Abstract
Over the past few years, considerable theoretical and experimental effort has been directed toward the study of radiative lifetimes of the diatomic rare-gas excimer states involved in vacuum ultraviolet (VUV) laser emission. Using the combined techniques of a monochromatic coherent VUV source together with dimer formation in a pulsed supersonic jet, we present results of radiative lifetime measurements for specific vibronic levels of the Alu state of Ar2, Kr2, and Xe2. This is the lowest stable excited state, which together with nearby and states is involved in the operation of electron-beam pumped excimer lasers. Earlier lifetime measurements were performed by using either charged particles1 or synchrotron radiation2 for excitation of the excimers formed at high pressures (>100 Torr). At these pressures, the collisional frequency is sufficiently high that rapid vibrational relaxation occurs, yielding observed fluorescence from low vibrational levels, v'~0, of the excited state. In the present work, dimers were formed in their van der Waals ground states by expansion in a supersonic jet and excited by a tunable coherent VUV laser source3 to the desired vibronic level. Franck-Condon overlap between the ground and excited states resulted in excitation of selected high vibrational levels of the Alu state. Only levels v' = 36-43 were studied for Xe2, v' = 32-38 for Kr2, and v' = 24-30 for Ar2. The use of the jet expansion enabled radiative lifetime studies to be performed in a pressure regime of <10-2 Torr, where lifetimes are shorter than mean collisional times.
© 1987 Optical Society of America
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