Widely tunable monochromatic THz sources based on phase-matched difference-frequency generation in nonlinear-optical crystals: A novel approach

Abstract

We review our up-to-date result on the development of widely tunable monochromatic THz sources, implemented based on difference-frequency generation (DFG) in GaSe, ZnGeP2, and GaP. Using a GaSe crystal, the output wavelength was tuned in the range from 66.5 μm to 5664 μm (from 150 cm−1 to 1.77 cm−1) with the highest peak power 389 W. This tuning range is the widest ever produced for a continuously tunable and coherent tabletop THz source. Moreover, the conversion efficiency 0.1% is also the highest ever achieved for a tabletop system. On the other hand, based on DFG in a ZnGeP2 crystal, the output wavelength was tuned in the ranges 83.1–1642 μm and 80.2–1416 μm for two phase-matching configurations. The output power has reached 134 W so far. Finally, using a GaP crystal, the output wavelength was tuned in the range 71.1–2830 μm, whereas the highest peak power was 15.6 W. The advantage of using GaP over GaSe and ZnGeP2 is that crystal rotation is no longer required for wavelength tuning. Instead, one just needs to tune the wavelength of one mixing beam within the bandwidth of as narrow as 15.3 nm.