Is this the step response of the single pole low pass???
It should have an exponential decay, shouldn't it? So it should be easier to comprehend the result with a log scale for vertical axis...
I think you need a fast shutter. It is not necessary to be an actual shutter but you can use faster thing
which can shut the light. Like PMC or IMC actuators.
Another point is that you may like to have a witness channel like the MC transmission to subtract other effect.