Diode-Pumped All-Solid-State Passively Qswitched Nd:La MgAl₁₁O₁₉ Laser

LD-pumped all-solid-state near-infrared passively Q-switched lasers have the advantages of compact structures,low cost,stable operations,easy implementations,and good beam qualities.They are often used to generate near-infrared laser pulses at us to ns level and are widely used in linear optics,material processing,medical diagnosis,optical fiber communications,laser rangings and other fields.Therefore,all-solid-state near-infrared passively Q-switched lasers have become a research hotspot at home and abroad.The Nd:LaMgAl₁₁O₁₉?Nd:LMA?disordered crystal mainly operates around 1?m,so that it is suitable for LD pumping.Owning to its advantages:high doping concentration,long fluorescence lifetime,and high thermal conductivity,it may be suitable to be the solid gain material for achieving high-power near-infrared Q-switched laser.This paper mainly theoretically and experimently studies LD-pumped Nd:LMA passively Q-switched laser and wavelength-switchable laser.Our main work can be summarized as follows:The formation process of passively Q-switched pulses is theoretically studied,and the principles of passive Q-switching are explained.Through the rate equations,the variations of various particles in the resonator are analyzed when Q-switched pulses are achieved.At meantime,the ABCD matrix theory is used to design and optimize the resonant cavity.Through software simulation,the beam waist spot radius and stabilities of the two resonant cavities are calculated.It is found that the V-shaped cavity and the W-shaped cavity have good stability,simple structures,and can excellently mach with the LD-pumped source.Therefor,they are suitable to build the LD-pumped solid lasers.We experimentally demonstrate a LD-pumped high-repetition-frequency Nd:LMA passively Q-switched laser,through adopting a semiconductor saturable absorber mirror?SESAM?as the Q-switched device.The output characteristics are analyzed under the different pump powers and different output couplers?OCs,transmittances of 0.5%,1.6%,2.5%,5.0%and 7.5%?.Without adopting SESAM,the laser is operating at a continuous-wave?CW?state,and the center wavelength of laser is around 1056 nm.When the OCs with low transmittances are used,a relatively high transmittance is helpful for achieving high output power,slope efficiency and light-to-light efficiency.For T=7.5%and a absorbed power of 6.17 W,the output power arrives at its maximum of 1160 mW,and the corresponding slope efficiency and light-to-light efficiency are 20.71%and 18.78%,respectively.After introducing SESAM into the cavity,the laser operates at a passively Q-switched state.Under this case,the largest slope efficiency is 13.14%under T=5.0%.Adopting five different OCs,with the increase of the absorbed power,the pulse repetition frequencies?PRFs?,the pulse energies and the peak powers will ascend while the pulse widths will decline.The observed maximum PRF is 175.88 kHz.Due to the Nd:LMA disordered crystal having multiple narrow emission peaks,we experimentally demonstrate a diode-pumped wavelength-switchable Nd:LMA Q-switched laser,through adopting a SESAM as the Q-switched device,an SF6 prism to switch wavelength,and an output coupler with transmittances of 10%.The Nd:LMA laser can operate at 1056 nm,1083 nm,1056 nm&1083 nm,respectively.Its laser characteristics of the three wavelengths including the pump threshold powers,output powers,frequency repetition rates,pulse widths,and optical spectrums are investigated in details.