The ring laser gyroscope is one of the earliest laser applications that reached the market, and it is still in use today, in particular in aircraft. It consists of a ring laser in which, due to the Sagnac effect, two counterpropagating modes exhibit a frequency difference proportional to the angular velocity of the system. Macek and Davis published the first experimental demonstration of this principle as early as 1963. These pioneers had built a ring laser based on the helium-neon laser, which had just been invented. At that time, the only neon line that was known to lase was in the infrared, at 1.15 µm wavelength. Later, after the discovery of the red He-Ne laser at 632.8 nm, all ring-laser gyro manufacturers based their products on this latter transition.
A group of researchers based in New Zealand and Germany has now revisited the possibility to use the 1.15-µm neon line for rotation measurements. But their application is not inertial navigation. They have built a large (2.56 m2
area) ring laser to monitor the rotation of the Earth. They prove the potentialities of this infrared transition, together with the newly developed GaAs/GaAlAs crystalline mirror technology, to monitor the Earth rotation rate for applications in geophysics.
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