Holograms: The Art Of Recording Wavefronts

December 3, 2024 by Maya Posch 22 Comments

The difference between holography and photography can be summarized perhaps most succinctly as the difference between recording the effect photons have on a surface, versus recording the wavefront which is responsible for allowing photographs to be created in the first place. Since the whole idea of ‘visible light’ pertains to a small fragment of the electromagnetic (EM) spectrum, and thus what we are perceiving with our eyes is simply the result of this EM radiation interacting with objects in the scene and interfering with each other, it logically follows that if we can freeze this EM pattern (i.e. the wavefront) in time, we can then repeat this particular pattern ad infinitum.

Close-up of the wavefront pattern recorded on the holographic film (Credit: 3Blue1Brown, YouTube)

In a recent video by [3Blue1Brown], this process of recording the wavefront with holography is examined in detail, accompanied by the usual delightful visualizations that accompany the videos on [3Blue1Brown]’s channel. The type of hologram that is created in the video is the simplest type, called a transmission hologram, as it requires a laser light to illuminate the holographic film from behind to recreate the scene. This contrasts with a white light reflection hologram, which can be observed with regular daylight illumination from the front, and which is the type that people are probably most familiar with.

The main challenge is, perhaps unsurprisingly, how to record the wavefront. This is where the laser used with recording comes into play, as it forms the reference wave with which the waves originating from the scene interact, which allows for the holographic film to record the latter. The full recording setup also has to compensate for polarization issues, and the exposure time is measured in minutes, so it is very sensitive to any changes. This is very much like early photography, where monochromatic film took minutes to expose. The physics here are significant more complex, of course, which the video tries to gently guide the viewer through.

Also demonstrated in the video is how each part of the exposed holographic film contains enough of the wavefront that cutting out a section of it still shows the entire scene, which when you think of how wavefronts work is quite intuitive. Although we’re still not quite in the ‘portable color holocamera’ phase of holography today, it’s quite possible that holography and hologram-based displays will become the standard in the future.

Continue reading “Holograms: The Art Of Recording Wavefronts” →

Out With The Circus Animals, In With The Holograms

September 11, 2023 by Maya Posch 25 Comments

As futuristic as holographic technology may sound, in a sense it’s actually already in widespread commercial use. Concerts and similar events already use volumetric projection, with a fine mesh (hologram mesh or gauze) acting as the medium on which the image is projected to give the illusion of a 3D image. The widespread availability of this technology has now enabled Germany’s Roncalli circus to reintroduce (virtual) animals to its shows after ceasing the use of live lions and elephants in 1991 and other animals in 2018.

For the sticklers among us, these are of course not true holograms, as they do not use a recorded wavefront, nor do they seek to recreate a wavefront. Rather they employ as mentioned volumetric projection to essentially project in ‘thin air’, giving the illusion of a tangible object being present. By simultaneously projecting multiple views, to an observer standing outside the projection mesh, it would thus appear that there is a physical, three-dimensional object which can be observed. In the case of the Roncalli circus there are 11 projectors lining the circumference of the mesh.

To a circus the benefits of this approach are of course manifold, as not only do they no longer have to carry lots of animals around every time the circus moves to a new location – along with the on-site demands – but they get to experiment with new shows and new visuals that were never before possible. Ironically, this could mean that after 3D fizzled out at movie theaters, circuses and similar venues may be in a position to make it commonplace again for the masses.

Holograms: The Future Of Speedy Nanoscale 3D Printing?

April 9, 2023 by Dave Rowntree 7 Comments

3D printing by painting with light beams on a vat of liquid plastic was once the stuff of science fiction, but now is very much science-fact. More than that, it’s consumer-level technology that we’re almost at the point of being blasé about. Scientists and engineers the world over have been quietly beavering away in their labs on the new hotness, nanoscale 3D printing with varying success. Recently IEESpectrum reports some promising work using holographic imaging to generate nanoscale structures at record speed.

