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Abstract

Apparatus and a related method for controlling the characteristics of a high-power laser beam to provide a desired beam divergence, spectral content, and phase. A high-power beam, as from a free-electron laser, is directed into a conical Raman amplifier, together with a Stokes seed beam having the desired characteristics. The amplified output from the amplifier is divergent and its intensity falls of rapidly enough to allow the use of solid material optics without damage or destruction of the optical elements. The Raman amplifier is contained in part by two moving-gas windows, which seal the amplifier from the vacuum environment of the laser without the use of solid material optics. In one embodiment of the apparatus, the resulting output beam is precorrected for phase aberrations caused by optical elements and the transmission medium through which the beam is directed. Pre-correction of the aberrations is achieved by passing the low-power seed beam through substantially the same path as the high-power beam, during an input cycle; then phase-conjugating the seed beam and injecting it into the amplifier at the same time as an output pulse from the laser. The same principle is applied in another embodiment to produce a phase-coherent composite output from multiple high-power lasers.

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First Claim