Research of the Features of Generation Pulsed Radiation in Gain-Switch Thulium Fiber Lasers

Our work is devoted to the study of the formation of relaxation pulses with a wavelength of 1.9 microns in thulium fiber laser with pumping modulation via erbium pulsed fiber laser (λ = 1.55 μm). This type of thulium pulsed fiber lasers is simpler, than scheme of master oscillator amplification due to high cost, exclusivity and low quality of 1.9 microns semiconductor laser. In addition, our approach permits to achieve shorter pulses, than conventional fiber Q-switch schemes. We have proposed a theoretical model that allowed determining to determine pulses duration and peak power as function of different parameters of the resonator, such as length, fiber Bragg grating reflection, Tm3+ concentration, wavelength of pump radiation, pumping pulse energy. Through those dependencies, we determined optimal parameters of resonator for achieving the shortest pulses. Results were approved by experimental work. Laser with optimized parameters provides pulsed radiation with pulsewidth lower than 10 ns, peak power 1.8 kW and repetition rate 50 kHz. We propose following steps to reduce pulse duration and narrow pulses spectral bandwidth.