Polarization-Dependent Anisotropy of LIPSSs' Morphology Evolution on a Single-Crystal Silicon Surface.

Utilizing the principle of laser-induced periodic surface structures (LIPSSs), this research delves into the morphological evolution of single-crystal silicon surfaces irradiated by a near-infrared picosecond laser through a scanning mode. With the increase in laser energy density, the nanostructure morphology on single-crystal silicon surfaces induced by incident lasers with different polarization directions sequentially produces high spatial-frequency LIPSSs (HSFLs) with a period of 220 nm ± 10 nm parallel to the laser polarization, low spatial-frequency LIPSSs (LSFLs) with a period of 770 nm ± 85 nm perpendicular to the direction of the polarization, and groove structures. Furthermore, by varying the angle between the laser polarization and the scanning direction, the study examined the combined anisotropic effects of the laser polarization scanning direction angle and the laser polarization crystal orientation angle on the genesis of LIPSSs on single-crystal silicon (100) surfaces.

Ultrafast laser-induced plasma anisotropy in pristine and surface pre-structured zinc telluride, probed by terahertz pulses.

We use THz probe pulses to detect and analyze the dynamics of charge transport anisotropies generated by ultrafast laser two-photon absorption in Zinc Telluride (ZnTe) semi-insulating crystal showing smooth and laser structured surfaces. The detected anisotropy consists in a modulation of the THz transmission as a function of the orientation of the <001 > axis of ZnTe. The change in THz transmission after pump excitation is attributed to free carrier absorption of the THz field in the laser-induced electron-hole plasma.

Ultrafast Cylindrical Vector Beams for Improved Energy Feedthrough and Low Roughness Surface Ablation of Metals.

The use of ultrafast cylindrical vector vortex beams in laser-matter interactions permits new ablation features to be harnessed from inhomogeneous distributions of polarization and beam geometry. As a consequence, the ablation process can yield higher ablation efficiency compared with conventional Gaussian beams. These beams prevent surface quality degradation during the ablative processes.

Polarization-Dependent Scattering of Nanogratings in Femtosecond Laser Photowritten Waveguides in Fused Silica.

The properties of polarization-selective, light-guiding systems upon subwavelength nanogratings formation in the case of type II refractive index traces induced by femtosecond laser pulses in bulk fused silica were studied. Polarization-dependent scattering is analyzed both in simulation using a finite-difference, time-domain method and in experiments. We argue that the polarization-sensitive optical guiding of type II waveguides is due to polarization-dependent scattering of nanogratings.

Ultrafast bandgap narrowing and cohesion loss of photoexcited fused silica.

Coupling and spatial localization of energy on ultrafast timescales and particularly on the timescale of the excitation pulse in ultrashort laser irradiated dielectric materials are key elements for enabling processing precision beyond the optical limit. Transforming matter on mesoscopic scales facilitates the definition of nanoscale photonic functions in optical glasses. On these timescales, quantum interactions induced by charge non-equilibrium become the main channel for energy uptake and transfer as well as for the material structural change.

Ruggedized, field-ready snapshot light-guide-based imaging spectrometer for environmental and remote sensing applications.

A field-ready, fiber-based high spatial sampling snapshot imaging spectrometer was developed for applications such as environmental monitoring and smart farming. The system achieves video rate frame transfer and exposure times down to a few hundred microseconds in typical daylight conditions with ∼63,000 spatial points and 32 spectral channels across the 470nm to 700nm wavelength range. We designed portable, ruggedized opto-mechanics to allow for imaging from an airborne platform.

Super-efficient drilling of metals with ultrafast non diffractive laser beams.

A highly efficient drilling process is found in non-transparent metallic materials enabled by the use of non-diffractive ultrafast Bessel beams. Applied for deep drilling through a 200 μm-thick steel plate, the Bessel beam demonstrates twofold higher drilling efficiency compared to a Gaussian beam of similar fluence and spot size. Notwithstanding that surface ablation occurs with the same efficiency for both beams, the drilling booster results from a self-replication and reconstruction of the beam along the axis, driven by internal reflections within the crater at quasi-grazing incidence, bypassing potential obstacles.

Index Modulation Embedded in Type I Waveguide Written by Femtosecond Laser in Fused Silica.

