Hybrid Reflective Interferometric System Combining Wide-Field and Single-Point Phase Measurements

We present a hybrid scan-free reflective interferometric system, which combines a wide-field phase measurement, together with a single-point phase measurement, for optical inspection of thin reflective elements. The wide-field interferometric system is composed of a compact portable off-axis interferometer and is illuminated by either a highly coherence source or a narrowband low-coherence source. This is a free-space time-domain self-phase-referenced interferometric setup that can be attached to the output port of an existing reflection microscope. It records a spatial off-axis interferogram, which yields the wide-field phase map of the reflective sample. The other part of the hybrid system is a fiber-based phase-sensitive spectral-domain optical coherence tomography setup, which is illuminated by a boarder-band low-coherence source. It records an on-axis common-path spectral interferogram, which yields a single-point phase measurement of the reflective sample. In this case, since the reference beam does not interact with the sample, the phase is not self-referenced, and slow phase variations are measured as well. None of the setups contains scanning elements. The combination of these systems allows simultaneous wide-field and single-point phase measurements without co-calibration problems. By measuring thin reflective models with these external interferometers, we experimentally illustrate the ability to discriminate between refractive index changes from height changes in the sample.