Picosecond laser ablation of poly-L-lactide: Effect of crystallinity on the material response

Abstract

The picosecond laser ablation of poly-L-lactide (PLLA) as a function of laser fluence and degree of crystallinity was examined. The ablation parameters and the surface modifications were analyzed under various irradiation conditions using laser wavelengths ranging from the ultraviolet through the visible. When processing the amorphous PLLA, both energy threshold and topography varied considerably depending on laser wavelength. Laser irradiation showed a reduction in the energy ablation threshold as the degree of crystallinity increased, probably related to photomechanical effects involved in laser ablation with ultra-short pulses and the lower stress accommodation behavior of semicrystalline polymers. In particular, cooperative chain motions are impeded by the higher degree of crystallinity, showing fragile mechanical behavior and lower energy dissipation. The experimental results on ablation rate versus laser energy showed that UV laser ablation on semicrystalline PLLA was more efficient than the visible ablation, i.e., it exhibits higher etch rates over a wide range of pulse energy conditions. These results were interpreted in terms of photo-thermal and photo-chemical response of polymers as a function of material micro-structure and incident laser wavelength. High quality micro-grooves were produced in amorphous PLLA, reveling the potential of ultra-fast laser processing technique in the field of micro-structuring biocompatible and biodegradable polymers for biomedical applications.

355, 532, and 1064 nm picosecond laser interaction with grass tissues

“…[5][6][7][8][9][10] Plant leaves, especially green leaves, are common landscaping and agricultural materials and lasers could be creatively used for many possible innovative applications. Plant leaves exhibit very complicated optical properties because they have complex multilayer structures and are basically a composite of many dissimilar optical elements, including photosynthesizing pigments.…”

CO2and Er:YAG laser interaction with grass tissues

“…Comparing interaction maps for CO 2 and Er:YAG lasers (Figures 11(c) and 11(d)), we can notice that, although different lasers were used, the two interaction maps are matched reasonably well. However, there are three major mismatches: the Er:YAG laser seems to have higher threshold values for carbonization, decoloration, and through-cut processes.…”

“…In this study, CO 2 and Er:YAG laser interaction with grass tissues was studied theoretically and experimentally. In both cases, the absorption of light is dominated by water and the amount of light absorption is >98%.…”

“…Scanning electron microscopy (SEM) and optical microscopy are employed for studying morphological and structural changes in grass tissues after laser irradiation. This study reveals interesting findings regarding carbonization and ablation mechanisms, the effect of laser beam diameter, and the ablation efficiency and quality of CO 2 and Er:YAG lasers.…”

“…[1][2][3][4][5][6] In recent years, laser interaction with biological tissues has become an important research topic. Biological tissues are multi-component composite systems and are much more difficult to study in comparison to common engineering materials: they are hard to manipulate, and accurate optical properties are not available.…”