Qi Weiao, Zhou Jiaqi, Cao Xinru, Cheng Zhi, Jiang Huawei, Cui Shuzhen, Feng Yan
Opt Express. 2022 Mar 14;30(6):8889-8897. doi: 10.1364/OE.452637.
Nonlinear optical gain modulation (NOGM) is a method to generate high performance ultrafast pulses with wavelength versatility. Here we demonstrate coherent femtosecond Raman pulse generation through cascaded NOGM process experimentally. Two single-frequency seed lasers (1121 and 1178 nm) are gain-modulated by 117 nJ 1064 nm picosecond pulses in a Raman fiber amplifier. Second-order (1178 nm) Stokes pulses are generated, which have a pulse energy of 76 nJ (corresponding to an optical conversion efficiency of 65%) with a pulse duration of 621 fs (after compression). Dynamic evolution of both pump and cascaded Stokes pulses within the Raman amplifier are investigated by numerical simulations. The influences of pump pulse duration and energy are studied in detail numerically. Moreover, the simulations reveal that NOGM pulses with higher energy and shorter pulse duration could be obtained by limiting the impact of walk-off effect between pump and Raman pulses. This approach can offer a high energy and wavelength-agile ultrafast source for various applications such as optical metrology and biomedical imagining.
非线性光学增益调制（NOGM）是一种能够产生具有波长通用性的高性能超快脉冲的方法。在此，我们通过实验证明了通过级联NOGM过程产生相干飞秒拉曼脉冲。在拉曼光纤放大器中，两个单频种子激光器（1121纳米和1178纳米）由117纳焦的1064纳米皮秒脉冲进行增益调制。产生了二阶（1178纳米）斯托克斯脉冲，其脉冲能量为76纳焦（对应光学转换效率为65%），脉冲持续时间为621飞秒（压缩后）。通过数值模拟研究了拉曼放大器内泵浦脉冲和级联斯托克斯脉冲的动态演化。详细数值研究了泵浦脉冲持续时间和能量的影响。此外，模拟结果表明，通过限制泵浦脉冲与拉曼脉冲之间走离效应的影响，可以获得能量更高、脉冲持续时间更短的NOGM脉冲。这种方法可为光学计量和生物医学成像等各种应用提供高能量且波长灵活的超快光源。
