I saw one with an eagle in it and stars. The image looked translucent or sintered. They are less than 10 dollars, so they must be mass produced, and seemed to be made of some kind of solid glass. How did they get that figure in there?
When I was in vegas there was a booth in one of the malls that was making them on the spot. They could even take your picture and do it with that. They were charging something like 50-100 dollars I think. (I assume they use lasers to make them)
I’ve never seen one, but the description sounds exactly like a hologram. It’s little more than a fancy photographic technique.
They’re made by aiming two lasers through the glass; where the lasers intersect, you get a “dot.” Enough dots, properly placed, and you have a picture. I’m not entirely sure how intersecting two lasers makes the dot, but I’d guess that local heating is involved. I don’t think this is holography.
I know what you’re talking about. They’re not holograms. Search online for “laser etched glass”; many places have them for sale. Here’s the best explanation I’ve found so far…[
I think it’s plastic, not glass. The lasers would make a dot by vaporizing some plastic and making a bubble, I suppose. And if not a bubble, just change the transparency of that spot by singeing it a bit. Definately not holography.
Oops, Achernar’s post somehow wasn’t there on preview.
I’ve been wondering if you could whip these things up at home.
I’m assuming that the cheap key chain laser pointers don’t have the power. But, what is you were to focus more than 2 on the spot?
What about the laser diodes from CD rom drives? DVD drives? CD burners?
I've seen the technique used on plastic too. I'm assuming this stuff is available to the public.
I realize that you’d need motorized mounts for the lasers, a way to link them in to the computer, and a program to control them.
Would a vacuum or partial vacuum be necessary?
Naturally, I should wear protective lenses of some kind in case I get a laser in the eye. What kind of eyewear would be needed? Would mirror clip ons, backed by a mylar mask, backed by my prescription specs smeared with finger prints(so as to further scatter and absorb the light) do it?
You are the closest, so far, Achenar.
The method whereby these images are produced internal to a solid object is similar to recent advances in polymer prototype modeling. This technique relies upon what it known in the world of laser optics as “positive incidence.” Another term for this phenomenon is “constructive interference.” A unique property of all lasers is their “coherence.” This dictates that all light waves emitted by the source remain in phase. Ordinary incandescent lamps emit numerous wavelengths (frequencies or colors) which are out of phase. To understand the concept of phase, imagine a waveform that looks like this:
-’’-…-’’-…’’-…-’’-…
Now picture several of these waveforms traveling in the same direction, but out of phase. They would look like this:
‘-…-’’-…-’’-…-’’-…-’
-’’-…-’’-…-’’-…-’’-…
-…-’’-…-’’-…-’’-…-’’
.-’’-…-’’-…-’’-…-’’-.
You can see that none of the various peaks or zero crossing points align with respect to each other. These are known as incoherent or “out of phase” waveforms. The coherent emission of a laser looks like this:
-’’-…-’’-…-’’-…-’’-…
-’’-…-’’-…-’’-…-’’-…
-’’-…-’’-…-’’-…-’’-…
-’’-…-’’-…-’’-…-’’-…
All of the peaks and zero crossing points in the above illustration occur “in phase.” This is what gives lasers their phenomenal brightness and power with respect to their diminutive wattages. Let’s now consider positive incidence. This is when two laser beams intersect at right angles and they are in phase. At the point of intersection, there will be a doubling of expressed power due to both beams colliding while at maximum strength. It should be mentioned that this effect does not rely upon the waveform being only at its upper “peak” or maximum positive amplitude. Two beams intersecting at their “trough” or maximum negative amplitude (bottom peak) will produce the same effect. Two laser beams constructively interfering will exhibit an intersecting point possessing double the brightness of either beam alone.
To illustrate negative incidence or destructive interference imagine the two beams shown below intersecting at right angles:
-’’-…-’’-…-’’-…-’’-…
-…-’’-…-’’-…-’’-…-’’
As you can see, the trough and peaks of each waveform are precisely aligned. Two laser beams undergoing negative incidence will show a dim spot where the their beam paths intersect.
