Crystal design: How do they do that?

Factual Questions
1

For Christmas, I got a block of crystal that has a 3-D image inside. When you look at it from various angles, the image changes, so there is clearly something carved or etched inside. How do they do that??? The outside is perfectly smooth.

2

They shine lasers through from lots of different angles. Each laser heats up the glass a little bit where it passes but not enough to matter. But where all the lasers intersect, the glass gets really hot and forms a visible dot. Do it enough times and you get an etching.

3

Ooo. I had to register and post to this thread because this process is so cool. The machines that I’ve seen used use a pulsed Nd:yag laser which is focused through a rather short focal length lense. giving a >< shaped beam. the intensity at the focus is above the damage threshold for the crystal, and dings it with a little white spot, but the intensity elsewhere is low enough that the light passes through the glass without damaging it. The same process has been used to write 3D waveguides into various glasses for making cool optical devices.

4

Thanks! I know that radiation for chemotherapy uses the same idea (multiple beams focused on a single spot) but it didn’t occur to me that this might be the same.

SummoningDark, a special thanks to you for registering just to reply to me. Watch out–I did the same thing, and ended up getting hooked. :slight_smile: I hope the same thing happens to you.

5

Brynda: Thanks for the welcome! I’ve been lurking on these boards for ~6 years, but i’m pretty shy and never posted. I used a similar technique to the glass etchers to make a 15um slot in glass for some people at work, so seeing a question on it was enough to bring me out of hiding.

6
      • I saw an ad for these things somewhere–the laser-machines, not the little plastic products they make. The laser machine looked about as big as a combo-printer/scanner/fax, and it hooked to and was operated by a PC, and the setup cost $27,000.
        ~
7

At Disney World you can get your face scanned (or more likely the face of your children) and duplicated in one of these. The 3-D ones are fascinating. All the equipment is right there and you can see it being done. BTW, based on the prices I saw at Walt Disney World that’s not an inexpensive gift you were given.

8

If I am reading this correctly, the multiple-laser concept mentioned by Shalmanese is incorrect? My nephew gave one of these to my wife and when we were discussing how it was made, I immediately assumed it was done with multiple lasers.
So, the real truth, following SummoningDark, is a single powerful laser that is focused with a spiffy lens to a dot right were you want to leave a spot.

Very cool. And thanks for registering to tell us.

9

I’m pretty sure both techniques are used. The intersecting beam technique has the advantage of higher resolution–the size of the focal point depends on the wavelength being used, the beam diameter and the focal length of the lens. Longer focus and smaller beams will result in a smaller spot size, given the same wavelength.

10

Is it one of these?

If so, here’s how the artist did it.

I bought a couple last year after seeing them in Wired magazine. Other people do them, but Bathsheba’s are better than most. And she has some other cool stuff, too, as you can see from her Web site.

11

Another interesting side note. In some setups, most noticeably those which use extreamly short pulses (~100fs or so, which I’m sure are not used in making these crystal images) the damage mechanism is non-linear, and the damage spot can be much smaller than the focus. Most laser beams are gaussian in intensity accross their cross section, so the center of the beam might cross the damage threshold, while the wings do not, thereby creating a spot/hole smaller than the 1/e spot size.

12

Here is a link to some information on micromachining with lasers: http://www.cmxr.com/Industrial/Handbook/Chapter5.htm
it has info on both short and long pulse mechanisims, in addition to machining inside bulke materials(chapter 11)