Optics: Destructive interference - Where does the light go?

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Recommends anna v · 2014-11 · Physics Stack Exchange · on “What happens to the energy when waves perfectly cancel each other?”

I had prepared this answer for a question that was made duplicate [LINK] , so here it comes, because I found an instructive MIT video. (the second link) This answer is for electromagnetic waves mainly Have a look at this video [LINK] to get an intuition how interference appears photon by photon in a two slit experiment. It comes because the probability distribution for the photons, as accumulated on the screen, has destructive and and constructive patterns, ruled by the underlying quantum mechanical solution of "photon + two slits". The classical electromagnetic wave emerges from a great plethora [LINK] of photons which have phases and such that they build up the electric and magnetic fields

Recommends anna v · 2017-01 · Physics Stack Exchange · on “Laser beam extinction - what happened to the photons”

This will make the beams more or less invisible. Here is an MIT course video [this video] showing destructive interference using beam splitters and mirrors from one laser source. Here is the set up, at the point where it is arranged that the beam on the left is the one returning to the source. [LINK] From a larger distance interference fringes appear [LINK] Here are the two beams , the one returning to the source(left) and the one coming from the source (right). The interferences are complementary. bringing the mirror closer concentrates on the central spot [LINK] The instructor ( Shaoul Ezekiel) presses on the table to change the wavelengths, and force total destructive on the right, [LINK] and

Recommends Farcher · 2017-07 · Physics Stack Exchange · on “Intensity of superimposed waves at the michelson inferometer”

You must first work with amplitudes and not worry about the mean intensity. Let the amplitude of the wave be $A$ as it leaves the laser. If the intensity is reduced by a half on reflection or transmission at the beam splitter then the amplitude is $\frac {A} {\sqrt 2}$ . So after all the reflection two waves of amplitude $\frac {A} {\sqrt 2}$ end up on the screen in phase with one another. Thus the total amplitude is $\frac {A} {\sqrt 2} + \frac {A} {\sqrt 2}=\sqrt 2A $ leading to an intensity which is twice that of the original laser but only at the centre of the screen. If you look at this video [this video] at time 1:35 you will see that the demonstrator produces a large bright spot on the scr

Recommends Mark H · 2017-07 · Physics Stack Exchange · on “Diffraction of monochromatic light”

The energy does not disappear. The energy that would have gone to the dark spots--if not for diffraction--is diverted to the bright spots. If you were to remove the slits and use a lens to make a band of light as wide as the diffraction pattern, you would find that the light at the center is dimmer than the central peak of the diffraction pattern. The light bands are concentrated light that was diverted from the dark bands. The total amount of light is the same. There's a great video from MIT to show that interference just moves light around. It does not create or destroy light. Where Does the Light Go? [this video]

Recommends HolgerFiedler · 2017-12 · Physics Stack Exchange · on “When light reflects off a mirror, does the wave function collapse?”

I’ll follow your argumentation step by step. So some passages of mine are more comments or affirmations of your thoughts. This question is specific to the Copenhagen interpretation, which states that the wave function collapses on interaction. No more photon after absorption, no more wave function. Obvious, even without Copenhagen interpretation. If we have a beam of light reflected off a mirror, ... the original photons have been absorbed in the mirror and new photons reemitted in a different direction. The wave function also is different accordingly. So on one hand, it would seem that the original wave function collapses at the mirror. Right, the new wave function is different with the fre

Recommends anna v · 2017-12 · Physics Stack Exchange · on “How is it possible to view destructive interference reflected from a screen?”

In optics a ray is [LINK] an idealized model of light, obtained by choosing a line that is perpendicular to the wavefronts of the actual light, and that points in the direction of energy flow. ... Ray theory (geometrical optics) does not describe phenomena such as interference and diffraction , which require wave theory (involving the relative phase of the rays). italics mine Two light beams are coherent if the phases between the wave fronts are fixed, and that is why in n this video [this video] , two parallel beams by construction hit the screen and show an interference pattern. They are coherent because mirrors and lenses are to used split an original coherent source into two beams, with known

Recommends anna v · 2019-04 · Physics Stack Exchange · on “Destructive interference of light and destroying energy?”

There is a series of instructive MIT videos treating the subject of interference of laser beams, and what happens to conservation of energy. [this video] It is all about quantum mechanics which is at the underlying nature of everything, including classical light beams. In the case of the laser experiments one has to consider the whole system, i.e. the lasing itself is taking part in the creation of the interference pattern. The energy lost in destructive interference are photons that have returned to their source. It is worth watching to get an intuition about light, and the comments are enlightening ;) too . Interference of light is not interaction of photons, but a pattern in the quantum mechan

Recommends anna v · 2019-06 · Physics Stack Exchange · on “EM waves cancelling each other - do they interact? Does this mean photons interact?”

The classical electromagnetic wave emerges from zillions of photons. Interference phenomena in classical waves does not mean that photons interact. Photon photon [LINK] interactions are very improbable. What happens to individual photons at interference regions can be seen in this single photon at a time double slit experiment [LINK] . The classical fringes appear after an accumulation of photons. An intuition of what happens to photons at total disappearance can be gained by watching this MIT video [this video] . . For the case you describe one would have to do a special experiment to see where the photons have gone.

Recommends anna v · 2019-07 · Physics Stack Exchange · on “Can two waves interfere head on?”

For sound waves and other waves that depend on the motion of atoms and molecules, destructive interference will eventually disperse the energy to the atoms and molecules finally ending up in heat (motion of matter). For light, which does not depend on a medium to propagate, it is more complicated. Light only superimposes, does not interact. This MIT video [this video] shows what is happening in superposition interference of a laser beam split in two and made to interfere. The energy not appearing in the pattern goes back to the lazing mechanism! In general for electromagnetic waves, when interference light patterns are seen, the energy goes from the dark regions to the bright regions, i.e.it is a

Recommends Gene Ruso · 2019-09 · Physics Stack Exchange · on “What happens when two opposite EM waves which completely destructs each other hits a wall?”

"Where does energy go in destructive interference" is a frequently asked question. (For example: What happens to the energy when waves perfectly cancel each other? [LINK] ) However, it is very counter-intuitive, and at some point there has even been a debate about it in serious physics journals, (probably Phys Rev, I do not recall at the moment.) Of course, destructive interference does happen in practice, and the light does indeed vanish completely. This happens all the time in interferometers. (You can see a demonstration here: [this video] ) But the essence of the paradox of seemingly vanishing energy has nothing to do with quantum mechanics -- the same effect can be demonstrated with waves in