no its not done in PS. it is simple render in maya software. i have used two spot lights. one for main white beam and another for colorful dispersion. I don't know much if it could be rendered directly depending upon the reflection of rays in prism.
this method might not be technically right but this prism dispersion effect can be achieved with this simple method. to create that multicolor dispersion effect all you need to take a spot light and apply light fog and then in fog intensity apply procedural noise or fractal map.
this way u will get rays in fog and to make it colorful simply apply 7 colored gradient in the light color later on you can increase the size of dispersion effect by using regions of fog. i hope this will solve your problem.