CoolLED pE-4000 shutter function?

Hi there, I’m using CoolLED pE-4000 together with Slidebook. Now, I have a problem during timelapse captures. I use two channels (for ratio captures), an intervall of 3 seconds and exposure times 300 ms (channel1) and 500 ms (channel2). During the captures, the excitation light of channel1 is always on. The excitation light of channel2 only switches on and off in the given intervall of 3 seconds (and for the given exposure time). How can I set a “shutter”, as I don’t want to expose my cells permanently with the excitation light of channel1?? Thought that the CoolLED light source can be switched on and off instead of using a shutter? But I don’t find a thing in the manuals… And I’m not able at the moment to get Slidebook, CoolLED and my microscope (Axiovert 200M) to cooperate this way :/. Any suggestions?