Uhm, ok, cause the thread was undead .....
The interference mode, is also used in old instruments for measure the wavelenght of a laser, you know ?
Make a cavity with 2 mirrors, where the space is a multiple of , as example, 600nm (must be a multiple just cause there's no way for mechanically build a cavity identical to the wavelenght ..... i want to see someone working on a 600nm lenght cavity, LOL :crackup
, and where one of the mirrors can be precisely moved, for adjust the distance from the mirrors from a multiple of 400nm and a multiple of 800nm (just as example, for remain in the "visible" field
), and where the mirrors are semitransparents (not total mirrors, like the OC mirrors of the gas lasers).
Place a photodetector rear to one mirror, and then shine your laser through the other laser ..... then tune the distance from the mirrors until you get the maximum reading at the photodetector ..... this is your wavelenght ..... (ok, ok, simplified a lot, but this is the principle of working
)
This happens cause, when the distance is a precise multiple of the wavelenght that you shine in, you generate a "constructive interference", as any laser cavity works, after all ..... ofcourse, if you get a lenght that is a multiple of the wavelenght plus half, you get a destructive interference for the same principle (but anyway you can never "destroy" totally the light, just decrease it a certain degree .....