Adherent Technologies (United States)

The TF7 Task Force of the US Optics and Electro-Optics Standards Council is responsible for laser damage standards and has proposed and is developing a type 1 protocol—that is, a “go/no-go” test protocol to determine whether an optic, when exposed to specified laser irradiation, will likely have more or fewer damage sites according to requirements based on what constitutes system failure as determined by the user. The mathematical framework for this proposed standard assumed top-hat laser beams that probe optical substrate areas that are a portion of the total area of an optic. We present this mathematical framework in the context of a range of fluences as opposed to a single fluence as would be the case for a top-hat laser beam. In addition, we report on some practical, measurement, and implementation aspects of using the range of fluences of Gaussian-beam central zones in this proposed “go/no-go” laser damage test protocol.

CTI has demonstrated Q-switched pulse amplification in Tm,Ho:YLF at >400 mJ output pulse energy for 60 mJ of input energy using a single stage 2-pass (on-axis) amplifier. The pulse duration was 800 ns. A double-pass gain of 10 was demonstrated for 35 mJ input pulse energy. The optical-to-optical efficiency for the 2-pass amplifier was 8%. This is the first demonstration of multiple hundred millijoule output and >10 times double-pass amplification in an all conduction-cooled two micron laser pump module: both the laser rod, operating at 200 K, and the pump laser diodes, operating at 300 K, are conduction-cooled to embedded cold-plates that remove heat from the pump module. As such, this design is directly compatible with the use of heatpipe and space radiator technology for thermal management in a space environment.

Coherent Technologies, Inc. has recently designed and developed an airborne Differential Absorption Lidar (DIAL) sensor that can rapidly and economically locate, identify, and quantitatively map hazardous chemical releases. The lidar was built under contract from Eastman Kodak Company and is capable of filling a broad range of chemical measurement needs. Topographic returns are used to provide simultaneous column content measurement of two (possibly three) chemical species with absorption features between approximately 2.4 microns and 3.5 microns. The system incorporates platform attitude correction and is optimized for mapping surface-source chemical plumes within swaths exceeding 50 m. This system can provide ground resolution better than 1 m at flight speeds in excess of 75 m/s. The 14-month transceiver design-and-build effort is currently in the final integration phase, and flight-testing is scheduled to begin this summer. A recently developed species-specific plume model developed by Kodak, enables reconstruction of the altitude distribution of the chemical plume and estimation of the source release rate, as well as providing realistic species-specific sensor performance predictions under differing environmental conditions. The paper discusses the system architecture, performance modeling, technology trades, and current status, and demonstrates the system measurement capabilities using modeled HCl plumes.

To increase performance and durability of high-temperature composites for potential rocket engine components, it is necessary to optimize wetting and interfacial bonding between high-modulus carbon fibers and high-temperature polyimide resins. Sizings commercially supplied on most carbon fibers are not compatible with polyimides. In this study, the chemistry of sizings on two high-modulus carbon fibers (M40J and M60J, Toray) was characterized as was the chemistry of PMR-II-50 fluorinated polyimide resin. The carbon fibers were characterized using single filament wetting, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopic measurements. The polyimide matrix resins were coated onto glass filaments for characterization by wetting measurements. Surface energy components were obtained by wetting with nondispersive (methylene iodide), acidic (ethylene glycol), and basic (formamide) probes. A continuous desizing system that uses an environmentally friendly chemical-mechanical process was developed for tow level fiber. Composites were fabricated with fibers containing the manufacturer's sizing, desized, and further treated with a reactive finish. Results of room temperature tests after thermal aging show that the reactive finish produces a higher strength and more durable interface compared to the manufacturer's sizing. When exposed to moisture blistering tests, however, the better-bonded composite displayed a tendency to delaminate, presumably due to trapping of volatiles.

Coherent laser radars require transmitters with pulse energies >1 mJ. We discuss the feasibility of building efficient diode-pumped 2-μm Tm and/or Ho lasers for such applications. Experiments and theory indicate that reaching 10-20 mJ/pulse at repetition rates >100Hz should be possible. Significant thermal problems are expected at higher energies.