Real-time measurement system using multi-wavelength THz-wave parametric generation and detection

In this study, we achieved real-time identification of reagents using combination of machine learning and simultaneous generation and detection of multiwavelength terahertz (THz) waves by injection seeded terahertz wave parametric generator (is-TPG)

Multi-Wavelength Terahertz Parametric Generator Using a Seed Laser Based on Four-Wave Mixing

In this study, we developed a multi-wavelength terahertz-wave parametric generator that operates with only one injection seeding laser. Tunable lasers used as an injection seeder must be single-frequency oscillators, and conventional multi-wavelength terahertz-wave parametric generator requires basically the same number of lasers as the number of wavelengths. In order to solve this problem, we developed a new external cavity semiconductor laser that incorporates a DMD in its wavelength-selective mechanism. In this process, stable multi-wavelength oscillation from a single laser was made possible by efficiently causing four-wave mixing. This seed laser can be applied to practical real-time terahertz spectroscopy by arbitrarily switching the desired wavelength to be generated and the interval between multiple wavelengths

Multi wavelength injection-seeded THz parametric generator

Recently, we have succeeded in the development of high power and high sensitivity THz wave spectral imaging system using injection-seeded THz parametric generation (is-TPG) and detection. A dynamic range of 100 dB has been obtained, and the peak output power of is-TPG approached 50 kW by introducing a microchip YAG laser with shorter pulse width of 420ps. Now we can detect drugs under much thicker obstacles than before using is-TPG spectroscopic imaging system

Collinear injection-seeded terahertz parametric generator

In a conventional injection-seeded terahertz (THz) parametric generator (is-TPG), a complicated achromatic optical system controlling the angle of incidence of the seed beam is used to ensure tunability because both the pump and seed beams must satisfy non-collinear phase-matching conditions. In this study, we found that a THz output and tunability similar to those characteristics of a conventional is-TPG can be obtained even when the pump and seed beams are coaxially injected into the LiNbO3 crystal. In this new generation mechanism, a weak THz-wave is generated by the difference frequency of optical mixing between the pump and seed beams at the Cherenkov phase-matching angle and then strongly parametrically amplified. Thus, we describe our device as a collinear is-TPG. Simplicity is improved by eliminating any need for achromatic optics

Wide dynamic range and real-time reagent identification and imaging using multi-wavelength terahertz parametric generation and machine learning

Abstract In this study, we propose a technique for identifying and imaging reagents through shielding over a wide dynamic range using a real-time terahertz (THz) spectroscopy system with multi-wavelength THz parametric generation/detection and machine learning. To quickly identify reagents through shielding, the spectral information of the “detection Stokes beam” is used for reagent recognition via machine learning. In general THz wave-based reagent identification, continuous spectra are acquired and analyzed quantitatively by post-processing. In actual applications, however, such as testing for illicit drugs in mail, the technology must be able to quickly identify reagents as opposed to quantifying the amount present. In multi-wavelength THz parametric generation/detection, THz spectral information can be measured instantly using a “multi-wavelength detection Stokes beam” and near-infrared (NIR) camera. Moreover, machine learning enables reagent identification in real-time and over a wide dynamic range. Furthermore, by plotting the identification results as pixel values, the spatial distribution of reagents can be imaged at high speed without the need for post-processing

Visualization 1: Terahertz wave three-dimensional computed tomography based on injection-seeded terahertz wave parametric emitter and detector

Pencil 3D image Originally published in Optics Express on 21 March 2016 (oe-24-6-6433