detected by a photodiode connected to an oscilloscope the laser beam itself is blocked by a beam stopper after crossing the cell the intensity of the light scattering signal is a measure for the bubble size and is calibrated by means of latex sphere equivalent sizes this approach may be applied in the presence of an acoustic field in one sound dispersion method an acoustic transmitter sends an acoustic signal towards a receiver through a fluid medium liquid containing gas bubbles the bubbles present in the fluid influence attenuation and a group velocity of the acoustic signal these two parameters can then be used to determine a measure of gas bubble size s and a number of bubbles in comparison with the light scattering method described above this sound dispersion method may not be applicable in the presence of an acoustic field due to influences of the acoustic field on the acoustic signal for measuring bubble size s and number in an example method the created gas bubbles or at least a portion of the bubbles are subjected to an acoustic field with a given acoustic pressure and a given frequency the applied acoustic field causes particular bubble activity growth pulsation and or collapse of bubbles all bubbles in the acoustic.