Bulk Transparent Materials Research Articles

Ultrafast Laser Direct Writing Nanogratings and their Engineering in Transparent Materials

AbstractFemtosecond laser direct writing is a powerful technique for fabricating micro‐nano devices as it can modify the interior of transparent optical materials in a spatially selective manner through nonlinear multi‐photon absorption. In this context, laser‐induced nanogratings, i.e., a sub‐wavelength assembly of nanolayers (≈20 nm in width, ≈200 nm period), are ultrashort self‐organized structures created by light in the bulk of transparent materials. These have been intensively explored over the last two decades opening a novel era of micro photonic devices due to their unique physicochemical properties, like orientable form birefringence, anisotropic light scattering, highly selective chemical etching, optical chirality, and extraordinary thermal stability. This review provides a throughout overview of the advances in this field, specifically focused on the formation of nanogratings, optical properties that can be exploited in various transparent solids, and the related main applications. Also, the fundamental characteristics, formation mechanism, tuning methods of nanogratings are reviewed.

Application of Ultrashort Lasers in Developmental Biology: A Review

The evolution of laser technologies and the invention of ultrashort laser pulses have resulted in a sharp jump in laser applications in life sciences. Developmental biology is no exception. The unique ability of ultrashort laser pulses to deposit energy into a microscopic volume in the bulk of transparent material without disrupting the surrounding tissues makes ultrashort lasers a versatile tool for precise microsurgery of cells and subcellular components within structurally complex and fragile specimens like embryos as well as for high-resolution imaging of embryonic processes and developmental mechanisms. Here, we present an overview of recent applications of ultrashort lasers in developmental biology, including techniques of noncontact laser-assisted microsurgery of preimplantation mammalian embryos for oocyte/blastomere enucleation and embryonic cell fusion, as well as techniques of optical transfection and injection for targeted delivery of biomolecules into living embryos and laser-mediated microsurgery of externally developing embryos. Possible applications of ultrashort laser pulses for use in Assisted Reproductive Technologies are also highlighted. Moreover, we discuss various nonlinear optical microscopy techniques (two-photon excited fluorescence, second and third harmonic generation, and coherent Raman scattering) and their application for label-free non-invasive imaging of embryos in their unperturbed state or post-laser-induced modifications.

Persistent luminescent phosphor-in-glass composites based on NaPO3 – Ga2O3 glasses loaded with Sr2MgSi2O7:Eu2+,Dy3+

Phosphor-in-glass (PiG) is a composite material that can combine the chemical stability and more versatile molding and processing of glasses and the singular properties of luminescent polycrystalline materials. Persistent luminescent phosphors have been raising attention due to their long emission times without the need for a steady irradiation source. The association of these polycrystalline materials with transparent glassy hosts leads to the obtainment of robust luminescent bulk materials and expands the possibilities of commercial applications. In this work, the Sr2MgSi2O7:Eu2+,Dy3+ (SMSO) persistent luminescent material was incorporated into a new gallium phosphate glass system with composition 80NaPO3 – 20Ga2O (NaPGa), through the conventional melt-quenching technique and fully characterized from the structural and spectroscopic viewpoints. The composites were prepared using 2, 5, 10, and 20 wt% of SMSO at 900 or 950 °C. It was observed that the higher melting temperature induces the oxidation of Eu2+ ions, which can reduce the persistent luminescent emission. High SMSO concentrations increase the glass melt viscosity, hampering the molding step but optimized samples were successfully obtained as transparent bulk materials with efficient emission in the blue spectral region and promising applications in emergency signaling and as solar cell sensitizers.

3D beam shaping methods for ultrashort‐pulsed laser material processing

AbstractUltrashort‐pulse (USP) lasers enable microlevel manipulation of material surfaces and work on the bulk of transparent materials with almost no thermal effects. One major bottleneck that is limiting the processing speed with USP lasers is the effective spreading of laser energy in the processed material. Diffractive optical elements (DOE) are a leading method of solving this bottleneck. In this article, we review the concept of 3D diffractive light shaping for USP lasers and show its usefulness in various industrial USP laser applications.

Passivation of black phosphorus nanoflakes embedded in a silica glass matrix affords ambient saturable absorption stability enhancement.

Black phosphorus (BP) is a graphene analogue with ultrafast broadband nonlinear optical properties that make it a promising nanomaterial for saturable absorption. However, BP nanoflakes chemically degrade in ambient conditions. We developed air- and photo-stable BP nanoflakes via incorporation in inorganic-organic hybrid matrices. This realized passivation and materialization through a sol-gel method that produced high-quality, transparent bulk materials. Saturable absorption parameters of the passivated BP were maintained after five months in ambient storage and after 8000 300 µJ nanosecond laser shots. The nonlinear absorption coefficient was still 62% after 12 months in open air, which was higher than that for non-passivated BP after three days. The stability was attributed to dense silica-gel glasses that enveloped the BP, essentially eliminating oxygen and water penetration. The simplicity of this approach may stimulate potential applications for environmentally sensitive high-performance solid-state devices.

