George W. York

Enhanced vacuum laser-impulse coupling by volume absorption at infrared wavelengths

We report measurements of vacuum laser impulse coupling coefficients as large as 90 dyne/W, obtained with single μs-duration CO 2 laser pulses incident on a volume-absorbing, cellulose-nitrate-based plastic. This result is the largest coupling coefficient yet reported at any wavelength for a simple, planar target in vacuum, and partly results from expenditure of internal chemical energy in this material. Enhanced coupling was also observed in several other target materials that are chemically passive, but absorb light in depth at 10-μm and 3-μm wavelengths. We discuss the physical distinctions between this important case and that of simple, planar surface absorbers [such as metals] which were studied in the same experimental series, in light of the predictions of a simple theoretical model. Ablation parameters for use with the model were determined in separate experiments near threshold in air and in vacuum. The transition from volume- to surface-absorption behavior in the infrared is described as being controlled by fluence-limiting and wavelength conversion in the uppermost target layer.

Cloud hole boring with long pulse CO 2 lasers: theory and experiment

Chemically generated CO(2) laser pulses at 10.6 microm have been used to clear a 5-cm diameter hole through a stratus-like cloud in a laboratory cloud chamber. The results show that 100% clearing can be achieved. The mechanism is shown to be droplet shattering followed by evaporation. In the experimental conditions, the channel closure is effected by turbulent mixing and droplet recondensation.

LASER AMPLIFIER DEVELOPMENTS AT MERCURY

Electron-beam pumped laser amplifiers have been modified to address the mission of krypton-fluoride excimer laser technology development. Methods are described for improving the performance and reliability of two pre-existing amplifiers at minimal cost and time. Preliminary performance data are presented to support the credibility of the approach.

Cloud hole-boring with long pulse CO2 lasers

Chemically generated CO laser pulses at 10.6 im have been used to clear a 5cm diameter hole through a stratus-like cloud in a laboratory cloud chamber. The results show that 100% clearing can be achieved. The mechanism is shown to be droplet shattering followed by evaporation. Under the conditions of the experiment, the channel closure is dominated by turbulent mixing and not droplet recondensation.

Aurora: multi‐Kilojoule KrF laser system for ICF studies

Aurora is a high power KγF laser system used to deliver multi‐kilojoule 5ns 248‐nm laser pulses to fusion targets. System specification are described.