The Sagnac effect (also called Sagnac interference), named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called a ring interferometer. A beam of light is split and the two beams are made to follow the same path but in opposite directions. To act as a ring the trajectory must enclose an area. On return to the point of entry the two light beams are allowed to exit the ring and undergo interference. The relative phases of the two exiting beams, and thus the position of the interference fringes, are shifted according to the angular velocity of the apparatus. This arrangement is also called a Sagnac interferometer.
A gimbal mounted mechanical gyroscope remains pointing in the same direction after spinning up, and thus can be used as a rotational reference for an inertial navigation system. With the development of so-called laser gyroscopes and fiber optic gyroscopes based on the Sagnac effect, the bulky mechanical gyroscope is replaced by one having no moving parts in many modern inertial navigation systems. The principles behind the two devices are different, however. A conventional gyroscope relies on the principle of conservation of angular momentum whereas the sensitivity of the ring interferometer to rotation arises from the invariance of the speed of light for all inertial frames of reference.
Read more about Sagnac Effect: Description and Operation, History, Theory, Practical Uses
Famous quotes containing the word effect:
“I care not by what measure you end the war. If you allow one single germ, one single seed of slavery to remain in the soil of America, whatever may be your object, depend upon it, as true as effect follows cause, that germ will spring up, that noxious weed will thrive, and again stifle the growth, wither the leaves, blast the flowers, and poison the fair fruits of freedom. Slavery and freedom cannot exist together.”
—Ernestine L. Rose (1810–1892)