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To reduce the reflections due to the laser light on the coverglass using the
Olympus FV300 we typically would put an ND filter in place to reduce the
light to between 5 and 20% of the incident power. Then we would use the AOTF
control to choose our power. Typically for live cell work we use 0.1% of the
488 nm line of a 40 mW Ar laser. So attenuating to 20% gives us 5x more
sensitivity with the AOTF now controlling the power from 0% to 20% rather
than 100%. It turns out AOTFs are good attenuators but not great blockers of
laser light so this will block reflections from both the 488 nm and the 514
nm lines (as well as weaker lines). I'm not sure other confocal microscopes
still have ND filters in the light path but this is certainly a cheap solution.

Claire Brown