James R. Lesh

3.5-W Q-switched 532-nm Nd:YAG laser pumped with fiber-coupled diode lasers.

A diode-pumped laser with greater than 11 W of cw 1064-nm output power and 3.5 W of frequency-doubled average power at a 50-kHz pulse repetition frequency has been developed. A single Nd:YAG rod was pumped with the combined output of three fiber-coupled diode-laser arrays. Each pump laser was capable of 10 W of cw output power. The fiber output of each pump laser was first collimated and then focused with a single lens onto one end of a Nd:YAG rod. The resonator mirrors for the L-shaped cavity were selected such that thermal lensing in the laser crystal was mostly compensated. The 532-nm output beam quality factor (M(2)) was less than 1.5.

Signal-to-Noise Ratios in Coherent Soft Limiters

Expressions for the output signal-to-noise power ratio of a bandpass soft limiter followed by a coherent detection device are presented and discussed. It is found that a significant improvement in the output signal-to-noise ratio (SNR) at low input SNRs can be achieved by such soft limiters as compared to hard limiters. This indicates that the soft limiter may be of some use in the area of threshold extension. Approximation methods for determining output signal-to-noise spectral densities are also presented.

A Cost-Performance Model For Ground-Based Optical Communications Receiving Telescopes

An analytical cost-performance model for a ground-based optical communication receiving telescope is presented. The model considers costs of existing telescopes as a function of diameter and field-of-view. This, coupled with communication performance as a function of receiver diameter and field-of-view yields the appropriate telescope cost versus communication performance curve.

High repetition-rate Q-switched and intracavity doubled diode-pumped Nd:YAG laser

A Nd:YAG laser was end pumped with 2.2 W of continuous-wave (CW) diode laser output. Efficient operation of the laser at high repetition rates was emphasized. This laser provides 890 mW of TEM/sub 00/ CW output at 1064 nm, and 340 mW of 532 nm average power at a Q-switched repetition rate of 25 kHz. Experimental data are compared with analysis. >

Deep Space Optical Communications Development Program

The technology development, spacecraft systems impact, design examples and overall development plan for optical deep space communications are described. Design examples include moderate distance links like ones from Mars to Earth, out through a potential mission to a distance of 1000 A.U. The technology development plan, which includes both ground-based as well as Earth orbit-based reception considerations, spans the period from 1985 to the year 2003. Past technology developments in high efficiency lasers, optical modulation and coding, and high power efficiency communications technqiues at multiple bits of information per detected photon are also discussed.

Three-dimensional acousto-optic spectrum analysis

A three-dimensional acousto-optic spectrum analyzer with subhertz resolution is demonstrated experimentally. The first and second dimensions are the two spatial dimensions of the output detector array, and the third dimension is time as sampled by the detector array frame rate. A superfine resolution of 0.12 Hz has been achieved.

Deep Space Optical Communications

The National Commission on Space was chartered by the President and Congress of the United States to formulate the future direction of the U.S. National Aeronautics & Space Agency civilian space program. One of the recommendations is the pursuit of an aggressive space science program. Its focus should be on three major objectives. The first is to understand the structure and evolution of the universe, our Galaxy, our Solar System and, finally, the Planet Earth. The second is to apply this understanding to forecast future phenomena of critical significance to humanity. Finally, the last objective is to use the environment of spaceflight and the tools of space technology to study the basic properties of matter and life.

Optical Communications Data Transfer from Venus

A design study for an optical communications link from Venus to the Earth is described. It is shown that 4.0 Mbps data can be returned over such a link with only 0.5 Watts of laser power.

A Compact Implementation Of A Real Time Acousto-Optic Synthetic Aperture Radar Processor

Architecture of a real time acousto-optic synthetic aperture radar processor is reviewed and recent efforts to develop a compact processor are presented. It employs an acousto-optic device operated in the space integrating mode to compress the signal in range. Two CCD cameras are used in the time-delay and integrate mode to focus data in azimuth and to remove unwanted bias from the image.

Optical communication demonstration and high-rate link facility

Motivated by demands for faster, better, cheaper spacecraft, NASA is developing deep-space optical communication technology which promises reduced mass, volume, and power consumption compared to radio-frequency technology. While earth-orbiting optical receivers may eventually be employed, initial deep-space optical communication links are expected to utilize terrestrial telescope receivers. As the communication beam passes through the atmosphere, atmospheric turbulence causes the beam to scintillate, dramatically impacting its temporal and transverse nature. The statistics of these effects must be measured extensively if optical deep-space communication links are to be fully modeled and the design of deep-space communication links optimized. Sponsored by the Engineering Research and Technology Development program, the purposes of the Optical Communication Demonstration and High-Rate Link Facility are to demonstrate a Gbps-class optical downlink, gather extensive link statistics, and provide high-rate down...