Phase contrast scanning confocal microscope

Abstract

We propose a novel technique for efficient imaging of phase-only or transparent objects based on a confocal microscope configuration with a modified illumination point-spread function (PSF). The illumination PSF is modified by engineering the wavefront of the incident beam such that a π-phase shift is introduced on half of the area of the beam. The lens used for confocal illumination carries out an optical Fourier transform resulting in an illumination PSF with two closely spaced first-order diffraction spots otherwise referred to as a high-order Hermite-Gaussian beam (HG₁₀) profile. When used as illumination in a confocal microscope to view a phase-only object, the HG₁₀ PSF results in enhanced contrast for phase edges that are perpendicular with the orientation of the spots. Taking images and rotating the orientation of the HG₁₀ PSF to enhance all the other edges in a random phase pattern results to a 25-fold increase in contrast. This work points to the possibility of three-dimensional imaging of phase-only objects with the improved axial resolution provided by the confocal setup.