Ultra-broadband terahertz heterogeneous quantum cascade lasers

Full text: We report an ultra-broadband heterogeneous quantum cascade laser emitting from 2.2 to 3.2 THz. The broad gain medium is obtained by placing different active-region designs into a common double metal waveguide that provides no cutoff and excellent figure of merit over a broad wavelength range. The active-region design is based on a four quantum well design which is then rescaled to obtain emissions with center-frequencies 2.1 THz, 2.4 THz and 2.6 THz. Lasers operate up to 125 K in pulsed mode. Studying the spectral emission as function of injected current we see progressive switching on of emission from the appropriate designs. Short devices provide broad-band emission also in continuous-wave operation. We also performed time-resolved measurements using a fast superconducting bolometer and 5ns wide gate. Strong gain-competition phenomena among the designs were observed. (author)