Self-adaptive laser resonators using degenerative four-wave mixing in a proximity-coupled side-pumped Nd:YVO₄ amplifier

Degenerate four-wave mixing (FWM) techniques used to produce self-adaptive laser resonator based on diffraction from a gain grating have shown considerable promise for correction of distortion in high-power solid-state laser systems. In these systems, the gain grating is formed by spatial hole burning caused by interference of coherent beams in the laser amplifier and modulation of the population inversion. The gain grating formation can be used for phase conjugation by using the amplifier in a four-wave mixing geometry, for self-pumped phase conjugation by using an input beam in a self-intersecting loop geometry and for formation of a self-starting adaptive oscillator by providing additional feedback from an output coupler and requiring no external optical input. Successful demonstrations of such a self-adaptive resonator have been performed recently in diode side-pumped Nd:YVO4 [1] whose operation is based on the very high reflectivities (>800%) [2] and more recently (>10,000%) of a gain grating formed in a diode-bar side-pumped NdYVO4, amplifier. This resonator has been shown to correct for severe distortions introduced inside the loop with a maximum output of ~7.2 W so far achieved. We will present results of increased resonator outputs by proximity-coupling of the pump diode straight to the FWM amplifier region resulting in higher gains, whereby the diode emitting facet is placed around 50 microns from the pump face of the amplifying crystal. Output powers of the order ~10 W should be achievable, and we will present modelling data for such proximity-coupled geometries

ORNL 10-m small-angle X-ray scattering camera

A new small-angle x-ray scattering camera utilizing a rotating anode x-ray source, crystal monochromatization of the incident beam, pinhole collimation, and a two-dimensional position-sensitive proportional counter was developed. The sample, and the resolution element of the detector are each approximately 1 x 1 mm/sup 2/, the camera was designed so that the focal spot-to-sample and sample-to-detector distances may each be varied in 0.5-m increments up to 5 m to provide a system resolution in the range 0.5 to 4.0 mrad. A large, general-purpose specimen chamber has been provided into which a wide variety of special-purpose specimen holders can be mounted. The detector has an active area of 200 x 200 mm and has up to 200 x 200 resolution elements. The data are recorded in the memory of a minicomputer by a high-speed interface which uses a microprocessor to map the position of an incident photon into an absolute minicomputer memory address. The data recorded in the computer memory can be processed on-line by a variety of programs designed to enhance the user's interaction with the experiment. At the highest angular resolution (0.4 mrad), the flux incident on the specimen is 1.0 x 10/sup 6/ photons/s with the x-ray source operating at 45 kV and 100 mA. SAX and its associated programs OVF and MOT are high-priority, pre-queued, nonresident foreground tasks which run under the ModComp II MAX III operating system to provide complete user control of the ORNL 10-m small-angle x-ray scattering camera

Voids in neutron-irradiated metals and alloys

Small-angle x-ray and neutron scattering are powerful analytical tools for investigating long-range fluctuations in electron (x-rays) or magnetic moment (neutrons) densities in materials. In recent years they have yielded valuable information about voids, void size distributions, and swelling in aluminum, aluminum alloys, copper, molybdenum, nickel, nickel-aluminum, niobium and niobium alloys, stainless steels, graphite and silicon carbide. In the case of aluminum, information concerning the shape of the voids and the ratio of specific surface energies was obtained. The technique of small-angle scattering and its application to the study of voids is reviewed in the paper. Emphasis is placed on the conditions which limit the applicability of the technique, on the interpretation of the data, and on a comparison of the results obtained with companion techniques such as transmission electron microscopy and bulk density. 8 figures, 41 references

Continuous wave holographic laser resonators using degenerate four-wave mixing in a diode bar side-pumped Nd:YVO₄ amplifier

Degenerate four-wave mixing techniques used to produce self-adaptive laser resonators based on diffraction from a gain grating have shown considerable promise for correction of distortion in high-average-power solid-state laser systems, as well as for spectral and temporal control of the laser radiation [1-4]. In these systems, the gain grating is formed by spatial hole burning caused by interference of coherent beams in the laser amplifier and modulation of the population inversion. The gain grating formation can be used for phase conjugation by using the amplifier in a four-wave mixing geometry [2], for self-pumped phase conjugation by using an input beam in a self-intersecting loop geometry [3] and for formation of a self-starting adaptive oscillator by providing additional feedback from an output coupler and requiring no external optical input. Experimental demonstrations have been performed successfully in several laser systems including flashlamp-pumped and quasi-c.w. pumped neodymium-doped amplifiers [1,2], in laser-pumped titanium-doped sapphire [4] and CO2 lasers. We present for the first time, demonstration of a continuous-wave self-adaptive holographic laser resonator. The operation is based on the very high reflectivities (>800%) [5] and more recently (>10,000%) of a gain grating formed in a diode-bar side-pumped Nd:YVO4 amplifier. We have subsequently modelled the FWM interactions and have found good agreement with experimental results. This resonator has been shown to correct for severe phase distortions introduced inside the loop. An output of ~1 W has so far been achieved, future steps include an additional power amplifier incorporated into the resonator loop geometry to give an expected multi-watt operation with a midterm goal of 10 W

Intelligent CAMAC I/O module based on the Signetics 8X300 microcontroller

An intelligent CAMAC I/O module based on the Signetics 8X300 microcontroller was developed. Sixteen 8-bit I/O ports were utilized; eight are dedicated for data transfers with external devices and/or processes, and eight are dedicated to communication with the CAMAC dataway. Separate status and data registers are provided. The input status port (SIN) can receive up to seven individual signals from external devices or the host computer, while the output status port (SOUT) can be used to provide up to seven internally graded LAMs and one bit can be used to generate a Q-response for termination of block transfers. Diagnostic software was developed to operate on the host computer which fully tests all implemented instructions. The device is used in a high-speed memory mapping scheme for data acquisition with a two-dimensional position-sensitive detector system. 8 figures, 3 tables

Demonstration of Independent Experimentation

No abstract available