Second Harmonic Generation, a second-order nonlinear process in which two photons at the fundamental frequency combine into one photon at twice the frequency, such as 1064 nm to 532 nm. It needs a non-centrosymmetric crystal such as KTP, LBO, BBO or PPLN and good phase matching. Efficiency grows with intensity, so pulsed lasers convert 50 percent or more while low-power CW beams need resonant cavities.
SHG efficiency is down to 30 percent, either the crystal temperature drifted or the waist moved off the middle.
Also heard as
- second harmonic generation
- frequency doubling
- doubling
- 2w
Related terms
Phase matching
Keeping interacting waves in a nonlinear crystal in step so the generated light builds up instead of canceling.
Doubler
Lab slang for the frequency-doubling crystal or module that turns an infrared laser into its second harmonic.
Quasi-phase matching
Phase matching by periodically flipping a crystal's nonlinear orientation instead of relying on birefringence.
Walk-off
The drifting apart of interacting beams in a crystal, either sideways from birefringence or in time from velocity mismatch.
Oven
The temperature-controlled mount that holds a nonlinear crystal at its phase-matching temperature.