<?xml version="1.0" encoding="utf-8"?><!DOCTYPE Zthes SYSTEM "http://zthes.z3950.org/xml/zthes-05.dtd">  <Zthes><term><termId>31301326</termId><termName>birefringence</termName><termType>PT</termType><termNote><![CDATA[ The tendency of a material to cause a ray of light to separate, or the degree to which the ray separates, into two unequally refracted, plane-polarized rays of orthogonal polarizations. ]]></termNote><termCreatedDate>2026-03-30 20:20:57</termCreatedDate><relation><relationType>UF</relationType><termId>31301327</termId><termName>birefraction</termName><termType>ND</termType></relation><relation><relationType>UF</relationType><termId>31301328</termId><termName>double refraction</termName><termType>ND</termType></relation><relation><relationType>UF</relationType><termId>31301329</termId><termName>extraordinary ray</termName><termType>ND</termType></relation><relation><relationType>UF</relationType><termId>31301330</termId><termName>ordinary ray</termName><termType>ND</termType></relation><relation><relationType>UF</relationType><termId>31301331</termId><termName>pockels effect</termName><termType>ND</termType></relation><relation><relationType>UF</relationType><termId>31301332</termId><termName>refraction, double</termName><termType>ND</termType></relation><relation><relationType>BT</relationType><termId>31298110</termId><termName>optical properties</termName><termType>PT</termType></relation></term>  </Zthes>