Fyravågsmikning

Fyravågsmikning, meaning "four-wave mixing" in English, is a nonlinear optical process that occurs when at least three different optical frequencies interact within a nonlinear medium. The fundamental outcome of this interaction is the generation of new frequencies, specifically a fourth frequency. This phenomenon is a consequence of the third-order nonlinear susceptibility of the material, often denoted as $\chi^{(3)}$.

In a typical four-wave mixing scenario, two or three input waves with frequencies $\omega_1$, $\omega_2$, and $\omega_3$ propagate through a nonlinear medium. Due to the nonlinear polarization induced by these waves, new frequencies can be generated. A common configuration involves two input beams with frequencies $\omega_1$ and $\omega_2$, which can generate a new frequency $\omega_3$ and a fourth frequency $\omega_4$ such that $\omega_4 = \omega_1 + \omega_2 - \omega_3$. If all three input frequencies are distinct, a sum frequency and two difference frequencies can be generated.

The efficiency of four-wave mixing is dependent on factors such as the intensity of the input beams, the nonlinear properties of the medium, and phase-matching conditions. Phase matching ensures that the generated wave propagates in phase with the interacting waves, maximizing the conversion efficiency.

Four-wave mixing has found applications in various fields, including optical communications for wavelength conversion and optical regeneration, as well as in scientific research for generating new laser frequencies, studying material nonlinearities, and in spectroscopy. The ability to generate new frequencies from existing ones makes it a versatile tool in nonlinear optics.