The present invention describes a method of determining the operating conditions of a particle detector 200 for detecting a particle density of particles having a size of less than 20 μm, preferably less than 10 μm in a fluid, and the particle detector 200 comprises a laser ( 111), wherein the laser is a multimode vertical cavity surface emitting laser, the method comprising: providing an electric drive current to the laser 111 such that the laser beam 112 is emitted by the laser, driving a predefined range. Changing the driving current within the current, determining the intensity signal of the light wave in the laser cavity of the laser 111 as a function of the driving current, determining the noise measurement value of the intensity signal as a function of the driving current, the noise measurement value Determining a range of the driving current that is less than a predefined threshold value, and determining at least a portion of the operating conditions of the particle detector 200 by selecting a driving current for particle detection from among the determined range of driving currents. The invention also relates to a particle detector 200 and a mobile device 190 comprising such a particle detector 200. The present invention finally relates to a related computer program product.