Highly doped ruby filters for stray light reduction in SCATPAK II

One of the major problems in Thomson scattering measurement of electron temperature is the suppression of stray light. Filters of AR-coated ruby with a high-percentage doping of Cr have been produced for use on SCATPAK II. The filters have negligible attenuation of the signal above 7000 Å and attenuate light at the laser line by a factor of ≂9. Experimental details of the filter performance, design, and fabrication are presented. The filter performance is compared with experimental measurements of the Cr-in-sapphire absorption cross section at the R1 line. Ruby filters present a cost-effective method of stray light suppression for experiments using ruby lasers and the red-shifted portion of the scattered spectrum.