| 摘要 |
A light source ( 1 ) sends towards an object under test ( 5 ) a light beam ( 2 ) with such a size as to encompass the object ( 5 ). Past the object, the beam ( 2 ) is processed by an optical processing system ( 6 ), comprising a band-pass spatial filter ( 8 ) located in the Fourier Plane of a converging lens ( 7 ), the object ( 5 ) being located in the front focal plane of that lens. The filtered beam is collected by a detector ( 10 ) that generates an electrical signal representative of the intensity of the field distribution associated with that beam. A system ( 11 ) for processing the electrical signal comprises a band-pass filter ( 12 ) with temporal cut-off frequencies corresponding with the spatial cut-off frequencies of the spatial filter in the optical processing system ( 6 ) and obtains the value of the requested quantity form the electrical signal.
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