A Cost-Effective Polychromator with a Single Interference Filter for Thomson Scattering Diagnostics

Abstract

We propose a cost-effective polychromator with a single interference filter, because interference filters account for large parts of polychromator costs in the conventional Thomson scattering diagnostics with a Nd:YAG laser. Since the interference filters are used to transmit the scattered light in a specific wavelength range, one polychromator tends to have as many interference filters as its spectral channels, which makes high-resolution measurement with a number of polychromators expensive. However, we can save the number of interference filters and thus their costs by reentering reflected light from an interference filter into the same filter at different angles. This is possible, because the larger angle of incidence on the interference filter makes the wavelength of the transmitted light shorter. We measured dependence of transmitted wavelengths on the angles of incidence on one interference filter custom-ordered to transmit 1059 nm and developed the cost-effective polychromator using this dependence. The developed polychromator with a single filter successfully separated three different spectral channels (1043.2, 1051.9, and 1058.4 nm), enabling us to realize the cost-effective Thomson scattering diagnostics.