基于随机激光的时域理论,利用时域有限差分法(FDTD)数值求解麦克斯韦方程组和速率方程组,分别计算了二维无序介质中抽运速率和散射颗粒折射率对随机激光辐射的影响,同时还分析了介质中不同区域的输出谱和空间模式分布.计算结果显示,对于二维随机介质,在其他条件保持不变的情况下,散射颗粒折射率与背景介质折射率差越大,随机激射的阈值越低.介质中不同区域的辐射谱是不同的,且随着激励源抽运强度而变化.随机激光辐射始终集中在介质中某几个固定区域,但各个区域的随机激射效率是不同的,同时在区域之间存在模式的空间范围重叠.

We report a systematic study based on the random laser behaviors of comparable systems in which the refractive indices are varied. Threshold and spectra features have been obtained. The experimental results indicate that the threshold (Eth) of the random laser depends on the refractive index of the scatterers and surrounding solvents. The larger the refractive index of scatters or smaller the refractive index of solvents is, the smaller the Eth will be. The theoretical explanation based on Mie scattering theory for this phenomenon is made. We introduce refractive index contrast-ratio w. The thresholds variation is attributed to the alteration of w which influences the scattering strength and the transport mean free path. As for the spectra, typical emission evolution spectra have been observed. The peak positions vary with the change of scatterers and solvents, the reason of the variation is the absorption of the samples.

Based on the time dependent theory, FDTD algorithm was used to numerically solve Maxwell's equations and rate equations. By dividing the two-dimension random medium, the emission spectra of different region under different pumping intensities were obtained. The calculated results show that the emission spectra of different region are different, the energy of emission is mainly distributed in some certain region, and the pumping efficiency is different. Also spatial extent overlap of modes is reproduced. With this method, the dependence of random distribution on lasing can be analyzed and it should be useful for the preparation of pseudo-random medium.

We experimentally measured the random laser action which pumped by 355 nm ns laser pulse. We focus on the emission spectra varying with the pump energies and study the lasing threshold of the random laser. It is found that, there a low threshold pumped by 355 nm laser pulse compared with 480 nm laser pulse. Meanwhile, we measured the emission spectra for different detect angles at the same pump energy. It shows that, the emission peak intensities are symmetric about the zero detect angle at X direction (vertical light path), and there are spikes at Z direction (light path).

Using the time-dependent theory, we calculate the random-laser emission spectra in a two-dimensional strongly disordered medium. The calculation results show that in low dimensional systems, such as thin-film disordered media and planar waveguides, the larger the difference of the refractive indices between the scattering and background media, the smaller the lasing threshold. We also reveal the existence of multi-mode survival and mode competition. We experimentally obtain the emission spectra of a dye solution with Al particles doped at different pumping energies, and the experimental results agree well with the calculated ones.

We have studied the random laser action in Rhodamine 6G (Rh6G) ethylene glycol solution with Al nanoparticles. The experiment results are obtained by pumping with a nanosecond (7 ns) laser pulse, which demonstrated the existence of effective random laser emission. It is found that the threshold of the random laser depends on the concentration of the Rh6G and the concentration of Al nanoparticles. The concentration and diameter of Al nanoparticles have effects on the optical path; a higher concentration or a larger diameter results in a shorter optical path length. Also multimode survival and mode competition have been observed at a relatively high concentration (0.08 M) of Rh6G, where the concentration of Al nanoparticles is 0.0015 M.

High transmittance of Nd-doped YAG transparent ceramics were synthesized by a traditional solid-state reactive sintering method. The crystalline and the optical properties of the samples were investigated. The results show the relative density and transmittance of Nd-doped YAG ceramics depended on the sintering time and temperature. The maximum transmittance of Nd:YAG ceramics is above 90%. All the transparent Nd:YAG ceramics present a main emission peak at 1064.5 nm, which is in accord with Nd:YAG single crystal.

The present paper analyzes the different pump wave theory under the fluorescence decay law and presents a different pump wave measured fluorescence lifetime of the new method-double-pulse detection method namely the use of pump pulse and probe pulse for the fluorescence decay methods to measure fluorescence lifetime By measuring the sample neodymium glass and Cr ZnSe crystal fluorescence lifetime results showed that using this method can be achieved under different pump wave in visible and near-infrared to the mid infrared laser medium of the fluorescence lifetime measurement Therefore using the measurement method can be convenient and effective to avoid seeking samples by deconvolution for fluorescence lifetime with the cumber some process of measuring laser medium at different pump wave under the fluorescence lifetime with a reference value

Starting from Nonlinear Schrodinger's equation and using the Split-step Fourier Method, we studied the characters of the supercontinuum generation of femtosecond laser pulse propagating in condensed media; many physical factors are included such as the propagation distance, the input pulse peak power, diffraction effect, dispersion effect and the nonlinear effect etc. The results show that, when the femtosecond pulse propagated inside condensed media, the process of supercontinuum generation can be divided into two main stages: the pulse compressed stage, which induced by the self-focus and other third nonlinear effects of the material; and the pulse splited stage, which leaded by the self-phase modulate and the group velocity dispersion of the material. When the femtosecond pulse propagated inside the condensed media with high input peak power, the 3rd- order nonlinear effect of material induced pulse compressed and then the sub-pulses were produced, so that new frequency components were introduced. At the same time, we also studied the spectral distribution of the pulse at different spatial locations; there are new frequencies around the central frequency. At last, some experiments were done to demonstrate the supercontinuum generation.

The free electron density and temperature of laser-induced plasma and the damage on the silicon surface were investigated. The results show that the volume and the free electron density of laser induced plasma, as well as the plasma temperature will determine the profile and the size of silicon superficial damage. It was also found that the volume of laser plasma will increase continuously and the temperature will increase slightly with the increase in the energy of laser pulse, while the density of free electrons will remain invariable. The free electron density and the temperature reduce gradually from centre to edge, so the damage appearance has the following features: The interior area of damage was melted so well that the periodic stripes were formed. The periodic stripes were quite irregular for the area not melted very well. The boundary of damage is apparent and sometimes color changes induced by plasma spattering were observed.

Starting from Nonlinear Schrodinger's equation and using the split-step Fourier method, the authors studied the characters of the supercontinuum generation of femtosecond laser Pulse propagating in fused silica, and many physical factors were included such as propagation distance, input pulse peak power, diffraction effect, dispersion effect and nonlinear effect etc. The results show that when the femtosecond pulse propagated inside the fused silica, the process of supercontinuum generation could be divided into two main stages: the pulse compression stage, which was induced by the self-focus and other third nonlinear effects of the fused silica; and the pulse split stage, which was caused by the self-phase modulation and the group velocity dispersion of the fused silica. When the femtosecond pulse propagated inside the fused silica with high input peak power, the 3rd-order nonlinear effect of material induced pulse compression and then the subpulses were produced, so that new frequency components were introduced. At the same time, the authors also studied the spectral distribution of the pulse at different spacial locations, and there are new frequencies around the central frequency. Finally, some experiments were done to demonstrate the supercontinuum generation.