When the incident beam of light into the cavity f-p interference, it will round-trip times between the mirrors reflecting, thus forming multiple-beam interference. It
When the incident beam into the interferometer FP cavity, it will be reflected back and forth several times to achieve between the mirrors, thus forming a multi-beam interference. it
When the incident light beam enters the F-P interference cavity, it will be reflected back and forth between the mirrors, thus forming a multi beam interference. it