laser beam propagation.

Yu, Jing-Xia; He, Shao-Bo; Xiang, Xia; Yuan, Xiao-Dong; Zheng, Wan-Guo; Lü, Hai-Bing; Zu, Xiao-Tao

2012-06-01

390

Development of Femtosecond Petawatt Laser Technology  

Microsoft Academic Search

Based on the scheme of chirped pulse amplification, a Ti:sapphire laser facility with output power of 0.89 PW has been developed. The compressed pulse width of ~29.0 fs was achieved by minimizing the dispersion introduced by the optical components. The effective suppression of parasitic lasing ensured the high-gain amplification in large aperture amplifiers.

Xiaoyan Liangt; Yuxin Leng; Cheng Wang; Chuang Li; Baozhen Zhao; Lihuang Lin; Yongliang Jiang; Xiaoming Lu; Mingyuan Hu; Chunmei Zhang; Haihe Lu; Dingjun Yin; Xingqiang Lu; Hui Wei; Jianqiang Zhu; Ruxin Li; Zhizhan Xu

2007-01-01

391

Coded aperture imaging for fluorescent x-rays  

NASA Astrophysics Data System (ADS)

We employ a coded aperture pattern in front of a pixilated charge couple device detector to image fluorescent x-rays (6-25 KeV) from samples irradiated with synchrotron radiation. Coded apertures encode the angular direction of x-rays, and given a known source plane, allow for a large numerical aperture x-ray imaging system. The algorithm to develop and fabricate the free standing No-Two-Holes-Touching aperture pattern was developed. The algorithms to reconstruct the x-ray image from the recorded encoded pattern were developed by means of a ray tracing technique and confirmed by experiments on standard samples.

Haboub, A.; MacDowell, A. A.; Marchesini, S.; Parkinson, D. Y.

2014-06-01

392

Volume self-sustained discharge stability in gas lasers  

NASA Astrophysics Data System (ADS)

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

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

393

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

394

High gain-production efficiency and large brightness X-UV laser at Palaiseau  

SciTech Connect

A large gain has been measured for the J=0-1 line of neonlike Zn at {lambda}=21.2 nm. The time evolutions and the localization of emission zones of the J=0-1 and J=2-1 lines are compared. It is shown that a train of very small prepulses before the main pulse has an important role in the J=0=1 emission. A half-cavity has been successfully used to attain a nearly saturated intensity with a 2 cm long plasma. The X-UV pulse energy is of 400 {mu}J, the laser power of 5 MW. The driving laser is the 0.4 KJ, 600 ps laser of LULI.

Jaegle, P.; Carillon, A.; Dhez, P.; Goedtkindt, P.; Jamelot, G.; Klisnick, A.; Rus, B.; Zeitoun, Ph.; Jacquemot, S.; Mazataud, D.; Mens, A.; Chauvineau, J. P. [Laboratorie de Spectroscopie Atomique et Ionique, Bat 350, Universite Paris-Sud, 91405 Orsay (France); C. E. A., Centre d'Etudes de Limeil-Valenton, 94190 Villeneuve-St.-Georges (France); Institut d'Optique Theorique et Appliquee, 91405 Orsay (France)

1995-05-01

395

Dynamic aperture of the ALS (Advanced Light Source) booster synchrotron  

SciTech Connect

Effect of the anticipated lattice imperfections on the dynamic aperture of the ALS booster synchrotron were studied using a particle tracking method. The dynamic aperture was found to be sufficiently large at the selected operating points and at the designed repetition rate. 4 refs., 4 figs., 3 tabs.

Kim, C.H.; Nishimura, Hiroshi

1989-03-01

396

Closed-loop Results from the MMT's Multi-Laser Guide Star Adaptive Optics System  

Microsoft Academic Search

Key advances in adaptive optics (AO) for both astronomical and military applications will be enabled through the deployment of multiple laser guide stars on a single large-aperture telescope. Wider compensated fields of view than are now seen with conventional AO systems, even those equipped with single laser beacons, will be achieved with less field dependence of the delivered point-spread function.