Slit-shaped laser beams focused in bulk optical materials can realize embedded waveguides with circular cross sections consisting of positive index change type I traces. In these kinds of waveguide traces, a peculiar periodical refractive index modulation was observed in type I waveguides with two different femtosecond lasers. The direction of refractive index modulation can be controlled with the slit configuration, and its period can be controlled by mechanical perturbation of the stages and the scanning speed.

Radiometric and design model for the tunable light-guide image processing snapshot spectrometer (TuLIPSS).

The tunable light-guide image processing snapshot spectrometer (TuLIPSS) is a novel remote sensing instrument that can capture a spectral image cube in a single snapshot. The optical modelling application for the absolute signal intensity on a single pixel of the sensor in TuLIPSS has been developed through a numerical simulation of the integral performance of each optical element in the TuLIPSS system. The absolute spectral intensity of TuLIPSS can be determined either from the absolute irradiance of the observed surface or from the tabulated spectral reflectance of various land covers and by the application of a global irradiance approach.

Nano-Crystal and Microstructure Formation in Fluoride Photo-Thermo-Refractive Glass Using Chirp-Controlled Ultrafast Laser Bessel Beams.

Nano-crystals were formed in the exposed regions of photo-thermo-refractive glass undergoing irradiation with zeroth order chirp-controlled ultrafast laser Bessel beams and subsequent heat treatment. Effects of various writing powers, pulse durations and heat treatment time on the distribution and the size of the nano-crystals were investigated. The results show that nano-crystals' distribution depended on the laser power density spatial shape, while the size of the nano-crystals is quasi-independent.

Non-Diffractive Bessel Beams for Ultrafast Laser Scanning Platform and Proof-Of-Concept Side-Wall Polishing of Additively Manufactured Parts.

We report the potential use of non-diffractive Bessel beam for ultrafast laser processing in additive manufacturing environments, its integration into a fast scanning platform, and proof-of-concept side-wall polishing of stainless steel-based additively fabricated parts. We demonstrate two key advantages of the zeroth-order Bessel beam: the significantly long non-diffractive length for large tolerance of sample positioning and the unique self-reconstruction property for un-disrupted beam access, despite the obstruction of metallic powders in the additive manufacturing environment. The integration of Bessel beam scanning platform is constructed by finely adapting the Bessel beam into a Galvano scanner.

Multiscale electronic and thermomechanical dynamics in ultrafast nanoscale laser structuring of bulk fused silica.

We describe the evolution of ultrafast-laser-excited bulk fused silica over the entire relaxation range in one-dimensional geometries fixed by non-diffractive beams. Irradiation drives local embedded modifications of the refractive index in the form of index increase in densified glass or in the form of nanoscale voids. A dual spectroscopic and imaging investigation procedure is proposed, coupling electronic excitation and thermodynamic relaxation.

Reconstructing of Embedded High-Aspect-Ratio Nano-Voids Generated by Ultrafast Laser Bessel Beams.

Ultrafast non-diffractive Bessel laser beams provide strong light confinement and show robust advantages for fabricating high-aspect-ratio nanoscale structures inside transparent materials. They take the form of nanoscale voids with typical diameters well below the wavelength and aspect ratio of more than 1000. Delivering 3D morphologies of such nanoscale voids is an important issue to evaluate the result for fabrication.

Light-guide snapshot imaging spectrometer for remote sensing applications.

A fiber-based snapshot imaging spectrometer was developed with a maximum of 31853 (~188 x 170) spatial sampling and 61 spectral channels in the 450nm-750nm range. A compact, custom-fabricated fiber bundle was used to sample the object image at the input and create void spaces between rows at the output for dispersion. The bundle was built using multicore 6x6 fiber block ribbons.

High fidelity visualization of multiscale dynamics of laser-induced bubbles in liquids containing gold nanoparticles.

Cavitation in pure liquids and in liquids containing nanoparticles enables applications in mechanics, bio-medicine, and energy. Its evolution carries a significant interest. We describe the multiscale dynamic evolution of ultrafast-laser-induced cavitation in pure and gold-nanoparticles-doped liquids in one-dimensional geometries induced by non-diffractive ultrashort Bessel-Gauss laser beams.

Femtosecond laser Bessel beam welding of transparent to non-transparent materials with large focal-position tolerant zone.

It is known that ultrashort laser welding of materials requires an accurate laser beam focusing and positioning onto the samples interface. This puts forward severe challenges for controlling the focus position particularly considering that the tightly focused Gaussian beam has a short, micron-sized Rayleigh range. Here we propose a large-focal-depth welding method to bond materials by using non-diffractive femtosecond laser Bessel beams.

