Abstract

High-order harmonic generation and frequency conversion with high power laser systems lead to the realization of quasi-tunable coherent light sources down to the soft X-ray region. The applications of such ultrashort XUV-pulses are only just beginning and offer unique possibilities in the studies of ultrafast phenomena in plasma and solid state physics. We are using high-order harmonics produced by subpicosecond KrF laser radiation for direct and time-resolved measurement of electron density in laser produced plasma. By using harmonics it is possible to probe plasmas with electron densities above the critical density for the fundamental wavelength. Fig. 1 shows the experimental set-up. The harmonics in the wavelength region between 50 nm to 30 nm irradiate a plasma generated by subpicosecond laser pulse in a 70-100 nm thick polycarbonat foil. The plasma of high electron temperature and an electron density in the range of solid state density or even above (N_c= 10²³-10²⁴ cm^-3), expands adiabatically after burning through the foil.

© 1996 IEEE