Yuan Zhijun

High Power Passive Phase Locking of Four Yb-Doped Fiber Amplifiers by an All-Optical Feedback Loop

We report the passive phase locking of four high power Yb-doped fiber amplifiers with ring cavity. The interference patterns at different output power are observed and the Strehl ratios are measured. The maximum coherent output power of the fiber array is up to 1062 W by multi-stage amplification. The stable beam profiles of various phase relationships are observed by controlling the position of the feedback fiber, in good agreement with the calculated results. By using master oscillator power-amplifier (MOPA) architecture and broadband operation of passively phased systems, higher power scaling with high beam quality appears to be feasible.

UV—visible spectral characterization and density functional theory simulation analysis on laser-induced crystallization of amorphous silicon thin films

The effect of laser energy density on the crystallization of hydrogenated intrinsic amorphous silicon (a-Si:H) thin films was studied both theoretically and experimentally. The thin films were irritated by a frequency-doubled (λ = 532 nm) Nd:YAG pulsed nanosecond laser. An effective density functional theory model was built to reveal the variation of bandgap energy influenced by thermal stress after laser irradiation. Experimental results establish correlation between the thermal stress and the shift of transverse optical peak in Raman spectroscopy and suggest that the relatively greater shift of the transverse optical (TO) peak can produce higher stress. The highest crystalline fraction (84.5%) is obtained in the optimized laser energy density (1000 mJ/cm2) with a considerable stress release. The absorption edge energy measured by the UV-visible spectra is in fairly good agreement with the bandgap energy in the density functional theory (DFT) simulation.