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Gigahertz (GHz) femtosecond (fs) lasers have opened possibilities for enhancing and controlling the laser machining quality to engineer the physicochemical properties of materials. However, fundamental understanding of laser-material interactions by GHz fs laser has remained unsolved due to the complexity of associated ablation dynamics. Here, we study the ablation dynamics of copper (Cu) by GHz fs bursts using in situ multimodal diagnostics, time-resolved scattering imaging, emission imaging, and emission spectroscopy. A combination of probing techniques reveals that GHz fs bursts rapidly remove molten Cu from the irradiated spot due to the recoil pressure exerted by following fs pulses. Material ejection essentially stops right after the burst irradiation due to the limited amount of remnant matter, combined with the suppressed heat conduction into the target material. Our work provides insights into the complex ablation mechanisms incurred by GHz fs bursts, which are critical in selecting optimal laser conditions in cross-cutting processing, micro/nano-fabrication, and spectroscopy applications.

In this work, we studied single-pulse ablation dynamics of a temporally modulated continuous wave laser-material interaction with Al using in situ multimodal time-resolved diagnostics that describe in detail the associated physical and chemical processes. Time-resolved scattering, emission imaging, and optical emission spectroscopy unveiled a sequence of events spread out across three distinct phases: (i) early phase ablation process, associated with particle generation and liquid Al column formation (

Graphite is a key material in a variety of cross-cutting applications in energy conversion, energy storage, and nuclear energy. Recently, temporally modulated continuous wave lasers have been shown to produce well-defined ablation features in graphite at relatively high processing speeds. In this work, we analyze in detail the laser ablation dynamics of single-pulse ablation in the sub-millisecond time regime to elucidate the origins of the resulting well-defined ablation craters using a combination of time-resolved emission imaging, diffuse reflection/scattering imaging, and optical emission spectroscopy. These multimodal in situ diagnostics revealed three main contributors to achieve well-defined ablation features: (1) rapid ejection of particles with ∼100 m/s speed, (2) ablation of the graphite in the gaseous form, and (3) absence of bulk liquid motion, which is typically observed in laser processing of metals. Plasma plume formation was sustained throughout the duration of the laser pulse (500 [Formula: see text]s). This work provides insights into the complex physical and chemical mechanisms of sub-millisecond laser–matter interactions, which are critical for parameter space optimization and tailoring of laser machining and drilling processes.

Polydopamine (PDA) is a simple and versatile conformal coating material that has been proposed for a variety of uses; however in practice its performance is often hindered by poor mechanical properties and high roughness. Here, we show that blue-diode laser annealing dramatically improves mechanical performance and reduces roughness of PDA coatings. Laser-annealed PDA (LAPDA) was shown to be >100-fold more scratch resistant than pristine PDA and even better than hard inorganic substrates, which we attribute to partial graphitization and covalent coupling between PDA subunits during annealing. Moreover, laser annealing provides these benefits while preserving other attractive properties of PDA, as demonstrated by the superior biofouling resistance of antifouling polymer-grafted LAPDA compared to PDA modified with the same polymer. Our work suggests that laser annealing may allow the use of PDA in mechanically demanding applications previously considered inaccessible, without sacrificing the functional versatility that is so characteristic of PDA., The ability to alter surface chemistry on a variety of materials makes polydopamine (PDA) and excellent surface coating material, but weak wear resistance and high surface roughness limits its application. Here, the authors demonstrate a laser annealing process to improve the mechanical properties of PDA coatings.

To examine the ablation dynamics of silver thin films by femtosecond laser, we experimentally investigate the plume evolution and behavior of ejected nanoparticles (NPs) via emission and scattering spectroscopy measurements under background pressures of 760 torr, 5 torr, 5 x 10-3 torr, to 3 x 10-5 torr. The emission spectroscopy experiments show that the propagation of the ablated plume is affected by ambient pressure. The higher the pressure, the more the propagation of the plasma is suppressed. Under higher vacuum, the lifetime of plasma is shorter due to diminished collisions with background molecules. The evolution of plasma lasts more than 200 ns under 760 torr while it does not exceed 200 ns under high vacuum (3 x 10-5 torr). Through the scattering measurements, the average propagation speed of NPs is 200 m/s under 3 x 10-5 torr, 190 m/s under 5 x 10-3 torr, 155 m/s under 5 torr, and 120 m/s under 760 torr. The ejected nanoparticles from the periphery of the ablated spot exhibit oblique trajectories because of the exerted recoil pressure at the spot center region that is subject to high incident energy densities.

Cardiac tissues are able to adjust their contractile behavior to adapt to the local mechanical environment. Nonuniformity of the native tissue mechanical properties contributes to the development of heart dysfunctions, yet the current in vitro cardiac tissue models often fail to recapitulate the mechanical nonuniformity. To address this issue, a 3D cardiac microtissue model was developed with engineered mechanical nonuniformity, enabled by 3D-printed hybrid matrices composed of fibers with different diameters. When escalating the complexity of tissue mechanical environment, cardiac microtissues started to develop maladaptive hyper-contractile phenotypes, demonstrated in both contractile motion analysis and force-power analysis. This novel hybrid system could potentially facilitate the establishment of “pathologically-inspired” cardiac microtissue model for deeper understanding of heart pathology due to nonuniformity of the tissue mechanical environment.

Time-resolved emission and scattering imaging are employed to analyze the ablation mechanisms of silver thin films induced by femtosecond laser irradiation of Gaussian intensity profile under different laser fluences and gas background pressures. At fluences near the ablation threshold, nanoparticles (NPs) of 40 nm–100 nm in size are ejected in the vertical direction from the target sample. The average ejection speed of these NPs increases with the laser fluence and also as the background gas pressure drops from ambient atmospheric to ∼10−5 Torr. At higher fluences, a plume is formed at the center of the laser beam and NPs are released in oblique trajectories from the peripheral area of the laser-irradiated spot.

The low temperature polycrystalline silicon (LTPS) method has proved to be a technical breakthrough, accomplishing semiconductor thin films with remarkable mobility for a range of high-performance displays, including liquid crystal display and organic light emitting diodes. However, utilizing a conventional excimer laser source for LTPS incurs high cost. In this paper, we demonstrate a comprehensive analysis of the crystallization mechanism of a-Si film (94 nm) and the thermal deformation of the glass substrate induced by Blue diode Laser Annealing (BLA). BLA provides high quality laterally grown crystals over 4 µm × 10 µm on glass substrates, which were examined by optical microscopy, scanning electron microscopy, and Raman spectroscopy. In addition, the permanent deformation introduced by the annealing process is numerically modeled, instantiating how to control the heat conduction from the thin film that affects the substrate. Our findings reveal that the permanent thermal deformation depth that can be obtained is comparable to the roughness of the silicon film for the optimum scanning speed and laser power. The combination of both experimental and numerical results elucidates the manifested physical mechanisms during the BLA process and provides the guidelines to improve the experimental parameters of this process.