Continuous Wave Semiconductor Laser at Terahertz Frequencies

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A continuous-wave mode-locked semiconductor laser, widely tunable in the terahertz frequency range, and with power and spectral density sufficient for applications, will be developed, based on the p-Ge active medium working on intra-valence-band transitions of hot holes. Continuous wave operation, which is inaccessible for traditional hot-hole pGe lasers, will be achieved in the mode-locked regime using a new traveling wave excitation scheme and an open cavity design in combination with gain optimization by uniaxial stress. Traveling wave excitation will decrease the intrinsic heating of the active medium by 1 to 2 orders of magnitude. Application of uniaxial stress will increase the gain by splitting the light-and heavy-hole subbands. The laser will generate a continuous train of ~ 10 ps pulses of THz radiation with ~1 GHz repetition rate. This continuous wave mode-locked operation will make this laser attractive for applications that include far-infrared molecular and solid-state spectroscopy, TRz radioastronomy, and satellite/near-earth THz communications. The knowledge gained will suggest future thin-flim/epi-layer schemes for THz lasers based on p-Ge population inversion mechanisms. Graduate and undergraduate research assistants will gain experience in semiconductor physics and processing, THz technology, laser principles, spectroscopic techniques, and rf/microwave electronics.