We report a high average power pulsed Tm-doped fiber laser with one stage MOPA (master oscillation power amplifier) structure. The seed source is an AOM (acousto-optic modulation) Q-switched thulium fiber laser with an average power of 2W, the wavelength is 1996.7nm, and the line-width is about 0.1nm. By one stage MOPA, we obtain the maximum average output power of 16W with nanosecond pulse width at 41kHz repetition rate, the central wavelength is 1996.7nm, and the pulse width is less than 200ns, the polarization extinction ratio is better than 20 dB. The optical-tooptical conversion efficiency is 41%, and no nonlinear effect is observed.
The propagation and split of the filamentation of femtosecond pulses in air have been paid much attention since last a few years. However, most research works are performed with few considerations of the turbulence effects of atmosphere due to the difficulties of utilizing analytical solutions and experiment conditions. In this work, we will attempt to introduce a kind of numerical simulation method to analyze the transmission features of femtosecond laser pulses in air or in the turbulent air, namely, it is called multi-phase screen method (MPSM) which use phase screen to simulate atmospheric turbulence. In this presentation, the main laser parameters are as follows: 85 fs pulse-width, 0.8cm radius of the beam, the two kinds of 160GW and 1.0 TW peak-power operating at 800 nm. Then utilizing the structure of Vortex soliton to control the filamentation is proposed. In our cases, four Gaussian pulses with a difference of π/2 in the phase of each adjacent beam as a ring to control the filamentation by utilizing its characteristics of the vortex soliton. Some results show that the coupling and interaction among four Gaussian pulses cause the rotational transfer of the energy of the four beams. Finally, we obtain the transmission features of the beams propagating in the turbulent air with different intensities by the MPSM.
Cross relaxation (CR) process in thulium ions is described. Performance of Tm-doped fiber lasers with different dopant concentrations is evaluated numerically with and without CR. Simulation shows that CR process can not only improve the slope efficiency and output of the laser system, but also lower the lasing threshold and extend the growth momentum of the laser performance. Backward LD-clad-pumped Tm-doped fiber lasers are built with Tm-doped fibers of different doping levels. A maximum output of 35.3W around 2μm is obtained with a slope efficiency of 47.2% from the 4.5wt.%- doped fiber laser while a higher slope efficiency of 54.1% was achieved from the 6.8wt.%-doped fiber laser. And, modeling shows that these laser systems are much more efficient than that without CR process.