Frequency Shift of Submm Waues with a Super Rotating Grating

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1. Frequency shift of omega_<IF>/2pi=1.45 MHz is obtained for 337 mum HCN laser beam by use of a rotating grating fabricated on the top of the rotor of a turbo-molecular pump with a high rotating speed of 43200 rpm. (Super Rotating Grating). The frequency shift is one order higher than those with usual rotating gratings. Using this as a local beam, heterodyne detection of low frequency microturbulence as well as high time resolution interferometry in plasmas becomes possible with a single FIR laser.2. The frequency-shifted beam is slightly frequency-modulated (modulation index M_f<similar or equal>1.2) with a period equal to the rotation period of the grating. This frequency modulation does no harm to these diagnostics.3. The power conversion efficiency of the SRG measured with a pyroelectric detector is 0.2 for a teflon window and 0.25 for a crystal quartz window. We will increase the efficiency in a future work. The present efficiency may be, however, sufficient to carry out multichannel detection with a channel number of 10 or more, since 337 mum HCN lasers generate a large power.4. We intend to make a multi-channel interferometer of high time resolution as well as a scattering apparatus with heterodyne detection system by using the SRG and to study transport phenomena such as sawtooth oscillations and low frequency microtubulences in tokamak plasmas.