If you are talking LASER diode in a TO type can, looking at the rear (bottom), you will notice that there are three notches in the rim (Base) of the can, two V shaped and one Rectangular. If you hold the can with the square or rectangular notch to the top (12 o'clock position) and the V shaped notches at 9 o'clock and 3 o'clock, you will see three or four pins: pin #1 at 9o'clock, #2 at 12 o'clock (attached to the case), #3 at 3 o'clock, and, if there is one, #4 at 6 o'clock.
USUALLY, for I.R. diodes (also what is used in 'Green DPSS modules), the case (and pin#2) are positive. For reds,blues and most violets, the case is negative. Pin #1 will usually be negative for I.R. and POSITIVE for the rest. Observe current and static electricty precautions. Don't look into the light.......