thank you.yes,maybe there is something we miss.In the parametric process,there is no virtual level involved,and total energy of photons never change. how could momentum exchanged?
also there is another question, consider a photon incident into a medium,such as quartz, from vacuum, its...
In optical parametric conversion process, such as second harmonic generation,the conversion efficient is determined by function sinc(ΔkL),where L is the length of the crystal,and Δk is the phase mismatch condition. When the sum of wave vectors of the two fundamental photon,equals to that of the...