The Velocity Interferometer System for Any Reflector (VISAR) is a critical diagnostic in Inertial Confinement Fusion and High Energy Density research as it has the ability to track shock fronts or interfaces moving 0.1-100 km/s with great accuracy. At the National Ignition Facility (NIF), the VISAR has recently been used successfully for implosion tuning and equation of state measurements. However, the initial design of the companion Streaked Optical Pyrometer (SOP) to measure spectral radiance - hence shock temperature - suffers from large background levels and poor spatial resolution. We report on an upgrade to improve the spatial resolution in the 560-640nm band by using custom lenses and replacing the Dove prism with a K-mirror and implementing a gating-circuit for the streak camera to reduce background signal. We envision that upgraded SOP will provide high quality data collection matching NIF VISAR's standards.
The National Ignition Facility (NIF) requires high resolution live images of regions inside the target chamber in order to align diagnostic instruments to fusion targets and to monitor target stability. To view the interior of the target chamber, we modified a commercial 11-inch Schmidt-Cassegrain telescope to develop the Opposed Port Alignment System (OPAS). There are two OPAS systems installed on the target chamber ports directly opposite the diagnostics. This paper describes the optical design, highlighting the two key modifications of the telescope. The first key modification was to reposition the Schmidt corrector plate and to uniquely mount the secondary mirror to a precision translation stage to adjust focus from 5.5 m to infinity. The stage is carefully aligned to ensure that the telescope’s optical axis lies on a straight line during focus adjustments. The second key modification was a custom three element lens that flattens the field, corrects residual aberrations of the Schmidt-Cassegrain and, with a commercial 1:1 relay lens, projects the final image plane onto a large format 50 mega-pixel camera. The OPAS modifications greatly extend the Schmidt-Cassegrain
telescope’s field of view, producing nearly diffraction-limited images over a flat field covering ±0.4 degrees. Also discussed in the paper are the alignment procedure and the hardware layout of the telescope.
The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, telescope design feeding a camera system that
includes a set of broad-band filters and three refractive corrector lenses to produce a flat field at the focal plane with a
wide field of view. Optical design of the camera lenses and filters is integrated in with the optical design of telescope
mirrors to optimize performance. We discuss the rationale for the LSST camera optics design, describe the methodology
for fabricating, coating, mounting and testing the lenses and filters, and present the results of detailed analyses
demonstrating that the camera optics will meet their performance goals.
A system of customized spatial light modulators has been installed onto the front end of the laser system at the National
Ignition Facility (NIF). The devices are capable of shaping the beam profile at a low-fluence relay plane upstream of the
amplifier chain. Their primary function is to introduce "blocker" obscurations at programmed locations within the beam
profile. These obscurations are positioned to shadow small, isolated flaws on downstream optical components that might
otherwise limit the system operating energy. The modulators were designed to enable a drop-in retrofit of each of the 48
existing Pre Amplifier Modules (PAMs) without compromising their original performance specifications. This was
accomplished by use of transmissive Optically Addressable Light Valves (OALV) based on a Bismuth Silicon Oxide
photoconductive layer in series with a twisted nematic liquid crystal (LC) layer. These Programmable Spatial Shaper
packages in combination with a flaw inspection system and optic registration strategy have provided a robust approach
for extending the operational lifetime of high fluence laser optics on NIF.
Customized spatial light modulators have been designed and fabricated for use as precision beam shaping devices in
fusion class laser systems. By inserting this device in a low-fluence relay plane upstream of the amplifier chain,
"blocker" obscurations can be programmed into the beam profile to shadow small isolated flaws on downstream optical
components that might otherwise limit the system operating energy. In this two stage system, 1920 × 1080 bitmap
images are first imprinted on incoherent, 470 nm address beams via pixelated liquid crystal on silicon (LCoS)
modulators. To realize defined masking functions with smooth apodized shapes and no pixelization artifacts, address
beam images are projected onto custom fabricated
optically-addressable light valves. Each valve consists of a large,
single pixel liquid cell in series with a photoconductive Bismuth silicon Oxide (BSO) crystal. The BSO crystal enables
bright and dark regions of the address image to locally control the voltage supplied to the liquid crystal layer which in
turn modulates the amplitude of the coherent beams at 1053 nm. Valves as large as 24 mm × 36 mm have been
fabricated with low wavefront distortion (<0.5 waves) and antireflection coatings for high transmission (>90%) and
etalon suppression to avoid spectral and temporal ripple. This device in combination with a flaw inspection system and
optic registration strategy represents a new approach for extending the operational lifetime of high fluence laser optics.
