Patent ID: 8830480
Filing Date: 2014-09-09
Classification: G01B

Abstract:
1. A measurement apparatus which measures a distance between a reference surface and a surface to be measured, comprising: a wavelength reference element configured to include a gas cell in which a plurality of types of gases having absorption lines different from each other are sealed; a light splitting element configured to split light emitted by a light source into a first light beam and a second light beam, and cause the first light beam to enter the reference surface and the second light beam to enter the surface to be measured; a phase detection unit configured to detect interference light between the first light beam reflected by the reference surface and the second light beam reflected by the surface to be measured, and detect, from a signal of the interference light, a phase corresponding to an optical path length between the reference surface and the surface to be measured; and a processing unit configured to set a wavelength of light emitted by the light source to a plurality of different wavelengths corresponding to a plurality of different absorption lines by using the wavelength reference element, control the phase detection unit to detect a phase corresponding to the optical path length between the reference surface and the surface to be measured for each of the plurality of different wavelengths, and perform processing of obtaining the distance, wherein the plurality of different wavelengths include a first reference wavelength, a second reference wavelength, a third reference wavelength, and a fourth reference wavelength, letting λ