I have a Optical trap that collects Raman. With Glass cover-slips we use a 1.51 refractice index oil (DF cargille). The trap works but glass has high auto-fluorescence at our excitation wavelength(785 nm9), the weak Raman cant be detected. So we use synthetic fused silica cover-slips with a refractive index of 1.48. The trap is weaker (no numbers yet, but I have been doing this for a while). Should an immersion oil with a lower refractive index ( like 1.48 for cargille FF) work better? That would be a mismatch with the glass from the objective. Any clues?