Optical null tests for three lenses and two subsystems were incorporated into the optical
design procedure for the Large-aperture Synoptic Survey Telescope [1]. The "skip surfaces"
feature in the OSLO optical design program was crucial. The resulting optical tests were
extremely simple, requiring only a retro reflecting spherical or flat mirror. This is only possible
because the optical tests were simultaneously designed and optimized as the telescope was
designed.
The Large Synoptic Survey Telescope will map out the dark matter in the universe and is scheduled to see "first light" in
2014. This telescope will require active correction of its mirrors to remove the aberrations that arise from changing
gravitational force vectors and from thermal drifts in the telescope during observational runs. In this article we present a
comprehensive evaluation of a Shack-Hartmann wavefront sensor and reconstruction algorithm which is capable of
meeting the unique challenges associated with this wide field-of-view survey telescope. The advantages of this technique
over other potential wavefront sensing technologies are discussed and the potential problems encountered with this
approach are analyzed and solutions to these problems presented.
The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design,
with an 8.4-meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a refractive camera design with 3
lenses (0.69-1.55m) and a set of broadband filters/corrector lenses. Performance is excellent over a 9.6 square
degree field and ultraviolet to near infrared wavelengths.
We describe the image quality error budget analysis methodology which includes effects from optical and
optomechanical considerations such as index inhomogeneity, fabrication and null-testing error, temperature
gradients, gravity, pressure, stress, birefringence, and vibration.
The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design, with an 8.4-
meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a camera system that includes a set of broad-band
filters and refractive corrector lenses to produce a flat focal plane with a field of view of 9.6 square degrees. Optical
design of the camera lenses and filters is integrated with optical design of telescope mirrors to optimize performance,
resulting in excellent image quality over the entire field from ultra-violet to near infra-red wavelengths. The LSST
camera optics design consists of three refractive lenses with clear aperture diameters of 1.55 m, 1.10 m and 0.69 m and
six interchangeable, broad-band, filters with clear aperture diameters of 0.75 m. We describe the methodology for
fabricating, coating, mounting and testing these lenses and filters, and we present the results of detailed tolerance
analyses, demonstrating that the camera optics will perform to the specifications required to meet their performance
goals.
Optical diagnostics are currently being designed to analyze high-energy density physics experiments at the National
Ignition Facility (NIF). Two line-imaging Velocity Interferometer System for Any Reflector (VISAR) interferometers
have been fielded to measure shock velocities, breakout times, and emission of targets sized from 1 to 5 millimeters. A
20-cm-diameter, fused silica triplet lens collects light at f/3 from the targets inside the 10-meter-diameter NIF vacuum
chamber. VISAR recordings use a 659.5-nm probe laser. By adding a specially coated beam splitter at the interferometer
table, light at wavelengths from 540 to 645 nm is split into a thermal-imaging diagnostic. Because fused silica lenses are
used in the first triplet relay, the intermediate image planes for different wavelengths separate by considerable distances.
A pair of corrector lenses on the interferometer table reunites these separated wavelength planes to provide a good
image. Streak cameras perform all VISAR and thermal-imaging recording. Alignment techniques are discussed.
