Enhanced nonlinear optical properties for SWNT-PVA composite film by thermal treatment

Single-walled carbon nanotube-polyvinyl alcohol (SWNT-PVA) composite film, which can be used as a saturable absorber, has exhibited an excellent nonlinear optical property, especially for ultrafast photonics application. However, the main issue is its low damage threshold, which can be attributed to the agglomeration phenomenon of carbon nanotube (CNT) and the thermal cumulation effect. Herein, we proposed a simple thermal treatment method for enhancing the damage threshold and nonlinear optical property of SWNT-PVA composite film. By subjecting the composite film to appropriate heating, the surface area of the film is significantly enlarged, thereby reducing the agglomeration of CNTs. The thermal treatment procedure not only improves the surface characteristics but also ensures an enhancement of damage threshold with time and power, respectively. Within a specific temperature range, the modulation depth and saturable intensity exhibited enhancements, whereas the non-saturable loss decreases owing to the thermal treatment. This work not only presents a straightforward approach to improve the nonlinear optical property of CNT-PVA based saturable absorber for mode-locking fiber lasers, but also offers valuable insights for optimizing the performance of other low-dimensional nanomaterials based on carbon elements for the application of ultrafast photonics.