• Korean Journal of Optics and Photonics
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• v.1 no.1
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• pp.52-57
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• 1990

Employing a picosecond laser and fast electronics. we developed a time -correlated single photon counting (TCSPC) system by which ltuninescence lifetimes can be measured in the subnanosecond to microsecond scale. We also studied non-radiative decay dynamics and rotational motion of DODC! laser dye in solution using this system. ystem.

• Korean Journal of Optics and Photonics
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• v.30 no.3
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• pp.114-119
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• 2019

This paper discusses the development of a Raman lidar system for remote detection and measurement of hydrogen gas by using a photon counter. The Raman signal of the hydrogen gas is very weak and has a very low signal-to-noise ratio. The photon counter has the advantage of improving the signal-to-noise ratio, because it has a discriminator to eliminate the background noise from the Raman signal of the hydrogen gas. Therefore, a small and portable Raman lidar system was developed using a low-power pulsed laser and a photon-counter system to measure the hydrogen gas concentration remotely. To verify the capability of measuring hydrogen gas using the developed photon-counting Raman lidar system, experiments were carried out using a gas chamber in which it is possible to adjust the hydrogen gas concentration. As a result, our photon-counting Raman lidar system is seen to measure a minimum concentration of 0.65 vol.% hydrogen gas at a distance of 10 m.

• Current Optics and Photonics
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• v.2 no.4
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• pp.368-377
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• 2018

In this paper, we evaluate cryptographic properties of a double random phase encoding (DRPE) scheme in the discrete Gyrator domain with avalanche and bit independence criterions. DRPE in the discrete Gyrator domain is reported to have higher security than traditional DRPE in the Fourier domain because the rotation angle involved in the Gyrator transform is viewed as additional secret keys. However, our numerical experimental results demonstrate that the DRPE in the discrete Gyrator domain has an excellent bit independence feature but does not possess a good avalanche effect property and hence needs to be improved to satisfy with acceptable avalanche effect that would be robust against statistical-based cryptanalysis. We compare our results with the avalanche and bit independence criterion (BIC) performances of the conventional DRPE scheme, and improve the avalanche effect of DRPE in the discrete Gyrator domain by integrating a photon counting imaging technique. Although the Gyrator transform-based image cryptosystem has been studied, to the best of our knowledge, this is the first report on a cryptographic evaluation of discrete Gyrator transform with avalanche and bit independence criterions.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.14 no.4
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• pp.332-339
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• 2014

Face classification has wide applications in security and surveillance. However, this technique presents various challenges caused by pose, illumination, and expression changes. Face recognition with long-distance images involves additional challenges, owing to focusing problems and motion blurring. Multiple frames under varying spatial or temporal settings can acquire additional information, which can be used to achieve improved classification performance. This study investigates the effectiveness of multi-frame decision-level fusion with photon-counting linear discriminant analysis. Multiple frames generate multiple scores for each class. The fusion process comprises three stages: score normalization, score validation, and score combination. Candidate scores are selected during the score validation process, after the scores are normalized. The score validation process removes bad scores that can degrade the final output. The selected candidate scores are combined using one of the following fusion rules: maximum, averaging, and majority voting. Degraded facial images are employed to demonstrate the robustness of multi-frame decision-level fusion in harsh environments. Out-of-focus and motion blurring point-spread functions are applied to the test images, to simulate long-distance acquisition. Experimental results with three facial data sets indicate the efficiency of the proposed decision-level fusion scheme.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3380-3389
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• 2022

We evaluated the performance of an improved hybrid median filter (IHMF) applied to X-ray computed tomography (CT) images obtained using a high-resolution photon-counting cadmium zinc telluride (CZT) detector. To study how the proposed approach improves the image quality, we measured the noise levels and the overall CT-image quality. We established a CZT imaging system with a detector length of 5.12 cm and thickness of 0.3 cm and acquired phantom images. To evaluate the efficacy of the proposed filter, we first modeled two conventional median filters. Subsequently, we were able to achieve a normalized noise power spectrum result of ~10^-8 mm², and furthermore, the proposed method improved the contrast-to-noise ratio by a factor of ~1.51 and the coefficient of variation by 1.55 relative to the counterpart values of the no-filter image. In addition, the IHMF exhibited the best performance among the three filters considered as regards the peak signal-to-noise ratio and no-reference-based image-quality evaluation parameters. Thus, our results demonstrate that the IHMF approach provides a superior image performance over conventional median filtering methods when applied to actual CZT X-ray CT images.

