High power continuous-wave frequency conversion in the visible and ultraviolet using diamond
thesisposted on 28.03.2022, 18:46 authored by Hadiya Jasbeer
Solid-state Raman lasers are a convenient technology for shifting the wavelength of conventional lasers to exotic wavelengths with enhanced brightness. Recently, diamond has emerged as an outstanding Raman medium due to its capacity for power handling with demonstrations of very high output powers (hundreds of watts) in the continuous wave regime. To date, these demonstrations have been performed in the near-infrared. However, t here is demand for continuous high brightness output at shorter wavelengths (visible and UV). This thesis aims to address this challenge by intracavity nonlinear frequency mixing. As nonlinear mixing is a polarization dependent process, the polarization behaviour of the Raman laser is critical to efficient operation. Thus as a first step, this thesis investigates the polarization properties of external cavity diamond Raman lasers including a detailed investigation of anomalous polarization effects that had been previously reported. In-grown stress-induced birefringence in the diamond is identified as critical to the polarization behaviour. Birefringence was characterized using Mueller polarimetry, a technique that provides a complete description of the Mueller matrix. Surprisingly, substantial circular retardance is observed in some locations of the sample and of sufficient magnitude to induce errors in measurements obtained using more standard polarimetric techniques such as Metripol. The analysis finds that most significant parameter influencing the laser performance is the linear birefringence axis direction. This parameter is found to dictate the threshold for laser operation and the polarization of the Stokes output. These outcomes provide a firm basis for selecting crystals, optimizing the input pump polarization. The knowledge was used to develop a high power intracavity frequency doubled CW diamond Raman laser operating in Quasi-CW mode. Using an external cavity Raman configuration and 1064 nm pumping, a 620 nm laser of output power 30W and M²<1.1, parameters that are difficult to achieve presently using any other laser technology. The critical design parameters that affects the visible conversion efficiency was evaluated experimentally. Furthermore, a model was developed to predict design parameters for optimum laser performance and power scaling. The concepts were also adapted to a DRL pumped at 532 nm. First Stokes output in the yellow (573 nm) was demonstrated with 15 W and 22.7% conversion efficiency. A model for the laser is presented to optimize efficiency and further increase power. The results were used to predict the design for deep-UV generation, a wavelength range that is otherwise very challenging to generate with high power in the CW regime.