Nonlinear Studies of Semiconductors and Molecular Gases with AN Optically Pumped Laser.

Available from UMI in association with The British Library. Requires signed TDF. This work has been concerned with aspects of both the technology and the application of optically pumped FIR lasers. The development of a high power waveguide CO_2 laser for use as a pump source is described, prior to the main body of the thesis on the use of high intensity far-infrared (cw and Q-switched) radiation for nonlinear magneto-optical spectroscopy. The measurement of inter-Landau level lifetimes in GaAs-Ga_{rm x}Al _{rm 1-x}As heterostructures by means of cyclotron resonance absorption saturation is reported. The results are analysed using a three level model, with the lifetimes thus obtained varying from 0.18 ns to 1.2 ns depending on carrier density. It is also demonstrated that in the case of high mobility material the laser pulse length is of crucial importance, with the sample exhibiting bulk characteristics (apparently losing its 2D properties) as the pulse length is shortened. Landau level lifetimes in bulk semiconductors have also been determined, with the results being well interpreted on a three-level model. At higher laser irradiances, cyclotron resonance saturation measurements in uncompensated n-GaAs have demonstrated that an electron-electron scattering mechanism results in an N = 1 Landau level electron lifetime of ~1 ns. The dependence of the cyclotron resonance linewidth (and hence the carrier momentum scattering time) on carrier density is shown to be consistent with ionized impurity scattering. The first observation of saturation of the cyclotron resonance absorption in n-InP is also made, and again this is fitted on a three -level model. The N = 1 Landau level lifetime has thus been determined to be 0.9 ns, in good agreement with the lifetime obtained from emission studies. Finally we report the observation of chaos in the far-infrared output, with all emissions investigated exhibiting the same characteristic signature.