Laser sensor module with indication of readiness for use

A laser sensor module for measuring a particle density of particles with a size of less than 20 pm, the laser sensor module comprising:

• a laser configured to emit a laser beam;
• a detector;
• an optical arrangement, the optical arrangement configured to focus the laser beam to a focus region;
• and
• an evaluator,
• wherein the laser is configured to emit the laser beam through the optical arrangement to the focus region,
• wherein the optical arrangement comprises an emission window,
• wherein the detector is configured to determine an interference signal of an interference of reflected laser light with emitted laser light of the laser beam,
• wherein the laser sensor module comprises a mechanical stimulator, and
• wherein the mechanical stimulator is configured to vibrate the emission window to move the emission window with respect to the laser to cause path length variations of the reflected laser light, and
• wherein the detector is configured to determine the interference signal based upon the interference of the reflected laser light with the emitted laser light of the laser beam detected during the vibration of the emission window, and
• wherein the evaluator is configured to provide an indication signal of a soiling of the emission window based on the interference signal determined during the mechanical excitation of the emission window.