• Nuclear Engineering and Technology
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• v.49 no.4
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• pp.776-780
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• 2017

To avoid imaging artifacts and interpretation mistakes, an improvement of the uniformity in gamma camera systems is a very important point. We can expect excellent uniformity using cadmium zinc telluride (CZT) photon counting detector (PCD) because of the direct conversion of the gamma rays energy into electrons. In addition, the uniformity performance such as integral uniformity (IU), differential uniformity (DU), scatter fraction (SF), and contrast-to-noise ratio (CNR) varies according to the energy window setting. In this study, we compared a PCD and conventional scintillation detector with respect to the energy windows (5%, 10%, 15%, and 20%) using a $^{99m}Tc$ gamma source with a Geant4 Application for Tomography Emission simulation tool. The gamma camera systems used in this work are a CZT PCD and NaI(Tl) conventional scintillation detector with a 1-mm thickness. According to the results, although the IU and DU results were improved with the energy window, the SF and CNR results deteriorated with the energy window. In particular, the uniformity for the PCD was higher than that of the conventional scintillation detector in all cases. In conclusion, our results demonstrated that the uniformity of the CZT PCD was higher than that of the conventional scintillation detector.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.573-577
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• 2003

We report an effect of photon pairs on single-photon detection rates, while Hong-Ou-Handel's two-photon interference experiment is performed with photons produced in noncollinear type-I parametric down-conversion. Photon pairing behavior or spatial bunching is measured and shown to cause a decrease in the single photon counting rate. Such a dip is found to result from the fact that the single-photon timing resolution of photodetectors is much longer compared to the time interval between the two photons incident on the single-photon detector.

• Proceedings of the KIEE Conference
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• 1989.11a
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• pp.512-514
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• 1989

A time-correlated single photon counting system combined with a mode locked $Ar^+$ laser has been utilized to measure the fluorescence decay. A side-on type photomultiplier tube has been used as a photon detector. By restricting the sensitive area and the position of the photocathode, the transit time differencies of photoelectrons in PMT has been reduced. The fluorescence life time of rhodamin 6G in ethylene glycol measured 3.9$\pm$10 ns.

• Journal of the Korean Society of Radiology
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• v.8 no.7
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• pp.423-428
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• 2014

Digital X-ray imaging devices using a TFT based flat panel array has been used in medical field. But, recently, lots of research on the photon counting sensor has been reported. In this study, we evaluated the physical properties of the photoconductor by suggesting the standard and testing method for quantitative performance evaluation of photon counting x-ray imaging sensor. First, we measured the leakage current and the sensitivity of photon counting x-ray imaging sensor and we evaluated the characteristic of rising time for determining the signal shaping time. In addition, the set-up study was conducted on the basis of the IEC 62220-1-2 recommendations to define the number of incident photons per unit area. And the efficiency of the charge collection was also evaluated. As a result, the characteristic was measured as $200pA/mm^2$ of the leakage current, $7{\mu}C/cm^2R $ of the X-ray sensitivity, and $0.765{\mu}s$ of the rising time.

• Electronics and Telecommunications Trends
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• v.35 no.4
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• pp.21-33
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• 2020

Single photon detector technologies have emerged as powerful tools in optical quantum information applications such as quantum communication, quantum information, and integrated quantum photonics. Owing to significant attempts in the previous decade at improving photon-counting detectors, several single photon detectors with high efficiency and low noise have been realized within the optical wavelength regime. In this paper, we provide an overview of current studies on single photon detectors operating at wavelengths from the ultraviolet to the infrared. In addition, we discuss applications of single photon detector technologies in quantum communication and integrated quantum photonics.