Synthetic holograms with a cnc mill

[Evan]

Heh heh. You bet, real white light holograms engraved via cnc. White light holograms are a special case of holography in that they only preserve horizontal phase information and do not operate via interference. It is possible to make a white light hologram with macroscopic line spacing although the resolution is extremely low.

I have been playing with this the last few days and tonight finally managed to make one that doesn't require an overactive imagination to see the resulting image.

This is how it looks under ordinary diffuse lighting. It's a very carefully placed set of arcs engraved on copper that has been blackened with potassium sulphide. Diffuse lighting is so spatially distributed that it cannot reveal the horizontal phase information in this synthetic hologram.



This is how it looks when in a darkened room and illuminated by a single white LED flashlight. The LED acts as a point source and so is highly spatially coherent.



In this next pair of pics you can see that the image is contained not just in one particular part of the the scribing pattern but in all parts, just the same as any other type of hologram. Changing the angle of view changes the apparent position of the cube. Also note that the hologram exhibits the same color diffusion characteristic that is a feature of a white light hologram.



I made up the pattern of scribe marks in a CAD program and used the DXF in CamBam to create the G-code. In the following pic you can see buried in the arcs a cube. The way this type of hologram is generated is to start with a 2d representation of the subject (the cube in this case). Then an arc is drawn using a point on the visible vertices and edges of the shape. A set of closely spaced points along all visible edges is then used to provide the anchor points for the radii of the arcs. The reason the image isn't perfect appearing is because of slight inaccuracies in the placement of the arcs (my fault) and some waviness in the copper plate which is only 26 gauge material.

[aostling]

This is an impressive demonstration. Did you devise the methods to achieve this result?

The image is quite low-rez, you will admit. What would it take to increase the detail? What applications do you foresee?

[aostling]

A further thought: this project of yours has stirred a memory I have, from over thirty years ago. There was an article in the magazine Camera 35, titled "Holy Holograms -- the Technological Beatles Are Here!" The story was about four young lads, I think perhaps from Berkeley, who were experimenting with white light holograms.

Was that you?

[Your Old Dog]

Pretty wild! Does this mean that a cast iron credit card with the master card hologram is not far behind? A card that won't melt under the extreme pressure of tool shopping?

[Evan]

I can't take credit for the idea. I saw it years ago in the Amateur Scientist column of Scientific American, I think. My only contributions to the process are using a CNC machine and making the marks in metal. The original process was done very laboriously by hand (I did maybe two, then quit) and used Plexiglas in which to scribe the lines with a compass. That often doesn't work well as the lines must be reflective and not just scratches.

I have been trying to make one in clear Lexan but the problem is that it is so soft that I haven't been able to make the grooves fine enough.

As most who follow my experiments may guess I have a particular interest in things optical.

Was that you?

I don't think so. Can't be entirely sure though.

[A.K. Boomer]

Very interesting, your first pic in the dark is unique in that it captured the "dissect" lines between the two far left arcs, even though they are not on a horizontal playing field they have to cross each other and this gives out a "blip" of info in that area, why it hasn't happend in all the other pics and also to the right side I really don't know although it might actually be not the high/low position of the flashlight as it appears that that was on the money but maybe it was a little off to one side or angled?

There is also the effect of the sequence in how the lines were crossed, another words which ones were laid down first, this can have an opposing effect in the way the intersections will be perceived from right to left esp. in an area where there not in a horizontal medium.

Way cool Ev.

[2ManyHobbies]

Heh, nice! Just to make sure I understand here, every "point" on the hologram is basically represented by an arc?

Would a form tool like a V or a tool with a flat spot help make things shinier? I mean that introduces other problems such as having to care about direction, but just a what-if...

What was the drag tool? Just the same engraver, or did you get the diamond on it?

[Evan]

It's the same tool as before. The tool is carbide and the tip is highly polished so it leaves a very shiny track. That is essential for this technique to work.

[lazlo]

Neat!

I can't take credit for the idea. I saw it years ago in the Amateur Scientist column of Scientific American, I think.

Evan, I found the CD collection of all the back-issues of the Amateur Scientist column for ~ $24 at a surplus site. If you're interested, drop me a PM...

[aostling]

The image is quite low-rez, you will admit. What would it take to increase the detail?

Sorry Evan, rereading your original post, I see you already discussed this. This is what happens when I post a reply at 3 AM when I am up for my "midnight" snack.