Fabrication and characterization of waveguide lasers operating in the infrared spectral range

Identifier:  TDX:2984

Handle: https://hdl.handle.net/20.500.11797/TDX2984

Authors:  Kifle, Esrom Aschenaki

Abstract:
This thesis work has dealt with the fabrication and the characterization of compact and efficient waveguide lasers operating in the continuous wave and passively Q-switched operation regimes around 2 μm in the spectral range. To achieve those, erbium (Er3+), thulium (Tm3+) or holmium (Ho3+) doped monoclinic double tungstate crystalline materials were employed. The gain media were chosen due to their ability to generate polarized laser emission and their large gain cross-sections which make them suitable for achieving compact devices. The combination of the top-seeded solution growth, liquid phase epitaxy, diamond saw dicing and femtosecond direct laser writing methods were employed for fabricating and structuring the waveguides. Furthermore, different characterization techniques such as confocal microscopy, μ-Raman, and μ-luminescence mapping were implemented to assess the quality and suitability of the fabricated waveguides for lasing application. In the passively Q-switched operation regime, the suitability of different saturable absorbers such as transition-metal-doped chalcogenide crystals (Cr2+:ZnSe or ZnS), few-layer transition metal dichalcogenide (MoS2) and carbon nanostructures such as graphene and single-walled carbon nanotubes deposited on a transparent substrate or directly onto the surface of the sample containing the waveguides were tested. The fabrication of an epitaxially grown surface channel waveguide resulted in a record slope efficiency almost approaching the theoretical limit. Femtosecond laser written buried channel waveguides (with circular and hexagonal optical-lattice-like cladding), surface channel waveguides (with half-ring-shaped cladding) and Y-branch splitters were fabricated and studied. Waveguide lasers capable of delivering a watt-level output power as well as those with a stable passive Q-switching operation were demonstrated.