Generation Of Structured Light Fields And Intracavity Optical Modulation

In the spatial domain,constructed light fields can be obtained by modulating the characteristic parameters such as amplitude,phase,polarization,spatial coherence and orbital angular momentum of the light fields.Many unique properties of the constructed light fields have great advantages in practical applications.For example,the structured light field with unique coherence distribution has obvious advantages in eliminating speckle and reducing intensity scintillation during propagation through turbulence.The special spatial polarization distribution of vector beam ensures better effect in laser processing.Vortex beam with orbital angular momentum has important scientific research value in optical manipulation,super-resolution imaging and so on.With the extensive research and application of structured light fields,there is an increasing demand for the generation and performance of the structured light field.Since lasers can achieve laser output with high beam quality,there is a great research potential for obtaining structured light fields with different properties by modulating the laser light field.This academic dissertation includes the following research work on multi-parameter joint regulation of light field:1.Based on the relation between phase correlation and optical coherence,we theoretically and experimentally investigate the generation of radially polarized partially coherent beam with non-uniform correlation structure and complete controllable coherence.The incident coherent Gaussian beam is modulated by a phase-only liquid crystal spatial light modulator(SLM)with dynamic random phase modulation.With the help of a radial polarization converter,radially polarized partially coherent beam is obtained.The coherent distribution of the generated partially coherent beam is experimentally measured.The measurement result verifies the non-uniform correlation structure of the partially coherent beam generated.Additionally,the effects of the phase control on the coherence and the intensity distribution are analyzed.The results show that the coherence of the beam can be adjusted and the beam intensity distribution can be shaped effectively by changing the Gaussian modulation half-width of the dynamic random phase.2.Based on the above method of generating partially coherent beam,another method is proposed to control the coherence of the two orthogonal polarization components of a partially coherent beam.Different regions of the SLM are used to conduct anti-Gaussian phase modulation on the orthogonal polarization components of a radially polarized beam.Radially polarized partially coherent beam is generated with the help of a non-polarized beam splitter.The experiment result verifies that the coherence distribution of radially polarized partially coherent beam was also non-uniform correlation structure and the coherence of orthogonal polarization components can be regulated respectively.The effect of the anti-Gaussian random phase modulation on the intensity distribution is also analyzed.3.Based on the theory of transverse mode selection in cavity,we propose a dual-cavity digital laser based on an intra-cavity SLM for on-demand mode selection and polarization control.We experimentally employ a SLM as the back mirror of a dual-cavity resonator.We digitally control and switch lasing modes with desired linear polarization by switching different phase pattern imposed on the SLM.The two resonators are controlled to simultaneously generate the Hermite-Gaussian modes(HG modes)of orthogonal polarization,and vector polarized beams are obtained by coherent superposition of the two HG modes.4.Further,we experimentally employ a SLM as the folding mirror to construct a V-folded digital laser.HG modes with desired mode orders are selected in the cavity by switching the phase pattern imposed on the intra-cavity SLM.With a /2 astigmatic mode converter outside the cavity,the corresponding Laguerre-Gaussian(LG)beams carrying orbital angular momentum(OAM)are obtained.The special design of the V-folded cavity realizes the flexible control of the mode size in the cavity,meanwhile,avoiding the damage of the SLM and the limitation of crystal size on the high-order modes.Thus,HG modes with a wide adjustable range of mode order are generated,and then high purity LG beams with corresponding OAM from to are obtained with the help of the mode converter.