2
$\begingroup$

Disclaimer: By no means am I a physicist of any kind so complete inability to grasp complex physical concepts without spending ridiculously unreasonable amounts of time on corresponding research is a given for me. I'm not attempting to understand some underlying principles in question, just would like an evaluation of certain claims found on web from a person competent enough in the respective field.

A while ago, a topic has been raised on some board, concerning this article. In short, it makes an implication of genuine volumetric displays (citation: "like the one R2D2 projected of Princess Leia in Star Wars: A New Hope") being now achievable due to the aforementioned means of metasurface holography. A link to the original article as well as to somewhat obscure video demonstration of what appears to be a functioning prototype was also included. Both look genuine to me. However, as I find the video completely failing at demonstrating if the imagery produced by the device actually floats mid-air, coupled with the original article referencing some sort of a screen in one of the figures it features, the whole situation fuels a buildup of quite contradictive impressions within myself. This forced me to perform some googling.

Now, first of all I've decided to locate a better, more clear visual depiction of such devices operating and failed, though I've managed to discover that the beginning of active research on the subject dates at least as far back as a decade ago, so the apparent lack of video material of acceptable quality on the matter comes across as rather surprising. Moreover, similar articles I've encountered during my search focused so much on the theoretical basis that I was unable to definitively deduce any relevant properties of an imagery such a device would actually be able to generate. I was able to notice though that a number of articles apparently carried no dependency on any kind of screen while exploring the subject. This even further facilitated the growth of my confusion.

Furthermore, any attempts at logical evaluation of the concept in question would even more incline myself towards thinking that the most scifi-ish properties of the device (the ability to actually fabricate a fully 3D imagery viewable from "almost any angle" of such scale) exist solely within the journalists' fantasies. As per my understanding, the human ability to truly see something comes from photosensitive cells within an eye exciting the optic nerve attached to it which in turn relays the signals to the brain for further processing. In order for an eye to actually catch some light, this light must be directed at its focusing system. And that is exactly where it gets tricky for me: how anything would actually be hit by any light which is projected in almost an opposite direction under the condition of said light not encountering any surface or medium along its path which would be able to alter its initial trajectory (as what is evident to be exactly the case here)?

Ultimately, any statement on truthfulness of the claims of the technology in question being able to facilitate generation of actual 3D imagery mid-air would be most welcomed. Additional gratitude guaranteed for a dumbed-down explanation of how the hell it is actually (if at all, with this particular approach, of course) possible.

P.S: I'm tagging nanoscience since the whole point of a metasurface here, as per my understanding, is to have orifices of sub-wavelength (regarding the visible electromagnetic spectrum) dimensions.

$\endgroup$

1 Answer 1

0
$\begingroup$

Your intuition is correct: a metasurface hologram cannot produce an image that is visible under any circumstances in which the line of sight does not intersect a surface that's part of the projection system.

In order to form a *Princess Leia" projection, something needs to make light change direction in mid-air, or else light needs to be emitted from points in mid-air. There actually are some prototype displays that can do it. One uses sound waves to move a tiny pith ball in a 3D pattern while the pith ball is illuminated with an intensity-modulated beam. Another uses a focused high-energy pulsed laser to cause a spark in the air, and the focal spot is rapidly scanned.

$\endgroup$
2

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.