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1 files changed, 6 insertions, 0 deletions

diff --git a/content/know/concept/fabry-perot-cavity/index.pdc b/content/know/concept/fabry-perot-cavity/index.pdc
index 2f1f84f..d40852f 100644
--- a/content/know/concept/fabry-perot-cavity/index.pdc
+++ b/content/know/concept/fabry-perot-cavity/index.pdc
@@ -120,6 +120,12 @@ $$\begin{aligned}
     &= (1 - r_R) B_m \exp\!\big( i (\tilde{n}_C \!-\! \tilde{n}_R) \tilde{k}_m L/2 \big)
 \end{aligned}$$
 
+Note that we have not demanded continuity of the electric field.
+This is because the mirrors are infinitely thin "magic" planes;
+if we had instead used a full physical mirror structure,
+then the we would have demanded continuity,
+as you might have expected.
+
 
 
 ## References