High-frequency photothermal processing of commercial polymers under femtosecond laser irradiation for waveguide writing

Abstract

The processing of three commonly used commercial polymer films (poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET) and polypropylene (PP)) with different thermal properties under femtosecond (450 fs) irradiations at high frequency (1 kHz-1 MHz) multi-pulse (N=10-18000) laser at λ=515 (1.34 J/cm2, radius 9 μm) is analysed in order to have knowledge of which material and laser conditions are more suitable to write waveguides. Thermal and ablative effects are observed after laser irradiations. Heat accumulation effects of successive pulses impinging are simulated through a photothermal model in order to explain the results of irradiating these materials. Thermal analyses (Modulated Differential Scanning Calorimetry (MDSC) and Thermogravimetry (TG)) are performed and used to explain the different behaviour of each polymer. Three different regimes (non-thermal, thermal and saturation) are identified and explained from the model and experimental results. A connection between ablation depth and simulated reached temperature is established. A study of which number of pulses/spot area and frequency are appropriate for a better shape and ablation depth for writing waveguides on these polymers is performed.