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http://dx.doi.org/10.3807/KJOP.2018.29.3.110

Athermalization and Narcissus Analysis of Mid-IR Dual-FOV IR Optics  

Jeong, Do Hwan (Department of Optical Engineering, Kongju National University)
Lee, Jun Ho (Department of Optical Engineering, Kongju National University)
Jeong, Ho (LIG Nex1 Co., Ltd.)
Ok, Chang Min (LIG Nex1 Co., Ltd.)
Park, Hyun-Woo (LIG Nex1 Co., Ltd.)
Publication Information
Korean Journal of Optics and Photonics / v.29, no.3, 2018 , pp. 110-118 More about this Journal
Abstract
We have designed a mid-infrared optical system for an airborne electro-optical targeting system. The mid-IR optical system is a dual-field-of-view (FOV) optics for an airborne electro-optical targeting system. The optics consists of a beam-reducer, a zoom lens group, a relay lens group, a cold stop conjugation optics, and an IR detector. The IR detector is an f/5.3 cooled detector with a resolution of $1280{\times}1024$ square pixels, with a pixel size of $15{\times}15{\mu}m$. The optics provides two stepwise FOVs ($1.50^{\circ}{\times}1.20^{\circ}$ and $5.40^{\circ}{\times}4.23^{\circ}$) by the insertion of two lenses into the zoom lens group. The IR optical system was designed in such a way that the working f-number (f/5.3) of the cold stop internally provided by the IR detector is maintained over the entire FOV when changing the zoom. We performed two analyses to investigate thermal effects on the image quality: athermalization analysis and Narcissus analysis. Athermalization analysis investigated the image focus shift and residual high-order wavefront aberrations as the working temperature changes from $-55^{\circ}C$ to $50^{\circ}C$. We first identified the best compensator for the thermal focus drift, using the Zernike polynomial decomposition method. With the selected compensator, the optics was shown to maintain the on-axis MTF at the Nyquist frequency of the detector over 10%, throughout the temperature range. Narcissus analysis investigated the existence of the thermal ghost images of the cold detector formed by the optics itself, which is quantified by the Narcissus Induced Temperature Difference (NITD). The reported design was shown to have an NITD of less than $1.5^{\circ}C$.
Keywords
Infrared optics; Lens design; Narcissus; Athermalization;
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