wasser@mosaic.DEC (John A. Wasser) (01/24/86)
> I just heard a discussion of a Fabre Preot interformeter. It involved the > use of 2 mirrors that had 95 % reflectance and 5 % transmission they were > set up parrellel to each other and a given number of wavelengths apart. > It was stated that if this device was raidated with 1 watt of light at that > waveleignth the output at the other end would be 1 watt. And that there would > be 20 wats of energy radiating back and forth between the mirrors. > Is this realy true and if so how does it work???? Looks like it is true. If you want to get 1 watt into the cavity between mirrors, you would shine 20 watts into the back of one of the mirrors. You would then get 5% lost on every bounce. At the end of 100 bounces, the original 1 watt would be down to .006 watts and the sum of the bounces would be 18.89 watts (they add up because of constructive interference). I looks like the number is reaching 20 watts asymtotically. If you put in 20 watts continuously long enough you should have 20 watts bouncing back and fourth in the cavity. If you move one of the mirrors half a wavelength, you get destructive interference and about .05 watts in the cavity (the difference between the 1 watt coming through the mirror from the source and the .95 watts that bounce of the opposite mirror). -John A. Wasser "No magic. If you put in 20 watts for long enough, you can get out up to 20 watts."