Abstract

Recently, Terahertz (THz) quantum cascade lasers (QCLs) displaying a continuous emission over a spectral bandwidth in excess of 1 THz have been demonstrated [1]. In this work we investigate the coherence properties of these lasers through the electro-optic sampling (EOS) of their emission using a fs-laser [2]. The advantage of this technique compared to commonly used Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy (~10GHz typical spectral resolution) resides in its orders of magnitude higher resolution, down to sub-kHz depending on the integration time, which allows the simultaneous real time-monitoring of the frequency jitter of the Fabry-Perot modes. EOS of the ultra-broadband QCLs was obtained thanks to a custom developed harmonic mode-locked fs-fiber laser with 1GHz repetition, and of a home-made balanced detection module with a 500MHz detection bandwidth. This setup was used to investigate ultra broadband QCLs operating both in free running and under an external RF modulation.

© 2015 IEEE