• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.70-72
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• 2002

Amplified pulsed laser beam with narrow linewidth was generated from CW laser beam with narrow linewidth by using frequency doubled Nd:YAG laser beam and Bethune cell. The degree of the frequency chirping of the amplified pulse laser was measured by using the heterodyne method and obtained by calculating instantaneous phase change from heterodyne beating signals. The frequency chirping of amplified pulsed laser beam from CW laser beam with sub-MHz linewidth by 10 ns pulse was 80 MHz so that pulsed laser beam with very narrow linewidth was obtained.

• 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.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.48-49
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• 2003

원자가 전자기파와 상호작용할 때 원자 전이의 결맞음 여기 (coherent excitation of atomic transitions)는 일반적인 현상이다. 이 상호작용은 라비 진동 (Rabi oscillation), 자유 유도 감쇠 (free induction decay), 단열 밀도 이송 (adiabatic population transfer), 결맞음 과도 (coherent transients； CT) 등 다양한 결과를 가져온다. 특히, 전자기파의 주파수가 원자의 공진주파수를 중심으로 스윕될 때 결맞음 과도 현상 (coherent transient phenomenon)은 밀도 반전 (population reversal)을 유도하기도 한다. (중략)

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.214-219
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• 1997

We propose a new scheme of high-resolution heterodyne interferometer that employs the two-axial mode He-Ne laser with an inter-mode beat frequency of 600-1000 MHz. An electronic RF-heterodyne circuit lowers the beat frequency down to 5 MHz, so that the phase change of the interferometer output is precisely measured with a displacement resolution of 0.1 nanometer without significant loss of dynamic bandwidth. A thermal control scheme is adopted to stabilize the cavity length with aims to suppress frequency drifts caused by the phenomena of frequency pulling and polarization anisotropy of the two-axial mode laser to a stability level of 2 parts in $10^9$. The two-axial mode HeNe laser yields a high output power of 2.0 mW, whlch allows us to perform multiple measurements of up to 10 machine axes simultaneously.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.530-536
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• 2002

The accurate measurements of thermal expansion coefficients is one of the most important techniques required not only in material science but also in industries. A high precision interferometric dilatometer, using acoustic optical modulator, has been constructed and its performance has been tested. The system consists of a double-path optical heterodyne interferometer and a radiant heating furnace. This provides highly accurate length measurement, and allows rapid heating and cooling method for the specimen. A three longitudinal mode frequency stabilized He-Ne laser, using the secondary beat frequency, is constructed. Its stability is found to be $5{\times}10^{-9}$. The uncertainty in the length measurement is estimated to be of nanometer order in the range between room temperature to 1100 K.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.324-330
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• 1995

Stimulated Brillouin scattering theory is described in an optical fiber. Frequency change with an optical heterodyne method is analyzed between reference signal of a source and stimulated Brillouin scattering signal in an optical fiber. By coupling a source with a few axial modes and an optical fiber ring resonator, Brillouin scattering is studied with a spectrum analyzer. Using reference beating signal of a source, we have reduced the Brillouin beating frequency from 13 GHz range to below GHz. Experimentally, we can see the Brillouin beating frequency from 13 GHz range to below GHz with a dispersion shifted fiber (1.32 GHz), Ti-doped fiber (900 MHz) and single mode optical fiber (870 MHz). MHz).

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.195-201
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• 2002

We propose a new scheme of high-resolution heterodyne interferometer that employs the two-axial mode He-Ne laser with an inter-mode beat frequency of 600~1000 MHz. An electronic RF-heterodyne circuit lowers the beat frequency down to 5 MHz, so that the phase change of the interferometer output is precisely measured with a displacement resolution of 0.1 nanometer without significant loss of dynamic bandwidth. A thermal control scheme is adopted to stabilize the cavity length with ainus to suppress frequency drifts caused by the phenomena of frequency pulling and polarization anisotropy of the two-axial made laser to a stability level of 2 parts in $10^9$. The two-axial mode HeNe laser yields a high output power of 2.0 mW, which allows us to perform multiple measurements of up to 10 machine axes simultaneously.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.73-76
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• 2004

에밀레종은 서기 771년도(신라 혜공왕 7년)에 완성한 것으로 성덕대왕의 공적을 기리기 위해 34년간 주조(높이 3.663m, 최대지름 2.227 m, 무게 18.900, 두께 $7.7\~21.5m$)한 에밀레종의 과학성은 놀랄만하다. 외형도 미려하지만 종소리는 천, 지, 인을 뒤흔드는 신비감을 갖추고 있다. 에밀레 종소리는 끊어질 듯 이어지는 소리, 애끓는 소리, 심금을 울리는 소리 등의 특징을 갖는데 끊어질듯 이어지는 소리는 맥놀이 현상으로 나타난다. 지금까지 에밀레 종소리 규명에 대한 많은 연구가 있었다. 본 연구에서는 스펙트럼 분석을 통하여 에밀레 종소리에서 나타난 기본 주파수 64Hz, 168Hz, 360Hz, 480Hz 특성과 중년 남성의 목소리를 음성 분석기의 분석한 파형, 스펙트럼, 스펙트로그램으로 상호간의 비교 분석을 통하여 유사성을 규명하였다.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.480-486
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• 1993

We propose and demanstrate a fiber laser as a sensor, whose output is the frequency of beat signals between eigenpolarization modes of the fiber laser. For the measurement of lateral stress, proportional constant of 4.8 kHz/gram is obtained with a good linearity. For the measurements of temperature and longitudinal strain applied to the polarization maintaining fiber laser, proportional constants of 30 kHz/$^{\circ}C$ -cm, and 43 kHz/${\mu}m$, respectively, are obtained.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.146-151
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• 1999

We demonstrated a harmonic mode locking scheme that used regeneratie phase modulation to get a high and stable repetition rate in a figure-of-eight fiber soliton laser. From the detected beat spectra of the laser output, a sinusoidal clock freguency tone of 400 MHz, the 96th harmonics of the fundamental mode locking frequency, was extracted with a high Q filter and was used to drive the phase modulator, resulting in stable output of soliton pulse train synchronized with the modulation signal. Generated soliton pulses had FWHM pulsewidth of 930 fs and 3.1 nm linewidth, yielding pulsewidth-bandwidth product of 0.359 that was close to the transform limit. As the modulation frequency always followed the beat frequency of laser modes, stable harmonic mode locking was achieved without the adjustment of the cavity length, which has been commonly required in actively mode-locked lasers.