• 한국광학회지
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• 제16권6호
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• pp.490-493
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• 2005

본 논문은 광자 결정 광섬유에서 100 fs의 펄스 폭을 갖는 펌프 광원의 파장과 입력파워에 따른 초 광대역 광원 생성에 대해 실험적으로 연구하였다. 적절한 파라미터들을 조절함으로써 광 스펙트럼 진폭의 균일함이 10 dB 이내에서 약 750 nm의 스펙트럼 폭을 갖는 초 광대역 광원을 얻어냈다. 사용한 광자 결정 광섬유의 길이는 2 m였고, 펌프광원으로는 모드 록킹된 Ti:Sapphire laser를 사용하였다. 또한, 펌프 광원의 여러 가지 변수들을 바꿔줌으로써 초 광대역 광원의 다양한 스펙트럼 현상을 조절할 수 있었다.

• Journal of the Optical Society of Korea
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• 제13권1호
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• pp.15-21
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• 2009

High-order harmonic generation from a solid surface affected by the contrast of a laser pulse was studied using an oscillating mirror model. High-order harmonics generated from solid surfaces have unusual properties such as spectral redshift, and an intensity difference between even- and odd-order harmonics which is not reported for high-order harmonics generated by a gas medium. We confirmed that high-order harmonics from solid surfaces have selectivity of polarization as well as cut-off extension and the enhancement of conversion efficiency proportional to laser intensity. And the principle of operation and the characteristics of a plasma mirror system developed for achieving high contrast laser pulses to pursue the experimental realization of high-harmonic generation from solid surfaces are reported. Energy fluence on the plasma mirrors is tunable between $10\;J/cm^2$ and $1000\;J/cm^2$ and around 1000 shots are available before the plasma mirrors require replacement.

• 한국정밀공학회지
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• 제30권10호
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• pp.1009-1015
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• 2013

Ultra-short laser pulses are effective, when high requirements concerning accuracy, surface roughness and heat affected zone are demanded for surface structuring. In particular, picosecond laser systems that are suited to be operated in industrial environments are of great interest for many practical applications. This paper focused on inducing optimum process parameters for higher volume ablation rate by analyzing a relationship between crater diameter and optical spot size. In detail, the dependency of the volume ablation rate, penetration depth and threshold fluence on the pulse duration 8 ps and wavelength of 515 nm was discussed. The experimental results showed that wavelength of 515 nm resulted in less threshold fluence ($0.075J/cm^2$) on copper than IR wavelength ($0.3J/cm^2$). As a result, it was possible that optimum fluence for higher volume ablation rate was achieved with $0.28J/cm^2$.

• 한국정밀공학회지
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• 제21권7호
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• pp.101-106
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• 2004

Measurements of linear motion accuracy for one axis of NC lathe have achieved with laser interferometer system, but measurement of plane motion accuracy for two axes on zx-plane of NC lathe have not achieved with the above system. Therefore in this study, measuring unit system is organized using two optical linear scales in order to acquire error. data during of plane motion of ATC(Automatic Tool Change.) of NC lathe by reading zx-plane coordinates. Two optical linear scales of measuring unit are fixed on zx-plane of NC lathe, and moving part of the scales are fixed to the ATC and then error motion data of z, x-coordinates of the ATC are received from the scales through the PC counter card inserted in computer at constant time intervals using tick pulses coming out from computer. And then, error motion data files acquired from measuring are saved in computer memory and the aspect of plane motion are modeled to plots, and range of the error data, means. average deviations, and standard deviations etc. are calculated by means of statistical treatments using computer programs.

• Current Optics and Photonics
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• 제4권4호
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• pp.368-372
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• 2020

We report the terahertz time-domain spectroscopy (THz-TDS) of transdermal drug delivery in human skin. The time evolution of transdermal nicotine delivery in nicotine patches was assessed by detecting the transmission coefficient of sub-picosecond THz pulses and using a semi-analytic model based on the single-layer effective medium approximation. Using commercial nicotine patches (Nicoderm CQ^®, 7 mg/24 h), THz transmission coefficients were measured to quantitatively analyze the cumulative amounts of nicotine released from the patches in the absence of their detailed specifications, including multilayer structures and optical properties at THz frequencies. The results agreed well with measurements by conventional in vitro and in vivo methods, using a diffusion cell with high-performance liquid chromatography and blood sampling respectively. Our study revealed the ability of the THz-TDS method to be an effective alternative to existing methods for noninvasive and label-free assessments of transdermal drug delivery, showing its high promise for biomedical, pharmaceutical, and cosmetic applications.

