Reflection can indeed be used! However, it's only useful for pushing apart two objects that you've built - e.g. a large station with a mirror and a laser, and a small probe with just a mirror.

This is called a photonic laser thruster (https://en.wikipedia.org/wiki/Photonic_laser_thruster) and is a variant of laser propulsion (https://en.wikipedia.org/wiki/Laser_propulsion). Like a mass driver, it gets around the rocket equation by separating the propulsion system from the spacecraft.