Abstract
Continuously-tunable and coherent THz and millimeter sources are in great demand for applications including high-resolution spectroscopy, communications, and bio-medical imaging. However, these applications cannot be put into practice until compact THz lasers are available. On the other hand, parametric processes based on second-order optical nonlinearities such as difference-frequency generation (DFG)1,2 offer a simple method for efficient THz and millimeter emitters. So far, LiNbO3, ZnGeP2 and DAST1 have been used based on this scheme. However, all of them have very large absorption coefficients in the THz domain. Among all second-order nonlinear crystals GaSe has the lowest absorption coefficients in the THz domain.4 As one of the important NLO crystals, GaSe can satisfy phase matching (PM) conditions in a large wavelength range.5 Moreover, this crystal possesses large second-order susceptibility. All these properties make GaSe a winner for efficient generation of THz and millimeter waves based on DFG. In this report, we have implemented a new coherent THz and millimeter source with the output wavelength continuously tunable in the range of 56.8-1618 μm (5.27–0.18 THz) in a GaSe crystal.
© 2002 Optical Society of America
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