• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.68-73
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• 2004

Flexure measurement of ring laser gyro was investigated by using an interferometer. A two-beam interferometer of Fiezo-fringe pattern obtained the flexure angle in 1-gravity acceleration and the higher acceleration environments. These environments were made with the addition of dummy mass to the ring laser gyro axis. The flexure angle change for 1-gravity acceleration change was measured as 2.37 arcsec/g with low repeatability error of 0.01 arcsec/g. The laser navigation system consisting of 3 flexure-reduced ring laser gyros showed the improvement of flexure error.

• Journal of the Optical Society of Korea
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• v.17 no.4
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• pp.323-327
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• 2013

A laser ultrasonic inspection system has the advantage of nondestructive testing. It is a non-contact mode using a laser interferometer to measure the vertical displacement of the surface of a material caused by the propagation of ultrasonic signals with the remote ultrasonic generated by laser. After raising the ultrasonic signal with a broadband frequency range using a pulsed laser beam, the laser beam is focused to a small point to measure the ultrasonic signal because it provides an excellent measurement resolution. In this paper, foreign materials are measured by a non-destructive and non-contact method using the laser ultrasonic inspection system. Mixed foreign material on the corroded part is assumed and the laser ultrasonic experiment is conducted. An ultrasonic wave is generated by pulse laser from the back of the specimen and an ultrasonic signal is acquired from the same location of the front side using continuous wave laser and Confocal Fabry-Perot Interferometer (CFPI). The characteristic of the ultrasonic signal of existing foreign material is analyzed and the location and size of foreign material is measured.

• Korean Journal of Optics and Photonics
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• v.23 no.5
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• pp.203-210
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• 2012

Sagnac interferometer gyroscopes can be divided into three large generations using starting points of time or highlights of their research. As the first generational Sagnac interferometer, the ring laser gyroscopes have been studied since the 1960s by laser invention, and as the second generational Sagnac interferometer, the fiber optic gyroscopes have been studied since the 1970s by invention of optical fiber for communication. In the latter half of the 1990s, after having confirmed the wave theory of the atom, studies of atomic interferometers were started for a next generation gyroscope application. This paper discusses the operation principles, application, and future prospects of these three generations of Sagnac gyroscopes.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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• pp.171-178
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• 2001

The nonlinearity of a laser interferometer usually ranges from sub-nanometer to several manometers. This nonlinearity, which has periodic characteristics, limits the accuracy of the interferometer at the sub-nanometer level. The nonlinearity error of the one-frequency homodyne interferometer with quadrature fringe detection results from a number of factors including polarization mixing by imperfect optical elements, unequal gain of photo detectors, lack of quadrature between two signals and misalignment. In this paper, we described a method for measuring and compensating the nonlinearity of homodyne interferometer using the elliptical fitting technique with least-square method. Experimental results demonstrate that $^\pm$3.5 nm nonlinearity can be reduced to $^\pm$0.2 nm level.

• 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.

• Korean Journal of Optics and Photonics
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• v.32 no.3
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• pp.108-113
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• 2021

We propose and experimentally demonstrate a method of remote sound extraction using laser Doppler interferometry. The output frequency of a laser Doppler interferometer changes to be the same as the frequency of the acoustic wave from than object vibrated by the sound due to the Doppler effect. Based on this phenomenon, we measure the vibrational frequency of a remote target affected by a sound wave in real time, via laser Doppler interferometry. We track the peak frequency of the interferometer's output via appropriate signal processing, which confirms that the characteristics of the so detected wave are the same as that of the original sound source. We also confirm that the same method can retrieve the sound waves not only from remote sources of single tones, but from those of any sound.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1225-1230
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• 2003

In this study, Real-time estimation and compensation procedure are developed for the laser interferometer. This system is designed with homodyne quadrature-phase detection method using the Laser interferometer. The errors in this system are due to noise, disturbance and undefined model dynamics. DSP(Digital Signal Processor) is applied for real time compensation of these errors. This estimator and compensation is verified with measurement test.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.195-198
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• 2002

Demand for high precision measurement of large area is increasing in many industrial fields. White-light Scanning Interferometer(WSI) is a well-known method for 3D profile measurement. However WSI has some limitations in a measurement range because of the sensing mechanism. Therefore, in this paper we use a heterodyne laser interferometer to get over the limitations of a short measurement range in WSI, We suggest a new WSI system combined with heterodyne laser interferometer. This system is aimed at eliminating Abbe error with measuring the focus point directly. With the use of triggering functionality of WSI, we can use this system as a probe of a precision stage such as a probe of CMM. The suggested system gives a repeatability of 87 nm in the absolute distance measurement test under the laboratory environment.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.174-179
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• 2003

Non-destructive test on the size and depth of cracks has been required for the safety evaluation of structures. Ultrasonic method based on laser techniques is one of the most popular non-destructive methods which overwhelm PZT based tests. In the present paper, ultrasonic was generated by high powered Q switching Nd:YAG pulse laser. Experiments were carried out using Fabry-Perot interferometer which was intensively discussed in the present study.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.195.1-195.1
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• 2016

Currently, as Plasma application is expanded to the industrial and medical industrial, low temperature plasma applications became important. Especially in medical and biology, many researchers have studied about generated radical species in atmospheric pressure low temperature plasma directly adapted to human body. Therefore, so measurement their plasma parameter is very important work and is widely studied all around world. One of the plasma parameters is electron density and it is closely relative to radical production through the plasma source. some kinds of method to measuring the electron density are Thomson scattering spectroscopy and Millimeter-wave transmission measurement. But most methods have very expensive cost and complex configuration to composed of experiment system. We selected Michelson interferometer system which is very cheap and simple to setting up, so we tried to measuring electron density by laser interferometer with laser beam chopping module for measurement of temporal phase difference in plasma jet. To measuring electron density at atmospheric pressure Ar plasma jet, we obtained the temporal phase shift signal of interferometer. Phase difference of interferometer can occur because of change by refractive index of electron density in plasma jet. The electron density was able to estimate with this phase difference values by using physical formula about refractive index change of external electromagnetic wave in plasma. Our guiding laser used Helium-Neon laser of the centered wavelength of 632 nm. We installed chopper module which can make a 4kHz pulse laser signal at the laser front side. In this experiment, we obtained more exact synchronized phase difference between with and without plasma jet than reported data at last year. Especially, we found the phase difference between time range of discharge current. Electron density is changed from Townsend discharge's electron bombardment, so we observed the phase difference phenomenon and calculated the temporal electron density by using phase shift. In our result, we suggest that the electron density have approximately range between 1014~ 1015 cm-3 in atmospheric pressure Ar plasma jet.