A laser sensor module for detecting a particle density of small particles with a particle size between 0.05 μm and 10 μm comprising: at least a first laser being adapted to emit a first measurement beam and at least a second laser being adapted to emit a second measurement beam, an optical arrangement being arranged to focus at least the first measurement beam to a first measurement volume, the optical arrangement being further arranged to focus at least the second measurement beam (112 `) to a second measurement volume, wherein the optical arrangement is characterized by a first numerical aperture with respect to the first measurement beam and a second numerical aperture with respect to the second measurement beam, wherein the first numerical aperture and the second numerical aperture are arranged with respect to the measurement beams (111', 112') to detect a predetermined minimum particle size at a reference velocity, wherein the reference velocity is chosen within a predetermined velocity range between 0.01 m/s and 7 m/s comprising the reference velocity, and wherein the first measurement beam and the second measurement beam mutually enclose an angle φ between 10° and 160°, at least a first detector being adapted to determine a first interference signal, at least a second detector being adapted to determine a second interference signal, an evaluator, wherein the evaluator is adapted to receive detection signals generated by at least the first detector and the second detector in reaction to the determined interference signals, wherein the evaluator is further adapted to determine at least a first average velocity of particles detected by the first detector and at least a second average velocity of particles detected by the second detector by means of the detection signals received in a predetermined time period, wherein the evaluator is further adapted to determine at least a first number of particles based on the detection signals provided by the first detector in the predetermined time period and at least a second number of particles based on the detected signals provided by the second detector in the predetermined time period, and wherein the evaluator is further adapted to determine a particle density based on an average particle velocity determined at least by means of the first average velocity and the second average velocity, at least the first number of particles and at least the second number of particles. at least a first laser being adapted to emit a first measurement beam and at least a second laser being adapted to emit a second measurement beam, an optical arrangement being arranged to focus at least the first measurement beam to a first measurement volume, the optical arrangement being further arranged to focus at least the second measurement beam (112 `) to a second measurement volume, wherein the optical arrangement is characterized by a first numerical aperture with respect to the first measurement beam and a second numerical aperture with respect to the second measurement beam, wherein the first numerical aperture and the second numerical aperture are arranged with respect to the measurement beams (111', 112') to detect a predetermined minimum particle size at a reference velocity, wherein the reference velocity is chosen within a predetermined velocity range between 0.01 m/s and 7 m/s comprising the reference velocity, and wherein the first measurement beam and the second measurement beam mutually enclose an angle φ between 10° and 160°, at least a first detector being adapted to determine a first interference signal, at least a second detector being adapted to determine a second interference signal, an evaluator, wherein the evaluator is adapted to receive detection signals generated by at least the first detector and the second detector in reaction to the determined interference signals, wherein the evaluator is further adapted to determine at least a first average velocity of particles detected by the first detector and at least a second average velocity of particles detected by the second detector by means of the detection signals received in a predetermined time period, wherein the evaluator is further adapted to determine at least a first number of particles based on the detection signals provided by the first detector in the predetermined time period and at least a second number of particles based on the detected signals provided by the second detector in the predetermined time period, and wherein the evaluator is further adapted to determine a particle density based on an average particle velocity determined at least by means of the first average velocity and the second average velocity, at least the first number of particles and at least the second number of particles.