Well done. I was worried that you didn't sanitize server side.
For sure I am going to spend some time on a breadboard testing out various things. Ideally I'd like to run on these 7.2V rechargable tool batteries I have. To do that I might need to put a voltage regulator on those though. That shouldn't be an issue. I am getting 10 LM317 ICs with my diode order.
A 3V diode won't need voltage regulation, it just needs at least 3V. Like all diodes the laser diode will simply drop the voltage by its Vf and pass the rest through. So you'd have ~4.2V left over to burn off and 1.2V of that is handled by the current regulating circuit. The rest can go straight to ground (similar to using a zener as a shunt regulator). That assumes that the 317 doesn't see the diode as an open circuit since no power will flow until 3V is reached.
If on the other hand you used the 317 as a voltage regulator to say 3.5V and used a series resistor to burn off the excess 0.5V you would get a constant current setup yet again. You would want smoothing caps in that setup though.
Your schematic looks fine, and nearly matches the sample circuit from the 317 datasheet. Using your values, it looks like you would be regulating to a 4 mA current. Your results will vary depending on the load you are using. No load should result in a 1.2V output, a diode may result in the forward voltage of the diode being the output, but you may need a parallel resistive load to trigger the 317 to get the output voltage above 1.2V. When you get your parts, breadboard and test it out.
Since you said you were building a laser pointer, you may want to look into a voltage thief circuit instead so you can run your pointer from a since cell battery, instead of what I'm guessing would be a 9V. It does need a few parts that you may not have, but overall it's not a complex circuit either.
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