We report on the realization and analysis of a 150 W peak-power passively Q-switched Yb-doped double-clad fiber laser with 30 μJ pulse energy, and 205 ns pulse duration using Cr 4+ :YAG saturable absorber. Analysis of the effect of mode area inside the saturable absorber on pulse characteristics has also been carried out.Fiber laser, Yb-doped fiber, passive Q-switch, pulsed laser, saturable absorber, Re-imaging magnification
INTRODUCTIONPulsed fiber lasers have attracted attention in several applications due to their high-peak power and short-duration pulses. Passive Q-switching is an efficient technique to generate high energy and high-peak power pulses. Further, passively Q-switched lasers are more compact and lower in cost than actively Q-switched lasers. Cr 4+ :YAG and AlGaInAs quantum wells have been effectively used for passive Q-switching of Yb-doped fiber lasers 1 . Co 2+ :ZnSe and Cr 2+ :ZnSe have been demonstrated as saturable absorbers for passive Q-switching of Er 3+ -doped 2 and Tm 3+ -doped fiber lasers 3 , respectively. Use of saturable absorber along with stimulated Brillouin scattering (SBS) has also been demonstrated to generate short duration pulses 4 . Huang et al. have reported generation of up to ~ 0.35 mJ pulse energy with 70 ns pulse duration from passively Q-switched Yb-doped fiber laser using Cr 4+ :YAG saturable absorber 1 . Further, Pan et al. have exploited Cr 4+ :YAG in combination with distributed SBS to generate ~375 kW peak power with 490 ps pulse duration 4 . However, there is still scope to understand physical mechanism involved in passive Q-switching and to achieve smooth pulses with better pulse to pulse stability. In this paper, we report on the realization of a passively Qswitched Yb-doped double-clad fiber (YDDC) laser using a single mode YDDC fiber of 5.5 μm mode field diameter and 125 μm inner clad diameter, which is compatible with standard fiber optic components used in optical communication; and Cr 4+ :YAG is used as the saturable absorber (SA). We have also carried out an analysis of the effect of mode area inside the saturable absorber on output pulse characteristics; and study of the variation in pulse energy, pulse frequency and pulse duration as a function of input pump power.