# Any device to measure frequency of photon?

1. Apr 29, 2012

### oem7110

Visible light, like sunlight, consists of photons. Each photon has a level of energy (radiant energy) directly proportional to its frequency. Does anyone have any suggestions on any device to measure the frequency of Photon?
Thanks in advance for any suggestions

2. Apr 29, 2012

### M Quack

One usually does not measure the frequency, but the wavelength. The most common device to do this is a grating spectrometer.

http://en.wikipedia.org/wiki/Spectrometer

Alternatively, you could try to measure the energy, e.g. via the photoelectric effect.

3. Apr 29, 2012

Staff Emeritus
One normally measures their energy or wavelength and then calculates the frequency.

4. Apr 29, 2012

### ZapperZ

Staff Emeritus
One can also use an antenna and look at the induced signal. This is what is often used to measure the RF frequency in cavities and accelerating structures. Something like a pick-up loop would do the job.

Zz.

5. Apr 29, 2012

### Staff: Mentor

Short version:

For frequencies up to ~100MHz (wavelength ~3m): just measure the electric field over time (frequency detection)
For frequencies up to ~1THz (wavelength ~30µm): Use resonance in antennas or circuits (wavelength detection)
For frequencies up to ~0.3PHz (wavelength ~100nm, energy ~10 eV): Use lenses or diffraction gratings (wavelength detection)
For higher frequencies: Measure the energy of the photons

The numbers are not hard limits, of course. They are just there to indicate different regions in the electromagnetic spectrum, where different detection methods are used.

6. Apr 29, 2012

### M Quack

and above ~2 keV up to 200 keV or so, use single crystal diffraction to determine the wavelength, as (more precise) alternative to measuring the energy. In that range nobody talks about frequency anymore.

7. Apr 29, 2012

### Bobbywhy

If you wanted to know the approximate frequency of a visible light photon you could use a prism or diffraction grating to spread the light out (like in a rainbow). Then you would use this table from the below Wiki page to find the frequency band. If you needed a really precise frequency measurement you would need a "spectrometer". You can google that, if you want to.

Color Frequency Wavelength

violet 668–789 THz 380–450 nm
blue 631–668 THz 450–475 nm
cyan 606–630 THz 476–495 nm
green 526–606 THz 495–570 nm
yellow 508–526 THz 570–590 nm
orange 484–508 THz 590–620 nm
red 400–484 THz 620–750 nm

By the way, THz stands for "TeraHertz" and nm stands for "nanometers"
http://en.wikipedia.org/wiki/Visible_spectrum

8. Apr 29, 2012

### Mindscrape

How big is *your* spectrometer? :p

Yeah, lots of spectrometers: Fabry Perot, pushbroom, and others that are (in my mind) mostly extensions of these two.