Wayne Stahnke recommends using parts from a point-of-sale barcode
scanning machine, such as you see at almost every supermarket in the
world nowadays!  The light source is a HeNe (helium-neon) laser, which
produces visible red light.  The output power is 50 milliwatts
maximum, as decreed by the US government.  The exit pupil size is
about 3 mm; the beam can be focused to about 0.1 mm diameter.  The big
barcode scanner also contains a nice multi- faceted rotating scanning
mirror, and many nice optical parts for the photo detector.

This method is much simpler to build than the 2-axis galvanometer
scanner, since the paper transport already provides the scan motion
along the orthogonal axis.

A laser diode light source is probably inferior to the HeNe laser for
this application.  If the laser diode were better, it would replace
the laser at the supermarket, but it hasn't!

-- Robbie Rhodes