We demonstrate an all-fiberized narrow-linewidth nanosecond amplifier with high peak power, tunable pulse width, and repetition rate. A fiber-coupled narrow-linewidth laser diode operating at 1064.1 nm is employed as the seed source, which is gain-switched to generate nanosecond pulses with tunable pulse widths of 1–200 ns and tunable repetition rates of 10 Hz–100 kHz. By utilizing a very-large-mode-area Yb-doped fiber with a core diameter of 50 μm in the power amplifier, thresholds of the stimulated Brillouin scattering at different pulse widths and repetition rates are increased. The maximum average power reaches 30.8 W at the pulse width of 4 ns and a repetition rate of 100 kHz, corresponding to an optical-to-optical conversion efficiency of ∼55.2%. Pulse energy and peak power are calculated to be 0.2 mJ and 50 kW, respectively, which are limited by stimulated Brillouin scattering. The 3-dB spectral linewidth remains around 0.05 nm during the power scaling process. The stimulated Brillouin scattering limited output powers at different pulse widths and repetition rates are investigated. Peak power of 47.5 kW (0.19 mJ) is obtained for the 4 ns pulses at a repetition rate of 50 kHz, which is nearly the same as that of 4 ns pulses at 100 kHz. When the pulse width of the seed source is increased to 8 ns, peak powers/pulse energies are decreased to 19.6 kW/0.11 mJ and 13.3 kW/0.08 mJ at repetition rates of 50 kHz and 100 kHz, respectively.
Received: 10 April 2020
Revised: 26 July 2020
Accepted manuscript online: 01 September 2020
Fund: the National Natural Science Foundation of China (Grant No. 61675009) and the Beijing Natural Science Foundation Program, China, and Scientific Research Key Program of Beijing Municipal Education Commission, China (Grant No. KZ201910005006).
Backward propagating pulses at 1.4 W (a) and 17.8 W (b).
Fig. 4.
Output average powers of the main amplifier at different pulse widths and repetition rates.
Fig. 5.
The M2 factor at the maximum output power of 30.8 W.
Fig. 6.
Seed pulses and amplified pulses of the main amplifier seeded by pulses of 4 ns/50 kHz (a), 4 ns/100 kHz (b), 8 ns/50 kHz (c), 8 ns/100 kHz (d). Insets: pulse sequences at each pulse width and repetition rate.
Fig. 7.
Output spectrums of the main amplifier seeded by 4 ns pulses with the PRF of 100 kHz. (a) Spectral distribution at 30.8 W, inset: enlarged spectrum; (b) evolutions of spectrum.
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