A floating face recoils from the impact of a snowball. Pandora’s Box floods open with a shift of the head.
These are just a few examples of holograms that mysteriously hover around the holography lab in the McLennan Physical Labs at U of T.
“I guess you can think of them as homework,” laughs professor Emanuel Istrate, who teaches and coordinates a course called Holography for 3-D Visualization. The course has been running since 2007 with involvement from the Ontario Academy of Design. Every spring, students from both scientific and non-scientific disciplines learn the art and science of holography. Most of them don’t know very much about holography to begin with.
“A hologram is really just a very precise three-dimensional reconstruction of real life,” says Istrate, who did his PhD in electrical engineering at U of T. Holograms work by capturing light from an object as grooves on a special holographic film, in a process that is similar in many ways to film photography.
A hologram owes its illusion of depth to the application of two scientific principles: interference and diffraction.
Diffraction is a term describing the wave-bending that occurs when a wave (whether sound, light, electromagnetic, X-ray or radio) encounters an obstacle. “[It] is the same phenomenon that makes the back of a CD give off all the colours of the rainbow,” explains Istrate. Light that has defracted off the object is combined with a reference beam (a laser used to read and write holograms), and the result is interference. Interference is the addition or interaction of multiple waves to create a new wave pattern. Interference patterns can be recorded on holographic film. When a hologram is read, the reference beam’s characteristics (including its wavelength and beam profile) have to reproduce identical conditions as when the beam was used to write the hologram. The images from a hologram change as the viewer moves position, creating the 3-D effect.
Holography has become a very useful scientific tool, as it has broad applications in the field of medicine. Medical doctors can use it to produce three-dimensional images from CAT scans. Moreover, it is possible to conduct an endoscopy without physically touching internal organs, thus decreasing the potential for damage during the procedure. On the other hand, archeologists use the technique to preserve ancient artifacts. It’s also one of the most accurate ways to make physical measurements. “Mechanical engineers use holography to measure vibrations of surfaces,” says Istrate.
Holograms may also have big potential for storing data. In April 2009, General Electric announced that it had the technology to store 100 DVDs on one disc via holograms. Currently, holographic memory is a still only a laboratory success, but the theoretical limits are in the tens of terabits per cubic centimetre. “The big challenge with holographic data is not how much data you can store, but how to read off it efficiently,” explains Istrate.
Before they became common on currency and stickers, holograms were the buzz among a number of major avant-garde artists, such as Salvador Dalí, who recognized the artistic potential in holography for 3-D visualization.
Istrate adds, “We teach the course in a very nonmathematical way—we don’t throw a bunch of equations at people.” He comments that many students come in during the summer to produce holograms outside of class.
“Make the science applicable to the arts student and the art applicable to the science student,” says Istrate. “We want [students] to think a bit more creatively about how to express themselves.”