Laser Transmitting And Receiving System Aberrations And Obscuration

In laser engineering system,there are two purposes for beam control.On the one hand,it can increase uniformity of intensity distribution characteristics of laser beam in the near field, or the beam speckle intensity may destroy the optical component.On the other hand,it can improve energy concentration in the far field,raise power density on the target,enlarge range of action,and propagate most of the energy on the target.Wavefront phase aberration in the near field was the biggest factor,which influences the beam quality in the inner optical system, furthermore,intensity distribution of the beam,including obscuration of secondary mirror of telescope,can also affect the beam quality.In this paper,primarily work was done on the factors affecting beam quality in the inner optical system,taking real laser engineering system into account.Firstly,the effects of peak-to-valley value(PV value)of some phase aberrations and the diameter(d) of optical component on beam quality were studied.Secondly,researches on obscuration were made, which were matching problem of Cassegrain Telescope system and laser beam parameters and the effects of all the factors of the obscurations on image quality in multibeam laser illumination system of laser launched and received in common aperture.In detail,it was divided into three parts:(1).the models of spherical aberration,astigmatism,defocussing and tilt in x direction were built.Numerical computation was made with MATLAB software,and the effects of PV value of the phase aberrations and the diameter(d) of the optical component on the beam quality factor(β) and Strehl Ration(SR) were obtained.(2).The propagation model of beam was built in the inner optical system.Matching problem of Cassegrain Telescope system and parameters of laser was discussed,the diffraction irradiance distribution of a Gaussian spreading beam which propagated through an annular aperture was deduced.The relationship between the parameters of laser and characteristics of focus spot(peak intensity,SR,normalized power,and average power) were studied.Then,the parameters of laser beam and laser system in some real experiment were analyzed,and different optimal spreading magnitudes were achieved corresponding to different characteristics in the far field,which were the highest peak intensity,the biggest SR, normalized power and average power.Finally,a method was put forward to decrease energy loss beacause of the obscuration of the secondary mirror,and simulation was done to find out its feasibility.(3).All kinds of factors of obscuration acting on image quality were studied in multibeam laser illumination system of laser launched and received in common aperture.The aperture factors to get the best image quality were discussed.According to the research on the effects of spherical aberration,stigmatism,defocussing, and tilt in x direction on beam quality in the inner optical system,the influence of typical phase aberrations to SR andβwere obtained.And the results could be used in designing process of optical component.After research on matching problem of Cassegrain Telescope system and parameters of laser,the relationship between the parameters of laser and characteristics of focus spot were deeply understood.In order to get different charactistics of focal spot,different spreading magnitude should be chosen.The method to decrease energy loss was confirmed,but at the same time,it also brought in peak intensity fall and beam spreading,so it had its prospect in laser illumination system.The conclusion got from the research of multiple laser illumination system of laser launched and received in common aperture could be used to guide the decision of number and positon of obscuration in laser engineering system.