A laser sensor module for detecting ultra-fine particles with a particle size of 300 nm or less, the laser sensor module comprising: - at least one laser being adapted to emit laser light to at least one focus region in reaction to signals provided by at least one electrical driver, - at least one detector being adapted to determine a self-mixing interference signal of an optical wave within a laser cavity of the at least one laser, wherein the self-mixing interference signal is caused by reflected laser light reentering the laser cavity, the reflected laser light being reflected by a particle receiving at least a part of the laser light, - at least one evaluator; - wherein the laser sensor module is arranged to perform at least one self-mixing interference measurement, characterized in that - the laser sensor module is adapted to determine a first particle size distribution function, wherein the first particle size distribution function is characterized by a first sensitivity with respect to particle size detection by means of at least one measurement result determined based on the at least one self-mixing interference measurement, the laser sensor module being further adapted to determine a second particle size distribution function, wherein the second particle size distribution function is characterized by a second sensitivity with respect to particle size detection, the second sensitivity being different from the first sensitivity, wherein either the first or the second sensitivity is chosen such that particles smaller than a defined threshold particle size of 300 nm or less are not detected, wherein the first and the second particle size distribution functions have essentially an identical shape above the defined threshold particle size scaled with a calibration factor q, - the at least one evaluator is adapted to determine a particle measure of the particle size of 300 nm or less by subtracting the second particle size distribution function multiplied with the calibration factor q from the first particle size distribution function. - at least one laser being adapted to emit laser light to at least one focus region in reaction to signals provided by at least one electrical driver, - at least one detector being adapted to determine a self-mixing interference signal of an optical wave within a laser cavity of the at least one laser, wherein the self-mixing interference signal is caused by reflected laser light reentering the laser cavity, the reflected laser light being reflected by a particle receiving at least a part of the laser light, - at least one evaluator; - wherein the laser sensor module is arranged to perform at least one self-mixing interference measurement, characterized in that - the laser sensor module is adapted to determine a first particle size distribution function, wherein the first particle size distribution function is characterized by a first sensitivity with respect to particle size detection by means of at least one measurement result determined based on the at least one self-mixing interference measurement, the laser sensor module being further adapted to determine a second particle size distribution function, wherein the second particle size distribution function is characterized by a second sensitivity with respect to particle size detection, the second sensitivity being different from the first sensitivity, wherein either the first or the second sensitivity is chosen such that particles smaller than a defined threshold particle size of 300 nm or less are not detected, wherein the first and the second particle size distribution functions have essentially an identical shape above the defined threshold particle size scaled with a calibration factor q, - the at least one evaluator is adapted to determine a particle measure of the particle size of 300 nm or less by subtracting the second particle size distribution function multiplied with the calibration factor q from the first particle size distribution function.