以被动调Q的固体薄片激光器作为种子光源,以中心波长976nm的半导体激光器为抽运源,通过端面抽运耦合,搭建了窄脉宽双包层掺镱光纤放大器。实验研究了前向、后向端面抽运方式对窄脉宽双包层掺镱光纤放大器的输出平均功率、激光光谱、脉冲宽度等特性的影响,并进行分析讨论。结果表明,采用后向抽运方式,窄脉宽双包层掺镱光纤放大器,获得了平均功率为9.3W的放大激光输出,重复频率为10kHz,脉冲宽度为450ps,峰值功率大于2MW。

研制了输出功率达17.3 W的单频保偏掺镱光纤放大器,并对其输出激光特性进行了实验研究.该光纤放大系统以Nd:YVO4单频固态激光器为种子源,以保偏光纤为增益介质,通过二级光纤放大,获得了波长为1064 nm的单频线偏振激光输出,输出激光功率达17.3 W.功率放大级光纤放大器的斜率效率为62.8%,光-光转换效率为57.6%,偏振消光比为24.3 dB.

1 中国研制第一台激光器的背景激光的发明借鉴了微波激射器的思想.20世纪50年代美国物理学家汤斯开始了激光的研究工作,1955年他制造了一台氨分子微波量子放大器.1958年他和肖洛在<物理评论>上发表的<红外和光量子放大器>一文提出了研制以受激发射为主的光源(即激光器)的设想,并就研制激光器的可能性和所需条件进行了阐述.1960年8月梅曼采用掺铬的红宝石作发光材料,应用发光强度很高的脉冲氙灯作抽运光源研制出了世界上第一台红宝石激光器,开创了激光技术研究和应用的时代.

利用倍频Nd∶YAG激光器使玻璃基底上沉积的非晶硅薄膜成功实现了晶化。YAG激光器的倍频绿光经蝇眼透镜阵列整形后得到一光强均匀分布的平顶光束,并用此光束对非晶硅薄膜进行扫描晶化处理。分别测量了激光晶化前后薄膜的拉曼谱和表面形貌。测量结果表明,非晶硅实现了到多晶硅的相变,且晶化处理后表面起伏度明显增大。根据拉曼谱的数据计算了不同激光能量密度下薄膜的粒度大小和结晶度。结果表明,在一定能量密度（400~850 mJ/cm2）范围内,结晶膜的晶粒粒度和结晶度随激光能量密度升高而增大。然而能量密度大于1000 mJ/cm2后,检测不到明显的多晶硅特征峰。激光能量密度在850 mJ/cm2左右可得到最佳晶化效果。

Laser-diode pumped Q-switched ytterbium-doped fiber laser is studied experimentally by controlling the switching time of acousto-optic modulator (AOM).The characteristics of Q-switched pulses with different rise time of AOM regulated by the laser beam size along the window of AOM are presented.Meanwhile, the behaviors of Q-switched pulses are achieved by regulating the switching time of AOM.The singlerepetition-rate and half-repetition-rate phenomena are described and discussed.The experimental results confirm that the fiber laser with lower level inversion population can be more easily operated for halfrepetition-rate generation.

We demonstrate a two-stage single frequency polarization maintaining Yb-doped fiber Amplifier at 1064nm. The gain is 7dB and 17.6dB for the first and the second fiber amplifier. The output power is 17.3W with 62.8% slope efficiency for second fiber amplifier and the polarization extinction ratio is better than 24.3 dB.

The effect of laser fluence on the crystallization of amorphous silicon irradiated by a frequency-doubled Nd:YAG laser is studied both theoretically and experimentally. An effective numerical model is set up to predict the melting threshold and the optimized laser fluence for the crystallization of 200-nm-thick amorphous silicon. The variation of the temperature distribution with time and the melt depth is analyzed. Besides the model, the Raman spectra of thin films treated with different fluences are measured to confirm the phase transition and to determine the optimized fluence. The calculating results accord well with those obtained from the experimental data in this research.

A high repetition rate ytterbium-doped double-clad (YDDC) fiber laser with amplifying effect is described by using acousto-optic modulator. The characteristic of Q-switched pulses are studied with accurate control of opening gate time of modulator. The stable Q-switched pulses with tens of nanoseconds width can be observed at high repetition rate varied from 50kHz to 500kHz using this laser. The stable operation area of the Q-switched fiber laser is discussed and the analysis results agree well with that of the experiment.

The frequency dependence of plasma-column antenna input impedance has been measured by a vector network analyzer with different applied exciting power. The experimental results show obvious resonance behavior of the impedance. The effect of plasma parameters on the input impedance was established by means of an equivalent circuit model and the characteristics of input current. This method is useful for the research of plasma antenna dynamic reconfiguration and the realization of fast impedance matching.