The Large Synoptic Survey Telescope (LSST) is a unique, three-mirror, modified Paul-Baker design with an 8.4m primary, a 3.4m secondary, and a 5.0m tertiary feeding a camera system that includes corrector optics to produce a 3.5 degree field of view with excellent image quality (<0.3 arcsecond 80% encircled diffracted energy) over the entire field from blue to near infra-red wavelengths. We describe the design of the LSST camera optics, consisting of three refractive lenses with diameters of 1.6m, 1.0m and 0.7m, along with a set of interchangeable, broad-band, interference filters with diameters of 0.75m. We also describe current plans for fabricating, coating, mounting and testing these lenses and filters.
The Large Synoptic Survey Telescope (LSST) is a three mirror modified Paul-Baker design with an 8.4m primary, a
3.4m secondary, and a 5.0m tertiary followed by a 3-element refractive corrector producing a 3.5 degree field of view.
This design produces image diameters of <0.3 arcsecond 80% encircled energy over its full field of view. The image
quality of this design is sufficient to ensure that the final images produced by the telescope will be limited by the
atmospheric seeing at an excellent astronomical site. In order to maintain this image quality, the deformations and rigid
body motions of the three large mirrors must be actively controlled to minimize optical aberrations. By measuring the
optical wavefront produced by the telescope at multiple points in the field, mirror deformations and rigid body motions
that produce a good optical wavefront across the entire field may be determined. We will describe the details of the
techniques for obtaining these solutions. We will show that, for the expected mirror deformations and rigid body
misalignments, the solutions that are found using these techniques produce an image quality over the field that is close to
optimal. We will discuss how many wavefront sensors are needed and the tradeoffs between the number of wavefront
sensors, their layout and noise sensitivity.
Optical diagnostics are currently being designed to analyze high-energy density physics experiments at the National Ignition Facility (NIF). Two independent line-imaging Velocity Interferometer System for Any Reflector (VISAR) interferometers have been fielded to measure shock velocities, breakout times, and emission of targets having sizes of 1-5 mm. An 8-inch-diameter, fused silica triplet lens collects light at f/3 inside the 30-foot-diameter NIF vacuum chamber. VISAR recordings use a 659.5-nm probe laser. By adding a specially coated beam splitter to the interferometer table, light at wavelengths from 540 to 645 nm is spilt into a thermal-imaging diagnostic. Because fused silica lenses are used in the first triplet relay, the intermediate image planes for different wavelengths separate by considerable distances. A corrector lens on the interferometer table reunites these separated wavelength planes to provide a good image. Thermal imaging collects light at f/5 from a 2-mm object placed at Target Chamber Center (TCC). Streak cameras perform VISAR and thermal-imaging recording. All optical lenses are on kinematic mounts so that pointing accuracy of the optical axis may be checked. Counter-propagating laser beams (orange and red) are used to align both diagnostics. The red alignment laser is selected to be at the 50 percent reflection point of the beam splitter. This alignment laser is introduced at the recording streak cameras for both diagnostics and passes through this special beam splitter on its way into the NIF vacuum chamber.
This paper presents an improved optical design for the LSST, an f/1.25 three-mirror telescope covering 3.0 degrees full field angle, with 6.9 m effective aperture diameter. The telescope operates at five wavelength bands spanning 386.5 nm to 1040 nm (B, V, R, I and Z). For all bands, 80% of the polychromatic diffracted energy is collected within 0.20 arc-seconds diameter. The reflective telescope uses an 8.4 m f/1.06 concave primary, a 3.4 m convex secondary and a 5.2 m concave tertiary in a Paul geometry. The system length is 9.2 m. A refractive corrector near the detector uses three fused silica lenses, rather than the two lenses of previous designs. Earlier designs required that one element be a vacuum barrier, but now the detector sits in an inert gas at ambient pressure, with the last lens serving as the gas barrier. Small adjustments lead to optimal correction at each band. Each filter has a different axial thickness, and the primary and tertiary mirrors are repositioned for each wavelength band. Features that simplify manufacturing include a flat detector, a far less aspheric convex secondary (10 μm from best fit sphere) and reduced aspheric departures on the lenses and tertiary mirror. Five aspheric surfaces, on all three mirrors and on two lenses, are used. The primary is nearly parabolic. The telescope is fully baffled so that no specularly reflected light from any field angle, inside or outside of the full field angle of 3.0 degrees, can reach the detector.
