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We report a wide bandwidth (Δ λ =8 nm) optical pulsed MOPA (master oscillator power amplifier) source emitting 11.23 mJ pulses (1.25 MW peak power) in the wavelength centered at ( λ =1064 nm). Pulse duration and repetition rate were 9 ns and from 10 Hz to 100 Hz, respectively. In order to suppress amplified spontaneous emission (ASE), multi-stage pulse pump technology is applied. And the large core diameter (90 μm) and wide bandwidth ensures the high peak power and energy output.

A Super-luminescent Diode (SLD) seeded all fiber cascaded pulsed laser system is reported. The signal line width is 8 nm confined by spectrum filers between stages, much wider than Laser Diode (LD) seeded laser. The wide spectrum of the seed source gives a good opportunity to get higher stimulated brillouin scattering threshold than LD seeded laser. The system emits up to 50 W pulses at a wavelength of 1064 nm and a repetition rate of 20 kHz with peak power 250 kW and beam quality M2 < 1.8. No SBS or SRS are observed and its output power is limited only by available pump power.

We report on an all fiber Master Oscillator Power Amplifier (MOPA) structured pulsed-pumped fiber-amplifier seeded by laser diode and modulated by current with an output of several nanojoule energy at 100 Hz repetition rate. To suppress ASE, pulse-pumped technology was adopted in four stages of amplification. By means of this technology, repetition could be adjusted freely without change of pump current which is different from continuous pump. 80 μJ output was achieved in 18 ns pulses in the 15 μJ amplification stage. Moreover, we achieved over 1.2 mJ/pulse with pulses of 10 ns between 1 Hz to 100 Hz repetition in the 30 μm core amplification stage with output beam quality of M2 ≈ 1.4. Energy was limited by launched pump power.

We describe a mopa structured all-fiber 15 μm fiber amplifier cascade. A single-mode diode laser generating 1064 nm wavelength, several nanosecond pulses at 100 Hz repetition was adopted to seed a corepumping amplifier featuring a 6 μm core Yb-doped fiber. Multi-stage pulse-pumping technology was applied to eliminate ASE as much as possible and ease the heat load of the system that leads to the freedom of temperature control of the laser diode. The master oscillator-power amplifier (MOPA) generated 1064 nm, 18 ns pulse-width, 100 Hz repetition of 220 μJ single pulse energy, peak power >12 kW with single transverse output. The pulse energy of 220 μJ is the largest to date in the all-fiber MOPA amplifier with core diameter around 15 μm to our knowledge.

A theoretical analysis of noise in a high-power cascaded fiber amplifier is presented. Unlike the noise theory in low power communication, the noise of a high power system is redefined as the leaked output energy between pulses with coherent beat noise uncounted. This definition is more appropriate for high power usage in which the pulse energy receives more attention than the pulse shape integrity. Then the low power pre-amplifying stages are considered as linear amplification and analyzed by linear theory. In the high-power amplification stages, the inversion is assumed to recover linearly in the time interval between pulses. The time shape of the output pulse is different from that of the input signal because of different gains at the front and back ends of the pulse. Then, a criterion is provided to distinguish the nonlinear and linear amplifications based on the signal-to-noise ratio (SNR) analysis. Then, an experiment that shows that the output SNR actually drops off in nonlinear amplification is performed. The change in the noise factor can be well evaluated by pulse shape distortion.

We report on the fiber-based amplification of a flash lamp pumped Q-switched Nd:YAG laser. At a repetition rate of 10 Hz and spectrum width of 0.1 nm, an output single pulse energy of up to 12 mJ is generated in a 95 µm core Yb-doped large mode area fiber with a seed pulse energy of 0.75 mJ and pulse duration of 11 ns. No stimulated Brillouin scattering, stimulated Raman scattering or saturation are observed. Furthermore, higher pulse energies will be achieved with higher pump powers.