In order to create micro-bubbles in the crystal or plastic substrate, the laser beams are made to constructively interfere. Each individual laser beam does not possess sufficient power to disrupt the substrate’s structure. Therefore a single beam’s passage through the substrate leaves no mark. Only where the beams intersect is enough power concentrated to alter the substrate’s appearance.
The beams themselves are carefully phase matched using wave plates known as “retarders.” These transparent and optically flat plates are coated with a material of known refractive index. The coating alters the speed of light during its passage through the optical element and thereby corrects the laser beam’s phase with respect to the other coinciding beam. Galvenometrically deflected first surface mirrors are used to scan the beams over a desired area occupied by the substrate. Ordinary mirrors cannot be used in this application. A typical household mirror is silvered on the backside of the glass. A laser beam striking such a mirror diverges into two separate beams thereafter. One beam is caused by primary reflection from the front side of the mirror’s glass itself. A second beam emerges from the reflective interface of the silvered backside of the glass. There is a substantial loss of power and undesirable scattering of the beams from back surface mirrors.
The laser industry relies heavily upon first surface reflectors. Made from submicron aluminized glass shapes, these first surface mirrors reflect the beam directly from their initial face and avoid the negative beam divergence effects of ordinary mirrors. High power applications often use diamond machined solid metal reflectors to withstand the beam’s near melting temperatures. These metal mirrors are often equipped with water cooling journals to perform heat removal from the reflector’s body.
A new method of polymer shape prototyping utilizes this exact same technology. It was developed by a group I knew in Berkeley back in the mid 1970s. Manufacturers often require fast turn models of shapes and bodies used in their product development research. It is extremely useful to fabricate a shape in less than an hour. Even if the final design requires metal construction, being able to determine proper fit and lack of mechanical or dimensional conflict is of extreme importance.
The fabrication bench consists of a tank filled with liquid polymer precursors. An apparatus similar to the laser array mentioned above is shone into the tank. Neither beam is capable of hardening the liquid polymer on its own. Only when the two laser beams intersect in a condition of constructive interference will the polymer actually harden. You literally reach into what was, several minutes ago, a liquid filled tank and pull out a three complex three dimensional shape. The value of this to modern manufacturing cannot be overstated.
There is another interesting nonoptical application for this sort of controlled incidence modulation. A new method of sound canceling relies on the same exact concept of destructive interference. Soon to arrive will be a new generation of acoustically tuned sound canceling automotive mufflers and similar noise suppression devices for leaf blowers and other sound emitting machines.
Doc, I believe that this entire operation is performed in room air. A vacuum chamber would reduce atmospheric scattering but also limit throughput and increase the cost of operation. The lasers involved are sufficiently high powered where a license is needed to own and operate one. We are talking about watts of power and such a beam can blind you instantly. We won’t go into how they tend to ignite most common household materials.
Using more than two lasers would exponentially increase the complexity of the mechanism and decrease its accuracy.
Only the highest cost servo motors have the positional accuracy and repeatability to match galvonometrically deflected mirrors.
To provide optimum safety, protective eyewear must be specifically matched to the output wavelength of the lasers being used.
And here I am just wondering how snowglobes are made – (anyone seen the 1980’s Pixar short film which precedes Saving Nemo?) Heh.
Search google on “3d laser crystal” for lots of hits.
Here’s one company selling the 3D scribing device. It appears to be an infrared pulse laser (the kind with a laser rod and flash tube). They claim 30Hz pulse rate.
http://www.lasermaxmed.com.tw/3d-e.htm
I doubt that more than one beam is necessary. They would be hard to align on one tiny spot, especially if the faces of the transparent block weren’t guaranteed absolutely parallel. On the other hand, if a fairly wide laser beam is brought to a focus with a short focal length lens, there will be an extremely bright, extremely small focal spot. Actually this is a classic physics demo: use an IR pulse laser with a short lens, and during each light pulse there is a “snap” and a tiny bright blue flash in the air at the lens focus.
