Polarimeter based on polarization ring-down cavity

The utility model discloses a polarimeter based on a polarization ring-down cavity comprising a laser source. A circulator, a polaroid, a raster and a Faraday rotation mirror are sequentially arranged along the direction of propagation of laser, wherein the raster and the Faraday rotation mirror form an F-P cavity; a container card slot is formed in the F-P cavity; and a detector is arranged on one side of the circulator. By utilizing the polarimeter, the measuring accuracy is effectively improved. The polarimeter is good in stability, high in economic and social benefits and strong in practicability.