Michael Lloyd-Hart; Christoph Baranec; N. Mark Milton; Thomas Stalcup; M. Snyder

2007-01-01

397

Waveguiding in nanoscale metallic apertures  

Microsoft Academic Search

We study the optical properties of subwavelength metallic waveguides made of nanoscale apertures in a metal. We develop analytical expressions for the fundamental optical modes in apertures. The results are in excellent agreement with finite element calculations. This model provides a physical understanding of the role of non-perfect metallic walls, and of the shape and size of the apertures. They

Stéphane Collin; Fabrice Pardo; Jean-Luc Pelouard

2007-01-01

398

Diffraction by fractally serrated apertures  

NASA Technical Reports Server (NTRS)

An investigation of light diffracted by irregularly serrated apertures yields a closed-form analytical solution that confirms experimental recording of the diffracted patterns. These serrated apertures are modeled by a fractal function. Examples are given for both sinusoidal and fractal aperture perimeters with varying fractal dimension. Relations between the far-zone diffracted fields and the fractal dimension are examined.

Kim, Y.; Grebel, H.; Jaggard, D. L.

1991-01-01

399

Aperture synthesis in digital holography  

Microsoft Academic Search

Resolution and speckle size in the reconstructed wavefields of digital holography depend on the aperture defined by the size of the CCD-array. Here we introduce the concept of synthesizing a larger aperture by recording simultaneously the same scene by at least two CCD-arrays. It is shown that an improvement in resolution can be obtained which corresponds to a virtual aperture

Thomas M. Kreis; Mike Adams; Werner P. Jueptner

2002-01-01

400

Potentials of the acousto-optical spectral data processing on a basis of a novel algorithm of the collinear wave heterodyning in a large-aperture KRS-5 crystalline cell  

NASA Astrophysics Data System (ADS)

Recently proposed modern technique of a precise spectrum analysis within an algorithm of the collinear wave heterodyning implies a two-stage integrated processing, namely, the wave heterodyning of a signal in a square-law nonlinear medium and then the optical processing in the same cell. Technical advantage of this approach is in providing a direct processing of ultra-high-frequency radio-wave signals with essentially improved frequency resolution. This algorithm can be realized on a basis of various physical principles, and we consider an opportunity of involving the potentials of modern acousto-optics for these purposes. From this viewpoint, one needs a large-aperture effective acousto-optical cell, which operates in the Bragg regime and performs the ultra-high-frequency co-directional collinear acoustic wave heterodyning. The technique under consideration imposes specific requirements on the cell's material, namely, a high optical quality of large-size crystalline boules, high-efficient acousto-optical and acoustic interactions, and low group velocity of acoustic waves together with square-low dispersive acoustic losses. We focus our attention on the solid solutions of thallium chalcogenides and take the TlBr-TlI (thallium bromine - thallium iodine) solution, which forms KRS-5 cubic-symmetry crystals with the mass-ratio 58% of TlBr to 42% of TlI. Analysis shows that the acousto-optical cell made of a KRS-5 crystal oriented along the [111] -axis and the corresponding longitudinal elastic mode for producing the dynamic diffractive grating in that crystal can be exploited. With the acoustic velocity of about 1.92 mm/?s and attenuation of approximately 10 dB/(cm GHz2), similar cell is capable to provide an optical aperture of 50 mm and one of the highest figures of acousto-optical merit in solid states in the visible range. Such a cell is rather desirable for applications to direct parallel multi-channel optical spectrum analysis with substantially improved frequency resolution.

Shcherbakov, Alexandre S.; Maximov, Jewgemij; Sanchez Lucero, Daniel

2010-02-01

401

Large-area plasmonic structures fabricated by laser nanopatterning and their applications  

NASA Astrophysics Data System (ADS)

Laser interference lithography is applied to fabricate large-area plasmonic nanostructures. This approach has the advantages of being non-contact process in air and able to achieve large-area and maskless nanolithography at a high speed with low system investment. Single layer Au or Ag noble metallic thin film and Ag/Au, Ag/Ni or Au/Ni bimetallic layer thin films are patterned into nano-dot, nano-rod and nano-nut arrays by laser interference lithography. Plasmonic effects of the fabricated metallic nanostructures are studied. Tunable and multi-peak surface plasmon resonances of these nanostructures can be obtained, which have potential applications in solar cells, bio-sensing and photonic circuits.

