Progress on widely-tunable monochromatic THz sources and room-temperature detections of THz waves

摘要

We have further developed widely-tunable monochromatic THz sources. These sources are based on difference-frequency generation (DFG) in GaSe and GaP crystals. Using a 47 mm long GaSe crystal the output wavelength was tuned in the range from 66.5 to 5664 mu m (from 150 to 1.77 cm(-1)) with the peak powers reaching 389 W. This record-high power corresponds to a conversion efficiency of similar to 0.1%. On the other hand, using a 20 mm long GaP crystal the output wavelength was tuned in the range 71.1-2830 mu m whereas the highest peak power was 15.6 W. The advantage of using GaP over GaSe is obvious: 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. Most recently, we implemented a new scheme for detecting THz waves based on upconversion at room temperature, i.e. by mixing the THz wave with an infrared laser beam, we observed the upconverted signal at a wavelength just slightly longer than that of the infrared laser. To date the detectable THz power is just an order of magnitude higher than that for a bolometer. This scheme allows us to measure the pulse energy density, wavelength, linewidth, and pulse width of a THz beam at room temperature. Using our widely-tunable monochromatic THz beam, we directly measured the absorption spectra of three different families of the homologues of the chemical vapors.