This work describes the development of an optical sensor for measurement of vibration without contact. The realized vibrometer is based on real-time digital elaboration of the signal obtained by a self-mixing interferometer, with an embedded autofocus system. Two different algorithms are implemented, for the continuous working on diffusive surfaces, with different levels of optical reflectivity. Thanks to the autofocus and the digital processing, the proposed sensor is easy to use and requires no assistance of a skilled operator.

This work describes the development of a novel laser instrument for non-contact absolute distance measurements, working in safety class I. The physical principle of operation is based on the self-mixing effect in a laser diode: the laser diode wavelength is modulated through a change of the supply current, inducing a self-mixing signal. The frequency of the produced fringes depends on the target distance, therefore a particular algorithm is applied, in real-time, to extract the frequency tone of the fringes, even in the case of very low signal-to-noise ratio. The final low-cost instrument is realized with an embedded digital signal processor and works in real-time over diffusive targets, with resolution better than 100 μm for distances up to 2 m.

Theoretical and experimental analysis of the spectral characteristics of the signal acquired from self-mixing laser Doppler of extracorporeal blood flow is presented. The theoretical spectrum of the predetected signal is calculated in the single scattering approximation and assuming a parabolic velocity profile in the duct. The resulting signal is mixed in a diode laser cavity to generate the sensor output. Theoretical predictions are verified by measurements performed on blood and phantoms flowing in an extracorporeal circulation system

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This work describes a novel instrument based on a self-mixing optical interferometer, able to reconstruct the target speed and direction, without heterodyne detection. The real-time elaboration employs the signal non-linearity in order to recover the speed sign in the frequency domain. The target speed is measured by the signal frequency, while the speed sign is evaluated by the phase of the harmonics in the frequency domain. The high-sensitivity of the elaboration allows the measurement over diffusive target with distances up to 10 m. The measurements results have been successfully compared with a very-high resolution a commercial calibrated instrument