Hong, M. H.; Liu, C. H.; Ma, F.; Chen, Z. C.; Luk'yanchuk, B.; Shi, L. P.; Chong, T. C.

2009-02-01

402

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

403

Chromatic aberration in petawatt-class lasers  

Microsoft Academic Search

In order to avoid optical damage and non-linear effects, high-power, high-energy lasers of the petawatt class like PHELIX (petawatt high-energy laser for heavy-ion experiments) use large-aperture optics. Usually, chromatic aberration associated with these optical elements is neglected. By means of numerical simulations, we show how the chromatic aberration affects the focal intensity pattern. In particular, we make quantitative predictions of

H.-M. Heuck; P. Neumayer; T. Kühl; U. Wittrock

2006-01-01

404

Multiple instrument distributed aperture sensor (MIDAS) science payload concept  

NASA Astrophysics Data System (ADS)

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

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

2004-10-01

405

Strongly Enhanced Transmission through a Subwavelength Aperture.  

NASA Astrophysics Data System (ADS)

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

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

2002-03-01

406

A Generalized Network Formulation for Aperture Problems.  

National Technical Information Service (NTIS)

A general formulation for aperture problems is given in terms of the method of moments. It applies to any two regions isolated except for coupling through the aperture. The aperture characteristics are expressed in terms of two aperture admittance matrice...

J. R. Mautz R. F. Harrington

1975-01-01

407

Cleaved-coupled-cavity lasers with large cavity length ratios for enhanced stability  

Microsoft Academic Search

The fabrication and operation of the first cleaved-coupled-cavity (C³) semiconductor lasers with large cavity length ratios are described. The internal cleaved facet is precisely positioned by photochemically etching a groove through most of the wafer. Single longitudinal mode operation is obtained over a temperature range of 21 °C and over a current range of threshold to greater than four times

J. E. Bowers; J. E. Bjorkholm; C. A. Burrus; L. A. Coldren; B. R. Hemenway; D. P. Wilt

1984-01-01

408

Compact hybrid video color mixer for large-area laser projection display  

Microsoft Academic Search

The present paper relates to an optical module of a compact hybrid video color mixer for large-area laser projection display. The compact optical arrangement gives a very small- sized and high-performance video image color mixing apparatus which uses a hybrid R\\/G\\/B color separator, modulate the light beam using a 3-channels acousto-optic modulator according to the video image signal and combines

Young M. Hwang; Jungho Park; Yonghoon Kim

1998-01-01

409

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

410

Multi-transmitter aperture synthesis.  

PubMed

Multi-transmitter aperture synthesis is a method in which multiple transmitters can be used to improve resolution and contrast of distributed aperture systems. Such a system utilizes multiple transmitter locations to interrogate a target from multiple look angles thus increasing the angular spectrum content captured by the receiver aperture array. Furthermore, such a system can improve the contrast of sparsely populated receiver arrays by capturing field data in the region between sub-apertures by utilizing multiple transmitter locations. This paper discusses the theory behind multi-transmitter aperture synthesis and provides experimental verification that imagery captured using multiple transmitters will provide increased resolution. PMID:21164838

Rabb, David J; Jameson, Douglas F; Stafford, Jason W; Stokes, Andrew J

2010-11-22

411

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

412

Aperture weighting technique for video synthetic aperture radar  

NASA Astrophysics Data System (ADS)

We present a technique for aperture weighting for use in video synthetic aperture radar (SAR). In video SAR the aperture required to achieve the desired cross range resolution typically exceeds the frame rate period. As a result, there can be a significant overlap in the collected phase history used to form consecutive images in the video. Video SAR algorithms seek to exploit this overlap to avoid unnecessary duplication of processing. When no aperture weighting or windowing is used one can simply form oversampled SAR images from the non-overlapping sub-apertures using coherent back projection (or other similar techniques). The resulting sub-aperture images may be coherently summed to produce a full resolution image. A simple approach to windowing for sidelobe control is to weight the sub-apertures during summation of the images. Our approach involves producing two or more weighted images for each sub-aperture which can be linearly combined to approximate any desired aperture weighting. In this method we achieve nearly the same sidelobe control as weighting the phase history data and forming a new image for each frame without losing the computation savings of the sub-aperture image combining approach.

