Monolithic top emitting room temperature THz DFG QCL with index grating for wavelength selection

We present a high performance top emitting room temperature monolithic terahertz (THz) quantum cascade laser based on difference frequency generation (DFG) and a buried modulated distributed feedback grating. Using a semi-insulating InP:Fe substrate combined with an index-coupled grating could minimize the internal losses for the THz mode. The laser consists of two separate transversely superimposed gratings. The first grating provides selective feedback for the mid-infrared pump modes and is realized in an index-coupled DFG grating designed for single-mode operation for two distinct MIR wavelengths. The second metallic grating for THz extraction is carefully aligned to the spatial distribution of the MIR modes. The resulting device lases pulses up to 150 °C in the single mode. The maximum THz output power at RT is 100 μW measured at 3.37 THz. A THz wavelength tuning of around 0.065 nm/K was achieved through thermal tuning of the MIR pump lasers.