AN APPARATUS AND A METHOD FOR ACQUIRING AND PROCESSING IMAGES TO DETERMINE A PHYSICAL PROPERTY OF A PRODUCT

An image acquisition and processing apparatus (1) to determine a physical property of a product (2) movable along an advancement direction (A) comprises: - a source of electromagnetic radiation (9) arranged to generate a beam of electromagnetic waves (10)， each electromagnetic wave having a frequency in the range of 0.05 – 5 THz， the product (2) being made of a material at least partially transparent to said frequency range; - a beam splitter (11) arranged to divide the beam of electromagnetic waves (10) into at least one reference beam (5) having a predetermined intensity and arranged to travel along a path in air and into at least one measure beam (6) arranged to travel a path through a section (22) of said product (2)， the at least one measure beam (6) hitting a first face (7) of the product (2) with a first intensity and emerging from a second face (8) of the product (2) with a second intensity different from the first intensity and dependent on a material of which the product (2) is made; - an image acquisition device (12) arranged to receive the at least one reference beam (5) and the at least one measure beam (6) and acquire an image of an interference pattern due to the recombination of said at least one reference beam (5) and the at least one measure beam (6) in the image acquisition device (12); - first optical means (14) arranged to direct the at least one reference beam (5) from the beam splitter (11) to the image acquisition device (12); - second optical means (15) arranged to direct the at least one measure beam (6) from the beam splitter (11) to the image acquisition device (12); - processing means arranged to process the image of an interference pattern and calculate a phase shift of the at least one measure beam (6) traversing the product (2) and recombined to the at least one reference beam (5) with respect to said at least one measure beam (6) recombined to said at least one reference beam (5) when said product (2) has been removed from the apparatus (1)， the processing means being configured to correlate the phase shift with a precalculated calibration curve that associates known values of a physical property with phase shift values of a measure beam (6); the first optical means (14) and the second optical means (15) being configured to recombine the at least one reference beam (5) and the at least one measure beam (6) with a recombination angle (Ψ) chosen so that on the image acquisition device (12) it is possible 35 to display at least two fringe peaks of the interference pattern due to the recombination of the at least one reference beam (5) and the at least one measure beam (6).