Hawley, Robert W.; Garber, Wendy L.

2011-05-01

413

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

414

Large-scale Production of Laser Polarized ^129Xe: A Comparison of LDA and Ti-sapphire Optical Pumping  

Microsoft Academic Search

We are investigating the polarization of large quantities of ^129Xe gas by spin-exchange with optically pumped rubidium. The laser-polarized ^129Xe gas will be used for biomedical magnetic resonance imaging studies. The efficacy of high-power, broadband laser diode arrays (LDA) for this polarization procedure is being compared to that of lower power, narrow band Ti-sapphire lasers. Several processes, such as pressure

R. L. Walsworth; R. E. Stoner; C. H. Tseng; G. A. Wong; E. R. Oteiza

1996-01-01

415

Nd:YAG laser versus transrectal microsurgery in the treatment of large sessile polyps of distal rectal stump  

NASA Astrophysics Data System (ADS)

Authors compared Nd:YAG laser and the transrectal microsurgery in the treatment of large sessile polyps of distal rectal stump. Disadvantages of using of the laser technique is necessity to repeat laser sessions and impossibility of the correct histology specimens of all adenomatous polyps. Necessity of general or spinal anesthesy, great diameter of operative rectoscope in contrast of the relative narrow optical field restricted usability of transrectal microsurgery in the treatment of large sessile adenomatous polyps of the rectum. Greatest advantage of laser treatment is using of the standard colonoscopy device in the outpatient procedure in contrast of the expensive transrectal microsurgery device which need special training of the medical staff. In conclusion authors considered Nd:YAG laser of the method of choice in the treatment of large sessile adenomatous polyps of distal rectal stump.

Horak, Ladislav; Faltyn, J.

1997-12-01

416

Large-area high-power VCSEL pump arrays optimized for high-energy lasers  

NASA Astrophysics Data System (ADS)

Practical, large-area, high-power diode pumps for one micron (Nd, Yb) as well as eye-safer wavelengths (Er, Tm, Ho) are critical to the success of any high energy diode pumped solid state laser. Diode efficiency, brightness, availability and cost will determine how realizable a fielded high energy diode pumped solid state laser will be. 2-D Vertical-Cavity Surface-Emitting Laser (VCSEL) arrays are uniquely positioned to meet these requirements because of their unique properties, such as low divergence circular output beams, reduced wavelength drift with temperature, scalability to large 2-D arrays through low-cost and high-volume semiconductor photolithographic processes, high reliability, no catastrophic optical damage failure, and radiation and vacuum operation tolerance. Data will be presented on the status of FLIR-EOC's VCSEL pump arrays. Analysis of the key aspects of electrical, thermal and mechanical design that are critical to the design of a VCSEL pump array to achieve high power efficient array performance will be presented.

Wang, Chad; Geske, Jonathan; Garrett, Henry; Cardellino, Terri; Talantov, Fedor; Berdin, Glen; Millenheft, David; Renner, Daniel; Klemer, Daniel

2012-05-01

417

Beam quality after propagation of Nd:YAG laser light through large-core optical fibers.  

