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Hi,

In fact you also have consider optical elements that are in the path.
But if you want a quick removal switch your choice will be on an AOM. Turn fast 
to generate short pulses. The AOM is a crystal and he will disperse most 
passing 100fs over 500fs. You can use a prechirp for dispersion.
The 20X, NA = 1.0 is a good choice. If you want to control the peak power you 
must know the average power under the lens. (Thorlabs sells power-meter) to 
measure the width of implusion you must use an autocorrelator. He alone will 
allow you to edit the values of your system: APE berlin.
http://www.ape-berlin.de/sites/default/files/Carpe_0.pdf
http://www.ape-berlin.de

Also you must be sure to fill the rear element of the lens and check the 
consistency of your field. For that I use a flat mirror and a visible laser to 
ensure the setting.

With a lens 10 NA = 0.5 , I obtain with the zoom mini 5% of in-homogeneity.
(diagonals of the square)
for your bleaching it is always best to use the laser where it is most powerful. 
Generally 800nm