We briefly introduce our microscope unit with an immersion objective and ionic liquid used as a refractive index matching medium, and describe its application to single molecular spectroscopy under high-vacuum and various ambient gas conditions. In this article, we particularly focus our attention on studies toward optimizing the microscope unit. For this purpose, the refractive index and background fluorescence, absorption spectrum for various ionic liquids wre investigated. We also measured the images of the beam spot of excitation laser at focal point by using an immersion objective and various ionic liquids. We found that some have more suitable characteristics than before.

doi:10.1016/j.phpro.2011.05.004