Position measuring apparatus and method of use thereof

A position measuring apparatus comprising

• an illumination device emitting a light beam;
• an optical instrument located downstream from the illumination device that splits the light beam at a first plane into at least two divergent partial beams;
• a first diffraction grid placed in a second plane, parallel to the first plane, downstream from the optical instrument, the first diffraction grid diffracting the partial beams in such a manner that they are oriented parallel to each other;
• a retro-reflecting element receiving the partial beams and maintaining them parallel to each other;
• a second diffraction grid receiving the partial beams from the retro-reflecting element and diffracting the partial beams;
• an optical element receiving the partial beams from the second diffraction grid and bringing the partial beams to an interference;
• a detection device detecting the partial beams in the optical element, thereby measuring a change in the optical path difference (.DELTA.OPD) of the partial beams which is directly proportional to a change in distance (.DELTA.s) between the first plane and the second plane.

A method of measuring position of a first object with respect to a second object, comprising:

• placing the first object on a first support, comprising an optical instrument;
• placing the second object on a second support, comprising a first diffraction grid;
• illuminating the optical instrument with a light beam;
• splitting the light beam by the optical instrument in a first plane into at least two divergent partial beams;
• causing the first diffraction grid to receive and diffract the partial beams in a second plane, parallel to the first plane, so that the partial beams are parallel to each other;
• conducting the partial beams to a retro-reflecting element which causes the partial beams to pass through the retro-reflecting element and which maintains the partial beams parallel to each other within the retro-reflecting element;
• conducting the partial beams to a second diffraction grid which diffracts the partial beams;
• conducting the partial beams to an optical element which brings the partial beams to an interference;
• and
• measuring with a detection device a change in the optical path difference (.DELTA.OPD) of the partial beams which is directly proportional to a change in distance (.DELTA.s) between the first plane and the second plane.