GaSb-Based Gain and Saturable Absorber Mirrors for Lasers Emitting at 2–2.5 µm

Abstract

The GaSb material system enables reaching the 2–3.5 µm wavelength range, which is important for many applications. Optically-pumped semiconductor disk lasers are attractive for producing high-power, high-brightness laser radiation with the wavelength controlled by the selection of materials. Such lasers can be quite compact, offer good beam quality, and produce ultra-short pulses by mode-locking with a semiconductor saturable absorber mirror. This thesis is concerned with the development of GaSb-based heterostructures for novel laser sources (i.e. semiconductor disk lasers) operating at 2–2.5 µm wavelengths, with both continuous wave and pulsed operation. In particular, the thesis includes new results concerning the development of GaSb/(AlGaIn)(AsSb) semiconductor disk lasers emitting high-power with broad wavelength tunability of about 50–150 nm. The broad tunability has been achieved by employing quantum wells with different operation wavelengths with asymmetric positioning in the microcavity. GaSb-based nonlinear saturable absorber mirrors were also studied and novel techniques related to their fabrication are presented. A semiconductor saturable absorber mirror was successfully used to mode-lock a high-power disk laser at 2 µm wavelength. Naturally fast absorption recovery of the absorber mirror was discovered and several techniques to control it were studied. Unlike for more conventional absorber materials, low-temperature growth revealed no relation to absorption recovery time. Instead the absorption recovery time could be changed by tailoring the strain and energy band structure in quantum wells and by using an optical cavity design with surface proximity quantum wells.