Methods, systems and apparatus of interferometry for imaging and sensing

An apparatus for quantitative imaging or sensing of a sample, comprising:

• an interferometer comprising a condenser optic and an objective optic, the interferometer being configured to receive a sample positioned between the condenser optic and the objective optic in an optical pathway of the interferometer;
• a light source configured to provide light to the interferometer at multiple wavelengths (λ), where the light is directed to the sample by optics of the interferometer;
• a detector configured to capture a plurality of images of the sample, each image among the plurality of images being captured at a different wavelength among the multiple wavelengths (λ);
• a processor configured to:
• calculate interference intensity points for the plurality of images captured at the different wavelengths;
• and
• calculate, for at least one image point of at least one image among the plurality of images, an optical path delay length between a reference field and a sample field in the apparatus based on the interference intensity points for the plurality of images;
• optical path delay (OPD) modifying optics positioned after an output of the interferometer and configured, based on the optical path delay length, to modify an interferometer output associated with the sample;
• and
• an add-on unit containing the OPD modifying optics, the add-on unit configured to attach to the interferometer for alignment of the OPD modifying optics with the interferometer output.