Generation Of Structured Light Fields And Their Nonlinear Effects

Constructed light fields are special light beams with special amplitude,phase,polarization,spatial coherence and orbital angular momentum.In actual applications,the structured light fields exhibit special characteristics in the process of optical propagation and transformation,as well as nonlinear effects.For example,partially coherent light beam,a special kind of constructed light field,has advantages in eliminating speckle and improving the image quality.The orbital angular momentum carried by the structured light field will be used in the field of manipulation of particles and optical trapping.In the process of laser material processing,the unique shape of constructed light fields make them more advantageous.Moreover,the unique phase distribution of the structured light fields also make their nonlinear effects be more scientific research value.The main contents of this thesis are listed as follows:1.We generate a stochastic electromagnetic beam(SEB)with complete controllable coherence,that is,the coherence degree can be controlled independently along two mutually perpendicular directions.We control the coherence of the SEB by adjusting the phase modulation magnitude onto two crossed phase-only spatial light modulators(SLM).We measure the light beam's coherence properties using Young's interference experiment,as well as the beam propagation factor.It is shown that the experimental results are consistent with our theoretical predictions.2.We theoretically and experimentally study the generation of non-uniformly correlated stochastic electromagnetic beams(NUC-SEB).Based on the relation between phase correlation and optical coherence,we investigate the 2 × 2 cross-spectral density matrix and the coherence distribution of the NUC-SEB.We employ two crossed SLM to modulate the phase distribution of two polarization directions.The coherence distribution is measured by Young's two-pinhole interferometer.It is shown that the coherence degree between two points in the generated light beam is found to be dependent on not only the distance between them,but also on the position of two points.The experimental observations are in agreement with our theoretical analyses.3.We demonstrate a new kind of laser,called as a partially coherent digital laser,producing non-uniformly correlated partially coherent light(NUC-PCL)beams by “playing a video” inside the cavity directly.In this laser,a spatial light modulator(SLM)with dynamic phase modulation acts as a cavity mirror.The coherence degree distribution of the output beams can be controlled simply by varying the waists of the computer-generated holograms on the SLM.The experimental results show that the coherence degree between two points is not only dependent on the distance between them,but also on the positions which are observed across the beam.4.Optical vortex amplification up to the joule level using flash-lamp-pumped Nd:YAG amplifiers has been demonstrated.In experiment,vortex seed pulses are converted from a spiral phase plate(SPP)and amplified with two Nd:YAG amplifier stages.A maximum output energy of optical vortex up to 995 mJ has been achieved with pulse width about 10 ns,corresponding to an amplification factor of 295%.A maximum second-harmonic energy up to 470 mJ is generated from the amplified vortex output by using a KD*P crystal.5.Radially polarized laser beam amplification up to the 772 mJ using flashlamp-pumped Nd:YAG amplifiers is demonstrated.In experiment,a nanosecond radially polarized seed beam is converted from a polarization converter and then amplified with two Nd:YAG amplifier stages.A maximum amplification output energy up to 772 mJ was achieved with pulse width about 10 ns,and repetitive rate at 10 Hz,corresponding to an amplification factor of 323%.Excellent conservation of polarization was also obtained during the amplification.6.We investigate the stimulated Brillouin scattering(SBS)properties of light beams carrying orbit angular momentum(OAM).The phase conjugation of light beams carrying OAM is experimentally achieved in an SBS mirror with a random phase plate.The spectrum and the pulse width compression of SBS light are measured.It is shown that the phenomena of pulse compression is observed and OAM conservation is confirmed in the SBS process.