Laser Gyroscope Princeton University（激光陀螺仪普林斯顿大学）.pdfVIP

Laser Gyroscope In this experiment you will explore a Helium-Neon laser with a triangular cavity and observe the Sagnac effect which is used for measurements of rotation rate. Recall that uniform linear motion cannot be detected by any means internal to the system, while uniform rotation makes a non- inertial frame and hence can be detected using a local measurement. The Sagnac effect is one physical mechanism for such inertial rotation sensing, it forms the basis of laser gyroscopes which are widely used for navigation on airplanes, for example. At present time the best gyroscopes are still mechanical in nature, using a large rotating mass, but there are a lot of efforts to develop high performance non-mechanical gyroscopes. 1) Helium-Neon laser Helium-neon laser is one of most common types of lasers, not counting semiconductor laser diodes. It uses electrical discharge to create the population inversion needed for laser operation. Helium and neon gases are used because of near coincidence of 1s2s metastable energy level in helium with 2p5s long-lived excited state in neon and because of favorable conditions for electrical discharge in noble gases. Electrical discharge populates 1s2s 1S0 state of helium (in spectroscopic notation 2S+1L ), which cannot decay electromagnetically because of angular J momentum selection rules. So a significant fraction of helium atoms accumulates in this state. In collisions with neon the whole excitation energy of 20.6 eV can be transferred to one of the electrons of the neon atom, promoting it to the 5s state in the 1P configuration because o