Development of short-wavelength far-infrared laser for high density plasma diagnostics

Self Cite

A short wavelength far infrared laser whose wavelength is about 50 m is preferable for a polarimeter and an interferometer for high density operations in the Large Helical Device ͑LHD͒ and on future large fusion devices such as ITER. This is because the beam bending effect ͑ϰ 2 ͒ in a plasma, which causes fringe jump errors, is small and the Faraday and the Cotton-Mouton effects are moderate. We have developed a polarimeter with highly resistive silicon photoelastic modulators ͑PEMs͒ for the CH 3 OD laser ͑ = 57.2 and 47.7 m͒. We performed bench tests of the polarimeter with a dual PEM and demonstrated the feasibility for the polarimeter. Good linearity between actual and evaluated polarization angles is achieved with an angular resolution of 0.05°and a temporal resolution of 1 ms. The baseline drift of the polarization angle is about 0.1°for 1000 s.

Section: Introductionmentioning

confidence: 99%

Short wavelength far infrared laser polarimeter with silicon photoelastic modulators

Akiyama

Kawahata

Tanaka

et al. 2008

Self Cite

“…The laser power fluctuation of the He-Ne laser was 1% during 1000 s. ITER poloidal polarimeter plans to use a far-infrared laser developed by Chubu University. 7,8 The Chubu University achieved stability of 1% with about an output power of about 1 W for a long-term operation of 24 h. 9 Thus, it is proper to use the He-Ne laser for the experiments assessing the performance of the rotating waveplate polarimeter. Regarding unsynchronized oscillation of components, measurement error using the He-Ne laser is larger than that using the far-infrared laser because amplitude of unsynchronized oscillation normalized by wavelength of the He-Ne laser is larger than that of the far-infrared laser.…”

Section: Methodsmentioning

confidence: 99%

Development of real-time rotating waveplate Stokes polarimeter using multi-order retardation for ITER poloidal polarimeter

Imazawa

Kawano

Ono

et al. 2016

Faraday rotation measurements on compact helical system by using a phase sensitive heterodyne polarimeter Rev. Sci. Instrum. 70, 730 (1999); 10.1063/1.1149314 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew. The rotating waveplate Stokes polarimeter was developed for ITER (International Thermonuclear Experimental Reactor) poloidal polarimeter. The generalized model of the rotating waveplate Stokes polarimeter and the algorithm suitable for real-time field-programmable gate array (FPGA) processing were proposed. Since the generalized model takes into account each component associated with the rotation of the waveplate, the Stokes parameters can be accurately measured even in unideal condition such as non-uniformity of the waveplate retardation. Experiments using a He-Ne laser showed that the maximum error and the precision of the Stokes parameter were 3.5% and 1.2%, respectively. The rotation speed of waveplate was 20 000 rpm and time resolution of measuring the Stokes parameter was 3.3 ms. Software emulation showed that the real-time measurement of the Stokes parameter with time resolution of less than 10 ms is possible by using several FPGA boards. Evaluation of measurement capability using a far-infrared laser which ITER poloidal polarimeter will use concluded that measurement error will be reduced by a factor of nine. C 2016 AIP Publishing LLC.[http://dx

“…We have achieved a lot of high power oscillation lines from 40 to 100 m in wavelength by changing FIR laser molecules. Among these oscillation lines the most powerful line was found to be a 57.2 m CH 3 OD laser line 5 which was able to oscillate simultaneously at 47.6 m every 5 ϫ 57.2 m ͑ϳ6 ϫ 47.6 m͒ by tuning the FIR laser cavity length. 6 Figure 2(a) shows a Fabry-Pérot (FB) interferometer which is used to measure the wavelength of the laser oscillation line.…”

Section: New Two Color Fir Laser Interferometermentioning

confidence: 99%

Development of a new two color far infrared laser interferometer for future fusion devices

Kawahata

Tanaka

Tokuzawa

et al. 2004

Self Cite

A new two color far infrared (FIR) laser interferometer under development for future fusion devices will be presented. The laser wavelength is optimized from the consideration of the beam refraction effect due to plasma density gradient and signal-to-noise ratio for an expected phase shift due to plasmas. Laser lines of 57.2 and 47.6 m are found to be suitable for the applications to high performance plasmas of Large Helical Device and future fusion devices such as the International Thermonuclear Experimental Reactor. The output power of 57.2 m CH 3 OD laser is estimated to be ϳ1.6 W, which is the highest laser power in the FIR wavelength regime. The optical configuration of a new interferometer system using two colors will be proposed. In the system, one detector simultaneously detects the beat signals of the 57.2 and 47.6 m laser lines, and each interference signal can be separated electronically (1 MHz for 57.2 m and 0.84 MHz expected for 47.6 m). Mechanical vibration can be compensated by using the two color interferometer. The present status of the development of the system is also presented.