Sherwin T. Amimoto

XeF laser pumped by high-power sliding discharges

We have developed a high‐power XeF laser photolytically pumped by two surface discharges. The discharges slide along 760‐mm‐long by 12‐mm‐wide ferrite rods. They were energized by a single 6 μF capacitor at 50 kV in a fast discharge circuit. Each emitted up to 38 kW nm−1 cm−2 at 140 nm in 3‐μs‐long pulses. This powerful radiation source was used to photolyze mixtures of 450 Torr argon, 50 Torr nitrogen, and up to 12 Torr XeF2 in an active volume of about 1 l. We extracted a maximum specific laser output energy density of 8 J/l at 351 nm from the B–X transition of XeF.

Stimulated-Brillouin-scattering properties of SnCl 4

Common liquid Brillouin media have poor optical and physical stability when they are pumped at high average powers. We demonstrate that tin tetrachloride, SnCl4, is stable and shows no thermal defocusing at 1064 nm for 20-ns pulses at fluences of 3 J/cm2 and a pulse-repetition frequency of 10 Hz. To characterize this new stimulated-Brillouin-scattering medium we measured the following stimulated Brillouin parameters: Brillouin shift at 35°C, νB = (2.21 ± 0.02) GHz or ωB = 7.37 × 10−2 cm−1; temperature dependence of the Brillouin shift, dνB/dT = −8.95 MHz/°C; small-signal gain coefficient at line center, g0 = (11.2 ± 0.5) cm/GW; Brillouin-gain linewidth, ΔνB = (182 ± 12) MHz, which corresponds to a phonon relaxation time τB = 1.75 ns; and refractive index n = 1.36 at 1.064 μm and 25°C.

Pulsed chemical laser with variable pulse‐length electron‐beam initiation and magnetic confinement

Performance of a pulsed HF/DF chain laser was investigated for the case of transverse initiation by a magnetically confined electron beam. Laser energy and beam quality are presented as functions of electron gun, magnetic field, gas mixture, and optical resonator parameters. The results include 79‐J/l HF output and electrical efficiency for conversion of total incident e‐beam energy to laser output energy of 45%.

Gain and phase-conjugation fidelity of a four-wave Brillouin mirror based on methane.

We report measurements of the gain and phase-conjugation fidelity of a nondegenerate four-wave Brillouin mirror (FWBM) based on high-pressure methane. In the experiments we used a Nd:YAG laser that produced single-mode pulses of 13-nsec duration. Depending on the energy of the pump we measured signal reflectivities between 10 and 10(3), constant over six orders of magnitude of signal energy. We also determined the conjugation fidelity of the FWBM by measuring the Strehl ratio of the conjugated return as a function of the energy of the input signal. We show that the Strehl ratio reduces to 0.5 for an input energy of 1.5 x 10(-13) J/mode of the FWBM. This noise-equivalent signal energy constitutes the limiting sensitivity of the FWBM. Our experiments show that a gas-filled FWBM could be used as a phase conjugator and high-repetition-rate optical image intensifier.

Single-photon detection and imaging with a 10-Hz repetitively pulsed ultrasensitive coherent amplifier.

We report an experimental investigation of an ultrasensitive coherent amplifier (USCA) operated at a 10-Hz repetition rate. We measure its quantum-noise-limited sensitivity, amplification, and image resolution. The USCA consisted of two Nd:YAG amplifiers in series with a high-gain four-wave Brillouin mirror with SnCl(4) as the Brillouin medium. We measure a noise-equivalent-energy sensitivity of 1.96 x 10(-19) J/mode or 1 photon/mode at a quantum efficiency of 96%. The system has an overall optical gain of 2.5 x 10(13). With a version of the USCA equipped with an imaging lens system, we demonstrate the amplification and phase conjugation of entire images with a resolution of 164 microrad across a field of view of 4 mrad or 21 x 21 resolution elements. To our knowledge, this is the first demonstration of a repetitively pulsed USCA.

Sensor node development of a low power, high data rate Multi-Parameter Sensor (MPS) system

The Aerospace Corporation is sponsoring research into the development and use of Nanotechnology Instrumentation in support of Space Launch applications. The intent is to use nanotechnology-based commercial-off-the-shelf components (COTS) micro-electromechanical (MEMS) and in-house developed sensors as basis for a wired or wireless sensors instrumentation and detection system. As part of this effort, the Aerospace Materials and Mechanics Technology Center (MMTC) is supporting the development and testing of a wireless Multi-parameter Sensor (MPS) instrumentation system and a chemical microsensor for the detection of hydrogen chloride (HCl) gas in solid rocket motor exhaust plumes. This paper documents and describes the progress made in the development and testing of these MEMS-based instrumentation.

Stress Measurements in Silicon Microstructures

Raman spectroscopy is used as a non-contact probe of stress with high spatial resolution in micro-machined silicon structures. The motivation for this work is that reliability or cycle life can be substantially increased by understanding the origin of stress including residual stress. Excessive stresses induced by workmanship shortcomings or design constraints may be addressed by Raman measurements. In microelectronics, stress is known to play a significant role in interconnects which limits reliability, life, and ultimately cost of many circuits. We wish to demonstrate the utility of Raman spectroscopy as a tool for the development and design of silicon microstructures. The equations for a general 2D stress field are discussed. Calibration studies using macro-mechanical fixtures for single crystal silicon specimens under 2D stress field are presented. Our measurements show good agreement with the theoretical values and thus validate the approach taken. Stress maps of conventionally fabricated test structures, laser machined, and polysilicon structures are presented.

Pulsed D 2 - F 2 Chain-Laser Damage To Coated Window and Mirror Components

Large-spot laser damage thresholds were measured for bowl-feed-polished CaF/sub 2/ and sapphire windows (bare and antireflection-coated) and for highly polished copper mirrors (bare and carbyne-coated) at DF chain-laser wavelengths (3.58-4.78 ..mu..m). Commercially available antireflection-coated CaF/sub 2/ and Al/sub 2/O/sub 3/ samples were found to have damage thresholds from 17 to 28 J/cm/sup 2/. Significantly larger damage thresholds were observed for uncoated, polished samples of Al/sub 2/O/sub 3/, but damage resistance of uncoated polished CaF/sub 2/ was found to equal that of the best antireflection-coated CaF/sub 2/ samples. A highly polished copper mirror had the highest damage threshold of all the materials tested, i.e., 58 J/cm/sup 2/. Carbyne films of diamond-like hardness, a type of carbon coating, were applied to polished copper mirrors and bowl-feed-polished CaF/sub 2/ surfaces. The carbyne coatings prepared in this work contained numerous carbon-bearing particles that were easily damaged (approx.10 J/cm/sup 2/). However, regions of the irradiated carbyne film that were free of carbon particles withstood high laser fluences (25 J/cm/sup 2/).

Pulsed Chemical Laser With Variable Pulse-Length E-Beam Initiation And Magnetic Confinement

Performance of a pulsed HF/DF chain laser was investigated for the case of transverse initiation by a magnetically confined electron beam. Laser energy and beam quality are presented as functions of electron-gun, magnetic field, gas mixture, and optical resonator parameters; results include 65 J/liter HF laser output.