We have determined the temporal history of the pressure of a confined low-temperature plasma generated under conditions of modest laser intensity (0.05–1 GW/cm2) by utilizing the target as a thin witness plate to interferometrically measure the particle velocity at its rear surface. The observed data are in agreement with a simple ideal gas model describing the behavior of the plasma. A 150-ns duration laser-driver pulse can deliver a multikilobar pressure ramp to a condensed phase sample for dynamic high-pressure studies.
Synchronous mode locking of a dye laser longitudinally pumped by the second-harmonic pulse train from a passively mode-locked, repetitively pulsed Nd:YAG laser has been studied. The dye laser, incorporating Fabry-Perot tuning elements, has produced intense TEM00 pulses as short as 12 psec in duration with a transform-limited bandwidth of 2 cm−1. The mode-locked dye pulses are time synchronizable with the intense Nd:YAG pulses and have been tuned from 549–727 nm using several laser dyes. Both lasing efficiency and pulse duration exhibit pronounced cavity length dependences that result from processes of gain depletion and population recycling during a pumping pulse. Pulses shorter than the pump are generated under cavity length conditions for which only gain depletion effects occur.
We have studied fragment emission in the spectral range 200 to 900 nm, following photolysis of acetylene (1-10 Torr) by short ultraviolet pulses (25 ps, 266 nm, 2.5-12 mJ). The dominant component of emission is the C, d 3ll.---->(l 3ll. Swan system. Weak singlet C, emission is observed. CH is also observed, in the A 'LI-->X 'll and C '.I + -->X 'll systems. With isotopic labeling and with streak camera recording, we have demonstrated distinct unimolecular and intermolecular processes yielding C, d 3 ll.. The unimolecular channel proceeds with risetime T[ = 215 ± 15 ps, while the pressure-dependent intermolecular component develops over a period of nanoseconds. We discuss the underlying kinetics and the mechanistic implications of the 25 ps excitation.5014
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