【作者】 陈文学；

【导师】 龙兴武； 张书练；

【作者基本信息】 国防科学技术大学 ， 光学工程， 2013， 博士

【摘要】 通过采用光回馈技术，激光回馈在谐振腔外部实现了对激光器输出光的强度、偏振态和相位等的控制，即通过激光器外部条件的改变，研究激光器的“内部”性质。对激光回馈的研究，丰富了激光物理的研究内容。激光各向异性回馈同时调制激光器输出的正交偏振光的强度和偏振态，属于二维矢量回馈，其丰富的研究内容是激光回馈的重要分支。回馈光携带有外部物体的信息，通过分析激光器的输出光特性，可解调出物体的相位延迟和位移等信息，据此可将激光回馈技术应用到精密测量领域。论文在前人工作的基础上，系统研究了各向异性回馈现象，建立了新的各向异性回馈理论模型，将一些各向异性回馈现象仪器化，并应用到工业生产检测中。论文的主要工作总结如下：发现了激光双折射回馈偏振跳变锁定现象，即当回馈腔中光学元件的各向异性较小时，将观察不到偏振跳变现象。锁定现象的存在，大大限制了激光各向异性回馈的应用。论文中基于Lamb半经典理论和三镜腔理论，建立了一个新的理论模型，该理论模型不仅解释了偏振跳变现象，而且揭示了锁定现象的物理本质。基于新理论模型的分析结果，通过增大激光器相互正交两偏振态频差，减小模竞争的方法消除了偏振跳变锁定。实验结果表明，当1级玻璃放入回馈腔中时，观察到偏振跳变现象。锁定现象的消除，大大拓展了测量的范围。分析了激光各向异性回馈时偏振跳变点位置与各向异性大小的关系，确立了两者严格的数学关系，并基于该关系，测量了一套波片。与其它相位延迟测量仪的测量结果比对表明，两种仪器的测量偏差小于0.5o。在消除锁定现象和建立偏振跳变点位置与各向异性大小关系的基础上，设计了满足工业化要求的光学、机械、电路和算法系统，完成了相位延迟测量系统的仪器化。并请相关领域人员，测试了仪器性能，形成了测试报告。测试结果表明，仪器的测量重复性优于0.05o，开机复现性为0.019o，测量范围0o-360o。发现波片表面的干涉效应影响相位延迟测量准确度，表现在波片测量过程中倾角的微小变化，将给相位延迟带来大到8o左右的变化。针对此问题，设计了一套消干涉机构。通过在波片表面涂覆折射率匹配液，加单面镀增透膜K9玻璃等措施，减小了波片表面的反射光，消除了干涉效应的影响。激光各向异性回馈系统所用光源是单波长光，而波片在生产中常常需要知道很多波长下的相位延迟量。为此，通过实验数据，拟合出经典色散方程Sellmeier公式的相关系数。拟合结果表明，在340nm1541.4nm波长范围内，折射率计算精度优于10-5。基于不同波长下折射率计算结果，通过多波长转化和标定的方法，实现了对所有波长相位延迟量的测量。温度影响波片的相位延迟量，设计了波片测量中的温控系统，可对波片精确控温。基于激光各向异性回馈的波片相位延迟测量仪已经应用到工业测量中。福建福晶科技股份有限公司（CASTECH）和福州通产光电技术有限公司已将该仪器应用到波片生产过程中的在线检测。北京人工晶体研究所用该仪器测量了KN晶体的相位延迟量。（见附件仪器应用证明）材料的内应力可表现为双折射效应，大小正比于内应力，通过测量双折射可反映出应力的大小。材料的内应力很小，传统的仪器只能定性检测。激光各向异性回馈在消除了偏振跳变锁定现象后，回馈腔中非常微小的各向异性即会引起偏振态的跳变，基于此现象可实现对回馈腔中微小各向异性的定量检测。北京大学物理学院用该仪器测量了GaN半导体的内应力，清华大学的张继涛博士后用该仪器测量真空管光胶封接引入的应力。内应力测量仪的研发成功，对于材料微小内应力的定量和实时监测具有重要意义。发现了一些新的物理现象和应用，包括：1.当双折射元件在回馈腔中旋转时，相位延迟与折射率、旋转角度存在特定关系，论文中推导出此关系式，并基于此关系式，提出折射率和厚度测量方案，并分析了测量误差。搭建了折射率和厚度测量系统，并测量了石英波片的相关参数。测量结果和其它仪器的比对表明，折射率测量精度优于6×10-4，厚度测量精度优于59nm，级数测量无偏差。分析了该方案应用到KN晶体、液晶和各向同性材料等光学元件折射率和厚度测量方面需要解决的问题。在精确建模的基础上，该方案可实现对单轴晶体、双轴晶体和各向同性材料等光学元件折射率和厚度的同时测量。2.当各向异性光学元件在回馈腔中旋转时，由于元件表面的干涉效应，相位延迟量对旋转角度非常敏感，按照最大振幅衰减的余弦规律震荡。当旋转体与光学元件连接时，通过检测光学元件旋转角度的变化，可实现对旋转体转动角度的测量。3.当置于回馈腔中晶体的光轴与激光初始偏振方向不平行时，经检偏器后偏振光强度随回馈腔长按照特定规律变化，据此可实现对光轴方位的检测。更多还原

【Abstract】 Through optical feedback technology, the modulation of intensity andpolarization state of laser outputting is realized in the outside of resonant cavity.The laser internal nature is researched by the variation of the resonant outsidecondition. The content of laser physics will be enriched based on laser feedbackresearch. Laser anisotropic feedback, which is an important branch of laserfeedback technology, modulates the intensity and polarization states of theorthogonally polarized laser. Some parameters, such as phase retardation,displacement and so on, can be demodulated by analyzing the lasercharacteristic, based on the fact that the objective information is contained inthe feedback light. This technology can be applied to the field of precisionmeasurement. The phenomena of laser anisotropic feedback are researched inthis thesis. A new physical model which reveals the physical nature of feedbackphenomena is built. Some experimental phenomena have been instrumented andapplied to the online detection of industrial production. Some new experimantalphenomena are found and the potential applications of the phenomena areresearched. The main works of this thesis are summarized as follows.The phenomenon that the orthogonal polarization states of laser will lockinto together and the polarization flipping will not be observed when theanisotropic of optical component placed in feedback cavity is little. This is thelocking phenomenon of polarization flipping. It is an obstacle of the applicationof the measurement technique based on the optical feedback effect. A newtheoretical model which integrates the model of equivalent cavity ofFabry-Perot interferometer and Lamb’s semi-classical is built to analyze thelocking phenomenon of polarization flipping. The new physical model explainspolarization flipping and locking phenomenon perfectly. The theoretical modelis universal and the modeling