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The dependence of the ablation rate on the laser fluence was measured in femtosecond laser processing of polydimethylsiloxane, and the slope of the ablation rate tended to change to three ablation regimes. The laser-irradiated area was analyzed using Raman and photoluminescence spectroscopy to investigate the cause of the changes in the slope in terms of chemical structural changes. We will show that microscopic observation of the cross-sectional sample enables the analysis of grooves with a high aspect ratio that could not be measured by conventional observation from the sample surface. This allows us to discuss the correlation between the ablation rate and chemical structural changes over a wide range of fluences up to the high fluence regime. As a result, it was found that in the low fluence regime, the photochemical process is dominant with the gentle slope of ablation rate, while both photochemical and photothermal processes lead to an increase in the slope in the middle fluence regime. Moreover, the steep slope in the high fluence regime was induced by high temperatures where carbon–carbon bond formation takes place. [ABSTRACT FROM AUTHOR]

The benefits of micro-textures on cutting tools have been confirmed widely in implementing sustainable machining. However, the derivative cutting processes induced by the sharp edges of textures weakened the potential benefits. In our preliminary work, the newly designed curvilinear micro-grooved cutting tool has been proved to eliminate derivative cutting processes and implement sustainable machining than non-textured tools by three-dimensional (3D) finite element (FE) simulations. In this paper, the curvilinear micro-groove structures were optimized and fabricated to further improve the cutting performance of minimizing specific cutting energy. The results indicated that all the micro-groove parameters, including the width, spacing, depth, and edge distance (the distance from cutting edge to the micro-grooved area), showed obvious influence on specific cutting energy in their own ways. Specific cutting energy of the metal cutting processes can be effectively reduced by the optimal curvilinear micro-grooved cutting tools, although the optimal structures used in rough and finish turning conditions were different. In addition, a new two-step method was developed in this work to prepare curvilinear micro-grooves on carbide tools with femtosecond laser. The optimal curvilinear micro-grooved cutting tools were fabricated and used in cutting experiments, which verified the simulative results. [ABSTRACT FROM AUTHOR]

In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Spikes produced at higher fluences and effective number of pulses per unit area present even thicker graded oxide layers that are also suitable for friction reduction and wear resistance. Ultimately, these femtosecond laser-induced nanostructured surface layers efficiently prevent a direct metal-to-metal contact in the RSTT and may act as an anchor layer for specific wear-reducing additives contained in the used engine oil. [ABSTRACT FROM AUTHOR]

In this paper, we reviewed the fabrications of functional microcavity lasers in soft materials such as polymer and protein by femtosecond laser processing. High-quality ( Q) microdisks with a laser dye (Rhodamine B, RhB) acting as gain medium were fabricated that produced whispering-gallery-mode (WGM) lasing output. We also obtained unidirectional lasing output with a low lasing threshold in a deformed spiral microcavity at room temperature. Photonic-molecule (PM) microlasers were prepared to investigate the interaction and coupling effects of different cavities, and it was found that the distance between the two disks plays an important role in the lasing behaviors. Single-mode lasing was realized from a stacked PM microlaser through Vernier effect. Furthermore we adopted the biocompatible materials, RhB-doped proteins as a host material and fabricated a three-dimensional (3D) WGM microlaser, which operated well both in air and aqueous environment. The sensing of the protein micro-lasers to NaSO concentration was investigated. Our results of fabricating high- Q microlasers with different materials reveal the potential applications of femtosecond laser processing in the areas of integrated optoelectronic and ultrahigh sensitive bio-sensing devices. [ABSTRACT FROM AUTHOR]

Bimetallic, initially spherical Ag/Au nanoparticles in glass prepared by ion implantation have been irradiated with intense femtosecond laser pulses at intensities still below the damage threshold of the material surface. This high-intensity laser processing produces dichroism in the irradiated region, which can be assigned to the observed anisotropic nanoparticle shapes with preferential orientation of the longer particle axis along the direction of laser polarization. In addition, the particle sizes have considerably been increased upon processing. [ABSTRACT FROM AUTHOR]

The article focuses on the demonstration of parallel femtosecond laser processing with a computer generated hologram displayed on a liquid crystal spatial light modulator (SLM). The SLM enables the performance of an arbitrary and variable patterning in laser processing. The hologram uses multiplexed phase Fresnel lenses that is optimized by changing the center phase and size of each lens.

The paper addresses the creation of circular optical properties from a femtosecond laser light beam with a linear polarization in an achiral material (glass) under an orthogonal incidence. In this situation, all aspects of the experiment are achiral and therefore should not give rise to chiral property creation. From that observation, we propose an interpretation that involves the action of a light-induced torque on the matter carrying a light-induced dielectric moment. We found that a direct current (DC) electric field could be produced in the lattice by the femtosecond laser in our conditions and that a non-collinear dielectric moment is created by a nonlinear effect between the DC electric field and the stress field due to the transformation of the material. We reveal that it is possible to break the chiral symmetry of glass using an intense, ultrashort laser light pulse., Competing Interests: The authors declare no conflict of interest.