MICROWAVE MEASUREMENTS ON LASER PRODUCED BLAST WAVES,

The development of Q-switched lasers has opened up extensive possibilities in studying the interaction of matter and radiation. One of the earliest observed and most interesting phenomena was the breakdown of gases and formation of sparks in the focus of a laser beam. Ionization occurs under these conditions if the radiation intensity exceeds a rather strongly pronounced threshold value. These threshold electric fields are 100,000 to 1,000,000 Vcm-- depending on the type and pressure of gas used and the lens focal length, and on other conditions. In this report, we are not concerned with the actual breakdown mechanisms and conditions but with the spark induced blast wave phenomena occurring when the laser power greatly exceeds the threshold for ionization. Author