Speckle resistant method and apparatus with chirped laser beam

Details Speckle resistant method and apparatus with chirped laser beam Speckle resistant method and apparatus with chirped laser beam

1993-12-23

1995-07-18

Hellner, Mark

Optics: measuring and testing

Range or remote distance finding

With photodetection

356 28, G01C 308

Patent

active

054346622

ABSTRACT:
Laser beam speckle effects are mitigated by frequency chirping a single-mode laser beam, reflecting it off a speckling surface, and then integrating the reflected beam over at least one chirp period. The speckle reduction is comparable to the use of a multi-longitudinal mode beam having a bandwidth similar to the chirped frequency excursion, while leaving the beam compatible with nonlinear optical processes that are not compatible with multi-longitudinal mode beams. Where the nonlinear process is stimulated Brillouin scattering (SBS) phase conjugation, the beam can be chirped at a rate up to the order of ##EQU1## where .DELTA..nu..sub.B is the gain bandwidth and L is the effective SBS interaction length of the phase conjugator, and C is the speed of light. Other nonlinear processes with which the beam may be used include harmonic generation and Raman-based beam cleanup or wavelength conversion.

REFERENCES:
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patent: 5150170 (1992-09-01), Morris
patent: 5275168 (1994-01-01), Reintjes et al.
Nosach et al., "Cancellation Phase Distortions In An Amplifying Medium With a `Brillouin Mirror`", JEPT Letters 16, 435, 1972, pp. 435-438.
Reintjes et al., "Beam cleanup with stimulated Raman scattering in the intensity-averaging regim", J. Opt. Soc. Am., B/vol. 3, No. 10, Oct. 1986, pp. 1408-1427.
Born and Wolf, Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light, 5th ed., Pergamon Press, 1975, pp. 316-323.
Schulz and Henion, "Frequency-modulated Nd:YAG laser", Optics Letters, vol. 16, No. 8/Apr. 15, 1991, pp. 578-580.
Yariv, Introduction to Optical Electronics, Holt, Rinehart and Winston, Inc., 1971, pp. 236-242.

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