Using PWM as a DC power source

Or: I'm clearly missing something.

I'm trying to get a simple 3VDC out of my Arduino Uno to flash a laser pointer, in place of AAA batteries. It works swimmingly when I simply hook it up to the 3.3V pin, but obviously that's bad if I want to turn it on and off.

In my trials, I've tried using digital logic as the power source - the pointer doesn't seem to mind the +5V when I hook it up to a power source, and I'm not concerned about the laser's long-term survival - and I've tried PWM with a 97% duty cycle from a function generator, and also an equivalent setting on the Arduino.. Still nothing.

So, I was considering an RC circuit with a big time constant, but I have to guess that there's a simple, known way to do this and I'm just missing it because I've spent so much time in college classes rather than actually building things.

Can anybody steer me right?

Do you understand PWM, if not read this:-

I'm trying to get a simple 3VDC out of my Arduino Uno to flash a laser pointer,

Do you know how much current this takes. Powering a laser from a PWM output is not a very good idea because there is a very grave danger of supplying too much voltage and damaging it. You need a proper power regulator.
Read this about powering Laser Pointers:-

I'd go with GrumpyMike & suggest a voltage regulator, with an Enable pin that you can turn on & off, for example:

vs PWM and adding a bunch of components trying to filter it.

Great! This makes a lot of sense. So basically I can take the 5V power supply from the Arduino to power the regulator, and then use a digital pin to turn it on with a high, and off with a low? I feel like a jackass for not just thinking of this. Oh well, chalk it up to learning.

That's pretty much it.

Thanks again, I really appreciate the advice.

How about the output power of your 300mw green laser pointer?