• Journal of the Korean Vacuum Society
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• v.21 no.5
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• pp.264-272
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• 2012

In this paper, we report THz generation and detection characteristics investigated by InGaAs semiconductor epilayers, as results of a basic study obtained from the InGaAs-based THz transmitter/receiver (Tx/Rx). High-temperature and low-temperature (LT) grown InGaAs epilayers were prepared by the molecular beam epitaxy technique for the characterization of THz generation and detection, respectively, and the surface emission based on the photo-Dember effect was tried for THz generation. THz wave was generated by irradiation of a Ti:Sapphire fs pulse laser (60 ps/83 MHz), and a LT-GaAs Rx was used for the THz detection. The frequency band shown in the spectral amplitudes Fourier-transformed from the measured current signals was ranging in 0.5~2 THz, and the signal currents were exponentially increased with the Tx beam power. The THz detection characteristics of LT-InGaAs were investigated by using an Rx with dipole (5/20 ${\mu}m$) antenna, and the cutoff frequency was ~2 THz.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1939-1943
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• 2012

In this paper we presented the detection of the explosive material RDX using a parallel plate waveguide (PPWG) THz time domain spectroscopy (TDS). Normally the explosive materials have been characterized through identification of vibrational fingerprint spectra. Until now, most of all THz spectroscopic measurements have been made using pellet samples where disorder effects contribute to line broadening such that individual resonances merge into relatively broad absorption features. In order to avoid such disadvantages we used the technique of PPWG THz-TDS to achieve sensitive characterization of explosive material RDX. The PPWG THz-TDS used in this work well established ultrafast optoelectronic techniques to generate and detect sub-picosecond THz pulses. The explosive material was analyzed as powder layers in $112{\mu}m$ gap of metal PPWG. The thin later mass was estimated to be about $700{\mu}g$. Finally, we showed spectra of explosives from 0.2 to 2.4 THz measured using PPWG THz-TDS.

• Smart Structures and Systems
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• v.21 no.6
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• pp.751-759
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• 2018

Glass fibre reinforced polymers (GFRP) are widely exploited in many industrial branches. Due to this Structural Health Monitoring systems containing embedded fibre optics sensors are applied. One of the problems that can influence on composite element durability is water contamination that can be introduced into material structure during manufacturing. Such inclusion can be a damage origin significantly decreasing mechanical properties of an element. A non-destructive method that can be applied for inspection of an internal structure of elements is THz spectroscopy. It can be used for identifications of material discontinuities that results in changes of absorption, refractive index or scattering of propagating THz waves. The limitations of THz propagation through water makes this technique a promising solution for detection of a water inclusion. The paper presents an application of THz spectroscopy for detection and localisation of a water drop inclusion embedded in a GFRP material between two fibre optics with fibre Bragg grating sensors. The proposed filtering method allowed to determine a 3D shape of the water drop.

• Korean Journal of Optics and Photonics
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• v.25 no.2
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• pp.72-77
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• 2014

We have demonstrated a terahertz (THz) time-domain spectroscopy and imaging system using compact fiber-coupled THz modules. Using this THz spectroscopy system we have measured the absorption spectrum of water vapor in free space over 3 THz, as well as the refractive indices of various substrates such as Si, $Al_2O_3$, and GaAs using the transfer-function method. Through the THz imaging system we have observed a high-quality THz image of a medical knife and metal clip sample, with a resolution of $192{\times}89$ pixels using a step size of 250 ${\mu}m$.

• Composites Research
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• v.35 no.1
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• pp.8-12
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• 2022

Analysis of defect signals inside glass fiber reinforced polymer (GFRP) was conducted through deconvolution of terahertz (THz) wave. The GFRP specimen with internal defects was manufactured and the THz signal was measured through the reflection mode of the Terahertz Time-Domain Spectroscopy (THz-TDS) system. For deconvolution of the measured THz signal, the peak position of the THz signal was amplified through Normalized Cross Correlation (NCC) of the incident and detected THz signals. The position and intensity of the amplified peak were extracted as impulse, and the extracted signal of the impulse position was removed from the THz original signal. By repeating the process, the critical impulses, which represent boundary of the specimen, were derived. The deconvolution process was verified by confirming that the original THz signal without noise can be restored through the convolution of the critical impulses and the incident signal. From the derived critical impulses, the thickness of the internal defect in the GFRP was calculated through the detection time of impulses within 15 ㎛ accuracy.

