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Abstract

A method of interferometrically obtaining measurements for properties associated with a spot on or in an object, the method involving: receiving a sequence of M optical pulses separated in time; from each pulse in the sequence of M optical pulses, generating an n-tuplet of measurement pulses, and an n-tuplet of reference pulses, wherein each measurement pulse has a corresponding reference pulse aligned with it in time; from each pulse of each n-tuplet of reference pulses for the sequence of M optical pulses, generating a reference beam; from each pulse of each n-tuplet of measurement pulses for the sequence of M optical pulses, (a) generating a measurement beam; (b) directing the measurement beam onto the spot to thereby produce a return measurement beam from the spot; and (c) combining the return measurement beam with the corresponding reference beam that was derived from the reference pulse corresponding to that measurement pulse to generate an interference beam, wherein the sequence of M n-tuplets of measurement pulses forms n interleaved sequences of M measurement pulses, and wherein the method further involves, for each of the n interleaved sequences of M measurement pulses, introducing a combination of phase shifts between the measurement beams and corresponding reference beams.

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