• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.3
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• pp.299-304
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• 2011

• Current Optics and Photonics
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• v.7 no.6
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• pp.683-691
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• 2023

A typical terahertz time-domain spectroscopy system requires large, expensive, and heavy hardware such as a lock-in amplifier and a function generator. In this study, we replaced the lock-in amplifier and the function generator with a single sound card built into a typical desktop computer to significantly reduce the system size, weight, and cost. The sound card serves two purposes: 1 kHz chopping signal generation and raw data acquisition. A unique software lock-in (Python coding program to eliminate noise from raw data) method was developed and successfully extracted THz time-domain signals with a signal-to-noise ratio of ~40,000 (the intensity ratio between the peak and average noise levels). The built-in sound card with the software lock-in method exhibited sufficiently good performance compared with the hardware-based method.

• 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.

• Journal of electromagnetic engineering and science
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• v.11 no.1
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• pp.42-50
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• 2011

One of the important applications of THz time-domain spectroscopy (TDS) is the detection of explosive materials through identification of vibrational fingerprint spectra. Most recent THz spectroscopic measurements have been made using pellet samples, where disorder effects contribute to line broadening, which results in the merging of individual resonances into relatively broad absorption features. To address this issue, we used the technique of parallel plate waveguide (PPWG) THz-TDS to achieve sensitive characterization of three explosive materials: TNT, RDX, and HMX. The measurement method for PPWG THz-TDS used well-established ultrafast optoelectronic techniques to generate and detect sub-picosecond THz pulses. All materials were characterized as powder layers in 112 ${\mu}m$ gaps in metal PPWG. To illustrate the PPWG THz-TDS method, we described our measurement by comparing the vibrational spectra of the materials, TNT, RDX, and HMX, applied as thin powder layers to a PPWG, or in conventional sample cell form, where all materials were placed in Teflon sample cells. The thin layer mass was estimated to be about 700 ${\mu}g$, whereas the mass in the sample cell was ~100 mg. In a laboratory environment, the absorption coefficient of an explosive material is essentially based on the mass of the material, which is given as: ${\alpha}({\omega})=[ln(I_R({\omega})/I_S({\omega}))]m$. In this paper, we show spectra of 3 different explosives from 0.2 to 2.4 THz measured using the PPWG THz-TDS.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.517-518
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• 2006

Optically pumped THz emission has been observed in a wide range of semiconductors, and this process is an important practical source of pulsed THz radiation for time-domain THz spectroscopy and THz imaging. We show that InAs quantum dots on GaAs can be used to significantly enhance THz emission compared with a bare GaAs surface.

• Current Optics and Photonics
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• v.7 no.2
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• pp.119-126
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• 2023

The vibratory and rotational levels of many biological macromolecules lie in the terahertz (THz) band, which means that THz techniques can be used to identify and detect them. Moreover, since the biological activity of most biomolecules only becomes apparent in aqueous solution, we use microfluidic technology to study the biological properties of these biomolecules. THz time-domain spectroscopy was used to study the THz absorption characteristics of graphene oxide (GO) aqueous solution at different concentrations and different exposure times in fixed electric or magnetic fields. The results show that the spectral characteristics of the GO solution varied with the concentration: as the concentration increased, the THz absorption decreased. The results also show that after placing the solution in an external electric field, the absorption of THz first increased and then decreased. When the solution was placed in a magnetic field, the THz absorption increased with the increase in standing time. In this paper, these results are explained based on considerations of what is occurring at the molecular scale. The results of this study provide technical support for the further study of GO and will assist with its improved application in various fields.

• Current Optics and Photonics
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• v.8 no.3
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• pp.225-229
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• 2024

This paper introduces a rapid measurement technique for the stress-optic coefficient, using terahertz time-domain spectroscopy. First we propose a design combining a four-point bending device with a scanning stage to streamline the loading process. Then we detail the measurement principle and outline the signal-processing algorithm. The experiments are carried out on Al₂O₃, a representative ceramic material. The experimental data reveal that the refractive index of Al₂O₃ exhibits a linear decrease with increasing stress. This work supplies an efficient method for stress measurement rooted in the stress-optic effect.

• Journal of the Optical Society of Korea
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• v.12 no.3
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• pp.196-199
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• 2008

We have investigated spectral properties of the periodic arrays of aluminum rods and holes on papers using the terahertz time-domain spectroscopy. The size of a rod(hole) is $600{\mu}m{\times}100{\mu}m$ and the spacing is $300{\mu}m$. The samples were fabricated by a femtosecond laser micromachining system. The periodic arrays of aluminum rods exhibit high reflection around 0.25 THz when the polarization of the THz pulse is parallel to the long axis of the rod, whereas the periodic arrays of holes exhibit high transmission around 0.25 THz when the polarization of the THz pulse is perpendicular to the long axis of the hole.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.515-516
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• 2006

A THz near-field microscope(THz NFM) is developed by a combination of THz time-domain spectroscopy and AFM(Atomic Force Microscopy). We have observed 80nm lateral resolution, demonstrating that the THz NFM technique has a great potential as a important probing tool for the analysis of the biological and semiconductor nanostructures.

• Proceedings of the Optical Society of Korea Conference
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• 2008.07a
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• pp.177-178
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• 2008