It appears that the power-efficiency for second-order nonlinear optical processes is proportional to the square of the nonlinear interaction length along the propagation direction (~ longitudinal_distance^2) and inversely proportional to the nonlinear overlap area (~ transverse_distance^-1) if the pump power is kept the same when changing these sizes [http://www.opticsinfobase.org/josab/abstract.cfm?uri=josab-29-8-2199].
Is there any intuitive explanation for such scaling, especially taking into account that it applies to both spontaneous and stimulated processes?
maybe I did not get the meaning of the question, but I suspect that intuitively there must be no reason for this scaling. Transverse_distance^-1 is due to MICROSCOPIC effect, i.e. due to larger nonlinear polarization of the unit cell of the medium. It does not require phase matching. Longitudinal_distance^2 is due to MACROSCOPIC effect, i.e. due to growth of intensity in the course of propagation over a number of unit cells of the medium and requires phase matching.
Thank you Aleksandr, what about the case when all distances are microscopic (i.e. the length is so small that phase-matching becomes unimportant)? Does this scaling still hold?
In a second order nonlinear optical process the output intensity grows proportional to the square of the coherence length. If no phase matching after one coherence length their is phase reversal between the electromagnetic wave and the generated polarization wave so output intensity decays. Therefore, if the length of the crystal is ~coherence length (normally it is ~micron, indeed it depends on the crystal type, etc.) the output intensity will grow quadratically with the length.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Optics