The discussion revolves around the concept of destructive interference of laser beams aimed at a mirror, specifically examining the implications of two lasers with the same intensity and wavelength aimed at an angle. Participants explore the nature of wave cancellation at the surface of the mirror and the resulting effects on the electric and magnetic fields.
Participants generally disagree on the feasibility of achieving perfect cancellation of the waves at the mirror surface, with multiple competing views on the nature of the interference and the implications of the angles involved.
The discussion includes assumptions about the synchronization of the lasers and the specific angles involved, which remain unresolved. The complexity of wave interactions at different phases and the limitations of the proposed experimental setup are also noted.
This is not possible.God Plays Dice said:Take two lasers of the same intensity and wavelength and aim them at 30 degrees at the same spot on a mirror, so that at the surface the waves cancel perfectly.
This will only happen in a small region. On either side of the cancellation region, the phases will not be 180° out and you will not get cancellation. Further still and the phase difference will be 0°, giving a peak. The total energy must remain unchanged - it's just rearranged into 'fringes' of maxes and mins. With an angle of 30° between the beams, the fringes will be quite close together.God Plays Dice said:Is just like when two waves cross over each other and cancel
If they cancel in one spot they will not cancel in the spot nearby. This is easiest to work out using plane waves, but the same conclusion will hold for any valid field.God Plays Dice said:Why not?
Yes, this also happens when two waves cross at an angle.God Plays Dice said:I can see the electric fields canceled and the magnetic fields added everywhere.
It seems the wave forms a magnetic wave that doesn't move and has a node at the mirror
That is a good question. I had assumed each was 30 degrees incidence from opposite sides of the normal. But now I am not sure of the intended geometry.nasu said:Is this 30 degrees the angle between the beams? Or you mean that they are both aimed at 30 degrees incidence angle?
I was assuming that there is 30 degrees between them. It would not be possible to arrange for them to be incident from exactly the same direction in such a say that they would cancel out completely because the sources would have to be coincident / superposed on one another. Then there could be no output.nasu said:Is this 30 degrees the angle between the beams? Or you mean that they are both aimed at 30 degrees incidence angle?