Research On Nonlinear Temporal-spatial Evolution Of Sinusoidal Phase Modulated Laser

Smoothing by spectral dispersion (SSD) is employed to smooth the laserirradiation in high-power solid lasers and its effectiveness can be affected bynonlinear effects because of some special modulation induced by its discretespectrum. In the paper, the spatial evolution dependent on the time period of thesinusoidal phase modulated laser from SSD is investigated theoretically andnumerically when the modulated laser is affected by the small-scale self-focusing(SSSF).The main research contents of the paper are provided as below:1.The smoothing effect of diffraction effect in near field using SSD isinvestigated. Numerical simulation results verify that the diffraction effect can besuppressed by SSD availably. Sinusoidal phase modulated laser is under the control ofthree parameters which are the modulation depth and modulation frequency ofelectro-optic crystal (E-O) and the dispersion coefficient of grating. The effect of eachparameter on the smoothing preference of SSD is examined respectively. Simulationresults show that the uniformity of sinusoidal phase modulated laser can be improvedby enlarging the modulation depth, modulation frequency and the dispersioncoefficient.2.The uniformity and time-dependent intensity distribution of sinusoidal phasemodulated laser under different color cycles are examined. Theoretical analysis andnumerical simulation results indicate that bigger color cycles will enhance the growthof spatial modulation from SSD and degrade the uniformity of laser beam. Spatialmodulation from SSD grows exponentially with nonlinear length in Kerr mediasimilar to noise, but the gain spectrum which is used to illustrate the growth of noiseis not suitable to spatial modulation, so the spatial intensity distribution of spatialmodulation varying with nonlinear length is deduced according to Schr dingerEquation. The propagation of sinusoidal phase modulated laser is simulated accordingto Schr dinger Equation to verify the correctness of theoretical derivation. Thesimulation results show that the optimum uniformity of sinusoidal phase modulatedlaser can be achieved with one color cycle.3.The effects of bandwidth and integration time on the uniformity of sinusoidalphase modulated laser are also investigated. A broad bandwidth can obtain uniformlaser irradiation. The optimum uniformity of laser beam with SSD can be available when the integration time is larger than a modulation period of laser beam. So thebandwidth and integration time is important to uniformity of laser beam, andSelecting Proper Parameters is necessary.