Optical measurement system and method for determining height differential between two surfaces

A method for measuring heights of two adjacent surfaces comprising, the method comprising the steps of:

• receiving a low-coherence light beam;
• splitting the low-coherence light beam into a primary beam and a walk-off beam;
• transmitting the primary beam onto a first surface and the walk-off beam onto a second surface;
• detecting reflections of the primary beam from the first surface and the walk-off beam from the second surface;
• and
• determining a distance between the first surface and the second surface based upon a change in a path distance of the detected reflections of the primary beam and the walk-off beam.

A system for measuring heights of two adjacent surfaces comprising:

• means for receiving a low-coherence light beam;
• means for splitting the low-coherence light beam into a primary beam and a walk-off beam;
• means for transmitting the primary beam onto a first surface and the walk-off beam onto a second surface;
• means for detecting reflection of the primary beam from the first surface and the walk-off beam from the second surface;
• and
• means for determining a distance between the first surface and the second surface based upon a change in a path distance of the detected reflections of the primary beam and the walk-off beam.

A system for measuring heights of two adjacent surfaces comprising:

• wave generator configured to generate a low-coherence wave;
• a probe head coupled to the wave generator, the probe head configured to receive the low-coherence wave from the wave generator, to transmit a primary beam onto a first surface and receive a reflected primary beam from the first surface, and to transmit a walk-off beam onto a second surface adjacent to the first surface and receive a reflected walk-off beam from the second surface;
• a polarizer residing in the probe head that polarizes the received low-coherence wave into a polarized light beam, and further polarizes the reflected primary beam and reflected walk-off beam into a single direction so that the reflected primary and reflected walk-off beams exhibit a desired interference;
• a crystal residing in the probe head configured to receive the polarized light beam and configured to split the polarized light beam into the primary beam and the walk-off beam;
• and
• a correlator coupled to the probe head, the correlator configured to detect at least a portion of the reflected primary beam and at least a portion of the reflected walk-off beam, and to determine a distance difference between the first surface and the second surface.