Pulsed Laser Device Development Program. Volume IV. ABEL II (Air-Breathing Electric Laser II) Preliminary Beam Quality Test Report

摘要

Single-pulse beam quality was measured on the ABEL laser, for output energies in the 2.0-2.8 kj range. No device adjustments or modifications to optimize beam quality were untertaken. Quantities measured were near-field intensity and total energy, farfield intensity and total energy, and fluence distribution in the focal spot region. This last measurement utilized pulsed IR photography, a new and promising technique. Comparsion cavity interferograms were also taken. Energy delivery from near-field to farfield was 60-65%, and was not dependent on laser output energy, flow rate, or resonator configuration. The intensity measurements showed a tendency for farfield intensity at the end of the optical pulse to decay sooner than that of the near-field. Beam quality, as measured by fraction of farfield energy within the first Airy disc, was equal to or less than 1.25 times diffraction limited for four shots analyzed in detail. Astigmatism was the largest contributor to the observed focal spot distortion. Cavity interferometry results predicted beam quality of 1.15 times diffraction limited.