During the fabrication of an aspherical mirror, the inspection of the residual wavefront error is critical. In the program of a spaceborne telescope development, primary mirror is made of ZERODUR with clear aperture of 450 mm. The mass is 10 kg after lightweighting. Deformation of mirror due to gravity is expected; hence uniform supporting measured by load cells has been applied to reduce the gravity effect. Inspection has been taken to determine the residual wavefront error at the configuration of mirror face upwards. Correction polishing has been performed according to the measurement. However, after comparing with the data measured by bench test while the primary mirror is at a configuration of mirror face horizontal, deviations have been found for the two measurements. Optical system that is not able to meet the requirement is predicted according to the measured wavefront error by bench test. A target wavefront error of secondary mirror is therefore analyzed to correct that of primary mirror. Optical performance accordingly is presented.
Cygnus is a high-energy radiographic x-ray source. The rod-pinch x-ray diode produces a point source measuring 1 mm
diameter. The target object is placed 1.5 m from the x-ray source, with a large LYSO scintillator at 2.4 m. Differentsized
objects are imploded within a containment vessel. A large pellicle deflects the scintillator light out of the x-ray
path into an 11-element zoom lens coupled to a CCD camera. The zoom lens and CCD must be as close as possible to
the scintillator to maximize light collection. A telecentric lens design minimizes image blur from a volume source. To
maximize the resolution of test objects of different sizes, the scintillator and zoom lens can be translated along the x-ray
axis. Zoom lens magnifications are changed when different-sized scintillators and recording cameras are used (50 or
62 mm square format). The LYSO scintillator measures 200 × 200 mm and is 5 mm thick. The scintillator produces blue
light peaking at 435 nm, so special lens materials are required. By swapping out one lens element and allowing all lenses
to move, the zoom lens can also use a CsI(Tl) scintillator that produces green light centered at 550 nm. All lenses are
coated with anti-reflective coating for both wavelength bands. Two sets of doublets, the stop, and the CCD camera move
during zoom operations. One doublet has XY compensation. The first three lenses use fused silica for radiation damage
control. The 60 lb of glass inside the 340 lb mechanical structure is oriented vertically.
A new fisheye lens design is used as a miniature probe to measure the velocity distribution of an imploding surface
along many lines of sight. Laser light, directed and scattered back along each beam on the surface, is Doppler shifted by
the moving surface and collected into the launching fiber. The received light is mixed with reference laser light in each
optical fiber in a technique called photonic Doppler velocimetry, providing a continuous time record.
An array of single-mode optical fibers sends laser light through the fisheye lens. The lens consists of an index-matching
positive element, two positive doublet groups, and two negative singlet elements. The optical design minimizes beam
diameters, physical size, and back reflections for excellent signal collection. The fiber array projected through the
fisheye lens provides many measurement points of surface coverage over a hemisphere with very little crosstalk. The
probe measures surface movement with only a small encroachment into the center of the cavity.
The fiber array is coupled to the index-matching element using index-matching gel. The array is bonded and sealed into
a blast tube for ease of assembly and focusing. This configuration also allows the fiber array to be flat polished at a
common object plane. In areas where increased measurement point density is desired, the fibers can be close packed. To
further increase surface density coverage, smaller-diameter cladding optical fibers may be used.
A novel fiber-optic probe measures the velocity distribution of an imploding surface along many lines of sight. Reflected
light from each spot on the moving surface is Doppler shifted with a small portion of this light propagating backwards
through the launching fiber. The reflected light is mixed with a reference laser in a technique called photon Doppler
velocimetry, providing continuous time records.
Within the probe, a matrix array of 56 single-mode fibers sends light through an optical relay consisting of three types of
lenses. Seven sets of these relay lenses are grouped into a close-packed array allowing the interrogation of seven regions
of interest. A six-faceted prism with a hole drilled into its center directs the light beams to the different regions. Several
types of relay lens systems have been evaluated, including doublets and molded aspheric singlets. The optical design
minimizes beam diameters and also provides excellent imaging capabilities. One of the fiber matrix arrays can be
replaced by an imaging coherent bundle.
