Attempting to use a greater portion of the light "cone" emitted by the laser chip can lead to a significant variation in the test surface illumination and may require anamorphic correction to circularise the laser beam. The cheapest solution is to only use the central F/8 cone and use a s...
Laser diodes typically emit from a waveguide junction with a rectangular shape so that the beam is neither circularly illuminated nor spherical (though some may be close--it depends heavily on the type of diode.) Less expensive laser collimators use cylindrical optics and anamorphic prism pairs to...