Paul J. M. Suni

Coherent laser radar at 2 mu m using solid-state lasers

The development of a coherent laser radar system using 2- mu m Tm- and Tm, Ho-doped solid-state lasers, which is useful for the remote range-resolved measurement of atmospheric winds, aerosol backscatter, and differential absorption lidar (DIAL) measurements of atmospheric water vapor and CO/sub 2/ concentrations, is described. Measurements made with the 2- mu m coherent laser radar system, advances in the laser technology, and atmospheric propagation effects on 2- mu m coherent lidar performance are discussed. Results include horizontal atmospheric wind measurements to >20 km. vertical wind measurements to >5 km, near-horizontal cloud returns to 100 km, and hard target (mountainside) returns from 145 km. >

1-mJ/pulse Tm:YAG laser pumped by a 3-W diode laser

Efficient 2-microm lasers are needed for many eye-safe laser radar applications. Pumping of a Tm:YAG crystal with the output from a 3-W diode laser has resulted in a cw output power of 0.5 W and Q-switched pulse energies in excess of 1 mJ/pulse at 100 Hz. Improved pump absorption with a near-circular pump beam could result in 2-mJ pulse energies.

Theory of phase conjugation by stimulated Brillouin scattering

The accuracy of the phase-conjugate signal produced by stimulated Brillouin scattering in a waveguide is theoretically investigated. Contradictions between earlier phase-conjugation theories are resolved and are shown to be due solely to differing treatments of the non-phase-matched Brillouin output. We find that this output dominates the nonconjugate signal from stimulated Brillouin scattering.

Measurements of stimulated Brillouin scattering phase-conjugate fidelity

We describe high-accuracy measurements of stimulated Brillouin scattering phase-conjugate fidelity. The dependence of fidelity on pump intensity and on pump-beam divergence is in rough agreement with theoretical predictions for the low-reflectivity limit, even for operation deep into the saturation regime.

Limits to the efficiency of beam combination by stimulated Brillouin scattering

The probability distribution function of the phase difference between two thermal-noise-initiated stimulated Brillouin scattering beams was calculated and measured as a function of the correlation between the noise sources. This correlation is determined by the spatial overlap of the two pump beams. Perfect phase locking of every pair of Brillouin-scattered pulses is shown to be impossible.

A statistical description of stimulated Brillouin scattering beam combination efficiency

The mutual coherence between two stimulated Brillouin signals produced by undepleted pump beams that are partially overlapped is studied. The mutual coherence of the stimulated-Brillouin-scattered beams determines the efficiency with which the two beams can be combined. The statistical properties of the mutual coherence are calculated. The mechanism for coupling of two stimulated-Brillouin-scattering outputs is four-wave mixing. Mutual coherence is found to depend on the pump beams pulse duration, the mediums phonon lifetime, and the degree of overlap between the laser pump beams. >

Single-Longitudinal-Mode and Q-Switched Diode-Pumped Tm, Ho:YLF Oscillators

We report on laser developments exploiting Tm,Ho:YLF pumped at 792 nm using 3- W diode lasers. Tunable CW and Q-switched laser results at various temperatures are described.

Statistical limits on beam combination by stimulated Brillouin scattering

We investigated the phase difference φ between the SBS outputs produced by two beams pumping slightly different portions of the same active medium. SBS is narrow‐band amplified noise and thus has a statistical nature. The parameter φ must be characterized by a probability distribution which can be calculated. A time average of cosφ can be evaluated theoretically and measured by interfering the two SBS outputs and using integrating detectors. For imperfect overlap of the pumping beams there is a significant probability that cosφ→1.

Measurements Of Stimulated Brillouin Scattering Beam Combination Efficiency

The phase difference between two beams generated by stimulated Brillouin scattering of two partially overlapped laser beams is measured. The measured phase difference is compared with predictions of computer simulations. Both theory and experiment show that the phase difference is a random process whose probability distribution depends on pulse-width, phonon lifetime and the degree of the overlap between the pumping lasers.

Laser interferometer with a multicentimeter sensitivity

An optical interferometer based on phase conjugation by stimulated Brillouin scattering is demonstrated. Two scattered orders from a phase grating provide the light input to the two arms of the interferometer. Phase conjugation eliminates all phase differences between the electric fields in the two arms except those that are due to the frequency shift of the stimulated Brillouin process.