This close-packed array of seven relay systems provides up to 476 beam trajectories. The pyramid prism has its six
facets polished at two different angles that will vary the density of surface point coverage. Fibers in the matrix arrays are
angle polished at 8°to minimize back reflections. This causes the minimum beam waist to vary along different
trajectories. Precision metrology on the direction cosine trajectories is measured to satisfy environmental requirements
for vibration and temperature.
The National Ignition Facility (NIF) has a need for measuring gamma radiation as part of a nuclear diagnostic program.
A new gamma-detection diagnostic uses 90° off-axis parabolic mirrors to relay Cherenkov light from a volume of
pressurized gas. This nonimaging optical system has the high-speed detector placed at a stop position with the
Cherenkov light delayed until after the prompt gammas have passed through the detector. Because of the wavelength
range (250 to 700 nm), the optical element surface finish was a key design constraint. A cluster of four channels (each
set to a different gas pressure) will collect the time histories for different energy ranges of gammas.
The National Ignition Facility will begin testing DT fuel capsules yielding greater than 1013 neutrons during 2010.
Neutron imaging is an important diagnostic for understanding capsule behavior. Neutrons are imaged at a scintillator
after passing through a pinhole. The pixelated, 160-mm square scintillator is made up of 1/4 mm diameter rods 50 mm
long. Shielding and distance (28 m) are used to preserve the recording diagnostic hardware. Neutron imaging is light
starved. We designed a large nine-element collecting lens to relay as much scintillator light as reasonable onto a 75 mm
gated microchannel plate (MCP) intensifier. The image from the intensifier's phosphor passes through a fiber taper onto
a CCD camera for digital storage. Alignment of the pinhole and tilting of the scintillator is performed before the relay
lens and MCP can be aligned. Careful tilting of the scintillator is done so that each neutron only passes through one rod
(no crosstalk allowed). The 3.2 ns decay time scintillator emits light in the deep blue, requiring special glass materials.
The glass within the lens housing weighs 26 lbs, with the largest element being 7.7 inches in diameter. The distance
between the scintillator and the MCP is only 27 inches. The scintillator emits light with 0.56 NA and the lens collects
light at 0.15 NA. Thus, the MCP collects only 7% of the available light. Baffling the stray light is a major concern in the
design of the optics. Glass cost considerations, tolerancing, and alignment of this lens system will be discussed.
The National Ignition Facility and the Omega Laser Facility both have a need for measuring prompt gamma radiation as
part of a nuclear diagnostic program. A new gamma-detection diagnostic using off-axis-parabolic mirrors has been built.
Some new techniques were used in the design, construction, and tolerancing of this gamma ray diagnostic. Because of
the wavelength requirement (250 to 700 nm), the optical element surface finishes were a key design consideration. The
optical enclosure had to satisfy pressure safety concerns and shielding against electromagnetic interference induced by
gammas and neutrons. Structural finite element analysis was needed to meet rigorous optical and safety requirements.
The optomechanical design is presented. Alignment issues are also discussed.
The design and assembly of a nine-element lens that achieves >2000 lp/mm resolution at a 355-nm wavelength
(ultraviolet) has been completed. By adding a doublet to this lens system, operation at a 532-nm wavelength (green) with
>1100 lp/mm resolution is achieved. This lens is used with high-power laser light to record holograms of fast-moving
ejecta particles from a shocked metal surface located inside a test package. Part of the lens and the entire test package are
under vacuum with a 1-cm air gap separation. Holograms have been recorded with both doubled and tripled Nd:YAG
laser light. The UV operation is very sensitive to the package window's tilt. If this window is tilted by more than 0.1
degrees, the green operation performs with better resolution than that of the UV operation. The setup and alignment are
performed with green light, but the dynamic recording can be done with either UV light or green light. A resolution plate
can be temporarily placed inside the test package so that a television microscope located beyond the hologram position
can archive images of resolution patterns that prove that the calibration wires, interference filter, holographic plate, and
relay lenses are in their correct positions. Part of this lens is under vacuum, at the point where the laser illumination
passes through a focus. Alignment and tolerancing of this high-resolution lens are presented. Resolution variation across
the 12-mm field of view and throughout the 5-mm depth of field is discussed for both wavelengths.
