by Din » Wed Nov 11, 2020 1:36 pm
Petr, strictly speaking, you're right. The Bragg orientation would not be 30 degrees. The K vector would depend on the two input waves within the material, and they would be 0 degrees and sin(60)/n. However, when the reconstruction wave is applied at 60 degrees, the input wave also refracts, to an angle of sin(60)/n, hits the Bragg planes correctly according to the Bragg condition. On diffraction, the output wave then refracts again the other way, or, in this case does not because it's normal, as is the other wave being simulated by the R wave,on creation of the Bragg planes. So, in effect, you can model the Bragg planes as if there were no refraction. In fact, Kogelnik starts by explicitly stating that refraction will not be taken into account, for this reason of two refractions. The S wave, for a given R wave, behaves as if there were no refraction because the planes were formed by two waves that simulate the S and R waves, refracting in and out.
Petr, strictly speaking, you're right. The Bragg orientation would not be 30 degrees. The K vector would depend on the two input waves within the material, and they would be 0 degrees and sin(60)/n. However, when the reconstruction wave is applied at 60 degrees, the input wave also refracts, to an angle of sin(60)/n, hits the Bragg planes correctly according to the Bragg condition. On diffraction, the output wave then refracts again the other way, or, in this case does not because it's normal, as is the other wave being simulated by the R wave,on creation of the Bragg planes. So, in effect, you can model the Bragg planes as if there were no refraction. In fact, Kogelnik starts by explicitly stating that refraction will not be taken into account, for this reason of two refractions. The S wave, for a given R wave, behaves as if there were no refraction because the planes were formed by two waves that simulate the S and R waves, refracting in and out.