Femtosecond laser-induced black silicon: a dual application in photodetection and surface-enhanced Raman scattering.

A multifunctional structured silicon with enhanced optical and photoelectric properties has been processed by femtosecond (fs) laser in ambient air. The structured surface decorated with Au nanoparticles (NPs) exhibits excellent infrared absorption properties related to localized surface plasmon resonance (LSPR) coupled to microstructures. Over 75% absorption is achieved at 1550 nm, which is three orders of magnitude higher than that of unprocessed Si.

Direct Fabrication of Te-Doped Black Si with an Enhanced Photoelectric Performance by Femtosecond Laser Irradiation under Water.

Tellurium (Te)-doped black silicon (Si) with enhanced absorption and photoelectric performance over a broad wavelength range of 0.2-2.5 μm was obtained using femtosecond (fs) laser irradiation in liquid water.

Periodic Surface Structuring of Copper with Spherical and Cylindrical Lenses.

The use of a cylindrical lens in femtosecond laser surface structuring is receiving attention to improve the processing efficiency. Here, we investigate the structures produced on a copper target, in air, by exploiting both spherical and cylindrical lenses for beam focusing, aiming at elucidating similarities and differences of the two approaches. The morphological features of the surface structures generated by ≈180 fs laser pulses at 1030 nm over areas of 8 × 8 mm were analyzed.

Generation of Supra-Wavelength Grooves in Femtosecond Laser Surface Structuring of Silicon.

Extensive research work has been carried out on the generation and application of laser-induced periodic surface structures (LIPSS). LIPSS with a sub-wavelength period generated by femtosecond laser irradiation, generally indicated as ripples, have been extensively investigated. Instead, the other ordered surface structures characterized by a supra-wavelength period, indicated as grooves, have been much less studied.

Parameter optimization of a visibility LiDAR for sea-fog early warnings.

Sea fog represents a significant risk for safe navigation of sea vessels. Visibility LiDAR systems might offer a striking way to reduce the risks associated with sea fog, but they should be appropriately designed to provide a proper level of detection for reliable forewarning of sea fog. Here we analyze the performances of a visibility LiDAR system with the aim of achieving optimal detection operation.

Surface structures with unconventional patterns and shapes generated by femtosecond structured light fields.

We present an investigation on ultrashort laser surface structuring with structured light fields generated by various q-plates. In particular, q-plates with topological charges q = 1, 3/2, 2, 5/2 are used to generate femtosecond (fs) vector vortex beams, and form complex periodic surface structures through multi-pulse ablation of a solid crystalline silicon target. We show how optical retardation tuning of the q-plate offers a feasible way to vary the fluence transverse distribution of the beam, thus allowing the production of structures with peculiar shapes, which depend on the value of q.

Analysis of nascent silicon phase-change gratings induced by femtosecond laser irradiation in vacuum.

The formation of periodic surface structures is a general effect of femtosecond laser irradiation of solid targets showing promising interest in material science and technology. However, the experiments are typically carried out in air, a condition in which the target surface becomes densely decorated with nanoparticles that can influence the formation of the surface structures in the early stage of the irradiation process. Here we report an investigation of structures generation on a silicon surface irradiated in vacuum (10 mbar) with a low number of laser pulses (N ≤ 10) that exploits several microscopy techniques (optical, atomic force, electron and Raman).

Surface Structuring with Polarization-Singular Femtosecond Laser Beams Generated by a q-plate.

In the last few years femtosecond optical vortex beams with different spatial distributions of the state of polarization (e.g. azimuthal, radial, spiral, etc.

Chromatic annuli formation and sample oxidation on copper thin films by femtosecond laser.

We report an experimental investigation on the irradiation of copper thin films with high repetition rate femtosecond laser pulses (1040 nm, 50 MHz), in ambient air and liquid water. We observe a novel, striking phenomenon of chromatic copper oxides (CuO and Cu2O) annuli generation. The characteristic features of the chromatic copper oxide annuli are studied by exploiting micro-Raman spectroscopy, optical and scanning electron microscopies.

On the generation of grooves on crystalline silicon irradiated by femtosecond laser pulses.

Irradiation of crystalline silicon with femtosecond laser pulses produces a variety of quasi-periodic surface structures, among which sub-wavelength ripples creation is largely studied. Here we report an experimental investigation and a theoretical interpretation focusing on the seldom considered issue of quasi-periodic, micron spaced grooves formation. We characterize the morphological evolution of the grooves generation and experimentally single out the variation of the threshold fluence for their formation with the number of pulses N, while typical ripples simultaneously produced in the irradiated area are always considered for comparison.

Direct Femtosecond Laser Surface Structuring with Optical Vortex Beams Generated by a q-plate.

Creation of patterns and structures on surfaces at the micro- and nano-scale is a field of growing interest. Direct femtosecond laser surface structuring with a Gaussian-like beam intensity profile has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. Here we present an approach for direct femtosecond laser surface structuring based on optical vortex beams with different spatial distributions of the state of polarization, which are easily generated by means of a q-plate.

Thermalization of a UV laser ablation plume in a background gas: From a directed to a diffusionlike flow.

Combined diagnostic measurements of deposition rates and ion time-of-flight signals have been employed to study the expansion of a laser ablation plume into a background gas. With increasing gas pressure the angular distribution of the collected ablated atoms becomes broader, while the total collected yield decreases. The total collected yield shows three separate regimes with increasing pressure, a vacuumlike regime, a transition regime with increasing plume broadening and splitting of the ion signal, and at the highest pressure a diffusionlike regime with a broad angular distribution.