• Journal of the Optical Society of Korea
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• v.7 no.3
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• pp.150-155
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• 2003

Femtosecond laser ablation mechanism was systematically investigated on sodalime glass in ambient conditions. The ablation crater diameter was measured for varying numbers of laser pulses as for varying well as the laser fluence. The analysis of the results with a one dimensional spatial Gaussian fluence distribution reveals that the inherent ablation mechanism has been altered from a multi-photon process to a single photon excitation due to defect sites that have been accumulated by successive laser pulses. Furthermore, the transition between the two regimes was found to be a function of both the laser fluence and the number of laser shots.

• Korean Journal of Optics and Photonics
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• v.5 no.2
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• pp.260-265
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• 1994

In the three-level atom interacting with a single mode radiation field, two-photon excitation between the ground state and the upper most excited state is investigated. Using the resolvant theory, the effective resolvant, containing the ground state and the final excited state, is found and the coupling constant and the detuning being taken as parameters, the excitation mechanism is analyzed. In particular. by introducing an ensemble of effective two-level atoms, a consistent interpretation in terms of inteference phenomena is pursued. rsued.

• Journal of the Optical Society of Korea
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• v.1 no.1
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• pp.10-14
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• 1997

Single pulse laser excitation at 656 nm and successive pulse excitation at 635.2 and 648.4 nm produced blue emission at 480 nm by two-step upconversion process in Tm/sup 3+/:LaF/sub 3/. The excited-state absorption cross-section of the /sup 3/F/sub 4/ to /sup 1/G/sub 4/ transition was estimated by a looping mechanism with cross-relaxation processes. The dynamics of up-conversion andthe possibility of the photon avalanche by a pulse laser excitation were studied by numerical simulation with the rate equation model.

• Bulletin of the Korean Chemical Society
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• v.14 no.5
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• pp.610-614
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• 1993

Laser induced impedance changes in hollow cathode lamps containing sputtered metal atoms have been employed to measure the spectroscopic properties of metal. This technique, known as optogalvanic spectroscopy, has been shown to be a powerful and inexpensive technique for the investigation of atomic and molecular species. Characteristic optogalvanic signals from hollow cathode lamps (HCL) made of different metal species and induced with a pulsed dye laser were observed, and the dependence of the optogalvanic signal on the discharge current and wavelength of laser was measured. Based on the results obtained, the mechanisms involved in evoking the optogalvanic signals were consisted of single-photon absorption, multi-photon absorption, and photoionization. Moreover the current dependence of the optogalvanic signal indicates that the optogalvanic technique could be one of the most sensitive optical methods of detecting atomic species.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1633-1637
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• 2019

While considering the photon attenuation coefficient (${\mu}$) and its related parameters for photons shielding, it is necessary to account for its transmitted and reflected photons energy spectra and dose contribution. Monte Carlo simulation was used to study the efficiency of clay ($1.99g\;cm^{-3}$) as a shielding material below 150 keV photon. Am-241 gamma source and an X-ray of 150 kVp were calculated. The calculated value of ${\mu}$ for Am-241 is higher within 5.61% compared to theoretical value for a single-energy photon. The calculated half-value layer (HVL) is 0.9335 cm, which is lower than that of ordinary concrete for X-ray of 150 kVp. A thickness of 2 cm clay was adequate to attenuate 90% and 85% of the incident photons from Am-241 and X-ray of 150 kVp, respectively. The same thickness of 2 cm could shield the gamma source dose rate of Am-241 (1 MBq) down to $0.0528{\mu}Sv/hr$. For X-ray of 150 kVp, photons below 60 keV were significantly decreased with 2 cm clay and a dose rate reduction by ~80%. The contribution of reflected photons and dose from the clay is negligible for both sources.

• The Korean Journal of Applied Statistics
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• v.26 no.4
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• pp.569-579
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• 2013

In the field of single-molecule spectroscopy, it is essential to analyze luminescence Intensity changes that result from a single molecule. With the CdSe/ZnS core-shell structured quantum dot photon emission data Bayesian multiple change-point estimation is done with the gamma prior for Poisson parameters and truncated Poisson distribution for the number of change-points.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.563-564
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• 2006

A single photon counting type image sensor which is applicable for medical diagnosis with digitally obtained image and industrial purpose has been designed using $0.25{\mu}m$triple well CMOS process.

• Clinical and Experimental Pediatrics
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• v.52 no.7
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• pp.804-810
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• 2009

Purpose : We investigated whether ictal single-photon emission computed tomography (SPECT) with prolonged injection of technetium-99m (99mTc) ethyl cysteinate dimer during repeated spasms can localize the epileptogenic foci in children with infantile spasms. Methods : Fourteen children with infantile spasms (11 boys, 3 girls; mean age, $2.2{\pm}1.3$ years) were examined. When a cluster of spasms was detected during video electroencephalography (EEG) monitoring, $^{99m}Tc$ ethyl cysteinate dimer was slowly and continuously injected for 2 minutes to determine the presence of ictal SPECT. For 7 children, the ictal and interictal SPECT images were visually analyzed, while for the remaining 7 children, the SPECT images were analyzed using the subtraction ictal SPECT coregistered to magnetic resonance imaging (MRI) (SISCOM) technique. Subsequently, we analyzed the association between the ictal SPECT findings and those of other diagnostic modalities such as EEG, MRI, and positron emission tomography (PET). Results : Increase in cerebral blood flow on ictal SPECT involved the epileptogenic foci in 10 cases6 cases analyzed by visual assessment and 4 analyzed by the SISCOM technique. The ictal SPECT and video-EEG findings showed moderate agreement (Kappa=0.57; 95% confidence interval, 0.18-0.96). Conclusion : Ictal SPECT with prolonged injection of a tracer could provide supplementary information to localize the epileptogenic foci in infantile spasms.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.6
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• pp.425-434
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• 2008

Dopamine transporter imaging is useful in the diagnosis of Parkinson's disease and the most successful technique in the clinical use of neuroreceptor imaging. Recently, several radiopharmaceuticals including I-123 FP-CIT, Tc-99m TRODAT, and F-18 FP-CIT for dopamine transporter imaging have been approved for the routine clinical use in several European countries, Taiwan and Korea, respectively. This review summarized the practical issue for the routine clinical examination of dopamine transporter imaging.

• 대한핵의학회:학술대회논문집
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• 2005.11a
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• pp.343.1-343.1
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• 2005