test-typst/section/perfect/non-polar/default.typ

@@ -10,7 +10,7 @@ This approximation is widely adopted (cite) and justified by the fact that,
     see orange dotted line in @figure-discont),
   and their dispersion at #sym.Gamma point is continuous with vanishing derivatives.
 Therefore, negligible-polar phonons involved in Raman processes
-    have nearly indistinguishable properties from those at the #sym.Gamma point.
+    have nearly indistinguishable frequencies and vibration amplitudes from those at the #sym.Gamma point.
 
 #include "figure-discont.typ"
 

test-typst/section/perfect/polar/default.typ

@@ -8,6 +8,26 @@
 // 若考虑到到入射光不是严格沿着 z 方向，而是有一个小的角度（例如 10 度），则此时有一个声子模式沿着 x 方向，另外两个声子模式则为 y-z 两个方向的混合。
 // (没有在图上表示)
 
+Strong-polar phonons heavily depend on the direction of their wavevectors
+  due to long-range Coulomb interactions between atoms in semiconductors.
+This causes the strong-polar phonon modes corresponding to different incident light directions
+  having different frequencies (i.e., discontinuity of colored lines near #sym.Gamma point in @figure-discont),
+  and their vibration directions also vary accordingly.
+For incident laser propagating along the z direction,
+  the relevant phonon modes are those along the A-#sym.Gamma line and symmetry of C#sub[6v] point group applies,
+  leading to two modes (two peeks in Raman spectra),
+  including an E#sub[1] mode (pink line in @figure-discont, vibration in-plane)
+    and an A#sub[1] mode (green line in @figure-discont, vibration along z-direction).
+When the light is incident along the y direction,
+  the relevant phonon modes are those along the #{sym.Gamma}-K line and only symmetry of C#sub[2v] applies.
+The mode vibration in z direction (A#sub[1] mode in C#sub[2v])
+  will have much lower frequency (green line in @figure-discont),
+  and the E#sub[1] mode C#sub[6v] will degenerate into two modes in C#sub[2v],
+  including B#sub[2] mode (blue line in @figure-discont, vibration along x direction)
+    and B#sub[1] mode (red line in @figure-discont, vibration in y direction).
+When the light is incident along random directions,
+  no symmetry applies, and there will be three phonon modes.
+
 // 极性声子模式还会与载流子发生较强的相互作用。
 
 @figure-discont