| This paper studies on acousto-optic Q-switched Yb3+-doped all-fiber laser in master-oscillator power amplifier (MOPA) configuration in theory and experiment and using it to generate hundred nanoseconds supercontinuum in experiment. Acousto-optic Q-switched Yb3+-doped all-fiber laser in MOPA configuration can be used as the laser source of laser marking. The supercontinuum generated by the laser can be used in the electro-optical countermeasure field and so on. To generate supercontinuum, pump sources are usually used femtosecond or picosecond pulses. Researches on using continuous laser or nanosecond pulse to generate supercontinuum are less. The paper gets all-fiber hundred nanoseconds supercontinuum laser, which average power breaks watts.Firstly, based on rate equation theory of the Q-switched fiber laser, pulse energy and pulse width are analyzed versus the pump power, core diameter, the gain fiber length, the output transmission, fiber intrinsic loss.The seed source of acousto-optic Q-switched Yb3+-doped all-fiber is using diode laser (LD) as pump source, ytterbium-doped fiber as the gain medium, fiber Bragg grating (FBG) as resonator mirrors, acousto-optic Q-switch (AOM) as a modulator in experiment. The optical isolator is used at the output. Seed source obtains the adjustable repetition rate 10-34 kHz, the center wavelength of 1064 nm laser pulse. When the repetition rate is 11 kHz, the pulse width is 150 ns. When the repetition rate is 23 kHz, the pulse width is 200 ns, the 3 dB spectral width is 2.029 nm and the average power is 212 mW. Experimental results meet the theoretical analysis based on rate equations.From the experimental results and the theoretical analysis, we can get the conclusion. When the length of gain fiber and the output transmission are certain, the average power of the seed source increases linearly as the pump power increasing. When pump power and the output transmission are certain, the average output power increase beginning, then reach the max, and fall finally as the gain fiber length increases. When pump power and the length of gain fiber are certain, the average output power increase beginning, then reach the max, and fall finally as the output transmission increases. When pump power and the output transmission are certain, the pulse width increases as the repetition rate increases or the length of gain fiber becomes longer. In experiments, when the pump power is small and the repetition rate is high, the repetition frequency of the output pulse is 1/2 or 1/3 of the set frequency. Only when the pump power exceeds a certain threshold, the repetition rate achieves the set value. The center wavelength of seed source output pulse is mainly affected by the spectral characteristics of fiber gratings, not with the pump power, repetition rate, length of gain fiber in change, changes significantly.In experiment of this paper, the output of seed source is amplified by two stage amplifier. The first stage amplifier obtains the pulses of 3 W average power, 10-34 kHz repetition rate, 1064 nm center wavelength. When the repetition rate is 11 kHz, the pulse width is 200 ns. When the repetition rate is 23 kHz, the pulse width is 250 ns, the 3 dB spectral width is 2.322 nm. Compared with seed source, the laser pulse width and 3 dB spectral width of the first stage amplifier increases slightly, the center wavelength did not change significantly. When the output power of the first stage amplifier is 2.7 W, the output pulses are put into the second stage amplifier. The second stage amplifier obtains the pulses of 10 W average power, 10-34 kHz repetition rate, 1064 nm center wavelength. When the repetition rate is 11 kHz, the pulse width is 250 ns. When the repetition rate is 23 kHz, the pulse width is 275 ns, the 3 dB spectral width is 2.492 nm. Compared with the first stage amplifier, the laser pulse width of the second stage amplifier increases slightly, the center wavelength did not change significantly. In the amplifier, the output power increases basic linearly with pump power.Using nanosecond pulsed laser to obtain all-fiber supercontinuum, average power breaking watts, have not been reported in the domestic. In this paper, using acousto-optic Q-switched fiber laser based on MOPA structure as the pump source, the photonic crystal fiber as the nonlinear medium, the hundred nanoseconds supercontinuum pulses are obtained. The spectral range is 600-1700 nm, continuously adjustable repetition rate is 10-34 kHz. When the repetition rate is 23 kHz, the pulse width is 250 ns and the average power is 1.46 W. |
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