Abstract-Electronically tunable aperiodic distributed feedback terahertz lasers

O. P. Marshall¹, S. Chakraborty¹, Md. Khairuzzaman¹, T. Folland¹, A. Gholinia², H. E. Beere³, and D. A. Ritchie³

¹School of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL, United Kingdom
²School of Materials, University of Manchester, Manchester M1 7HS, United Kingdom
³Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom 

http://jap.aip.org/resource/1/japiau/v113/i20/p203103_s1?isAuthorized=no

Focussed ion beam milling can be used to introduce aperiodic distributed feedback (ADFB) gratings into fully packaged, operational terahertz (THZ) quantum cascade lasers to achieve electronically controlled, discretely tunable laser emission. These aperiodic gratings—designed using computer-generated hologram techniques—consist of multiple slits in the surface plasmon waveguide, distributed along the length of the laser cavity. Tuning behaviour and output power in ADFB lasers operating around 2.9 THz are investigated with a variety of slit dimensions and grating scales. Mode selectivity and grating losses are found to be strongly dependent on milling depth into the upper waveguide layers, dramatically increasing as the metallic layers are penetrated, then rising more slowly with deeper milling into the laser active region. Grating scale and placement along the laser cavity length are also shown to influence mode selection.http://jap.aip.org/resource/1/japiau/v113/i20/p203103_s1?isAuthorized=no