Ultrashort-pulsed lasers have been used for high precision processing of a wide range of materials including dielectrics, semiconductors, metals, and polymers/polymer composites, enabling numerous applications ranging from micromachining, photonics to life sciences. However, there are challenges when applying this technology in the industry, which requires scale and throughput different from lab use. The goal of this research is to understand how ultrafast laser pulses interact with thin polymers/polymer composite materials and develop a method that is efficient for ultrafast laser processing of these materials. It is a common practice in industrial applications to run the laser at a high repetition rate and hence high average power. However, the heat accumulation under such processing conditions will deteriorate the processing quality, especially for polymers, which typically have a low melting temperature. An analytical solution for two-dimensional modeling of the temperature distribution has been presented and the solution is used to understand the effect of laser parameters on ultrafast laser processing of polypropylene (PP), which is an important polymer for both scientific and industrial applications. Laser cutting experiments are carried out on PP sheets to correlate with the theoretical calculation. This study shows that in laser cutting, the total energy absorbed in the material and the intensity are two important figures of merit to predict the cutting performance. It is found that heat accumulation can be avoided by a proper choice of the processing conditions and the optical properties (i.e. reflectance, transmittance, and absorptance) are important parameters to control processing with ultrafast lasers. To determine the reflectance, transmittance, and absorptance, time-resolved, single-shot measurements are performed in ultrafast laser interaction with polypropylene for a wide range of laser pulse energies. The absorptance during the ultrafast laser interaction with polymers is divided into the different linear and non-linear effective absorption channels and the absorption mechanism of ultrafast laser interaction with polymers in near-infrared wavelength are explained with a model that takes into account different effective absorption channels and suggests that the non-linear absorption originates from vibrational overtone/combination absorption. The enhancement of the absorptance has been investigated for efficiently processing thin polymers with ultrafast lasers by changing pulse duration. It is suggested from this study that the intense shorter pulse (167 fs) is more efficient for surface processing as most of the energy absorbed at the surface due to the strong nonlinear absorption, while a longer pulse (1000 fs) is more efficient for bulk processing for polymers. The results are useful for designing and controlling ultrafast laser processing of polymers and optimizing laser process parameters for the most efficient processing of polymers.
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Doctor of Philosophy (Ph.D.)
College of Optics and Photonics
Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Rahaman, Arifur, "Enhancement of absorptance by ultrafast laser pulse shaping for efficient laser processing of thin polymers" (2020). Electronic Theses and Dissertations, 2020-. 616.