Renishaw Plc

Mark A V Chapman

Tingdi Liao

Raymond J Chaney

Jan Linnenbuerger

Damon Mark Northeast

Apparatus for producing and guiding a light beam, in particular for a laser interferometer, includes a laser having a laser tube ( ) and an external cavity ( ). Two laser beams ( A&prime; and B&prime;) of orthogonal polarization states are directed from the cavity into polarization maintaining fibers ( ). The two beams are generated from a single beam ( ) by a birefringent prism ( ) in the cavity. Additional beam steering prisms ( A and B) are included to direct the beams from the birefringent prism to the fibers. The additional steering prisms compensate for temperature induced beam deviations in the birefringent prisms. Interferometric sensing heads ( ) receive the beams from the fibers and include a rotatable wedge prism and mechanical adjustment means for guiding the beams onto reflecting surfaces on an object for positioning the object. The ends of the fibers attached to the sensing heads are kinematically located in the head.

Apparatus for producing and guiding a light beam

A beam deflector has first and second wedge prisms having refractive indices and geometries which are similar (in the case of the geometry to within arc minutes). The prisms are rotatable about an optical axis O defined by the direction of propagation of the incident light beam, to adjust the angle through which the incident beam is deflected. A third prism has a wedge angle which is greater than that of the first and second prisms by a factor of 2. When the directions in which the first and second prisms refract the beam away from the optical axis are aligned about the optical axis at notional angles of 0&deg; and 90&deg; respectively, and the third prism is aligned with its direction of refractive deviation at a notional angle of 225&deg; about the optical axis, the light beam will pass undeviated through the deflecting device. The provision of the third prism ameliorates the need to match closely the geometries and refractive indices of the first and second prisms, and yet avoids the occurrence of angles through which the beam may not be deflected as a result of insufficiently closely matched prisms.

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Wotton-under-Edge, United Kingdom

Mark A V Chapman