A method of determining operation conditions of a particle detector for detecting a particle density of particles with a size of less than 20 μm, preferably less than 10 μm in a fluid, wherein the particle detector comprises a laser, wherein the laser is a Vertical Cavity Surface Emitting Laser, the method comprising the steps of: providing an electrical drive current to the laser such that a laser beam is emitted by the laser, characterized in that the Vertical Cavity Surface Emitting Laser is a multimode Vertical Cavity Surface Emitting Laser, and in that the method further comprises the steps of: varying the drive current within a predefined range of drive currents, determining an intensity signal of an optical wave within a laser cavity of the laser as a function of the drive current, determining a noise measure of the intensity signal as a function of the drive current, determining a range of drive currents in which the noise measure is below a predefined threshold value, determining at least a part of the operation conditions of the particle detector by choosing a drive current for particle detection out of the determined range of drive currents, detecting a trigger event during operation of the particle detector, determining the noise measure of the intensity signal in the laser cavity of the optical wave within the laser cavity of the laser during operation of the particle detector, determining a new range of drive currents if the noise measure during operation of the particle detector exceeds an operation threshold, determining at least a part of the operation conditions of the particle detector by choosing a new drive current for particle detection out of the determined new range of drive currents. providing an electrical drive current to the laser such that a laser beam is emitted by the laser, characterized in that the Vertical Cavity Surface Emitting Laser is a multimode Vertical Cavity Surface Emitting Laser, and in that the method further comprises the steps of: varying the drive current within a predefined range of drive currents, determining an intensity signal of an optical wave within a laser cavity of the laser as a function of the drive current, determining a noise measure of the intensity signal as a function of the drive current, determining a range of drive currents in which the noise measure is below a predefined threshold value, determining at least a part of the operation conditions of the particle detector by choosing a drive current for particle detection out of the determined range of drive currents, detecting a trigger event during operation of the particle detector, determining the noise measure of the intensity signal in the laser cavity of the optical wave within the laser cavity of the laser during operation of the particle detector, determining a new range of drive currents if the noise measure during operation of the particle detector exceeds an operation threshold, determining at least a part of the operation conditions of the particle detector by choosing a new drive current for particle detection out of the determined new range of drive currents. varying the drive current within a predefined range of drive currents, determining an intensity signal of an optical wave within a laser cavity of the laser as a function of the drive current, determining a noise measure of the intensity signal as a function of the drive current, determining a range of drive currents in which the noise measure is below a predefined threshold value, determining at least a part of the operation conditions of the particle detector by choosing a drive current for particle detection out of the determined range of drive currents, detecting a trigger event during operation of the particle detector, determining the noise measure of the intensity signal in the laser cavity of the optical wave within the laser cavity of the laser during operation of the particle detector, determining a new range of drive currents if the noise measure during operation of the particle detector exceeds an operation threshold, determining at least a part of the operation conditions of the particle detector by choosing a new drive current for particle detection out of the determined new range of drive currents.