Temperature Effect Of The Mica Crystal Birefringence

Birefringence is an important optical parameter of nonisotropic crystal,which is determined by materials composition and crystal structure.Generally,the birefringence takes on greater dispersive for light waves.When a light beam transmits perpendicularly to optical axis in crystal by taking crystalline face parallelling optical axis as a clear area,the birefringence is the maximum and named as maximal birefringent index.The maximal birefringent index which is an important parameter designing polarized devices,is the function of wavelength but also vary with temperature and other external conditions.Polarized devices are influenced by outfield especially temperature field when used,so is wave-plate.The optical capability of devices is influenced because of the change of both the refraction index and the appearance which are caused by the change of temperature.So thermal maximal birefringent index coefficient is used to describe the effect on crystal birefringence by the change of temperature.Refer to some reference literatures,most researches focused on measuring the maximal birefringent index of crystal varying with wavelength basically but not with temperature till now.Mica crystal is a kind of perfect birefringent material for producting single-level wave-plate. Multiple reflection is easy to generate because of its thin wafer.Its surface is distorted when aperture is little larger.So the temperature effect studyied of mica crystal is much less and the research of thermal maximal birefringent index coefficient of mica crystal has not be reported yet.Therefore,the accurate measurement of maximal birefringent index of mica crystal varying with temperature is of great significance.The relation between maximal birefringent index and temperature of mica crystal is studied in the article mostly.In this paper,different thickness mica wave-plates are studied in the way of the polarization interference spectrum which measuring the thermal maximal birefringent index coefficients. Firstly,the polarization interference spectrums of mica wave-plates in different temperature are measured and analysed.Then the maximal birefringent index of the mica wave-plate can be calculated exactly and expressions of the thermal maximal birefringent index coefficients for mica crystal are deduced at visible spectral band and ultraviolet spectral band.At last,the dispersion curve is gained from visible spectral band to ultraviolet spectral band and expressions of the birefingent dispersion at random wavelength for mica crystal is achieved.The article is divided into the following parts mainly:The first chapter is introduction,in the chapter,the development of polarized devices and the temperature effect are introduced and the innovation work of the article is explained.The second chapter is basic knowledge of the maximal birefringent index.The concept of the maximal birefringent index and application of birefringent index and mica crystal are introduced respectively.Then the temperature effect's theoretical analysis is done to birefringent index of wave-plate,the results show that the variation of the retardation is caused by the variation of thickness and birefringence of wave-plate varying with temperature.Many wave-plate phase's series can be de from a few dozen to hundred,but their physical effects in retardation is almost same with single-level wave plate.But the effects will be different because the series of wave-plate is different when the temperature changes.The levels is higher,the influence of thickness is more obvious.For single-level wave-plate,the influence of birefringence is more obvious when the temperature changes,because thickness is very small.The third chapter mainly introduces the measurement system to measure thermal birefringent index coefficients in the way of the polarization interference spectrum.First,the survey principle of the measurement system is described and schematic diagram is drew,then the choice of various parts and the survey procedure flow are explained.The polarization interference spectrums of mica wave-plates in different temperature measured by experiments are analysed;The polarization interference spectrums of different thickness mica wave-plates are found to drift to short wavelength.Moreover,the drift is more obvious when the variation of temperature is larger.The results show that the impact of birefringence is greater than thickness for mica wave-plates and determines the direction to drift.The fourth chapter is the part of data processing and error analysis.Firstly,through accurate judgment of extreme points of the polarization interference spectrums,the maximal birefringent index of the mica wave-plate can be calculated exactly and expressions of the thermal maximal birefringent index coefficients for mica crystal are deduced at visible spectral band and ultraviolet spectral band.At last,the dispersion curve is gained from visible spectral band to ultraviolet spectral band and expressions of the birefingent dispersion at random wavelength for mica crystal can be achieved through polynomial fitting data processing.At the same time, theoretical analysis is done to the errors that may occur in experiment and it is found that the measuring accuracy will be improved by some methods which can guarantee the reliability of the test results.The third and fourth chapters are the most important parts in this paper and my main job. Summing up the above,the innovation of this paper lies in:Firstly,for the first time,the polarization interference spectrums of mica wave-plates in different temperature measured by experiments are analysed;The polarization interference spectrums of different thickness mica wave-plates are found to drift to short wavelength. Moreover,the drift is more obvious when the variation of temperature is larger.The results show that the impact of birefringence is greater than thickness for mica wave-plates and determines the direction to drift.Secondly,expressions of the thermal maximal birefringent index coefficients for mica crystal are gained at visible spectral band and ultraviolet spectral band.Thirdly,expressions of the birefingent dispersion at random wavelength for mica crystal is achieved through least square method and two-dimension hood face chart about the thermal maximal birefringent index following temperature and wavelength through MATLAB process.In this paper,the finally results comparing experimental data with experimental data show that the result of the article is of value for the producting mica wave-plate,which offered. parameter choice basis for correctly using and designing mica devices.