Single-aperture SLAM microscopy with amplitude-tailored vector beams

Switching laser mode (SLAM) microscopy is a promising method for achieving super resolution while maintaining compatibility with two photon imaging at depth and in vivo. SLAM microscopes typically employ multiple paths for generating the requisite spot-like and donut-like beams; however, having two paths necessitates sub-wavelength-scale alignment which is prone to differential drift, causing degradation of the image quality. Here we demonstrate a single aperture, inline SLAM microscope which makes use of one phase element and polarization switching to generate colinear radially polarized and azimuthally polarized vector beams, which focus to a spot and a donut, respectively. By tailoring the spatial profile of the electric field at the back aperture of the microscope objective, we ensure that the resolution of the spot-like beam is comparable to conventional Gaussian beam imaging. Through subtraction of the two images, we demonstrate a 1.5X narrower focal spot and a resolution of ~0.28 λ corresponding to ~290 nm. Accordingly, this method is of great utility for imaging with sub-diffraction-limited resolution at depth in living tissue.