Distance 1.6 A.U.
or             239,356,593 km
Beam divirgence 0.05 mRad
or 0.00005 Rad
Exposure field, diameter                     11,968 km
Sphere area formula: V=4*pi*R*R
Like distance 30.86048645 km
Imagine a laser, placed at the distance of 1.6 Astronomical Units from you.
Laser is pointing at you; you are trying to detect it with telescope.
It will be as hard for you to detect this laser, as the light with the same intencity, placed 30.9 km away.