Natural population inversion in a gaseous molecular filament

We propose a new mechanism/scheme to explain the ultrafast population inversion of molecular ions which takes place in a time scale comparable to the femtosecond laser pulse. The nonlinear pumping process including the pump photons and the self-generated harmonic photons of the pump laser would be responsible for building up population inversion to realize remote molecule lasers in femtosecond laser filaments in gases. It is shown that the remote laser emissions in molecular ions of gases may be a universal process in the femtosecond laser filament.     

旋转对称椭球颗粒沿轴脉冲光声波波形的几何计算

针对旋转对称椭球颗粒脉冲光声波的产生,推导沿其对称轴方向的波形的解析表达式.结果表明,无论是长椭球还是扁椭球颗粒,沿轴波形相对于球形颗粒所产生的N形波都有一定的形变,并且在近场条件下显示出能反映椭球颗粒形状与大小的明显特征.因此通过对脉冲光声波的测量和分析,能对旋转对称椭球颗粒进行形貌判定.     

Generation of high power laser at 1314 nm from a diode-side-pumped Nd:YLF module

We demonstrate a high power continuous-wave （CW） and acoustic-optically （AO） Q-switched 1314-nm laser with a diode-side-pumped Nd：YLF module. A maximum CW output power of 21.6 W is obtained with a diode pump power of 180 W, corresponding to an optical-to-optical conversion efficiency of 12.0% and a slope efficiency of 16.1%. In the Q-switching operation, a highest pulse energy of 3.8 mJ is obtained at a pulse repetition rate of 1 kHz. The shortest pulse width and maximum single peak power are 101.9 ns and 37.3 kW, respectively.     

Nonlinear polarization rotation-induced pulse shaping in a stretched-pulse ytterbium-doped fiber laser

We report on controllable pulse shaping in a Yb-doped stretched-pulse fiber laser followed by a high-power chirped pulse amplifier. We demonstrate that the pulses after an extra-cavity grating pair change their intensity profile from Lorentz to Gaussian and then to sech2 shapes by adjusting the intra-cavity polarization through a quarter-wave plate inside the fiber laser cavity. The laser pulses with different pulse shapes exhibit pulse-to-pulse amplitude fluctuation of -- 1.02%, while the sech2-shaped pulse train is provided with a more stable free-running repetition rate as a result of the stronger self-phase modulation in the fiber laser cavity than Lorentz- and Gaussian-shaped pulse trains.     

New terahertz dispersive device for single-shot spectral measurements of terahertz pulse

A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.     

μ介子氢原子在双色激光场驱动下产生单个仄秒脉冲

本文利用强场近似理论研究了一束强度稍弱的X射线脉冲辅助另一束强X射线脉冲作用于μ介子氢原子产生高次谐波的过程.研究发现当弱X射线的频率为强X射线频率的一半时,可以生成超宽高次谐波频谱.通过合成高次谐波的连续谱,得到宽度为130 zs的单个仄秒脉冲.单个仄秒脉冲为超快变化过程的研究提供了工具.     

Optimization of Single or Range of Harmonics by Using Two Gas Jets

The interference of high-order harmonics generated by two successive gas jets within a single laser pulse is discussed by a modeling with the inclusion of macroscopic propagation of the fundamental and harmonic fields in an ionizing medium. Based on the interference, we show that one can extract the laser Rayleigh range from the interference of harmonics and the accuracy of retrieve is independent of carrier-envelope phase while dependent on the pulse duration. Moreover~ we demonstrate that it is possible to optimize the single or range of harmonics with a high ratio relative to the adjacent orders by changing the separation of two gas jets, which is unavailable by using a single gas jet and linear polarized laser pulse.     

Passively Q-Switched Tm,Ho：YVO4 Laser with Cr：ZnS Saturable Absorber at 2 μm

A stable diode-pumped passively Q-switched Tm,Ho：YVO4 laser with Cr：ZnS saturable absorber is reported. The shortest pulse duration of -500 ns with the central wavelength of 2041 nm is obtained at the pump power of 7.4 W, corresponding to the pulse energy of 3.5 μd at repetition rate of 65 kHz.     

哈肯激光方程自脉冲解的稳定性分析

本文详细地研究了哈肯激光方程的自脉冲不稳定性,得出了自脉冲解的解析表达式,并对其进行了稳定性分析。结果表明,无论是对于第三类激光系统还是对于第四类激光系统,哈肯激光方程的自脉冲解都是不稳定的。