Femtosecond Laser Nanostructuring Research Articles

Optical configurations for applying antireflective nanotexture on spherical lenses by ultrashort laser structuring

This paper focuses on minimizing the optical reflection on spherical fused silica lenses using femtosecond (fs) laser nanostructuring. A unique type of nanopillar formation has been observed on SiO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{SiO}_2$$\\end{document} surfaces possessing antireflective properties when irradiated with a specific number of overlapping pulses, polarization, and fluence levels. Maintaining precise control over these sensitive technological parameters such as defocus and incident angle during the processing of geometrically complex shapes presents a significant challenge. This study proposes a theoretical optical arrangement to address this limitation by the design of a custom scanner system optimized for curved surfaces. The paper details the optimization process of such a bent image space (inverse-hypercentric) optical system using Zemax OpticStudio. Although the practical realization of the arrangement has not been performed, simulations are conducted to prove the functionality of the concept. Furthermore, we propose a practical method for segmented structuring of spherical surfaces based on consecutive repositioning and irradiation using an industrial robotic arm. By constructing the optical model, the necessary resolution of the segmentation has been calculated for a typical F-Theta scanner system and experimental verification has been performed.

Noble-Metal Nanoparticle-Embedded Silicon Nanogratings via Single-Step Laser-Induced Periodic Surface Structuring.

Here, we show that direct femtosecond laser nanostructuring of monocrystalline Si wafers in aqueous solutions containing noble-metal precursors (such as palladium dichloride, potassium hexachloroplatinate, and silver nitrate) allows for the creation of nanogratings decorated with mono- (Pd, Pt, and Ag) and bimetallic (Pd-Pt) nanoparticles (NPs). Multi-pulse femtosecond-laser exposure was found to drive periodically modulated ablation of the Si surface, while simultaneous thermal-induced reduction of the metal-containing acids and salts causes local surface morphology decoration with functional noble metal NPs. The orientation of the formed Si nanogratings with their nano-trenches decorated with noble-metal NPs can be controlled by the polarization direction of the incident laser beam, which was justified, for both linearly polarized Gaussian and radially (azimuthally) polarized vector beams. The produced hybrid NP-decorated Si nanogratings with a radially varying nano-trench orientation demonstrated anisotropic antireflection performance, as well as photocatalytic activity, probed by SERS tracing of the paraaminothiophenol-to-dimercaptoazobenzene transformation. The developed single-step maskless procedure of liquid-phase Si surface nanostructuring that proceeds simultaneously with the localized reduction of noble-metal precursors allows for the formation of hybrid Si nanogratings with controllable amounts of mono- and bimetallic NPs, paving the way toward applications in heterogeneous catalysis, optical detection, light harvesting, and sensing.

Femtosecond laser nanostructuring on a 4H-SiC surface by tailoring the induced self-assembled nanogratings.

Ultrafast laser micromachining of crystalline silicon carbide (SiC) has great perspectives in aerospace industry and integrated circuit technique. In this report, we present a study of femtosecond laser nanostructuring on the surface of an n-type 4H-SiC single crystal. Except for uniform nanogratings, new types of large-area periodic structures including nanoparticle array and nanoparticle-nanograting hybrid structures were induced on the surface of 4H-SiC by scanning irradiation. The effects of pulse energy, scan speed, and the polarization direction on the morphology and periodicity of nanogratings were systematically explored. The proper parameter window for nanograting formation in pulse energy-scan speed landscape is depicted. Both the uniformity and the periodicity of the induced nanogratings are polarization dependent. A planar light attenuator for linear polarized light was demonstrated by aligning the nanogratings. The transition between different large-area periodic structures is achieved by simultaneous control of pulse energy and scan interval using a cross scan strategy. These results are expected to open up an avenue to create and manipulate periodic nanostructures on SiC crystals for photonic applications.

