• Journal of the Korean Magnetics Society
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• v.10 no.5
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• pp.246-249
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• 2000

An Fe$_{49}$ Co$_{49}$ V$_2$alloy is annealed in thermal annealing furnace at 50$0^{\circ}C$, 75$0^{\circ}C$, 80$0^{\circ}C$, and 90$0^{\circ}C$. Annealed samples were cooled in air. The magnetostriction is measured by using a Michelson laser interferometer. Receiving the feedback signal of interference, a mirror attached to piezoelectric transducer (PZT) maintains the optical path length (OPL) between two arms of laser interferometer relatively constant. The feedback voltage is calibrated to the OPL variation. A magnetostriction of 2$\times$10$^{-6}$ at H = 60 Oe increases up to 33.68$\times$10$^{-6}$ at an annealing temperature of 90$0^{\circ}C$, suggesting that the magnetostrictive characteristics are improved by the microstructural modification.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.7
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• pp.939-947
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• 1997

An experimental study of the skin friction measurement in a turbulent boundary-layer has been carried out. The skin friction measurements are made using the laser interferometer skin friction (LISF) meter, which optically detects the rate of thinning of an oil applied to the test surface. This technique produces reliable skin friction data over a wide range of flow situations up to 3-dimensional complicated flows with separation, where traditional skin friction measurement techniques are not applicable. The present measured data in a turbulent boundary-layer on a flat plate using the LISF technique shows a good comparison with the result from the previous velocity profile techniques, which proves the validity of the present technique. An extensive error analysis is carried out for the present technique yielding an uncertainty of about .+-.8%, which makes them suitable for CFD code validation purposes. Finally the measurements of the skin friction in a separated region after a surface-mounted obstacle are also presented.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.1
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• pp.1-10
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• 1994

The flow and heat transfer characteristics behind a backward facing step located in a vertical channel has been studied. In this study, the numerical prediction has been performed by solving the Navier-Stokes equation and energy equation simultaneously with the SIMPLE algorithm embedied in TEACH code. Local heat flux was measured by using Schlieren Interferometer. The flow visualization was performed using the cylindrical lens and the laser beam that is scattered by the supplied glycerine particles. The velocity and temperature distributions, recirculation region, reattachment length, and local heat flux are obtained under the various parameters to investigate the buoyancy effect on the flow and heat transfer characteristics behind the step.

• Korean Journal of Optics and Photonics
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• v.10 no.5
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• pp.369-372
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• 1999

We have constructed an interferometric microscopy using a Michelson interferometer and a He-Ne laser. The three dimensional image was obtained by the interference from the reflected signal by a sample surface and from the reflected signal by a mirror. The axial resolution obtained by Michelson interferometric microscopy is as good as that of the white-light interferometer, but the same fringe is obtained when optical path difference is half-wavelength. The image from Michelson interferometric microscopy was compared with the images from the various types of confocal microscopy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.792-796
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• 2003

In this paper, to detect external sound frequency on the latticed structure, fiber optic sensor net using Sagnac interferometer was fabricated and tested. The latticed structure fabricated with dimension of 50cm in width and 50cm in height, the optical fiber, 50m in length, distributed and fixed on the latticed structure. Single mode fiber, a laser with 1,550nm in wavelength, 2${\times}$2 coupler were used. External sound signal applied to the fiber optic sensor net and the detected optical signals were compared and analyzed to the detected microphone signals against time and frequency domain. Based on the experimental results, fiber optic sensor net using Sagnac interferometer detected external sound frequency, effectively. This system can be expanded to the structural health monitoring system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.436-437
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• 2005

3-dimension object's feature measurement is used several industrial field to produce for examination of demanded high quality products by using optical measurement method. 3-dimension object's feature measurement is separated surface scanning and surface non-scanning. In this research, we illuminated interfero-pattern to object, it was constructed with Michelson interferometer by using laser is one of surface non-scanning method. And we extracted phase-map, it is one of featural measurement analysis of 3-dimensional object by using a phase shifting theory.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.7
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• pp.569-576
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• 2004

In this paper, to detect external sound frequencies on the latticed structure, fiber optic sensor net using Sagnac interferometer was fabricated and tested. The latticed structure was fabricated with a dimension of 50 cm in width and 50 cm in height. The optical fiber of 50m in length was distributed and fixed on the surface of the latticed structure. Single mode fiber, a laser with 1,550 nm in wavelength, 2 ${\times}$ 2 coupler were used. External sound signal, 240 Hz, 495 Hz, 1.445 kHz, 2k Hz, applied to the fiber optic sensor net and the detected optical signals were compared to the detected microphone signals against time and frequency domains. Based on the experimental results, fiber optic sensor net using Sagnac interferometer detected external sound frequency, effectively. This system can be expanded to the structural health monitoring system.

• Korean Journal of Optics and Photonics
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• v.16 no.1
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• pp.50-55
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• 2005

A method for measuring the wavefront error and the modulation transfer function(MTF) of large aperture optics using an unequal path interferometer is presented. A bidirectional shearing interferometer is used for collimation testing of the measurement system. A large aperture Fizeau interferometer with long optical path difference measures the wavefront error of the optics under test by using a $\Phi$ 400 mm off-axis parabolic mirror. The MTF is also measured at the wavelength of the interferometer by changing the laser light into partially incoherent light. Test results of a $\Phi$ 300 mm Cassegrain type satellite telescope made in Korea are presented.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.6
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• pp.380-389
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• 2006

A new laser-based ultrasonic receiver that is based on multi-channel interferometry is shown to be well suited for robust and sensitive detection of ultrasound in industrial environment. The proposed architecture combines random-quadrature detection with detector arrays and parallel multi-speckle processing. The high sensitivity is reached, thanks to the random phase distribution of laser speckle caused by surface roughness. High-density parallel signal processing is achieved by using a simple demodulation technique based on signal rectification. This simple detection scheme is also demonstrated for rejection of the laser intensity noise, making possible the use of lower cost laser without reduction in performances. Results demonstrating this new principle of operation and its performances are presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.3
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• pp.204-210
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• 1986

In this paper, a new method is suggested to stabilize the frequency of semiconductor laser diode for heterodyne optical communication systems. In order to stabilize the frequency of semiconductor laser, the method of the injection current controal has been widely used, in which the laser frequency is locked to a F-P interferometer. By adding another servoloop to stabilize the output power of semiconductor laser, we could stabilize the laser frequency and the output power simultaneously and the frequency stability is improved by a factor of fice times.