会聚偏光干涉测量晶体双折射率

Measurement of the crystal birefractive index by conoscopic interference

光轴平行表面的晶片的会聚偏光干涉对晶体的双折射率非常敏感。干涉图的对称中心对应于正入射光线,双折射率正比于此点的干涉级md,md的小数部分主要由中央暗条纹的位置决定,md的整数部分由自洽的办法求出。干涉条纹可以用双曲线很好地拟合,使干涉图特征点的提取更为精确。用不同厚度的铌酸锂晶片作了测量,双折射率不确定度为1×10-4。

The conoscopic interference pattern of wafer with optical axis parallel to the surface of a crystal is sensitive to the crystal birefractive index. The symcenter of conoscopic interference pattern is corresponding to vertical incident light and crystal birefractive index is proportional to interference order rrtd. Decimal fraction of interference order md is calculated by the placement of central dark fringe and integer part is ascertained by self-consistent method. The interference fringe is fitted by hyperbola so perfectly that it is more precise to obtain the feature points of interference figure. When different thickness niobate crystal are measured, it is shown that uncertainty of birefractive index is 1 × 10^-4.