Grating-like Structure Research Articles

Nanosecond Laser Fabrication of Dammann Grating-like Structure on Glass for Bessel-Beam Array Generation

The generation of optical beam arrays with prospective uses within the realms of microscopy, photonics, non-linear optics, and material processing often requires Dammann gratings. Here, we report the direct fabrication of one- and two-dimensional Dammann grating-like structures on soda lime glass using a nanosecond pulsed laser beam with a 1064 nm wavelength. Using the fabricated grating, an axicon lens, and an optical magnification system, we propose a scheme of generation of a diverging array of zero-order Bessel beams with a sub-micron-size central core, extending longitudinally over several hundred microns. Two different grating fabrication strategies are also proposed to control the number of Bessel beams in an array. It was demonstrated that Bessel beams of 12 degrees conical half-angle in an array of up to [5 × 5] dimensions can be generated using a suitable combination of Dammann grating, axicon lens and focusing optics.

Angle-Resolved Fluorescence of a Dye Coupled to a Plasmonic Nanohole Array

Gold nanohole arrays are periodic metasurfaces that are gathering huge interest in biosensing applications. The bi-dimensional grating-like structure defines their plasmonic response, together with the corresponding mode of angular dispersion. These properties can be used to investigate the interaction processes with the fluorescence features of a properly chosen emitting molecule. By employing a custom gold nanohole array alongside a commercial organic dye, we conducted an accurate angle-resolved optical characterization resorting to fluorescence, reflectance, and transmittance spectra. The coupling between the plasmonic modes and the fluorescence features was then identified as a modification of the dye fluorescence signal in terms of both spectral redistribution and enhancement. By carefully analyzing the results, different measurement efficiencies can be identified, depending on the set-up configuration, to be properly engineered for sensitivity maximization in plasmon-enhanced fluorescence-based applications.

Effect of film thickness on laser induced surface structures formation on optically transparent polymer films

Laser-induced periodic surface structures can be prepared on polymer thin films, despite the absence of light absorption at the wavelength of the irradiating laser, by using a bilayer approach. Nanostructuring of a poly(3-hexylthiophene-2,5-diyl) (P3HT) layer, by laser irradiation at 532 nm, covered by a thin layer of a non-absorbing polymer, in this case, the ferroelectric copolymer poly(vinylidene fluoride - trifluoro ethylene),P(VDF-TrFE), allows the development of a grating-like structure on the surface. The range of thicknesses of the upper layer, which leads to the formation of LIPSS, has been determined. It is verified that for a thickness larger than 40 nm, no periodic structures are formed, neither in the upper layer nor in the bottom P3HT one. This can be explained considering a mechanical restriction which prevents P3HT rearrangement. The upper nanostructured surface layer exhibits ferroelectric properties as proven by piezoresponse force microscopy measurements.

Characterizing the Grating-like Nanostructures Formed on BaF2 Surfaces Exposed to Extreme Ultraviolet Laser Radiation

Monocrystalline barium fluoride (BaF2) slab targets were irradiated by focused 46.9-nm laser radiation at various fluence levels above the ablation threshold. Well-developed ablation patterns with sharp edges were studied by AFM (atomic force microscopy). Their inner surfaces were uniformly covered by periodic structures. The spatial period of the ripples depends on the laser fluence. When the sample is rotated by 45°, the orientation of the grating-like structure changes accordingly. Thus, the grating vector of the periodic structure seems to be coupled to the crystallographic planes of the single crystal. This means that the XUV-laser induced ripples reported here differ from LIPSS (laser-induced periodic surface structures) associated with interference phenomena occurring on illuminated surfaces. Therefore, other mechanisms are discussed to explain the formation of the periodic nanostructures reported in this article.

