Study on Ablation Characteristics of Femyosecond Laser Nanoscale Processing for Aluminum Nitride and LeadZirconate Titanate Ceramics

This paper analytically investigates an ultrashort pulsed laser nanoscale processing for aluminum nitride (AIN) and lead zirconate titanate (PZT) ceramics. Processing characteristics of an ultra-short pulsed laser is different from that of long-pulsed laser due to ultrahigh intensity, ultrahigh power, and ultrashort time. The ultrasmall processing for materials can achieved by an ultra-short pulsed laser. This study proposes a model to analyze an ultrashort pulsed laser nanoscale processing for aluminum nitride (AIN) and lead zirconate titanate (PZT) ceramics. The effects of optical penetration absorption and thermal diffusion on temperature are also discussed. The results reveal that the variation of ablation rate with laser fluences predicted by this work agrees with the available measured data for an ultrashort pulsed laser processing for AIN and PZT. For femtosecond lasers, the optical absorption and thermal diffusion, respectively, governs the ablated depth per pulse at the low and high laser fluences. The thermal diffusion length is small relative to the optical penetration depth for femtosecond laser. The optical penetration absorption governs the temperature in the workpiece. On the other hand, for the picosecond laser, the thermal diffusion length is large compared to the optical penetration depth. The thermal diffusion determines the temperature in the workpiece.

Heat impact during laser ablation extraction of mineralised tissue micropillars

The underlying constraint of ultrashort pulsed laser ablation in both the clinical and micromachining setting is the uncertainty regarding the impact on the composition of material surrounding the ablated region. A heat model representing the laser-tissue interaction was implemented into a finite element suite to assess the cumulative temperature response of bone during ultrashort pulsed laser ablation. As an example, we focus on the extraction of mineralised collagen fibre micropillars. Laser induced heating can cause denaturation of the collagen, resulting in ultrastructural loss which could affect mechanical testing results. Laser parameters were taken from a used micropillar extraction protocol. The laser scanning pattern consisted of 4085 pulses, with a final radial pass being 22 $$\upmu {\text {m}}$$ μ m away from the micropillar. The micropillar temperature was elevated to 70.58 $$^{\circ }{\text {C}}$$ ∘ C , remaining 79.42 $$^{\circ }{\text {C}}$$ ∘ C lower than that of which we interpret as an onset for denaturation. We verified the results by means of Raman microscopy and Energy Dispersive X-ray Microanalysis and found the laser-material interaction had no effect on the collagen molecules or mineral nanocrystals that constitute the micropillars. We, thus, show that ultrashort pulsed laser ablation is a safe and viable tool to fabricate bone specimens for mechanical testing at the micro- and nanoscale and we provide a computational model to efficiently assess this.