With the ability to penetrate non-conducting materials, terahertz (THz) radiation can be used for non-invasive imaging and other non-destructive measurements, benefiting medical imaging, security, communication, and manufacturing industries. The quantum cascade laser (QCL) is a promising candidate for a large scale, compact and powerful THz source, but current THz QCL is restricted to cryogenic operating temperatures below 200 K.
Bosco et al. introduce the first thermoelectrically cooled THz QCL with an operational temperature above 200 K in a cryogenic-free system. They were able to measure the laser spectra with a room temperature detector. This measurement indicates that THz quantum cascade lasers are no longer restricted to expensive and bulky setups involving liquid helium or nitrogen.
“Being able to operate and measure a THz QCL in a cryogenics free setup is a considerable step towards widespread applications, that demand cheap, easy-to-use, and high-power devices that provide a wide range of THz frequencies,” Bosco said.
The authors used nonequilibrium Green’s function modeling to optimize their THz QCL designs, while working on improving the molecular beam epitaxial growth and reducing the optical losses of the wave guide.
They are now trying to further improve the design by performing new optimizations and taking additional variables into account, and already have preliminary results showing designs that in theory will be even better than the one presented in the article.
The team hopes that their thermoelectrically cooled devices can provide the sought-after THz radiation for advancing technologies in the field, possibly towards a new generation of on-chip, portable THz devices based on high power THz coherent sources.
Source: “Thermoelectrically cooled THz quantum cascade laser operating up to 210 K,” by L. Bosco, M. Franckié, G. Scalari, M. Beck, A. Wacker, and J. Faist, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5110305.