The thing about a laser is that you only see it from the scattering of light by dust particle. And, at weapon powers, from the heating of the air. So I'd look at using one of the noise-like nodes (granite, noise, cellular, marble, clouds--there's a lot of choice) to switch the transparency and colours on and off. Dust scatter should have a lot of specks of light. Superheated air should be more nearly continuous, and much brighter.