Displacement measurement sensor head and system having measurement sub-beams comprising zeroth order and first order diffraction components

A sensor head for use with a measurement grating, the sensor head comprising:

• a splitter grating configured to split a light beam into first and second measurement beams;
• a first retroreflector configured to retroreflect the first and second measurement beams toward the measurement grating;
• and
• a second retroreflector configured to retroreflect the first and second measurement beams toward the measurement grating, wherein the first and second measurement beams are diffracted by the measurement grating to form respective first and second sub-beams of each of the first and second measurement beams and the first and second sub-beams each comprise a zeroth order diffraction component and a first order diffraction component.

A sensor head for use with a measurement grating, the sensor head comprising:

• a splitter grating configured to split a light beam into first and second measurement beams;
• a first retroreflector configured to retroreflect the first and second measurement beams toward the measurement grating;
• and
• a second retroreflector configured to retroreflect the first and second measurement beams toward the measurement grating, wherein the first and second measurement beams are diffracted by the measurement grating to form respective first and second sub-beams of each of the first and second measurement beams and the first and second sub-beams each comprise only zeroth order diffraction components or first order diffraction components.

A method of measuring a displacement, the method comprising:

• splitting a light beam into first and second measurement beams;
• directing the first measurement beam toward a measurement grating;
• directing the second measurement beam toward the measurement grating;
• and
• diffracting the first and second measurement beams into respective first and second sub-beams, wherein one of the sub-beams comprises a zeroth-order diffraction component and a first order diffraction component.