PLease see if you could help me over this.. I have a laser beam emanating from am aperture of 50 mm dia. The beam divergence being 0.4 mrad. If i now choose a situation where say instead of the conventional beam expander design to expand the beam size and reduce the beam divergence, i choose to simply put a diverging lens in front (immediate exit) of the beam aperture. what should be the focal length of this lens to produce a spot size of 1m (say) at 100m ?