WHAT if you could capture light in a box? Lasers work on that very principle. Light is a wave and any colour is described by a particular wavelength. To trap light in a box, mirrors are used, with the dimensions specially chosen so that the light can reflect off the mirrors and “resonate” at its own wavelength.

Just like a musical instrument, these resonant waves reinforce each other. For a musical instrument, these reinforced waves come out as a sound wave making a note at a particular frequency, which is related to the wavelength.

In the case of a laser, light is trapped at a high intensity, again at a singular frequency related to the wavelength of the light. Some of the light is allowed to burst out of the container, seen as a laser beam.

The most quotidian use of a laser is in small laser pointers, largely marketed as cat toys. But these are a tiny portion of the global consumption of lasers, which has continued to grow consistently for 60 years, doubling every 5-10 years.

Lasers are now used ubiquitously in control systems, largely thanks to the same wave feature that makes the trapping of light in the “box” so effective.

The wavelength of light can be used to measure lengths itself. As light bounces off the surfaces it interacts with with back to its source — a sensor that has an integrated laser — it comes back having travelled a distance equal to a certain number of its own wavelengths.

A very tiny change in the path it has travelled means fractionally more or less of the wavelength cycle is completed, and so minuscule distances can be measured.

These measurements are incredibly precise — the distances can be far smaller than the light’s own wavelength — and lasers are crucial to achieving this precision.

Regular sensing techniques such as imaging works by simply taking in light from the environment, and building up an image from that direct input.

This simple process can’t be used to measure distances, because it doesn’t register where in the wavelength cycle the returning light is. In order to do that, the returning light has to be compared to the light that was sent out in the first place.

But how to compare the returning and outgoing light? This is where lasers come in. The light in a laser beam is very pure and stable, as well as being highly concentrated. By splitting a beam in two, one part can be used as a reference to compare with the other part.

This technique of using the reference beam was what Dennis Gabor, a Hungarian-British physicist who had fled Nazi persecution, used to invent the hologram.

In a hologram, these reference waves are compared to the field of light that has reflected back from a whole three-dimensional scene. The reference beam means that the state of the waves from the scene is more fully recorded, not just in 2D, but to make a 3D image.

Gabor first conceived of the idea of a hologram for the case of electron microscopes, which use the wave properties of electrons. When lasers were invented 13 years later in 1960, they were the perfect source to make optical holograms.

Though holograms have been used since the invention of lasers, the technique of using a reference beam is still one that is being developed in new scientific applications, for instance in optical microscopes in which tiny features can be tracked as they move in three dimensions, such as in living cells.

The biggest laser in Britain is the Vulcan laser. In 2005 it was the highest intensity laser in the world, delivering a petawatt (1 PW) of power in a short pulse. For that fraction of a second, it delivers about a hundred times more power than Drax, the largest British power station, onto a small spot of space.

British taxpayers are currently paying for an £85 million upgrade to increase its power twenty-fold. The Science and Technology Facilities Council who run the laser claim it is then expected to be the “most powerful laser in the world.”

When the refurbished Vulcan laser runs a pulse, 20 PW will be delivered to a small area in one go. As a comparison, the peak energy consumption for the whole of Europe is between 2-3 PW. This will be used to simulate astrophysical explosions and better understand the universe.

The smallest lasers look very different to the mighty Vulcan. They consist of little discs and spheres of lasing material, the boundaries of which trap light, making it bounce around inside the lasing material.

These particles are on a nanometre or microscopic scale, and can therefore be put into other materials – including living things. This can create focused light in one particular place eg for therapeutic light treatments.

But they can also be used to measure the materials that surround them on a tiny scale. The particles are very small and sensitive to their environment — so the light signature that they produce tells us about the materials they are in contact with.

Lasers were vital to the use of CD players, reading off the information encoded in the bumps on a disc. Modulating the flow of light to encode information is nothing new — just think of a semaphore flashlamp.

However, the capacity and ambition of laser information transfer continues to expand ever further. The spacecraft Psyche was launched in 2023 by Nasa and the Jet Propulsion Laboratory (JPL). It is on its way (it should arrive in 2029) to orbit an asteroid which is at least 2.5 times further away from Earth than the sun.

The spacecraft has already got further out than Mars. It’s being used as a test case to demonstrate lasers as space communication tools.

Videos and pictures (of pets, naturally) have been exchanged with the spacecraft 290 million miles away to demonstrate the features of laser communication at such a great distance.

It is said that at this distance, they achieved “similar to broadband internet download speeds.”

Lasers turn out to have been one of the most important discoveries ever made. Trapping light in a box has opened a box of technological marvels.