Abstract-Dielectric property measurements of corneal tissues for computational dosimetry of the eye in terahertz band in vivo and in vitro

 

Maya Mizuno, Hideaki Kitahara, Kensuke Sasaki, Masahiko Tani, Masami Kojima, Yukihisa Suzuki, Takafumi Tasaki, Yoshinori Tatematsu, Masafumi Fukunari, and Kanako Wake

 Schematic diagram of the setups of specimens for (a) ATR and (b) T-type dielectric constant measurement, and reflectance measurement systems for (c) vertical and (d) oblique incidences. The white arrow in the left x-y image of (c) indicates the position with the largest reflection signal.

https://www.osapublishing.org/boe/fulltext.cfm?uri=boe-12-3-1295&id=447535

The dielectric constant of the normal corneal tissue of a rabbit eye was obtained in vitro in the range from approximately 0.1 to 1 THz, and the drying process on the eye surface exposed to high-power terahertz waves was investigated by in vivo reflectance measurement using terahertz time-domain spectroscopy. When the rabbit eye was exposed to terahertz waves at 162 GHz for 6 min with an irradiation power of 360 or 480 mW/cm2, the reflectance temporally increased and then decreased with a temperature increase. Based on multiple-reflection calculation using the dielectric constant and anterior segment optical coherence tomography images, those changes in reflectance were attributed to drying of the tear and epithelium of the cornea, respectively. Furthermore, the drying progressed over a temperature increase of around 5°C under our exposure conditions. These findings suggest that the possibility of eye damage increases with the progress of drying and that the setting of the eye surface conditions can be a cause of disagreement between computational and experimental data of absorbed energy under high-level irradiation because reflectance is related to terahertz wave penetration in the eye tissue. The time-domain spectroscopic measurements were useful for the acquisition of the dielectric constant as well as for the real-time monitoring of the eye conditions during exposure measurement.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-An Experimental Investigation of a 0.8 THz Double-Beam Gyrotron

Seitaro Mitsudo, Mikhail Glyavin, Eduard Khutoryan, Ilya Bandurkin, Teruo Saito. Yuya Ishikawa, Vladimir ManuilovIrina,  Zotova Alexey Fedotov.  Alexei  Kuleshov.  Svilen Sabchevski, Yoshinori Tatematsu, Vladislav Zaslavsky, Toshitaka Idehara,

https://link.springer.com/article/10.1007%2Fs10762-019-00629-6

In this paper, we present and discuss the new experimental results that characterize the output parameters, and the overall performance of the recently developed 0.8 THz double-beam gyrotron operating at the second harmonic of the cyclotron frequency on the TE8,5 mode. Alongside with this design mode, several other resonances excited at both the fundamental and second harmonic operations in a wide frequency range have been studied. These experiments demonstrate that the usage of a double-beam electron-optical system opens more possibilities for realization of such regimes of operation that otherwise are not accessible in a conventional (single-beam) gyrotron due to a severe competition between the neighboring modes and the narrowness of the zones of a stable single mode operation. Most notably, the results prove that second harmonic operation at higher beam currents and respectively at higher levels of the output power are possible as expected from the preceding theoretical considerations and numerical studies. The results of this study are helpful for getting a better insight in the physics of the operation of the double-beam gyrotrons and suggest some possibilities for further optimization of both the design of the tube and the experimental setup.

Abstact-Development of second harmonic gyrotrons, Gyrotron FU CW GII and Gyrotron FU CW GIII, equipped with internal mode converters

Yoshinori Tatematsu, 

Yuusuke Yamaguchi, 

Toshitaka Idehara, 

Tatsuru Kawase, 

Ryoichi Ichioka,

Isamu Ogawa, 

Teruo Saito, 

Toshimichi Fujiwara

http://link.springer.com/article/10.1007%2Fs10762-014-0048-1#

Second harmonic gyrotrons, Gyrotron FU CW GII and Gyrotron FU CW GIII, were developed at the Research Center for Development of Far-Infrared Region, University of Fukui, Japan to achieve two goals. Each gyrotron was equipped with an internal quasi-optical mode converter. Using Gyrotron FU CW GII allowed the design of the cavity and mode converter to be validated, which was the first goal. After that, Gyrotron FU CW GIII, which is an improved version of Gyrotron FU CW GII, allowed us to achieve a high power output of up to 420 W, which was the second goal, with a cathode voltage setting of −21 kV and a beam current of 0.57 A. This was achieved using a newly developed electron gun and with the careful sitting of the gyrotron on the magnet.