# Are there any ways to alter frequency of wave?

I want to know how can we change frequency of wave, both sound and light, and what is the nature of "changing frequency"

Such as, any material could absorb and re-emit wave in another wavelength. Or any kind of field could make an interference in a way that making new wave in difference frequency

p.s. please exclude refraction (which is not really change frequency, just change wavelength and speed) and Doppler shift

• Are changes in mediums off the table? That is, can I put the wave through something? – HDE 226868 Oct 11 '14 at 18:08
• Frequency doubling ( en.wikipedia.org/wiki/Second-harmonic_generation ) is a widely applied technique in nonlinear optics. – Johannes Oct 11 '14 at 18:14
• @HDE226868 If you let wave pass some medium then came out with difference frequency then I would love to count, but if it just change wavelength in that medium then came out with same frequency is no – Thaina Oct 11 '14 at 19:27
• Look up how radios work. It's fascinating, not too hard to understand, ad involves exactly what you're asking about. – DanielSank Oct 12 '14 at 0:48

• Frequency doubling, also called second-harmonic generation as Johannes mentions. Here, you put one wave into a medium, and some fraction of it is converted to a wave with a different frequency. By carefully engineering the medium you can get quite a high conversion percentage.
• Other nonlinear optical processes, not just frequency doubling, but includes difference frequency generation, optical parametric oscillators, N-wave mixing, etc. These involve putting one or more waves with different frequencies into a medium and, getting an additional wave out with a frequency that you didn't put in.
• Raman scattering which is spontaneous, and its stimulated equivalents CARS and CSRS. In Raman scattering you don't really get a coherent wave out; you just put one wave into a medium and a tiny portion of the scattering has a different frequency. CARS and CSRS use the same mechanism (a molecule absorbing a photon, using its energy to transition to a different level, then re-emitting a photon with the excess energy) but they are types of four-wave mixing and really belong in the previous point.

Although normally considered as photon interactions, any inelastic scattering process will result in the alteration of the frequency of the electromagnetic radiation.

An obvious example is Compton scattering, where high energy (X-rays+) light scatters from free electrons. The scattered light has lower energy and longer wavelengths than the light incident upon the electrons.

Raman scattering of (often optical or infrared) light from molecules results in the scattered light having a slightly lower frequency, corresponding to a transition between energy levels in the molecule.

Yes.

Materials that absorb electromagnetic radiation and emit it in a different frequency are known as fluorescent. You probably see them as the coating on the inside of fluorescent tubes, where they absorb ultra-violet light and emit a lower frequency visible light.

That happens in phyics everyday. It is how we use any of our energy. It creates a change in physical makeup of matter through a chemical process, ei burning wood. All matter is EMR at different frequencies. When you burn wood, you are changing the emr frequency of the wood and harvesting a change of radiated emr in other frequencies like heat and light. A change in frequency is literally the conversion of matter, even in organic decay. All frequencies can be modified just some undiscovered, like turning light frequency into physical matter for instance. My theory is that you would have to create a very strong electromagnetic field that we do not have the math and means to create yet. when getting to certain frequencies converting to a specific desired frequency