Femtosecond laser nano-structuring for surface plasmon resonance-based detection of uranium

Surface plasmon resonance (SPR) is a proven technique in sensorics. Wide application of the method is still limited by a necessity of a complex optical equipment using special dispersion elements like a prism or diffraction grating (DG). We have implemented a novel and inexpensive way for fabrication of the DG on a silicon substrate using femtosecond laser ablation (highly regular laser-induced periodic surface structures - HR-LIPSS) technique. The potential of the method has been illustrated for the case of detection of uranium in water. For this purpose, fabricated gratings were coated with thermally evaporated nanofilms of gold and then used as substrates for deposition of nanoparticles of bioinspired polymer polydopamine (PDA) highly selective to uranium under neutral pH. Synergistic combination of the advanced nanofabrication and SPR sensing techniques with advanced PDA ligand allowed preparation of sensing elements with a sub-microgram sensitivity to uranium (∼1.0 × 10−7g/cm2). Even though the results reported here are just a proof of concept, we believe the approach can be expanded to selective detection of various types of analytes (heavy metals, biomolecules, viruses etc.) under different environments (water, air, aerosols) in the future.

Формирование и оптические свойства нанорешеток на поверхности фторида кальция, генерируемых при фемтосекундном лазерном воздействии

Femtosecond laser structuring of dielectrics is an urgent problem for the creation of optical elements. In this work, we performed femtosecond laser nanostructuring of the calcium fluoride surface with the formation of self-organizing periodic gratings with subwavelength periods of the order of 200 and 350 nm. During the work, the dependence of the period of the structures on the wavelength of laser radiation was established, which was confirmed by the simulation results. The structures show a decrease in transmission over the entire visible range, predominantly due to diffraction and light scattering. Keywords: direct laser recording, femtosecond laser pulses, surface functional nano- and micro-optical structures, diffraction.

Reduced bacterial adhesion on zirconium-based bulk metallic glasses by femtosecond laser nanostructuring.

As high-performing materials, bulk metallic glasses have attracted widespread attention for biomedical applications. Herein, the bacterial adhesion properties of femtosecond laser-nanostructured surfaces of four types of zirconium-based bulk metallic glasses are assessed. Laser-induced periodical surface structures and nanoparticle structures were fabricated by femtosecond laser irradiation under different energy intensities (0.23 and 2.3 J/mm2). Surface topography, roughness, wettability, and surface energy were investigated after femtosecond laser irradiation and the surface bacterial adhesion properties were explored using Escherichia coli and Staphylococcus aureus as respective representatives of Gram-negative and Gram-positive bacteria. 4',6-Diamidino-2-phenylindole fluorescence staining was used to characterize and assess the bacterial surface coverage rate. The in vitro cytotoxicity of polished and laser-nanostructured surfaces was investigated using MC3T3-E cells. The obtained results demonstrate that femtosecond laser surface nanostructuring retained the amorphous structure of zirconium-based bulk metallic glasses and led to an obvious decrease in bacterial adhesion compared with polished surfaces. The inhibition of bacterial adhesion on laser-induced periodical surface structures was greater than on nanostructured surfaces after 24 h of bacterial incubation. In addition, femtosecond laser nanostructuring did not have an apparent effect on the cytotoxicity of zirconium-based bulk metallic glasses.

Femtosecond laser nanostructuring of reinforcement bars surface for improvement of its interaction with concrete

Femtosecond laser nanostructuring of metal surfaces is a powerful tool for improvement of their various properties. Namely, increase of optical absorption (“black metals”), superhydrophobity, surface hardening, as well as improvement of tribological properties have been reported previously. Here we show the improvement of bond slip of nanostructured reinforcement bars with concrete. We demonstrate strong dependence of straining force and pulling force on the regime of surface nanostructuring. In particular, two-fold increase of straining force and pulling force can be achieved at the highest fluence in the regime of “black metal”. Our finding has high practical importance for advanced civil engineering.

Ultrafast laser induced nanostructured ITO for liquid crystal alignment and higher transparency electrodes

Femtosecond laser nanostructured indium tin oxide (ITO) coated glass is shown to act both as a liquid crystal (LC) alignment layer and as an electrode with higher transparency. The nanopatterns of the 120 nm period were created using ultrashort laser pulses directly on ITO films without any additional spin coating materials or lithography process. Nine regions of laser-induced nanostructures were fabricated with different alignment orientations and various pulse energy levels on top of the ITO confirming the follow-up of the LC director to the line orientation. The device interfacial anchoring energy was found to be ∼1μ J/m2, comparable to the anchoring energy of nematic LC on photosensitive polymers. The transparency as an electrode was found to improve due to the better antireflection and lower absorption expected from a nanostructured surface.

