Third-order dispersion role on parabolic pulse propagation in dispersion-decreasing fiber with normal group-velocity dispersion

Parabolic pulse propagation in a dispersion-decreasing fiber with normal group velocity dispersion (ND-DDF) has been studied when the third-order dispersion (TOD) is included. The results show that the characteristic of exact self-similarity and linear chirp will be lost due to the third-order dispersion. However, by using the dispersion compensation technique, one can obtain efficient and high-quality compressed pulses. The analytic results have been confirmed using numerical simulations.     

Intense few-cycle laser pulses from self-compression in a self-guiding filament

Sub-10-fs-pulses are generated by self-compression in a noble gas filament. Using input pulses from a Ti:sapphire amplifier system with an energy of about 1.5 mJ at a repetition rate of 3 kHz and a pulse duration of 30 fs self-compressed sub-10-fs pulses with energies of about 0.3 mJ have been generated. These pulses are characterized with spectral phase interferometry for direct electrical-field reconstruction (SPIDER). Depending on the laser parameters, we observe a significant change in the chirp of the white-light. The spectral distribution of the outcoming beam profile is measured to distinguish the white-light core from the surrounding halo.     

Time resolved spectroscopy with femtosecond soft-x-ray pulses

The most challenging application of time resolved spectroscopy is to directly observe the structural and electronic dynamics. Here we present the combination of x-ray absorption spectroscopy with laser driven x-ray sources, offering atomic spatial and temporal resolution. Our new approaches for optimization of laser driven x-ray sources resulted in the demonstration of spatially coherent sub-20 fs x-ray pulses in a range up to several keV. We excited polycrystalline silicon with an ultrashort laser pulse and characterized the collective motion of atoms with time resolved x-ray absorption spectroscopy at a temporal resolution of less than 20 fs. Finally, we have shown the feasibility of probing the dynamics of the electronic structure of silicon and carbon with near edge x-ray absorption spectroscopy.     

Coloured Conical Emission in BBO Crystal Pumped by Second Harmonic Femtosecond Pulses

Coloured conical emission （CCE） is investigated experimentally in a β-barium borate crystal excited by intense second harmonic femtosecond pulses. Contrary sequences of green and red conical emission with variable diameters are observed at different incidence angles, which is consistent with the calculation results based on the phase matching condition. As its broad range spectrum, CCE offers an alternative means to produce an ultrafast broadband light source. It is found that the spectrum of green CE shifts toward longer wavelengths as the length of BBO crystal increased.     

Energy Squeeze of Ultrashort Light Pulse by Kerr Nonlinear Photonic Crystals

Self-phase modulation can efficiently shape the spectrum of an optical pulse propagating along an optical material with Kerr nonlinearity. In this work we show that a one-dimensional Kerr nonlinear photonic crystal can impose anomalous spectrum modulation to a high-power ultrashort light pulse. The spectrum component at the photonic band gap edge can be one order of magnitude enhanced in addition to the ordinary spectrum broadening due to self-phase modulation. The enhancement is strictly pinned at the band gap edge by changing the sample length, the intensity or central wavelength of the incident pulse. The phenomenon is attributed to band gap induced enhancement of light-matter interaction.     

Optimization of Pulse Temporal Contrast in Optical Parametric Chirped Pulse Amplification

In optical parametric chirped pulse amplification （OPCPA）, the degradation of temporal contrast of the compressed signal pulse mainly results from spectral clipping in the grating stretcher with finite size of the optics, parametric fluorescence （PF） and the spectral variations transferred from temporal fluctuation of the pump pulse. The temporal contrast of the recompressed amplified pulse in the OPCPA system is studied numerically and a number of solutions are considered and optimized to achieve the highest temporal contrast.     

Experimental confirmation of high-stability of fluorescence in a femtosecond laser filament in air

Femtosecond laser filamentation is particularly interesting for remote sensing pollutant in the atmosphere. In this work, we investigate the local shot-to-shot stability of the filament induced fluorescence of nitrogen in air. It is found that the root-mean square fluctuation of the fluorescence signal is at least one order of magnitude lower than that of the linear propagation case. In practice, it would contribute to improve the robustness of long distance spectroscopic analysis of the fluorescence of pollutant molecules inside the filament. We further point out that this unique property of filament induced fluorescence spectroscopy is because of the intensity clamping, a profound phenomenon of filamentation.     

Synthesis, photophysical properties, and theoretical studies on pyrrole-containing bromo Re(I) complex

Two bromo rhenium(I) carbonyl complexes with the formula of [Re(CO)₃(L)Br], where L = 1,10-phenanthroline (Phen-Re) and 5-(1H-pyrrol-1-yl)-1,10-phenanthroline (Pyph-Re), were successfully synthesized with the aim to analyze the effect of the pyrrole (Py) moiety on the photophysical properties of Pyph-Re. It was found that the triplet metal-to-ligand charge-transfer dπ (Re) → π*(N-N) emission of Phen-Re and Pyph-Re centered at ca. 527 nm with the luminescence quantum yield (LQY) of 0.015 and ca. 578 nm with the LQY of 0.011, respectively. At the same time, the geometrical structures of the ground state and the absorption spectral properties of Phen-Re and Pyph-Re were also calculated with the 6-31G* basis set employed on C, H, N, O, and Br atoms, and LANL2DZ adopted on Re atom. According to the experimental and theoretical analysis, the red-shift of the photoluminescent spectrum and the lower LQY of Pyph-Re should be mainly attributed to the narrower energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital and the more LLCT transition ration of Pyph-Re, respectively.     

Highly Efficient Organic Ultraviolet Photodetectors Based on Re(I) Complexes

High response organic ultraviolet photodetectors(UV-PDs) were demonstrated with 4,4',4'- tris[3-methyl-pheny(phenyl)amino]triphenylamine(m-MTDATA) and two Re(I) complexes, (bathocuproine)- Re(CO)₃Cl(Re-BCP) and (bathophenanthroline)Re(CO)₃Cl(Re-Bphen) to act as the electron donor and acceptor, respectively. UV-PDs have the configuration of indium tin oxide(ITO)/m-MTDATA(25 nm)/m-MTDATA:Re-complex (25―35 nm)/Re-complex(20 nm)/LiF(1 nm)/Al(200 nm) with different blend layer thicknesses of 25, 30 and 35 nm. The optimized PD based on Re-Bphen offers a corrected-dark photocurrent up to 760 μA/cm² at ?10 V, corresponding to a response of 310 mA/W which is among the best values reported for organic UV-PDs. Excellent electron transport ability makes for such high photo-to-electron conversion.     

热管堆在不同基体材料下的燃耗特性分析北大核心CSCD

热管冷却核反应堆具有非能动传热、模块化和固有安全性高等特点,在航空探索、深海作业和偏远地区电力市场上有广泛的应用。以洛斯阿拉莫斯国家实验室开发的5 MWth热管堆为研究对象,选择SS-316,Mo-14Re和SiC作为基体候选材料,采用反应堆蒙特卡罗中子输运分析程序对比分析了以上三种基体堆芯的反应性、中子能谱、增殖性能和燃耗演化。结果表明:为了维持堆芯的10年运行,SS-316,Mo-14Re和SiC三种基体堆芯所需的初始燃料235U富集度分别约为19.35%,28.80%和17.10%,SiC基体堆芯所需的初始燃料235U富集度最小;10年后,SiC基体堆芯产生的易裂变核素(239Pu和241Pu)和次锕系核素(通过分离嬗变可被再次利用)的量最高,分别约为11.91 kg和92.08 g。综合以上研究结果,推荐SiC作为热管冷却核反应堆的基体。