Current stereolithography printers make use of UV laser scanned over the bottom of a vat of UV-sensitive liquid photopolymer resin, which is chemically tweaked to make it sensitive to the UV frequency photons. This is all fine, but as we know, this method is slow and can be of limited resolution, and has been largely superseded by LCD technology. Recent research has focussed on two-photon lithography, which uses a resin that is largely transparent to the wavelength of light concerned, but critically, can be polymerized with enough energy density (i.e. the method requires multiple photons to be simultaneously absorbed.) This is achieved by using pulsed-mode lasers to focus to a very tight point, giving the required huge energy density. This tight focus, plus the ability to pass the beam through the vat of liquid allows much tighter image resolution. But it is slow, painfully slow.

Continue reading “Holograms: The Future Of Speedy Nanoscale 3D Printing?” →

HOPE XII: Make Your Own Holograms

July 23, 2018 by Mike Szczys 28 Comments

Prior to this weekend I had assumed making holograms to be beyond the average hacker’s reach, either in skill or treasure. I was proven wrong by a Club-Mate box full of electronics, and an acrylic jig perched atop an automotive inner tube. At the Hope Conference, Tommy Johnson was sharing his hacker holography in a workshop that let a few lucky attendees make their own holograms on site!

The technique used here depends on interference patterns rather than beam splitting. A diffused laser beam is projected through holographic film onto the subject of the hologram — say a bouquet of flowers like in the video below. Photons from that beam reflect from the bouquet and pass back through the film a second time. Since light is a form of electromagnetic radiation that travels as a wave, anywhere that two peaks (one from the beam the other from the reflected light) align on the film, exposure occurs. With just a 1/2 second exposure the film is ready to be developed, and if everything went right you have created a hologram.

Simple, right? In theory, at least. In practice Tommy’s been doing this for nearly 30 years and has picked up numerous tips along the way. Let’s take a look at the hardware he brought for the workshop.

Continue reading “HOPE XII: Make Your Own Holograms” →

Retrotechtacular: Shedding Light On Holograms

March 11, 2014 by Kristina Panos 10 Comments

This week’s Retrotechtacular is a 1972 introduction to holography produced by the fine folks at Encyclopædia Britannica. It details quite admirably what holograms are and how they’re made.

Holograms are quite different from photographs, though both are recorded on film. Holography is based on the additive effects of waves: two crests of equal amplitude create a larger crest, while a crest and a trough of equal amplitude cancel each other out, causing an interference effect. The video demonstrates the concept nicely with water ripples and explains that the same effect happens with sound waves and light waves.

Lasers are the key to the intense and spectrally pure light required for holography. Incandescent light consists of too many wavelengths to be effectively split into two identical light wave sources. To create a hologram, a laser is split with an optical device into two beams. One beam is focused directly on the object being recorded and is called the object beam. The second beam is directed away from the scene through a series of mirrors and shone directly onto a film emulsion.

The film records the interference between the waves of the two beams. It appears to be blank after development, but upon close inspection reveals stripes of light and dark. When the exposed film is placed in the path of only the reference beam, the interference patterns recorded on the film split the beam back into two, recreating the scene. With the aid of a screen for projection, the hologram can be seen showing the original object in 2D. Another big difference between photographs and holograms is that even a small portion of a hologram can reproduce the entire scene, but a piece of a photograph is just that.

Continue reading “Retrotechtacular: Shedding Light On Holograms” →

Pepper’s Ghost – Halloween Ghosting

October 6, 2013 by James Hobson 17 Comments

Peppers Ghost is a classic technique for making ghosts appear in pictures, video, and even in front of live audiences. In this week’s Halloween themed Instructable, learn how to recreate the effect at home.

It’s really quite simple. By positioning a clear piece of lexan at a 45 degree angle to your “ghost” object, and having the audience (or camera) looking at the lexan at the opposite 45 degree angle, you can produce a very simple ghost effect. This is a great trick for producing some scary ghosts in your haunted house.

But wait. Isn’t this a bit too simple? This is Hack a Day isn’t it? How about making a real moving hologram, isn’t that a bit more of our speed?

Well, this is the exact same technique that is used to make real holograms — just replace that object with a projected image or video! We’ve covered it a couple of times before, explaining the Tupac hologram, and showing off a cool leap motion controlled globe hologram.

Our challenge to you is to make a moving hologram Halloween decoration. After all, you can get pico projectors for less than $100 these days, so why not give it a try? There’s a few more ideas and techniques for positioning the lexan in the video after the break.

Continue reading “Pepper’s Ghost – Halloween Ghosting” →