A simple actively Q-switched double-clad fiber laser combining an amplifying cavity is reported by using a dynamic acoustooptic Q-switching as a beam splitter. Sub-100-ns. pulses independence of the repetition rate of acoustooptic modulator are almost changeless with repetition rate varied from 50 kHz to 1.5 MHz. With 4.5-W absorbed power, 9.4-W peak-power pulses at 1.5-MHz repetition rate with 75-ns pulse duration are generated.

We adopt cylindrical-coordinate FDTD algorithm to simulate and analyse a 0.4-m-long column configuration plasma antenna. FDTD method is useful for solving electromagnetic problems, especially when wave characteristics and plasma properties are self-consistently related to each other. Focus on the frequency from 75 MHz to 400 MHz, the input impedance and radiation efficiency of plasma antennas are computed. Numerical results show that, different from copper antenna, the characteristics of plasma antenna vary simultaneously with plasma frequency and collision frequency. The property can be used to construct dynamically reconBgurable antenna. The investigation is meaningful and instructional for the optimization of plasma antenna design.

The radiation characteristics of a plasma-column antenna is analyzed by using the moment method when the operating frequency is greatly lower than the plasma frequency, the current distribution along the plasma column, radiation pattern, input impedance, and antenna efficiency are obtained. It has been demonstrated that the plasma antenna can operate similar to a copper antenna, and the radiation characteristics can be varied by varing the plasma parameters. Furthermore, not only the dynamic reconfiguration of the plasma antenna, but also selecting fixed plasma parameters with reduced efficiency enables the wideband characteristics of plasma antenna.

A pulsed master-oscillator fiber power amplifier system with near diffraction-limited output by use of China-made large-mode-area fiber and a (2+1)×1 multimode combiner is reported. The effect of the seed power on the amplification performance is found. For the seed power, there exists a range within which the pulsed fiber amplifier can operate safely and reliably at a certain pump power. With the seed average power of 70 mW, the amplification performances of the fiber amplifier are investigated.

A narrow-linewidth master-oscillator fiber power amplifier system with homemade large-mode-area fiber is demonstrated. Some fundamental characteristics of this system, including the output power characteristics, the emission spectrum characteristics, as well as the confirmation of single-frequency operation are investigated in detail. The system generates up to 7.3 W of single-frequency radiation at a wavelength of 1064 nm with 39% slope efficiency and 26% optical-optical power conversion efficiency.

Based on the heat conductivity principles,a mathematic model about pulsed laser induced crystallization of a-Si thin film had been developed.With the finite difference method,the effect of varied parameters,such as wavelength and energy density of laser,on the temperature distribution and phase change of the thin film during crystallization was analyzed.The melt threshold energy densities for 500 nm a-Si irradiated with different lasers were calculated.The results show that the crystallization with excimer lasers requires the lowest threshold energy densities.However,it does not create the deepest melt depth,compared with green or red lasers.The effect of different substrate temperatures on the crystallization speed and grain size was analyzed,and the calculated results accord with the experimental results and laws.

The characteristics of acoustic-optic double-clad fiber laser end-pumped by diode laser are reported for different pumping constructions. The comparison and discussions of average power, pulse width and stability of Q-switched pulses under the forward pump and back ward pump conditions are presented. In experiment, the output of Q-switched pulses with 60% slope efficiency of average power, 52ns pulse width and 03mJ single pulse were obtained at the repetition rate of 10kHz. Finally, the rate equations with different pump configurations are deduced to analyze the Q-switched pulse, and the theoretical results agree with well experimental results.

Propagation of the surface waves along a two-dimensional plasma column and thefar-field radiation patterns are studied in thin column approximation.Wave phase and attenuationcoefficients are calculated for various plasma parameters.The radiation patterns are shown.Re-sults show that the radiation patterns are controllable by flexibly changing the plasma length andother parameters in comparison to the metal monopole antenna.It is meaningful and instructionalfor the optimization of the plasma antenna design.

Radio-frequency excitation enables the plasma to contain two, three or more harmonic waves, and the modulating signal produced by signal source and excitation source under the plasma nonlinear influence should not be ignored. A new wave-plasma interaction model is set up considering the electron thermal motion, recombination and diffusion effect. It verifies the modulations of signal in different frequencies and explains the production of the second and high order harmonic waves in plasma excitation. The variation of the EM wave pedigree is analyzed taking into account the parameters such as input power, ionization field threshold and electron average energy. The result is of use in tuning the matching circuit or selecting the coupling element in plasma discharge, and it is helpful in electric magnetic interface design, plasma antenna transmission, etc.