Holography facts for kids

For other uses, see Holography (disambiguation).

Two photographs of a single hologram taken from different viewpoints, showing how the image changes with your view.

Imagine seeing a picture that looks so real, you feel like you could reach out and touch it! That's what holography is all about. It's a special way to record and show 3D images. This amazing technique captures light waves and can recreate them later. Holography is used for many things, like storing information, looking at tiny objects, and even measuring very small changes.

A hologram is the actual recording of a special light pattern. This pattern can make a 3D image using something called diffraction. Think of diffraction as light bending around tiny obstacles. Holograms can be made from real scenes or created by computers. To record a hologram from a real scene, you need a special kind of light called a laser. The image you see from a hologram looks deep and changes as you move, just like looking at a real object.

When you look at a hologram under normal light, it often just looks like a blurry, random pattern. But when you shine the right kind of light on it, the pattern bends the light in a way that perfectly recreates the original scene. This makes the objects in the hologram appear to have real depth. You can see different parts of the image by looking from different angles, just as if the real object were there.

A traditional hologram is made by mixing two light waves. One wave comes from the object you want to record. The other is a "reference beam." When these two waves meet, they create an interference pattern. This pattern is then captured on a special material. Later, when you shine the reference beam back onto this recorded pattern, it brings the original 3D image back to life.

Computer-generated holograms are made by digital models. Computers combine two virtual light waves to create an interference pattern. This pattern can then be printed or shown on a special screen. When lit correctly, it reconstructs the desired 3D image.

Making holograms of moving people used to be very hard. It required powerful, dangerous lasers to "freeze" movement. But today, much smaller and cheaper laser diodes are available. These are like the lasers found in DVD players. This has made holography much easier for students, artists, and hobbyists to explore. Most holograms show still objects, but scientists are working on displays that can show moving 3D scenes.

The word holography comes from two Greek words. Holos means "whole," and graphē means "writing" or "drawing." So, it means "writing the whole picture."

Discovering Holography

The Hungarian-British scientist Dennis Gabor invented holography in 1948. He was trying to make electron microscopes see even smaller details. Gabor's idea was based on earlier work by other scientists. His invention was a surprise result of his research. He even filed a patent for it in 1947. This technique is still used in electron microscopy today. Gabor won the Nobel Prize in Physics in 1971 for his amazing discovery.

Horizontal symmetric text, by Dieter Jung, showing how art can use holography.

Holography didn't really take off until the laser was invented in 1960. Lasers provided the perfect light needed to make clear holograms. In 1962, Yuri Denisyuk in the Soviet Union and Emmett Leith and Juris Upatnieks in the US made the first practical holograms of 3D objects.

Early holograms used special photographic films. These films weren't very good at letting light through. Scientists then found ways to make them more efficient.

A big step forward came from Stephen Benton. He invented a way to make holograms that you could see with normal light, not just lasers. These are called rainbow holograms.

How Holograms Work

Recording a hologram: Light from a laser is split. One part lights the object, the other is a reference beam. They meet on the recording medium.

Reconstructing a hologram: The reference beam shines on the recorded pattern, bringing the 3D image to life.

This is a tiny part of a hologram seen through a microscope. It looks like a random pattern, but it holds all the information for the 3D image.

Holography is a way to record and recreate light waves. Think of it like recording sound. When you record music, you capture the vibrations that make the sound. Later, you can play it back. Holography does something similar with light. It captures all the light coming from an object, so you can see it again later, even if the object isn't there.

Using Lasers to Record

To make a laser hologram, you need a laser light source. This light is very pure and organized. There are different ways to set up the equipment, but they all involve light coming from different directions. This light creates a tiny, detailed pattern. A special film or plate then records this pattern.

In a common setup, a laser beam is split into two parts. One part is called the 'object beam'. It's spread out with a lens and shines on the object you want to record. The light then bounces off the object and travels to the recording material. The other part is called the 'reference beam'. It's also spread out and shines directly onto the recording material.

The recording material needs to be exposed to light for the right amount of time. This is like taking a photograph. But for holography, everything must be perfectly still during the exposure. Even a tiny movement, smaller than the width of a human hair, can blur the pattern and ruin the hologram. This is why making holograms of living things is so difficult. Usually, a continuously operating laser is used, and exposures can last from seconds to minutes.

The Holography Setup

To make a hologram, a laser beam is first sent through a beam splitter. This device divides the beam into two identical beams:

The first beam, the 'object beam', is spread out using lenses. It's then directed by mirrors to shine on the scene or object. Some of the light that bounces off the scene then hits the recording material.
The second beam, the 'reference beam', is also spread out by lenses. But this beam goes directly to the recording material, without touching the scene.

The recording material is often a film similar to photographic film. However, it has much smaller light-sensitive particles. This allows it to capture the incredibly fine details that holograms need. This special film is usually on a clear base, like glass or plastic.

The Recording Process

When the two laser beams meet on the recording material, their light waves cross and create an interference pattern. This pattern is what gets printed onto the material. The pattern looks random and doesn't resemble the object at all. It's like a secret code for the scene. To unlock this code, you need a special "key"—the original reference beam.