Shock waves passing through a metal sample can produce ejecta particulates at a metal-vacuum interface. Holography
records particle size distributions by using a high-power, short-pulse laser to freeze particle motion. The sizes of the
ejecta particles are recorded using an in-line Fraunhofer holography technique. Because the holographic plate would be
destroyed in an energetic environment, a high-resolution lens has been designed to relay the scattered and unscattered
light to a safe environment where the interference fringes are recorded on film. These interference fringes allow particles
to be reconstructed within a 12-mm-diameter, 5-mm-thick volume. To achieve resolution down to 0.5 μm, both a high-resolution
optical relay lens and ultraviolet laser (UV) light were implemented. The design and assembly of a nine-element
lens that achieves >2000 lp/mm resolution and operates at f/0.89 will be described. To set up this lens system, a
doublet lens is temporarily attached that enables operation with 532-nm laser light and 1100 lp/mm resolution. Thus, the
setup and alignment are performed with green light, but the dynamic recording is done with UV light. During setup, the
532-nm beam provides enough focus shift to accommodate the placement of a resolution target outside the ejecta
volume; this resolution target does not interfere with the calibrated wires and pegs surrounding the ejecta volume. A
television microscope archives images of resolution patterns that prove that the calibration wires, interference filter,
holographic plate, and relay lenses are in their correct positions. Part of this lens is under vacuum, at the point where the
laser illumination passes through a focus. Alignment and tolerancing of this high-resolution lens will be presented, and
resolution variation through the 5-mm depth of field will be discussed.
A velocimetry experiment has been designed to measure shock properties for small cylindrical metal targets
(8-mm-diameter by 2-mm thick). A target is accelerated by high explosives, caught, and retrieved for later inspection.
The target is expected to move at a velocity of 0.1 to 3 km/sec. The complete experiment canister is approximately
105 mm in diameter and 380 mm long. Optical velocimetry diagnostics include the Velocity Interferometer System for
Any Reflector (VISAR) and Photon Doppler Velocimetry (PDV). The packaging of the velocity diagnostics is not
allowed to interfere with the catchment or an X-ray imaging diagnostic. A single optical relay, using commercial lenses,
collects Doppler-shifted light for both VISAR and PDV. The use of fiber optics allows measurement of point velocities
on the target surface during accelerations occurring over 15 mm of travel. The VISAR operates at 532 nm and has
separate illumination fibers requiring alignment. The PDV diagnostic operates at 1550 nm, but is aligned and focused at
670 nm. The VISAR and PDV diagnostics are complementary measurements and they image spots in close proximity on
the target surface. Because the optical relay uses commercial glass, the axial positions of the optical fibers for PDV and
VISAR are offset to compensate for chromatic aberrations. The optomechanical design requires careful attention to fiber
management, mechanical assembly and disassembly, positioning of the foam catchment, and X-ray diagnostic field-of-view.
Calibration and alignment data are archived at each stage of the assembly sequence.
The National Ignition Facility (NIF) requires optical diagnostics for measuring shock velocities in shock physics experiments. The nature of the NIF facility requires the alignment of complex three-dimensional optical systems of very long distances. Access to the alignment mechanisms can be limited, and any alignment system must be operator-friendly. The Velocity Interferometer System for Any Reflector (VISAR) measures shock velocities and shock breakout times of 1- to 5-mm targets at a location remote to the NIF target chamber. A third imaging system measures self-emission of the targets. These three optical systems using the same vacuum chamber port each have a total track of 21 m. All optical lenses are on kinematic mounts or sliding rails, enabling pointing accuracy of the optical axis to be systematically checked. Counter-propagating laser beams (orange and red) align these diagnostics to a listing of tolerances. Floating apertures, placed before and after lens groups, display misalignment by showing the spread of alignment spots created by the orange and red alignment lasers. Optical elements include 1-in. to 15-in. diameter mirrors, lenses with up to 10.5-in. diameters, beam splitters, etalons, dove prisms, filters, and pellicles. Alignment of more than 75 optical elements must be verified before each target shot. Archived images from eight alignment cameras prove proper alignment is achieved before each shot.
