Differential confocal microscopy with a wide measuring range based on polychromatic illumination

A differential confocal microscopy based on polychromatic illumination is proposed to achieve both wide range and high lateral resolution during measurement of a 3D deep-etching microstructure. Two alternating response ranges are obtained by controlling the axial dispersion amount of two focusing beams. Noise in additive and multiplicative modes can be suppressed by using the proposed differential confocal microscopy because an output function is reestablished as the ratio of subtraction and sum values of the two defocusing detectors' responses. The sensing method is very useful for the measurement of micro and sub-micro 3D profiles of microstructures with hybrid material or non-uniform surface reflectance.