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

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.

Noise-free terahertz-wave parametric generator.

We achieved noise-free terahertz (THz)-wave output from an injection-seeded THz-wave parametric generator (is-TPG) employing high-power injection seeding. A conventional is-TPG uses a weak continuous-wave (CW) seed beam. The position in which broadband noise is generated (via spontaneous parametric down-conversion) and the position of the THz signal overlap.

Real-time wide dynamic range spectrometer using a rapidly wavelength-switchable terahertz parametric source.

In this study, we demonstrate real-time terahertz (THz) spectroscopy using a rapidly wavelength-switchable injection-seeded THz parametric generator. We developed a wavelength-switchable external cavity diode laser using a digital micromirror device as a seed source for the generator. We realized fast acquisition of THz spectra by switching the wavelength of the laser for each pump beam pulse.

High-power ASE-free fast wavelength-switchable external cavity diode laser.

We developed a high-power amplified spontaneous emission (ASE)-free fast wavelength-switchable external cavity diode laser (ECDL) using a digital micromirror device (DMD) as the wavelength selector. Generally, with a conventional fast wavelength-switchable ECDL with a DMD, the output power is limited by the damage threshold of the DMD. However, with our ECDL, a high-power output was realized by optimizing the beam focus on the DMD.

Highly sensitive multi-stage terahertz parametric detector.

In this Letter, we developed a high-sensitivity multi-stage terahertz (THz)-wave parametric detection system that operates at room temperature. This detection system has high sensitivity over a wide wavelength range through upconversion of a THz wave to near-infrared light. The broadband noise associated with parametric generation limited the detection sensitivity in the previous setup; however, in the multi-stage configuration using multiple crystals, the THz parametric detection sensitivity was improved by spatially eliminating the broadband noise using an iris between the former and latter stages.

Terahertz tag identifiable through shielding materials using machine learning.

In recent years, there has been great interest in chipless radio-frequency identification (RFID) devices that work in the terahertz (THz) frequency range. Despite advances in RFID technology, its practical use in the THz range has yet to be realized, due to cost and detection accuracy issues associated with shielding materials. In this study, we propose two types of low-cost THz-tags; one is based on the thickness variation of coated polyethylene and the other on the fingerprint spectra of reagents.

Adaptive spatiotemporal optical pulse front tilt using a digital micromirror device and its terahertz application.

We report a new method to temporally and spatially manipulate the pulse front tilt (PFT) intensity profile of an ultrashort optical pulse using a commercial microelectromechanical system, also known as a digital micromirror device (DMD). For our demonstration, we show terahertz generation in a lithium niobate crystal using the PFT pumping scheme derived from a DMD chip. The adaptive functionality of the DMD could be a convenient alternative to the more conventional grating required to generate a laser beam with a PFT intensity profile that is typically used for efficient optical rectification in noncollinear phase-matching conditions.

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.

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.