Research On The Generation Mechanism Of Higher-Order Poincaré Beams Based On Solid-State Laser

In recent years,cylindrical vector beams with spatially non-uniform polarization and vortex beams with helical wavefronts have been extensively uesd as classical higher-order Poincarébeams in particle capture,optical communication technology,quantum technology,super-resolution imaging,biomedical and chemical detection applications.The cylindrical vector beams and vortex beams can be described at the equator and poles of the higher-order Poincarésphere,respectively.The output beam based on solid-state laser has high quality and good stability,but at the same time,there are some shortcomings such as the single type of higerh-order mode of the output laser,poor controllability of the mode,low optical conversion efficiency of the laser and complex structure of the laser.With the continuous development of technology and the demand for practical applications,higher-order Poincarébeams with controllable polarization states of high beam quality and polarization purity that can be freely switched between different orders are required.In response to the above issues,this thesis systematically studies the generation of order switchable higher-order Poincarébeams in solid-state laser cavities.The main research contents are as follows:（1）On the basis of Jones vector and Jones matrix theory,the mode modulation theory of higher-order Poincarébeams based on vortex half wave plates is researched.It is proposed to insert two quarter wave plates in the middle of the cascaded vortex half wave plates to achieve the addition and subtraction of the order of the vortex half wave plates;Furthermore,higher-order switchable cylindrical vector beam solid-state laser was designed and constructed,and its mode and dynamic characteristics were experimentally studied.The results show that by controlling the polarization state in the laser cavity,the arbitrary cylindrical vector beam with high mode purity and order switchable output can be obtained.When cylindrical vector beam with order of m=2 is output,its center wavelength is 1064.6nm,mode purity is 95.2%,and slope efficiency is 8.9%.This method provides new ideas for the generation of order switchable cylindrical vector beams and the research of cylindrical vector beam solid-state lasers.（2）On the basis of the above research,further research is conducted on the generation methods of order switchable cylindrical vector beams and vortex beams based on solid-state lasers.The insertion of Faraday rotators and other devices into the cavity achieved the free appearance of cylindrical vector beams and vortex beams,and was verified by the Dirac operator theory of Poincarésphere;Then an experimental device is built to directly generate cylindrical vector beam and vortex beam based on solid state laser.The center wavelength is1064.6nm.the slope efficiency of m=3-1 and m=3+1 order output beam is 12.5%and 10.2%respectively,and the mode purity is 95.7%and 94.8%.This method is the first to achieve controllable output of order switchable cylindrical vector beams and vortex beams based on solid-state laser.（3）An experimental setup for generating high-order nanosecond pulse Poincarébeams based on Q-switched solid-state lasers was constructed.Passive Q-switched pulse output was achieved using Cr⁴⁺:YAG crystals,and the output pulse characteristics of different order Poincarébeams were analyzed through experiments.The research results indicate that when the pump power is ranged from 4 W to 7.5 W,the pulse width of the m=3-1 order Poincarébeam decreases from 1.5μs to 415 ns,the pulse repetition frequency increases from 40k Hz to 227k Hz,and the single pulse energy decreases from 2.25μJ to 1.57μJ;When the pump power is ranged from 5 W to 7.5 W,the pulse width of the m=3+1 order Poincarébeam decreases from 1.5μs to 590 ns,the pulse repetition frequency increases from 38k Hz to135k Hz,and the single pulse energy decreases from 3.15μJ reduced to 1.85μJ.