• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.102-105
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• 2000

A simple digital control system has been developed for the frequency stabilization of an internal mirror He-Ne laser. The system is based on one chip microprocessor with embedded Basic interpreter. To stabilize the laser output frequency, the signal such as power difference or beat frequency between two modes is supplied and processed by a microprocessor, and control signal is fed to the heating coil would round the laser tube for adjusting the spacing of the laser cavity mirror. Newly developed frequency stabilization system is totally digitized. The system and the frequency stability performance are briefly described.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.317-323
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• 1995

Doppler-free circular polarization spectroscopy in 87Rb Dz line has been carried out by using a diode laser whose linewidth was narrowed by an external cavity, and experimental results were compared with an optical pumping polarization spectroscopy theory. A dispersive spectrum obtained in a weak pump beam was completely fitted to a single cycle optical pumping theory. The laser frequency was locked to a Rb atomic hyperfine transition line without any frequency modulation by using the dispersive curve as an error signal. ignal.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.188-191
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• 2005

A common feature in various methods of optical interferometry for absolute distance measurements is the use of multiple monochromatic light components either in sequence or in parallel at the same time. Two or multiple wavelength synthesis has been studied though its performance is vulnerable to the frequency instability of the light source. Recently continuous frequency modulation is considered a promising method with availability of wide band tunable diode lasers, which also have frequency instability errors. We can lock frequencies of these third-party light sources to the modes of the femtosecond laser which is stabilized to the precision of the standard radio frequency. To this end, we have stabilized all the modes of the femtosecond laser to the atomic frequency standard by using powerful tools of frequency-domain laser stabilization.

• Elastomers and Composites
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• v.39 no.3
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• pp.179-185
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• 2004

Frequency dependency or electrical property stabilization during vulcanization of modified NR/IR composite materials was studied using in-situ electrical property measuring technique. Volume resistivity(p) before and after vulcanization reaction of the sample was measured as the function or frequency in the range or 1Hz to 10kHz at reaction temperatures of 130, 140, 150, and $160^{\circ}C$, respectively. A double stabilization mode of frequency dependency was observed, in which a slow stabilization process of p to a value of ca. $1.0{\times}10^7\;{\Omega}-cm$ occurred after a drastic initial decrease from ca. $9.0{\times}10^7\;{\Omega}-cm$. In addition, notable temperature dependencies of p values were also observed before and after vulcanization reaction, that is, p values at 130 and $140^{\circ}C$ after vulcanization were observed as about 1/3 of those values before vulcanization. All the observed facts were considered as the results from the interaction between the electrode and the bulk sample materials, i.e., electronic charge-discharge, and from the structure change of samples including CB rearrangement by the vulcanization.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.569-574
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• 2004

We stabilized the frequency and power of a CW radio-frequency-excited $CO_2$ laser on the peak of the Doppler broadened gain curve using the photoacoustic effect generated from the laser itself. The condenser microphone is installed in the radio frequency discharge chamber to detect a photoacoustic signal. The photoacoustic signal is fed to a lock-in stabilizer as a reference signal for stabilization. The frequency stability is estimated to be better then 5.4${\times}$10$^{-8}$ at the P(20) line. The stabilized output variation was reduced 9.3%, compared to 100% for a free running laser.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.113-114
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• 2007

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1991.06a
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• pp.49-49
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• 1991

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.1
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• pp.23-33
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• 2022

The horizontal-to-vertical spectral ratio (HVSR) of ambient noise is widely used to identify the resonant frequency of a site. The frequency at the largest HVSR is regarded as the resonant frequency. The source of ambient noise is impossible to identify and control. Therefore, obtaining reliable HVSR of ambient noise requires sufficient measurement time and absence of near-field vibration. In this study, we investigated the minimum stabilization time required for a portable seismometer and the effect of the distance between the seismometer and artificial vibration on HVSR estimation. In the case of a soil site, the HVSR was stabilized after 5 minutes after sensor installation. In the case of a rock site, stabilization required more than an hour. Human-footsteps within 10 m of the seismometer strongly influenced the HVSR for the soil site. These results provide a field guideline when measuring ambient noise for HVSR.

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.224-225
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• 2002

펨토초 모드록 레이저는 공진기의 왕복시간 $\tau$마다 펨토초 폭을 갖는 펄스를 발생시키고, Fourier 변환에 의해 주파수 공간에서는 일정한 주파수 간격 $\Delta$ = 1/$\tau$을 가지는 불연속 스펙트럼, 즉 광빗 스펙트럼을 갖게 된다(1). 광빗의 간격, 즉 펄스의 반복률, 은 $\Delta$ ： v$_{g}$l$_{c}$의 관계식에 의해 그룹속도(v$_{g}$)와 공진기 길이(l$_{c}$)에 의해 결정된다. 광빗의 간격을 고정시키기 위한 가장 일반적인 방법은 공진기 길이를 일정하게 유지하는 것이다. (중략)

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2249_2250
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• 2009

전력계통이 대규모, 다양화됨에 따라 계통의 안정화를 위한 광역보호계전 지능화 기술 개발이 요구되고 있다. 이를 위해서 네트워크 기반 주파수 모니터링 및 고장예측 시스템 개발 분야에 관심이 증대되고 있다. 본 논문은 정확한 주파수 계측을 위해서 요소기술로 필수적으로 사용해야하는 DFT 필터의 크기 응답, 위상 응답 등에 대해 연구하였다.