Phonon probe microscopy: towards acoustically-resolved Brillouin spectroscopy

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Imaging living cells at super-optical resolution is a major breakthrough in microscopy which has enabled discovery in numerous areas of cell biology. However, the existing technologies present limitations. In particular, super-resolution based in fluorescence microscopy requires the use of dyes that are toxic to cells and can only be used for short periods. Electron microscopy is completely incompatible with live cells and atomic force microscopy is invasive and limited to the vicinity of the surface. Moreover, the characterisation of material properties with any of these techniques remains extremely challenging. To this day, the damage caused by short-wavelength radiation enforces strong restrictions to biological imaging. These limitations do not apply to phonons, which carry orders of magnitude less energy than electromagnetic radiation. This offers an exciting path for label-free, super-optical resolution microscopy. Moreover, imaging with phonons provides information related to the elasticity of the specimens. The combination of these aspects offers new possibilities in life sciences and healthcare applications. In this project, I propose a new way of achieving super-optical resolution by means of phonon acoustics. By using laser-generated phonon fields, it is possible to produce lenses small enough to produce tightly focused phonon beams with sub-optical wavelengths. The fields are to be detected by Brillouin scattering to provide elasticity-based contrast at safe optical wavelengths: proof of concept of the phonon-probe microscope.