Abstract

Laser-produced plasmas have long attracted the attention of researchers because of their unusual properties coupled with ease of generation. With laser power densities above approximately 10¹³ W/cm² high electron densities and temperatures can be achieved and here x-ray lasers and laser fusion are important applications. At lower intensities, among other applications plasma etching and spectrochemical analysis make use of laser plasmas. We have found¹ that for laser power densities of about 10¹⁰ W/cm² the temperatures in the aftermath of Q-switched laser sparks in air (or other gases) can be several thousand degree Kelvin, even at times as late as 100 μs after ignition. Obviously, the plasma must eventually decay and approach ambient temperature. At least in principle, this opens the possibility to access conditions relevant for combustion and other high temperature chemical processes-even if only on a small spatial scale and during short time intervals. To study the feasibility of such high rep rate generation of temperatures in the range from say 300 to 3000 K we have investigated the spatial and temporal structure of Nd:YAG laser generated sparks in air and other gases during their final stages of decay, i.e. when their temperature and pressure approaches that of the surrounding gas.

© 1996 Optical Society of America