Self-mixing laser velocimeter for retinal blood flow measurements

A Doppler velocimeter exploiting a self-mixing laser diode is proposed. The system has been design to evaluate the retinal blood flow velocity. The central frequency of the Doppler band obtained from the self-mixing laser diode measurement is related to the blood flow velocity in the vessel under test. The measurement can be done under the light-intensity feedback ratio below -100 dB without using highly sensitive electronics since the laser acts as a high-efficiency mixer oscillator and a shot-noise-limited quantum detector. The advantages in adopting such technique consist in its low cost, easiness of implementation and small size. Moreover, the self-mixing laser diode method offers the advantage to have the excitation and measurement beams spatially overlapped overcoming the alignment difficulty due to limited optical accessibility imposed by the finite aperture of the pupil.