基于棱镜对的超短脉冲倍频系统的光学设计

Optical Design of Frequency-Doubling System for Ultrashort Pulses Based on Prism Pairs

针对宽带超短脉冲的倍频,用光学设计软件设计了10 fs、0.8μm超短脉冲的倍频系统,该系统包括4个棱镜、2个聚焦透镜。宽带倍频系统要求脉冲中所有的波长成份在非线性晶体中均能实现相位匹配,据此选择操作数建立系统评价函数;以非线性光学倍频中的允许角度评价光学系统的质量;分别对基波和谐波的光路优化设计,获得的棱镜尺寸、棱镜间距和透镜焦距等参数能够使脉冲中的各频率成份以相位匹配方向入射到非线性晶体或无空间啁啾的合束。此外,编写宏对光学系统中群延色散进行控制,使基波在晶体中心无啁啾,以获得最佳倍频效果,谐波光路引入一定的群延色散补偿谐波中的啁啾,消除了谐波中的时间啁啾,获得高质量的谐波脉冲。

To realize frequency-doubling of ultrashort pulses, optical design software is employed to design the frequency-doubling system for 10 fs 、0.8 μm ultrashort pulses in which contains four prisms, two lenses and a nonlinear crystal and all of them can be made by common glass materials. Firstly, the principle of frequencydoubling system is introduced. The optical system requires that all of frequency components can reach phase matching in nonlinear crystal and the merit function is built based on this point. The quality of the optical system is evaluated by permitted angle. Consequently, the optimization is executed for parts of fundamental wave and second harmonic wave. Size of prisms, distance between prism pairs and focus length of lenses which can make each frequency component in fundamental wave or second harmonic wave strike into nonlinear crystal in phase- matching direction or superpose in space without spatial chirp are obtained. In addition, a macro program to compute group delay dispersion in optical system is used as an operand to control group delay dispersion in optical system. Finally, in order to reach optimal second harmonic generation, fundamental wave has no chirp at the center of crystal and the part second harmonic wave passes by introducing group delay dispersion to compensate the chirp in second harmonic wave. Then chirp in second harmonic pulse is eliminated and high quality second harmonic pulse output is obtained.