| Acousto-optic Q-switching,electro-optic cavity-dumping and regenerative amplification are the basic techniques for obtaining short-pulse and ultra-short-pulse lasers.Thin-disk gain medium has the characteristics of large oscillating laser spot and low nonlinear effect.Compared with rod-shaped,optical fiber and slab-shaped medium,higher pulse energy and higher peak power laser output can be achieved by thin-disk gain medium with high average power.Therefore,pulsed thin-disk lasers based on the technology of acousto-optic Q-switching,electro-optic cavity-dumping and regenerative amplification occupy an increasingly important position in the field of laser research and applications.In this paper,based on acousto-optic Q-switching,electro-optic cavity-dumping and regenerative amplification technologies with the similar work principle,all have resonant cavities,all of them have periodic modulation of the loss in the cavity,single-mode and multi-mode dynamic equations have been developed for the pulse formation process of acousto-optic Q-switching,electro-optic cavity-dumping and regenerative amplification techniques based on the thin disk medium,and the theoretical and experimental researches on the pulse dynamics of the thin-disk laser has been carried out systematically.The main research contents and conclusions are as follows:(1)The single-mode dynamic equation is qualitatively analyzed by using discrete dynamic system theory.It is found that under normal working conditions,with the increase of switching time,the working areas of the pulsed thin-disk laser are:the first stable region,the period-doubling bifurcation region,the chaotic region and the periodic window region,reversal period bifurcation region,and second stable region.When parameters such as pump,repetition frequency,or seed intensity(regenerative amplifier)vary,the laser will undergo regular transitions in the above working area.Conventional Q-switched lasers usually work in the second stable region with a longer switching time,and can obtain a stable and complete pulse output with the same repetition frequency as the Q switching frequency.In addition,the Q-switched laser can also work in the reversal period bifurcation region and the period three window region,and the repetition frequency of the output pulse is half and one third of the Q switching frequency,respectively.Conventional cavity-dumped lasers or regenerative amplifiers need to work in the first stable region with a short switching time.Only when the gain of the laser is extremely high(low repetition frequency and high pumping),a higher power output can be obtained by working in the second stable region than in the first stable region.(2)A single transverse-mode operating acousto-optic Q-switched thin-disk laser was developed,and the phenomenon that the pulse frequency was reduced to half and one-third of the Q-switching frequency was observed in the experiment,which verified the theoretical analysis results of the single-mode rate equation.It is further found that the output pulse will have strong instability of time and peak jitter.An in-depth simulation study was carried out using a dynamic model of multi-longitudinal mode.The theoretical simulation waveform and the experimental results are in perfect agreement.Therefore,it is confirmed that the multi-longitudinal mode competition caused by the spatial hole burning effect is the key reason for the unstable pulse of the acousto-optic Q-switched thin disk laser.An acousto-optic Q-switched thin-disk laser with multi-transverse mode was built.The pulse bifurcation phenomenon caused by mode bifurcation was observed in the experiment.The multi-transverse mode operation dynamic model was used to simulate this phenomenon,and the simulation results were consistent with the experimental results,which verified that transverse mode competition can also cause pulse instability.Therefore,a high-power acousto-optic Q-switched thin-disk laser was further constructed,and a relatively stable laser pulse output with an average power of 312 W,a repetition frequency of 8 k Hz,a single pulse energy of 39 m J,a pulse width of 390 ns and a peak power of 100 k W was obtained,and an acousto-optic Q-switched thin-disk laser prototype was developed for high-speed drilling of alumina ceramics.Compared with the traditional millisecond laser ceramic drilling,the drilling speed and quality have been significantly improved.(3)Theoretical simulations show that the multi-mode competition does not affect the pulse stability of the electro-optic cavity-dumped thin-disk laser.Therefore,the experimental study of the electro-optic cavity-dumped thin-disk laser was carried out under the conditions of single transverse mode and multi transverse mode,and the phenomenon of period-doubling bifurcation and deterministic chaos were observed,which verified the theoretical results.Therefore,through the optimization of the switching time,the laser is guaranteed to work in the first stable region,and a pulse-stable electro-optical cavity-dumped thin-disk laser with an average power of 253 W,a single pulse energy of 2.5 m J and a pulse width of about 10.4 ns was realized.Further research on the pulse width control technology of electro-optic cavity-dumped thin-disk laser,when the relative position of the cavity element changes,the out-coupling ratio of the cavity-dumped laser varies with the voltage of the electro-optical switch and the angle of the quarter-wave plate,and two kinds of technical method for the pulse width control in cavity-dumped laser output lasers have been proposed by the Jones matrix method:reducing the voltage of the electro-optical switch combined with rotating the angle of the quarter-wave plate or directly rotating the angle of the quarter-wave plate.In the experiment,the output pulse width could be adjusted from 13.4 ns to 90 ns.(4)Theoretical and experimental studies point out that the low gain-to-loss ratio makes the thin-disk regenerative amplifier particularly sensitive to intra-cavity losses.As a result,by optimizing the system losses and switching times,when the repetition frequency was 200 k Hz,the laser output with an average power of 81.4 W,a pulse width of 15.7 ps,and a beam quality M~2 factors of 1.34 and 1.19 in the x and y directions were realized,respectively.At the same time,when the repetition frequency is 100 k Hz,a picosecond laser output with a pulse energy greater than 500μJ is achieved.In summary,based on the pulse dynamics theory of thin-disk lasers,this paper reveals the mechanism of pulse instability in pulsed thin-disk lasers,optimizes the working parameters of pulsed thin-disk lasers,and avoids damage to optical devices caused by chaotic pulses,so it lays the foundation for the application of high-power pulsed thin-disk lasers,which is of great significance. |
