Axial Resolution of a Confocal Scanning Optical Microscope

It is well known that the type II scanning optical microscope has important advantages over conventional optical microscopes. These advantages lie primarily in their ability to eliminate out of focus signals so that the image contains information from a thin axial slice. In this paper we quantify this effect for several typical microscope configurations. We have calculated the axial response of the microscope as a function of the numerical aperture and the focal length of each lens in the system. The effect of misalignment of the point detector has been investigated. In addition the effect of feature size has been analysed; we have demonstrated that the depth discrimination differs substantially for a point and large area object. These analytical results have been extended numerically to account for arbitrary size objects. The computations have been performed using both Fresnel diffraction theory and a hybrid approach which combines diffraction theory and ray optics. The latter method greatly reduces computational complexity and the results agree with those obtained using diffraction theory in cases where comparison is applicable.