Technology

Philips Laser Doppler Technology

Philips Laser Doppler sensors employ laser Doppler self-mixing technology. Laser Doppler refers to the phenomenon that laser light, reflected on a moving target, contains information about the target’s velocity. Self-mixing refers to the fact that a single laser is used both for emitting and receiving the reflected light.

Principle of Laser Doppler technology

When the laser is aimed at a scattering object at a distance (see figure), a small portion of the scattered light reflects back into the cavity where it mixes with the strong laser field. When the movement of the object has a component along the direction of the laser beam, the phase of the reflected light continuously shifts with respect to the original laser light, resulting in a periodic variation of the feedback into the laser cavity at a frequency, equal to the Doppler frequency.

The feedback from this moving object generates a changing interference signal inside the laser cavity with this Doppler frequency, and hence the laser output power is modulated with a frequency, from which the velocity of the scattering object can be derived, according to the equation above.

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