Beam divergence and use of lenses Wavelength, color, and visibility. Please, save yourself a few tons of trouble and get a laser pointer or laser diode module from someone who has already taken the time and trouble to get those infamously fussy laser diodes to do what you probably want. Go here for a partial list of suppliers of working diode lasers. They are easily ruined.
Laser diodes are rather fussy.
The light-emitting area of a laser diode typically emits more light than a similar area of the surface of the sun. Since more power must go into this area than into a similar size piece of the sun just to get things working at all, it should be understandable that things can easily go wrong. Laser diodes can be damaged by exceeding the maximum safe optical output, which may be hardly at all over the rated optical output. Damage can occur in this way even if no other limits are exceeded or reached. Excessive amounts of light can fry particularly vulnerable subregions of the bacterium-sized working region.