In periodically poled crystals such as PPLN, PPKTP and PPLT, the sign of the nonlinear coefficient is reversed every coherence length, so conversion keeps growing instead of reversing. The poling period, often a few microns to tens of microns, is chosen for the wavelengths involved, and fine tuning is done with temperature. It lets all beams share one polarization, uses the crystal's largest coefficient and eliminates walk-off.
PPLN chip has nine gratings and we're on the 6.9 micron one for the 1064 doubling, so leave the translation stage alone.
Also heard as
- QPM
Related terms
Phase matching
Keeping interacting waves in a nonlinear crystal in step so the generated light builds up instead of canceling.
SHG
Second Harmonic Generation: converting light to exactly double its frequency, half its wavelength, in a nonlinear crystal.
OPO
Optical Parametric Oscillator: a tunable source that splits pump photons into two longer-wavelength beams in a nonlinear crystal.
Oven
The temperature-controlled mount that holds a nonlinear crystal at its phase-matching temperature.