Abstract
Understanding the mechanical properties of biological cells is a challenging problem for the life sciences partly because there are limited methods for mapping elasticity with high resolution. Phonon microscopy is a form of Brillouin light scattering which uses coherent phonons for imaging with elasticity-related contrast, phonon resolution and without labels. It can measure material properties such as sound velocity, acoustic impedance and attenuation. To use it as a contrast mechanism in microscopy, high numerical aperture (NA) lenses are key to high resolution. However, increasing NA induces apparent attenuation, a premature decay of the detected signal. To reduce signal decay and quantify the sound attenuation coefficient in cells, it is necessary to understand the mechanisms that affect signal decay. Here we define opto-acoustic defocus as a signal decay mechanism and propose methods to achieve quantitative sound attenuation measurements, and to optimise in-depth imaging at high resolution which is crucial for cell imaging.
Highlights
Elasticity is emerging as an important parameter for the characterisation of biological materials
TRBS detection takes place by collecting the reflected signal as usually observed in previous works [13,33,34], the pump beam is delivered from the opposite side with another objective
We have identified opto-acoustic defocus as a strong cause of premature decay of TRBS signals which we call apparent attenuation
Summary
Elasticity is emerging as an important parameter for the characterisation of biological materials. Among the available techniques for elasticity characterisation, those based on Brillouin light scattering (BLS) are promising because they offer a non-invasive measure of the product of the refractive index and the speed of sound with optical resolution [6,7,8,9,10,11]. Phonon microscopy is a novel technology that uses coherent phonon fields to image biological cells with contrast provided by BLS [9,12]. An interesting consequence of the high temporal resolution phonon microscopy provides, is that material properties such as sound velocity, acoustic impedance and sound attenuation can be measured directly in the time domain with sub-optical resolution provided by the phonon wavelength [14]
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