# Can Young's double slit experiment be considered a holographic setup?

As described in his landmark paper on holography, "A new microscopic principle", Denis Gabor sent coherent light through a transparent plate with some black letters on it. The light that was diffracted by the letters then interfered with non-diffracted waves.

In Thomas Young's famous double slit experiment (or at least the way it is taught today), coherent light is sent through two small slits. Some light is diffracted when passing through and interferes with non-diffracted waves. Can this be seen as an in-line holographic setup? If I were to record the resulting pattern of light and dark, could I reconstruct the two slits?

• Minor comment to the post (v2): Please consider to mention explicitly author, title, etc. of link, so it is possible to reconstruct link in case of link rot. Commented May 14, 2018 at 18:59

The answer is an unequivocal "yes": Young's double-slit experiment can be considered an in-line holographic setup. Strictly speaking, light going through one of the slits can be considered an object beam and light going through the other slit can be considered a reference beam. So, if you record the pattern and reconstruct using just the "reference beam", you will reconstruct the "object beam". In principle, that means you will reconstruct just one slit. However, you're very likely to obtain higher diffraction orders as well -- so you will probably see multiple slit reconstructions.

Note that the first-order reconstruction, using the light from the original "reference slit" to illuminate the hologram, will produce a virtual image of the other slit, located in its original position. In an in-line setup in which the object is at the same distance from the recording plane as the (nominally) point reference source, there also typically will be a real image reconstructed at infinity.

• Thank you. What do you mean by reconstruction "using just the 'reference beam'"?
– smcs
Commented May 16, 2018 at 14:11
• The beam from one slit is designated the "reference beam", and the other is designated the "object beam". Illuminating the recording using just the reference beam is easy: simply block the object beam slit so light can only pass through the reference beam slit. Then only the reference beam illuminates the recording. Commented May 16, 2018 at 14:42
• Yeah that makes sense. But I don't understand the sentence "record the pattern and reconstruct using just the reference beam". If I use both slits to record the pattern, how would I reconstruct just one of them?
– smcs
Commented May 17, 2018 at 8:01
• In holography, two beams illuminate a photographic plate to form an interference pattern. The plate is developed and put back in position. Then one of the beams can be blocked off so that just the other beam illuminates the developed plate. The illuminating beam is diffracted by the interference pattern recorded on the plate, so that it precisely reconstructs the blocked beam. The same thing happens with the pattern in Young's experiment. Just put a piece of tape over one of the slits for reconstruction. Diffraction from the pattern will reconstruct that slit. Search "holography". Commented May 17, 2018 at 13:44
• Ahh, I see now. I was thinking about digital holography, where there is no equivalent to the reconstruction you described I think.
– smcs
Commented May 17, 2018 at 17:16