Method and system for profiling objects having multiple reflective surfaces using wavelength-tuning phase-shifting interferometry

A system for profiling a transparent measurement object having multiple reflective surfaces said system comprising:

• a tunable coherent light source configured to generate light at any one of multiple wavelengths;
• an unequal path length interferometer having a reference surface and comprising a mount configured to position a selected one of said multiple reflective surfaces of the measurement object at a non-zero distance Z from the zero optical path difference (OPD) position of the interferometer, wherein Z is less than about nT/2, nT being the smallest optical distance between two of the multiple reflective surfaces of the measurement object, and wherein the interferometer is configured to receive the light from the light source and generate an optical interference image comprising a superposition of multiple interference patterns, each of which is produced by a pair of wavefronts reflected from a corresponding different one of the multiple surfaces of the measurement object and said reference surface;
• a detector configured to record the optical interference image generated by the interferometer;
• and
• a system controller connected to the light source and the detector and which during operation causes the light source to generate light at each of the multiple wavelengths, causes the detector to record the image for each of the multiple wavelengths of the light source, and implements a phase-shifting algorithm to determine phases of a selected one of the multiple interference patterns from the recorded images.

A system for profiling a transparent measurement object having multiple reflective surfaces said system comprising:

• a tunable coherent light source configured to generate light at any one of multiple wavelengths spanning a range greater than or equal to about λ2/nT where λ is an intermediate one of the multiple wavelengths and nT is the smallest optical distance between two of the multiple reflective surfaces of the measurement object;
• an unequal path length interferometer having a reference surface and configured to support the measurement object, receive the light from light source, and generate an optical interference image comprising a superposition of multiple interference patterns, each of which is produced by a pair of wavefronts reflected from a corresponding different one of the multiple surfaces of the measurement object and said reference surface;
• a detector configured to record the optical interference image generated by the interferometer;
• and
• a system controller connected to the light source and the detector and which during operation causes the light source to generate light at each of the multiple wavelengths, causes the detector to record the optical interference image for each of the multiple wavelengths of the light source, and implements a phase-shifting algorithm to determine phases of a selected one of the multiple interference patterns from the recorded images.