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

Conical third harmonic generation from volume nanogratings induced by filamentation of femtosecond pulses in transparent bulk materials

We report on observations of conical third harmonic emission that emerges during supercontinuum generation produced by self-focusing and filamentation of high (20-200 kHz) repetition rate 180 fs, 1035 nm pulses from an amplified Yb:KGW laser in various nonlinear crystals and glasses: YAG, sapphire, YLF, LiF, CaF2, MgF2, LiSAF, fused silica and BK-7 glass. We show that conical third harmonic generation is a phase-matched four-wave mixing process, where noncollinear phase matching is achieved by means of reciprocal lattice vector, inversely proportional to the period of nanograting, which is inscribed by femtosecond filament in the volume of nonlinear material. The existence of a particular period required to phase match conical third harmonic generation was indirectly verified by investigations of periodicity features of high and low spatial frequency laser-induced periodic surface structures, in which matter is reorganized in a similar fashion.

Tough Bioinspired Composites That Self-Report Damage

The increasing use of lightweight composite materials in structural applications requires the development of new damage monitoring technologies to ensure their safe use and prevent accidents. Although several molecular strategies have been proposed to report damage in polymers through mechanochromic responses, these approaches have not yet been translated into lightweight bioinspired composites for load-bearing applications. Here, we report on the development of bioinspired laminates of alternating polymer and nacre-like layers that combine optical translucency, high fracture toughness, and damage-reporting capabilities. The composites signal damage via a fluorescence color change that arises from the force activation of mechanophore molecules embedded in the material's polymer phase. A quantitative correlation between the applied strain and the fluorescence intensity was successfully established. We demonstrate that optical imaging of mechanically loaded composites allows for the localized detection of damage prior to fracture. This fluorescence-based self-reporting mechanism offers a promising approach for the early detection of damage in lightweight structural composites and can serve as a useful tool for the analysis of fracture processes in bulk transparent materials.

Transparent Nacre‐like Composites Toughened through Mineral Bridges

AbstractBulk materials with remarkable mechanical properties have been developed by incorporating design principles of biological nacre into synthetic composites. However, this potential has not yet been fully leveraged for the fabrication of tough and strong materials that are also optically transparent. In this work, a manufacturing route that enables the formation of nacre‐like mineral bridges in a bioinspired composite consisting of glass platelets infiltrated with an index‐matching polymer matrix is developed. By varying the pressure applied during compaction of the glass platelets, composites with tunable levels of mineral bridges and platelet interconnectivity can be easily fabricated. The effect of platelet interconnectivity on the mechanical strength and fracture behavior of the bioinspired composites is investigated by performing state‐of‐the‐art fracture experiments combined with in situ electron microscopy. The results show that the formation of interconnections between platelets leads to bulk transparent materials with an unprecedented combination of strength and fracture toughness. This unusual set of properties can potentially fulfill currently unmet demands in electronic displays and related technologies.

Video-rate upconversion display from optimized lanthanide ion doped upconversion nanoparticles.

Volumetric displays that create bright image points within a transparent bulk are one of the most attractive technologies in everyday life. Lanthanide ion doped upconversion nanoparticles (UCNPs) are promising luminescent nanomaterials for background free, full-colour volumetric displays of transparent bulk materials. However, video-rate display using UCNPs has been limited by their low emission intensity. Herein, we developed a video-rate upconversion display system with much enhanced brightness. The integral emission intensity of the single UCNPs was fully employed for video-rate display. It was maximized by optimizing the emitter concentration and, more importantly, by temporally synchronizing the scanning time of the excitation light to the the raised emission time of the single UCNPs. The excitation power dependent emission response and emission time decay curves were systematically characterized for the single UCNPs with various emitter concentrations from 0.5% to 6%. 1%Tm3+ doped UCNPs presented the highest integral emission intensity. By embedding this UCNPs into a polyvinyl acetate (PVA) film, we achieved a two-dimensional (2D) upconversion display with a frame rate of 29 Hz for 35 by 50 pixels. This work demonstrates that the temporal response as well as the integral emission intensity enable video-rate upconversion display.

