|I will finish the quantum mechanical approach to light by saying a few words about photons at Fermilab.
- At Fermilab, we use photons to detect highly energetic particles entering our detectors. This detection is based on collecting Cerenkov light.
- At circular colliders, photons are extremely unwanted. Why? We talked about EM waves radiated out from accelerated charged particles. When a particle moves around the collider circle, it is constantly accelerated toward the center of the collider circle. (This causes the circular motion.) Therefore it radiates EM waves, which means it loses energy. In some colliders, this is a limiting factor. Whatever you do, particles lose more energy by this radiation than they actually gain in order to increase their kinetic energy.
- In high-energy collisions of particles, photons are often created as byproducts. One of the most famous reactions for creating photons is matter-antimatter annihilation. When a particle meets its antiparticle, and create two photons. This is the process people usually refer to when they are talking about matter being converted to radiation.
- On the other hand, we often create matter from radiation, or from an electromagnetic field. Under certain circumstances (in the presence of atoms or other media), it is possible that a photon will create a matter - antimatter pair (for example, an electron-positron pair). Fermilab uses this phenomenon to detect high-energy photons. When such a photon enters the detector, it creates an electron-positron pair which is easily detectable.
This page more or less concludes my series of pages devoted to light from the quantum mechanical point of view. Please read the last page, on which I summarize what we learned on this tour of light.