| A thumb (and finger as well) dwarf a terahertz-emitting quantum-cascade laser that puts out a peak power of almost a watt. (Image: Vienna University of Technology) |
Vienna, Austria--A dual-facet pulsed quantum-cascade laser (QCL) that emits terahertz radiation with a center wavelength of 3.9 THz and a (very) broad bandwidth of 0.42 THz was created by researchers at the Vienna University of Technology (TU VIenna).1 The device puts out 470 mW peak power per facet, for a total of 940 mW. Pulse durations were about 200 ns, with a pulse repetition rate of 10 kHz, but gated to emit at 10 Hz.
Although the TU Vienna pulsed terahertz QCL puts out a peak power of almost a watt, keep in mind that its average optical power is much lower -- on the order of a couple of miiliwatts at 10 kHz and a couple of microwatts at 10 Hz. For comparison, a continuous-wave (CW) QCL recently developed by a Swiss group produces 3 mW of terahertz optical power.
To achieve its maximum peak power, the TU Vienna QCL must be operated at 5 K (liquid-helium temperature), but can be operated at a reduced output at temperatures up to 122 K. At the liquid-nitrogen temperature of 70 K, the device puts out a peak power of about 600 mW (300 mW per facet).
The researchers joined two gallium arsenide (GaAs) symmetrical laser structures (GaAs/Al0.15Ga0.85As heterostructures) together via direct wafer bonding; the joining results in a nonlinear growth of about fourfold in laser-light production. In fact, joining more than two structures in this way could lead to a further boost in output, say the researchers.
REFERENCE:
1. Martin Brandstetter et al., Applied Physics Letters 103, 171113 (2013); doi: 10.1063/1.4826943