| The light intensity of the vortex beam is distributed in a ring shape.The central light intensity is zero and the phase is spirally distributed.It carries orbital angular momentum during the propagation process,and the vortex beam has a strong long-distance propagation stability.There is no heat loss when manipulating particles and other characteristics,so the vortex beam provides different methods and approaches for space optical communication,physical mathematics,optical calculation and optical information processing.Due to the wavelength sensitivity of optical vortex converters,researchers focused on the(quasi)continuous wave field in previous studies on vortex beams.However,in recent years,people have made great developments and progress in the field of ultrafast optics,which has led to a lot of related research on the combination of vortex beams and time-domain control technology to generate vortices with ultra-short pulses.Ultrafast vortex has the advantages of both ultra-short pulses and vortex beams.It has both high energy density and orbital angular momentum.Therefore,the generation of ultrafast vortex helps people study physics experiments under high intensity field conditions,and ultrafast vortices can also bring new degrees of freedom in the interaction of light and matter.At the same time,ultra-short vortex pulses have huge potential in the fields of ultra-fast physics and chemistry,ultra-fast nonlinear spectroscopy,and precision machining,which opens up new application prospects for vortex beams.Therefore,we have carried out related research on the ultrafast vortex laser in the visible band in this thesis.The research work mainly includes the following parts:(1)Analyzing the mode theory of the laser resonator cavity,and using Matlab software to simulate the cavity mode and mode superposition;(2)Experimental studies of a continuous wave high-order vortex laser Pr:YLF crystal were carried out.A high-order HG0,120 mode was obtained for Pr:YLF crystal at 639 nm of red light,combing with the operation of off-axis pumping operation and rotating output mirror.By placing a pair of cylindrical lenses outside the cavity and using a suitable focusing lens to focus the output HG spot to meet the mode matching conditions of the cylindrical lens conversion,the corresponding LG0,120 mode was obtained;(3)Experimental studies of a Q-switched high-order vortex laser of Pr:YLF crystal were carried out.For the Pr:YLF crystal,a V-cavity structure was used,and Co:ASL was used as the saturable absorber to obtain a Pr:YLF passive Q-switched laser.The maximum average power,shortest pulse width,maximum pulse energy and peak power of Q-switched laser were 230 mW,158 ns,2.5 ?J and 17 W respectively,and the Q-switched performance was stable in the experiment.Using the same operation as the continuous wave laser,that is,off-axis pumping combined with a rotating output mirror,a HG0,12 mode of up to 12th order under Q-switched operation was obtained,and the LG0,12 mode was also obtained by means of extra-cavity conversion;(4)Experimental studies of a Pr:YLF crystal passive mode-locked laser were carried out.In the experiment,we used a Pr:YLF crystal as the laser gain medium,used a double-end pumped X-cavity type,and used a graphene saturable absorbed mirror to obtain a deep red optical mode-locked pulse.And no large-period modulation envelope was observed in the detected pulse sequence during the experiment,indicating that the system was in a stable continuous wave mode-locked state rather than a Q-switched mode-locked state,and the single pulse width of the mode-locked pulse was 73.4 ps,the fundamental frequency signal-to-noise ratio was 46dB,which proves that the system was in a stable mode-locked state;(5)Experimental studies of Pr:YLF crystal deep red ultrafast vortex were carried out.After obtaining the mode-locked pulse in the above experiment,the ultrashort pulse vortex was obtained by adjusting the tilt angle of the cavity mirror.The signal-to-noise ratio of the fundamental frequency was 42dB.Since the loss will be introduced in the process of fine-tuning the cavity mirror,it was slightly wider than the single-mode pulse width of the above experiment.In addition,in order to verify the spiral phase of the obtained vortex beam,a simple homemade Fizeau interferometer was used to verify whether the obtained vortex beam has a spiral wave surface.Using a plano-concave mirror,spherical wave and plane wave will be generated respectively after passing the test beam through the lens,and the position and tilt angle of the lens are continuously adjusted so that the two light waves can interfere well and a clear spiral can be obtained in the CCD Interference fringes.In the experiment,chirality of the LG mode remained stable.In addition,the chirality of the vortex can be controlled by translating the laser crystal.This is the first time in the world that an ultrafast vortex laser in the visible band has been realized directly from the resonator. |
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