Broadly tunable lens-coupled nonlinear quantum cascade lasers in the sub-THz to THz frequency range

Abstract

Room-temperature terahertz (THz) quantum cascade laser sources with intracavity difference-frequency nonlinear mixing are electrically pumped monolithic semiconductor laser sources operating in the 0.6–6 THz spectral range. We report widely tunable, low-frequency THz quantum cascade laser sources using a lens-coupled Cherenkov waveguide scheme. Based on a watt-class high-power, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mi>λ</mml:mi> <mml:mo>∼</mml:mo> <mml:mn>13.7</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μm</mml:mi> </mml:mrow> </mml:math> quantum cascade laser, the monolithic THz source is strongly coupled with a high-resistivity silicon lens, which causes a major increase in the THz coupling efficiency and demonstrates significant performance improvements. A room-temperature 1.5 THz device produces a 0.2 mW peak output power with a high-quality beam pattern. Improved THz outcoupling efficiency using the lens-coupled scheme enabled the demonstration of a high-performance external-cavity semiconductor THz source that is tunable from 420 GHz to 2 THz. The external-cavity, lens-coupled device configuration can technically be assembled into a butterfly-style package for a thumb-sized, widely frequency tunable THz semiconductor source.