Holographic scanner insensitive to mechanical wobble

Claim 1

In a holographic scanning system which includes a holographic spinner disposed in the path of a light ray from a source of coherent light; said holographic spinner having at least one holographic facet formed on its surface, a method of creating a condition whereby the spinner is insensitive to tilting caused by mechanical wobble during rotation including the steps of: (a) directing said light ray incident upon the holographic spinner at an angle of incidence θ i , said spinner diffracting said ray at a first order diffraction angle θ d , (b) disposing a spherical mirror in the path of said diffracted ray, said mirror having an axis which is perpendicular to the spinner axis and having its center of curvature lying on said spinner axis, (c) selecting a spacing D of the holographic facet from the spinner axis and a spacing H of the mirror axis from the spinner surface so as to satisfy the following Equation: ##EQU4## where φ is the nominal angle about which the spinner is tilted and where the upper signs apply to transmission type spinners and the lower to reflection type and (d) focusing the diffracted rays which are reflected in parallel paths from the mirror upon an imaging surface.