Photon-Rifles often fall under the more general term Particle-Rifle, which refers to a range of rifles that shoot a stream of particles like photons, protons, and others.
Photon-Rifles are essentially high-powered lasers that output incredible heat. Their practical usability is greatly limited, but their advantages make them unique in special circumstances.
Being a stream of particles, the rifles shoot at the speed of light, they are not affected by gravity, and their range is measured in kilometers, not in meters. They are a great weapon against magnetic shields and for disarming electronics. Their output is very power inefficient, so when using a Photon-Rifle, you have to be calculated with the ammo you have.