Confocal reflectance microscopy may enable screening and diagnosis of skin cancers noninvasively and in real-time,
as an adjunct to biopsy and pathology. Current instruments are large, complex, and expensive. A simpler, confocal
line-scanning microscope may accelerate the translation of confocal microscopy in clinical and surgical
dermatology. A confocal reflectance microscope may use a beamsplitter, transmitting and detecting through the
pupil, or a divided pupil, or theta configuration, with half used for transmission and half for detection. The divided
pupil may offer better sectioning and contrast.
We present a Fourier optics model and compare the on-axis irradiance of a confocal point-scanning microscope in
both pupil configurations, optimizing the profile of a Gaussian beam in a circular or semicircular aperture. We
repeat both calculations with a cylindrical lens which focuses the source to a line. The variable parameter is the fillfactor,
h, the ratio of the 1/e2 diameter of the Gaussian beam to the diameter of the full aperture. The optimal values of h, for point scanning are 0.90 (full) and 0.66 for the half-aperture. For line-scanning, the fill-factors are 1.02
(full) and 0.52 (half).
Additional parameters to consider are the optimal location of the point-source beam in the divided-pupil
configuration, the optimal line width for the line-source, and the width of the aperture in the divided-pupil
configuration. Additional figures of merit are field-of-view and sectioning. Use of optimal designs is critical in
comparing the experimental performance of the different configurations.