Height measurement using optical interference
Methods and systems for measuring a distance include measuring a first interference pattern between a lens and a target surface using a light source at a first wavelength. A second interference pattern is measured between the lens and the target surface using a light source at a second wavelength, different from the first wavelength. An absolute measurement of a distance between the lens and the target surface is determined based on the first interference pattern and the second interference pattern.
1. A method for measuring a distance, comprising:
positioning a spherical lens within a maximum measurement distance from a target surface;
measuring a first interference pattern between a the spherical lens and a the target surface using a light source at a first wavelength by measuring a radius of a smallest ring in the first interference pattern;
measuring a second interference pattern between the spherical lens and the target surface using a light source at a second wavelength, different from the first wavelength, by measuring a radius of a smallest ring in the second interference pattern; and
determining an absolute measurement of a distance between the spherical lens and the target surface using a processor based on the first interference pattern and the second interference pattern.
2. The method of claim 1 , wherein the first and second wavelength are not integer multiples of one another.
3. The method of claim 1 , wherein the first and second interference patterns are in the form of Newton's rings.
4. The method of claim 1 , wherein the light source at the first wavelength and the light source at the second wavelength are both lasers.
5. A computer readable storage medium comprising a computer readable program for distance measurement, wherein the computer readable program when executed on a computer causes the computer to perform the steps of claim 1 .