Laser-Induced optical breakdown often occurs unexpectedly at optical intensities far lower than those predicted by ultra-short pulse laser experiments, and is usually attributed to contamination. To determine the physical mechanism, optical coatings were contaminated with carbon and steel microparticles and stressed using a 17 kW continuous-wave laser. Breakdown occurred at intensity levels many orders of magnitude lower than expected in clean, pristine materials. Damage thresholds were found to strongly follow the bandgap energy of the film. A thermal model incorporating the particle absorption, interface heat transfer, and free carrier absorption was developed, and it explains the observed data, indicating that surface contamination heated by the laser thermally generates free carriers in the films. The observed bandgap dependence is in direct contrast to the behavior observed for clean samples under continuous wave and long-pulse illumination, and, unexpectedly, has similarities to ultra-short pulse breakdown for clean samples, albeit with a substantially different physical mechanism.

We investigate the variations that occur with changes in the number of layers and with the use of the assist beam main and assist beam energy on the morphology of HfO 2 /SiO 2 quarter wave stacks deposited by dual ion beam sputtering. We show how the addition of sequential HfO 2 /SiO 2 bilayers, up to eight, affects the surface roughness and micro-crystallinity of the top HfO 2 layer. We also show that use of the assist source significantly smooths the surface while simultaneously reducing microcrystallinity. The HfO 2 /SiO 2 structures are very robust and can withstand fluences in excess of 3 J/cm 2 generated by 1ps pulses from a chirped amplified Ti:Sapphire laser.

This paper describes the physical processes that occur when high-power continuous-wave laser light interacts with absorbing particles on a low-absorption optical surface. When a particulate-contaminated surface is illuminated by high-power continuous-wave laser light, a short burst of light is emitted from the surface, and the particles rapidly heat over a period of milliseconds to thousands of degrees Celsius, migrating over and evaporating from the surface. The surviving particles tend to coalesce into larger ones and leave a relatively flat residue on the surface. The total volume of the material on the surface has decreased dramatically. The optical surface itself heats substantially during illumination, but the surface temperature can decrease as the material is evaporated. Optical surfaces that survive this process without catastrophic damage are found to be more resistant to laser damage than surfaces that have not undergone the process. The surface temperature of the conditioned surfaces under illumination is lower than that of unconditioned surfaces. These conditioning effects on particles occurred within the first 30 s of laser exposure, with subsequent laser shots not affecting particle distributions. High-speed photography showed the actual removal and agglomeration of individual particles to occur within about 0.7 ms. Elemental changes were measured using time-of-flight secondary ion mass spectroscopy, with conditioned residuals being higher in hydrocarbon content than pristine particles. The tests in this study were conducted on high-reflectivity distributed Bragg reflector coated optics with carbon microparticles in the size range of 20-50 μm, gold particles of size 250 nm, and silica 1 μm in size.

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Comparison of performance measurements are presented for a Raytheon (Amber) Sentinal Uncooled Micro-Bolometer Focal Plane Array (UMFPA) camera and a Raytheon (formerly Texas Instruments Defense Systems and Electronics Group) Technology Reinvestment Project (TRP) Ferroelectric Uncooled Focal Plane Array (UFFPA) camera. The two cameras were tested for numerous performance-related issues involving time, temperature, FPA region and image translation related dependencies. The performance parameters of interest were 1) nonuniformity versus environmental temperature 2) Changes in non-uniformity with time since power up and as a function of time since nonuniformity correction update, 3) Noise Equivalent Temperature Difference (NETD), 4) V-curves, 5) Minimum Resolvable Temperature Difference (MRTD), 6) response linearity, 7) power consumption and readiness time as a function of system soak temperature, and 8) image smear distortion characteristics.The Sentinel camera tested is a DC coupled system employing a shutter for nonuniformity correction. The temperature of the shutter is neither controlled nor monitored. The Sentinel cameras can be operated off a battery pack or AC power through a converter. This camera comes equipped with a small viewer and the necessary controls required for optimizing the camera parameters. External RS170 and digital image data ports are provided, as is an RS232