Development of laser systems capable of surviving extreme conditions experienced in military applications requires mounts and components that are able to survive these conditions. The characterization of mounted and/or bonded optical assemblies in harsh environments is critical for the development of laser and optical systems for functionality in these extreme conditions. Customized mounts, bonding assemblies and packaging strategies are utilized to develop and field reliable and robust optical subassemblies. Thin film polarizers operating at 45° and polarizing beam splitter cubes were chosen for initial testing based on past experiences, advancements in optical coating and construction technologies and material properties. Shock, vibration, shear strength, tensile strength and temperature testing are performed on mounted polarizing beam splitter cubes and thin film polarizers from two manufacturers.
Previous testing showed that polarizing beam splitter cubes constructed using epoxy would become damaged in the laser resonator. The cubes being tested in this report are constructed using epoxy- free direct optical contact bonding. Thin film polarizers operating at 45° are chosen opposed to Brewster’s angle thin film polarizers to reduce the size and simplify design and construction since an optical wedge is not required. The components and mounts are each environmentally tested beyond the manufacturers’ specifications for shock, vibration, and temperature. Component functionality is monitored during and after the environmental testing. Experimental results from the testing will be discussed as will the impact on future laser resonator designs.
Solid state pulsed laser systems are of interest for industrial applications. Flashlamps are an effective method for
pumping solid state pulsed laser systems. Flashlamp lifetime is hard to quantify past the specification provided by
the manufacture and is of concern for applications that are not used or tested on a frequent basis. The flashlamp
lifetime can be shortened by three main failure modes: manufacturing quality escapes, shipping and handling
damage, and shelf life. Manufacturing and shipping failure modes will be the focus of this research. Manufacturing
and shipping failure modes are hard to detect, beyond the obvious non-functioning flashlamp, without testing to
failure, which is not a feasible option.
A method is being proposed that can estimate the lifetime of flashlamps as well as other key characteristics of the
flashlamp while a relatively low number of shots are taken with the flashlamp. Fill pressure and fill gas will be
determined by monitoring the input voltage, current, and output spectrum with comparison to the arc length, bore
diameter, wall thickness and electrode configuration. Flashlamp lifetime estimations will be determined by
monitoring the current, wavelength shift, and output intensity. Experimental results will be discussed focusing on the
characteristics and lifetime estimations of flashlamps.
High energy laser pulses were fired into a 365μm diameter fiber optic cable constrained in small radii of curvature
bends, resulting in a catastrophic failure. Q-switched laser pulses from a flashlamp pumped, Nd:YAG laser were injected
into the cables, and the spatial intensity profile at the exit face of the fiber was observed using an infrared camera. The
transmission of the radiation through the tight radii resulted in an asymmetric intensity profile with one half of the fiber
core having a higher peak-to-average energy distribution. Prior to testing, the cables were thermally conditioned while
constrained in the small radii of curvature bends. Single-bend, double-bend, and U-shaped geometries were tested to
characterize various cable routing scenarios.
The design, assembly and characterization of the latest generation of a small, ruggedized laser-optical firing system will
be discussed. This work builds upon earlier results in an effort to continue the development of robust fiber-coupled laseroptical
firing systems.[1][2] This newest prototype strives to improve on earlier designs, while continuing to utilize many
of the environmentally proven opto-mechanical sub-assemblies.[2][3] One area of improvement involves the
implementation of a second optical safing and arming component. Several additional design improvements were also
incorporated to address shortcomings uncovered during environmental testing.[4][5] These tests and the subsequent failure
analysis were performed at the laser sub-system level. Four identical prototypes were assembled and characterized. The
performance of the units were evaluated by comparing a number of parameters including laser output energy, slope
efficiency, beam divergence, spatial intensity profile, fiber injection and splitter-coupler transmission efficiency. Other
factors evaluated were the ease of alignment, repeatability of the alignment process and the fabrication of the fiberoptical
cables. The experimentally obtained results will be compared and contrasted to the performance of earlier
prototypes.
