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LD End-pumped 1 Nanosecond Electro-optic Q-switched Nd:YVO4 Laser

Author: XieXiYing
Tutor: LeiZuo
School: Beijing University of Technology
Course: Optical Engineering
Keywords: laser electro-optical Q-switch narrow pulse width nanosecond Brewster angle
CLC: TN248
Type: Master's thesis
Year: 2011
Downloads: 82
Quote: 0
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Abstract


Q-switched solid state lasers with high peak power and narrow pulse width are suitable for machining in small heat affected zone, due to its slight mechanical work damage and high precision during interaction. Compared to femtosecond and picosecond lasers, nanosecond lasers have low cost, higher machining efficiency and speed. Thus, 1ns or sub-nanosecond pulse, are widely applied in fields such as laser micromachining, nonlinear optics, electro-optical countermeasure, laser 3D scanning, DNA analysis.Nanosecond high peak power laser pulses are usually produced by Q-switching for controllable pulses with narrower pulse width. An innovative electro-optic Q-switched short pulse solid state laser with a short cavity is introduced. Important factors that affect pulse width are considered to obtain narrow pulse width. Gain medium and the structure of active Q-switching are optimized.By fiber-coupled output with polarization, the efficiency of pumping is improved. Nd:YVO4 crystal is cut along the a axis and pumped byπpolarized beam paralleled c axis, thus polarized emission is obtained. High gain and low intra-cavity loss are achieved by optimizing the extinction coefficient of Q-switching and the pump polarization, as well as matching the beam mode and delay parameter. Meanwhile, with theoretical analysis and experimental adjustment, optimized parameters such as medium crystal, cavity length, output coupler transmittance, focus position of pump beam and delay time of trigger signal are decided to obtain a 1 ns pulse width.A 1.0 at.% doped Nd:YVO4 crystal cut at the Brewster angle along the a axis is end pumped by a fiber-coupled quasi-continuous semiconductor laser. So, a polarized oscillation is directly obtained without a polarizer needed for conventional electro-optic Q-switching structures. Voltage-decreased electro-optical actively Q-switching structure is used with DKDP crystal. The physical cavity length L=20 mm and output coupler transmittance T=70%. With the repetition frequency of 10 Hz, pump pulse width of 130μs, trigger signal delay time of 180μs and pump pulse energy of 5.33 mJ, a stable 1064nm laser output with pulse width of 1.049 ns, pulse energy of 0.32 mJ, peak power of 0.3 MW, pulse stability less than 3% and beam quality factor （M2） of 1.9 are obtained.

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