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Study On Influence Of Optical Components' Mid-High Frequency Parameters On High Power Laser System And Measurement Technology

Posted on:2020-02-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:H RenFull Text:PDF
GTID:1362330602961004Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
In order to achieve controlled thermonuclear fusion,many countries have started the development of high-power solid laser driver.With the increasing power of the device,the influence of the mid-high frequency parameters of the optical components on the performance of the device has become increasingly prominent,and the evaluation and detection methods of the traditional low frequency parameters have been unable to meet the demand.Here,the mid-high frequency parameters refer to the surface defects ranging from microns to millimeters(such as scratches and pits)and the wavefront errors whose space periods range from 0.12mm?33mm.This paper studies the influence of surface defects on the typical positions of optical components and transmission position of beam,shallow scratch measurement,wavefront data preprocessing,and the key technology to improve the calculation precision of the mid-high frequency Power Spectral Density(PSD).The main contents and results are as follows:1)In view of the fact that the beam quality will be destroyed by surface defects,and the thermal image effect will lead to subsequent component damage,the nonlinear paraxial wave equation is proposed and deduced as the basic equation,in order to study the beam diffraction,self focusing and thermal imaging in laser amplifiers.The small-scale self focusing B-T theory is imported.The split-step-Fourier transform is used to solve the propagation behavior of beams in nonlinear media.2)The split-step-Fourier transform is adopted to solve the nonlinear paraxial wave equation,and the light field transmission model of scratches and pits are built.Under the conditions of the scratch parameters(length,width and depth)or pits parameters(diameter and depth)change,the intensity distributions inside of optical element,the beam near-field,the different distances behind the component and the beam far-field are calculated separately.The results indicated that the defect parameters,especially the width and depth,should be strictly limited according to the system design,so as to ensure the light-throughput and safe operation of the system,and to guarantee the quality of the near field and far field mass of light beam.3)Reason why there is a big difference between the results of artificial visual and microscopic dark field imaging quantitative measurement method for scratch are analyzed.Combined the measurement results of optical profilometer.According to the measurement results of optical profilometer,it is clear that the shallow scratch detection of depth less than 25nm is the main reason for the difference of the results,and the difference in the calculation method of spot scratch length is the secondary cause of the difference of the result.On this basis,the influence of the background intensity of flaw image on feature extraction of the weak scratch is studied.A method for quantitative measurement of shallow scratches based on image background suppression technique is proposed and verified experimentally.Besides,functional upgrades for the data analysis software of the existing defects quantitative detector are made,thus the problem of weak scratch measurement is solved.4)The algorithm and measurement technique of mid-high wavefront PSD in optical components are studied.A preprocessing specification for wave surface data is set up.The bilinear interpolation method is used to fill the invalid data in the rectangular calculation area and the chamfer area.Background correction of transmission wavefront data depends on the relative value of the wavefront PSD of the components and the measurement device,as well as the deflection distance of the beam.The reflected wavefront error needs to be corrected by space period transformation according to the use angle.In addition,the reason why PSD of wavefront data obviously changes after using Hanning window in spatial data is analyzed.The proportion relation of rms of PSD before and after windowing is deduced,and the data after windowing is corrected reasonably.5)Aiming at the two key factors affecting the measurement accuracy of wavefront PSD,the aberration processing for rectangular aperture optical components and the wavefront spurious fringe,an algorithm based on least square fitting for wavefront aberration of rectangular aperture is proposed,which avoids the limitation of Zernike orthogonal fitting for circular aperture and guarantees the accuracy of wavefront measurement data for the large length-width ratio rectangular components.From the mechanism of production of interference spurious fringe,a multi surface interference technique based on wavelength shifting is proposed,and successfully extracted the information of the front and rear surface profile,thickness and inhomogeneity.The parasitic fringe suppression technique based on angle matching is established,which suppresses the parasitic fringe in the transmitted wavefront effectively.As a result,the measurement of large aperture plate with high parallel becomes much simpler and more convenient.The research results have been used for the detection of large aperture optical components in SG-? laser device,which fills the blank of the high precision detection field of the wavefront PSD of the plane optical components in China.
Keywords/Search Tags:high power laser system, mid-high frequency, surface defects, wavefront PSD, dark field scattering, interference
PDF Full Text Request
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