English: Electric fields in a Fabry-Pérot resonator.
[1] The electric-field mirror reflectivities are
![{\displaystyle r_{1}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/ea214f2b31fb3869344bb9311da41c5cc38a99e1)
and
![{\displaystyle r_{2}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/4cbe9b0b294fdd6fadbf9a7249813f016dcbc44f)
. Indicated are the characteristic electric fields produced by an electric field
![{\displaystyle E_{inc}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/384382613fe2e4ae51d6a5f397b9a57477bc411f)
incident upon mirror 1:
![{\displaystyle E_{refl,1}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/049ac080bf2c2ca78420ee66874a03902152e3d0)
initially reflected at mirror 1,
![{\displaystyle E_{laun}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/b697285b6c4817cc0ca56a4e94d79b156bb059b8)
launched through mirror 1,
![{\displaystyle E_{circ}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/7a04a369e4953e0ceb512826d5c1585d6adccd17)
and
![{\displaystyle E_{b-circ}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/9f71fa1febd3acaab1ea41e7af5597ff455e8bc7)
circulating inside the resonator in forward and backward propagation direction, respectively,
![{\displaystyle E_{RT}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f90e5c2050ce9cc52c8f99f8eaf777a82195f407)
propagating inside the resonator after one round trip,
![{\displaystyle E_{trans}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/abc5d8a2097b9d4db8be7d3c0e2d6fcab077ef27)
transmitted through mirror 2,
![{\displaystyle E_{back}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/272fd86a654a608c85285f8ce8024e2675698313)
transmitted through mirror 1, and the total field
![{\displaystyle E_{refl}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0b8b00e72febb985722ea891c5d4285de3a2af06)
propagating backward. Interference occurs at the left- and right-hand sides of mirror 1 between
![{\displaystyle E_{refl,1}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/049ac080bf2c2ca78420ee66874a03902152e3d0)
and
![{\displaystyle E_{back}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/272fd86a654a608c85285f8ce8024e2675698313)
, resulting in
![{\displaystyle E_{refl}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0b8b00e72febb985722ea891c5d4285de3a2af06)
, and between
![{\displaystyle E_{laun}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/b697285b6c4817cc0ca56a4e94d79b156bb059b8)
and
![{\displaystyle E_{RT}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f90e5c2050ce9cc52c8f99f8eaf777a82195f407)
, resulting in
![{\displaystyle E_{circ}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/7a04a369e4953e0ceb512826d5c1585d6adccd17)
, respectively.