The National Ignition Facility (NIF) requires optical diagnostics for measuring shock velocities in shock physics experiments. The velocity interferometer for any reflector measures shock velocities at a location remote to the NIF target chamber. Our team designed two systems, one for a polar port orientation, and the other to accommodate two equatorial ports. The polar-oriented design requires a 48-m optical relay to move the light from inside the target chamber to a separately housed measurement and laser illumination station. The currently operational equatorial design requires a much shorter relay of 21 m. Both designs posed significant optomechanical challenges due to the long optical path length, large quantity of optical elements, and stringent NIF requirements. System design had to tightly control the use of lubricants and materials, especially those inside the vacuum chamber; tolerate earthquakes and radiation; and consider numerous other tolerance, alignment, and steering adjustment issues. To ensure compliance with NIF performance requirements, we conducted a finite element analysis.
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.
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.
Robert Malone, John Bower, David Bradley, Gene Capelle, John Celeste, Peter Celliers, Gilbert Collins, Mark Eckart, Jon Eggert, Brent Frogget, Robert Guyton, Damien Hicks, Morris Kaufman, Brian MacGowan, Samuel Montelongo, Edmund Ng, Ronald Robinson, Thomas Tunnell, Phillip Watts, Paul Zapata
The National Ignition Facility (NIF) requires diagnostics to analyze high-energy density physics experiments. A VISAR (Velocity Interferometry System for Any Reflector) diagnostic has been designed to measure shock velocities, shock breakout times, and shock emission of targets with sizes from 1 to 5 mm. An 8-inch-diameter fused silica triplet lens collects light at f/3 inside the 30-foot-diameter vacuum chamber. The optical relay sends the image out an equatorial port, through a 2-inch-thick vacuum window, and into two interferometers. A 60-kW VISAR probe laser operates at 659.5 nm with variable pulse width. Special coatings on the mirrors and cutoff filters are used to reject the NIF drive laser wavelengths and to pass a band of wavelengths for VISAR, passive shock breakout light, or thermal imaging light (bypassing the interferometers). The first triplet can be no closer than 500 mm from the target chamber center and is protected from debris by a blast window that is replaced after every event. The front end of the optical relay can be temporarily removed from the equatorial port, allowing other experimenters to use that port. A unique resolution pattern has been designed to validate the VISAR diagnostic before each use. All optical lenses are on kinematic mounts so that the pointing accuracy of the optical axis can be checked. Seven CCD cameras monitor the diagnostic alignment.
Robert Malone, John Bower, Gene Capelle, John Celeste, Peter Celliers, Brent Frogget, Robert Guyton, Morris Kaufman, Gregory Lare, Tony Lee, Brian MacGowan, Samuel Montelongo, Edmund Ng, Thayne Thomas, Thomas Tunnell, Phillip Watts
The National Ignition Facility (NIF) requires diagnostics to analyze high-energy density physics experiments. As a core NIF early light diagnostic, this system measures shock velocities, shock breakout times, and shock emission of targets with sizes from 1 to 5 mm. A 659.5 nm VISAR probe laser illuminates the target. An 8-inch-diameter fused silica triplet lens collects light at f/3 inside the 33-foot-diameter vacuum chamber. The optical relay sends the image out an equatorial port, through a 2-inch-thick vacuum window, and into two VISAR (Velocity Interferometer System for Any Reflector) interferometers. Both streak cameras and CCD cameras record the images. Total track is 75 feet. The front end of the optical relay can be temporarily removed from the equatorial port, allowing for other experimenters to use that port. The first triplet can be no closer than 500 mm from the target chamber center and is protected from debris by a blast window that is replaced after every event. Along with special coatings on the mirrors, cutoff filters reject the NIF drive laser wavelengths and pass a band of wavelengths for VISAR, for passive shock breakout light, or for thermal imaging light (bypassing the interferometers). Finite Element Analysis was performed on all mounting structures. All optical lenses are on kinematic mounts, so that the pointing accuracy of the optical axis can be checked. A two-color laser alignment scheme is discussed.
