High frequency ultrasonics using optical fibres

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Optical fibres have been used to propel the fields of optical and acoustic endoscopy, due to their ability to transmit information (such as an image) in and out of extremely confined environments. There is great interest in developing an optical fibre probe which functions using GHz frequencies of ultrasound. This would allow high resolution inspection of microscopic environments and specimens, where lateral resolution would be dictated by the diamter of the fibre core (~ 5 μm), and axial resolution would be determined by the acoustic wavelength (~ 300 nm). The fact that the device operates acoustically means that label-free high contrast can be achieved through the mechanical properties of the specimen, while still remaining non-contact. Such a device could be implemented in a wide range of scenarios, especially ones in which access to the sample plane is limited and ill-suited for traditional bench-top acoustic and photoacoustic microscopy. For example, optical fibre sensors could be readily integrated through the bore of a needle during fine needle aspiration procedures and other biopsies, or in the form of imaging bundles which are already widely utilised in clinical endoscopes.

Device concept

Brillouin fibre-spectrometer

Phonon imaging probe