Research On Agility Control Technology Of Laser Beam By Using Phase-only Liquid Crystal Spatial Light Modulator

Laser beam agility control technology researches the variation law andcontrollability law of laser beam’s splitting number, shape distribution, energydistribution. Splitting number, shape distribution, energy distribution， pointorientation and focus position of an incident laser beam can be programmablecontrolled by using the technology without mechanical-inertia, in which thecharacteristic (i.e. Energy concentrated, good directional and good coherence) of alaser is fully utilized. It has been applied in many fields and is showing greatpotential applications.The key of this technology is the design of phase distribution loaded onto aspatial light modulator, which makes the splitting number, shape distribution,energy distribution，Point orientation and focus position of a modulated laser beamcontrolled as expected. However, so far, laser beam agility control technologybased on liquid crystal spatial light modulator still exist the following two problems:First, how to dynamically realized that a incident laser beam is split into multiplelaser beams and focus spot of each of the beams can be independently programmedto move as expected in3D space domain without other significant "ghosting spot"and "noise spot". Second, How to make each of the beams tailored into arbitraryintensity distribution as expected in far-field with high accuracy and highdiffraction efficiency.Intend to solve the above two problems, the dissertation make the relevanttheoretical and experimental researches, as follows:First, in order to solve the first problem, a phase distribution design methodbased on multiple independent iterations plane is proposed. And then, necessarytheoretical simulations and preliminary experimental validations of the proposedmethod are conducted. Far-field is divided into the work area and the noise zone, atthe same time, spectral bandwidth of the phase plane is limited, which arecombined to suppress the "noise spot" in the work area. Phase distribution splicingmethod is adopted to form the phase distributions for multiple beam independentcontrol, thereby, the "ghosting spot" and "noise spot introduced by the phasemultiple distributions’ superposition can be avoided and suppressed.Second, in order to solve the second problem, an adaptive weight optimizationphase distribution design method is proposed for far-field variable shape or variablecaliber flat-top beam shaping. And then, necessary theoretical simulations of theproposed method are conducted. Root mean square error (RMSE) and thediffraction efficiency (DE) of the shaped intensity distribution are used as evaluation criteria during the adaptive weights optimization process of the methodfor beam shaping, which not only greatly reduces fluctuations of the shapeddistribution, but also keeps high diffraction efficiency.Then, in order to further enhance the beam shaping capabilities, which canshape the intensity distribution of incident laser beam into arbitrary desired shapeintensity distribution, a double phase distributions cascade design method, whichcan independently code the amplitude and phase the controlled wave-front, isproposed. And then, necessary theoretical simulations of the proposed method areconducted. This method is different from the conventional phase retrieval algorithm,it has two-phase iterative plane, the first phase iterative plane determines theamplitude distribution of the controlled wave-front, the second phase iterative planedetermines the phase distribution of the controlled wave-front, thus avoids thedrawback of traditional phase retrieval algorithm, in which only amplitude isoptimize as expected but the phase can not be controlled. Because the amplitudeand phase of the controlled wave-front can be independently coded, the method canshape the Gauss intensity distribution of incident laser beam into arbitrary desiredshape intensity distribution with high accuracy on the target plane.Finally, experimental setup is established. Using the above proposed threemethods to design phase distributions, the design phase distributions are loadedonto a phase-only liquid crystal spatial light modulator for the experimentalverification of each above methods. Experimental results consistent with thetheoretical simulation, which further proves the feasibility and correctness of theproposed methods.