There is one problem area with diode lasers in so far as they prefer a ‘soft start’ if they are to enjoy their expected lifespan but this would not be practical with CNC usage as it would make everything far too slow. The attached circuit could be used to interface your PC and Mach3 to the diode laser and you could perhaps, initially, use the M3 M5 combination configured to the output pin of your choice to actually turn it on and off but as mentioned earlier you must expect a reduced diode life when using this method.
A reasonable alternative solution would be to use a shutter system for the switching and leave the diode on for the duration of the program. There are some more details of the shutter I have used and diode lasers in general here
http://www.cooperman.talktalk.net/files/18.htm .
Hope this helps.
Tweakie.