WPCD 2 B V P Z Courier 10cpi ? x x x , k x 6 X @ 8 ; X @ HP LaserJet Series II HPLASEII.PRS x @ , t 0 OpX @ #| x 2 B 9224520 Milchberg The generation of coherent vacuum ultraviolet and soft X ray radiation by the nonlinear interaction of intense picosecond and subpicosecond pulses with moderate density rare gases is an area of great practical and fundamental interest. We propose experiments to address a number of questions that have arisen in the field and to proceed from the answers to the development of more efficient sources of coherent, soft X ray radiation. (i) The effect of shifting of atomic resonances by an intense laser field on the high harmonic generation efficiency will be investigated using a two color experiment: a longer (100 ps), infrared pulse to shift the levels, and a variably delayed subpicosecond visible pulse to generate harmonics. (ii) The role played by ions in generating harmonics will be determined using both one and two color pump probe techniques. (iii) High precision spectroscopy of the high harmonics (generated with both long and short pulses) will be performed with a 6.7 m VUV spectrometer. (iv) Multiwave mixing involving two driving wavelengths will be studied to achieve efficient phase matching and near resonant conditions. This is expected to dramatically increase the efficiency of short wavelength generation. (v) Our recently achieved success in optical guiding of intense short laser pulses will also be exploited to determine the effect of guiding structures on harmonic generation efficiency. ***
