Everything you want to know about Holography

-Karthik Gurumurthy

So, holography (pronounced ho-LOG-ra-fee) is this wild process that creates those trippy 3D images we call holograms. Unlike regular photos, holograms let you see all around an object just by moving your head. The word itself comes from Greek – “holo” meaning “whole” and “gram” meaning “picture.”

What’s super cool about holograms is they capture the actual depth of objects. You can literally look behind something in a hologram by moving your head to the side. Of course, if you try to reach out and grab it, your hand just passes through empty air – which is kind of disappointing but also part of the magic!

The whole hologram thing started with this Hungarian scientist Dennis Gabor back in 1947. He was working in England and got frustrated with the crappy images from electron microscopes. These microscopes use electron beams instead of light and can see stuff thousands of times smaller than regular microscopes. Gabor figured he could get better images by taking an “electron picture” first, then using light to focus it better.

But his idea had to wait 14 years before anyone could actually make a real hologram! It turns out you need super pure light of a single exact wavelength, which only lasers can provide. The first working laser wasn’t demonstrated until 1960 by American physicist Theodore Maiman.

The following year, two University of Michigan researchers – American Emmett Leith and Latvian Juris Upatnieks – heard about Gabor’s theory and managed to create the first actual hologram using a laser in 1963. Gabor eventually won the Nobel Prize in 1971 for developing holography theory. Ironically, holography never ended up being used for electron microscopy – the very thing it was invented for!

These days, they’ve figured out how to make color holograms and even master negatives that let them produce copies.

The way holograms are made is pretty fascinating. There are two main types: transmission holograms (the first kind) and reflection holograms (the newer, more practical ones).

For transmission holograms, they split a laser beam in two. One part (the object beam) points at whatever they’re making a hologram of – like a coffee mug. That beam reflects onto a photographic plate. The second part (reference beam) aims directly at the same plate. When these two beams meet, they create an interference pattern on the plate.

After developing the plate (which doesn’t show the coffee mug image but contains this invisible interference pattern), they shine another laser through it at the same angle as the original reference beam but from the opposite direction. This laser light gets scattered by the interference pattern, creating a projected, three-dimensional image of the coffee mug. What you’re seeing is basically a reconstruction of the original light waves as they reflected off the mug, forming an infinite number of 2D pictures seen from different angles.

Reflection holograms work similarly, but the two laser beams hit opposite sides of the photographic plate. The cool thing about reflection holograms is you can view them with regular light instead of lasers, which is why they’re much easier to display.

Holography has become a multi-million dollar industry with tons of applications. You’ve definitely seen holograms as security features on credit cards and in magazine illustrations. Architects use them to create 3D models of buildings, and artists love them for creating eye-catching images.

They’re even developing computer memory devices called holographic storage that could hold way more data than traditional 2D storage like magnetic tape. Doctors use holography to get 3D views of lab specimens, and dentists use it to make 3D records of patients’ teeth – which beats making plaster casts!