Low drift reference for laser radar
AssigneeNikon Metrology NV
InventorsAnthony R. Slotwinski, Mina A. Rezk
Life of this patent
Estimating the term…
Abstract
Laser radar systems include a pentaprism configured to scan a measurement beam with respect to a target surface. A focusing optical assembly includes a corner cube that is used to adjust measurement beam focus. Target distance is estimated based on heterodyne frequencies between a return beam and a local oscillator beam. The local oscillator beam is configured to propagate to and from the focusing optical assembly before mixing with the return beam. In some examples, heterodyne frequencies are calibrated with respect to target distance using a Fabry-Perot interferometer having mirrors fixed to a lithium aluminosilicate glass-ceramic tube.
Claims21
A laser distance measurement apparatus, comprising:
- a probe beam source configured to direct a probe beam to a target;
- a reference length defining a circulating optical path having an optical path length based on an ultralow coefficient of thermal expansion (ULE) support structure, wherein the circulating optical path defined by the reference length is configured to receive a reference beam and direct the reference beam so as to propagate along the circulating optical path;
- a first photodetector configured to receive at least a portion of the probe beam from the target and a second photodetector configured to receive at least a portion of the reference beam from the circulating optical path defined by the reference length;
- and
- a signal processor coupled to the first photodetector and the second photodetector, wherein the signal processor is configured to establish an estimate of a target distance based on the portion of the probe beam received from the target by the first detector and the portion of the reference beam received from the circulating optical path defined by the reference length by the second detector.
A method, comprising:
- directing a reference optical beam to an optical resonator that defines an optical path length so as to produce a reference beam portion associated with a transit along the optical path, wherein the optical path length is based on a dimension of an ultralow thermal expansion (ULE) support;
- receiving the reference beam portion at a reference beam detector;
- directing a probe beam to a target and receiving at least a portion of the probe beam returned from the target at a probe beam detector;
- and
- estimating a propagation length associated with propagation of the probe beam to the target based on the reference beam portion received by the reference beam detector and the probe beam portion received by the probe beam detector.
A method, comprising:
- directing a reference optical beam to an optical resonator that defines an optical path length so as to produce a reference beam portion associated with a transit along the optical path, wherein the optical path length is based on a dimension of an ultralow thermal expansion (ULE) support;
- receiving the reference beam portion at a reference beam detector;
- directing a probe beam to a target and receiving at least a portion of the probe beam returned from the target at a probe beam detector;
- and
- estimating a propagation length associated with propagation of the probe beam to the target based on the reference beam portion received by the reference beam detector and the probe beam portion received by the probe beam detector, wherein the reference optical beam is a swept frequency optical beam, and the propagation length estimate is based on a frequency difference established in part by the swept frequency beam.
Dependencies are inferred from the claim text.