Phase cancellation of light - Is it possible to make light disappear?

[sophiecentaur]

Many years back I remember asking a physics friend a similar question. The gedanken experiment was that you have two lasers, and you combine the output of the two lasers with (I guess?) a reverse beam splitter, but at pi phase offset. Now, the resulting beam would be no beam at all!
Apparently this was a common student exercise, and IIRC the outcome was that the energy would actually end up going backwards, essentially ending up inside the laser.

Many years ago, and many beers were involved. Mileage may vary.

That's exactly what you would expect. It is easy to achieve cancellation of waves in one place or in one direction. Fact is that the energy never disappears, it just turns up in other places / directions. In your case, the beam splitting arrangement will end up directing all the power out of the 'other' port of your beam splitter. This effect of re-directing power happens with noise cancelling headphones. the extraneous sound level on the outside of the phones will be twice as high as when the phones are turned off.

 

[Science23413]

It's Possible. Light is an electromagnetic wave, which like radio waves can 'interfere' with corresponding waves. But the fact is that the speed and frequency of light makes it hard to not only cancel out, but to make a large differerence in the surrounding area. Light will only cancel out in the smallest fraction of a second, which can not be seen by human eyes.

 

[sophiecentaur]

It's Possible. Light is an electromagnetic wave, which like radio waves can 'interfere' with corresponding waves. But the fact is that the speed and frequency of light makes it hard to not only cancel out, but to make a large differerence in the surrounding area. Light will only cancel out in the smallest fraction of a second, which can not be seen by human eyes.

Cancellation happens in particular places and not at particular times. Interference of waves (light [EM], sound, water) produces 'fringes' where the waves augment and fringes where they cancel. You don't have to be 'quick enough' to spot it happening because the fringes stay where they are and are there all the time. The only thing about light that makes interference patterns 'hard' to produce is that the wavelength is short and the trains of waves from most sources are very short (many short bursts which are uncorrelated. I am not talking of Photons, here, BTW). You need coherent sources and a split laser beam is particularly suitable.
You should look up the basics of interference, which are well documented all over the place. 'Alternative' views are very confusing for questioners on PF.

 

[mfb]

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