# Is there an instrument that measures the Frequency of light directly

Is there an instrument that measures the frequency of light DIRECTLY? By "DIRECTLY" I mean without using any properties of the Wavelength.

• What sort of light? I believe you tune your radio to a frequency. – Rob Jeffries Feb 15 '16 at 12:45
• And caesium clocks count the individual cycles in a microwave – John Rennie Feb 15 '16 at 12:48
• Above microwave: There are no direct ways of measuring frequency, because there are no recording devices capable of operating anywhere near optical frequencies. – Anubhav Goel Feb 15 '16 at 12:50
• @RobJeffries and John Rennie posting answers as comments? These suddenly give context to the question. – Bill N Feb 15 '16 at 17:21
• en.wikipedia.org/wiki/Frequency_comb – Norbert Schuch Feb 16 '16 at 0:02

You have to be clear as what you mean by "frequency" and "directly." If what you mean is an instrument like an oscilloscope with a photo-detector, where the light is incident on the photo-detector without any other source coincident with it. Then what you'll need is an oscilloscope and a photo-detector capable of responding to electric fields at $10^{15}$ Hz, and as such does not yet exist.