<title>Birefringence dispersion inhomogeneity testing in optical materials by imaging polarimetry</title>

Abstract

in many optical applications of anisotropic ciystals birefringence dispersion (BD) is at least so important as birefringence spatial inhoinogeneity itself in this work a new technique of 2-D mapping of paratneten related to BD in plane-parallel wafers of optical materials is reported. A computer-controlled imaging spectro-poiariineter is used for recording the wafers' images for consecutively varying wavelengths. Examples of practical measurements carried out on undoped and Cu-doped LiNbO3 are presented.1 ThITRODUCTION DBD(AJ) RDBD(A1) Optical inhomogeneity (01) is defined as a refractive index (isotropic materials) or birefringence (anisotropic materials) change per unit length. However, in frequent cases birefringence is not a sole parameter of the material that should be considered. It seems that birefringence dispersion (BD) rather than birefringence itself is a key parameter in manufacture of e.g. retardation plates, 2nd harmonic generators, or polarizers [ 1]. It is a well known fact that BD depends on composition in mixed crystals of the LiNhO3-type structure [2]. It is therefore possible that BD can be also influenced by stoichiornetry and crystalline imperfections in homogeneous crystals, although this hyphothesis needs stronger experimental verification. It seems then that definition of the 01 effect in crystalline materials should be reconsidered, and that BD ought to play here an important role.In this work a method of BD testing on the entire area of plane-parallel plate of crystalline material is presented and illustrated by measurement of undoped and Cu-doped LiNbO3 wafers. A TV camera and video frame grabbing (VFG) techniques are used for collecting the input data from the whole surface of the investigated wafer, and hence BD inhomogeneity (BDI) maps can be obtained in short time. Since one can not map a physical phenomenon, i.e. a curve showing birefringence changes with wavelength, a set of parameters characterizing the BD effect, including their values for the extreme wavelengths used in experiment, an average value, etc. , has been proposed. This technique can be also used for calculating the piezooptic (photoelastic) coefficients' dispersion in isotropic materials, i.e. when birefringence is involved by residual stresses. SPIE Vol. 3729 • 0277-786X/991$1O.OO 2 PRINCIPLES OF TIlE METHOD Only a brief account of the method will be given here, since it has been described with full detailes elsewhere [3],including also its error analysis. Before one begins describing the method it should be precisely defined what exactly has to be measured. At first sight it might be expected that the BD phenomenon could be most correctly defined by differential birefringence dispersion, i.e.An(A.)-An(A.where n is birefringence, X is wavelength (an increasing subscript denotes longer wavelength). However, it will be shown later that relative differential birefringence dispersion, i.e.(2) yields less erroneous results in practical measurements, and this parameter will be further considered in this work. It should b...

<title>Czochralski growth and characterization of SrLaGa<formula><inf><roman>3</roman></inf></formula>O<formula><inf><roman>7</roman></inf></formula>:Ho<formula>^{<roman>3+</roman>}</formula>single crystals</title>

“…The crystal and wafers have been checked for their optical properties in the macroscale in the plane and circular polariscopes, an automated polarimeter capable of measuring the three maps on wafer area (birefringence, the principal azimuth (one of the principal residual stresses in the case of Z-cut wafers), and transmission) 5 ' 6 , and on automated spectropolarimeter used for mapping of parameters associated with birefringence dispersion on wafer area 7 .…”

<title>Investigation of thermal annealing by gamma irradiation at room temperature in LiNbO<formula><inf><roman>3 </roman></inf></formula>crystals</title>

“…in ref. [3]) that the so-called Birefringence Dispersion Coefficient (BDC) in sample cut out from an isotropic crystal, or, alternatively, cut perpendicularly to the Z-optical axis in an anisotropic crystal, is a function of the stress-optic coefficients CQ, i.e.…”

“…[1,2]) having the capacity of measuring the three maps on the entire sample area (birefringence, the principal azimuth (one of the principal residual stresses in the case of birefringence induced by residual stresses), and transmission), an automated spectropolarimeter (refs. [3][4][5]) utilizing a novel technique of mapping of parameters associated with the birefringence optical dispersion, and optical spectroscopic measurements of the so-called additional absorption. In the latter case the additional absorption was measured in a few (usually five) sample points, and an average or the most typical result has been taken into consideration.…”