In LIGO they use 20W laser source, but then the light gets into Fabry-Perot cavity and this light's power inside it is 100kW [1].

How is that possible? It seems to me that in order to gather so much power we need highly reflective mirrors of the cavity. On the other hand, the more reflective mirror, the less light can enter the cavity.

[1] PRL 116, 061102 (2016)

  • $\begingroup$ write a note to Professor Nergis Mavalvala at MIT - SHE KNOWS! nergis@ligo.mit.edu $\endgroup$ – Walter Lewin Mar 18 '17 at 22:22
  • $\begingroup$ What do you mean by power in the cavity? Perhaps you mean to refer to the energy in the cavity? $\endgroup$ – DanielSank Mar 18 '17 at 22:32
  • $\begingroup$ In steady state, the power input to the cavity equals the power transmitted out of the cavity. For highly reflective mirrors, the transmitted power is a small fraction of the power incident on the internal mirror surface and thus, that incident power is much larger than the input power. $\endgroup$ – Alfred Centauri Mar 19 '17 at 0:24
  • $\begingroup$ @AlfredCentauri In the paper I refer, they write they have 20W laser source and 100kW inside the cavity. How comes? $\endgroup$ – Rafcik Mar 19 '17 at 23:48
  • 2
    $\begingroup$ @Rafcik, put simply, the light that enters the cavity bounces back and forth between the mirrors. On resonance, these reflected fields add constructively and the power builds up inside the cavity until the power transmitted through the output mirror equals the power entering the cavity. $\endgroup$ – Alfred Centauri Mar 20 '17 at 23:33

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