Nonray-tracing determination of the 3D refractive index profile of polymeric fibres using single-frame computed tomography and digital holographic interferometric technique

In this paper, we present a nonray-tracing technique for evaluating
the three dimensional distribution of the refractive
index values inside polymeric fibres. This technique, named
‘single-frame computed-tomography (SFCT)’, is applied to digital
holography. A comparative study between the calculated
optical phase values using ordinary tomography and SFCT is
carried out,andanegligible deviation isdetected.Theproposed
technique is used to determine the three-dimensional refractive
index profile of isotactic Polypropylene fibres, IPP. The
variation of the optical properties is measured before, during
and after the formation of the necking phenomenon. In addition,
SFCT technique is applied to the online determination of
the change of the optical properties of IPP fibres. Holograms
are given for illustration.