Research On High Pulse Energy Composite Crystal Passively Q-switched Laser

With the advantages of simple structure,good reliability,high efficiency,and compact size,high pulse energy and narrow pulse width composite crystal passively Q-switched lasers have been widely used in medical,military,scientific research,and industrial fields.In this paper,through theoretical and experimental research on composite crystal passively Q-switched lasers,output laser pulse with single pulse energy of the order of 100 millijoules and pulse width of the order of nanoseconds is obtained.The main research contents of this article are summarized as follows:Nd:YAG crystal and saturable absorber Cr⁴⁺:YAG are used as the laser working medium and the Q-switch crystal of the passively Q-switched laser,respectively.The basic characteristics of the laser gain medium and the saturable absorber are discussed in detail.According to the characteristics of flash lamp pump,the rate equations of non-uniform pump are established,which can analyze the pulse energy and pulse width of the output pulse train.Simulation analysis found that non-uniform pump can cause a relative change on the pulse energy and pulse width of each pulse;shortening the cavity length can reduce the pulse width,but it has almost no effect on single pulse energy;Reducing the initial transmittance of the Q-switch crystal can increase the output single pulse energy and reduce the pulse width.And,the lower the initial transmittance of the saturable absorber,the more obvious the output single pulse energy change.According to the theoretical analysis,the Nd:YAG/Cr⁴⁺:YAG composite crystal is used to shorten the cavity length,and the lower initial transmittance of the Q-switch crystal is used to obtain large pulse energy and narrow pulse width laser output.The experimental parameters are optimized by numerical simulation.The output coupling mirror reflectance of 30%is adopted.Firstly,the Nd:YAG/Cr⁴⁺:YAG(non-composite crystal)passively Q-switched laser is studied experimentally.The effects of the pump control voltage,the initial transmittance of saturable absorber and the cavity length on the output parameters are studied.Based on this,the Nd:YAG/Cr⁴⁺:YAG composite crystal passively Q-switched laser are further studied experimentally.The initial transmittance of Q-switch Cr⁴⁺:YAG is 14%and the cavity length is 9.7 cm.At the maximum pump control voltage,that is,when the pump control voltage is 6V,an output pulse train with four pulses is obtained,and the impacts of the non-uniform lamp pump on each pulse of the output pulse train are analyzed in detail.The four pulses energy are 156.5,151,149.7,and 145.8 m J in turn with corresponding intervals of20.8,24.2,and 46us.The energy of the four pulses decreases,the pulse interval increases,and the pulse width is basically unchanged.The average single pulse energy is 150.8m J,the average pulse width is 5.72ns,and the Q-switch efficiency is 63.2%.