What is an Interferometer?

Jeri Sullivan

An interferometer is an instrument used to measure waves through interference patterns. Interferometry is the process by which two waves are combined so they can be studied for differences in their patterns. The fields of study where interferometry is used are astronomy, physics, optics, and oceanography.

Interferometers are used to study gravitational waves from supernovas and other stars.
Interferometers are used to study gravitational waves from supernovas and other stars.

In astronomy, interferometers are actually two or more telescopes and mirrors working together to provide high resolution of images of objects in space. The telescopes are generally located thousands of miles apart. The process works by spacing the mirrored lenses of the telescope at planned intervals. The light from outside the Earth's atmosphere bounces off the lenses as in a reflecting telescope and is combined into an interferometer as radio waves. The radio waves are then measured to produce a high resolution image.

Typically, interferometers are two or more telescopes and mirrors working together while located thousands of miles apart.
Typically, interferometers are two or more telescopes and mirrors working together while located thousands of miles apart.

A special observatory known as the Laser Interferometer Gravitational-Wave Observatory (LIGO) is devoted solely to detecting gravitational waves. This observatory uses its research to detect astronomical events such as gamma-ray bursts and possible collisions to Earth. Gravitational waves from supernovas, black holes, and neutron stars are observed and measured for research and understanding of how and when they formed.

In physics and optical interferometry, as well as astronomy, the Michelson interferometer is used to detect gravitational waves and to generate an optical differential-phase shift keying (DPSK) demodulator. A DPSK converts the phase-coded signal into an intensity-coded signal. This allows the signal to be amplified and increases both the quality and the amount of data that can be transmitted.

The Michelson interferometer works by having two mirrors set at a 90 degree angle. A third, partially-silvered mirror is set between them at a 45 degree angle. As light moves through the partially silvered mirror, it splits the beam of light and each beam takes a different path. This interference due to separate wavelengths is converted to a wavelength path which is detected by the interferometer. The signal is amplified as it comes back together, which increases the quality of the transmission.

Interferometric data is used in oceanography to determine the state of oceanic activity. The interferometer detects wavelengths using an algorithm known as parametric retrieval algorithm (PRA). PRA is able to use information gathered from Along-Track Interferometric Synthetic Aperture Radar (AT-InSAR) with wind data and converts it to information useful for weather centers. Information such as the height of waves, length of waves, and wave directions is helpful in determining weather patterns and possible ocean floor activities.

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Discussion Comments


@everetra - I don’t know that you have to look for symmetry or order in these patterns.

If scientists are looking for gamma bursts, for example, I hardly think that they’re going to find nice, orderly patterns. They’re not looking for intelligence. They’re looking for wave fluctuations that are out of the ordinary.

As long as they have a baseline for comparison, they should be able to answer that question easily.

If an earthquake triggers a tsunami, for example, oceanographic scientists can quickly determine that something potentially catastrophic is taking place based on huge spikes in the wave patterns.


@Charred - That’s a good point – and it raises the larger issue, what is a meaningful pattern? In my opinion, anything that shows symmetry would be meaningful and worthy of investigation.


@hamje32 - For a scientist to draw any reasonable conclusions about the final patterns, I would guess that these would have to be pretty unique signatures.

What I mean is that radio is infamous for “noise,” a lot of static that probably would appear as jerky, random spikes on a waveform monitor. I think that the scientist would have the responsibility of looking at the phase shifts returned from these radio waves and determining what is meaningful and what is not.

If you want a comparison, consider the folks at SETI – the organization that searches for signals of extraterrestrial life in outer space. They have to filter through a lot of noise to find something that is meaningful.


In college I remember the professor discussing the question, “Is light a particle or a wave?” The reason that he brought it up is that light behaves as both, and supposedly these two phenomena are contradictory. I guess the interferometer exploits the wave like quality of light, to convert it to radio waves that can be studied.

I think that meshing together the two resulting radio waves should produce some interesting patterns. I wonder if, depending on the routes that the two lights travel before they’re recombined as waves, they produce patterns similar to what we would find in nature or mathematics, like fractals. I don’t know, but it would be interesting to see what the final composites would look like.

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