Investigation on optical switching behaviour of regenerated and non-regenerated silk by nanosecond Z-scan technique

Abstract

The nonlinear optical behaviour of silk, a natural fibre, is investigated in this study. We have considered silk in the cocoon, fibre and film forms of bivoltine and multivoltine breeds. The nonlinear absorption and optical limiting studies were performed using the open aperture Z-scan technique at 1064 nm. Interestingly, silk in cocoon and fibre form possess saturable absorption (SA), whereas silk in the film form exhibits reverse saturable absorption (RSA). This shift is attributed to the removal of sericin during the regeneration of silk into a film. Further, silk films exhibit optical limiting behaviour, whose limiting thresholds are in the order of 1012 W cm−2. Functional data analysis (FDA), a statistical approach, is employed to draw correlations amongst physical parameters. FDA offers good insight into the dependencies between silk varieties and their optical parameters. This helps in identifying the sample possessing the best properties.