Later, when you shine a laser (just like the one used to record) onto the developed film, it acts as the key. The light bends as it passes through the hologram's surface pattern. This bending recreates the exact light waves that originally came from the scene. So, it looks like the object is still there, even if it has been removed!

Holography vs. Photography

Let's look at how holography is different from regular photography:

A hologram captures light from many directions, not just one. This means you can see the scene from different angles, just like it's really there. A photograph only shows one flat view.
You need a laser to record a hologram. Photographs can be taken with any light, like sunlight.
Photography uses a lens to focus the image. Holography scatters light directly onto the recording material without a lens.
Holography needs a second light beam (the reference beam) during recording. Photography does not.
Photographs can be viewed in almost any light. Holograms need specific lighting to be seen properly.
If you cut a photograph in half, you only see half the scene. If you cut a hologram in half, you can still see the whole scene in each piece! This is because every part of a hologram holds information about the entire object. It's like looking at a street through a big window, then through a smaller one. You can still see everything through the small window by moving your head.
A photograph shows a clear image of the scene. A developed hologram's surface looks like a random, sparkly pattern. You can't tell what the scene is just by looking at the hologram itself.

Cool Uses for Holography

Holography in Art

Artists quickly saw the potential of holography. They started working with scientists to create amazing holographic artworks. Many holographic artists are also scientists!

Salvador Dalí, a famous surrealist artist, was one of the first to use holography in art. Other early holographic art shows happened in Michigan in 1968 and New York in 1970. In Britain, Margaret Benyon began making holographic art in the late 1960s.

During the 1970s, many art studios and schools focused on holography. Today, places like the Center for the Holographic Arts in New York still offer artists a place to create and show holographic work. Artists like Harriet Casdin-Silver, Dieter Jung, and Moysés Baumstein explored new ways to use this 3D medium. They wanted to do more than just make holographic copies of sculptures.

A small group of artists still use holographic elements in their work today. The MIT Museum has a large collection of art holograms.

Storing Information with Holograms

Holographic data storage is a way to store huge amounts of information inside special crystals or plastics. This is very important because many electronic devices need to store lots of data. Current storage methods, like Blu-ray Discs, are reaching their limits. Holographic storage could be the next big thing. The cool part is that it uses the entire volume of the material to store data, not just the surface.

In 2005, companies like Optware and Maxell created a 120 mm disc. This disc used a holographic layer to potentially store 3.9 TB of data. This format was called Holographic Versatile Disc. However, these products did not become widely available commercially. Another company, InPhase Technologies, also worked on a similar format but stopped operations in 2011.

Scientists are also researching "microholograms." These tiny holograms could lead to new 3D optical data storage solutions. While they might not store data as fast as other holographic methods, they are much easier and cheaper to make.

Holograms That Change

Most holograms are permanent. But there are special holographic materials that can record a hologram very quickly. They don't even need a developing process. These "dynamic holograms" can be used for things like "time-reversal" of light. This means they can fix light beams that have been distorted. They can also be used for image processing and even optical computing.

These systems can process a lot of information very fast. Scientists are always looking for new materials to make these dynamic holograms even better.

Holography for Hobbies

Peace Within Reach, a Denisyuk DCG hologram made by amateur Dave Battin.

Since holography began, many people have enjoyed making their own holograms.

In 1971, Lloyd Cross opened the San Francisco School of Holography. He taught people how to make holograms using small, inexpensive lasers and homemade equipment. People used to think you needed very expensive, heavy tables to keep everything still. But Cross showed that a simple sandbox on old tires could work! Mirrors and lenses were stuck into the sand to direct the laser light.

In 1979, Jason Sapan opened Holographic Studios in New York City. His studio has made many holograms for artists and companies. Sapan is known as a leading professional holographer in New York.

In 1983, Fred Unterseher, a co-founder of Cross's school, published the Holography Handbook. This book made it even easier for hobbyists to make holograms at home.

A big change came in 2000 when Frank DeFreitas published the Shoebox Holography Book. He showed how to use inexpensive laser pointers to make holograms. For a long time, people thought these lasers wouldn't work. But it turned out some laser pointers were perfect for holography! This was great news for amateurs, as laser pointers became very cheap. Now, thousands of amateur holographers exist worldwide.

By 2005, holography kits with laser pointers became popular gifts. In 2003, kits with self-developing plates arrived. This meant hobbyists could make holograms without messy chemicals.

Around 2006, special green lasers became available. This allowed amateurs to experiment with a material called dichromated gelatin (DCG). Scientists were surprised at how well DCG reacted to green light.

Today, major suppliers of holographic film, like Kodak and Agfa, are no longer in the market. But other companies have stepped in. Many amateurs even make their own holographic materials. Some dedicated hobbyists are even building their own powerful pulsed lasers. These allow them to make holograms of living subjects or moving objects.

