We report a diode-pumped 1.94μm Tm:YLF laser, the maximum output power of which was 50.3W at the incident pump power of 156.9W, corresponding to the optical-to-optical efficiency of 32.1% and slope efficiency of 41.6%. The wavelength was selected and restricted at 1940.2nm by a volume Bragg grating (VBG) and an etalon inserted in the cavity. The laser beam quality factors M2 were measured to be 1.05, 1.75 and 2.40 at the output power of 4.6W, 26.2W and 50.3W respectively.

We have demonstrated a homemade high-efficient ytterbium-doped fiber laser with up to 1.75 kW of continuous-wave output power at 1.09 mu m with a slope efficiency of 76%. The fiber is pumped by two laser diode array (LDA) sources launched through opposite ends. No undesirable effect is observed with increasing pump power, which suggests that the homemade fiber laser could produce higher power output by using more pump sources. (C) 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1668-1671, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25226

We experimentally demonstrate the phase locking of a two-dimensional (2D) array of four fiber lasers using an improved self-imaging resonator with a spatial filter. The high visibility interference round stripes of the coherent beam profile are observed. The coherent output power of the fiber array exceeds 134 W. The entire system operates quite stably, and no thermal effects observe in the spatial filter, indicating that the coherent output power can be increased using this method.

>The characteristics of fiber laser coherent beam combination are investigated by using a 2×2 fiber laser array with a self-Fourier cavity.The experimental results show that with a certain output width the power ratio of the center spot is increased with the increase of space duty cycle,meanwhile the number of secondary spots is decreased correspondingly.The results are in agreement with theoretic analysis.

A new method to obtain linear polarization operation by Brewster's angle-polished fiber end is demonstrated.By using the special polarization operation technique together with introducing a narrow-linewidth fiber grating into the laser cavity, a cladding-pumped linear polarization and single-transverse-mode (M 2 < 1.1) Yb-doped fiber laser with narrow linewidth whose full-width at half-maximm (FWHM) is less than 0.2 nm, is obtained in a simple configuration.The output power is up to 10 W which is continuouswave output at 1085 nm, and the slope efficiency is 63% with respect to the coupled pump power and 75% with respect to the absorbed pump power, respectively.The measured 21-dB polarization extinction ratio does not degrade with the output power.The simplicity of such an approach is highly beneficial for a number of applications, including the use of a fiber laser for the nonlinear wavelength conversion (especially for the intracavity frequency doubling) and for the coherent and spectral beam combination.

在光纤激光相干组束中,受到各种因素的影响,各个单元激光器出射激光的相位、振幅和偏振态不能保持一致,并随着时间而变化,均会降低相干组束后的光束质量、减弱光束中心的峰值光强和中心区域内的功率.针对光纤激光相干组束中每个单元光束的出射时的相位、振幅和偏振方向扰动对相干组束远场光强分布的影响进行了理论分析,并给出数值计算结果.结果表明远场光强分布的图形、峰值光强度和中心区域内的功率,受到各因素的影响,都会不同程度的变差或减弱.

The Beam quality of multimode fiber lasers is studied Coiling technique is ineffective for fibers with too large core diameter or NA The Influence of coiling on the performance of fiber lasers is discussed.

研究了阶跃折射率分布的百微米芯径双包层光纤激光器的输出特性及其模式控制技术。理论上对光纤缠绕法模式控制技术应用于百微米芯径光纤激光器的可行性进行了分析。实验中,采用腔内小孔法对百微米芯径光纤激光器的输出激光模式进行控制,研究了不同孔径对输出激光光束质量的影响。在腔内不加小孔时输出激光x,y方向的光束质量因子M2分别为4.67和4.60,在腔内加入直径为2 mm的小孔后,x,y方向的光束质量因子M2分别为1.96和2.01,腔内小孔对输出激光的光束质量有明显的改善。

The change of pulse shape in a MOFPA system was experimentally demonstrated. Through optimized the pulse shape, the amplifier can provide 59-W 1064 nm laser with pulse duration of 22.7ns at 50 kHz repetition rate.

In this paper, it is discussed relationship between the beam quality factor and high order mode in fiber laser, and the relationship between the divergence angle and the beam quality factor. An aperture with adapted diameter in cavity could introduce low loss for the fundament mode but high loss for high order modes. In this method, it is easy to realized mode-selection. By using this method, experiment demonstrated that 23.4W output from a single fiber laser with 1.20 of M2 is obtained.

A top hat beam of frequency-doubled Nd: YAG laser is obtained from our beam shaping optical system. With this beam, amorphous silicon thin films deposited on glass by plasma-enhanced chemical vapor deposition (PECVD) are successfully crystallized. The surface morphology of the laser-crystallized materials is studied by atomic force microscopy (AFM). Pronounced increase in surface roughness after the laser treatment could be observed from the Microscope Photos. Raman spectra of the Si films are measured to confirm the phase transition from amorphous to polycrystalline and to investigate the silicon structural properties. Crystalline fraction evaluated from the Raman spectra are found to increase almost linearly with the laser fluence. There exists the optimized laser fluence to produce the best crystallization in the range of 400 ~1000mJ/cm2.

In this paper,we studied on the principle and technical difficulties of beam coherent combination with three self-imaging cavity,which were Talbot cavity,self-Fourier cavity and self-imaging cavity of Fourier transform.Finally,we implemented 1×2 fiber lasers coherent combination and 2×2 fiber lasers coherent combination with self-Fourier cavity,and the coherent output powers reached 122 W and 26 W,respectively.

A pulse master-oscillator fiber power amplifier system with china-made large-mode-area fiber and a (6+1)×1 multimode combiner is demonstrated. The system generates up to 4.8W of amplified radiation (100kHz) at a wavelength of 1064nm with a near-diffraction-limited beam quality (M2=1.2), and the overall slope efficiency with respect to the launched pump power is 50%. Some basic characteristics of this system, including the pulse-amplification characteristics, the gain characteristics, as well as the emission spectrum characteristics are investigated in detail.

Based on the frustrated total internal reflection theory, a leaky large-mode-area double clad fiber is designed. The propagation constants and leakage loss of the fundamental mode LP01 and sub-low order mode LP11 is investigated by using of the matrix method. Results show that the designed fiber can operate with single-mode.

Phase locking of a two-dimensional fiber laser array is experimentally demonstrated by using a self-imaging resonator and a spatial filter. The stable beam profiles of in-phase mode and out-of-phase mode are observed by controlling the position of spatial filter. The phase locking fiber array with in-phase mode has produced 26 W coherent output. An antisymmetric eigenmode is also observed in our experiments. The phase locking is not sensitive to power variations among the pump beams and the configuration has the ability to repair a missing element. (C) 2008 American Institute of Physics.