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.femtosecond pulse filamentation nonlinear compression
High Power Laser Science and Engineering
2023, 11(6): 06000e84
Mid-infrared (MIR) ultra-short pulses with multiple spectral-band coverage and good freedom in spectral and temporal shaping are desired by broad applications such as steering strong-field ionization, investigating bound-electron dynamics, and minimally invasive tissue ablation. However, the existing methods of light transient generation lack freedom in spectral tuning and require sophisticated apparatus for complicated phase and noise control. Here, with both numerical analysis and experimental demonstration, we report the first attempt, to the best our knowledge, at generating MIR pulses with dual-wavelength spectral shaping and exceptional freedom of tunability in both the lasing wavelength and relative spectral amplitudes, based on a relatively simple and compact apparatus compared to traditional pulse synthesizers. The proof-of-concept demonstration in steering the high-harmonic generation in a polycrystalline ZnSe plate is facilitated by dual-wavelength MIR pulses shaped in both spectral and temporal domains, spanning from 5.6 to 11.4 μm, with multi-microjoule pulse energy and hundred- milliwatt average power. Multisets of harmonics corresponding to different fundamental wavelengths are simultaneously generated in the deep ultraviolet region, and both the relative strength of individual harmonics sets and the spectral shapes of harmonics are harnessed with remarkable freedom and flexibility. This work would open new possibilities in exploring femtosecond control of electron dynamics and light–matter interaction in composite molecular systems.
2023, 3(1): 0022
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 (BGSe) crystal, which is the first realization of 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.
2023, 11(5): 808
煤矸石作为固体废弃物虽然被用作发电燃料、煤矿填料与建筑材料，但其利用率仍然不高，如何提高煤矸石的高值化利用率成为了目前研究的热点。本文以山西煤矸石为原料，采用一步酸溶和溶胶-凝胶法，并经过常压干燥得到了Al2O3-SiO2气凝胶粉体。在溶剂置换与改性过程中引入超声波，研究了其对气凝胶的制备与性能的影响。采用BET、XRD、SEM、FT-IR、TG-DSC及接触角测试对所得Al2O3-SiO2气凝胶粉体的结构与性能进行表征。结果表明，超声波的引入加快了反应速率，缩短了气凝胶的制备周期，所制备的Al2O3-SiO2气凝胶是一种具有纳米三维网络结构的介孔材料，堆积密度低至0.120 g/cm3，比表面积为635 m2/g，高温下收缩性小于传统水玻璃制备的SiO2气凝胶，并具有较好的疏水性。煤矸石 活化 超声辅助 Al2O3-SiO2气凝胶 耐高温 疏水性 coal gangue activation ultrasonic assist Al2O3-SiO2 aerogel high temperature resistance hydrophobicity
2021, 50(10): 20210118