Monday – Make a Hologram: Holographic Keypad with FLOATING NUMBERS!

This is a concept that originally we bounced around and played with during the start of Covid. Remember trying NOT TO TOUCH ANYTHING?! But then having to enter your PIN for every credit card transaction, essentially “touching” EVERYONE ELSE who came before you! We thought holographic buttons floating out in front of the pinpad would give the proper visual cues to indicate where you should press, but without actually touching anything.

This is what we came up with, and it’s pretty cool! The numbers float about 1/2″ above the hologram film plate, and when you try to reach out and touch them, it looks like they’re really there (but they’re not). Hologram magic!

Making the Hologram

Technical mumbo-jumbo

This one requires knowing a little “secret” about how holograms work. When you make a hologram, it needs to be illuminated from the same direction and location as the original laser beam that constructed it (the reference beam). But did you know you can also illuminate the hologram from exactly the opposite reverse angle, and also see an image? This is called the phase-conjugate image, and because you flipped the hologram to illuminate it in reverse, the hologram image itself also has a “reverse” image (it’s really more like inside-out) that flips the depth too!

Imagine that a hologram captures a perfect 3D “mold” of an object, but with photons instead of clay or plaster. When you view the hologram you see the wavefront reconstruction of the object (the “mold”) as if the object was still there! Now, if you flip the hologram over and view it with the illumination coming from the reverse direction, the hologram image will look like you are looking at the inside of the mold.

The effect (the phase-conjugate image) is really strange. If you’ve ever been to the Disney Haunted Mansion and remember the statue heads that seems to turn and follow you as you walk around, you are actually looking at an inside-out mold of the statue head (you can buy your own on Etsy!), and it is similarly strange. But one of the effects is that it flips the depth of the image, making things inside the hologram now look like they are out in front of the hologram!

Less technical mumbo-jumbo

If you didn’t get all that, it’s okay! We want holographic floating numbers, and here’s how we actually achieved that!

To get a reversed hologram image (see technical mumbo-jumbo above) that looks like numbers are floating in front of the hologram, we started with a design of some numbers in a keypad design.

We only wanted the numbers and button outlines to show up (like they are glowing in the hologram), so we made the design on a black background with the numbers and button outlines in white. When the laser light hits this as the object for the hologram, the white areas will reflect the laser light and show up in the hologram, while the black areas will disappear.

We took the keypad design and did a vertical mirror image (vertically flipping the image). While this looks a little strange while we are making the hologram, when we flip the hologram over to get the floating image it will look right.

Print out the image, and this will become the object for the hologram. We did several tests with just paper, and it did work but paper is not very stable (it moves a little during the exposure). To keep thinks more stable, we printed the design onto white labels, and then adhered the label to a piece of glass (or any rigid material). This worked really well.

Using the Hologram Kit together with the 4″x5″ Hologram Upgrade Kit, we set up a 4″x5″ reflection hologram. The keypad design (label on glass plate) sat flat on the Plate Holder, with the laser light coming down from the Laser Tower from above at an angle and illuminating the keypad with the numbers and buttons.

We want the numbers and buttons to have some separation (depth) behind the hologram plate, so we used a stack of small glass plates on either side of the keypad design to provide support for the hologram film plate. The hologram film plate sat on top of the supports, with the keypad numbers about 10mm below it.

We checked that the laser light was giving good illumination to the film plate area with a white card, and also checked that the laser light was illuminating the full keypad area (adjust as needed). It is also important to make sure the supports holding the hologram film plate are stable and the film plate will sit flat without any wobble during the exposure.

Then we made the hologram exposure! We took a fresh 4″x5″ hologram film plate out of the box, placed it on the supports, and exposed the laser light onto the film plate and keypad. Using the Upgraded Laser (~20mW) the exposure was about 5-6 minutes.

Floating Hologram Numbers and Buttons!

Viewing the hologram normally, you can see the hologram image of the number keypad floating a distance BEHIND the hologram (as you would expect). But then we flipped the hologram over vertically to see the “reversed” image (phase-conjugate image), now the numbers and buttons are FLOATING IN FRONT of the hologram!

Our keypad looked like the buttons were floating about 1/2″ in front of the hologram. It was so fun to take your finger and “press” the buttons! You put your finger there to press the button, and you keep expecting to hit something, but you don’t. They look like they are really there floating out in front of the hologram!

Where next?

Because the hologram is transparent, you could even take this keypad with the floating numbers and add some electronics (Sparkfun anyone?) or a camera to detect the proximity and location of your finger and make the keypad fully functional. The holographic floating keypad would give the proper visual cues to press the buttons without ever touching anything, and the electronics would register the location.

We had fun brainstorming some fun follow-on ideas:

• Holographic play/pause button that controls your music
• Holographic palm scanner
• Floating button that says “Press Me” and you watch people try to press it

Tell us your ideas below. See more Monday – Make a Hologram posts here. And check out our Hologram Hump Day – Ask a Hologram Expert posts.

– LitiHolo

P.S. – LitiHolo is very close to being back in production after the massive office flood (see details here if you haven’t already). We think we might even start shipments this week! But you can “reserve” your order right now to be at the head of the shipping queue. “Reserve” your Hologram Kit, Hologram Film, and Upgrade Kits, and we’ll contact you for full payment when they’re ready. This helps us stay ahead of the curve and project customer needs as our production ramps back into action (thanks for your help!).