二轴晶临界干涉图的发现及其消光影特征

DISCOVERY OF CRITICAL INTERFERENCE FIGURE OF BIAXIAL CRYSTALS AND CHARACTERISTICS OF THEIR ISOGYRES

在偏光显微镜的锥光系统中，垂直二轴品光率体─—圆切面与光轴面交线的切面干涉图此处定义为临界干涉图。结合球面和平面解析法可以证明，这种干涉图消光影一般为双曲线形，但具体形状与晶体2V角及从0°位置（光轴面平行上或下偏光镜振动方向）旋转的角度有关。它与已知其它切面干涉图的最大区别是，当晶体从0°位置旋转45°时，消光影为一条与目镜横丝或纵丝夹45°角的直线，它到视域中心的距离随晶体2V角的减小而加大，因而在特定物镜数值孔径和晶体折射率的情况下，只有较大2V角晶体的这条消光影才会处在视域之内。在观察橄榄石和角闪石晶体临界干涉图时证实了它的上述特性。

The critical interference figure is defined here as the figure which is produced in the conoscopic system of polarized microscope when a biaxial crystal plate is cut perpendicularly to the intersecting line of the circular section and optic axis plane (ICO) of the indicatrix. In combination of spherical and plane ana1yses it is proved that the isogyre shape in the interference figure is generally hyperbolic but is related to the 2V of the crystal and the angle at which the crystal is rotated from 0°position (the optic axis plane is parallel to the vibrating direction of the upper or lower nicol). Of all the known interference figures the most special aspect of the figure is that the isogyre is a straight line in shape intersecting to the horizontal or vertical bair of the ocular by 45°while the crystal is rotated for 45°from the 0°position, and the distance of which to the center of the view field decreases as the 2V increases, therefore the isogyre could come into the view field only when the crystal has a sufficient 2V given a certain numerical aperture of the objective and refractive index of the crystal. The characteristics of the lsogyre are identified with olivine and amphibole crystals.