We have measured the wavefront and the divergence of the Beamlet prototype laser under a variety of conditions. Emphasis of the tests was on quantifying best attainable divergence in the angular regime below 30 (mu) rad to benchmark propagation models that are used to set wavefront gradient specifications for NIF optical components. Performance with and without active wavefront correction was monitored with radial shearing interferometers that measured near-field wavefront at the input and output of the main amplifier with a spatial resolution of 1 cm, and cameras which measured the corresponding intensity distributions in the far field with an angular resolution of 0.3 (Mu) rad. Details of the measurements are discussed and related to NIF focal spot requirements and optics specifications.
KEYWORDS: Mirrors, Spatial filters, Optical amplifiers, National Ignition Facility, Laser systems engineering, Polarizers, Telescopes, Optical design, Crystals, Control systems
The National Ignition Facility (NIF) is a laser fusion facility being constructed at Lawrence Livermore National Laboratory. The neodymium-doped phosphate glass pulsed laser system will produce over 3.5 MJ of laser energy at a fundamental lasing wavelength of 1.053μm(1ω). The final optics assembly contains a pair of crystals (KDP/KD*P) and a focusing lens to convert the light by sum- frequency-mixing to 3ω(λ=0.35μm) and focus 1.8 MJ onto the target. The NIF optical system is large and complex. To give some perspective the NIF building is roughly 200 meters long X 85 meters wide. There are approximately 7500 optical components in the large aperture laser system--lenses, mirrors, polarizers, laser slabs, crystals, and windows--each with a clear aperture greater than 40 cm square. The front-end of the laser system contains more than 8000 smaller (5 - 15 cm) precision laser components. In this paper we will describe the optical system configuration, layout, and general design considerations. We will explain the path of the pulse through the various subsystems. Some of the top-level optical system and sub-system design requirements will be presented.
Mark Henesian, P. Renard, Jerome Auerbach, John Caird, B. Ehrlich, Steven Haney, John Hunt, Janice Lawson, Kenneth Manes, David Milam, Richard Sacks, Lynn Seppala, I. Smith, David Speck, Calvin Thompson, Bruno Van Wonterghem, Paul Wegner, Timothy Weiland, C. Clay Widmayer, Wade Williams, John Trenholme
An exhaustive set of Beamlet and Nova laser system simulations were performed over a wide range of power levels in order to gain understanding about the statistical trends in Nova and Beamlet's experimental data sets, and to provide critical validation of propagation tools and design `rules' applied to the 192-arm National Ignition Facility at Lawrence Livermore National Laboratory.
KEYWORDS: Near field optics, Diagnostics, National Ignition Facility, Near field, Telescopes, Prototyping, Diffraction, Frequency conversion, Light scattering, Optical diagnostics
This paper describes the major optical and mechanical design features of the Beamlet Focal Plane Diagnostic system as well as measurements of the system performance, and typical data obtained to date. We also discuss the NIF requirements on the focal spot that we are interested in measuring, and some of our plans for future work using this system.
KEYWORDS: Crystals, National Ignition Facility, Near field, Frequency converters, Prototyping, Diagnostics, Modulation, Spatial filters, Near field optics, Laser crystals
The Beamlet laser is a nearly full-scale, single-aperture prototype of the driver design for the National Ignition Facility (NIF). As part of a test and validation plan for the NIF design, Beamlet was recently equipped with final focusing optics and diagnostics for the purpose of evaluating integrated component performance and equivalent target-plane irradiance conditions at the 0.351-micrometers output wavelength specified for NIF targets. A 37-cm aperture two- crystal converter scheme generates the third harmonic of the Nd:glass 1.053-micrometers wavelength with high efficiency. The efficiency of the converter has been characterized and is reported, along with detailed measurements of the near-field and far-field UV irradiance distributions at operating conditions up to and exceeding red-line levels for the NIF. Dependences of observed beam quality on critical laser parameters including output power, B-integral, and spatial filtering are discussed and compared with numerical simulations.
