# How does a laser gyroscope work?

I came across this term, but I have not seen a good explanation of how it operates.

What I gather is that a laser beam is split into teo and travel in a ring and meet each other. The two beams should match if the laser is going straight. How does laser gyroscope know when the two beams are off and what is done to get it poining in the right direction?

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I had to look it up. On the sub we used a regular gyroscope for navigation…laser stuff was not around then.

Here’s what the AI on my browser came up with:

A laser gyroscope is a type of inertial measurement unit that uses the Sagnac effect to measure angular rotation. It consists of a ring-shaped laser cavity with two counter-propagating laser beams that travel in opposite directions. The laser beams are split and then directed on opposite paths through the ring, which is attached to a vehicle. When the vehicle rotates, the distance traveled by the two beams changes, causing a phase shift between the two beams.

The Sagnac Effect

The Sagnac effect is a phenomenon where the phase of a light beam changes when it travels around a rotating ring. This effect is caused by the difference in the distance traveled by the light beam when it moves with the rotation of the ring and when it moves against the rotation. The phase shift is directly proportional to the angular velocity of the ring.

Operation of a Laser Gyroscope

Here’s a step-by-step explanation of how a laser gyroscope works:

Laser Beam Splitting: The laser beam is split into two counter-propagating beams, which travel in opposite directions around the ring.

Ring Shape: The ring is designed to have a specific shape, such as a triangle, square, or rectangle, and is filled with an inert gas, such as helium-neon.

Rotation: When the vehicle rotates, the ring and the laser beams move with it.

Phase Shift: The distance traveled by the two beams changes due to the rotation, causing a phase shift between the two beams.

Detection: The phase shift is detected by a photodetector, which measures the difference in phase between the two beams.

Signal Processing: The detected signal is then processed to extract the angular velocity of the vehicle.

seawulf575 (16870)

I came across a similar explanation, but I don’t see how the gyroscope resitsts change. With a regular physical gyroscope this is easy to see.

I’m not sure I understand what you are asking. How does it not just change on its own? Or how does it change back to square one after a move?

seawulf575 (16870)

A regular gyroscope resists being turned. Does a laser gyroscope resist being turned? If so,, how does it resist?

From what I can gather it sounds like you have laser beams going on opposite sides of the ring and hitting a photoelectric tube. As the vehicle turns, the change in inertia due to the Sagnac effect results in one of the beams to change phase slightly, resulting in a change seen by the photoelectric tube. This difference in the beams will be fed through the electronics to be evaluated on how much of a change was seen and equate that to a change in direction.

seawulf575 (16870)

You give a way of detecting a change in direction, but not a way of resisting a change in direction as is the case for an ordinary gyroscope.

An ordinary gyroscope is mechanical. The resistance to turning is what is being measured. This doesn’t sound like there are moving parts…just the vehicle. And the laser beams, of course. It’s all electronic as opposed to mechanical.

seawulf575 (16870)

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