In-situ high-resolution visualization of laser-induced periodic nanostructures driven by optical feedback.

Optical feedback is often evoked in laser-induced periodic nanostructures. Visualizing the coupling between surfaces and light requires highly-resolved imaging methods. We propose in-situ structured-illumination-microscopy to observe ultrafast-laser-induced nanostructures during fabrication on metallic glass surfaces.

Scattering effects and high-spatial-frequency nanostructures on ultrafast laser irradiated surfaces of zirconium metallic alloys with nano-scaled topographies.

The origin of high-spatial-frequency laser-induced periodic surface structures (HSFL) driven by incident ultrafast laser fields, with their ability to achieve structure resolutions below λ/2, is often obscured by the overlap with regular ripples patterns at quasi-wavelength periodicities. We experimentally demonstrate here employing defined surface topographies that these structures are intrinsically related to surface roughness in the nano-scale domain. Using Zr-based bulk metallic glass (Zr-BMG) and its crystalline alloy (Zr-CA) counterpart formed by thermal annealing from its glassy precursor, we prepared surfaces showing either smooth appearances on thermoplastic BMG or high-density nano-protuberances from randomly distributed embedded nano-crystallites with average sizes below 200 nm on the recrystallized alloy.

Expanded-core waveguides written by femtosecond laser irradiation in bulk optical glasses.

Expanded-core structures based on layered increased index (type I) waveguiding traces are fabricated by ultrafast laser photoinscription in bulk optical glasses, with examples for fused silica and chalcogenide glasses. The expanded-core waveguides can serve for large-mode-area guiding concepts and their feasibility is experimentally investigated. A parametric study of the geometry, number of traces and index contrast indicates the possibility to design guided modes characteristics as exemplified in fused silica.

Embedded optical waveguides fabricated in SF10 glass by low-repetition-rate ultrafast laser.

Symmetric embedded waveguides were fabricated in heavy metal oxide SF10 glass using slit-shaped infrared femtosecond laser writing in the low-repetition frequency regime. The impact of the writing parameters on the waveguide formation in the transverse writing scheme was systemically studied. Results indicate that efficient waveguides can be inscribed in a wide parameter space ranging from 500 fs to 1.

Formation of nanogratings in a transparent material with tunable ionization property by femtosecond laser irradiation.

Irradiation inside some transparent materials such as fused silica can induce nanograting structures at the focal area. Here, we investigate experimentally how the nanograting formation can be influenced by tuning the ionization property of the transparent material, which is achieved by irradiation inside a porous glass immersed in water doped with NaCl at variable concentrations. Our results show that the doping of NaCl not only reduces the threshold fluence of optical breakdown, but also leads to nanograting structures with shorter periods.

Femtosecond multi-beam interference lithography based on dynamic wavefront engineering.

A method for precise multi-spot parallel ultrafast laser material structuring is presented based on multi-beam interference generated by dynamic spatial phase engineering. A Spatial Light Modulator (SLM) and digitally programming of phase masks are used to accomplish the function of a multi-facet pyramid lens, so that the laser beam can be spatially modulated to create beam multiplexing and desired two-dimensional (2D) multi-beam interference patterns. Various periodic microstructures on metallic alloy surfaces are fabricated with this technique.

Stressed waveguides with tubular depressed-cladding inscribed in phosphate glasses by femtosecond hollow laser beams.

We report on the single-step fabrication of stressed optical waveguides with tubular depressed-refractive-index cladding in phosphate glasses by the use of focused femtosecond hollow laser beams. Tubelike low index regions appear under direct exposure due to material rarefaction following expansion. Strained compacted zones emerged in domains neighboring the tubular track of lower refractive index, and waveguiding occurs mainly within the tube core fabricated by the engineered femtosecond laser beam.

Polarization behavior of femtosecond laser written optical waveguides in Ti:Sapphire.

Ultrashort pulsed laser photoinscription of Ti:Sapphire crystals may result in the self-organization of nanoscale material redistribution regions in regular patterns within the laser trace and stress-induced birefringence around the laser trace. We report on the formation of anisotropic optical waveguides in Ti:Sapphire by a procedure that involves femtosecond laser inscription of adjacent nonguiding birefringent traces with nanopatterned crosssections and the accumulation of stress birefringence in the region between. Double parallel line structures with a separation of 25μm with vertical and horizontal nanoscale arrangements were written with a choice of orthogonal polarizations.