Frequencydoubled
Frequencydoubled is the term used for the nonlinear optical process of second-harmonic generation (SHG). In SHG, two photons at a fundamental frequency f combine to yield a single photon at frequency 2f, effectively halving the wavelength of the light. The process relies on a material with a nonzero second-order susceptibility and requires phase matching so that the generated second-harmonic wave stays in phase with the driving polarization as light propagates through the crystal.
Achieving efficient SHG involves selecting appropriate nonlinear crystals and employing techniques such as angle tuning, temperature
A widely cited example is frequency doubling of 1064 nm light from Nd:YAG lasers to 532 nm
See also nonlinear optics, second harmonic generation, quasi-phase matching, and frequency mixing.