English: Electric fields in a Fabry-Pérot resonator.
[1] The electric-field mirror reflectivities are
and
. Indicated are the characteristic electric fields produced by an electric field
incident upon mirror 1:
initially reflected at mirror 1,
launched through mirror 1,
and
circulating inside the resonator in forward and backward propagation direction, respectively,
propagating inside the resonator after one round trip,
transmitted through mirror 2,
transmitted through mirror 1, and the total field
propagating backward. Interference occurs at the left- and right-hand sides of mirror 1 between
and
, resulting in
, and between
and
, resulting in
, respectively.