Enhanced field-of-view high-resolution lattice light sheet microscopy with phased array beam formers

Abstract

The data acquisition speed of point scanning microscopy techniques at sub-cellular resolution limits imaging of large samples, as sample stability and focus drift are becoming an issue. Therefore, light sheet fluorescent microscopy (LSFM) has become the method of choice for imaging cleared samples. However, this method still suffers from a trade-off between imaging depth and resolution, due to diffraction of the illuminating beam limiting the achievable field of view. After improvement of the latter with non-diffracting Bessel beams, lattice light sheet microscopy has further reduced the imaging point-spread-function (PSF) as well as substantially reduced illumination intensities and the resulting phototoxicity by enabling illumination of entire light sheets over large lateral extents. Here, we propose further improvement by generation of structured light sheets via phased arrays implemented as silicon nitride photonic integrated circuits (PICs). Beam generation with PICs results in much higher power efficiency than beam forming with conventional liquid crystal based spatial phase modulators, as it does not require the use of narrow blocking apertures. Moreover, this approach enables increased control over the generated field profile. Modeling of concrete PIC concepts indicates that sub-cellular resolution with mm scale imaging depths can be concomitantly achieved. Maintaining a small PSF across the entire light sheet, along the axis perpendicular to the direction of light propagation, is sacrificed in order to maintain it over an increased imaging depth along the beam propagation axis. Rapid lateral scanning of the illumination beam inside the plane of the light sheet is then obtained by scanning of the laser wavelength within the excitation spectrum of the target fluorescent protein, allowing for a wide bidirectional field-of-view with high resolution.