Room temperature operating continuous wave terahertz light source via shallow electronic states transitions in semiconductors

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Compact THz light source based on the optical transitions via shallow levels in semiconductors was successfully developed and those performances have been improved. Ge and other various semiconductor crystals have been used. CW semiconductor laser with 1 micron wavelength was used as an excitation light source. The generation of THz light via optical transitions by shallow levels can be confirmed. Crystal temperature dependences of output intensity have been shown. In case of GaAs, below gap excitation by 1 micron wavelength light can be successfully used for the indirect two photon excitation process via EL2 level. This kind of below gap excitation has a superior feature in that the homogeneous excitation can be possible. In particular, the specific temperature dependences of THz output can be well understood in view of the photoquenching and photo recovery effect of EL2 levels in GaAs. Generation THz wavelength was well estimated by using THz band pass filters. THz surface emission characteristics by edge light excitation was also realized. This result can be successfully applied for the THz wavelength selective resonant cavity constructions for future THz lasers.