<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<p>I believe:</p>
<p>delta_n=n_zz-n_xx</p>
<p>However, you may check it for yourself:</p>
<p>Birefringence := delta_n=n_e-n_o [1,2]</p>
<p>Orthorhombic ɛ_xx and <span class="st">ɛ_yy perpendicular and </span><span
class="st"><span class="st">ɛ_zz parallel [3] a bit similar to
tetragonal that has </span></span><span class="st"><span
class="st">ɛ_xx = <span class="st">ɛ_yy and </span></span></span><span
class="st"><span class="st"><span class="st"><span class="st"><span
class="st">ɛ_zz tensor (Table 1.1) [4]<br>
</span></span></span></span></span></p>
<p>n_x = sqrt(ɛ_xx/ɛ_o) and n_z = sqrt(ɛ_zz/ɛ_o) [5,6]</p>
<p>Section 1.4 of [4]:</p>
<p>n_e = n_z (or n_zz) and n_o = n_x (or n_xx)<br>
</p>
[1] <a class="moz-txt-link-freetext" href="https://en.wikipedia.org/wiki/Birefringence#Uniaxial_materials">https://en.wikipedia.org/wiki/Birefringence#Uniaxial_materials</a><br>
[2]
<a class="moz-txt-link-freetext" href="http://shodhganga.inflibnet.ac.in/bitstream/10603/4722/13/13_chapter%203.pdf">http://shodhganga.inflibnet.ac.in/bitstream/10603/4722/13/13_chapter%203.pdf</a>
(Equation 3.24)<br>
[3] <a class="moz-txt-link-freetext" href="https://pubs.acs.org/doi/abs/10.1021/jp410786w">https://pubs.acs.org/doi/abs/10.1021/jp410786w</a><br>
[4]
<a class="moz-txt-link-freetext" href="http://www.physics.ucc.ie/fpetersweb/FrankWeb/courses/PY4118/Notes/Symmetry%20of%20Tensor%202.pdf">http://www.physics.ucc.ie/fpetersweb/FrankWeb/courses/PY4118/Notes/Symmetry%20of%20Tensor%202.pdf</a><br>
[5] <a class="moz-txt-link-freetext" href="https://www.as-photonics.com/book_page/book-preview.pdf">https://www.as-photonics.com/book_page/book-preview.pdf</a>
(Equations 2.13 and 2.15)<br>
[6]
<a class="moz-txt-link-freetext" href="https://nanoed.tul.cz/pluginfile.php/1598/mod_resource/content/1/Optick%C3%A9%20vlastnosti%20krystal%C5%AF.pdf">https://nanoed.tul.cz/pluginfile.php/1598/mod_resource/content/1/Optick%C3%A9%20vlastnosti%20krystal%C5%AF.pdf</a>
(slide 5)
<p><br>
</p>
<div class="moz-cite-prefix">On 12/4/2018 5:54 PM, Wien2k User
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAHYowjERRZBYnNbqL4bRuAS5aOKjWqcNZ=rt6UUe7-_7ZMkCzg@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">Dear Wien2k users;<br>
<br>
<span class="gmail-tlid-translation gmail-translation"><span
title="" class="gmail-">for a tetragonal material, the
birefringence is given by :<br>
</span></span></div>
<div><span class="gmail-tlid-translation gmail-translation"><span
title="" class="gmail-">delta_n=n_xx-n_zz <br>
or </span></span><br>
<span class="gmail-tlid-translation gmail-translation"><span
title="" class="gmail-"><span
class="gmail-tlid-translation gmail-translation"><span
title="" class="gmail-"><span
class="gmail-tlid-translation gmail-translation"><span
title="" class="gmail-">delta_n=</span></span>n_zz-n_xx<br>
</span></span></span></span></div>
</div>
</div>
</div>
</blockquote>
<blockquote type="cite"
cite="mid:CAHYowjERRZBYnNbqL4bRuAS5aOKjWqcNZ=rt6UUe7-_7ZMkCzg@mail.gmail.com"></blockquote>
</body>
</html>