Measuring Tiny Changes

Holographic interferometry (HI) is a technique that can measure very small movements or changes in objects. It can detect changes smaller than the wavelength of light! This is useful for seeing how engineering structures bend or vibrate. It can also show how fluids flow or help with radiation measurements.

Super Microscopes

Interferometric microscopy uses holograms to get more information about light. By analyzing several holograms, scientists can make microscopes see much finer details. This technique helps improve the resolution of optical microscopy, allowing us to see tiny things even more clearly.

Holographic Sensors

Holograms can also be used as sensors. These are made with special materials that change when they interact with certain molecules. This change can alter the hologram's color, showing that a specific substance is present.

Security Holograms

An Identigram hologram used as a security feature on a German identity card.

A dove hologram used on some credit cards to prevent fakes.

Holograms are often used for security because they are very hard to copy. Making a master hologram requires expensive and advanced equipment. This makes them difficult for counterfeiters to fake. You can find holograms on many important items:

Many currencies, like the Brazilian, British, South Korean, Japanese, Indian, Canadian, Croatian, Danish, and Euro banknotes.
Credit cards and bank cards.
Passports and ID cards.
Books, food packaging, DVDs, and sports equipment.

These holograms help protect identities and show if an item is genuine or fake.

Holographic scanners are also used in places like post offices. They can measure the 3D size of a package. This helps with automated packing and shipping. Holograms made in stretchy materials can even act as stress sensors. They change color based on pressure or force.

High-Security License Plates

High-security holograms are used on license plates for cars and motorcycles. As of April 2019, holographic license plates were required on vehicles in parts of India. They help with identification and security, especially to prevent car theft. These plates can hold electronic data about vehicles and have unique ID numbers to prove they are real.

Holography with Other Waves

Holography isn't just for light waves! In theory, you can make a hologram for any kind of wave.

Electron holography uses electron waves instead of light waves. Dennis Gabor invented it to make electron microscopes better. Today, it helps scientists study electric and magnetic fields in very thin materials.

Acoustic holography creates "sound maps" of objects. It measures sound waves around an object and then uses computers to create images.

Atomic holography uses beams of atoms. While not yet commercial, scientists are developing ways to create holograms with atoms.

Neutron beam holography has been used to look inside solid objects.

X-ray holograms are made using powerful X-ray sources and special detectors. Because X-rays have much shorter wavelengths than visible light, they can create images with higher detail. X-ray holography can even capture very fast changes, like those happening in femtoseconds (a quadrillionth of a second!).

What Are NOT Holograms?

A Pepper's ghost illusion made from a clear plastic pyramid. This is often mistaken for a hologram.

Many cool visual effects are often mistakenly called "holograms." These are sometimes called "fauxlography" (fake holography).

One common illusion is Pepper's ghost. This technique uses a clear sheet of glass or plastic to reflect an image. The reflection appears to float in mid-air. In theaters, it used to reflect real objects or people. Modern versions use digital screens to project images. While these images can look 3D, the reflection itself is still flat. So, it's not as realistic as a true hologram.

Famous examples of this digital Pepper's ghost illusion include:

The Gorillaz performances at the 2005 MTV Europe Music Awards and the 48th Grammy Awards.
Tupac Shakur's virtual performance at the Coachella Valley Music and Arts Festival in 2012, where he rapped alongside Snoop Dogg.
Digital avatars of the Swedish supergroup ABBA were displayed on stage in May 2022.
American rock group Kiss unveiled similar digital avatars in December 2023 to tour in their place.

Another simple illusion uses rear-projection onto semi-transparent screens. This makes images appear to float. For example, Crypton Future Media has produced concerts where Hatsune Miku and other virtual singers perform on stage using this "holographic" effect.

In 2011, the apparel company Burberry had a fashion show in Beijing. It featured life-size 2D projections of models. Many news reports called these "holograms," but they were simply flat projections.

On April 10, 2015, in Madrid, a public display called "Hologramas por la Libertad" (Holograms for Liberty) showed a ghostly crowd of virtual demonstrators. This was a protest against a new law. Although called a "hologram protest," it was another version of the Pepper's ghost illusion.

It's important to remember that true holography uses interference and diffraction to create 3D light fields. These illusions do not.

Holography in Fiction

Holography has been a popular idea in movies, books, and TV shows, especially in science fiction. Often, these fictional holograms are shown as fully three-dimensional computer projections. Sometimes, they even seem solid, thanks to force fields. These unrealistic depictions have given people very high expectations for what holography can do.

Some famous examples of fictional holograms include:

The hologram of Princess Leia in Star Wars.
Arnold Rimmer from Red Dwarf, who later became a "hard light" hologram.
The Holodeck and Emergency Medical Hologram from Star Trek.

Holography has also inspired many video games. In games like Command & Conquer: Red Alert 2, "mirage tanks" can disguise themselves as trees. In Halo: Reach and Crysis 2, players can use holographic decoys to trick enemies. The character Nova in Heroes of the Storm also uses "holo decoys."

Even though fictional holograms are often far from reality, they have inspired new technologies. For example, augmented reality aims to create similar immersive experiences, even if it uses different methods than true holography.