Research On Three-plan Resonant Single-longitudinal Mode Laser With Hybrid Q-switching

Since the first laser was invented in 1960,the technologies and applications of laser have been developing rapidly.One of its technical direction is to produce the laser output with high energy,high power,high stability and good beam quality.And this output has many application requirements such as laser processing,medical and cosmetology,technical researchment and national defense.We can obtain a high-power laser beam by using the Q-switching technology.And if the laser were working in the situation of single-longitudinal and single-transverse mode by the way of mode selecting,the good beam quality output can be achieved.This paper studied a single-longitudinal laser with high energy,high power,high stability and good beam quality by the use of Hybrid Q-switching technology and Three-Plan Resonant mode selecting method.First of all,the research states and progress of single-longitudinal mode laser in the last decade in the world was introduced,and the mode selecting methods with their own relative merits was summarized.Also,the research states and progress of Hybrid Q-switching technology was introduced,and the feasibility,implementation procedure and superiority of this technology can be comprehended.On the basis of these,the main contents of this paper were presented.Secondly,the theories of longitudinal mode and Q-switching were discussed.The mode formation cause of laser and several representative ways of single-longitudinal mode selecting were explained first.The theory of Q-switching technology and the realization principle of passively Q-switching and actively Q-switching were explained next.The Q-switching progress was simulated in the end.Then,the laser system used in the experimental study was designed.The longitudinal mode selecting principle of Three-Plan Resonant was introduced.The Three-Plan Resonant structure using in the Xenon-lamp flash pumped Nd:YAG laser was designed and its reflection spectroscopy was simulated.The flat-flat cavity was chosen as the laser resonator.The relationship between beam spot size and resonator length or thermal focal length was simulated,too.The Cr⁴⁺:YAG was chosen as the passively Q-switching crystal and the BBO Pockels Cells was chosen as the actively Q-switching modules.Finally,the experimental studies were accomplished.In the study of Three-Plan Resonant laser without Q-switching,it was found that the mode restrain ability of this method was very well.In the study of Three-Plan Resonant laser with passively Q-switching only,the laser beam output with pulse energy 9.84mJ,pulse width 11.2ns and peak power 0.879MW was obtained under the 475V pump voltage which was a little higher than the threshold voltage.What’s more,in this case the occurrence probability of the single-longitudinal mode was about 93%.In the study of Three-Plan Resonant laser with actively Q-switching only,it was found that the laser was not working in the single-longitudinal status.In the study of Three-Plan Resonant laser with Hybrid Q-switching,the laser beam output with pulse energy 18.78mJ,pulse width 8.89ns and peak power 2.112MW was obtained under the 500V pump voltage.Moreover,in this case the occurrence probability of the single-longitudinal mode was about 98%.To summarize,it was obvious that the laser under the Hybrid Q-switching can produce beam with higher pulse energy,narrower pulse width,higher peak power and better stability.