Formation of Slantwise Surface Ripples by Femtosecond Laser Irradiation.

We report on the formation of slantwise-oriented periodic subwavelength ripple structures on chromium surfaces irradiated by single-beam femtosecond laser pulses at normal incidence. Unexpectedly, the ripples slanted in opposite directions on each side the laser-scanned area, neither perpendicular nor parallel to the laser polarization. The modulation depth was also found to change from one ripple to the next ripple. A theoretical model is provided to explain our observations, and excellent agreement is shown between the simulations and the experimental results. Moreover, the validity of our theory is also confirmed on bulk chromium surfaces. Our study provides insights for better understanding and control of femtosecond laser nanostructuring.

Form-Birefringence in ITO Thin Films Engineered by Ultrafast Laser Nanostructuring

The field of surface nanostructuring is growing rapidly with the need to search for more advanced fabrication solutions. The major challenge is the lack of appropriate combination of time/cost efficient techniques and medium possessing the advantages of both flexibility and tunable optical properties. Here we demonstrate direct-write femtosecond laser nanostructuring of indium–tin-oxide thin film where the deep-subwavelength ripples with periodicity of down to 120 nm are realized originating the form birefringence (|Δn| ≈ 0.2), which is 2 orders of magnitude higher than the commonly observed in uniaxial crystals or femtosecond laser nanostructured fused quartz. The demonstrated nanoripples with its continuously controlled space-variant orientation lead to the high density two-dimensional printing of flat optical elements. The technique can be extended to any highly transparent films that support laser-induced periodic surface structures, and can be effectively exploited for the integration of polarization...

Ultrafast Laser‐Induced Metasurfaces for Geometric Phase Manipulation

Direct-write femtosecond laser nanostructuring of 300 nanometer thick a-Si:H films results in space-variant functional metasurfaces with form birefringence of up to ne-no=–0.5. Engineering the orientation of local optical axis allows implementing continuous phase profiles of nearly any optical element including arrays of polarization micro-converters and micro lenses, polarization gratings and computer generated holograms with continuous phase gradients of ~1 rad/µm.

Implementation of a SVWP-based laser beam shaping technique for generation of 100-mJ-level picosecond pulses.

We present implementation of the energy-efficient and flexible laser beam shaping technique in a high-power and high-energy laser amplifier system. The beam shaping is based on a spatially variable wave plate (SVWP) fabricated by femtosecond laser nanostructuring of glass. We reshaped the initially Gaussian beam into a super-Gaussian (SG) of the 12th order with efficiency of about 50%. The 12th order of the SG beam provided the best compromise between large fill factor, low diffraction on the edges of the active media, and moderate intensity distribution modification during free-space propagation. We obtained 150 mJ pulses of 532 nm radiation. High-energy, pulse duration of 85 ps and the nearly flat-top spatial profile of the beam make it ideal for pumping optical parametric chirped pulse amplification systems.

Femtosecond laser nanostructuring of titanium metal towards fabrication of low-reflective surfaces over broad wavelength range

We investigated experimentally the formation of laser induced periodic surface structures (LIPSS) on titanium (Ti) metal upon irradiation with linearly polarized Ti:Sapphire femtosecond (fs) laser pulses of ∼110fs pulse width and 800nm wavelength in air and water environments. It is observed that initially formed random and sparsely distributed nano-roughness (nanoholes, nanoparticles and nanoprotrusions) gets periodically structured with increase in number of laser pulses. In air at lower fluence, we observed the formation of high spatial frequency-LIPSS (HSFL) oriented parallel to the laser polarization direction, whereas at higher fluence formation of low spatial frequency-LIPSS (LSFL) were observed that are oriented perpendicular to the incident laser polarization. In water two types of subwavelength structures were observed, one with spatial periodicity of ∼λ/15 and oriented parallel to laser polarization, while the other oriented perpendicular to laser polarization with feature size of λ/4. The optimal conditions for fabricating periodic sub-wavelength structures are determined by controlling the fluence and pulse number. The fs laser induced surface modifications were found to suppress the specular reflection of the Ti surface over a wide wavelength range of 250–2000nm to a great extent.

