Laser Based Gyroscope: How do they Measure the Earth’s Rotation?

Gyroscopes are among the coolest devices ever invented. Not only are they very useful for a lot of applications, but they are also interesting to watch in action, especially if you’re not a science person – watching a gyroscope spin while keeping its position almost feels like magic. In case the name doesn’t ring any bells to you, a gyroscope that consists of a spinning element fixed inside some rings, which will maintain its position against horizontal and vertical axes as long as it is spinning. It is used in numerous fields as a stabilization and guidance mechanism, but recent advancements are about to expand its use. Researchers are currently working on a more advanced version of the classical gyroscope, based on lasers, and intend to use it to accurately measure the Earth’s rotation. To understand the importance of this, though, it’s important to get a bit familiar with the science behind gyroscopes.

Introduction to Gyroscopes

Gyroscopes are fairly simple devices, once you understand how they work. They consist of a centerpiece, usually, a wheel, fixed inside one of two rings, each of them on a different axis. Due to the rotational equivalent of Newton’s Third Law of motion, the forces applies to the exterior rings will generate opposing forces, but will apply to those rings only, and will not interact with the centerpiece as long as it is spinning. The centerpiece will preserve its motion and position, essentially being a solid indicator of position despite the state of the outside factors. This ability is very valuable and is a key feature used by guidance and localization systems, especially in environments where other simpler localization systems such as compasses cannot work, such as in space, or deep underwater.

Laser Gyroscopes

There are multiple types of gyroscopes, each having a somewhat different operating principle, but the end result is always the same. One particularly interesting type is the laser gyroscope, which uses a laser light that’s split into two beams and go through a system of mirrors before returning to a receptor. In an idle state, the beams take an equal time to return to the receptor, but if the setup rotates one way or another, there will be a discrepancy between the times it takes each beam to make it to the receptor. Using some calculations, the exact rotation speed and angles can be determined.

Experimenting with Laser Gyroscopes

One of the most interesting initiatives to date in this field is the research program started by some scientists at the Italian National Institute for Nuclear Physics, which intend to use ring laser gyroscopes to accurately measure the Earth’s rotation. While measuring the Earth’s rotation is already something scientists have been able to do for a while now, it was mostly done by calculating the position of the Earth in relation to numerous other astronomical bodies such as other stars or planets – a process that’s both difficult and costly to achieve. By being able to develop a laser-based gyroscope that’s sensitive enough, and install it in the underground, scientists hope to be able to accurately calculate the Earth’s rotation speed in relation to itself directly, which would greatly simplify the calculations. However, given the size and moving speed of the frame of the gyroscope – the Earth, the device needs to be scaled up significantly to provide accurate measurements, and, more importantly, needs to be isolated from external factors that can influence it, such as atmospheric pressure or humidity, just two elements that can interfere with the light beams.

The device built by the Italian scientists is significantly larger than a regular laser gyroscope: while a regular gyroscope has a side of 10 cm, the side of the experimental one is 4 meters. The sensibility of the laser beam is also greatly enhanced, being able to pick up differences in the equivalent of one part per billion, or, if you want to get technical, differences in rotation rates of 10^-14 radians per second.

While the proof-of-concept device, known as GINGER (short of Gyroscope in General Relativity), is already operational, having been installed in a seismic-active place in Italy with the dual-purpose of also providing some additional data on seismic activity, more such devices are expected to be installed soon, with the ultimate goal of creating an array of devices capable of measuring the Earth’s wobble movement as well, and provide scientists with other useful data as well.