Helium- Neon laser light source generating two harmonically related, single- frequency wavelengths for use in displacement and dispersion measuring interferometry

A laser light source comprising:

• a single-mode Helium-Neon laser which during operation generates a single-frequency input beam at a first wavelength;
• a nonlinear optical crystal external to the laser which during operation converts a portion of the input beam at the first wavelength into optical radiation at a second wavelength that is a harmonic of the first wavelength;
• and
• a plurality of mirrors enclosing the nonlinear crystal to define a resonant external cavity, wherein one of the mirrors couples optical radiation at the first wavelength from the input beam into the external cavity and another one of the mirrors couples optical radiation at the first and second wavelengths out of the external cavity to produce two harmonically related, single-frequency, output beams at the first and second wavelengths.

An interferometry system comprising:

• a Helium-Neon laser light source that generates two harmonically related, single-frequency output beams;
• an interferometer which during operation directs first and second measurement beams along a common path contacting a reflective measurement object and combines the reflected first measurement beam with a first reference beam to form a first exit beam and the reflected second measurement beam with a second reference beam to form a second exit beam, the first measurement and reference beams derived from the output beam from the laser light source having the first wavelength and the second measurement and reference beams derived from the output beam from the laser light source having the second wavelength, the first and second exit beams indicative of changes in the optical path length to the measurement object at the first and second wavelengths;
• and
• an optical analysis system which during operation determines changes in the geometric path length to the measurement object based on the first and second exit beams.