Transparent and tough bulk composites inspired by nacre

Materials combining optical transparency and mechanical strength are highly demanded for electronic displays, structural windows and in the arts, but the oxide-based glasses currently used in most of these applications suffer from brittle fracture and low crack tolerance. We report a simple approach to fabricate bulk transparent materials with a nacre-like architecture that can effectively arrest the propagation of cracks during fracture. Mechanical characterization shows that our glass-based composites exceed up to a factor of 3 the fracture toughness of common glasses, while keeping flexural strengths comparable to transparent polymers, silica- and soda-lime glasses. Due to the presence of stiff reinforcing platelets, the hardness of the obtained composites is an order of magnitude higher than that of transparent polymers. By implementing biological design principles into glass-based materials at the microscale, our approach opens a promising new avenue for the manufacturing of structural materials combining antagonistic functional properties.

Femtosecond laser direct writing of an integrated path-encoded CNOT quantum gate

Femtosecond lasers enable three-dimensional direct writing of waveguides inside bulk transparent materials and have been applied to the fabrication of integrated photonic quantum logic gates. Up to now, the controlled-NOT (CNOT) gate, the key two-qubit quantum gate, has been realized only for polarization-encoded photonic qubits, which consists of three partially polarizing directional couplers (DCs) or two polarizing DCs. In this work, we demonstrate the femtosecond laser direct writing of a path-encoded CNOT gate formed by five DCs all with precisely controlled splitting ratios and stable symmetric phases inside glass for the first time. The quantum CNOT operation is performed using single photons with an average fidelity higher than 0.98. This provides a novel venue for the fabrication of large-scale 3D quantum computation circuits based on femtosecond laser writing.

Characteristics of 1064 nm picosecond laser induced filamentary tracks and damages in sapphire

The induction of structural modifications by focused laser pulses in bulk transparent materials is a versatile technique for the microfabrication of photonic devices. In this paper, the influence of repetition rate, pulse energy and number of pulses was studied by comparing picosecond laser induced structural modifications in sapphire. The observed structural modifications consisted of a uniaxial void zone surrounded by smooth refractive index changes, and micro cracks followed by a submicrometer filamentary track. The number of laser pulses was found to be the primary factor in causing cracks surrounding the focal volume while pulse repetition rate and pulse energy were observed to have minor roles in these cracks. However, with increasing repetition rate, length of the filamentary track decreased, whereas no significant difference was observed in the length by changing number of pulses. Furthermore, filamentary track length has increased with the increase of laser energy. At 107 µJ energy, a maximum filamentary track of length 1180 µm was observed.

Printing and mechanical characterization of cellulose nanofibril materials

Cellulose nanofibrils (CNF) are a promising building block of structural materials because they are biodegradable, can be made into optically transparent bulk materials, and have exceptional specific strength and stiffness compared to common synthetic polymers. The manufacturing of bulk materials from CNFs is a challenge because CNFs form networks in solution at low solids concentration, which can result in long processing times as well as large residual stresses and distortion upon water removal. Here, a method to form materials from CNF suspensions via direct ink writing, a type of additive manufacturing, is demonstrated. Multilayer printing of CNFs provides a route to control drying time by depositing thin layers one at a time. A printing system with a pressure-controlled dispensing system was used to deposit aqueous CNF suspensions onto a temperature-controlled substrate. The geometry, roughness, and mechanical properties of the printed structures were characterized. The shape of the printed line profile is controlled by a combination of the wettability of the substrate, dispense rate, printing speed, and temperature of the substrate. Spatial variation of the elastic modulus of printed CNF structures was assessed with nanoindentation and the average percent difference was found to be small at ± 2.6% of the mean over the area of the printed lines. Through multilayer printing freestanding films with thicknesses greater than 60 μm were achieved. Tensile specimens were printed and characterized; a tensile strength of 72.6 MPa ± 7.4 MPa and a Young’s modulus of 10.2 GPa ± 1.2 GPa were measured.

Experiment-Based Quantitative Analysis of Picosecond Pulse-Induced Morphological Changes in Fused Silica

Due to its excellent quality, fused silica has been widely used in various industrial applications. The nonlinear absorptive nature of ultrafast laser pulses enables the induction of morphological changes within the bulk transparent materials. In this study, the interior modification of fused silica is induced by a picosecond pulsed laser, and the relationship between processing parameters and the modification geometry is demonstrated. Three different patterns are identified according to the geometric characteristics of the modification. Furthermore, a simple experiment-based model considering the incubation effect is put forward to predict picosecond pulse-induced morphological changes in fused silica.

Light-driven mass density wave dynamics in optical fibers.

