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Proceedings Paper

Simple alignment procedure for a VNIR imaging spectrometer with a Shack-Hartmann wavefront sensor and a field identifier
Author(s): Jun Ho Lee; Sunglyoung Hwang; Dohwan Jeong; Jinsuk Hong; Youngsoo Kim; Yeonsoo Kim; Hyunsook Kim
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Paper Abstract

We report an innovative simple alignment method for a VNIR spectrometer in the wavelength region of 400–900 nm; this device is later combined with fore-optics (a telescope) to form a f/2.5 hyperspectral imaging spectrometer with a field of view of ±7.68°. The detector at the final image plane is a 640×480 charge-coupled device with a 24 μm pixel size. We first assembled the fore-optics and the spectrometer separately and then combined them via a slit co-located on the image plane of the fore-optics and the object plane of the spectrometer. The spectrometer was assembled in three steps. In the initial step, the optics was simply assembled with an optical axis guiding He-Ne laser. In the second step, we located a pin-hole on the slit plane and a Shack-Hartmann sensor on the detector plane. The wavefront errors over the full field were scanned simply by moving the point source along the slit direction while the Shack-Hartmann sensor was constantly conjugated to the pin-hole position by a motorized stage. Optimal alignment was then performed based on the reverse sensitivity method. In the final stage, the pin-hole and the Shack-Hartmann sensor were exchanged with an equispaced 10 pin-hole slit called a field identifier and a detector. The light source was also changed from the laser (single wavelength source) to a krypton lamp (discrete multi-wavelength source). We were then easily able to calculate the distortion and keystone on the detector plane without any scanning or moving optical components; rather, we merely calculated the spectral centroids of the 10 pin-holes on the detector. We then tuned the clocking angles of the convex grating and the detector to minimize the distortion and keystone. The final assembly was tested and found to have an RMS WFE < 90 nm over the entire field of view, a keystone of 0.08 pixels, a smile of 1.13 pixels and a spectral resolution of 4.32 nm.

Paper Details

Date Published: 5 September 2017
PDF: 6 pages
Proc. SPIE 10402, Earth Observing Systems XXII, 104020H (5 September 2017); doi: 10.1117/12.2275404
Show Author Affiliations
Jun Ho Lee, Kongju National Univ. (Korea, Republic of)
Sunglyoung Hwang, Kongju National Univ. (Korea, Republic of)
Dohwan Jeong, Kongu National. Univ. (Korea, Republic of)
Jinsuk Hong, Hanwha Systems Co., Ltd. (Korea, Republic of)
Youngsoo Kim, Hanwha Systems Co., Ltd. (Korea, Republic of)
Yeonsoo Kim, Agency for Defense Development (Korea, Republic of)
Hyunsook Kim, Agency for Defense Development (Korea, Republic of)


Published in SPIE Proceedings Vol. 10402:
Earth Observing Systems XXII
James J. Butler; Xiaoxiong (Jack) Xiong; Xingfa Gu, Editor(s)

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