Research On Coherent Superposition Of Vortex Light And Reflection Of Vortex Light In Relativistic Space-tim

The emergence of the laser was a major advance in the history of human science and technology.The first LASER’s was manufactured by T.Meiman in 1960,which signifying the beginning of the"laser revolution".Laser-matter interactions have become one of the most cutting-edge and hottest research areas in this field.The invention of chirped pulse amplification technology has enabled the laser intensity to rise out of the flat type,and the laser focusing intensity of 10²³ W/cm² with pulse width in the order of femtosecond was obtained in the laboratory,providing extreme light field conditions for laser-matter interactions.Since then,the laser-plasma interaction has entered the field of nonlinearity.Vortex beams carry orbital angular momentum,which gives them greater advantages than ordinary beams in the fields of particle capture,material processing,and spiral electron beams generation,attracting much research interest.However,the intensity of the vortex beam produced in the conventional way is low.The coherent beam combining（CBC）technique is used experimentally to obtain ultra-intense vortex beams because it can break the limitation of the output power of a single laser.Meanwhile,spatiotemporal vortex light carrying transverse orbital angular momentum（OAM）was recently generated in the experiment,and many research work on its theory and application has emerged.When the intensity of spatiotemporal vortex light reached to relativistic intensity,we can predict the appearance of new nonlinear effects when interacting with the plasma.Recent studies have shown that spatiotemporal vortex light can be focused to subwavelength spatial scales and femtosecond pulse widths,possessing the ability to generate high-intensity spatiotemporal vortex light.Some plasma-based methods have also been proposed to obtain ultra-intense spatiotemporal vortex light carrying tilted or transverse orbital angular momentum.Motivated by the above achievements,in this thesis we explore the generation of ultra-intense vortex light fields and the relativistic spatiotemporal vortex laser plasma interaction.The corresponding results are given as follows:1.We theoretically propose a practical method to generate a high-power beam carrying orbital angular momentum by considering oblique incidence for the sub-vortex beams.A vortex beam field with relativistic intensity is observed in the common focal plane.The combined field generated in this scheme has ultra-high-intensity local spots,and the peak intensity is close to²₀,when all the sub-beams are perfectly coherent.Notably,most of the energy in the combined field is concentrated in high-intensity spots that remain spatially stable in the Rayleigh distance.The spatial distribution of the OAM in the combined field is similar to that of the incident Laguerre-Gaussian（LG）light.This vortex field with both OAM and strong spot distribution provides a new development opportunity for intense vortex laser–plasma interaction.The power-in-ring ratio in the synthetic field remains above 70%within the Rayleigh distance.The highest power-in-ring ratio is 88%at the focal plane.Even when the initial phase between the sub beams is not zero,the power in the ring ratio slightly decrease.In addition,we consider the influence of the random phase between the incident sub-beams on the combined field,owing to the inevitable phase fluctuation between the sub-beams in the actual experiment.It was observed that the intensity of the combined field presents a slightly discrete distribution,which is promising to play an important role in the field of large-scale nuclear fusion,such as suppressing stimulated Raman scattering and filamentation when a laser beam propagates in plasma.2.A novel deflection effect deviating the optical reflection law is revealed in the relativistic regime of intense spatiotemporal vortex laser plasma interaction,which makes an important addition to the beam reflection phenomenon.When a spatiotemporal vortex light with relativistic intensity is normal incident on an overdense plasma target,the reflected light deviates from the specular reflection direction specified by the reflection law with an appreciable deflection angle.The mechanism is demonstrated by two-dimensional particle-in-cell simulation as well as analytical modeling using the Maxwell stress tensor.It is intrinsically originating from the destruction of the rotational symmetry of the target,which is induced by the inhomogeneous stress exerted by the spatiotemporal optical vortex（STOV）beam on the target.A series of simulations show that using STOV beam with larger intensity,tightly focused spot and higher topological charge can enhance the deflection angle of reflected light,which provides parameter guidance for realistic experiments.This deflection essentially falls under the category of angular Goos-H?nchen effect.However,it is worth emphasizing that the deviation induced by STOV beam can even exists in normal incidence,revealing an essentially nonlinear effect.