Breakthrough solutions in resonance NIR laser texturing of polymers

The main project goal was to evaluate the performance of resonant photo-ablation of polymer films in the near infrared pulses. Every polymer has its own unique infrared absorption spectrum that serves as its “molecular fingerprint”. The ability to access many mid-IR wavelengths in this molecular fingerprint region is therefore necessary in order to resonantly excite different polymers. Therefore, tuneable OPO (optical parametric oscillator) based lasers offer possibilities to apply them in Resonant IR (RIR) ablation of polymers. The key to RIR ablation is that the excitation is resonant with a vibrational mode of the polymer target. Typical optical penetration depths of resonant IR light are much larger than penetration depths at UV wavelengths, and the corresponding volumetric energy density is much less. The criterion of resonant excitation is necessary in order to achieve successful material ablation. With lasers available in PONT experiment, RIR was tested in the overtone range of polymer vibrational modes of 1.5-1.8 µm. A comparison test was performed with ablation using UV laser sources. No evidence of the laser-induced polymer resonant ablation was observed in investigated IR region. The resonant ablation effects were negligible in the multi-pulse ablation regimes. Processing at this wavelength induced high thermal damage of samples (large heat affected zone, unstable melting of the material). To do significant damage to a sample by a single scan, it was required to use low scanning speed and high overlap (99.3%). At higher scanning speed thermal damage was lower, however, at such regime only irregular subsurface modifications were observed. A clean cut was not achieved even using higher scanning speed and multiple-scan technique. Possibly IR ablation was triggered by surface defect absorption, while bulk absorption was the very weak for investigated materials. In the case of UV (355 nm wavelength) laser ablation, the results were auspicious. Nanosecond UV pulses showed potential for membrane cutting applications. However, only picosecond UV pulses showed precise processing quality in the case of polymer structuring