EQMResearch group
Level 4 · Light in layered structures

Standing wave & |E(z)|²

Inside the cavity light freezes into a stripe pattern. The bright stripes are where the material can soak up energy most efficiently.

Build on:Fabry-Pérot microcavity

Where the light lives

Inside a resonant cavity the wave doesn't travel anywhere; it sets up a frozen standing wave. The square of its amplitude, |E(z)|², draws stripes of bright and dark inside the cavity — antinodes and nodes.

Pick a mode

Each mode index m has mantinodes between the two mirrors. The simulator's "E-field" panel shows you exactly this curve for the cavity mode you click in the reflectance spectrum.

CrSBr regionAuDBRDepth z →|E(z)|² (mode m = 5)

With both mirrors clamping the wave to zero, only modes with an integer number of half-wavelengths fit. Notice how some modes line their antinodes up with the CrSBr region (good coupling) while others sit at nodes there (poor coupling).

Standing wave inside the cavity for mode m. The CrSBr region is shaded; modes that put antinodes there couple strongest to the exciton.

Why we care about the antinodes

Light–matter coupling is proportional to |E|²at the material's position. To boost the coupling you place the active layers right where the antinode sits. That's why aligning CrSBr with the cavity mode is half the experiment's art.

Key takeaways
  • The cavity mode is a standing wave with m antinodes.
  • Coupling to material ∝ |E|² at the material's depth.
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