Some of these websites seem to be talking about optical glass rather than plastic.
http://www.npionline.com/products/thumbnails/tn003000.html
http://65.108.81.194/products/pr003002.444.html
Zenster
Thank you. As soon as you described the mirrors and plates needed to phase match the lasers, I knew that expensive, industrial/lab grade equipment was required. I was holding out the hope that the process could be replicated by the public, but that businesses were counting on the laziness and ignorance of their buyers.
Ah well.
My other laser project should still be workable, a computer controlled laser show for your home ceiling. Cheap keychain lasers will work for this. I still need a mount and motors. Though they don’t need to be nearly as steady or precise. I still need to cobble together a cable from the motors to the pc, and get some friends to write code.
Re Lasers
What happened to make them so cheap? I remember a day in the 80’s when our science teacher showed us something special. The laser was three feet long, five inches wide, and five high. It had cost the school thousands[sub]*[/sub]. A few years later, high end catalogues began selling laser pointers with the same capabilities for a few hundred dollars. Then, came the laser fad of a few years back. The same laser, now the size of a pinkie, could be bought for twenty dollars or less. What breakthrough made this possible?
[sub]*[/sub] It couldn’t burn through anything. The beam grew too difuse to see clearly over more than 15 feet or so. I believe the same model of laser was used in the fine Troma film Nukem High.
DocCathode, what kind of laser was it, e.g., CO[sub]2[/sub], helium-neon? What beam did it produce, e.g., visible, infrared? How powerful was the beam?
Maybe it cost a lot because it was older and they bought it in the very early days of lasers when prices were higher. In 1967 my HS had a low-power helium-neon laser which was about 1’x4"x4". IIRC it was only $100 in the Edmund Scientific catalog. I actually considered buying one with my savings just because I thought it was so cool, but finally decided not to. Adjusting for inflation, that’s about $550 in 2003 dollars. But as you note, the equivalent laser today would cost less than $100.
Doc, more than anything, the solid state laser has driven down the cost of coherent optical emission sources. For gas lasers, automated glass envelope fabrication and high performance epoxies that replace bi-material fused seals have brought reductions in their expense as well. Your school probably had a helium neon gas laser (red beam, right?). They were standard issue up into the 1980s. That laser’s beam was visible for much more than just a few yards. You merely have to see its spot strike a special diffuse surface to notice it. I obtained my first 5 mw HeNe gas laser back in 1978 and discovered LIDAR (laser radar) on my own, just as it was finding military application. I could dazzle automobile tail lights and stop signs that were almost one or two hundred feet away.
There are low cost home laser light shows available on the market. I doubt that you could assemble one for any less. I built a super low cost rig out of motors, dimmer switches, shaft pulleys and some submicron aluminized 2" silicon wafers. However, I had access to a loadlocked longitudinal transport industrial sputter coating system to deposit my first surface mirrors. [big grin] Since I already owned a 20 mW argon and 5 mW HeNe laser, the hardware only ran about $50.00. It will produce three stage lissajoue patterns, but doesn’t respond to audio input. I’ve collected all sorts of optical elements (beam splitters, diffractors, lenses, mounts) and recently snagged a couple of drilled and tapped plates to hang it all on. I also picked up a Stanford Research variable frequency optical chopper that I’m looking forward to playing with.
The biggest breakthrough of all has been the blue laser diode. Its short wavelength makes possible the bit densities required for DVDs and viable bulk data storage. One single Japanese man is largely responsible for its advent. Shuji Nakamura nearly bankrupted himself developing the nitrided III-IV (GaAs) structure needed to reliably generate the blue wavelength. Now, violet solid state lasers are in the works that promise even greater data densities for optical media and fiber transmission. This guy is one of my heros.