Research On The Femtosecond Four-wave Mixing And The Generation And Modulation Of Novel Ultrafast Singular Light Fields

Ultrafast lasers have been intensively studied owing to their ultrafast and ultra-intense properties and have been widely used in many fields such as materials science,chemistry,biology and physics.With the in-depth research and expanding applications of femtosecond ultrafast light fields,some ultrafast light fields with special modes and polarizations,such as ultrafast vector,vortex light fields,present unique properties and advantages in many applications,which in turn receive more and more attention.The combination of ultrafast lasers and singularity light fields,such as vortex,vector and spatiotemporal vortex light fields will further promote the development and application of ultrafast lasers.In this dissertation,by multi-dimensional modulation of the spectra,energies,spatiotemporal structures,phases and polarization of the two-incidence optical fields in femtosecond cascaded four-wave mixing(FWM),novel multicolor femtosecond ultrafast optical fields containing multiple dimensions of frequency,pulse duration,spatiotemporal structure,orbital angular momentum and polarization,including novel ultrafast singularity beams such as multicolor concentric annular ultrafast vector beams(MUCAU-VBs)and multicolor concentric annular ultrafast vortex beams(MUCU-VBs),are constructed.Furthermore,the fundamental properties of the generation,propagation and diffraction of ultrafast spatiotemporal vortex light fields are also studied.These novel ultrafast singularity light beams have potentially important applications,such as ultrafast optical tweezers,microparticle manipulation,super-resolution microscopy,novel ultrafast spectroscopy,chirality detection and optical communication.The main works and achievements are shown as follows:1.Multicolor concentric annular ultrafast vector beams(MUCAU-VBs)are generated in H-ZLAF90 glass plate using cascaded FWM.Up to 10 frequency up-conversion concentric annular radially polarized sidebands are obtained simultaneously.The spectral range of the first 7 order sidebands are extended from545 nm to 725 nm.The pulse duration of the first order sideband is 74 fs.The polarization transfer property from the pump beams to the generated sidebands is proved.The multicolor sidebands are simultaneously manipulated in the polarization state,temporal,spatial,and spectral domains.The method can be extended to generated MUCAU-VBs in other wave ranges,such as ultraviolet,deep ultraviolet,infrared,mid-infrared.2.Multicolor concentric ultrafast vortex beams(MUCU-VBs)are generated in an yttrium aluminum garnet(YAG)plate using cascaded FWM.The topological charges(TCs)of the sidebands can be controlled by changing the TCs of the pump beams.Nine frequency up-conversion concentric annular vortex sidebands can be generated,where the spectra of the first 6 sidebands extend from 550 nm to 750 nm.The generated multicolor sidebands can be manipulated in orbital angular momentum(OAM)state,temporal,spatial,and spectral domains simultaneously.The method can also be used to generated MUCU-VBs in other wave ranges.3.The amplification of ultrafast laser pulses with different spectral bandwidths are analyzed.Signals with broader spectral bandwidths can be obtained using seeds with narrow or broad spectral bandwidths in a YAG plate using FWM.Not only the seed energy is increased but also the spectral bandwidths are extended in the FWM processes.The generation of broad signals using narrow band seeds can be explained using “ping-pong FWM”.We provide a new method to generate broadband ultrafast laser pulses.4.The properties of the generation and propagation of spatiotemporal optical vortices(STOVs)are analyzed step by step based on diffraction theory.STOVs can be generated in the far-field when spiral phase mask is placed in the Fourier plane of the4 f pulse shaper.In the near-filed,the wavepackets have multi-lobe structures,and they evolve into STOVs during propagation.For STOV with topological charges of n,there are n holes in the wavepacket.Furthermore,by using a π-0-π phase mask,it may be possible to generate l = 2 STOV in the near-field.5.The diffraction properties of lights with transverse OAM are analyzed theoretically and experimentally.The diffraction patterns of STOV pulses that were diffracted by a grating exhibit multi-lobe structures with n + 1 lobes and n gaps.The gap number corresponds to the topological charge of the STOV.The diffraction rules of STOVs are revealed.A novel approach for the fast detection of STOVs is provided using their special diffraction properties.