| High-power laser is an important way to research inertial confinement fusion,weapons physics, astrophysics, solid-state physics and so on. In order to achieve high-power density laser in the focal point, multi-beam lasers with short or super-shorttime duartion are focused in the target point. The success of such physicalexperiments are determined by thre presise coupling between multi-beam laesers andthe target. The techniques of mearuing and positioning focal spots for long pulses arenot suitable for super-short pulses, where smaller spots will be utilized and higher-presion detections are essential. For soving the problem, the positioning of small-scale focal spots are studied in this dissertation, which focus on solving the two mainproblems existing in this technology, i.e.: how to measure the centroid position ofsmall focal spot with high accuracy and how to achieve precise control of the smallfocal spot position.Limited by the dimension of one single pixel, general techniques for thedetection of focal spots based on CCD are unable to measure spots of micromter scale.A method of high-presion detection based on scaning imaging of CCD is proposed.In this method, a CCD is moved by PZT when imaging. The model providestheoretical support for experimental study of Chapter3and Chapter5. Using thismodel, the centroid position and the intensity distribution of the small-scale focal spotare studied numerically. The measurement of spots of ideal Gaussian distribution,Gaussian distribution with noise, the Gaussian focal spot with gauss-modulated, andthe irregular focal spot are simulated. The simulations prove the feasibility of themeasurement of small scale spots via this method. Experimental research shows thatthe error is less than0.9μm for the spots with the dimesion of10μm. Besides, anenhancement algorithm for the small-scale focal spot measurement is proposed. Inthis method, maximize the use of the information acquired from the neighboringpixels to reduce the scanning step geometrically and shorten the measurement time.Presise focusing is the premise of positioning for small-scale spots. In order toavoid the dispersion and nonlinear effect produced by beam propagation through thefocusing elements, off-axis parabolic (OAP) mirror focusing system is employed inshort pulse laser focusing. In order to realize the precise control of the position ofsmall-scale focal spot, the optical simulation model of the OAP mirror focusingsystem based on ray tracing method is established. The influences of the focusingcharacteristics of short pulse laser’s focal spot have been analyzed by simulating theprocessing of beam propagating and focusing. The data and conclusion obtained bythe simulation provide a necessary fundamental theory for the optical design, optical assembly and control flow design of the OAP mirror focusing control system. Theresults prove that the characteristics of the focusing of OAP mirror is very sensitiveto the detuning angle of the incident beam, while that is not so sensitive to thedivergence of the input beam.The off-axis parabolic mirror focusing control demonstration system isestablished according to the theoretical analysis results. This system follows theintegal removal technique of the optical path to the control the focal spot position.Using two mirrors linkage adjusted to achieve the overall optical path translation.And the collimated optical detection unit is established. This system is valid forachieving precise positioning for the focal spot. The results show that the focal spotposition control accuracy of the system is better than1μm.
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