Towards compact deep UV laser modules

Diode-based laser modules have become a ubiquitous feature of modern society, with their small size, robustness, and low cost making them suitable for a vast range of applications, from hair removal to space exploration. Their contribution to the advancement of science and the enhancement of the quality of daily life is considerable. Despite the considerable advancements in diode laser technology across a range of electromagnetic spectra, the utilization of these devices in the ultraviolet (UV) range, particularly in the lower wavelengths, remains relatively constrained. The need for laser devices in the UV spectrum has become increasingly apparent in a multitude of significant applications, including those pertaining to biotechnology, sensors, communications, and numerous other major fields. This thesis presents an extended study and development of laser diode-based setups with the main objective: the laser emission in the UVC range and the partial miniaturization of them. A Coherent Beam Combining (CBC) setup was first studied and developed on a tabletop setup and produced an optical power up to 8.8 W with 75% combining efficiency and a single longitudinal mode at 761.1 nm. Based on these results, the first miniaturized laser module with dimensions of 76 x 43 x 15 mm³ implementing the CBC concept and capable of generating a maximum optical power of 5 W with a combining efficiency of 85% at 761.1 nm has been implemented. These laser systems based on the CBC concept were utilized as seeds on a second harmonic generation setup with a 3rd order periodically poled waveguide crystal of stoichiometric LiTaO₃ doped with MgO (PP-MgSLT). The nonlinear crystal exhibited a normalized conversion efficiency of 1.6%/W, resulting in optical powers of up to 13 mW and 18.5 mW at 380.55 nm when seeded with 5 W from the single MOPA of the benchtop setup and the CBC laser module, respectively. The laser emission in the UVC range was achieved by employing a second-order periodically poled bulk LaBGeO5 crystal for the sum frequency generation of the 761.1 and 380.55 nm wavelengths. The setup employs the CBC laser module and the second harmonic from the PP-MgSLT crystal as seeds, and has successfully generated 5 μW at 253.7 nm resulting a normalized conversion efficiency of 0.03%/W by supplying 18 mW at 380.55 nm and 1.1 W at 761.1 nm. A comprehensive description of the setup, including the challenges encountered and the steps taken to overcome them, is provided. Additionally, potential upgrades for the CBC laser module, nonlinear processes, and further miniaturization of these concepts are discussed and presented with designs.