飞秒激光中脉冲内差频技术进展

中红外激光具有多种优势，可以广泛地用到生物、化学、物理等科学研究领域。通常采用直接激射和非线性频率转换这两种方式产生中红外激光，然而，为了实现中红外宽带超短脉冲的发射，非线性频率下转换是现今的唯一方法。脉冲内差频（IP-DFG）是一种简单的非线性频率转换方法，文中对红外IP-DFG的工作做了详细的回顾，从中红外激光晶体和基于IP-DFG产生具有超宽带的中红外超短脉冲的先进工作两个方面做了综述和评论，分别比较了非线性晶体类型、驱动脉冲源、产生超宽带中红外脉冲的光谱范围、转化效率等，并在最后讨论和阐明了IP-DFG领域面临的机遇和挑战。

Progress on intra-pulse difference frequency generation in femtosecond laser

Mid-infrared (MIR) lasers have various advantages and can be widely used in either fundamental research fields or practical applications such as strong-field physics, molecular sensing and minimally-invasive tissue ablation. Generally, there are two categories of methods to generate MIR laser emission: one is direct lasing and the other is nonlinear frequency down-conversion. However, for the ultra-broadband few-cycle MIR generation, nonlinear down-conversion is the only available method. Intra-pulse Difference Frequency Generation (IP-DFG) is a simple method of nonlinear frequency conversion. In this article, the IP-DFG technology for the ultra-broadband MIR few-cycle pulses generation is reviewed. Different MIR nonlinear crystals, various driving laser sources, the spectral coverage of the MIR-IPDF output, and the conversion efficiency are compared and discussed. Last but not least, the prospects and challenges of MIR IP-DFG are presented.