Numerical investigation into the impact of Q-switch rise time on the output pulse characteristics in an actively Q-switched ytterbium-doped fiber laser

Abstract

We report the results of our theoretical investigation into the impact of the Q-switch rise time on three key parameters of the output pulses in an actively Q-switched fiber laser, namely the multipeak phenomenon, pulse energy, and pulse peak power. Our investigation is conducted over a Q-switch time range of up to 12 times the cavity round-trip time (τ round ). We show that when a longer Q-switch rise time is applied to the cavity, a trade-off exists between multipeak phenomenon suppression and pulse energy maintenance. The results show that the Q-switch rise time (τ rise ) for the efficient suppression of multipeak phenomenon without loss of pulse energy varies, depending on the cavity parameters. In an exemplary, actively Q-switched fiber laser operating under the condition of a repetition rate of 15 kHz, τ rise is estimated to be approximately five times larger than τ round .

Numerical study on an optimum Q-switching profile for complete multipeak suppression in an actively Q-switched Ytterbium fibre laser

“…As such, a slow build-up of ASE can usually be achieved by enlarging the transient time interval of Q-switching [24]. One critical issue in simply enlarging the transient time interval of Q-switching is that a longer transient time interval could induce a substantial decrease in the output pulse energy [18]. It should be noted that full conversion of most of the stored active fibre energy into photons under low Q-factor conditions is very difficult to achieve in the case of longer transient intervals.…”

“…To date, many theoretical works modelling actively Q-switched YDF lasers have been published giving us a better understanding of the static and dynamic responses of Q-switched fibre lasers as well as a better understanding of how to optimize fibre laser configurations in terms of output power and multi-peaks [11][12][13][14][15][16][17][18][19]. More specifically, a simulation model based on rate equations and propagation equations was introduced by Huo et al [12].…”

“…Also, a technique called 'smart Q-switching', which is based on a symmetrical fibre laser cavity design and a special modulation pattern, was proposed to obtain smooth Q-switching pulses [26]. Recently, our group conducted a numerical simulation for actively Q-switched YDF lasers, and this showed that when Q-switch has a longer rise time, the MPP can be suppressed but the pulse energy losses of output pulses are generated [18].…”

“…As mentioned above, most of the proposed approaches to suppress MPP have been based on adjustment of the rise time of the Q-switch and have assumed that the Q-switching profile used in the laser has a trapezoidal temporal shape with a linear leading edge, as shown in figure 1. Even if a simple approach based on the elongation of Q-switch rise time allows efficient MPP suppression, its critical drawback will be the inevitable substantial losses of the pulse energy [18]. Taking into account that the most critical part of the switching profile is the leading edge, one fundamental question is whether or not there is an optimum leading edge profile other than a simple linear one, one which can be used for complete suppression of the MPP without loss of pulse energy.…”