The design and characterization of small, ruggedized laser-optical subsystems is required for the continued development
of robust laser-optical firing systems. Typically, these subsystems must be capable of generating the needed laser optical
energy, delivering that energy via fiber-optical cables while occupying a volume as small as possible. A novel beam
splitting and fiber injection scheme has been proposed which utilizes two diffractive optical components. These
components were utilized to reduce the volume of a previously designed system. A laser-optical prototype system was
assembled and tested which utilized this beam splitting and fiber injection scheme along other modifications to the laser
module and power supply. This prototype was based on earlier designs that utilized environmentally proven opto-mechanical
sub-assemblies. The system was tested to characterize the laser performance, the splitter-coupler
transmission efficiency, channel-to-channel energy balance and fiber interchangeability. The results obtained for this
design will be compared to the performance of a prototype system based on a more traditional beam splitting and fiber
injection scheme. The traditional design utilized partially reflecting mirrors for beam splitting and plano-convex lenses
for fiber injection. These results will be discussed as will their ultimate impact on future designs and packaging
strategies.
The design and characterization of small, ruggedized laser and optical subsystems is required for the continued
development of robust laser driven optical firing systems. Typically, these subsystems must be capable of generating the
needed optical energy, delivering that energy via fiber-optical cables and occupying a volume as small as possible. A
novel beam splitting and fiber injection scheme has been proposed as a way to further reduce the volume of an earlier
laser-optical firing systems. The new design approach incorporates two diffractive optical components; a beam
homogenizer and a grating-splitter. Other modifications incorporated into this system included a custom designed fiber
optical connector ferrule, capable of holding three optical fibers, a laser subsystem utilizing a dual-flashlamp pumping
scheme and changes to the power supply to effectively drive the new flashlamp assembly. A set of prototype hardware
was obtained and initial assembly and characterization has begun. The proposed alignment strategy will be discussed
along with expected performance in the areas of: laser beam splitting efficiency, fiber injection efficiency, channel-to-channel
energy balance, air breakdown margin and fiber-optical cable interchangeability. The information and
performance obtained to date will be compared and contrasted with that from earlier systems on which this newly
designed prototype is based. These earlier or "Baseline" systems, utilized more traditional beam splitting and fiber
injection schemes. Earlier systems successfully utilized partially reflecting, dielectric coated mirrors, for beam splitting,
plano-convex lenses, for fiber injection and discrete SMA-905 connectors fiber-optical cables.
The characterization of laser-optical subsystems packaged for survivability in harsh environments is crucial for the
development of robust laser-optical firing systems. Previously, custom mounts and bonded optical assemblies were
environmentally tested to ensure their survivability1. The results verified the sub-assemblies would enable the design of
a laser-optical initiation system that could be fielded for use in extreme conditions.
A design package, which utilized the proven opto-mechanical sub-assemblies, was selected. This design was based on
past experience and desired performance criteria. The packaged laser-optical assembly was tested to the same
environmental levels as the sub-assemblies. This test regiment encompassed the harshest environments currently
utilized. Temperature tests were performed ranging from a maximum of +75 degrees C to a minimum of -55 degrees C,
allowing for a two hour soak at each temperature set point. Vibration tests were performed to a maximum level of 15.5
grms for forty seconds in each of three critical axes. Shock tests were performed until failure which was an impulse
level of 5700 G's with a 1.1 millisecond long pulse. The laser-optical assembly was visually inspected and functionally
tested before and after each test to verify survival. As designed, the system was intended to be hermetically sealed via
laser welding. Therefore the visual inspection of the interior was performed post mortem. Experimental results obtained
from the environmental tests will be discussed as will their impact on future packaging strategies.
