• Korean Journal of Optics and Photonics
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• v.33 no.4
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• pp.146-158
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• 2022

The detector of a focal-plane-array mid-wave infrared (MWIR) camera has different response characteristics for each detector pixel, resulting in nonuniformity between detector pixels. In addition, image nonuniformity occurs due to heat generation inside the camera during operation. To solve this problem, in the process of camera manufacturing it is common to use a gain-and-offset table generated from a blackbody to correct the difference between detector pixels. One method of correcting nonuniformity due to internal heat generation during the operation of the camera generates a new offset value based on input frame images. This paper proposes a technique for dividing an input image into block image patches and generating offset values using only homogeneous patches, to correct the nonuniformity that occurs during camera operation. The proposed technique may not only generate a nonuniformity-correction offset that can prevent motion marks due to camera-gaze movement of the acquired image, but may also improve nonuniformity-correction performance with a small number of input images. Experimental results show that distortion such as flow marks does not occur, and good correction performance can be confirmed even with half the number of input images or fewer, compared to the traditional method.

• Korean Journal of Optics and Photonics
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• v.33 no.5
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• pp.201-209
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• 2022

The previously developed microspot spectroscopic ellipsometer (SE) is upgraded to a microspot SE compatible with the atomic force microscope (AFM). The focusing optical system of the previous microspot SE is optimized to incorporate an AFM head. In addition, the rotating compensator ellipsometer in polarizer-sample-compensator-analyzer configuration is adopted in order to minimize the negative effects caused by beam wobble. This research leads to the derivation of the expressions needed to get spectro-ellipsometric constants despite the fact that the employed rotating compensator is far from the ideal achromatic quarter-wave plate. The spot size of the developed microspot SE is less than 20 ㎛ while the AFM head is mounted. It operates in the wavelength range of 190-850 nm and has a measurement accuracy of δΔ ≤ 0.05° and δΨ ≤ 0.02°, respectively. Fast measurement of ≤3 s/sp is realized by precisely synchronizing the azimuthal angle of a rotating compensator with the spectrograph. The microspot SE integrated with an AFM is expected to be useful in characterizing the structure and optical properties of finely patterned samples.

• Korean Journal of Optics and Photonics
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• v.34 no.3
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• pp.99-105
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• 2023

The performance of astronomical telescopes can be negatively affected by atmospheric turbulence. To address this issue, techniques for atmospheric turbulence correction have been developed, requiring the simulation of atmospheric turbulence in the laboratory. The most practical way to simulate atmospheric turbulence is to use a phase plate. When measuring a phase plate that simulates strong turbulence, a Shack-Hartmann wave-front sensor is commonly used. However, the laser power decreases as it passes through the phase plate, potentially leading to a weak laser signal at the sensor. This paper investigates the need to control the laser power when measuring a phase plate that simulates strong atmospheric turbulence, and examines the effects of the laser power on the measured wavefront. For phase plates with relatively high Fried parameter r₀, the laser power causes a variation of over 10% in r₀. For phase plates with relatively low r₀, the laser power causes a variation of less than 5%, which means that the influence of the laser power is negligible for phase plates that simulate strong atmospheric turbulence. Based on the system described in this paper, a phase plate simulating strong atmospheric turbulence can be measured at a laser power of 5 mW or higher. Therefore, controlling the laser's output power is necessary when measuring a phase plate for simulating atmospheric turbulence, especially for phase plates with low r₀ values.