An optical head for confocal microscopy that is especially advantageous for measurements on thick samples is provided. An interface between the optical head and the sample is index matched, to avoid beam aberration at this interface. The optical head includes a window having a convex surface facing away from the sample, so that light beams crossing this convex surface do so at or near normal incidence and are therefore not significantly aberrated. The window is rotationally symmetric about an axis perpendicular to the interface between the head and the sample. The head also includes at least two optical fibers, which can be used for input and/or output. Beams passing to and/or from the fibers are collimated by collimators. A single focusing element couples all the collimated beams to focused beams which pass through the window to intersect within a target region of the sample as confocal beams.