Terahertz sources have always been one of the most important technologies in the field of THz radition.Lots of ways had been proved functional to achieve THz radition.Typically, telectronics and photonics techologies. In the filed of photonics, nonlinear optical difference-frequency generation based on large nonlinear coefficient, high optical damage threshold nonlinear crystals is one of the ways to obtain high power, tunable, portable, and room temperature operating THz wave. GaSe and ZnGeP2(ZGP) nonlinear crystals are mostly appiled.
GaSe crystals with low absorption at millimeter & THz wave, high damaged threshold and high second nonliear coefficient( d22 = 54 pm/V), are commonly used to process Terahertz wave within 40μm and also long waveband tunable Thz wave(beyond 40μm). It was proved tunable THz wave at 2.60 -39.07μm when match angle at 11.19°-23.86°[eoo (e - o = o)], and 2.60 -36.68μm output when match angle at 12.19°-27.01°[eoe (e - o = e)]. Furthermore, 42.39-5663.67μm tunable THz wave was obtained when the match angle at 1.13°-84.71°[oee (o - e = e)].
ZnGeP2 (ZGP) crystals with high nonlinear coefficient, high thermal conductivity, high optical damaged threshold are also been researched as an excellent THz source. ZnGeP2 also have second nonlinear coefficient at d36 = 75 pm/V), which is 160times of KDP crystals. The two type phase match angle of ZGP crystals(1.03°-10.34°[oee (o-e = e)]& 1.04°-10.39°[oeo (o-e= e)]) processing similar THz output(43.01 -5663.67μm), the oeo type proved to be a better choice due to it higher efficient nonlinear coefficient. In a very long time, the output proformance of ZnGeP2 crystals as Terahertz source was limited, because the ZnGeP2 crystal from other suppliers have high absorption in near infrared region (1-2μm):Absorption coefficient >0.7cm-1 @1μm and >0.06cm-1@2μm. However, DIEN TECH provides ZGP( Model: YS-ZGP) crystals with super low absorption:Absorption coefficient<0.35cm-1@1μm and <0.02cm-1@2μm. The advanced YS-ZGP crystals enable users to reach much better output.
Reference:'基于 GaSe 和 Zn GeP2 晶体差频产生可调谐太赫兹辐射的理论研究'2008 Chin. Phys. Soc.
