大幅度提高纳秒太赫兹参量源输出能量和效率的研究

Terahertz parametric sources are important and indispensable terahertz sources. They have outstanding advantages including laser-like properties, tunable operation, narrow spectral line width, long lifetime, and room-temperature operation. They have also obvious disadvantages, low available pulse energies and low conversion efficiencies. Based on the analysis on the causes resulting in the low available pulse energies and low conversion efficiencies, this project will research on the measures to increase the available pulse energies and conversion efficiencies greatly. The combined system of a terahertz-wave parametric oscillator (TPO) and a surface-emitted terahertz-wave parametric generator (SE-TPG) will be used. Stokes pulses with large energies are generated first from the TPO. And then the Stokes pulses are injected into the SE-TPG pumped by large-beam-size and large-energy pulses. The temporal overlapping and the spatial matching between the pumping and Stokes pulses are maintained. And multiple-beam output from the SE-TPG with a slab nonlinear crystal will be realized. The following goals are expected. The obtained nanosecond terahertz pulse energy is larger than 1 mJ, 1000 times larger than the obtained maximum pulse energy from a current SE-TPG. The conversion efficiency from the pumping laser to the terahertz wave has an increase of more than 10 times. The corresponding theoretical model for the system will be established. It can be used as the theoretical tool for the system design and the theoretical basis for the system generating much larger terahertz pulses.

太赫兹(THz)参量源是重要的不可或缺的THz辐射源。它的优点很突出，如具有类激光特性，可调谐运转，谱线宽度窄，长久耐用，室温运转等。它的缺点很明显，即脉冲能量和转化效率低。本项目在分析造成THz参量源输出能量和效率低原因的基础上，拟探讨大幅度提高THz参量源输出能量和效率的措施。将利用THz参量振荡器(TPO)和表面垂直发射式THz参量发生器(TPG)相结合的系统，先由TPO产生能量尽量大的Stokes脉冲，再将该Stokes脉冲作为大面积TPG的种子注入，通过保证泵浦脉冲与Stokes脉冲时间和空间上匹配、选用板条状非线性晶体获得多束THz波输出等措施，达到以下目标：获得纳秒THz脉冲能量1 mJ以上，相对于目前表面垂直发射式TPO，输出能量提高1000倍以上，效率提高10倍以上。建立相应的理论模型，为这种THz参量源的设计提供理论工具。为更高能量和效率THz脉冲的获得提供理论依据。

太赫兹(THz)参量源是重要的不可或缺的THz辐射源。它的优点很突出，如具有类激光特性，可调谐运转，谱线宽度窄，长久耐用，室温运转等。它的缺点很明显，即脉冲能量和转化效率低。本项目在分析造成THz参量源输出能量和效率低原因的基础上，利用THz参量振荡器(TPO)和表面垂直发射式THz参量发生器(TPG)相结合的系统，先由TPO产生能量尽量大的Stokes脉冲，再将该Stokes脉冲作为大面积TPG的种子注入，通过保证泵浦脉冲与Stokes脉冲时间和空间上匹配等措施，大幅度提高太赫兹参量源的输出能量和转化效率。主要研究内容包括：(A) 利用THz参量振荡器获得高能量、大脉冲宽度Stokes光脉冲的研究。(B) Stokes脉冲注入的表面垂直发射式THz参量发生器性能研究。(C) Stokes脉冲注入的板条状MgO:LiNbO3晶体多点输出THz参量发生器性能研究调谐特性研究。(D) THz参量源的理论研究。(E) 大能量太赫兹脉冲的获得。当泵浦能量是2.26 J时，获得的最大太赫兹脉冲能量为114 微焦，比原来太赫兹参量振荡器的输出脉冲能量提高了110倍。相应的转化效率为5.04*10^(-5)，比原来太赫兹参量振荡器的转化效率提高到5倍。并为种子注入的THz参量发生器建立了理论模型，数值模拟结果与实验结果基本相符。还探索了一些新的太赫兹参量源材料。