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width: 12px; height: 12px; background-image: url(images/ext.png); background-size:24px 12px; background-repeat:no-repeat; background-position:-12px 0; margin-left:8px; float:none; } /* ---- Flex Gallery ---- */ .children { display: flex; flex-flow: row wrap; justify-content: space-around; min-height: 200px; } .child { flex: 0 0 auto; list-style-type: none; width: 30%; padding: 25px; border: solid 1px #ddd; font-size: 1.6rem; } .child a { background-color: #fff; display: block; padding: 0; background-repeat: no-repeat; background-size: contain; background-position: center top; color: #333333; text-decoration: none; text-align: center; position: relative; } .child h3 { text-decoration: none; text-align: center; font-size: 2.3rem; font-weight: 600; /* letter-spacing: 3px; */ color: #fff; line-height: 0; margin-bottom: 0; } /* ---- FOOTER ---- */ .social-links img { height: 40px; padding-right: 20px; } a.footer-button { color: white; padding: 16px; text-align: center; text-decoration: 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class="site-header" itemscope itemtype="https://schema.org/WPHeader"><div class="wrap"><div class="title-area"><p class="site-title" itemprop="headline"><a href="https://www.desi.lbl.gov/">Dark Energy Spectroscopic Instrument (DESI)</a></p></div><div class="widget-area header-widget-area"><section id="nav_menu-20" class="widget widget_nav_menu"><div class="widget-wrap"><nav class="nav-header" itemscope itemtype="https://schema.org/SiteNavigationElement"><ul id="menu-main-navigation" class="menu genesis-nav-menu js-superfish"><li id="menu-item-59" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-has-children menu-item-59"><a href="https://www.desi.lbl.gov/science/" itemprop="url"><span itemprop="name">/ science /</span></a> <ul class="sub-menu"> <li id="menu-item-994" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-994"><a href="https://www.desi.lbl.gov/science/" itemprop="url"><span itemprop="name">science overview</span></a></li> <li 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itemprop="url"><span itemprop="name">target selection and survey validation</span></a></li> <li id="menu-item-3083" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-3083"><a href="https://www.desi.lbl.gov/for-scientists/theory-and-simulations/" itemprop="url"><span itemprop="name">theory and simulations</span></a></li> <li id="menu-item-3084" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-3084"><a href="https://www.desi.lbl.gov/for-scientists/other-desi-science/" itemprop="url"><span itemprop="name">other DESI science</span></a></li> <li id="menu-item-1513" class="menu-item menu-item-type-custom menu-item-object-custom menu-item-1513"><a href="https://ui.adsabs.harvard.edu/public-libraries/XCj7bW-vSMaNZVV0C0QyGA" itemprop="url"><span itemprop="name">all DESI papers</span></a></li> <li id="menu-item-393" class="ext menu-item menu-item-type-custom menu-item-object-custom menu-item-393"><a target="_blank" 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href="https://www.desi.lbl.gov/education-outreach/interactive-visualizations/" itemprop="url"><span itemprop="name">interactive visualizations</span></a></li> <li id="menu-item-2663" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-2663"><a href="https://www.desi.lbl.gov/education-outreach/desi-merch/" itemprop="url"><span itemprop="name">DESI Merch</span></a></li> </ul> </li> </ul></nav></div></section> </div></div></header><div class="site-inner"><div class="content-sidebar-wrap"><h1 class="entry-title" itemprop="headline">spectrograph</h1> <main class="content" id="genesis-content"><article class="post-23 page type-page status-publish entry" aria-label="spectrograph" itemscope itemtype="https://schema.org/CreativeWork"><div class="entry-content" itemprop="text"><p><a href="https://www.desi.lbl.gov/es/spectrograph-spanish"><img decoding="async" class="alignleft" src="https://www.desi.lbl.gov/wp-content/uploads/sites/8/2019/12/spanish-1-e1576602273893.png" width="50" height="50" /></a><a href="https://www.desi.lbl.gov/ca/spectrograph-catalan"><img decoding="async" class="alignleft" src="https://www.desi.lbl.gov/wp-content/uploads/sites/8/2021/08/3253480-catalonia-icon-flag_106770-e1629935057530.png" width="50" height="50" /></a><a href="https://www.desi.lbl.gov/it/spectrograph-italian"><img loading="lazy" decoding="async" class="alignleft" src="https://www.desi.lbl.gov/wp-content/uploads/sites/8/2021/12/flag_italy-600x600.png" alt="" width="50" height="50" /></a></p> <p><img