Imaging beyond the fundamental slope limit in surface metrology using fluorophore-aided scattering microscopy

Liu, J.; Liu, C.G.; Li, L.; Su, R.; Leach, R.K.

Abstract

Topography measurement for smooth surfaces with high slopes, e.g. freeform optics, is a challenging task for optical measuring instruments as the light reflected by the tilted surface cannot be sufficiently collected by the objective, resulting in low signal-to-noise ratio and detectability, and large measurement uncertainty. To overcome this fundamental physical limitation, we develop a novel method, called fluorophore-aided scattering microscopy (FAM) (see Figure 1), in which the first step is to ‘label’ the surface by depositing an easily-removable fluorescent film with a thickness of tens of nanometres on to the specimen. Rhodamine B is used as it can emit intense fluorescence under laser illumination. The uniform and removable fluorescent film is coated on the surface through a layer-by-layer self-assembly technique. Compared with traditional physical vapour deposition, this method could prepare coatings with thinner thicknesses and higher luminescence efficiency on much more complex surfaces. A fluorescent confocal microscope is utilised to obtain a sequence of confocal fluorescent images by scanning the focal region of the objective in the lateral and axial directions. The highest intensity within the three-dimensional image correlates with the local height on the surface. The detected signal is significantly enhanced with the aid of fluorescence due to the scattering by the surface now being more isotropic, i.e. the number of back-scattered photons is increased. We have shown that the surface topography of a deep vee-shaped groove specimen (with slope angle of 57.4°) can be easily measured using a 0.4 NA objective (which has a conventional slope limitation of around 20°). This approach may be used with other organic or inorganic fluorophore materials, since biocompatibility is not required for engineering surfaces.

Citation

Liu, J., Liu, C., Li, L., Su, R., & Leach, R. (2018, November). Imaging beyond the fundamental slope limit in surface metrology using fluorophore-aided scattering microscopy. Paper presented at Special Interest Group Meeting: Structured & Freeform Surfaces, Paris, France

• Presentation Conference Type: Conference Paper (unpublished)
• Conference Name: Special Interest Group Meeting: Structured & Freeform Surfaces
• Start Date: Nov 27, 2018
• End Date: Nov 29, 2018
• Deposit Date: Jun 21, 2019
• Public URL: https://nottingham-repository.worktribe.com/output/2215832
• Related Public URLs: https://www.euspen.eu/events/special-interest-group-meeting-structured-freeform-surfaces-18/