Friday, September 23, 2016

Abstract-Short pulse generation and mode control of broadband terahertz quantum cascade lasers

Dominic Bachmann, Markus Rösch, Martin J. Süess, Mattias Beck, Karl Unterrainer, Juraj Darmo, Jérôme Faist, and Giacomo Scalari

Ultra-short pulses are an attractive way of expanding today’s terahertz time-domain systems toward frequencies above 2 THz, and moreover mode control enables reliable generation of terahertz frequency combs based on quantum cascade lasers. We report on a waveguide engineering technique that enables the generation of a bandwidth up to ~ THz ~ 1  and an ultra-short pulse length of 2.5 ps in injection-seeded terahertz quantum cascade lasers. The reported technique is able to control and fully suppress higher order lateral modes in broadband terahertz quantum cascade lasers by introducing side-absorbers to metal–metal waveguides. The side-absorbers consist of a top metallization setback with respect to the laser ridge and an additional lossy metal layer. In continuous wave operation, the side-absorbers lead to octave-spanning laser emission, ranging from 1.63 to 3.37 THz, exhibiting a 725 GHz wide flat top within a 10 dB intensity range, as well as frequency comb operation with a bandwidth of 442 GHz. Numerical and experimental studies have been performed to optimize the impact of the side-absorbers on the emission properties and to determine the required increase of waveguide losses. Furthermore, these studies have led to a better understanding of the pulse formation dynamics of injection-seeded quantum cascade lasers.
© 2016 Optical Society of America
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