- #1

Erik Ayer

- 75

- 4

In a type II downconversion, the light comes out in two cones. I imagine that, since the pump has a finite cross-secional area and the nonlinear optic has some thickness, where downconversion happens can be anywhere within the intersection of these two things. Hence, an infinite number of overlapping sets of cones would be generated, making the output non-coherent, spatially. Feeding that to a double-slit would result in varying phase shifts between the waves of the photons, shifting the interference pattern around such that it all adds up to a big mess.

It would seem like, to get coherent light out, the laser beam would need to be infinitely concentrated into a geometric line and the optic would need to be infinitely thin. Obviously that does not constitute a Sagnac Source, so how can coherence be increased?

Thanks,

Erik