Gain in terahertz quantum cascade lasers

• Main Author: Houghton, M.
• Published: University of Cambridge 2008
• Subjects: 535
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604257

This thesis focuses on experiments involving coupled cavity THz QCLs. These take the form of either monolithic devices with etched gaps to form two cavities on the same device, or separate devices aligned under vacuum and at cryogenic temperatures using a specially built piezo-electric micropositioner system. After an introductory chapter briefly reviewing the current state of QCL research, processing techniques and other standard experimental techniques, the thesis begins with the presentation of some experiments dealing with the effects of optical feedback between the two cavities. This leads on to a theoretical chapter in which a mathematical model of a double section QCL is presented, along with some explanation of some unexpected results seen experimentally. The final chapter returns to experimental work. Findings from the previous chapters are used to attempt to develop methods for the measurement of gain and loss in QCLs using coupled cavities, something for which there is currently no reliable method at THz frequencies and which involves considerable experimental difficulties. The thesis concludes with a discussion of possible future work including an extension of the mathematical model, and other possibilities to improve the gain measurement method.