Study on the Manufacturing and Key Technology for KDP Crystal Using IBF Method

Author:Li Fu Ren

Supervisor:jie xu hui


Degree Year:2018





KH2PO4(KDP)crystal is a key nonlinear optical element used in laser system.It can achieve two times and three times conversion of laser frequency.KDP crystal has special physical and chemical properties:such as soft,high sensitive to temperature,easy to absorb moisture in the air and produce deliquescence.The laser system has very strict index demanding for the processing quality of KDP crystal.The KDP crystal should be larger than 400 mm.The surface frequency error after processing should be controlled below a certain level.No processing defects such as scratch,damage,and so on after processing.The special physical and chemical properties of KDP crystals and the strict processing index of laser system require high challenges to the existing processing technology.High accuracy and high quality of KDP crystals,especially large diameter KDP crystals,is today’s hotspots.Ion beam figuring process is a new high precision polishing technology at present.It has the advantages of non contact,no pollution and high accuracy.It is very proper to manufacturing KDP crystal.But during ion beam figuring,the temperature of KDP crystal increases because of the ion beam bombardment.It is easy to cause thermal damage of KDP crystal.This paper takes a full study on the manufacturing process of KDP crystal using IBF method.Based on the temperature gradient error control,the ion beam large step scanning method is proposed in order to solve the thermal damage problem of KDP crystal.The ion beam processing technology was introduced into the KDP crystal processing technology.The main research work of this paper contains the following contents:1.The processing possibility analysis of KDP crystal using IBF method.In this paper,the temperature change during ion beam figuring is accurately measured.It is proved that the structure of KDP crystal will not change during IBF processing.Through actual experiment,the heat deposited on the work piece and the heat scattering coefficient of the work piece in the vacuum chamber are obtained.It provided the basis for the modeling of temperature field in the figuring process.The mechanism of heat damage in KDP crystal is analyzed.The thermal damage criterion is given.The damage of KDP crystal in the process of IBF is effectively prevented.It provides the basis for the subsequent processing of KDP crystal using IBF method.2.Research on the medium and high frequency error and surface quality evolution characteristics of KDP crystal.The surface roughness and frequency error of KDP crystal are the key indicators that affect the surface quality of KDP crystal.This paper focuses on the evolution rule of the surface roughness of KDP crystal during IBF processing.Large diameter IBF processing and heavy ion bombardment of KDP crystal is proposed in order to remove the surface frequency error.The KDP scratching defects can be removed by IBF processing.The protection method in the process of KDP crystal is given,which provides the basis for the ion beam process of KDP crystal.3.Study on the cleaning and figuring technology for KDP crystal using IBF.The key technology of IBF processing KDP crystal is studied in this paper.The accurate removal efficiency of KDP crystal was achieved by material comparison method and ion beam interrupted bombardment method.The large scanning process is proposed to solve the thermal damage problem.Finally,a new dwell time method based on the surface error is adopted to achieve the high precision figuring of large diameter KDP crystal.4.Study on the composite processing theory of KDP crystal.The processing of KDP crystal requires a variety of processing techniques in order to meet the requirement of laser system.This paper briefly analyzes the SPDT technology,MRF technology and IBF technology of KDP crystal.The advantages and disadvantages of different processing method are discussed.A combined processing method is proposed to realize the rapid convergence of KDP crystal.The high precision and high quality processing of KDP crystal is realized by the combined processing method.Through the study of this paper,we introduce the IBF method to achieve the manufacturing of KDP crystal.This work provides effective technical support for the processing of the key optical component in laser system.It also provides an effective reference for the processing of other soft brittle crystal.