# Crystal design: How do they do that? **URL:** \ **Category:** Factual Questions\ **Created:** [December 25, 2005, 4:38pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174 "2005-12-25T16:38:26Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Brynda](https://avatars.discourse-cdn.com/v4/letter/b/e79b87/32.png) [@Brynda](https://boards.straightdope.com/u/Brynda)\ **Post date:** [December 25, 2005, 4:38pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/1 "2005-12-25T16:38:26Z")
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. ---
**Author:** ![Shalmanese](https://avatars.discourse-cdn.com/v4/letter/s/45deac/32.png) [@Shalmanese](https://boards.straightdope.com/u/Shalmanese)\ **Post date:** [December 25, 2005, 4:44pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/2 "2005-12-25T16:44:53Z")
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. ---
**Author:** ![SummoningDark](https://avatars.discourse-cdn.com/v4/letter/s/e19b73/32.png) [@SummoningDark](https://boards.straightdope.com/u/SummoningDark)\ **Post date:** [December 25, 2005, 4:49pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/3 "2005-12-25T16:49:26Z")
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. ---
**Author:** ![Brynda](https://avatars.discourse-cdn.com/v4/letter/b/e79b87/32.png) [@Brynda](https://boards.straightdope.com/u/Brynda)\ **Post date:** [December 25, 2005, 6:13pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/4 "2005-12-25T18:13:37Z")
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. 🙂 I hope the same thing happens to you. ---
**Author:** ![SummoningDark](https://avatars.discourse-cdn.com/v4/letter/s/e19b73/32.png) [@SummoningDark](https://boards.straightdope.com/u/SummoningDark)\ **Post date:** [December 25, 2005, 6:27pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/5 "2005-12-25T18:27:51Z")
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. ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [December 25, 2005, 6:55pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/6 "2005-12-25T18:55:17Z")
- - - 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. ~ ---
**Author:** ![lalaith](https://avatars.discourse-cdn.com/v4/letter/l/96bed5/32.png) [@lalaith](https://boards.straightdope.com/u/lalaith)\ **Post date:** [December 25, 2005, 10:19pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/7 "2005-12-25T22:19:15Z")
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. ---
**Author:** ![minor7flat5](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/minor7flat5/32/258_2.png) [@minor7flat5](https://boards.straightdope.com/u/minor7flat5)\ **Post date:** [December 25, 2005, 11:59pm UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/8 "2005-12-25T23:59:17Z")
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. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [December 26, 2005, 12:11am UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/9 "2005-12-26T00:11:18Z")
> [@minor7flat5](#): > > If I am reading this correctly, the multiple-laser concept mentioned by **Shalmanese** is _incorrect_? 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. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [December 26, 2005, 2:00am UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/10 "2005-12-26T02:00:54Z")
Is it [one of these?](http://www.bathsheba.com/crystal/) If so, [here’s](http://www.bathsheba.com/crystal/process/) how the artist did it. > [@Bathsheba Grossman](#): > > The points are tiny (.1mm) fractures created by a focused laser beam. The conical beam, with a focal length of about 3", shines into the glass without damaging it except at the focal point. At that one point, concentrated energy heats the glass to the cracking point, causing a microfracture. > > To draw more points, the laser is pulsed on and off. To make the beam move between points, it’s reflected from a mirror that is repositioned between pulses. The mirror is moved by computer-controlled motors, so many points can be drawn with great speed and accuracy. A typical design might use several hundred thousand points, or half a million isn’t unusual in a large block, each placed with .001" accuracy. > > This can be done with different types of laser, and the results vary – you’ve probably seen cheap crystals with fuzzy points, which mean that the laser is either low-frequency or not well focused. I’m currently using a high-frequency laser, which draws points that are barely visible to the naked eye. I’m told it’s a ND:YAG laser, after its active medium: yttrium-aluminum-garnet crystal doped with neodymium. > > The glass itself must be clear optical crystal, since any ripples or bubbles would block or blur the laser. It’s also necessary to draw in layers, moving from rear to front of the glass, so that previous points don’t block the laser from drawing new ones. 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. ---
**Author:** ![SummoningDark](https://avatars.discourse-cdn.com/v4/letter/s/e19b73/32.png) [@SummoningDark](https://boards.straightdope.com/u/SummoningDark)\ **Post date:** [December 26, 2005, 4:06am UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/11 "2005-12-26T04:06:24Z")
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. ---
**Author:** ![SummoningDark](https://avatars.discourse-cdn.com/v4/letter/s/e19b73/32.png) [@SummoningDark](https://boards.straightdope.com/u/SummoningDark)\ **Post date:** [December 26, 2005, 4:13am UTC](https://boards.straightdope.com/t/crystal-design-how-do-they-do-that/337174/12 "2005-12-26T04:13:04Z")
Here is a link to some information on micromachining with lasers: [http://www.cmxr.com/Industrial/Handbook/Chapter5.htm](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)