Development of Novel Compact Laser Sources for Bio-Medical Applications

摘要

The focus of this thesis relates to the development and characterisation of novel semiconductor based lasers sources tunable in the broad spectral ranges that are unattainable by conventional lasers due to a lack of suitable laser gain materials.Within the first part, the broad gain spectrum from quantum dot (QD) materials is seen to be an appealing feature for the development of broadly tunable lasers, broadband amplifiers and ultra short pulse generation. As has been previously shown quantum-dot external-cavity passively mode-locked lasers (QD-ECMLLs) are excellent candidates for versatile ultra short pulse generation. This is due to the flexibility that anexternal-cavity mode-locking configuration can offer in terme of a broad tunability for both repetition rate and wavelength which could be achieved. Similarly quantum-dot semiconductor optical amplifiers (QD-SOA) are suitable for the broadband pulse power amplification.Furthermore, master oscillator power amplifier (MOPA) picosecond optical pulse sources using all chirped QD structures were investigated using the MOPA system consisting of two parts, firstly QD-ECMLL and secondly a tilted taper QD-SOA. A further investigation involved a comparison between 1st-order diffraction grating and 2nd-order diffraction grating for this tunable QD-MOPA. The result found was the maximum fundamental mode-locking (FML) wavelength tuning range. Nearly 100 nm (from 1187nm to 1283nm) wavelength tuning range was achieved under a 900 mA current applied to the gain chip with a 2nd-order grating diffraction. Furthermore it was also demonstrated that the peak power spectral density achieved with the 2nd-order diffraction (max; 31.4dBm/nm) is much higher (2-4dB) than that from the 1st-order diffraction under similar conditions. The narrowest optical spectrum width was achieved from the 2nd-order diffraction and the narrowest pulse of 13 ps was found for the setup with the 1st-order diffraction grating. The wavelength tuning range from both orders can be amplified by increasing the injection current of the gain chip without deteriorating the stability of FML.The second part of this thesis focussed on experimental testing of EP-VECSELs, also known as electrically-pumped semiconductor disc lasers (SDLs), which produce high multi watt output power with diffraction limited output beam profile. EP-VECSELs have great potential within the applications where the watt level CW output power and mode-locked light with picosecond pulses sources are required.