*Article* **Interferometric Instrument for Thickness Measurement on Blown Films**

**Michele Norgia \* and Alessandro Pesatori**

Politecnico di Milano, Dipartimento di Elettronica e Informazione e Bioingegneria (DEIB), Piazza Leonardo da Vinci 32, 20133 Milano, Italy; alessandro.pesatori@polimi.it **\***Correspondence:michele.norgia@polimi.it

**Abstract:** Real-time measurement of plastic film thickness during production is extremely important to guarantee planarity of the final film. Standard techniques are based on capacitive measurements, in close contact with the film. These techniques require continuous calibration and temperature compensation, while their contact can damage the film. Different optical contactless techniques are described in literature, but none has found application to real production, due to the strong vibration of the films. We propose a new structure of low-coherence fiber interferometer able to measure blown film thickness during productions. The novel fiber-optic setup is a cross between an autocorrelator and a white light interferometer, taking the advantages of both approaches.

**Keywords:** low-coherence interferometry; thickness measurement; optical coherence tomography; plastics measurement
