Quantitative 3D phase metrology
Holographic photopolymers allow us to record complex 3D refractive index structures with scale down to ~100 nm in volumes as large as cubic cm. Modelling and device optimizatoin requires us to precisely and accurately measure these 3D index structures which is generally not possible with off-the-shelf instrumentation. We have thus developed a number of different custom microscopic and tomographic measurement systems specifically for quantifying properties at the micron scale within much larger 3D volumes. By combinging these refractive index measurents with precise models of how local concentrations create that index, these instruments serve to quantify the composition of the sample, often at spatial and temporal scales unavailable by (e.g.) infrared spectroscopy.
The team
- David Glugla
- Martha Bodine
- Eric Moore
- Amy Sullivan
- Mark Ayres
Learn more
- D. J. Glugla, M. B. Chosy, M. D. Alim, A. C. Sullivan, R. R. McLeod, “Transport-of-Intensity-Based Phase Imaging to Quantify the Refractive Index Response of 3D Direct-Write Lithography,” Optics Express 26, pp. 1851-1869, 2018
- M. I. Bodine, R. R. McLeod, Superresolved swept-wavelength interferometry using frequency estimation methods, Optics Letters 41, pp. 159-162, 2016.
- E. D. Moore, R. R. McLeod, Phase-sensitive swept-source interferometry for absolute ranging with application to measurements of group refractive index and thickness, Optics Express 19, 8117-8126, 2011.
- A. C. Sullivan and R. R. McLeod, Tomographic reconstruction of weak, replicated index structures embedded in a volume, Optics Express 15, 14202-14212, 2007.
- M. R. Ayres and R. R. McLeod, Scanning transmission microscopy using a position-sensitive detector, Applied Optics 45, 8410-8418, 2006.
This work has been generously funded by
Sample results
This scanning, quantitative 3D phase microscope measures the deflection of a focused beam by index gradients at the focus. By inverting the coherent transfer function of the instrument, it can measure n(x,y,z) with resolution limited by the point spread function of the objective lens.
This image of a coin surface was measured by multi-static, super-resolved optical frequency domain reflectometry. This technique can measure the internal positions and refractive indices of multi-layer parts with very high precision.
The set of bright-field microscope images, with +1, 0, and -1 micron defocus show a refractive index feature written in a holographic photopolymer by direct write lithography. The transport of intensity equation was used to extract the phase that, with a precise measurement of part thickness, reveals the index profile of the written feature.