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Using lasers to achieve controlled crystallographic phase changes in silicon with high spatial precision promises new manufacturing solutions in semiconductor technologies, including silicon photonics. Recent demonstrations of improved amorphization thicknesses position ultrafast lasers as an optimum tool to meet current challenges. Here, the literature on silicon transformations is reviewed and complemented with new experimental data. This includes amorphization and ablation response as a function of pulse duration (τ = 13.9 to 134 fs at λ = 800 nm) and laser wavelength (λ = 258 to 4000 nm with τ = 200 fs pulses). For pulse duration‐dependent studies on Si(111), the amorphization fluence threshold decreases with shorter durations, emphasizing the significance of non‐linear absorption in the range of considered conditions. For wavelength‐dependent studies, the amorphization threshold increases sharply from λ = 258 to 1030 nm, followed by near‐constant behavior up to λ = 3000 nm. Conversely, the ablation threshold fluence increases in these specified ranges. Differences in the obtained amorphization thicknesses on Si(111) and Si(100) are also discussed, identifying an anomalously large fluence range for amorphization at λ = 258 nm. Finally, the question of the lateral resolution, shown as independent of the interaction nonlinearity is addressed. [ABSTRACT FROM AUTHOR]

All‐dielectric nanophotonic devices are usually fabricated by engraving arrays of nanoholes at the surface of high‐index materials, to engineer dedicated optical functions. However, their direct 3D integration in the volume of a material is challenging, inaccessible to current planar nanolithography methods. Here is introduced an ultrafast laser‐machining method that opens the possibility to realize scalable arrays of hollow nanochannels directly inside the bulk of silica glass within a single‐step, maskless, and digital approach. Using a custom‐shaped micro‐Bessel beam and by tuning laser pulse durations from femtoseconds to picosecond to boost processing versatility, dense assemblies of nanochannels with adjustable lengths (up to 30 µm), and submicron lattice periodicity (down to 0.7 µm) are achieved. As a proof‐of‐principle demonstration, a gradient‐index metaphotonic structure is realized and its performance is experimentally characterized, demonstrating its relevancy for imprinting phase functions with magnitude up to π/2$\pi /2$ in the short‐wave infrared spectral range. Results show that the unique flexibility and scalability provided by individual control of each channel opens a new realistic alternative approach for 3D fabrication of monolithic integrated nanophotonic devices inside a wide range of low‐index standard optical materials. [ABSTRACT FROM AUTHOR]

Carrier kinetics in the density range of N = 1017 - 1020 cm-3 is investigated inside the bulk of crystalline silicon. Most conventional experimental techniques used to study carrier mobility are indirect and lack sensitivity because of charging effects and recombination on the surface. An all optical technique is used to overcome these obstacles. By focusing 1.3-µm femtosecond laser pulses in the volume, we inject an initial free-carrier population by two-photon absorption. Then, we use pump-and-probe infrared microscopy as a tool to obtain simultaneous measurements of the carrier diffusion and recombination dynamics in a microscale region deep inside the material. The rate equation model is used to simulate our experimental results. We report a constant ambipolar diffusion coefficient Da of 2:5 cm² s-1 and an effective carrier lifetime τeff of 2:5 ns at room temperature. A discussion on our findings at these high-injection levels is presented. [ABSTRACT FROM AUTHOR]

Two-photon ionization by focused femtosecond laser pulses initiates the development of micrometer-scale plasmas in the bulk of silicon. Using pump-and-probe transmission microscopy with infrared light, we investigate the space-time characteristics of these plasmas for laser intensities up to 101 2W/cm2 . The measurements reveal a self-limitation of the excitation at a maximum free-carrier density of ffi1019cm~3, which is more than one order of magnitude below the threshold for permanent modification. The plasmas remain unchanged in the --100 ps timescale revealing slow carrier kinetics. The results underline the limits in local control of silicon dielectric permittivity, which are inherent to the use of single near-infrared ultrashort Gaussian pulses. [ABSTRACT FROM AUTHOR]

Single-shot Gaussian-Bessel laser beams of 1 ps pulse duration and of ~ 0.9 μm core size and ~ 60 μm depth of focus are used for drilling micro-channels on front side of fused silica in ambient condition. Channels ablated at different pulse energies are fully characterized by AFM and post-processing polishing procedures. We identify experimental energy conditions (typically 1.5 µJ) suitable to fabricate non-tapered channels with mean diameter of ~ 1.2 µm and length of ~ 40 μm while maintaining an utmost quality of the front opening of the channels. In addition, by further applying accurate post-polishing procedure, channels with high surface quality and moderate aspect ratio down to a few units are accessible, which would find interest in the surface micro-structuring of materials, with perspective of further scalability to meta-material specifications. [ABSTRACT FROM AUTHOR]