A Nanosecond Kerr Magneto-Optic Camera

Abstract

A Kerr magneto-optic camera has been constructed which takes 10 nsec exposures of the dynamic magnetization configuration in a magnetic thin film during high speed flux reversal. The photographs obtained have 10 μ resolution and sufficient contrast and brightness to record, in a single exposure, the dynamic state during a 50 nsec or longer flux reversal. The time at which the photograph is taken relative to the application of the switching field is variable from -100 nsec to +10 μsec with a relative time stability at any setting of ±3 nsec. A Q-switched ruby laser is used as a light source. The 10 nsec exposure time is obtained with a Kerr electro-optic shutter. The reversing field has a risetime of 10 nsec, decay time of 20 nsec, variable amplitude (<30 Oe), duration (<10 μsec), and is applied with a stripline. Included in the description of the system are discussions of a blocking oscillator circuit used to drive KU-27 thyratrons with a jitter of less than 1 nsec, an electron multiplier pulse amplifier with a 6 nsec risetime and a 0 to 1.5 kV output into 50 Ω, and a thyratron pulse amplifier with a 10 nsec risetime and a 1.0 to 10 kV output into 50 Ω. The apparatus is particularly suitable for studying high speed flux reversal in that it gives a visual picture of the dynamic state of the magnetization. Examples of sequences of photographs depicting dynamic flux reversal are also included.