For weak fileds, polarization is proportional to electric field (P ~ E), thus you have linear response. In strong fields in the BBO, there is a second order effect (with small probability) with polarization proportional to square of electric field (P ~ E^2). Decomposed in frequencies, you can have one photon split into a pair of two with half the frequency. Look up at: "parametric down-conversion"
How does the BBO work?
For weak fileds, polarization is proportional to electric field (P ~ E), thus you have linear response. In strong fields in the BBO, there is a second order effect (with small probability) with polarization proportional to square of electric field (P ~ E^2). Decomposed in frequencies, you can have one photon split into a pair of two with half the frequency. Look up at: "parametric down-conversion"
I really love your videos ... Thanks for making videos for students like us ❤❤
You are welcome! You find a documentation and mathematical comment of all videos here: www.quantumvisions.net/media/QuantumVisions.pdf