Research On Intracavity Generation Of High Power All-solid-state Ultrafast Vortex Lasers

Vortex beams are a type of light beam with a spiral phase front,where the wavefront phase can be expressed as exp（ilθ）,withθbeing the angular coordinate and l representing the topological charge of the vortex beam.When the wavefront of a vortex beam rotates around the center of the beam by one revolution,the phase will change by 2πl.The helical phase creates the phase singularity,leading to zero intensity at the center of the beam and a ring-shaped distribution.Due to these unique characteristics,vortex beams have broad applications in fields such as optical trapping and manipulation,optical communication,quantum entanglement,optical processing,and optical imaging.Mode-locking in all-solid-state lasers is a common technique for generating ultrafast lasers.Among them,passively mode-locked technology can not only generate shorter pulses,but also is simple to operate without complex structures and additional components.Common passively mode-locked technologies include semiconductor saturable absorber mirror mode-locking and nonlinear mirror mode-locking based on nonlinear crystals.Laguerre-Gaussian modes are eigenmodes of the paraxial wave equation in cylindrical coordinates,allowing for direct generation within the laser cavity through mode selection.Ultrafast vortex lasers combine the advantages of vortex beams and ultrafast lasers,carrying not only orbital angular momentum but also short pulse and high energy.Ultrafast vortex lasers have been widely used in fields such as optical communication,optical tweezers,nonlinear optics,and ultrafast spectroscopy.This thesis conducts a series of theoretical and experimental studies on the direct generation of vortex lasers,ultrafast vortex lasers,and ultrafast optical vortex arrays lasers for solid-state lasers using the method of direct generation within the cavity.The main research contents and innovative achievements are summarized as follows:1.Generation and detection of OAM frequency-degenerate states in solid-state vortex lasers.Using point defect mirrors,vortex beams with composite OAM states and single OAM states were generated in solid-state lasers,and a one-dimensional optical vortex diffraction grating of third order was designed for precise detection of the OAM states of the vortex beams.The intensity weights of composite OAM states with topological charges of-1 and+1 can be arbitrarily controlled by adjusting the angles of cavity components.The modal purities of single OAM states with topological charges of-1 and+1 reach up to 93.2%and 92.4%,respectively.Both simulation and experimental results demonstrate that the diffraction grating can simultaneously and accurately detect vortex beams with dual OAM states.This study provides an effective method for directly generating frequency-degenerate OAM states of vortex lasers with arbitrarily adjustable weights and accurately detecting their OAM states.2.Nonlinear mirror mode-locked dual-wavelength vortex lasers.Dual-wavelength picosecond vortex lasers were directly generated in solid-state lasers based on nonlinear mirror mode locking.The eigenmodes of a cavity with a defect mirror were simulated using the Fox-Li numerical iteration method.Simulation results were consistent with experimental results.Experimental results show that both the frequency and orbital angular momentum of the fundamental wave can be converted to the second harmonic,and this process is reversible,leading to nonlinear positive feedback-initiated mode locking.The average output powers of the fundamental wave and second harmonic picosecond vortex lasers reached 2.6 W and 116 m W,respectively.The repetition frequency of the fundamental wave was 97.16 MHz,with a minimum pulse width of 23.4 ps and a corresponding maximum pulse energy of approximately 26.5 n J.3.High-power picosecond optical vortex array solid-state lasers.A high-power picosecond optical vortex array laser was constructed,where the optical vortex array was achieved by transverse mode locking using cavity point defect mirrors,and picosecond laser pulses were obtained through SESAM mode locking.Both experimental and simulation results demonstrate that transverse and longitudinal modes are simultaneously locked in the laser resonator,directly generating picosecond optical vortex array lasers within the resonator.The maximum output powers of the second-order and fourth-order vortex arrays were 3.7 W and 3 W,respectively,with pulse durations of 16.2 ps and 17.0 ps.The intensity distribution,interference pattern,phase distribution,and temporal evolution of the vortex arrays were theoretically simulated and matched well with experimental results.High-power solid-state picosecond optical vortex array lasers provide an ideal light source for applications such as particle manipulation,free-space optical communication,and nonlinear orbital angular momentum conversion.4.2μm self-Q-switched pulse optical vortex array Tm:YAP lasers.A compact self-Q-switched pulse optical vortex array laser with only three components was built based on the self-Q-switching characteristics of Tm:YAP crystals.The phase singularity number of the obtained vortex pulse vortex array can be tuned from 1 to 4.All self-Q-switched pulse optical vortex array lasers have high output power,high slope efficiency,and high single-pulse energy.The narrowest pulse widths of TEM₀₀,LG_0,-1,two-vortex array,three-vortex array,and four-vortex array were543,1266,1281,2379,and 1615 ns,respectively.Additionally,the intensity distribution,interference pattern,and phase distribution of vortex arrays with phase singularity numbers ranging from 1 to 8 were simulated.This study provides a method for realizing 2μm pulse structured light sources,which will have broad applications in optical trapping and manipulation,free-space optical communication,and laser medicine.