Chemical reactivity testing of optical fluids and materials in the DEIMOS spectrographic camera for the Keck II Telescope

The DEIMOS Spectrograph Camera contains two doublets and a tripler. Each group contains materials differing in thermal coefficient expansion, mechanical and optical properties. To mate the elements and at the same time accommodate large camera temperature changes, we will fill the space between with an optical fluid couplant. We selected candidate couplants, lens-support materials, and fluid-constraining materials based on published optical, mechanical and chemical properties. We then tested the chemical reactivity between the coupling fluids, lens-support and fluid-constraining materials. We describe here the test configurations, our criteria for reactivity, and the results for various test durations. We describe our conclusions and final choices for couplant and materials.