If the glass fiber supplies light to the probing tip, measurements can be performed in the self-illuminating mode (Fig. 24). It is also possible to use the fiber probe in the transmitted-light mode. Due to its small dimensions, the resulting probing forces are negligible (up to several micronewtons). For this reason, it can be used to measure especially contact-sensitive workpieces. The fiber probe belongs to the measuring sensor group. For this reason, it is primarily suitable for scanning material surfaces.