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<h1 class="title">NASS - Short Stroke Metrology</h1>
<div id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
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<li><a href="#orgbab5500">1. Measurement Principle</a></li>
<li><a href="#org8f0a94b">2. X-Y-Z measurement</a></li>
<li><a href="#orgda8f2a5">3. Tilt measurement</a></li>
<li><a href="#org6ff8891">4. Conclusion</a></li>
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</ul>
</div>
</div>
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<hr>
<p>This report is also available as a <a href="./short-stroke-metrology.pdf">pdf</a>.</p>
<hr>
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<p>
The goal of this document is to analyze the feasibility of a short stroke metrology system for the NASS using fixed interferemoter and the same reflector as for the long stroke metrology system.
</p>
<p>
It is structured as follow:
</p>
<ul class="org-ul">
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<li>Section <a href="#org81efe49">1</a>: the meaurement principle is described.</li>
<li>Section <a href="#orga41b53c">2</a>: the requirements for the interferometers measuring translations are described</li>
<li>Section <a href="#org8b209d1">3</a>: the same is done for the rotations</li>
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</ul>
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<div id="outline-container-orgbab5500" class="outline-2">
<h2 id="orgbab5500"><span class="section-number-2">1</span> Measurement Principle</h2>
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<div class="outline-text-2" id="text-1">
<p>
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<a id="org81efe49"></a>
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</p>
<p>
Here are the defined wanted displacement of the reflector that should be inside the measurement stroke of the metrology system.
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The defined translations and rotations are defined with respect to the frame shown in Figure <a href="#org25ba32a">1</a>.
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</p>
<div class="org-src-container">
<pre class="src src-matlab">d_x = 0; <span class="org-comment">% Wanted translation of the reflector in the x direction [m]</span>
d_y = 1e<span class="org-type">-</span>3; <span class="org-comment">% Wanted translation of the reflector in the y direction [m]</span>
d_z = 1e<span class="org-type">-</span>3; <span class="org-comment">% Wanted translation of the reflector in the z direction [m]</span>
R_x = 10e<span class="org-type">-</span>3; <span class="org-comment">% Wanted rotation of the reflector along the x axis [rad]</span>
R_y = 0; <span class="org-comment">% Wanted rotation of the reflector along the y axis [rad]</span>
</pre>
</div>
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<div id="org25ba32a" class="figure">
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<p><img src="figs/short_stroke_metrology_concept.png" alt="short_stroke_metrology_concept.png" />
</p>
<p><span class="figure-number">Figure 1: </span>Short Stroke Metrology - Concept. Blue interferometers are used to measure the X-Y-Z motion of the reflector. Red interferometers are used to measure tilt motion of the reflector.</p>
</div>
<p>
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Here are the approximate dimensions shown in Figure <a href="#org25ba32a">1</a>:
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</p>
<ul class="org-ul">
<li>\(d_0 \approx 10\,[mm]\)</li>
<li>\(L \approx 150\,[mm]\)</li>
<li>\(R \approx 250\,[mm]\)</li>
</ul>
<div class="org-src-container">
<pre class="src src-matlab">d0 = 10e<span class="org-type">-</span>3; <span class="org-comment">% [m]</span>
L = 150e<span class="org-type">-</span>3; <span class="org-comment">% [m]</span>
R = 250e<span class="org-type">-</span>3; <span class="org-comment">% [m]</span>
</pre>
</div>
</div>
</div>
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<div id="outline-container-org8f0a94b" class="outline-2">
<h2 id="org8f0a94b"><span class="section-number-2">2</span> X-Y-Z measurement</h2>
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<div class="outline-text-2" id="text-2">
<p>
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<a id="orga41b53c"></a>
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</p>
<p>
