22P092-P
Developments of High-Temperature and High-Density Plasma Diagnostics Usinga Terahertz Wave (II)
テラヘルツ波を用いた高温高密度プラズマ計測法の開発(Ⅱ）
T. Tokuzawa1, Y. Kadoya2, M. Hangyo3, M. Tani4, K.Tanaka1, I. Yamada1, and K. Kawahata1
徳沢季彦1、角屋豊2、萩行正憲3、谷正彦4、田中謙治1、山田一博1、川端一男1
1)

National Institute for Fusion Science322-6 Oroshi-cho, Toki 509-5292, Japan2)
Department of Quantum Matter, Hiroshima University
1-3-1 Kagamiyama, Higashihiroshima, 739-8530, Japan3)
Institute of Laser Engineering, Osaka University
2-6 Yamadaoka, Suita, Osaka 565-0871, Japan4)
Research Center for Development of Far-Infrared Region, University of Fukui (FIR-FU)
Bunkyo 3-9-1, Fukui 910-8507, Japan1)
核融合科学研究所 〒509-5292 土岐市下石町322-62)
広島大学大学院先端物質科学研究科 〒739-8530 広島県東広島市鏡山1-3-1
3)
大阪大学レーザーエネルギー学研究センター 〒565-0871 大阪府吹田市山田丘 2-64)
福井大学 遠赤外領域開発研究センター 〒910-8507 福井市文京 3-9-1

The terahertz wave diagnostics have been developing for current and future high- temperature and density
plasma measurements. Since it requires wide-band frequency components, terahertz pulse is one of thepossible sources. Recently, the terahertz time domain spectroscopy (THz-TDS) test system has been
constructing diagnostic in NIFS. At the conference we will point out the current status and issues.

1. Introduction
In the high density plasma measurement using anelectromagnetic wave, the demanding frequency isgetting into terahertz regime [1] shown in Fig. 1.
However, the generation and detection of terahertz
waves are not a well-developed technology atpresent. In addition, since the transmission ofterahertz wave is not easy, the terahertz diagnosticsystem have to be set adjoined to the plasma
apparatus. A terahertz time domain spectroscopy(THz-TDS) configuration [2-4] is a possible
candidate, where the generator and detector
mounted in small units are activated byfemtosecond optical pulses delivered via opticalfibers. To keep the pulse width in 100 fs order after
a propagation of more than several meters distance,
one needs to use the optical pulses in telecom band(~1.5 µm wavelength) [5,6]. The first goal of thisresearch is to develop the terahertz generators anddetectors exciting by a fiber laser at 1.5 µm. We
have been constructing the THz-TDS test system atthe diagnostic building in NIFS.
2. THz-TDS Test System
The photograph of terahertz TDS test system isshown in Fig. 2. A mode-lock fiber laser (MenloT-light 780), which wavelength is 780 nm, pulse

Fig. 1. Characteristic frequencies in a typical plasma
parameter of DEMO

width ~ 120 fs, and repetition rate ~ 50 MHz, isused for excitation. In addition, this laser launches
1.5 µm light simultaneously. The laser light focuses
to the THz radiation antenna, which is a bow-tie
type photoconductive (PC) antenna made on
low-temperature-grown (LTG) GaAs (Hamamatsu
G10620-12). A part of the laser output is led to theT-light
λ=780nm±4.8nm
Poutput=79.3mW
PulseWidth=120fs

NT60/65
stroke : 65mm
resolution : 0.1um
speed : 1000mm/s

References[1] G. Vayakis, et al., Nucl. Fusion 46, S836
(2006).
[2] 萩 行 , 分 光 研 究 ， 54, 3, 181(2005).(inJapanese)[3] 阪 井 , 応 用 物 理 75, 2, 153 (2006). (inJapanese)[4] M.Hangyo, et al., PFR, 2, S1020 (2007).
[5] A.Takazato, et al., Appl. Phys. Lett. 90(2007) 101119.
[6] A. Takazato, et al., Appl. Phys. Lett. 91(2007) 011102.

Fig. 2. Photograph of THz-TDS systemdelay section for the optical sampling detection.
The excited power of THz wave is received by thesame designed antenna. The output of detector
antenna is amplified by a current amplifier (NILI-76, gain ~106 V/m, fc ~ 20kHz). The signal is led
to a lock-in amplifier for high sensitive
measurements and then the time domain trace of thesignalis
acquiredbythePCI-based
analog-to-digital converter (ADC).
3. Example of the current THz pulse
Example of the THz wave is shown in Fig. 2.
Here, the femtosecond laser output is around 40
mW, the bias voltage of excited PC antenna is 10 V,
and the lock-in amplifier sensitivity is 10 mV. The
shape of frequency component of this signal is
obtained by a Fourier transform analysis and it
shows a typical spectrum shape of the bow-tie
antenna. The peak of frequency components isaround 0.1 THz.
4. Summary
We have been developing the THz-TDS system
in NIFS for the high-temperature and density
plasma measurements. Currently, the pulse signalof frequency range with sub millimeter is obtained.
In near future, the pulse spectrum should be
optimized for the plasma measurements and the testof long distance transimission will be done.
Acknowledgments
This work was partially supported in part by
KAKENHI (Nos. 22360394, and 22017007). Alsoit was in part by a budgetary Grant-in-Aid of NIFS
LHD project and the Joint Research of ILE OsakaUniversityFig. 3. Detector output signal (upper) and its
frequency spectrum (bottom).