Abstract-Monitoring the Progress of Lactic Acid Fermentation in Yogurt Manufacturing Using Terahertz Time-Domain–Attenuated Total-Reflection Spectroscopy

Koichiro Akiyama, Kazuki Horita, Tomoaki Sakamoto, Hiroshi Satozono, Hironori Takahashi, Yukihiro Goda,

https://link.springer.com/article/10.1007/s10762-019-00642-9

Lactic acid fermentation in yogurt manufacturing can be monitored using terahertz (THz)-attenuated total-reflection (ATR) spectroscopy. Yogurt manufacturing was performed on an ATR prism. The THz absorption coefficient and pH were measured for the entire 1000 min of the fermentation process. The absorption spectra were similar to the spectrum of water at the THz range. Temporal changes in the absorption coefficient at 0.4, 1.0, and 1.6 THz all decreased during the fermentation process, with two inflection points. The absolute value of the change in temporal absorption was greater at high frequencies than at low frequencies. However, the normalized absorption coefficient was larger at 0.4 THz. Because temporal changes in absorption corresponded with temporal changes in pH, the absorption changes appeared to be caused by the decomposition of the milk ingredients during the lactic acid fermentation. THz measurements can therefore be applied to the nondestructive monitoring of lactic acid fermentation in yogurt manufacturing.

Abstract-Terahertz imaging with room-temperature terahertz difference-frequency quantum-cascade laser sources

Atsushi Nakanishi, Kazuue Fujita, Kazuki Horita, and Hironori Takahashi

Fig. 1 Properties of THz DFG-QCL at –30 °C: (a) Spectrum, (b) far-field profile, (c) horizontal and vertical sections of the beam profile.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-3-1884

We demonstrate high-quality non-destructive imaging using a broadband terahertz quantum cascade laser source based on Cerenkov difference-frequency generation. The source exhibited ultra-broadband terahertz emission spectra, as well as a single-lobed Gaussian-like far-field pattern at –30 °C. These features allowed us to build a compact imaging system with a high spatial resolution, from which a nearly theoretical minimum beam spot size was obtained. As a result, we achieve well-resolved, high-contrast images of objects obscured by opaque materials. We also achieved terahertz imaging with the THz DFG-QCL operated at room temperature.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Tunable Terahertz Device Using Refractive Index Control

Atsushi Nakanishi, Takashi Yasuda, Kazuki Horita, Hironori Takahashi,

https://link.springer.com/article/10.1007%2Fs10762-017-0430-x

We measured the thermal dependencies of the refractive index and the absorption coefficient of high-resistivity silicon. We found that the refractive index varied slightly with temperature, and the absorption coefficient was very low and remained approximately constant as the temperature was changed. As a result, the conditions for terahertz propagation in silicon could be controlled by changing the refractive index without any absorption loss. As one application of this effect, we developed a terahertz time delay generator that can generate a terahertz time delay by changing the temperature of the medium through which the terahertz beam passes, without the need for any mechanical delay. We demonstrated generation of a terahertz time delay of approximately 6.6 ps.

Abstract-Detection of Terahertz Pulsed Radiation by Using Heterodyne Electro-Optic Sampling Scheme

1. Masahiko Tani¹, 
2. Michael I. Bakunov²,
3. Kohji Yamamoto¹, 
4. Kazuki Horita¹, 
5. Tetsuya Kinoshita¹ and
6. Tomohiro Nagase¹

Article first published online: 8 MAY 2014

DOI: 10.1002/ecj.11553

http://onlinelibrary.wiley.com/doi/10.1002/ecj.11553/abstract

© 2014 Wiley Periodicals, Inc.

A new electro-optic (EO) sampling scheme, which we refer to as “heterodyne EO sampling,” for the detection of pulsed terahertz (THz) waves is proposed and demonstrated. In this heterodyne EO sampling scheme, the intensity change in the sampling optical pulse induced by a THz field in a nonlinear crystal is measured without using any polarization optics. Applied in conjunction with the noncollinear Cherenkov phase matching technique, this method allows efficient and easy detection of pulsed THz wave using a simpler optical setup than in the conventional EO sampling method.

Abstract-Fast-Scan Terahertz Time Domain Spectrometer Based on Laser Repetition Frequency Modulation

Takashi Furuya1, Elmer S. Estacio1, Kazuki Horita1, Christopher T. Que1, Kohji Yamamoto1, Fumiaki Miyamaru2, Seizi Nishizawa2,3 and Masahiko Tani1

1 Research Center for Development of Far-Infra Red Region, University of Fukui, Fukui 910-8507, Japan
2 Shinshu University, Matsumoto, Nagano 390-8621, Japan
3 Advanced Infrared Spectroscopy Co., Ltd., Hachioji, Tokyo 193-0835, Japan 

http://iopscience.iop.org/1347-4065/52/2R/022401/

We propose a high-speed scanning terahertz (THz) time-domain spectrometer (TDS) based on optical sampling by repetition frequency modulation (OSREFM) using a repetition-frequency-tunable femtosecond fiber laser. Repetition frequency modulation is controlled by a highly stabilized external sweep generator. The fast scan of the time-delay between the pump and probe pulses is similar to an optical sampling with cavity tuning (OSCAT) THz-TDS system. However, the advantage of this technique is that it does not require physically moving components and uses only one laser system having an electronically modulated repetition rate. The time window and scanning time of this system depend on the modulation frequency range and the sweeping speed of the laser. In this study, we demonstrate the acquisition of a ~300 ps-window THz time waveform within 3 ms at a scan rate of 333 Hz.