Research On Q-Switched Technology Of Laser Pumped By CW Laser Diode

In order to obtain high repetition rate and high average output power pulsed laser,with the theoretical and experimental methods,the passive Q-swithing technology of cw LD-pumped is studied using cw high-power LD arrays as pump source,Nd:YAG as laser gaining medium,and Cr⁴⁺:YAG as passive Q-switching.The spectral character,level structure and passive saturable absorption character of Cr⁴⁺:YAG crystal are analysised,and the curve of Cr⁴⁺:YAG transmissivity with the optical power density is abtained by numerical methods.The rate equations of passively Q-switched laser pumped by cw LD and the expressions of threshold pump rate,the single-pulse energy, peak power and pulse width are given.The curve of single-pulse energy,peak power and pulse width with the initial transmission of Cr⁴⁺:YAG crystal are achieved by numerical methods.The mode parameters of Gaussian beam are analysised and calculated basing on ABCD matrix theory.The parameters of Cr⁴⁺:YAG crystal are determined basing on laser gain.Designing the ring-direct water-cooled structure for Cr⁴⁺:YAG crystal,and the Cr⁴⁺:YAG crystal easily burst problem under the high-power cw-pumping is solved.The variation of average output power,repetition rate,pulse width,lasing mode with LD injection current,resonant cavity length,Cr⁴⁺:YAG's location in cavity,Cr⁴⁺:YAG initial transmission are studied using experimental method.Using plano-plano resonator,the initial transmission of 91.52%of Cr⁴⁺:YAG crystal,TEM₀₀ mode Q-switching pulse with average output power of 7.30 W,pulse width of 196.30 ns,repetition rate of 18.96 kHz are obtained when the LD injection current is 13A,the optical-to-optical conversion efficiency is 4.9%, and the dynamic to static ratio is about 66.97%.Using piano-convex resonator,the initial transmission of 83.69%of Cr⁴⁺:YAG crystal,a single-pulse energy of 2.46mJ,average output power of 10.40 W,pulse width of 101.00 ns,repetition rate of 4.22 kHz are obtained when the LD injection current is 12A,the optical-to-optical conversion efficiency is 7.6%; using the initial transmission of 91.52%of Cr⁴⁺:YAG crystal,an average output power of 17.60 W,pulse width of 329.00 ns,repetition rate of 14.17 kHz are obtained when the LD injection current is 12A,the optical-to-optical conversion efficiency is 12.9%,and the dynamic to static ratio is about 58.27%.