Dual-axes tri-differential confocal sensing technique with higher axial resolution and SNR

The axial response curve of dual-axes confocal microscopy (DCM) has a shift while the point detector has a transverse offset from the optical axis. Based on this, a dual-axes tri-differential confocal sensing technique (DTCST) with absolute zero and high axial resolution is proposed. DTCST sets three micro-regions as virtual pinholes on DCM detecting plane to achieve the Airy spot division detection, which one micro-region is set at the focus and two micro-regions are set symmetrically about the focus along determined direction. DTCST uses a CCD as detector and adjusts the size and position of pinholes freely in software, can significantly simplify detection system and can eliminate the errors attributed to the dissymmetrical placement of pinholes and property difference of the detectors. DTCST uses the pairwise differential subtraction of three intensity responses detected simultaneously from the three micro-regions to achieve high resolution absolute measurement and low noise. Theoretical analyses and preliminary experiments indicate that DTCST has an improved axial resolution, an extended measurement range, as well as strong anti-interference capability and sectioning detection capability.