Patent ID: 8416422

Claim:
A measurement apparatus configured to measure a geometric distance between a reference optical path and a target optical path utilizing lightwave interference, the measurement apparatus comprising: a phase detector configured to detect a phase of a signal of an interference between light emitted from a distance-measurement light source and reflected on a reference surface and light emitted from the distance-measurement light source and reflected on a target surface; an intensity detector configured to detect an intensity of light emitted from a non-distance-measurement light source having a wavelength different from that of the distance-measurement light source and reflected on the reference surface and an intensity of light emitted from the non-distance-measurement light source and reflected on the target surface; and an analyzer configured to calculate the geometric distance based on an optical path length calculated from the phase and a wavelength of the distance-measurement light source, and an average value of a vapor pressure distribution between the target surface and the reference surface calculated from intensity information of the light emitted from the non-distance-measurement light source.