Fig. 1. (a) Schematic diagram of the high-repetition-rate burst generator. OC, optical fiber coupler; ISO, fiber isolator; LD, laser diode; WDM, wavelength division multiplexer; YDF, Yb³⁺-doped fiber; PF, passive fiber; AOM, acoustic-optic modulator; AWG, arbitrary waveform generator. (b) Burst-mode and single-pulse-mode laser output from the out1 port of the coupler. (c) Variational biburst-mode laser output from AOM2. (d) Identical burst-mode laser output from AOM2. RF, radio frequency signal.

Fig. 2. (a) Scheme of the mode-locked fiber laser oscillator. YSF, Yb³⁺-doped single mode fiber; SMF, passive single mode fiber; FBG, fiber Bragg grating. (b) Typical pulse train of the oscillator recorded using a digital oscilloscope (Keysight DSOS404A) and a photodetector (Thorlabs DET08CL/M). (c) RF spectrum of the mode-locked pulse measured by the oscilloscope mentioned above. Inset: the broad-span RF output spectrum. (d) Optical spectrum of the mode-locked pulse measured with an optical spectrum analyzer (Yokogawa AQ6370D). (e) Autocorrelation trace of the mode-locked pulse obtained using an autocorrelator (APE SM2000).

Fig. 3. (a) Identical burst modes with burst repetition rates of 2.06 MHz, 1.03 MHz, 412 kHz, 206 kHz and 103 kHz, respectively. (b) Single burst with two to seven sub-pulses. Inset: RF spectrum of the bursts.

Fig. 4. Burst envelope shapes in different cases. (a) AOM1 switch frequency set to 1.03 MHz with an open time of 350 ns, and amplifier pump powers of 200, 400, 550 and 600 mW. (b) Pump power of 500 mW with AOM1 switch frequency at 412 kHz, and pulse cycle counts of 6, 10, 14, and 18. (c) Pump power of 500 mW with AOM1 open time of 350 ns, and switch frequencies of 2.06 MHz, 1.03 MHz, 412 kHz and 206 kHz.

Fig. 5. Experimental setup of the burst amplification system. IBP, isolator with bandpass filter; ISO, isolator; CPS, cladding pump stripper.

Fig. 6. Output characteristics of bursts with repetition rates of 2.06 MHz, 1.03 MHz and 412 kHz, and sub-pulses number of seven and three, respectively. (a) Output spectra at an average output power of approximately 10 W. (b) Average sub-pulse peak power (black solid curve) and the first-order SRS power ratio (red dotted curve) versus pump power.

Fig. 7. Output spectra of bursts with seven sub-pulses and burst repetition rates of (a) 2.06 MHz, (b) 1.03 MHz and (c) 412 kHz at different output powers.

Fig. 8. (a) Average sub-pulse peak power (solid line) and first-order SRS power ratio (dotted line) versus pump power for bursts containing seven sub-pulses at repetition rates of 2.06 MHz, 1.03 MHz and 412 kHz. (b) Output average power of bursts containing two to seven sub-pulses at a repetition rate of 2.06 MHz as a function of pump power. Inset: net signal average power of bursts containing two to seven sub-pulses at a repetition rate of 2.06 MHz as a function of pump power, where the line and symbol colors are consistent with the main figure for the same number of sub-pulses.

Fig. 9. Characteristics of bursts at the maximum average power of 606 W. (a) Output spectrum, where the light red region represents the first-order SRS component. Inset: detailed spectrum in the range of 1059–1069 nm. (b) Autocorrelation trace.

Fig. 10. Envelope shapes of bursts containing (a) seven sub-pulses, (b) five sub-pulses and (c) three sub-pulses at different output powers.

Fig. 11. (a) Relative intensity noise (RIN) measured of the mode-locked seed, burst generator and main amplifier. (b) Beam profile and M² factor at the maximum output power of 606 W.