H. Tazawa

K. Kawahata

K. Mizuno

K. Nakayama

K. Tanaka

S. "Okajima

T. Tokuzawa

Y." Ito

National Institute for Fusion Science (NIFS-Repository)

§20. Development of Powerful 57f.1m CH30D Laser and the Detector for High Density Plasma Diagnostics Okajima, S., Nakayama, K., Tazawa, H. (Chubu Univ.), Mizuno, K. (Tohoku Univ.), Kawahata, K., Tanaka, K., Tokuzawa, T., Ito, Y. We have developed a powerful and stable ll9-l1m CH30H laser pumped by 9P(36) cw C02 laser for the optical source of LHD diagnostics[ 1,2]. The laser system is installed in 13-ch interfero-meter and is using routinely as the probing source[2]. For high density operation of LHD and large plasma machine such as ITER, short wavelength far-infrared (FIR) lasers of 40-to 70-11 m range should be useful rather than the I 19-IL m laser and 10-l1m C02 laser from the view points of refraction and vibration effects and amount of fringe shifts in the interferometer. For the purpose, we have searched powerful short wavelength FIR lasers from methanol and the isotopes pumped by cw C02 lasersl3]. As the result, we have discovered that a 57-!1 m CH30D laser pumped by 9R(8) C02 laser is the most powerful line under 100 11m range. In this experiment, a twin type FIR laser pumped by cw C02 laser has been used[4]. The C02 laser is about 3 m in length, and the cavity is formed by a grating (150 lines/mm) and a ZnSe output mirror (55% reflection for 10.6 11m) attached on PZT. The maximum output power is over 200 W for IOP(20) line. The FIR laser is about 2.9 m in length, and the laser tube diameter is 25 mm. The laser cavity is formed by a plane metal mirror having off-axis input coupling hole (3 mm) and a Si hybrid mirror having an FIR output coupling hole of 14 mm at its center. The output coupling mirror and FIR laser window are optimized for 119-l1m CH30H laser. Using this laser system we have obtained 119-Jlm CH30H laser output power of 0.68W. On the CH30D laser pumped by 9R(8) C02 laser, 57-II m and 47- /1 m lines have been observed. But, the two laser lines can be selected easily by using an FIR polarizer, because the polarization of 57-!l m laser is perpendicular and that of 47- /1 m laser is parallel for that of pumping C02 laser. The pressure dependence of the laser outputs is shown in Fig.l . Addition of He to CH30D is effective for the 57-11m laser output same as the case of 119-l1m CH30H laser(Fig.2). The maximum output power over 0.53W has been obtained by 125W C02 laser pumping. For the 57-11m (5.2 THz) detector, a GaAs Schottky barrier diode (SBD) has been tested. The detector is constructed with a corner cube mount developed by NIFS and a diode chip surprised by Tohoku Uni versity. The video sensitivity of the detector has been estimated to be 3V/W. ~ 7 PUMPING: 9R(8)C02 LASER u.:i VJ (l23W) « ~ 6 Q 57,um(--.l) 0 ('<j 5 ::c u 8 S 4 ::i ~ ::l ~ ...; '<T :e 3 0(3 r-- ~ In (..L. 2 0 E--< ::J 0... f-< ::J 0 Co 20 40 60 80 100 PRESSURE OF CH30D (Pa) Fig.l. Pressure dependence on output power of 57-11m and 47-l1m CH30D Laser. 5 PUMPING: 9R(8)C02 LASER (80W) CH30D BASE PRESSURE : 51 Pa 5 10 15 20 PRESSURE OF He (Pa) Fig.2. The effect of He for 57-11m CH30D laser output power. References I) Kawahata, K. Ejiri, A. et.al, Fusion Engin. and Design, 34-35 (1997) 393. 2) Kawahata, K., Tanaka, K.,et.al, Rev. Sci. Instr.,1SJ (1999) 707. 3) Okajima, S., Nakayama, K., et.al., Proc. of 5th Australia-Japan Workshop on Plasma Diagnostics, (JAERI-Conf. 2000-0(7) 46. 4) Okajima, S.,et.aI., Ann. Rep. NIFS, April 1998-March 1999 (1999) 14R. 169 

Development of Powerful 57μm CH3OD Laser and the Detector for High Density Plasma Diagnostics

Development of Powerful 57μm CH3OD Laser and the Detector for High Density Plasma Diagnostics

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