Optical system

An optical system for detecting radiation from a measuring area, comprising:

• at least one radiation source arranged to radiation along an excitation beam path that guides radiation from the radiation source to the measuring area;
• a detection beam path that guides radiation from the measuring area to at least a first and a second detector;
• the detection beam comprising in succession exactly one tube lens comprising a first end and an opposite second end, a first beam splitter, a first detector in a reflection direction of the first beam splitter and a second detector in a transmission direction of the first beam splitter;
• wherein the first detector comprises a first detection surface and the second detector comprises a second detection surface spaced from the first detection surface;
• wherein the first and second detection surfaces are arranged along the detection beam at the same distance (f) from the second end of the tube lens, wherein the radiation source of the optical system is controllably movable along a first axis and at an angle thereto along a second axis starting from a zero point, wherein the two axes span a plane at right angles to the excitation beam path;
• wherein a beam splitter is configured to redirect the radiation towards an XY detection arm;
• wherein the XY detection arm comprises a beam splitter in the reflection direction and transmission direction of which one detector each for the radiation of the radiation source is arranged, wherein the one detector) is configured to determine the location of the radiation incident thereon and to determine therefrom the displacement relative to the zero point along the first axis, and wherein the other detector is configured to determine the location of the radiation incident thereon and to determine therefrom the displacement relative to the zero point along the second axis,
• and the optical system comprises a control device configured to move the radiation source along the first and/or second axis towards the zero point in dependence on the determined signal of the two detectors.