Grab a 50 - 100mw green laser off ebay, the beams are clearly visible, not just a dot. These lasers are usually way overrated ( mW ) and pwm can greatly reduce the actual output to a few mW, while leaving a nice beam. Got 2 off ebay for $9 each.For pwm you will need a laser without a driver unless the driver has its own pwm input. Diode lasers are not like LED's apart from the fact that they are an LED, They will instantly die from the slightest misuse, or at the least have their output dramatically reduced. Some general diode laser info, may be helpful
@astrodadCan you post a picture of the laser you are using. I am curious to see it.
The more powerful the laser the farther/more reflections away you can blind someone. It's all fun and games till then.You could make foot-step switches like baseball bases and forgo the whole beam interrupt thing for all that. They would be easier to set up for one.
could make your own system out of 2 laser pointers and 2 Light dependant resistors.or search ebay for 'doppler radar sensor' and make your own speed gun.