YCOB晶体非主平面相位匹配OPCPA输出特性研究

高效、宽带OPCPA技术是实现数拍瓦级乃至百拍瓦级激光放大的两大技术路径之一。本项目主要开展YCOB晶体在800nm中心波段的非主平面相位匹配OPCPA技术及放大特性研究，并分析该匹配模式应用于数拍瓦级OPCPA主放大器的可行性。其目的是基于非主平面匹配方式可以获得的有效非线性系数比主平面高30%左右，以及更宽的带宽(160nm)。宽带宽意味着可以实现更短的脉冲压缩。更高的有效非线性系数意味着在相同的泵浦和注入条件下，可以采用更短的晶体，就可以实现高效率的放大。短晶体在OPCPA过程中也比较大的优势，可以降低走离效应的影响，同时泵浦光和信号光吸收小，高阶非线性效应小，可以降低热效应对非线性性质的影响，比较适合应用于高重频OPCPA放大激光装置中。同时YCOB晶体口径可以生长至大5英寸，未来有望生长到更大，因此本项目的研究可以为基于OPCPA的百拍瓦级激光装置的主放大器研制提供技术途径。

High-efficiency and brandband OPCPA is one of two methods to achieve amplification of muti-petawatt and even hundreds petawatt laser system. We will study the output characteristics of OPCPA of phase matching in Stereoscopic space of YCOB crystal in this project. A higher effective nonlinear coefficient (about 30%) and a broader bandband (about 160 nm) will be achieved in the OPCPA process out of the principal plane. It is import that the pulse can be compressed to a shorter duration with a brander bandband of OPCPA. Compared with OPCPA in principal plane, the high efficiency can be achieved by a shorter YCOB crystal at the same pump and injected condition in OPCPA out of principal plane because of the higher effective nonlinear coefficient. There are some advantages of OPCPA with shorter crystal, for example, low absorption of pump and signal, reducing high order nonlinear effect and reducing the impact of walk off effect on the OPCPA. It is very suitable to apply this type phase matching to a high repetition rate OPCPA laser amplifier system. It can also supply a technical path for a mult-petawatt OPCPA laser system because it is good prospect that YCOB crystal can be grown to a size larger than 5 inch which is the largest size at existing technical conditions.