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The geometry for the interferometers measuring translations is shown in Figure <a href="#org0718921">2</a>:
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</p>
<ul class="org-ul">
<li>\(R = 250\,[mm]\)</li>
<li>\(d_0 > 10\,[mm]\)</li>
<li>\(d_x = \pm 1\,[mm]\)</li>
<li>\(d_y = \pm 1\,[mm]\)</li>
</ul>
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<div id="org0718921" class="figure">
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<p><img src="figs/translation_interferometers.png" alt="translation_interferometers.png" />
</p>
<p><span class="figure-number">Figure 2: </span>Interferometers that are measuring translation</p>
</div>
<p>
The angle of the reflected beam is approximately equal to:
</p>
\begin{equation}
\theta \approx 2 \frac{d_y}{R}
\end{equation}
<p>
And we obtain:
</p>
<p>
\[ \theta \approx 8.0\,[mrad] \]
</p>
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<table id="org27e7f4b" border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">
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<caption class="t-above"><span class="table-number">Table 1:</span> Specifications for the translation interferometers</caption>
<colgroup>
<col class="org-left" />
<col class="org-left" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Specification</th>
<th scope="col" class="org-left">Value</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left">Axial Acceptance</td>
<td class="org-left">\(\pm 1\,[mm]\)</td>
</tr>
<tr>
<td class="org-left">Angular Acceptance</td>
<td class="org-left">\(\pm 8\,[mrad]\)</td>
</tr>
<tr>
<td class="org-left">Distance to target</td>
<td class="org-left">\(10\,[mm]\)</td>
</tr>
</tbody>
</table>
</div>
</div>
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<div id="outline-container-orgda8f2a5" class="outline-2">
<h2 id="orgda8f2a5"><span class="section-number-2">3</span> Tilt measurement</h2>
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<div class="outline-text-2" id="text-3">
<p>
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<a id="org8b209d1"></a>
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</p>
<p>
The tilt \(\theta\) of the flat mirror is directly equal to the tilt of the reflector.
However, the \(z\) displacement on the flat part is equal to:
</p>
\begin{equation}
z \approx d_z + L \theta_y
\end{equation}
<p>
And we obtain:
</p>
<p>
\[ z \approx 2.5\,[mm] \]
</p>
<p>
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The geometry for the interferometers measuring rotations is shown in Figure <a href="#org5e4c6eb">3</a>:
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</p>
<ul class="org-ul">
<li>\(d_0 > 10\,[mm]\)</li>
<li>\(\theta = \pm 10\,[mrad]\)</li>
<li>\(z = \pm 2.5\, [mm]\)</li>
</ul>
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<div id="org5e4c6eb" class="figure">
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<p><img src="figs/rotation_interferometers.png" alt="rotation_interferometers.png" />
</p>
<p><span class="figure-number">Figure 3: </span>Interferometers that are measuring tilt</p>
</div>
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<table id="org0d63b1d" border="2" cellspacing="0" cellpadding="6" rules="groups" frame="hsides">
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<caption class="t-above"><span class="table-number">Table 2:</span> Specifications for the rotation interferometers</caption>
<colgroup>
<col class="org-left" />
<col class="org-left" />
</colgroup>
<thead>
<tr>
<th scope="col" class="org-left">Specification</th>
<th scope="col" class="org-left">Value</th>
</tr>
</thead>
<tbody>
<tr>
<td class="org-left">Axial Acceptance</td>
<td class="org-left">\(\pm 2.5\,[mm]\)</td>
</tr>
<tr>
<td class="org-left">Angular Acceptance</td>
<td class="org-left">\(\pm 10\,[mrad]\)</td>
</tr>
<tr>
<td class="org-left">Distance to target</td>
<td class="org-left">\(10\,[mm]\)</td>
</tr>
</tbody>
</table>
</div>
</div>
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<div id="outline-container-org6ff8891" class="outline-2">
<h2 id="org6ff8891"><span class="section-number-2">4</span> Conclusion</h2>
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</div>
</div>
<div id="postamble" class="status">
<p class="author">Author: Dehaeze Thomas</p>
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<p class="date">Created: 2021-02-19 ven. 11:13</p>
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