Laser photothermal investigation of non-radiative bulk and surface sources in solid-state laser materials

grantor: University of TorontoThe understanding of the problem of non-radiative energy conversion in solid-state laser materials is the key factor in improving the overall efficiency of solid-state lasers. Furthermore, the reduction of the heat generated in an optically pumped laser crystal can lead to several new applications of solid state lasers, especially in the high-power region. To improve the quality of grown crystals, laser crystal growers require accurate techniques to perform the quality control that is so vital to improving the growth process. In this work, we quantified the problem of non-radiative (heat) energy conversion by using three techniques to monitor laser crystal quality. We used a technique known as photopyroelectric spectroscopy (PPES) to measure the optical absorption and nonradiative energy conversion efficiency of Ti: Sapphire laser materials. We unexpectedly found that the non-radiative processes at the surface of the crystal form a greater fraction of the overall losses in a crystal than had previously been assumed. Based on our finding using PPES, we used the photothermal radiometry technique, which is more sensitive to surface effects than PPES. Using a time-domain approach and a time-domain theoretical treatment of the IR radiative emission signal, we determined that we can probe non-radiative surface and bulk processes by monitoring different time ranges. Our results show that photothermal radiometry can be used as a single technique to evaluate both the bulk and surface non-radiative energy conversion rates in a solid state laser material. The final technique we used was the standard method of laser crystal evaluation: measuring the laser output from a material in a laser cavity. By testing the same materials using PPES, PTR and a laser cavity, we were able to correlate our results with the standard method and also show that the PTR technique can give us information as to why a particular crystal is better than another, which cannot be done by the standard method.Ph.D