Nonlinear compression has become an obligatory technique along with the development of ultrafast lasers in generating ultrashort pulses with narrow pulse widths and high peak power. In particular, techniques of nonlinear compression have experienced a rapid progress as ytterbium (Yb)-doped lasers with pulse widths in the range from hundreds of femtoseconds to a few picoseconds have become mainstream laser tools for both scientific and industrial applications. Here, we report a simple and stable nonlinear pulse compression technique with high efficiency through cascaded filamentation in air followed by dispersion compensation. Pulses at a center wavelength of 1040 nm with millijoule pulse energy and 160 fs pulse width from a high-power Yb:CaAlGdO₄ regenerative amplifier are compressed to 32 fs, with only 2.4% loss from the filamentation process. The compressed pulse has a stable output power with a root-mean-square variation of 0.2% over 1 hour.

Nonlinear frequency conversion of wavelength agile and high-power random fiber lasers can provide a promising way to generate continuous-wave (CW) visible and mid-infrared (MIR) light with unique properties such as the continuous modeless spectrum, low temporal/spatial coherence, and high temporal stability. Here, we report a dual-wavelength switchable and tunable random Raman fiber laser (RRFL) based on a phosphosilicate fiber that has two Raman gain peaks for the first time and demonstrate its superior capability to generate widely tunable CW visible and mid-infrared light via nonlinear frequency conversions. By using the combination of a tunable pump and two tunable gratings in Littrow configuration that can provide separated point feedback for the two Stokes wavelengths corresponding to silica- and phosphorus-related Raman peaks, the spectrum of an RRFL can be flexibly manipulated for the aim of nonlinear frequency conversions, including single-wavelength tunable emission at the 1.1 μm or 1.2 μm band for second-harmonic generation (SHG), dual-wavelength simultaneously tunable emission at the 1.1 μm and 1.2 μm bands for the sum-frequency generation (SFG), and dual-wavelength separation tunable emission for difference-frequency generation (DFG). As a result, with the combination of SHG and SFG in a periodically poled lithium niobate crystal array, we experimentally demonstrate the broadest tuning range (560–630 nm) of visible light generated from an RRFL, to the best of our knowledge. The tunable MIR light in the range of 10.7–12.3 μm is also demonstrated through DFG of an RRFL operating in separation tunable dual-wavelength emission mode in a BaGa4Se7 (BGSe) crystal, which is the first realization of >10μm CW DFG in the BGSe crystal. We believe the developed dual-wavelength switchable and tunable RRFL can provide a new compact, robust, and cost-effective platform to realize broadly tunable light in both the visible and MIR regions, which can also find potential applications in imaging, sensing, and temporal ghost imaging in various spectral bands.

中红外(2.5 μm~25 μm)波段包含许多重要的原子和分子共振峰，因此中红外超连续谱广泛应用于生物医学、光谱学和环境科学等领域。碲化镉(cadmium telluride, CdTe)在中红外波段具有超宽的透射光谱范围0.86 μm~25 μm，同时CdTe具有较大的三阶非线性系数，是实现中红外超连续谱的理想材料。本文设计并加工了一种基于CdTe为芯层、低折射率介质硫化镉为缓冲层、硅为衬底的波导。采用广义非线性薛定谔方程仿真了该波导以中心波长为5.5 μm中红外激光作为泵浦，能够实现4.1 μm~9.7 μm的超连续谱输出。实验中通过湿法刻蚀制作CdTe多晶波导，并采用中心波长为1030 nm，脉冲宽度为250 fs的激光器作为泵浦源，观察到在波导中发生明显的自相位调制而产生的光谱展宽。该工作为CdTe集成波导应用于中红外超连续谱及中红外波段的片上光学器件提供了新的可能。

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。

近十年来，超强超短脉冲是激光光学发展的一个重要趋势。尤其是在中红外（MIR）波段，由于中红外波长具有更大的有质动力并且其光谱范围几乎包含了所有分子“指纹”共振峰，这使得中红外激光的研究在强场物理、中红外光谱学、材料加工以及生物医学研究等领域中至关重要。目前已经有许多比较成熟的激光技术可以对脉冲进行整形、放大，例如差频（DFG）、啁啾脉冲放大（CPA）、光学参量放大技术（OPA）以及光学参量啁啾脉冲放大（OPCPA）等。利用OPCPA技术具有的高放大增益、高信噪比、宽增益带宽的优点在高非线性系数的非线性晶体中进行脉冲放大已经成为当前获取超强超短中红外脉冲的主要手段之一。文中总结了利用OPCPA技术在2~20 μm波长范围内产生和放大MIR少周期脉冲的研究进展，并对其在强场物理、分子频谱探测以及生物医学方面的应用进行了简要的阐述。

Lasers with high average and high peak power as well as ultrashort pulse width have been all along demanded by nonlinear optics studies, strong-field experiments, electron dynamics investigations, and ultrafast spectroscopy. While the routinely used titanium-doped sapphire (Ti:sapphire) laser faces a bottleneck in the average power upscaling, ytterbium (Yb)-doped lasers have remarkable advantages in achieving high average power. However, there is still a substantial gap of pulse width and peak power between the Ti:sapphire and Yb-doped lasers. Here we demonstrate a high-power Yb:CaAlGdO4 (Yb:CALGO) regenerative amplifier system, delivering 1040 nm pulses with 11 W average power, 50 fs pulse width, and 3.7 GW peak power at a repetition rate of 43 kHz, which to some extent bridges the gap between the Ti:sapphire and Yb lasers. An ultrabroadband Yb-doped fiber oscillator, specially designed spectral shapers, and Yb:CALGO gain medium with broad emission bandwidth, together with a double-end pumping scheme enable an amplified bandwidth of 19 nm and 95 fs output pulse width. To the best of our knowledge, this is the first demonstration of sub-100 fs regenerative amplifier based on Yb-doped bulk medium without nonlinear spectral broadening. The amplified pulse is further compressed to 50 fs via cascaded-quadratic compression with a simple setup, producing 3.7 GW peak power, which boosts the record of peak power from Yb:CALGO regenerative amplifiers by 1 order. As a proof of concept, pumped by the high-power, 50 fs pulses, 7.5–11.5 µm mid-infrared (MIR) generation via intrapulse difference-frequency generation is performed, without the necessity of nonlinear fiber compressors. It leads to a simple and robust apparatus, and it would find good usefulness in MIR spectroscopic applications.

In this Letter, we experimentally investigate fast temporal intensity dynamics and statistical properties of the cladding-pumped Er/Yb co-doped random Rayleigh feedback fiber laser (EYRFL) for the first time, to the best of our knowledge. By using the optical spectral filtering method, strong and fast intensity fluctuations with the generation of extreme events are revealed at the output of EYRFL. The statistics of the intensity fluctuations strongly depends on the wavelength of the filtered radiation, and the intensity probability density function (PDF) with a heavy tail is observed in the far wings of the spectrum. We also find that the PDF of the intensity in the central part of the spectrum deviates from the exponential distribution and has the dependence on the laser operating regimes, which indicates some correlations among different frequency components exist in the EYRFL radiation and may play an important role in the random lasing spectrum stabilization process.