The National Ignition Facility (NIF) requested an optical diagnostic for measuring shock velocities, shock breakout times, and shock emission of objects with sizes of 1 to 10 mm. For the polar port of the target chamber, an 8-inch triplet lens collects light at f/3 inside a 30-foot-diameter vacuum chamber and uses an optical relay to send the image into two interferometers located at a distance of 160 feet. Light propagates through a VISAR (Velocity Interferometry System for Any Reflector) interferometer employing a Mach-Zehnder configuration. After exiting the interferometers the images are recorded, both by streak cameras and CCD gated imagers. Discrete magnification changes are accomplished by swapping out optical elements. Large dove prisms are used to rotate the image to align a selected region of the object with the slits of the streak cameras. Unique mounting structures are required to remotely control the alignment of the optical axis. Finite Element Analysis (FEA) was performed on all mounting structures. The first 8-inch triplet can be no closer than 500 mm from the target chamber center and is protected by a blast window that has to be replaced after every event. The first several lens groups have to be fused silica for radiation resistance. A frequency-doubled Nd:YAG laser, operating at 659.5 nm, is used to illuminate the moving object. The VISAR laser wavelength had to be different than the first, second, and third harmonics of the NIF drive lasers.
In-line Fraunhofer holography has been developed and implemented at the Los Alamos National Laboratory to measure particle distributions of fast moving particles. Holography is a unique diagnostic that gives unambiguous information on the size and shapes of particle distribution over a 3D volume. Currently, the capability of measuring particles two microns in size which travel many mm/microsecond(s) ec has been demonstrated in hydrodynamic experiments at the Pegasus Pulsed Power Facility. Usually, for setting up an in-line holography experiment for measuring particles a few microns in size, the holographic film would be placed less than one centimeter from the particles. However, due to the high kinetic energy associated with the dynamic experiment, an optical relay system is used to relay the interference pattern 35 cm so that the glass hologram will survive. After the hologram has been recorded the data must be extracted. A spatially filtered laser is used to reconstruct a real image which is a projection of the particles over a 3D volume. Planes of data from this volume are digitized via a CCD camera by moving the hologram with a three axis actuator. After the data has been digitized it is then analyzed with intelligent image processing algorithms.
Bechtel Nevada, in collaboration with Los Alamos National Laboratory, has designed a radiographic imaging system that takes advantage of large format electron optical elements to produce a highly sensitive system for large diameter radiographic fluxes. Using specially designed fast lenses, the system is able to observe scintillator screens as large as 300 mm in diameter.A gated microchannel plate intensifier allows the system to be synchronized to pulsed gamma, proton and neutron sources of radiation to help reduce background noise levels. The entire system is deployed in a transportable housing with sealed heat exchanger and electrical patch panel that is designed to be lighttight so that the electron optics can be operated at extremely high gain. External controls allow manipulation of system gain, gate width and focus. The resolution is about 1 to 2 line pairs per millimeter at the radiation-to-light converter, and the f-number of the optical system is f/1. The image is digitized from a fiber-optically coupled 1024 X 1024 cooled charge-coupled device array. The system will have interchangeable components so that system performance can be optimized to meet specific recording requirements. The major trade-off is between field of view and resolution.
An optical lens system with varying magnification has been designed for a 70-mm image format. Twenty optical
elements were needed to provide for the 345- to 1050-mm focal length zoom range as well as the proper color correction
over the visible spectrum. A 4-in diameter port window limits thef/# of the optical lens system. Operation of the lens
system is done by actuating stepping motors through a MacPlus computer.
This lens system was designed for Los Alamos National Laboratory Group M-8, because no commercial zoom lens
existed that would change its reduction from 1/15 to 1/4 at a focusing range of 5 meters. Additionally, we required a larger,
non-standard image size that could be recorded by a rotating mirror streak camera. A Nikkor lens sales manual does offer a
long focal length, 35-nun lens only upon special order. The closest focusing range of this Nikkor lens is 6 meters.
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