We have recently developed the mass-polariton (MP) theory of light to describe the light propagation in transparent bulk materials [Phys. Rev. A 95, 063850 (2017)]. The MP theory is general as it is based on the covariance principle and the fundamental conservation laws of nature. Therefore, it can be applied also to nonhomogeneous and dispersive materials. In this work, we apply the MP theory of light to describe propagation of light in step-index circular waveguides. We study the eigenmodes of the electric and magnetic fields in a waveguide and use these modes to calculate the optical force density, which is used in the optoelastic continuum dynamics (OCD) to simulate the dynamics of medium atoms in the waveguide. We show that the total momentum and angular momentum in the waveguide are carried by a coupled state of the field and the medium. In particular, we focus in the dynamics of atoms, which has not been covered in previous theories that consider only field dynamics in waveguides. We also study the elastic waves generated in the waveguide during the relaxation following from atomic displacements in the waveguide.

Surface Modifier-Free Organic-Inorganic Hybridization To Produce Optically Transparent and Highly Refractive Bulk Materials Composed of Epoxy Resins and ZrO2 Nanoparticles.

Surface modifier-free hybridization of ZrO2 nanoparticles (NPs) with epoxy-based polymers is demonstrated for the first time to afford highly transparent and refractive bulk materials. This is achieved by a unique and versatile hybridization via the one-pot direct phase transfer of ZrO2 NPs from water to epoxy monomers without any aggregation followed by curing with anhydride. Three types of representative epoxy monomers, bisphenol A diglycidyl ether (BADGE), 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate (CEL), and 1,3,5-tris(3-(oxiran-2-yl)propyl)-1,3,5-triazinane-2,4,6-trione (TEPIC), are used to produce transparent viscous dispersions. The resulting ZrO2 NPs are thoroughly characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), and solid-state 13C CP/MAS NMR measurements. The results from DLS and TEM analyses indicate nanodispersion of ZrO2 into epoxy monomers as a continuous medium. A surface modification mechanism and the binding fashion during phase transfer are proposed based on the FT-IR and solid-state 13C CP/MAS NMR measurements. Epoxy-based hybrid materials with high transparency and refractive index are successfully fabricated by heat curing or polymerizing a mixture of monomers containing epoxy-functionalized ZrO2 NPs and methylhexahydrophthalic anhydride in the presence of a phosphoric catalyst. The TEM and small-angle X-ray scattering measurements of the hybrids show a nanodispersion of ZrO2 in the epoxy networks. The refractive index at 594 nm ( n594) increases up to 1.765 for BADGE-based hybrids, 1.667 for CEL-based hybrids, and 1.693 for TEPIC-based hybrids. Their refractive indices and Abbe's numbers are quantitatively described by the Lorentz-Lorenz effective medium expansion theory. Their transmissivity is also reasonably explained using Fresnel refraction, Rayleigh scattering, and the Lambert-Beer theories. This surface modifier-free hybridization provides a versatile, fascinating, and promising method for synthesizing a variety of epoxy-based hybrid materials.

Optical elements containing semitransparent wavelike films.

Novel optical elements containing semitransparent wavelike films embedded into the bulk of transparent material, which form a reflection image without transmitted light distortion, are studied. The dynamic theory of light diffraction by a locally periodic multilayer semitransparent wavelike film is developed. A simple analytical formula for near Bragg diffraction order intensity is obtained for the case when only one diffraction order lies within the hologram angular selectivity. The phase modulation of light transmitted through the optical element containing wavelike films is estimated for single-layer and multilayer wavelike films with an arbitrary shape of surface. The restrictions on the structure parameters for which transmitted light distortions would be negligible are obtained. A new type of high-quality color hologram is proposed and shown to be feasible by calculation of hologram diffraction efficiency and spectral selectivity for three colors. Other possible applications, such as monochrome and color head-up and head-mounted displays, and imaging on spectacle lenses, are discussed.

Setup for high-temperature surface Brillouin light scattering: Application to opaque thin films and coatings

A setup combining surface Brillouin light scattering with a high-temperature chamber has been developed. The temperature of the sample is controlled with a Bühler HDK chamber for optical measurements (maximum temperature of 1600 °C), in controlled atmospheres or high vacuum (10-6 mbar). This setup allows the study of sound velocity of surface acoustic waves and of the elastic constants of opaque thin films and coatings in situ as a function of temperature from surface Brillouin light scattering, by analyzing the backscattered light from the sample at a fixed angle of incidence. In this paper, we will demonstrate the applications of this setup for metallic glass thin films devitrification study and evaluation of high temperature elastic properties of hard nitride coatings. This kind of study using surface acoustic waves is rare, in contrast to those made on transparent bulk materials.

Optical find of hypersonic surface acoustic waves in bulk transparent materials

Optical find of hypersonic surface acoustic waves in bulk transparent materials