Spatially extended high-resolution Thomson scattering diagnostics with volume Bragg grating filters

In this work, we elaborate on details of one-dimensional Thomson scattering (TS) measurement with volume Bragg grating (VBG) filters. The VBGs act as a spectral/angular filter and reject the narrow linewidth lights near the laser line such as Rayleigh scattering, Mie scattering, and stray light to access the electron TS component. The TS technique with VBGs has often been used as a point measurement technique, however, the technique can be easily extended to measure several mm with a higher resolution for a 1D measurement with a proper angle tuning. Methods to further extend the measurable region using multiple VBG filters are also proposed and demonstrated, which differs from the commonly known application of multiple filters to improve the optical density. The 1D TS measurements are carried out on a DC discharge plasma source with ~1 mm thick column and electron density in 10^11-13/cm^3. A sharp gradient of plasma properties along the laser line over a few hundred µm is successfully observed with a 26 µm spatial resolution.