What Is a Beamsplitter Used for? 5 Fast Facts

Everyone has been there. You look up at a rainbow or see a cloud and wonder why it is white. Both of these occur because of the way small droplets of water in the atmosphere interact with rays of light from the sun.

In the case of a rainbow, these water droplets act like a prism, splitting the light into rays of different colors that come off at different angles. This is similar to how an optical beamsplitter works.

But what is a beamsplitter and what can it be used for? Keep reading to learn 5 interesting facts about beamsplitters.

1) History of the Beamsplitter

While prisms have been around for thousands of years because they form naturally in certain crystals, beamsplitters have a more recent history.

Although there may have been similar experiments before this, the first noteworthy one was done by Isaac Newton in 1666.

He showed that when white light hits a prism, it splits into different colors, but if only one color hits a prism, it remains a single color. He gathered from this that white light consists of all the other colors at once.

He then showed that light would split into two beams by putting another prism next to the first one, but he did little else with this result.

It wouldn’t be until the middle of the 19th century that someone would expand on the experiments performed with a beamsplitter.

In 1851, a French physicist named Hippolyte Fizeau used a beamsplitter to make an interferometer in order to measure changes in the speed of light in water.

Beamsplitters and interferometers remain an important part of some of the leading physics experiments performed today. Along with lenses, they are one of the most important devices in optics experiments.

2) How Does a Beamsplitter Work?

Although there are other types, the most common beamsplitters are cube beamsplitters. These are made of two triangular prisms connected together to form a cube.

Normally, a prism splits light into all of its constituent colors, leaving a rainbow of light on the other side. This happens because the different colors of light have slightly different wavelengths.

When light hits an object light a prism, it bends a certain amount depending on the refractive index of the material. Since the refractive index depends on the wavelength of light, different colors bend different amounts.

But what happens when you put another prism where the rainbow of light is coming out of the first one?

The first thing to note is that all of the light that was bent by the first prism gets bent by the same amount but in the opposite direction by the second one.

This means that the different colors of light are recombined into white light. But this isn’t the end of the story. Not all of the light keeps going straight through.

Some of the light reflects at right angles to the other beam. This means there are now two perpendicular beams of light.

3) Beamsplitters in Interferometers

In 2017, the Nobel Prize in physics was awarded to three people for their work on the discovery of gravitational waves.

These are ripples in the fabric of spacetime that represent the last missing piece in Albert Einstein’s general theory of relativity. However, he thought they were so small that they could never be measured.

This is where the beamsplitter comes in. Without it, we never could have measured gravitational waves. But a collaboration called LIGO, which stands for Laser Interferometer Gravitational-wave Observatory did in 2015.

Although the details of the experiment are complicated, the basic idea is simple. Imagine you use a beamsplitter to break up a beam of light into two beams.

Then, you let these beams travel perpendicular to each other for some distance and put a mirror at the end to reflect them.

If the mirrors are the same distance from the source, when the two beams get back to you, they should have traveled the same distance, right? Well, only if there isn’t a gravitational wave in the way.

The gravitational wave changes the length in one of the directions by a distance smaller than the size of an atom but enough to measure.

4) More Common Applications

Even though the discovery of gravitational waves rocked the physics world, there are some applications of beamsplitters that feel a little closer to home.

Doctors can use beamsplitters when performing laser skin treatments. These can be important whenever they need more than one beam or only part of a laser beam to hit the skin.

When people use lasers to mark metals or glass in processes like engraving or ablation, they sometimes use beamsplitters to make the process more efficient.

Printers and artists can use beamsplitters in the process of lithography. In this method, a laser hits a surface and changes it in a way such that ink no longer stays in the areas where the laser hit.

When manufacturers make things like coffee filters or food packaging, they can use a laser with a beamsplitter to create perforations in the material.

Beamsplitters can also help to create a 3D image of an object or area by using many different laser beams.

Whether you work in a doctor’s office, a manufacturing plant, or a research lab, you can check out PFG optics for all of your beamsplitter needs.

5) Beamsplitters in Quantum Computing

Quantum computing is the newest innovation in the computing world. Although these computers aren’t commercially available yet, they do exist and have the potential to vastly improve the speed and security of computers.

Quantum computers rely on the ideas that a single photon, or unit of light, can be in more than one state at the same time and that two of these photons can be entangled.

In 2000, a team of researchers proved that it was possible to build a quantum computing system consisting mainly of beamsplitters.

Although it needs other optical devices to work, the beamsplitters are responsible for the entanglement of two or more photons.

It is this entanglement that allows the logic gates that are familiar from classical computing but with quantum bits (qubits) instead of normal bits.

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