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

The 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.