Revealing the nature of morphological changes in carbon nanotube-polymer saturable absorber under high-power laser irradiation

Composites of single-walled carbon nanotubes (SWNTs) and water-soluble polymers (WSP) are the focus of significant worldwide research due to a number of applications in biotechnology and photonics, particularly for ultrashort pulse generation. Despite the unique possibility of constructing non-linear optical SWNT-WSP composites with controlled optical properties, their thermal degradation threshold and limit of operational power remain unexplored. In this study, we discover the nature of the SWNTpolyvinyl alcohol (PVA) film thermal degradation and evaluate the modification of the composite properties under continuous high-power ultrashort pulse laser operation. Using high-precision optical microscopy and micro-Raman spectroscopy, we have examined SWNT-PVA films before and after continuous laser radiation exposure (up to 40 hours) with a maximum optical fluence of 2.3 mJ•cm−2. We demonstrate that high-intensity laser radiation results in measurable changes in the composition and morphology of the SWNT-PVA film due to efficient heat transfer from SWNTs to the polymer matrix. The saturable absorber modification does not affect the laser operational performance. We anticipate our work to be a starting point for more sophisticated research aimed at the enhancement of SWNTPVA films fabrication for their operation as reliable saturable absorbers in high-power ultrafast lasers.