James T. Murray

Generation of 1.5-μm radiation through intracavity solid-state Raman shifting in Ba(NO 3 ) 2 nonlinear crystals

An intracavity solid-state Ba(NO3)2 Raman shifter produces 1.535–1.556-μm radiation when pumped by a Nd3+:YAG laser operating at 1.318–1.338 μm. Raman beam cleanup and 48% energy conversion efficiency have been observed. Second Stokes lines at 1.82–186 μm were observed in the output at higher pump input energy levels. Diffraction-limited pulses of 0.25 J at 1.535–1.56 μm have been achieved.

Division by 3 of optical frequencies by use of difference-frequency generation in noncritically phase-matched RbTiOAsO_4

A new scheme for coherently connecting optical frequencies in a 3:1 ratio has been demonstrated. To phase lock a Nd:YAG laser at 1064 nm with a CO overtone laser at 3192 nm, we generated their difference frequency in RbTiOAsO(4) (RTA) and beat it against the second harmonic of 3192 nm that was generated in AgGaSe(2).

PROPERTIES OF STIMULATED RAMAN SCATTERING IN CRYSTALS

Abstract This paper summarizes our current research on the development of solid-state Raman lasers based on new materials and novel cavity designs. Criteria for selecting good materials for stimulated Raman scattering are reviewed and a theoretical model is presented to demonstrate the origin of Raman beam cleanup.

Advanced 3D polarimetric flash ladar imaging through foliage

High-resolution three-dimensional flash ladar system technologies are under development that enables remote identification of vehicles and armament hidden by heavy tree canopies. We have developed a sensor architecture and design that employs a 3D flash ladar receiver to address this mission. The receiver captures 128×128×>30 three-dimensional images for each laser pulse fired. The voxel size of the image is 3”×3”×4” at the target location. A novel signal-processing algorithm has been developed that achieves sub-voxel (sub-inch) range precision estimates of target locations within each pixel. Polarization discrimination is implemented to augment the target-to-foliage contrast. When employed, this method improves the range resolution of the system beyond the classical limit (based on pulsewidth and detection bandwidth). Experiments were performed with a 6 ns long transmitter pulsewidth that demonstrate 1-inch range resolution of a tank-like target that is occluded by foliage and a range precision of 0.3” for unoccluded targets.

Marine Raman image amplification

Lite Cycles has developed a new type of range-gated, LIDAR sensing element based on Raman image amplification in a solid-state optical crystal. Marine Raman Image Amplification (MARIA) is a feasible technology for producing high-resolution imagery in an underwater environment. MARIA is capable of amplifying low-level optical images with gains up to 106 with the addition of only quantum-limited noise. The high gains available from MARIA can compensate for low quantum efficiency detectors. The range-gate of MARIA is controlled by the pulsewidth of the amplifier pump laser and can be made as short as 30 - 100 cm, using pump pulses of 2 - 6.7 nsec FWHM. The use of MARIA in an imaging LIDAR system has been shown to result in higher SNR images throughout a broad range of incident light levels, in contrast to the increasing noise factor occurring with reduced gain in ICCDs. The imaging resolution of MARIA in the marine environment can be superior to images produced by a laser line scan or standard range-gated imaging system. MARIA is also superior in rejecting unwanted sunlight background, further increasing the SNR of images. MARIA has the potential of providing the best overall system resolution and SNR, making it ideal for the identification of mine-like objects, even in bright sunlight conditions.

Near infrared optical parametric oscillators

Abstract Optical parametric oscillators are becoming important sources of tunable coherent radiation in the near infrared spectral region. This paper summarizes some of the basic concepts of infrared optical parametric oscillators and presents the results of calculated performance parameters of devices based on arsenate crystals.

2.5 W Eye-safe Solid-state Raman Laser

We report on a 2.5 W average power 250 mJ/pulse eye-safe solid-state Raman laser with an output wavelength of 1.56 µm.

Intracavity solid state Raman marine transmitters

The design and performance of a short-pulse (1.5 ns), high- energy (90 mJ/pulse) nonlinear cavity-dumped, frequency- doubled, solid-state intracavity Raman laser is presented. The laser described is utilized as the transmitter in a high- resolution surf-zone marine imaging lidar system.

Pulse Instabilities and Chaos in Intracavity Solid State Raman Lasers

The roundtrip pulse dynamics of intracavity solid state Raman lasers are theoretically and experimentally studied. A generalized Ikeda map is implemented to predict the coupled-cavity dynamics under cw pumping conditions. Period doubling bifurcations and chaotic instabilities are predicted and compared to experiments.

Solid state Raman lasers: materials, design, and applications

Several years after the discovery of Raman scattering of light, solid state Raman lasers are beginning to reach the stage of commercial applications. This talk will review the basic concepts of Raman gain with a special emphasis on Raman laser crystals. Examples of spectroscopic properties of important materials are presented. The use of these materials in shared-, coupled,- and external-resonator Raman laser systems is described. Design parameters affecting efficiency, beam quality, and temporal pulse width are discussed. Examples will be presented of the use of these lasers for transmitters in atmospheric lidar, marine imaging lidar, adaptive optics guide-stars, and materials processing applications.