为提高强激光场与惰性气体靶作用产生的孤立阿秒激光脉冲的能量, 给出了一种实现高次谐波过程中最佳谐波相位匹配的定量实验方法。研究了气体靶源与高斯型驱动激光场聚焦点相对空间位置对谐波相位匹配及谐波产率的影响, 得出了其最佳相位匹配位置始终位于驱动激光场聚焦点后3～5 mm, 而在聚焦点之前的位置区域, 严重的高次谐波相位失配导致谐波产率非常低。同时, 在最佳相位匹配条件下, 高次谐波场与驱动场具有相类似的空间强度分布特性, 该结果印证了目前通常采用的高次谐波场为高斯光束的假设。

This paper presents an experimental method to realize the best high-order harmonic generation(HHG) phase matching in the interaction of strong optical field and gas target. By studying the effects of the relative location between gas target source and Gaussian-type driving field focus on the harmonic phase matching, conclusions are obtained that the optimum position of gas target for phase matching is always 3-5 mm behind the focal point of the driving field, with much lower HHG yield before the focus caused by serious harmonic phase mismatch. At the same time, in the optimum relative position, the driving field and the high-order harmonic field have similar spatial distribution characteristics, providing the experimental basis for the commonly used assumptions of Gaussian beam for high-order harmonic field.