Patent ID: 8502986

Claim:
A lightwave interference measurement apparatus comprising: a wavelength-variable laser configured to periodically perform wavelength scanning between a first reference wavelength λ 1 and a second reference wavelength λ 2 to emit light beam; a wavelength-fixed laser configured to emit light beam having a third reference wavelength λ 3 ; a wavelength reference element configured to be able to set a wavelength of the light beam emitted from the wavelength-variable laser to the first reference wavelength λ 1 and the second reference wavelength λ 2 ; a light beam splitting element configured to split the light beams emitted from the wavelength-variable laser and the wavelength-fixed laser into reference light beam and light beam under test; a phase detector configured to detect a phase based on an interference signal of the reference light beam that is reflected on a reference surface and the light beam under test that is reflected on a surface under test; and an analyzer configured to sequentially determine an interference order of the third reference wavelength λ 3 based on the third reference wavelength λ 3 , a first synthetic wavelength Λ 12 , a second synthetic wavelength Λ 13 , an integer component of a phase change amount in the wavelength scanning, and interference orders of the first synthetic wavelength Λ 12 and the second synthetic wavelength Λ 13 , and calculates an absolute distance between the surface under test and the reference surface, where the first synthetic wavelength Λ 12 is represented by λ 1 ·λ 2 /|λ 1 −λ 2 | and the second synthetic wavelength Λ 13 is represented by λ 1 ·λ 3 /|λ 1 −λ 3 |.