An experimental and theoretical investigation of laser-induced breakdown was carried out at 0.53 and 0.35 mu m for the following gases: N2, Ar, Ne and Xe. A Nd:YAG laser of 15 ns pulse duration was used in its second and third harmonics. The breakdown threshold intensity Ith in the pressure range 0.2

The physical processes leading to laser-induced breakdown of argon in the flux range 10 &I &10' W/cm have been analyzed. A model has been developed to predict breakdown thresholds which includes multiphoton ionization of ground-state atoms and electron-impact excitation of 4s and 4p states of Ar followed by photoionization of these states. Important processes that occur when the electron concentration exceeds 10' cm, such as three-body recombination, dimer formation, dissociative recombination, photodissociation, and photoionization of the excited molecular and/or atomic species formed, have been included in a late-time breakdown model in order to determine the channels through which the laser energy is deposited in the gas. Experiments have been carried out with use of a frequency-tripled neodymium-doped yttrium-aluminum-garnet beam with 15-ns pulse length, yielding a breakdown threshold of 3&10' W/cm at. p=1 atm in good agreement with model predictions. Comparison of theoretical thresholds and thresholds reported in the literature for pulse lengths in the range 0.4 -500 ns is presented.

Negatively biased, high-voltage solar arrays in low Earth orbit are known to undergo arcing below a critical voltage with respect to the plasma environment. It is proposed that the arcing is due to the breakdown of gas which is emitted under electron bombardment from the coverglass on the solar cells. A voltage threshold is predicted along with the scaling of the threshold on the key parameters.

An experimental and theoretical study has been performed on the response of a titanium alloy surface in vacuum to a XeF laser pulse (λ = 0.35 μm, pulse time = 1 μs). Thermal coupling measurements indicate an optical absorptance of 0.4–0.5. The onset of a measurable impulse is shown to result from bulk target vaporization for fluences ?5 J/cm2. The plasma formation threshold is obtained both theoretically and from experimental data, and good agreement is found. The theoretical model includes laser absorption in the target vapor through inverse bremsstrahlung and photoionization absorption, and collisional energy transfer between free electrons and bound electronic states of Ti.

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