Abstract: Improved detector and processing circuitry for use with a vorticity measurement optical probe system is disclosed. The invention makes use of a dual axis position indicating photodetector so that two components of vorticity may be simultaneously measured. Reflective spherical particles are disposed in a fluid whose vorticity is to be measured, and a light beam is reflected off of the particles and onto the photodetector. Analog and digital processing circuitry is connected to the outputs of the photodetector, and generate data that is indicative of the position of the reflected light beam on the photodetector as a function of time. Computer interface circuitry is also provided which enables the beam position data to be read into a digital computer so that the two vorticity components may be calculated therefrom. Embodiments which utilize plural axis photodetectors are also disclosed.