*Depth-resolved phase-contrast optical metrology in life sciences and engineering

Novel phase contrast optical techniques that can provide 3-D displacement distributions within the volume of weakly scattering materials will be developed and applied. Their feasibility and promise have been recently demonstrated by the PI with proof-of-principle experiments either by using wavelength scanning, broadband spectral detection, or by changing illumination direction. The techniques have some exciting features: they are full-field, non-contact, have a displacement sensitivity of order 10nm due to the use of optical phase information, and can be used to study static and dynamic depth-resolved deformation fields. They also provide the volume microstructure of the material to which the deformation fields can be superimposed. These techniques are, however, limited to study semitransparent materials, as they rely in ligth retroreflected or backscattered from the material internal microstructure. Biological tissues and transparent polymers are examples of semitransparent materials and include skin, cornea, retina, arteries, epoxy and polyester resins, photo-polymers, etc.This project builds upon lessons learned from those preliminary experiments and aims to establish and mature these techniques as a platform technology by developing the necessary instrumentation and data analysis tools and to overcome identified technical limitations. Two important but hitherto insoluble problems in life sciences and engineering will be investigated with this new technology: 1) Compliance characterization of the vertebrate eye cornea, in which 3-D displacement fields measured within the corneal tissue will be used to extract material property distributions inside it by using novel inverse problem approaches (Finite Element Updating and the Virtual Fields Method); and 2) Micromechanics of granular materials, in which contact forces between individual grains will be evaluated from 3-D displacement field distributions. This will serve to quantify the loads transmitted through 3-D granular packs and also to check the hypothesis of force chains within the packs.