We report the operation of a quantum cascade laser emitting at a 103μm wavelength (2.9THz). The active region is based on a bound-to-continuum design allowing a low parasitic leakage current, and a high upper-to-lower-state lifetime ratio. The latter is demonstrated by a pronounced decrease of the differential resistance at threshold, which is visible up to high temperatures, and by a weak temperature dependence of the slope efficiency. At 4K, we report a threshold current density of only 105A∕cm2 both in pulsed and continuous-wave operation, and an emitted peak power of 15mW independent of the duty cycle. Maximum operating temperatures of 95K and 70K are observed in pulsed and continuous wave modes, respectively.

By directly modulating the bias voltage of a double-metal waveguide, 2.8THz quantum cascade laser, we observe the appearance of multiple gigahertz sidebands in the emission spectrum, with a spacing that can be continuously tuned up to 13GHz. By using an upconversion technique, the terahertz spectrum is shifted at 1.57μm, and displayed on an optical spectrum analyzer. A marked increase in the number of sidebands is observed when the modulation frequency approaches the round-trip frequency (∼12.3GHz). The laser packaging high frequency response has been measured using a microwave rectification technique, and is limited by the bond-wire parasitic inductance.

Results are presented for the first imaging system that combines the high power of terahertz quantum cascade lasers with three-dimensional image reconstruction based on filtered back-projection. Images of various phantoms have been successfully reconstructed revealing both their external and internal structures.

We report the operation of a 2 THz quantum cascade laser based on a GaAs/Al(0.1)Ga(0.9)As heterostructure. The laser transition is between an isolated subband and the upper state of a 14 meV wide miniband. Lasing action takes place on a high order vertical mode of a 200 microm thick double-metallic waveguide. In pulsed mode operation, with a 3.16mm long device, we report a threshold current density of 115 A/cm(2) at T = 4K, with a maximum measured peak power of 50 mW. The device shows lasing action in continuous wave up to 47K, with a maximum power in excess of 15 mW at T = 4K.

We compare the thermal properties of THz quantum cascade lasers (QCLs) fabricated with metal-metal optical waveguides based on Au∕Au or In∕Au wafer bonding. This information was obtained from the analysis of microprobe band-to-band photoluminescence spectra measured on devices operating in continuous wave (cw). The experimental normalized thermal resistances (RL*), show that the use of Au∕Au wafer bonding optimizes the heat dissipation. Comparison with surface-plasmon based THz QCLs, demonstrates that the use of metal-metal wafer bonding can allow cw operation at progressively higher temperatures.