• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.351-355
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• 2017

In this paper, we conduct a simulation of manipulating various pulsed laser operations through tuning the modulation depth of the saturable absorber in a laser cavity. The research, showing that various pulsed operations could be manipulated from Q-switching through Q-switched mode locking to mode locking by tuning the modulation depth of the saturable absorber in a cavity, has been studied by experimental means. We conduct a simulation with the Haus master equation to verify that these experimental results are consistent with expectations from theory. The time dependence of the gain was considered to express Q-switching fluctuation through applying a rate equation with the Haus master equation. Laser operation was manipulated from mode locking through Q-switched mode locking to Q-switching as modulation depth was increased, and this result agreed well with the theoretical expectation.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.173-179
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• 1999

The defects on the metal surface. such as the ended circular pressed hole. the penetrated circular drilled hole, and the linear hollow lanes have been investigated by means of the microwave. In this experiment, frequency was set at 9.2GHz with 3kHz modulation, and the methods of reflection, transmission, fixed carrier frequency, and mod-demodulated technique have been used for investigating defects. The magnitudes of the microwave signals have been changed at the ended circular pressed hole and the penetrated circular drilled hole. The defect sizes that were estimated from the reflected microwave signals had the dimensions enlarged by twice the original size of the penetrated circular drilled hole and 2.5 times the original size of the ended circular pressed hole. The magnitudes of the reflected microwave signals from the linear hollow lane have increased with expansion of the width of the notch. In the linear hollow lane with the depth of 2.4mm, the reflected microwave signals versus the defect widths had a maximum value at the defect width of 50mm, and in the linear hollow lanes with the depths of 1.2mm and 0.45mm, the reflected microwave signals versus the defects widths had the maximum values each at the defect depths of 55mm.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.190-191
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• 2000

종래의 자기광학 디바이스는 자성체막을 빛이 투과할 때 얻어지는 페러데이 회전각을 이용했기 때문에, 페러데이 회전각을 증가시켜서, 광학적 성능을 증가시키려면 자성체막의 두께를 증가시켜야만 했다. 그러나, 자성체막의 두께를 증가시키면, 화소를 자기적으로 분리하기 위하여 자성체 막을 물리적으로 제거 해야하여 깊이가 깊어지고 그 후에 도선막을 구조화하기 위하여 파낸 화소간 갭을 다시 평탄화해야 하는 등의 제조 공정이 기술적으로 매우 어려워진다는 문제점을 가지고 있었다. 또한, 자성체 막의 두께가 증가하면, 도선막에 전류를 흘려 발생하는 자장은 도선막으로부터의 거리의 제곱에 반비례하므로, 두꺼운 자성체 막 전체에 강한 자장을 인가하기 위해서는, 도선막에 흘리는 전류를 증가시켜야만 한다는 문제점을 안고 있었다. (중략)

• Journal of the Korean Society of Radiology
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• v.6 no.3
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• pp.207-215
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• 2012

As one of photo dynamic therapies, the existing LED photo irradiation method with 635 nm continuous wave has most frequently been used for acne treatment, it suffered from a low energy efficiency and generation of a large amount of heat in tissues requiring improvement measures. In this thesis, a LED photo irradiation system for acne treatment has been designed using PWM(Pulse Width Modulation) mode to enhance the energy efficiency and prevent thermal destruction in tissues. System configuration consisting largely of timer module, PWM module, and photo transfer device has been designed with the use of 1 W LED at a wavelength of 660 nm for the photo transfer device to increase skin penetration depth for treatment of acne. Frequency and wave form generated by using PWM control was verified along with confirmation of output energy of 660 nm LED and surface temperatures of tissues, followed by evaluation of stable energy outputs and stability of tissues. The results indicated that whereas power loss was high and thermal destruction in tissues was exhibited when C.W mode was used to obtain the optical energy of 1 W LED at a wavelength of 660 nm for acne treatment, realization of PWM mode allowed lowering of power consumption for LED through pulse width modulation, and no occurrence of thermal destruction in tissues, suggesting that PWM mode is safer and more effective for treatment of acne than C.W mode.

• The Journal of Korean Society for Radiation Therapy
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• v.25 no.1
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• pp.1-8
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• 2013

Purpose: A selection of proper energy in treatment planning is very important because of having different dose distribution in body as photon energy. In generally, the low energy photon has been used in intensity-modulated radiation therapy (IMRT) for head and neck (H&N) cancer. The aim of this study was to evaluate the effect of partially used high energy photon at posterior oblique fields on IMRT plan for H&N cancer. Materials and Methods: The study was carried out on 10 patients (nasopharyngeal cancer 5, tonsilar cancer 5) treated with IMRT in Seoul National University Bundang Hospital. CT images were acquired 3 mm of thickness in the same condition and the treatment plan was performed by Eclipse (Ver.7.1, Varian, Palo Alto, USA). Two plans were generated under same planing objectives, dose volume constraints, and eight fields setting: (1) The low energy plan (LEP) created using 6 MV beam alone, (2) the partially used high energy plan (PHEP) created partially using 15 MV beam at two posterior oblique fields with deeper penetration depths, while 6 MV beam was used at the rest of fields. The plans for LEP and PHEP were compared in terms of coverage, conformity index (CI) and homogeneity index (HI) for planning target volume (PTV). For organs at risk (OARs), $D_{mean}$ and $D_{50%}$ were analyzed on both parotid glands and $D_{max}$, $D_{1%}$ for spinal cord were analyzed. Integral dose (ID) and total monitor unit (MU) were compared as addition parameters. For the comparing dose to normal tissue of posterior neck, the posterior-normal tissue volume (P-NTV) was set on the patients respectively. The $D_{mean}$, $V_{20Gy}$ and $V_{25Gy}$ for P-NTV were evaluated by using dose volume histogram (DVH). Results: The dose distributions were similar with regard to coverage, CI and HI for PTV between the LEP and PHEP. No evident difference was observed in the spinal cord. However, the $D_{mean}$, $D_{50%}$ for both parotid gland were slightly reduced by 0.6%, 0.7% in PHEP. The ID was reduced by 1.1% in PHEP, and total MU for PHEP was 1.8% lower than that for LEP. In the P-NTV, the $D_{mean}$, $V_{20Gy}$ and $V_{25Gy}$ of the PHEP were 1.6%, 1.8% and 2.9% lower than those of LEP. Conclusion: Dose to some OARs and a normal tissue, total monitor unit were reduced in IMRT plan with partially used high energy photon. Although these reduction are unclear how have a clinical benefit to patient, application of the partially used high energy photon could improve the overall plan quality of IMRT for head and neck cancer.