# Oscillations of Photons

1. Jul 29, 2014

### Rob Hoff

Is there a resonant frequency of light? I was just wondering because the higher the frequency of light, the higher the energy. Or is there an optimal frequency?

2. Jul 29, 2014

### Matterwave

Different atoms have different emission and absorption spectra, these are "resonant frequencies" of light for those atoms. Same for molecules. But there aren't any "resonant frequencies of light in a vacuum", which is what I think you're thinking of.

3. Jul 29, 2014

### Rob Hoff

Is there a limit to how much energy a photon can carry? Let's be friends matterwave, my physics teacher would have a harder time answering this. No offense Mr Asmann.

4. Jul 29, 2014

### Staff: Mentor

I hope I can butt into this budding friendship :tongue::tongue::tongue::tongue:

There is theoretically no limit - but of course there is a practical limit depending on our level of technology.

Thanks
Bill

5. Jul 30, 2014

### Matterwave

There is one "kind of" limit to the photon energy, but it's probably not really the kind of "limits" (absolute) in the sense that you are probably thinking.

If the photon becomes too energetic, it might interact with a photon in the CMB to produce a particle-anti-particle pair. The limits for this interaction is that the photon must carry more energy than the rest energy of the particle-anti-particle pair. But of course, for this interaction to matter, the cross sections must also be consulted. If the photon is only slightly more than 2MeV in energy (a gamma ray), for example, although it CAN produce a electron-positron pair, it probably won't due to the small cross section. The electron-positron pair can also annihilate each other and in that case you have basically a 4 gamma interaction with a fermion internal loop. This leads QED to become non-linear, and is called the Schwinger limit.

This limit does not exist for a single photon traveling by itself. The presence of the CMB photon is important because it gives rise to a center of momentum frame in which there is a minimum total energy, whereas a single photon may always be red shifted by the doppler effect until it has a lower energy.

The practical reaches of this limit is so high, I don't think it has been probed experimentally.

6. Aug 7, 2014

### Rob Hoff

Thanks matterwave!!