• Composites Research
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• v.34 no.3
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• pp.143-147
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• 2021

Full width half maximum (FWHM) analysis of superimposed terahertz (THz) signals in the glass fiber reinforced polymer (GFRP) was studied to detect fine delamination inside GFRP. The THz signals were measured for each fine delamination size inside the GFRP using the reflection mode of the terahertz time domain spectroscopy (THz-TDS) system. Then, the FWHM of the superimposed THz signal reflected at the fine delamination was extracted. Thereafter, the complex refractive index of the GFRP was measured using transmission mode of the THzTDS system. Based on this, the FWHM of the superimposed THz signal at the fine delamination were calculated and compared with respect to the fine delamination size. From the theoretically calculated superimposed signals, the relationship between the fine delamination size and the FWHM in the superimposed THz signal was derived. Consequently, the fine delamination size could be predicted through the analysis of the FWHM extracted from the THz signal at the fine delamination.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.6
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• pp.286-292
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• 2005

Terahertz wave is a kind of electromagnetic radiation whose frequency lies in 0.1THz $\~$10THz range. In this paper, generation and detection characteristics of terahertz (THz) radiation by photoconductive antenna (PCA) method has been described. Using modern integrated circuit techniques, micron-sized dipole antenna has been fabricated on a low-temperature grown GaAs (LT-GaAs) wafer. A mode-locked Ti:Sapphire femtosecond laser beam is guided and focused onto photoconductive antennas (emitter and detector) to generate and measure THz pulses. Ultra-wide band THz radiation with frequencies between 0.1 THz and 3 THz was observed. Terahertz field amplitude variation with antenna bias voltage, pump laser power, pump laser wavelength and probe laser power was investigated. As a primary application example. a live clover leaf was imaged with the terahertz radiation.

• Electronics and Telecommunications Trends
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• v.35 no.4
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• pp.53-64
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• 2020

The terahertz (THz) region lies in between the millimeter and infrared spectral bands. A THz wave has the characteristics of non-invasiveness and non-ionization due to low photon energies, while having high penetrability in dielectrics. In addition, since the resonance frequencies of various molecules are included in the THz band, research on the application of spectral analysis and non-destructive testing has been widely studied. Towards this end, the research and development of THz detectors has become increasingly important in order to assess their applications in different areas such as astronomy, security, industrial non-destructive evaluations, biological applications, and wireless communications. In this report, we summarize the operating principles, characteristics, and utilization of various broadband technologies in THz detection devices. Further, we introduce the development status of our Schottky barrier diode technology as one of the broadband THz detectors that can be easily adopted as direct detectors in many fields of applications.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.845-846
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• 2011

• Current Optics and Photonics
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• v.6 no.3
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• pp.337-343
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• 2022

Microfluidic chips are new devices that can manipulate liquids at the micrometer level, and terahertz (THz) time-domain spectroscopy has good applicability in biochemical detection. The combination of these two technologies can shorten the distance between sample and THz wave, reduce THz wave absorption by water, and more effectively analyze the kinetics of biochemical reactions in aqueous solutions. This study investigates the effects of different external magnetic field intensities on the THz transmission characteristics of deionized water, CuSO₄, CuCl₂, (CH₃COO)₂Cu, Na₂SO₄, NaCl, and CH₃COONa; the THz spectral intensity of the sample solutions decrease with increasing intensity of the applied magnetic field. Analysis shows that the magnetic field leads to a change in the dipole moment of water molecules in water and electrolyte solutions, which enhances not only the hydrogen-bond networking ability of water but also the hydration around ions in electrolyte solutions, increasing the number of hydrogen bonds. Increasing the intensity of this magnetic field further promotes the hydrogen-bond association between water molecules, weakening the THz transmission intensity of the solution.