PubMed

Laser beam characteristics are altered during propagation through large-core optical fibers. The distribution of modes excited by the input laser beam is modified by means of mode coupling on transmission through the fiber, leading to spatial dispersion of the profile and, ultimately and unavoidably, to degradation in the quality of the delivered beam unless the beam is spatially filtered with consequent power loss. Furthermore, a mismatch between the intensity profile of a typical focused high-power laser beam and the profile of the step-index fiber gives rise to additional beam-quality degradation. Modern materials processing applications demand ever higher delivered beam qualities (as measured by a parameter such as M(2)) to achieve greater machining precision and efficiency, a demand that is currently in conflict with the desire to utilize the convenience and flexibility of large-core fiber-optic beam delivery. We present a detailed experimental investigation of the principal beam-quality degradation effects associated with fiber-optic beam delivery and use numerical modeling to aid an initial discussion of the causes of such degradation. PMID:18354689

Kuhn, A; Blewett, I J; Hand, D P; Jones, J D

2000-12-20

418

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

419

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

420

An all-optronic synthetic aperture lidar  

NASA Astrophysics Data System (ADS)

Synthetic Aperture Radar (SAR) is a mature technology that overcomes the diffraction limit of an imaging system's real aperture by taking advantage of the platform motion to coherently sample multiple sections of an aperture much larger than the physical one. Synthetic Aperture Lidar (SAL) is the extension of SAR to much shorter wavelengths (1.5 ?m vs 5 cm). This new technology can offer higher resolution images in day or night time as well as in certain adverse conditions. It could be a powerful tool for Earth monitoring (ship detection, frontier surveillance, ocean monitoring) from aircraft, unattended aerial vehicle (UAV) or spatial platforms. A continuous flow of high-resolution images covering large areas would however produce a large amount of data involving a high cost in term of post-processing computational time. This paper presents a laboratory demonstration of a SAL system complete with image reconstruction based on optronic processing. This differs from the more traditional digital approach by its real-time processing capability. The SAL system is discussed and images obtained from a non-metallic diffuse target at ranges up to 3m are shown, these images being processed by a real-time optronic SAR processor origiinally designed to reconstruct SAR images from ENVISAT/ASAR data.

Turbide, Simon; Marchese, Linda; Terroux, Marc; Babin, François; Bergeron, Alain

2012-09-01

421

Aperture shape optimization for IMRT treatment planning.  

PubMed

We propose an algorithm for aperture shape optimization (ASO) for step and shoot delivery of intensity-modulated radiotherapy. The method is an approach to direct aperture optimization (DAO) that exploits gradient information to locally optimize the positions of the leafs of a multileaf collimator. Based on the dose-influence matrix, the dose distribution is locally approximated as a linear function of the leaf positions. Since this approximation is valid only in a small interval around the current leaf positions, we use a trust-region-like method to optimize the leaf positions: in one iteration, the leaf motion is confined to the beamlets where the leaf edges are currently positioned. This yields a well-behaved optimization problem for the leaf positions and the aperture weights, which can be solved efficiently. If, in one iteration, a leaf is moved to the edge of a beamlet, the leaf motion can be confined to the neighboring beamlet in the next iteration. This allows for large leaf position changes over the course of the algorithm. In this paper, the ASO algorithm is embedded into a column-generation approach to DAO. After a new aperture is added to the treatment plan, we use the ASO algorithm to simultaneously optimize aperture weights and leaf positions for the new set of apertures. We present results for a paraspinal tumor case, a prostate case and a head and neck case. The computational results indicate that, using this approach, treatment plans close to the ideal fluence map optimization solution can be obtained. PMID:23257284

Cassioli, A; Unkelbach, J

2013-01-21

422

Dynamics of gain-guided solitons in a dispersion-managed fiber laser with large normal cavity dispersion  

NASA Astrophysics Data System (ADS)

The intra-cavity pulse dynamics of gain-guided solitons in a dispersion-managed fiber laser with large normal cavity dispersion was investigated experimentally and numerically. It was found that in the laser the gain-guided solitons have a similar evolution as that of the parabolic pulses.

Zhao, L. M.; Tang, D. Y.; Wu, X.; Zhang, H.; Lu, C.; Tam, H. Y.

2008-06-01

423

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

424

Ytterbium-doped large-mode-area all-solid photonic bandgap fiber lasers.  

PubMed

Single-mode operation in a large-mode-area fiber laser is highly desired for power scaling. We have, for the first time, demonstrate