Giant birefringence and dichroism induced by ultrafast laser pulses in hydrogenated amorphous silicon

A femto- and picosecond laser assisted periodic nanostructuring of hydrogenated amorphous silicon (a-Si:H) is demonstrated. The grating structure with the subwavelength modulation of refractive index shows form birefringence (Δn ≈ −0.6) which is two orders of magnitude higher than commonly observed in uniaxial crystals and femtosecond laser nanostructured silica glass. The laser-induced giant birefringence and dichroism in a-Si:H film introduce extra dimensions to the polarization sensitive laser writing with applications that include data storage, security marking, and flat optics.

Nonlinear optical dynamics during femtosecond laser nanostructuring of a silicon surface

Non-linear cumulative self-organization dynamics of femtosecond laser-induced surface relief ripples was for the first time experimentally revealed on a silicon surface as their primary appearance, degradation and revival, reflecting ultrafast non-linear dynamics of corresponding optical interference surface patterns. Such dynamics were revealed by electrodynamic modeling to be directly driven by related instantaneous surface optical patterns, which are sensitive not only to cumulative ripple deepening (steady-state feedback factor), but to laser-induced instantaneous variation of surface dielectric function, providing either positive or negative fluence-dependent optical feedbacks.

Far-Field Nanostructuring in Dielectric Materials Beyond the Diffraction Limit Using Femtosecond Laser

We review the latest progress in the development of far-field nanostructuring technologies based on femtosecond laser direct writing. The principles for breaking through the diffraction limit in the interaction of a focused ultrafast laser beam with dielectric materials are presented, and applications of the femtosecond laser nanostructuring are discussed.

Seemingly Unlimited Lifetime Data Storage in Nanostructured Glass

We demonstrate recording and retrieval of the digital document with a nearly unlimited lifetime. The recording process of multiplexed digital data was implemented by femtosecond laser nanostructuring of fused quartz. The storage allows unprecedented parameters including hundreds of terabytes per disc data capacity, thermal stability up to 1000 °C, and virtually unlimited lifetime at room temperature. We anticipate that this demonstration will open a new era of eternal data archiving.

Polarization sensitive camera by femtosecond laser nanostructuring

A polarization imaging device based on a femtosecond laser nanostructured birefringent array is demonstrated. The device enables instant measurement of the distribution of the Stokes vectors in the visible spectrum. Polarimetric measurements with radially and circularly polarized light distributions are demonstrated.

Femtosecond laser nanostructuring in porous glass with sub-50 nm feature sizes

We report on controllable production of nanostructures embedded in a porous glass by femtosecond laser direct writing. We show that a hollow nanovoid with a lateral size of ~40 nm and an axial size of ~1500 nm can be achieved by manipulating the peak intensity and polarization of the writing laser beam. Our finding enables applications ranging from direct construction of 3D nanofluidics in glass to clean stealth dicing of transparent plates.

Nanoscale cavitation instability of the surface melt along the grooves of one-dimensional nanorelief gratings on an aluminum surface

Femtosecond laser nanostructuring at low fluences produces a onedimensional quasiperiodic grating of grooves on an aluminum surface with a period (≈0.5 μm) that is determined by the length of a surface elec� tromagnetic wave. The structure of the grooves of the surface nanograting is formed by regular nanopeaks fol� lowing with a period of about 200 nm. Some nanopeaks manifest craters at their tops. It is suggested that nanopeaks are formed due to the frozen nanoscale spallative ablation of a nanolayer of an aluminum melt in quasiperiodic regions corresponding to interference maxima of the laser radiation with the surface electro� magnetic wave. The periodicity of the appearance of nanopeaks along grooves is due to the previously pre� dicted mechanism of cavitation deformation of the melt surface in the process of macroscopic spallation ablation. However, in this case, cavitation is coherent (similar to a nearcritical spinodal decay) rather than spontaneous. DOI: 10.1134/S0021364011160065