Suppression of self-focusing through relay imaging and low pass spatial filtering
Inherent but undesirable properties of high power glass laser systems result from the phenomenon of nonlinear self-focusing. If left unchecked, self-focusing will degrade the quality of the near field intensity profile and decrease the focusable power that can be extracted from the clear aperture of an amplifier. As a beam traverses the long paths required in high power glass laser systems, intensity fluctuations caused by diffraction, small scatterers, etc., will develop on an otherwise smooth profile. The intensity gradients will in general increase in a non-uniform manner. This sharpening is a direct result of the accumulating nonlinear phase retardation and the long propagation path. The fluctuations themselves will grow to significant power content and thus reduce the focusable power. The use of fully relayed, sequential, spatial filtering systems helps to obtain the maximum focusable power from high power glass laser systems. The optical relaying property of an individual filter may be used to provide an effective zero propagation path through an amplifier stage, and, as a consequence, the growth of intensity fluctuations induced by self-focusing is minimized. The zero propagation path also makes the usual diffraction modulation negligible. The overall laser performance is limited by the nonlinear growth of two sources of spatial filter bandpass modulation, small scatterers and truncation of the Fourier spectrum of the beam by the filtering process itself, but proper pinhole selection will minimize their effects.
- Research Organization:
- California Univ., Livermore (USA). Lawrence Livermore Lab.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 7316701
- Report Number(s):
- UCRL-79904; CONF-770826-1
- Country of Publication:
- United States
- Language:
- English
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