Generation of Coherent, Vacuum Ultraviolet and Extreme Ultraviolet Radiation.

The research work involved in this thesis can be broadly divided into three phases. The first phase is the generaion of transform limited radiation at 193 nm with a pulse duration of either 10 ns or 10 ps. The method adopted to obtain this radiation is as follows: the output of either a single frequency continuous wave, 10 ns pulsed or 10 ps pulsed dye laser ((lamda) = 581 nm) is first amplified in a dye amplifier chain pumped by a XeCl* laser and then frequency tripled in a heat pipe containing strontium as the nonlinear medium and xenon as the phase matching gas. The 193 nm radiation thus obtained is finally amplified in a series of ArF* amplifiers. Since the beam quality is maintained throughout the entire process, the final output is transform limited with the following characteristics with a single frequency CW dye laser, energy (TURN) 400 mJ, bandwidth (TURN) 260 NHz, divergence (TURN) 5 x 15 (mu)rad, and pulse duration (TURN) 10 ns; with 10 ps pulsed dye laser, energy (TURN) 40 mJ, bandwidth (TURN) 5 cm(' -1), pulse duration (TURN) 10 ps, and divergence is near transform limited. Phase 2 consists of upconverting the frequency of the ArF* radiation via harmonic generation and sum frequency mixing. Power levels up to 20 kW at the third harmonic ((TURN) 64 nm) and up to 200 W at the fifth harmonic ((TURN) 38 nm), with an efficiency of 10('-5) and 10('-7), respectively, have been obtained using H(,2), Ar, Kr, Ne, He, and N(,2) as the nonlinear media and 10 ps ArF* (193 nm) radiation as the primary source. Similar measurements were done with the 10 ns, 193 nm laser also. In all these cases, self absorption of the harmonic radiation by the nonlinear media proved to be the limiting mechanism. By sum frequency mixing of two ArF* photons and one dye photon ((lamda) (TURN) 480 nm), tunable coherent radiation at (TURN) 79 nm has been obtained. Qualitative analysis of the third order nonlinear susceptibility indicates that the optical Stark broadening of the energy levels involved plays a significant role in reducing the frequency dependence of the nonlinear susceptibility. In the third phase, the 10 ps radiation has been used as the pump source for two photon excitation of H(,2). Following this excitation, stimulated emission at a number of discrete frequencies in the infrared and vacuum ulraviolet has been observed. The VUV radiation corresponds to Werner and Lyman bands, the shortest wavelength observed being 117.6 nm. The conversion efficiency for the strongest line has been estimated to be (TURN) 0.5% and the pulse duration (TURN) 10 ps and the corresponding power (TURN) 10 MW.