Holography & How it Works

Credit cards now have holograms for security purposes.

When you think of holography, you may imagine the ghostly 3D images of people and objects, a staple of science fiction films. However, we see and use holograms every day; they store information and protect our credit cards, among other things. Though holography is a complicated scientific process, even the layman can understand the basic principles of how holography works. In basic terms, holograms record the interference of light waves to reconstruct images of objects in 3D.

History

In 1947, Hugarian physicist Dennis Gabor coined the term holography, from the Greek words "holos" and "graph," which mean whole and writing. Gabor is known as the father of holography, as he made the first hologram while working on electron microscopes. However, it wasn't until 1960 that the laser nearly perfected holography. This is because the laser, unlike other light sources, emits coherent light, meaning the light does not vary in frequency or speed.

What is a Hologram?

According to Christopher Outwater and Eric Van Hamersveld, authors of Practical Holography, a hologram is essentially a film with very high resolution. Unlike a photograph, a hologram is more than a recording of an image--it is a recording of light waves rebounding off the object being filmed and interfering with the light waves of another laser beam. Holograms are not projected images; rather, as Jason Sapan at Holographic Studios in New York defines them, they are reconstructions of light, with the hologram being the "cast" that the light fills during this reconstruction.

How It Works

A hologram captures the whole light field to reconstruct a 3D imagine of the object. It does this using two light beams, the first called the object beam, which is directed straight at the object and the second called the reference beam, which is directed at the object using a mirror. The photographic plate or film, captures the interference of light waves. To reconstruct the hologram, the holographer positions the photographic plate and illuminates it with the laser light in the same way as during the recording process. Now, in place of the object, a hologram appears.

Types of Holograms

Outwater and Van Hamersveld outline several types of holograms. These include the transmission hologram, the plane hologram, the volume hologram and the multiplex hologram; all of these differ from each other in process. However, all holograms fall into one of two categories: virtual or real. With a virtual hologram, the image shows on the other side of the hologram, as if you are looking at it through a window, while a real hologram emerges from the film to appear in front of it.

Holography in Everyday Life

Holograms store information, appear in credit cards for security purposes and adorn the covers of software programs. Head-up displays in aircrafts allows pilots to look at holograms on the windscreen in front of them, so they no longer have to look down at the instrument panels. Holography has also influenced the creation and application of barcode readers in stores and libraries.

References

• Holo: Practical Holography; Christopher Outwater and Eric Van Hamersveld
• Holo: Practical Holography: Chapter 5; Christopher Outwater and Eric Van Hamersveld
• Holo: Practical Holography: Chapters 6-10; Christopher Outwater and Eric Van Hamersveld
• Holographic Studios: FAQ's; Jason Sapan; 2003
• Martin Richardson Holograms & Lenticulars; What are Holograms?; David Gerrard; 2005