In some analytical problems the size of available samples is limited and you have to know how large the illuminated sample spot is. Placing a screen slightly above the sample position is the easiest way to visualize the illuminated sample area.
The following pictures show the intensity distribution on a quadratic screen (10 mm by 10 mm) for different rotation angles of the rotatable mirrors. First almost normal incidence of light is taken:
An almost circular spot of about 2 mm diameter is found:
For larger angles of incidence the spot broadens:
For extremely large angles of incidence the spot gets even larger than the screen:
