Kosuke Murate

Non-destructive drug inspection in covering materials using a terahertz spectral imaging system with injection-seeded terahertz parametric generation and detection

In 2003, we reported the first-ever development of a spectral imaging system for illicit drugs detection using a terahertz (THz) wave parametric oscillator (TPO) [K. Kawase et al., Opt. Exp. 11(20), 2549 2003]. The system has a dynamic range below four orders of magnitude, which enables it to identify reagents only through thin envelopes using spectral imaging. Recently, we succeeded in developing a high power and high sensitivity THz wave spectral imaging system using injection-seeded THz parametric generation and detection. A dynamic range in excess of 80 dB has been obtained, which is much higher than that of the 2003 system. In this study, the new spectral imaging system successfully identified reagents through thicker material than the thin envelopes used previously.

A High Dynamic Range and Spectrally Flat Terahertz Spectrometer Based on Optical Parametric Processes in LiNbO

A wideband, wavelength tunable, spectrally flat terahertz (THz) spectrometer with a dynamic range in excess of 70 dB was demonstrated. The emission of THz-wave was achieved using an injection-seeded THz parametric generator (is-TPG), and detection was achieved using nonlinear optical wavelength conversion, both in magnesium-oxide-doped lithium niobate crystal. This system has potential applications in non-destructive sensing and imaging of a wide variety of materials.

Terahertz wave three-dimensional computed tomography based on injection-seeded terahertz wave parametric emitter and detector.

We demonstrate a high dynamic range, three-dimensional (3-D) terahertz (THz) wave computed tomography system in which frequency tunable, Fourier transform-limited, high-power THz waves are emitted by an injection-seeded parametric source and ultrasensitive detection of THz waves is accomplished by heterodyne detection. This system covers the frequency range of 0.95 to 2.7 THz and has a maximum dynamic range in excess of nine orders of magnitude, enabling the acquisition of high-resolution 3-D tomographic images of samples with strong THz absorption. As an illustration, we obtained 3-D computed tomographic images of a pencil and a plastic product with an internal defect that demonstrates the potential applications of our imaging system in non-destructive testing and evaluation of industrial products.

Expansion of the tuning range of injection-seeded terahertz-wave parametric generator up to 5 THz

In this paper, we report the improvement of the frequency tuning range of an injection-seeded terahertz (THz)-wave parametric generator (is-TPG). A significant previous limitation was the high absorption coefficient in the higher-frequency region of a MgO:LiNbO3 crystal. Here, we inclined the crystal slightly, so that a fraction of the pump beam was internally reflected at the THz-wave exit surface of the crystal. In this configuration, it was easier for a higher-frequency THz wave to reach the crystal surface, because the center core region of the pump beam was closer to the exit surface. As a result, the upper limit of the frequency tuning range increased from 3.0 to 5.0 THz.

A Terahertz Wave Parametric Amplifier With a Gain of 55 dB

We report a terahertz (THz) wave amplifier based on optical parametric processes in magnesium-oxide-doped lithium niobate (MgO:LiNbO3) crystals. The amplifier operates at room temperature and has a gain of 55 dB. The non-linear crystals used for the purposes of emission and amplification of the THz waves are pumped separately using a microchip laser, which leads to an enhancement of the gain in comparison with existing approaches.

Multiwavelength terahertz-wave parametric generator for one-pulse spectroscopy

In this study, the simultaneous generation of multiwavelength terahertz (THz) waves by an injection-seeded THz parametric generator (is-TPG) was achieved for the first time. The output and stability of the multiwavelength THz waves were equivalent to those of the THz waves generated via a single-wavelength is-TPG. Spatial separation of frequencies and high-sensitivity detection were achieved by converting the THz waves to near-infrared detection beams. Furthermore, one-pulse spectroscopy of saccharides was realized, and a dynamic range of more than 60 dB was obtained. The results demonstrated the possibility of using the is-TPG to significantly shorten the measurement times of spectroscopic systems.

THz Spectroscopic Imaging of Chemicals Using IS-TPG

In 2003, we demonstrated a non-destructive terahertz spectroscopic imaging of illicit drugs hidden in envelopes using a widely tunable THz-wave parametric source, though its dynamic range at that time was less than four orders. Recently, we have realized more than nine orders of dynamic range with an evolved injection seeded THz-wave spectrometer. Now we can detect drugs under much thicker obstacles than before. In this report, we introduce the result of THz spectroscopic imaging of chemicals under thick envelopes and related topics; Enhanced tuning range of is-TPG up to 5 THz and >90 dB dynamic range THz spectroscopic system.

Frequency tunable, high dynamic range THz spectrometer using parametric processes in Lithium Niobate crystal

We developed spectrally flat THz wave spectrometer with the dynamic range of more than 7 orders, based on optical parametric processes in Lithium Niobate crystals for the emission and detection of THz waves.