Abstract Nd3+ ions have a large emission cross-section in the 1000 ∼ 1100 nm band. In this study, we focus on the spectral properties of Nd3+ ions, simulate the power transfer equation of the Nd-doped ion fiber laser. The design of the Nd-doped fiber laser is aimed at laser generation by considering parameters such as absorption cross section, particle number concentration, loss coefficient, and reflectivity of the front and rear cavity mirrors. The experimental process begins with the design of specific parameters for the two cavity mirrors at 1060 nm using Matlab, based on the required reflectivity parameters. The simulation demonstrates that laser generation begins at a pump light power of 9.8 W, and the laser power reaches 36.8 W. Observe the propagation power of the signal light and pump light, when the pump light propagates in the forward direction, the forward propagation power of the pump light will decrease. This paper summarizes and innovates the numerical simulation parameters of Nd-doped ion fiber laser. The specific innovations are reflected in the proposed new emission cross section of pump light and absorption cross section of signal light, as well as the novel mathematical model for designing the front cavity mirror and the back cavity mirror. The experiments provide better data support for the preparation of 1000 ∼ 1100 nm doped Nd-doped fiber lasers.

飞秒激光大气传输具有丰富的非线性效应,产生的等离子体光丝由于传输距离长、发散角小、峰值功率高等特点,有望推动新型天基激光雷达发展.文章面向遥感应用,瞄准飞秒激光脉冲400km超长距离传输可行性开展研究,完成飞秒激光脉冲在轨传输规律仿真研究.文章首先介绍飞秒激光在轨传输仿真模型的构建机理,验证其有效性,在此基础上,仿真分析了飞秒激光脉冲宽度、脉冲半径、脉冲能量对飞秒激光在轨传输规律的影响,解决了飞秒激光脉冲大气超远程传输仿真的关键问题,说明了其在天基产生、传输与应用的可行性,为后续天基系统论证提供必要基础.

通过数值模拟分析了初始脉冲能量对环形高斯光束在大气中成丝的影响.研究表明,当增加初始脉冲能量时,环形高斯光束在大气中生成的等离子体通道的长度被延长;而当脉冲能量增大到一定值时,虽然等离子体通道的长度继续增加,但是等离子体通道的稳定性却有所下降.因此,对于环形高斯光束,合适的初始脉冲能量将有利于稳定的等离子体通道的远距离传输.

We have numerically investigated the supercontinuum generation by a femtosecond annular Gaussian beam in air. Compared with the spectra broadening of the Gaussian filament under the same initial condition, the smooth supercontinuum spectra of the annular Gaussian filament are wide enough to cover the whole visible frequency range in the first focusing cycle. The spectra broadening is analyzed from the frequency shift induced by the ionization and the self-phase modulation. For the blue side of the enhancement of the spectra broadening, the ionization-induced and intensity-induced frequency shifts play the dominant role in the onset distance of the filament and the first maximum value of the spectra broadening, respectively. Then, we have also discussed the influences of the initial pulse energy and the spatial chirp for wide and smooth supercontinuum spectra to cover the whole visible frequency range. Therefore, it is an efficient route to produce the supercontinuum spectra by the annular Gaussian beam.

We have explored a novel approach to generate a long-distance two-color filament by three collinear ultrashort pulses in air. The characteristics and dynamics of the two-color filament are investigated numerically. It is attractive that the coherent superposition of two low-intensity annular beams (both 400 nm) makes the length of the two-color filament increase about one order of magnitude over the Gaussian filament alone. Because two annular beams supply coherently the energy to the filament core and the clamp intensity of 400 nm filament is lower than the 800 nm one, the low input energy (1.2 mJ) can maintain sufficiently a long-distance propagation of the two-color filament, which is great efficient and economical.

用数值模拟的方法研究了不同透镜聚焦和不同输入脉冲能量对环形高斯光束在大气中传输的影响.结果显示,在初始能量固定时,光丝的特性及其超连续波谱强烈依赖于凸透镜的焦距f和锥透镜引入的空间啁啾系数C.透镜聚焦能力减弱(f增大和C减小),成丝起点延后,光丝变长且不稳定,但更有利于波谱在短波方向上的展宽.由锥透镜聚焦所产生的超连续波谱会更加的光滑,在传播方向的作用区域也更长.频率变化最大值(Δωmax)的峰值更有利于光谱展宽,但与最大展宽位置并不完全对应.此外,固定透镜焦距f和空间啁啾系数C,适当的初始脉冲能量对获得宽而光滑的超连续谱也起着关键作用.

本文利用一个具有隧穿耦合效应的四能级结构模型来描述超冷铯原子制备超冷铯分子的过程,理论分析了受激拉曼绝热通道过程中的两激光脉冲参数对铯原子-分子转换效率的影响。结果表明,在原子-分子暗态条件下,通过双色光缔合利用双光子共振条件的最优化处理方法可以使转换效率提高到90%以上,并给出了两激光脉冲参数的最优化区间。另外,通过分析原子态和束缚分子基态上粒子数布居的动力学演化,给出了光场的最优化条件,只有适当的匹配两激光场的有效Rabi频率、延迟系数和脉冲宽度时,才能高效地实现超冷铯原子-分子的相干布居转换。

Strong energy sharing is shown by numerically investigating coupled multi-component Bose–Einstein condensates（BECs） with a harmonic trap to simulate the Fermi–Pasta–Ulam model（FPU）. For two-component BECs, the energy exchanging between each part, from regular, quantum beating to complete energy sharing, is explored by simulating their Husimi distributions, the time evolution of energies and the statistical entropy. Meanwhile, in the three-component case, a more complex energy sharing behavior is reported and a strong energy sharing is found.

We numerically investigate the effects of the external focusing and the pulse parameters on the propagation of the ring Gaussian filaments in air. The simulation results indicate that the onset distance of filament, the length and uniformity of the plasma strings, and the energy deposition strongly depend on these optical parameters. The length of optical filament can be extended greatly by adjusting the lens parameters near the maximum energy deposition. In addition, we find that, under the same initial intensity, the length and uniformity of the plasma strings can be tuned by increasing the beam width better than increasing the beam radius.

A weak gravity-like force detector is proposed using a novel scheme, through which thesubtle modification of a weak gravity-like force on the interference pattern can beobtained. The weak gravity-like force creates two spatially imbalanced Bose-Einsteincondensates (BECs) trapped in a symmetric double-well and makes a shift of theinterference fringes yielded after expansion of the BECs. The strength of the weakgravity-like force is revealed by investigating the Loschmidt echo and it can be read outby analysing the density profile of interference fringes. For the weak gravity-like force,we predict that the sensitivity can be δg ∼ 10−6.