The characterization of mounted and/or bonded optical assemblies for survivability in harsh environments is crucial for
the development of robust laser-optical firing systems. Customized mounts, bonded assemblies and packaging strategies
were utilized for each of the laser resonator optics with the goal of developing and fielding a reliable initiation system
for use in extreme conditions. Specific components were selected for initial testing based on past experience, material
properties and optical construction. Shock, vibration and temperature testing was performed on three mounted optical
components; polarizing cube beam splitters, Q-switch assemblies and xenon flashlamps.
Previously, flashlamps of a solder-sealed construction type were successfully tested and characterized. This test regiment
characterized the more fragile glass-to-metal seal constructed flashlamps. Components were shock-tested to a maximum
impulse level of 5700 G's with a 1.1 millisecond long pulse. Vibration tests were performed to a maximum level of 15.5
grms for forty seconds in each of three axes. During each test, components were functionally tested and visually
inspected at a specified point to verify survival. Temperature tests were performed over a range extending from a
maximum of 75 degrees C to a minimum of -55 degrees C, allowing for a two hour soak at each temperature set point.
Experimental results obtained from these tests will be discussed as will their impact on future component mounting
strategies.
A compact, ruggedized 12-channel, dual wavelength, fiber-coupled laser system was designed, assembled and tested to support fiber injection experiments. A flashlamp pumped, Q-switched, Nd:Cr:GSGG laser, operating at 1061 nm was assembled and characterized. To optimize the laser for fiber injection, a stable, multimode, Polarization Output Coupled (POC) resonator design was utilized. The design did not use any active cooling and was ideal for low duty cycle applications requiring no more than one shot every 30 seconds. The laser output was frequency doubled to 530 nm utilizing a Type II interaction in a KTP crystal. A nonlinear conversion efficiency of 56% was obtained. Two beam splitting and fiber injection modules, one for each wavelength, were utilized to transform the single laser input beam into six parallel fiber channels. Four of the channels were provided for high output energy and two for low energy monitoring. In addition to the 12 fiber optical outputs, full aperture 1061 nm and 530 nm output ports were provided with independent energy adjustments. The entire laser system was packaged into a rugged 0-ring sealed aluminum housing to maintain cleanliness. The housing measured 18" x 22" x 2.75" and weighed 43.5 pounds. The capability to externally select wavelength, beam format (fiber coupled or full aperture) and output energy was provided. This was to preserve internal cleanliness and facilitate system operation in dirty environments. Alignment strategies and performance results including laser efficiency, far field beam divergence, nonlinear conversion efficiency, fiber-to-fiber energy uniformity, and fiber output intensity profiles will be presented.
A compact, 2-J Master Oscillator, Power Amplifier (MOPA) laser system was designed and built to support a multiple- fiber injection experiment. The system was built in a breadboard configuration to support a risk-reduction/proof- of-concept effort. A common design approach for MOPA systems is to utilize a single-mode oscillator as the input source to the amplifier. However, to optimize this system for fiber injection, a multi-mode oscillator was chosen. A stable, multi-mode, 1053-nm, Nd:YLF laser oscillator was designed and built. A plano/concave resonator was utilized, with a 4.0-mm diameter Nd:YLF laser rod, pumped in a dual flashlamp, diffuse, close-coupled pump cavity. A lithium niobate (LiNbO3) Q-switch crystal was used in a quarter- wave scheme. This pump cavity design did not use any active cooling and was ideal for low duty cycle applications requiring no more than one shot every 60 seconds. The oscillator output was amplified using a neodymium-doped phosphate glass laser rod in a four-pass configuration. Two Joules of output energy with an output pulsewidth of 12 ns were obtained. The 9.53-mm diameter Nd:Glass amplifier rod was pumped in a dual flashlamp, diffuse, close-coupled pump cavity. Output energy, pulsewidth, far-field beam divergence and intensity profile results will be presented for a Schott LG750 amplifier rod.
The X1 accelerator project at Sandia National Laboratory/New Mexico utilizes SF6 insulated, multi-stage, UV laser triggered gas switches. A 265 nm UV laser system was designed and built to generate eight simultaneous output pulses of 10 mJ each with a 13 nsec pulsewidth.
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