Highly tunable room temperature quantum cascade lasers
An investigation was conducted into the feasibility of novel Quantum Cascade Laser (QCL) technology to replace Optical Parametric Oscillator based light sources in real-time video-rate gas imaging systems. Such a laser must produce pulses of >5ns in duration at a repetition rate of at least 5kHz with peak pulse powers of >10mW. The main QCL examined was an InAs/AlSb based device which had been carefully designed to maintain efficient electron injection and reduce thermal backfilling at high temperatures. This allowed wavelength emission at ~3.3µm in pulsed mode at room temperature. A system was developed which could drive the laser by delivering an electrical pulse as brief as 5ns and with frequencies into the MHz range. This system was used to investigate the QCL, a PbSe photodiode was used as the detector. The investigation showed that the QCLs can be pulsed with electrical pulses from 50ns-200ns safely, that repetition rates up to 680kHz are feasible and that even at these extremely high repetition rates powers higher than 10mW are easily reached. This demonstrates that the QCLs are able to meet the defined criteria. Additional work was carried out to determine if these devices were capable of tunability. An external cavity set-up in the Littrow configuration was used with a back-coupled high-reflectivity mirror to show feedback occurs and that therefore selective feedback could also occur with the use of a selective component such as a diffraction grating.
Quantum Cascade Laser (QCL), QCL, Tunable, Gas imaging
Networked Digital Library of Theses and Dissertations