Laser speckle reduction
A substantial reduction in the speckle effect is achieved by:
- choosing large lens apertures/small aperture numbers for the objective, which improves depth discrimination but at the expense of depth of focus,
- altering the distance between the object and the sensor, which is most convenient when a scanning measurement is being performed anyway, such as profile measurement of railroad tracks while the train is moving,
- using a laser beam source with decreased coherence length, such as a superluminescent diode or laser of the LNC-Series.
Laser Speckle and Laser light sectioning
3D profiling by use of laser light sectioning: Measured object with generated laser line, at an incident angle of 60° and with an additional dome illumination of the object.
The generation of laser speckle cannot be avoided as the principle of laser light-sectioning relies upon the imaged surface being roughly textured and diffusely reflecting optically.
Object imaged with a large aperture, f/# 2.8. The imaging lens acts as a spatial frequency filter, restricting the measurement to a shallower dissecting plane and minimizing the speckle effect.
Object imaged with a small aperture, f/# 22, which increases speckle and granularity, bringing uncertainty in the contour of the line.
Laser Modules of series LNC
- Low noise laser module (<0.1% RMS,@ 1 MHz)
- Reduced coherence
- Mode hopping free laser operation
- Internal RF-modulation