idea can be applied to any feedback areas.Based on the analysis result of the new theoretical model, a scheme whichincreases the frequency difference between the orthogonal polarized laser todecrease the mode competition is given to release the locking of polarizationflipping. The experimental result shows that when a glass with very smallinternal stress is placed into the feedback cavity, the polarization flippinghappens. The system without the locking phenomenon of polarization flippingmay be used to measure the stress of optical component. This will expand theapplication field of the laser anisotropic feedback instrument. The relationship between the flipping point displacement and phaseretardation of optical component placed in feedback cavity is analyzed and themathematical relationship between them is built. The phase retardation of waveplates can be measured based on the relationship by analyzing the polarizationflipping points. A set of wave plates have been measured by the laser feedbackinstrument and frequency splitting instrument and the results of them arecompared. The results show that the phase retardation error between these twoinstruments is smaller than0.5o. This is an important application of the laserfeedback phenomenon.The optical, mechanical, electric circuit and algorithm systems of laserfeedback setup which can fulfill the industrial requirements are designed aftereliminating the polarization flipping locking and building the relationshipbetween the polarization flipping point and phase retardation. The laserfeedback setup has been instrumented. Some experts are invited to evaluate theinstrument performance and the test report is generated. The report shows thatthe measurement repeatability of the instrument is better than0.05o. The bootreplicability is better than0.019o. The measuring range is between0and360o.The application of laser anisotropic feedback in the online measurement ofwave plates manufacture is researched. Some problem are found and resolved.In wave plate manufacture, the thin slices of birefringent crystals are attached toa tray using optical cement for grinding and polishing. The phase retardation ofthe wave plate is measured while it is attached to the optical cement tray. If theresults do not meet the required phase retardation value, the wave plate can bere-ground and re-polished for modification. After meeting the required phaseretardation value, the wave plate is scraped off the optical cement tray. Theprecision of the wave plate phase retardation measured on the optical cementtray determines the wave plate quality. To manufacture high-precision waveplates, high-precision measurements are required at the manufacture stage ofwave plate. The polishing precise of wave plates polished on the same opticalcement tray is about2nm. The phase retardation deviation due to the polishingprecise is1.3°at the wavelength of632.8nm. However, the phase retardationdeviation of wave plates on the same optical cement tray is almost8o measuredby laser feedback instrument. The measurement deviation on wave platemanufacture can be subjected to the influence of optical interference effects. Anelimination structure for the optical interference effects of the wave plates hasbeen designed. The reflectivity at each of the different interfaces of the structureis tiny and the interference effects of the wave plates can be eliminated. The accuracy of wave plate manufacture can be improved greatly on the basis of thiswork. The light source of laser feedback instrument a single wavelength of632.8nm, thus, just only the phase retardation of wave plate under632.8nm ismeasured. If the phase retardation under other wavelengths needs to know, theconversion method must be used. In this process, the refractive index precisedetermines the conversion precise. In this thesis, a method for multi-wavelengthconversion is