KEYWORDS: Reflection, Antireflective coatings, Reflectivity, Near field optics, Laser systems engineering, Spatial filters, Mirrors, Diffraction, Laser amplifiers, National Ignition Facility
Reflections from lens surfaces create parasitic beams that can damage optics in high-powered laser systems. These parasitic beams are low in energy initially, because of the low reflectivity of antireflection (AR) coated lens surfaces and because they are clipped by spatial filter pinholes, but subsequent amplification can raise them to damage fluence levels. Also, some of the pencil beams in multipass laser systems become pre-pulses at the output by by-pass of one or more of the passes, arriving at the output ahead of the main pulse in time. They are insidious because pencil beams that are not initially a problem can become so due to a slow degradation of the AR coatings. Both the Nova and Beamlet laser systems at LLNL have had optics damaged by pencil beams. The best solution for pencil beams is to tip the lenses far enough to eliminate them altogether. This is the approach taken for the National Ignition Facility (NIF).
The conceptual design of the National Ignition Facility (NIF) 192 beam laser incorporates a low-power alignment beam injected in the pinhole plane of the final spatial filter with a wavelength intermediate between the 1053 nm laser output and the 351 nm frequency- converted beam that illuminates the target. Choosing the specific wavelength for which the spatial filter plane is reimaged in the same target chamber plane as the frequency-converted main laser pulse, achieves optimum accuracy without the need for additional means to insure precise overlap between the two beams. Insertion of the alignment beam after the last laser amplifier also allows alignment to the target while the amplifiers are still cooling from a previous shot.
We document the concept and the design method for dome lenses that have
a compressive pressure applied to the periphery. Dome (meniscus) lenses can
eliminate both birefringence and tensile stresses if used in evacuated spatial
filters where a pressure difference is present across the lenses. Calculations show
that spatial filter birefringence is an insignificant 3 nm within the portion of a
740-mm Nova spatial filter dome lens illuminated by the laser beam. Membrane
stresses are everywhere compressive, varying from -1.2 to -2.4 MPa, and are
nearly uniform over the illuminated portion of the lens.
Eliminating sources of birefringence on the Nova laser could increase the
energy on target with Type 11/Type II frequency conversion from '-50% to the
'70% level attainable with Type I/Type II frequency conversion. Eliminating
tensile stresses may reduce the damage and catastrophic failure that has occurred
in some Nova spatial filter input lenses. The major disadvantage of using dome
lenses on Nova is the cost of new lenses which could range up to $50,000 per lens
for the material and $20,000 per lens for finishing.
Telescopes designed for non-conventional imaging of near-earth satellites must follow a unique set of design rules. Costs must be reduced substantially and the design must accommodate a technique to circumvent the atmospheric distortions of the image. Apertures to 12 meters and beyond are required along with alt-alt mounts providing high tracking rates. A novel design for such a telescope has been generated which is optimized for speckle imaging. Its mount closely resembles a radar mount and it does not employ the conventional dome. Costs for this design are projected to be considerably reduced compared to conventional designs. Results of a detailed design study will be presented. Applications to astronomy will be discussed.
An automated multi-object spectroscopy system (AMOS)
is being developed for use on the 3-meter telescope at Lick Observatory.
The overall design is compatible with the eventual goal of acquiring up
to one hundred spectra simultaneously in a one degree field of view.
The speed and accuracy of AMOS preserve the real time decision
making and field changing flexibility associated with traditional singlesource
observing techniques. AMOS will operate at the 3-meter prime
focus and will feed a floor-mounted spectrograph. We describe some
engineering design details and the results of laboratory and 1-meter
telescope testing of AMOS.
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