loading="lazy" decoding="async" class="size-medium wp-image-507 aligncenter" src="https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/07/spectro-600x364.png" alt="" width="600" height="364" srcset="https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/07/spectro-600x364.png 600w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/07/spectro-768x466.png 768w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/07/spectro-1024x621.png 1024w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/07/spectro.png 1856w" sizes="auto, (max-width: 600px) 100vw, 600px" /></p> <p>Each of DESI’s 10 identical spectrographs will accept one fiber-optic cable with 500 fibers. The light from the fibers will enter the spectrograph through a slit that has a shutter in front of it. If the shutter is open, the light from the fibers will be split using dichroics into three cameras that are each sensitive to different wavelength ranges and have different resolutions (R = λ/∆λ):</p> <ul> <li>Blue: 360 < λ ≤ 555 nm; R = 2,000 − 3,200</li> <li>Red: 555 < λ ≤ 656 nm; R = 3,200 − 4,100</li> <li>Infrared: 656 < λ ≤ 980 nm, R = 4,100 − 5,000</li> </ul> <p>Before the light lands on the detectors, <img loading="lazy" decoding="async" class="size-full wp-image-2281 alignleft" src="https://www.desi.lbl.gov/wp-content/uploads/sites/8/2022/01/completed_spec-300x157-1.jpg" alt="" width="300" height="157" />it is spread using a volume phase holographic (VPH) grating. The detector arrays have 4096×4096 15μm pixels and are each housed in their own cryostat so that they can be kept very cold to maintain stability.</p> <figure id="attachment_224" aria-describedby="caption-attachment-224" style="width: 400px" class="wp-caption alignright"><img loading="lazy" decoding="async" class="wp-image-224" src="/wp-content/uploads/sites/8/2018/06/grating-300x177.png" alt="" width="400" height="235" srcset="https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/grating-300x177.png 300w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/grating-600x353.png 600w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/grating-768x452.png 768w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/grating-1024x603.png 1024w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/grating.png 1490w" sizes="auto, (max-width: 400px) 100vw, 400px" /><figcaption id="caption-attachment-224" class="wp-caption-text">VPH grating</figcaption></figure> <p>The throughput of each arm of the spectrograph has been measured to demonstrate 70 percent efficiency across the whole redshift range. If the shutter in front of the slit is closed, there are several bright LEDs that will be turned on so that the fibers are “backlit” and can be seen with the fiber-view camera.</p> <figure id="attachment_226" aria-describedby="caption-attachment-226" style="width: 396px" class="wp-caption aligncenter"><img loading="lazy" decoding="async" class="wp-image-226 " src="/wp-content/uploads/sites/8/2018/06/tput-300x218.png" alt="" width="396" height="288" srcset="https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/tput-300x218.png 300w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/tput-600x436.png 600w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/tput-768x558.png 768w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/tput-1024x744.png 1024w, https://www.desi.lbl.gov/wp-content/uploads/sites/8/2018/06/tput.png 1355w" sizes="auto, (max-width: 396px) 100vw, 396px" /><figcaption id="caption-attachment-226" class="wp-caption-text">Throughput of a spectrograph</figcaption></figure> <p style="text-align: right"><a href="https://www.desi.lbl.gov/instrument-control-system/"><strong>instrument control system »</strong></a></p> </div></article></main><aside class="sidebar sidebar-primary widget-area" role="complementary" aria-label="Primary Sidebar" itemscope itemtype="https://schema.org/WPSideBar" id="genesis-sidebar-primary"><h2 class="genesis-sidebar-title screen-reader-text">Primary Sidebar</h2><section id="nav_menu-53" class="widget widget_nav_menu"><div class="widget-wrap"><div class="menu-instrument-container"><ul id="menu-instrument" class="menu"><li id="menu-item-483" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-483"><a href="https://www.desi.lbl.gov/instrument/" itemprop="url">instrument overview</a></li> <li id="menu-item-247" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-has-children menu-item-247"><a href="https://www.desi.lbl.gov/telescope/" 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