Optical Gain and Amplified Spontaneous Emission in Lead Salt Semiconductor Thin Film Waveguides

Abstract

The work described in this thesis involves the measurements of the optical gain and amplified spontaneous emission (A.S.E) spectrum of Pb1-xSnxTe epilayers and the establishment of conditions under which optically pumped Pb1-xSnxTe laser using a CO2 laser as pump source can be produced. Pb1-xSnxTe epilayers have been grown by a hot wall epitaxy (HWE) technique on BaF2 single crystal substrates and the optical gain which can be produced in these layers has been measured by pumping the films transversely with a N2 laser. A model for optical gain and stimulated emission as a function of pump intensity has been developed which has permitted for the first time in these materials, a direct comparison between the magnitude of the gain pumping rate, and the optical gain generated. The measured optical gain is in very good agreement with the model predicted gain. Good fits to the measured stimulated emission spectra were also obtained from the model prediction. It is shown that the gain for a given pump wavelength has a drastic dependence on the material doping density. According to the model, CO2 laser optically pumped Pb1-xSnxTe laser can be readily achieved, provided that epilayer doping densities can be reduced to values of 1017 cm-3 or less. Nevertheless, doping densities even in nominally undoped layers are generally at least an order of magnitude too high. In some initial attempts to achieve lower doping densities, using a thermal annealing technique, doping densities as low as 2 x 10 17 cm-3 have been obtained and significant pump absorption was achieved at CO2 laser wavelength, as predicted by the model.