The Q-Switched Mode Locking (QML) regime provides the generation of relatively high peak power picosecond pulses train with energies of a few muJ each in a simple resonator. The fully modulated efficient QML regime was demonstrated in the diode-pumped Nd:YVO4 laser. The acousto-optic cell playing a double role of Q-switch and Mode Locker was located near flat output coupler. The two folding mirrors were mounted on the translation stages for matching the resonance frequency of the cavity to the radio frequency of acousto-optic modulator. The QML pulses with envelope durations of 100-150 ns and near 100% modulation depth were observed for wide range of pump powers and repetition rates. Up to 3 W of output average power, 100 muJ of the envelope energy, having approximately 5-8 mode-locked pulses were achieved.

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An all-fiber, gain-switched, single-mode, thulium-doped silica fiber laser operating at a wavelength of 1994.6 nm was developed. The laser was pumped by a 1.55 μm master oscillator power amplifier (MOPA) system and operated at a repetition rate ranging from 50 to 300 kHz. Different configurations of the laser cavity were tested. When operating at a 100 kHz repetition rate the laser delivered a maximum average power as high as 1.08 W with a slope efficiency of 49%. For a repetition rate of 50 kHz, stable 23 ns pulses with an energy of 15.3 μJ, corresponding to a peak power of 623 W, were achieved. We also report, to the best of our knowledge, the first demonstration of 2 μm gain-switched, mode-locked pulses with 100% modulation depth obtained in a Tm-doped fiber laser.

6 W of output power and near 50% slope efficiency with respect to absorbed pump power was demonstrated in free-running mode for a short, 40-mm long resonator. The uncoated, with 3.5% dopant of thulium YLF rod of ⌀ 3 × 8 mm size wrapped with indium foil was mounted in copper heat-sink maintaining 293 K temperature of coolant water and inserted in a short, 40-mm long resonator. For pumping the fiber coupled (0.4 mm core diameter) laser diode bar at 792-nm wavelength was deployed. The fused silica acousto-optic modulator with above 80% diffraction efficiency for 25-W power of RF was taken as the Q-switch for such a laser. In the best case of Q-switching mode up to 2-mJ output energy with 20-ns pulse duration corresponding to 100-kW peak power was demonstrated for rep. rate of a few Hz. Emission wavelength was around 1904 nm for both free-running and Q-switching regimes.

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