• 반도체디스플레이기술학회지
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• 제16권3호
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• pp.111-115
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• 2017

Terahertz waves are superior to conventional X-ray or Magnetic Resonance Tomography(MRI), and the amount of information that can be transmitted is as large as thousands of times that conventional X-ray or MRI. In addition, Terahertz waves have great performance in analyzing an object which have some layered structure. By using this advantage, we can extract the letters of a page by analyzing information such as absorption amount and reflection amount by irradiating a closed book with pulses of various frequencies within gap of a terahertz wave. However, in the image of each page using the Terahertz wave might be obtained various kinds of noise and the different character occlusion region. So, to extract letters from the terahertz image, we must take the noise and occlusion region away. We have been working to enhancement the image quality in various ways, and keep on studying de-noising processing for enhancement about the image quality and high resolution. Finally, we also keep on studying about OCR(Optical Character Recognition) technology, which based on pattern matching technique, to read letters.

• 한국산학기술학회논문지
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• 제1권2호
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• pp.63-68
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• 2000

어븀 첨가된 고리형 광섬유 레이저를 제작하여 외부 조절기를 적용하지 않은 수동형 모드로킹을 구현하였다. 모드로킹 현상은 단일 모드로킹 과정과 이중 모드로킹 과정이 관측되었고 분산천이 광섬유의 길이를 변화시켜 65 fs의 시간폭을 갖는 초단 펄스를 얻었다. 한편 고차조화모드로킹과 Q스위치된 고차조화 모드로킹도 구현하였는데, 연속파 고차조화 모드로킹은 17차까지 구현하였으며, 펌프 전력의 감소가 연속파 고차 조화 모드로킹에서 Q스위치된 고차조화 모드로킹으로 변화시키며 이러한 과정이 편광조절기에 의해서도 이루어 졌다 이러한 일련의 초단 펄스열의 연구는 광통신용 신호원으로 개발에 중요한 역할을 한다.

• 대한의용생체공학회:의공학회지
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• 제10권3호
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• pp.229-236
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• 1989

This paper describes an idea of design and construction for a radial pulse wave detector, In acquiring arterial pulse signal noninvasively, a new combinational fiber-optic transducer was used which has a detecting part and a sensing part. The mechanism of detecting part is composed of special form of structure that can detect changing pulses in contact with skin, and transmits arterial wall movements to the sensing part. It consists of elastic reflector and optical fibers, which are arranged in a fiber pair. Then, the intensity of the reflected light will be proportional to the displacement changed by inclined reflector. Using this transducer, it expected to make a clinically useful tool for arterial pulse wave diagnosis, especially on the application of "MACK- CHIN" in the field of Korean traditional medicine, since : his transducer has a simple structure and has an easy and clear signal acquisition method.on method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.1191-1193
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• 2001

In switched reluctance motor(SRM) drive, it is necessary to synchronize the stator phase excitation with the rotor position. Therefore, the rotor position information is essential. Usually, optical encoders or resolvers are used to provide the rotor position information. These sensors are expensive and are not suitable for high speed operation. This paper proposes a new encoder for high performance excitation control of SRM. The proposed encoder has complex structures of incremental and absolute encoder. An each phase inductance profile can be synchronized with 4-bit absolute position signal and incremental pulses are used for speed detection. Low cost and simple structure are possible.

• 한국정밀공학회지
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• 제30권4호
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• pp.409-413
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• 2013

A polypropylene film was ablated using a $CO_2$ laser, Ti-sapphire femtosecond laser, and UV nanosecond laser. For modified atmosphere packaging, polypropylene films were ablated by laser pulse with different pulse energies and measured on an optical microscope. Also, we observed the shelf life of a banana contained within packaging of a breathable zipper bag. As a result, we have demonstrated that the breathable film can efficiently extend the shelf life of respiring foods, particularly fresh fruits and vegetables. The development of breathable film laser microfabrication system will more useful for industrial applications.