Cheng Yuk Shan, McCracken Richard A, Reid Derryck T
Opt Lett. 2020 Feb 1;45(3):768-771. doi: 10.1364/OL.45.000768.
Stable operation of a doubly resonant femtosecond optical parametric oscillator (OPO) requires submicron matching of the OPO and pump laser cavity lengths, which is normally implemented using a dither-locking feedback scheme. Here we show that parasitic sum-frequency mixing between the pump and resonant pulses of a degenerate femtosecond OPO provides an error signal suitable for actuating the cavity length with the precision needed to maintain oscillation on a single fringe and at maximum output power. Unlike commonly used dither-locking approaches, the method introduces no modulation noise and requires no additional optical components, except for one narrowband filter. The scheme is demonstrated on a Ti:sapphire-pumped sub-40-fs PPKTP OPO, from which data are presented showing a tenfold reduction in relative intensity noise compared with dither locking.
双共振飞秒光学参量振荡器（OPO）的稳定运行需要OPO与泵浦激光腔长度实现亚微米级匹配，这通常采用抖动锁定反馈方案来实现。在此我们表明，简并飞秒OPO的泵浦光与共振脉冲之间的寄生和频混频提供了一个误差信号，该信号适合以维持单条纹振荡和最大输出功率所需的精度来驱动腔长度。与常用的抖动锁定方法不同，该方法不会引入调制噪声，除了一个窄带滤波器外，不需要额外的光学元件。该方案在钛宝石泵浦的亚40飞秒PPKTP OPO上得到了验证，给出的数据表明，与抖动锁定相比，相对强度噪声降低了十倍。
