Faraday rotation in a multimode optical fiber in a fast rise-time, high magnetic field

A magneto-optic Faraday rotation diagnostic was implemented on a Z-pinch driven flux-compression generator to measure line-averaged, megagauss, axial-magnetic fields up to 1.6 MG with rise times of 30 kG/ns. The axial-magnetic field rotated the plane of polarization of a 2-W argon laser beam in a 0.725-mm-diam, fused silica quartz fiber mounted coaxial with the Z pinch. The rapid rise time and the high radiation environment presented by the Z-pinch plasma caused a high-pressure impulse <100 kbar, to be coupled into the quartz-fiber probe disrupting the polarization-preserving properties of the fiber. The time scale for disruption was characteristic of a shock propagating radially through the fiber to its core. This paper will describe the response of the Faraday diagnostic under these conditions and present a simple model that describes the effects of fiber depolarization that is consistent with previous observations of stress-induced depolarization in optical fibers.