Analysis of Output Pulse Characteristics in $Q$ -Switched Yb-Doped Fiber Laser

Characteristics of the output pulses of a high-peak-power Q-switched Yb-doped fiber laser are presented. A Q-switched fiber laser with 1.3 kW peak power and with typical pulse duration of 240 ns at 20 kHz modulation frequency was realized, variations of pulse duration, average power, peak power, and pulse energy with variation in the modulation frequency were studied. The effect of the modulation duty cycle (DC) on the Q-switched pulse characteristics was analyzed both theoretically and experimentally. It is shown that, for a particular pump power and repetition rate, the DC of modulation needs to be optimized to achieve high-peak-power single-pulse output. If the DC of modulation is long, satellite pulses of low peak power are also observed along with the main peak, when the DC is made short enough, the satellite pulses disappear and single peak pulses appear in the output. Theoretical analysis and simulation to predict the pulse build-up time, output pulse shape, and effect of modulation window time on the output pulse characteristic were carried out. Simulation results show good agreement with experimental results. This paper reported here will be useful in the development of high-peak-power Q -switched fiber lasers.