Normally laser diodes are powered by a controlled-current source in feedback loop. There are 3 pins on a laser diode, and the 3rd connection is for monitoring light-output for the feedback loop to maintain constant/controlled light output.
DVDdoug is positively correct about that!! Jogging my memory you are! But, these cheap, low-wattage Red laser pointers run fairly well on a constant current, as long as the current is set to a point between the functional extremes.