introduced. The conversion error is eliminated by the systemcalibration. The maximum error after conversion is0.26degrees. Through thismethod, the laser feedback instrument designed for a single wavelengthmeasurement can be expanded to multi-wavelength field. Temperature doesinfluence phase retardation by changing the refractive index and thickness of awave plate. In this thesis, a new nonlinear model is developed to describe thephysical mechanism underlying the temperature dependence of the phaseretardation. Whereas the refractive index is modeled using Sellmeier’s equation,wave-plate thickness is expressed as a quadratic function of temperature.Combining the two gives the temperature dependence of phase retardation in ourmodel. A set of temperature control devices is designed to modulate wave platetemperature. Based on the experimental data, the coefficients in the Sellmeier’sequation are parameter fitted. Once established, changes in phase retardation atany temperature can be calculated using the equation.The instrument for phase retardation measurement based on laser feedbackeffect is applied to industrial production. The instruments are applied to onlinemeasurement of wave plates manufacture in Castech Co., Ltd and FuzhouTongchan optoelectronic technology company. Beijing Institute of IOLmeasures phase retardation of KN crystal by this instrument.The application of laser feedback instrument in internal stress measurementis researched. Internal stress is ubiquitous in material, which is an inherentconsequence of the crystal lattice defects, processes, assembling, andtemperature gradient. Internal stress of materials and elements makes systemsusing them detracted. Therefore it is important to know the magnitude anddistribution of stresses in materials. In this thesis, the internal stress is measuredby laser feedback instrument. The vacuum tubes with optical cement stress havebeen measured and the measurement results have a reference value to airrefractive index measurement. The measurement results of stress distribution ofNd:YAG crystal are significant to improve laser quality. The measurementresults of stress of GaN semiconductor, for improving manufacturing process ofGaN semiconductor, have very important significance. Some new physical phenomena are found. These phenomena include:1.Thickness and refractive index are fundamental to the characterization ofmaterials in optical devices. A simultaneous measurement method of thickness dand refractive index n for birefringent materials is proposed in this thesis basedon laser feedback phenomenon. Results show that the precise of thickness is59nm and refractive index is0.0006. The problems are analyzed when thetechnique is used to measure the refractive index and thickness of KN crystal,liquid crystal and isotropic materials. On the basis of accurate model, thistechnique can simultaneous measure the refractive index and thickness ofuniaxial crystal, biaxial crystal and isotropic materials.2. The position ofpolarization flipping will be modulated when the wave plate which is placed inthe external cavity rotates. The position of polarization flipping is sensitive tothe rotating angle. We build a relationship between the position of polarization,or the phase retardation and the rotating angle of wave plate. The high-precisesmall-angle measurement is realized by detecting the variation of phaseretardation.3. When the optic axis direction is not consistent with the initiallaser polarization direction, the polarization states of laser output will changefrom linear polarized to elliptical polarization. The polarization states are highlysensitive to the relative position of optic axis and the initial laser polarizationdirection. Through detecting the polarization state of laser output, the optic axisazimuth can be determined. The system is low cost, fast response, compact, andpower effective.更多还原