But to do that you need some way of communicating with it. The easy approach would be a microcontroller on the serial port with a transistor to turn on/off the laser - except that this means you need a microcontroller, a circuit board, and a transistor. Since so few PCs now have serial ports, an FT232 might be necessary as well. That's at least an extra $10 on top of the original price, and realistically it'd be more like $20. You can skip the FT232 and talk to the microcontroller through the same audio channel that drives the mirrors, but that makes coding a bit of a challenge. In contrast, just pointing the laser away from the bath costs nothing.