diff --git a/content/zettels/quadrant_photodiodes.md b/content/zettels/quadrant_photodiodes.md
index bdf2586..c5828cc 100644
--- a/content/zettels/quadrant_photodiodes.md
+++ b/content/zettels/quadrant_photodiodes.md
@@ -146,3 +146,10 @@ We now that the maximum translation of the beam is \\(\Delta z = 1\\,mm\\) and t
 \end{equation}
 
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+
+<style>.csl-entry{text-indent: -1.5em; margin-left: 1.5em;}</style><div class="csl-bib-body">
+  <div class="csl-entry"><a id="citeproc_bib_item_1"></a>Lee, Eun Joong, Youngok Park, Chul Sung Kim, and Taejoon Kouh. 2010. “Detection Sensitivity of the Optical Beam Deflection Method Characterized with the Optical Spot Size on the Detector.” <i>Current Applied Physics</i> 10 (3): 834–37. doi:<a href="https://doi.org/10.1016/j.cap.2009.10.003">10.1016/j.cap.2009.10.003</a>.</div>
+  <div class="csl-entry"><a id="citeproc_bib_item_2"></a>Li, Qing, Shaoxiong Xu, Jiawei Yu, Lingjie Yan, and Yongmei Huang. 2019. “An Improved Method for the Position Detection of a Quadrant Detector for Free Space Optical Communication.” <i>Sensors</i> 19 (1): 175. doi:<a href="https://doi.org/10.3390/s19010175">10.3390/s19010175</a>.</div>
+  <div class="csl-entry"><a id="citeproc_bib_item_3"></a>Manojlović, Lazo M. 2011. “Quadrant Photodetector Sensitivity.” <i>Applied Optics</i> 50 (20). Optical Society of America: 3461–69.</div>
+  <div class="csl-entry"><a id="citeproc_bib_item_4"></a>Wu, Jiabin, Yunshan Chen, Shijie Gao, Yimang Li, and Zhiyong Wu. 2015. “Improved Measurement Accuracy of Spot Position on an Ingaas Quadrant Detector.” <i>Applied Optics</i> 54 (27). Optical Society of America: 8049–54.</div>
+</div>