Better than holograms: new 3-D projection | Hacker News Reader

Better than holograms: new 3-D projection

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52 pointsadventured9 comments

Unfortunately the article has precisely no information about how it’s done. Here’s the original Nature article with a précis that provides a little more info: https://www.nature.com/articles/nature25176

Am I understanding the abstract correctly:

This research is basically using laser(s) in some manner to "trap" one or more dust particles (using something called "a photophoretic trap created by spherical and astigmatic aberrations") and move them around (not sure how - maybe mirrors, or some kind of phased array?) quickly - scanning what seems to be multiple light sources (best guess - an RGB DLP or similar projector system)...?

That's what I got from the abstract, anyhow - I could be completely wrong. It's neat, no matter how it's being done, though.

EDIT: Just to clarify - they are using lasers to move a trapped "particle(s)" scanning a 3D volume with this particle, while selectively illuminating it using normal RGB light sources. The "particle" basically forms a physical "retroreflective point" for the light sources to bounce off of, forming a "virtual" screen.

Using the term thin air is misleading IMO.

I saw a slightly different version of this a few years ago [1]. It basically used pulsed laser to create plasma at certain x,y,z without any additional reflective medium added to the environment. However it's crazy loud [2].

From the Nature paper [3] it seems to work on similar principles with the drawback that you need "light scattering (or absorbing and generating) surfaces" instead of free air. In other words you still need some medium for projection/reflection, like a smoke cloud for example:

"it is unlikely that the display would function outdoors without an enclosure unless particles were much more strongly confined or steps were taken to refresh trapped particles regularly"

[1] https://www.youtube.com/watch?v=AoWi10YVmfE

[2] https://www.youtube.com/watch?v=ZeqIZyUMDP4

[3] http://www.nature.com.https.sci-hub.hk/articles/nature25176

Wow. If you try to do it on a large scale it would be somewhat dangerous too, I suspect.

Article mentioned that other volumetric displays could cut off your fingers if you put your hand inside the volume, but heavily features use of fingers in the pictures to show scale.

This only requires enough power to push a tiny speck of dust around.

If you had a precise enough means of determining the position of a particle, and a precise enough means of painting it with visible light, you could rely on Brownian motion to trace out your image. You project the color and intensity of whatever voxel the particle happens to be in at that moment, and the dust scatters that light everywhere.

But if you can force the particle to trace out a specific path instead of a random one, you can make it walk through all the voxels in sequence, and paint your whole volume reliably.

The problems with scaling up are controlling multiple particles at once without making any of them occlude the others from the perspective of the painter lights and pusher lasers. One speck can only travel through so many voxels in the time required to paint one frame. And the more specks you have, the more likely it is that one that is supposed to display transparent will be occluding one that is supposed to be colored. The image would get "foggy".

I haven't read the article in detail, but it seems to look similar to:

http://digitalnature.slis.tsukuba.ac.jp/2015/06/fairy-lights...

There's some cool videos on that link too.

Edit: It seems they function using different techniques though. The one in this HN post, seems to make use of airborne particles.

Sounds like it's not thin air, but some kind of medium... maybe vaporized glycol?

I could see this being used in a cyberpunk film. You enter a foggy dimly lit room, and the projection system vaporizes a THC/glycol combo, and also uses it to project VR Wizard of Oz.

They use a single particle of cellulose in the 5-100um range which gets quickly scanned through the entire display volume. So, yes there is a medium but it's hardly a foggy room.

> You can have a circle of people stand around it and each person would be able to see it from their own perspective. And that’s not possible with a hologram.

But... that is possible with a hologram (a round one anyway).

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