Optical physicists and chemists need a laser with a knob on it to tune the laser to an exact desired color. In the 70s and 80s, the preferred method was the use of liquid dyes as the laser medium, typically dissolved in alcohol. The dye was pumped at high speed through quartz cells, and was gotten to lase by striking it with a fixed wavelength green or ultraviolet laser. Now the best practice was to use Teflon tubing. It cleans up better, and that’s important because when changing colors, the new dye’s wavelength might be absorbed by the previous dye residue, if any. Man, the triboelectric shock you can get from high speed flow of alcohol through Teflon! The Livermore Lab was worried about this during the laser isotope separation program, as a fire hazard. The problem is solved by installing stainless steel ground wires in the Teflon tubes.