Optical receiving device
This device is different depending on the chosen configuration:
■ in the reference beam LDA, it consists of a series of very small orifices, e. g. 1 mm in diameter, and a photodetector. The diaphragms are designed to intercept all the light except that coming in the direction of the reference beam:
■ the crossed beams LDA includes a lens that allows the capture of scattered light in a large solid angle; a diaphragm in the image plane of the measurement zone stops the light scattered by particles passing through only one of the two laser beams, or worse, possible reflections of laser beams from the model or from the walls and the windows of the test chamber;
■ an interferometric filter with the wavelength of the laser stops the light from the environment or from any other source.