frequency doubling

https://doi.org/10.1351/goldbook.F02527
See: harmonic frequency generation, non-linear optical effects
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2244 (https://doi.org/10.1351/pac199668122223)