Irradiance compensation control for high-energy laser propagation

Technical Report · Thu Apr 18 04:00:00 EDT 1991

OSTI ID:5218390

Gavel, D T

The quality of propagated Laser light strongly depends on the degree of phase uniformity across the beam at its source. When propagating through turbulent atmosphere, a Strehl ratio of nearly 0.9 is possible if phase correction is made at all spatial scales greater than approximately r{sub o}, the Fried atmospheric cell size. Therefore r{sub o} is a reasonable choice for actuator spacing on the phase compensating adaptive optics. However, analysis of high energy laser propagation has shown that a control law designed to compensate only for atomspheric index fluctuations will drive thermal blooming instabilities. Small initial perturbations in beam irradiance will grow exponentially until the beam breaks up. Therefore it is necessary also to compensate for irradiance perturbations at the same spatial scale as the compensation for phase. Combined phase and irradiance compensation of an HEL has been shown to be stable in theory. Irradiance control can be accomplished with a pair of deformable mirrors spaced apart over a propagation path. Laser light reflected off of the first deformable mirror surface at z = 0 will result in magnitude perturbations some distance away at z = L. The second deformable mirror then recollimates the light. The purpose of simulating the irradiance compensation system is to test the baseline design in such a way that the effect of discrete actuator/sensors and beam edge effects is taken into account in a more realistic manner than can be performed by a 2-D fourier analysis. 7 refs., 9 figs.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5218390
• Report Number(s): UCRL-ID-107112-Pt.2; ON: DE91018489
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
426002 -- Engineering-- Lasers & Masers-- (1990-)
657000* -- Theoretical & Mathematical Physics
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ACTUATORS
ALGORITHMS
COMPUTERIZED SIMULATION
DESIGN
ELECTROMAGNETIC RADIATION
LASER RADIATION
MATHEMATICAL LOGIC
MIRRORS
OPTICAL SYSTEMS
OPTICS
RADIATIONS
SIMULATION
WAVE PROPAGATION