In this paper, we investigated the association between beam quality and beam characteristic in theory in a spectral beam combining system and built a model to describe the dispersion. We analyzed that how the beam quality varies with different input beam parameters such as the waist radius 𝑤𝑤0 and the spectral width Δλ. There is a surprising result that the increased w0 and Δλ have a coefficient influence on the beam quality degradation, and the degradation is pretty sensitive to the increase of waist radius w0. The result gives us a guidance that besides using the narrow linewidth laser, we also need reduce the waist radius of the input beam in the SBC system appropriately to abate the beam quality degradation caused by dispersion.
The effect of surface morphology on laser-induced crystallization of hydrogenated intrinsic amorphous silicon (a-Si:H) thin films deposited by PECVD is studied in this paper. The thin films are irritated by a frequency-doubled (λ=532 nm) Nd:YAG pulsed nanosecond laser. An effective melting model is built to identify the variation of melting regime influenced by laser crystallization. Based on the experimental results, the established correlation between the grain growth characterized by AFM and the crystalline fraction (Xc) obtained from Raman spectroscopy suggests that the crystallized process form amorphous phase to polycrystalline phase. Therefore, the highest crystalline fraction (Xc) is obtained by a optimized laser energy density.
Laser-induced fluorescence (LIF) of high-purity fused silica irradiated by ArF excimer laser is
studied experimentally. LIF bands of the fused silica centered at 281nm, 478nm and 650nm are
observed simultaneously. Furthermore, the angular distribution of the three fluorescence peaks is
examined. Microscopic image of the laser modified fused silica indicates that scattering of the
generated fluorescence by laser-induced damage sites is the main reason for the angular distribution
of LIF signals. Finally, the dependence of LIF signals intensities of the fused silica on laser power
densities is presented. LIF signals show a squared power density dependence, which indicates that
laser-induced defects are formed mainly via two-photon absorption processes.
A master-oscillator fiber power amplifier system with a 4.5-m-long Yb3+-doped homemade large-mode-area double-clad fiber is reported. Up to 156 W average power of 1064 nm amplified pulse, corresponding to a slope efficiency of 64.9%, has been demonstrated. The amplified pulse possesses a pulse duration of 24 ns and a repetition rate of 50 kHz and demonstrates a good beam quality (M=2.81 and M=2.66), although no special transverse-mode-controlling techniques were adopted.
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.