【求助】

stevie

什么是晶体的一类和二类相位匹配？

请大家发表意见，谢谢！

小妖精

The choice of the harmonic crystals used to double or triple the energy of Nd:YAG can be done to either optimize the energy at 532 nm OR to optimize the energy at 355 nm.

The maximum energy at 532 nm is obtained by using Second Harmonic Generator with type II crystal In this case the polarization of the laser beam at 1064 nm is at 45 degrees to the optical axis of the crystal (one ordinary and one extraordinary photons) and the 532 nm beam is generated as an extraordinary beam. Please refer to the lower drawing in the attachment. This type of crystal has the highest conversion efficiency. However, it is not the preferred choice when a system is designed for a maximum energy at 355 nm.

If maximum energy at 355 nm is desired the SHG has to be of type I. In this case the polarization of the 1064 nm laser beam has to be perpendicular to the optical axis of the harmonic crystals (ordinary beam) and the 532 nm is generated as an extraordinary beam (see the upper drawing). Type I SHG is less efficient in doubling than the type I, but the polarization of the 1064 in this case makes a better generation of 355nm. If we will use type II for SHG, the horizontally polarized 1064 beam will not contribute to the generation of 355 nm.

In example: Nd:YAG that generates 350 mJ at 1064 nm can generate 180 mJ at 532 nm when using type II SHG. If we add a THG the energy at 355 nm will be only about 65 mJ.

stevie

谢谢！

不过上面好像没有提到二者的区别，只是说应用上需要的是哪类，是不是这样还是我没看懂？