High-Speed Recording by a Rotating-Mirror Method

Abstract

IN the course of a series of experiments on the propagation of transient stress waves in solids, we have developed an optical method of high-speed recording which does not appear to be described in the literature. The duration of the stress pulses is often of the order of 50 microsec., and the only feasible method of recording the phenomena optically is to use a stationary-film camera in conjunction with a mirror rotating at high speed, the recording film being fixed on a circular arc the centre of which lies on the axis of the mirror. If the radius of this arc is 27 cm., a writing speed of 3 mm. per microsec. (measured on the film) will be obtained when the mirror rotates at 1,000 rev. per sec. Rotational speeds of this order of magnitude can be obtained most easily by means of the high-speed air turbines developed for ultracentrifuge work¹, and, in our camera, the rotating mirror consists of an octagonal, stainless steel mirror mounted on the rotor of a small turbine of this type.