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.
Technology capabilities and application coverage
- Accurate speed measurement over 360km/h
- Nominal working distance from mm’s up to meters
- Working range from 30 to 60% of nominal distance
- Accuracy better than 0.01% (interferometric)
- Resolution from wavelengths to cm’s
- Works on virtually all surfaces
- Insensitive to environmental light
- Robust to smoke, mist or dust
