Evaluation of the optical performance of a novel high-speed focal-distance-modulated fibre-coupled confocal sensor

This article presents the evaluation of the optical performance of a new high-frequency focal-distance-modulated confocal point sensor. While maintaining the known advantages of the confocal measurement principle, the sen- sor represents an innovative combination of a fibre-coupled confocal illumination and detection with a tuneable, acoustically driven gradient-index fluid lens (TAG lens) for the modulation of the focus distance and a novel signal processing utilizing a lock-in amplifier. The new arrangement is able to achieve an approximately linear characteristic curve for the optimised feedback control of nano coordinate measuring systems (CMS) in scanning sample mode. This article emphasises the implementation and use of the sensor in nano CMS (NMM-1) and the advantages of the new signal processing. Measurements on different resolution standards are conducted and compared with the focal-distance-modulated sensor and without focus-distance-modulation as conventional confocal microscope (CCM).