Abstract

For laser fusion applications, many highpower laser beams must propagate over long air paths to a target chamber. Because of the high intensity–length products required for this application, the generation of stimulated rotational Raman scattering (SRRS) in air is of utmost concern.^1,2 addition, schemes for smoothing the intensity distribution on the target require large optical bandwidths. We report for the first time the effects of laser bandwidth on the SRRS process in air at a wavelength of 351 nm. A 600 ps pulse from a Kuizenga oscillator at a wavelength of 1054 nm is sent through a LiNbO₃ electro-optic modulator to impose a sinusoidal phase modulation with a 2.4 GHz modulation frequency onto the beam. The beam is then amplified by one beam line of the OMEGA fusion laser, frequency-tripled in a pair of KD^*P crystals, down-collimated to a 5 cm beam diameter, and propagated over a distance of 35 m in air. The energy of the beam is varied up to 25 J per pulse and is measured with calibrated detectors. At the end of the path, the spectra are recorded on calibrated film with a 1 m spectrometer, digitized with a microdensitometer, and analyzed.

© 1990 Optical Society of America