Pulsed Heat Source

Hello,

As someone new to COMSOL, I am need of help on how to implement a pulsed heat source. I currently have a circle on a micro beam acting as a heat source that corresponds to an infrared laser. I now wish to pulse that laser with a square-wave function. How do you take the function and apply it to the circular area as a heat source. Any help is appreciated!

Thanks,

Paul