Last time I checked, you would have to be pretty quick with the brake pedal to slow down in enough time to not be caught by a laser gun. A little math please professor:
Speed of light ~ 300 million meters / second
One mile = 1609 meters
Speed of light ~ 186,451 miles / second
If the cop was 1/4 mile away, you would have to hit the brakes and slow down in 1.34 microseconds. But WAIT, if the beam of light has already reached your car so that you were able to detect it, it must then be on its way back to the gun for measurement.

The reason radar detectors work is because radar guns cast a huge dispersion pattern. If you are to poor sucker out front, you are having to rely on the fact that the guns emit trace radiation when they are in standby mode. If you have a good detector, you can pick this up. If not, you are toast.

Best bet, make sure you have some sucker out in front of you to take the heat. I used to run with a detector, but since laser has become prevalent, you never know when you are going to get hit. It's not even worth spending the money on if you ask me.