Optical tunable multifunctional slow light device based on double monolayer graphene grating-like metamaterial

A very simple optical tunable device, which can realize multiple functions of frequency selection, reflection and slow light, is presented at the investigation. The proposed device is constructed by a periodic grating-like structure. There are two dielectrics (graphene and silicon) in a period of the equivalent grating. The incident light will strongly resonate with the graphene of electrostatic doping, forming an evanescent wave propagating along the surface of graphene, and this phenomenon is the surface plasmon. Under constructive interference of the polaritons, a unique plasmonic induced transparency phenomenon will be achieved. The induced transparency produced by this device can be well theoretically fitted by the bright and dark mode of optical equivalent cavity which can be called coupled mode theory. This theory can well analyze the influence of various modes and various losses between the function of this device. The device can use gate voltages for electrostatic doping in order to change the graphene carrier concentration and tune the optical performance of the device. Moreover, the length of the device in y-direction is will be much larger than the length of single cycle, providing some basis for realizing the fast tunable function and laying a foundation for the integration. Through a simulation and calculation, we can find that the group index and group delay of this device are as high as 515 and 0.257 picoseconds (ps) respectively, so it can provide a good construction idea for the slow light device. The proposed grating-like metamaterial structure can provide certain simulation and theoretical help for the optical tunable reflectors, absorbers, and slow light devices.

Periodic surface nanostructures induced by orthogonal femtosecond laser pulses on tungsten

Three types of surface nanostructures are fabricated on tungsten by adjusting azimuth angle θ of YVO4 birefringent crystal and laser parameters in experiment. Different surface structure morphologies are introduced and their features are investigated. The frequency characteristics of the three type laser-induced surface nanostructures are studied by the fast Fourier transformation (FFT). By varying the azimuth angle of YVO4 crystal we can not only convert one-dimensional (1D) grating-like structures into two-dimensional (2D) surface structures, but also control the structural arrangement. Compared with traditional two-step sequential processing method, the dual orthogonal pulses generating through YVO4 birefringent crystal can induce better periodical 1D grating-like structure. Moreover, the 2D microbumps are mainly dependent on the energy deposition effect from dual pulses. We also provide the underlying texturing mechanism of final periodic surface structures.

Investigation of the characteristics of the dual-band electromagnetic induction transparent-like terahertz spectrum in a grating-like structure

In this paper, a new structure is proposed which is expected to realize a dual-band electromagnetically induced transparency (EIT)-like effect in the terahertz spectrum. It can be regarded as a metamaterial of grating-like elements composed of dual-band U-shaped resonators. The near-field coupling between bright modes can produce an EIT-like effect. After optimizing the parameters, our numerical simulated results are in good agreement with the theoretical analysis. The EIT-like effect can significantly reduce the group speed near the transparent window, and may gain more significant potential applications in slow-light transmission and optical storage.

Non-plasmonic improvement in photoconductive THz emitters using nano- and micro-structured electrodes.

We investigate here terahertz enhancement effects arising from micrometer and nanometer structured electrode features of photoconductive terahertz emitters. Nanostructured electrode based emitters utilizing the palsmonic effect are currently one of the hottest topics in the research field. We demonstrate here that even in the absence of any plasmonic resonance with the pump pulse, such structures can improve the antenna effect by enhancing the local d.c. electric field near the structure edges. Utilizing this effect in Hilbert-fractal and grating-like designs, enhancement of the THz field of up to a factor of ∼ 2 is observed. We conclude that the cause of this THz emission enhancement in our emitters is different from the earlier reported plasmonic-electrode effect in a similar grating-like structure. In our structure, the proximity of photoexcited carriers to the electrodes and local bias field enhancement close to the metallization cause the enhanced efficiency. Due to the nature of this effect, the THz emission efficiency is almost independent of the pump laser polarization. Compared to the plasmonic effect, these effects work under relaxed device fabrication and operating conditions.

Phase retrieval and adaptive optics correction for systems with diffractive surfaces.

Adaptive optics (AO) is a powerful technique for correcting extrinsic aberrations, such as those caused by atmospheric turbulence or biological sample thickness variations, by using measured phase information and a wavefront-correcting element. To extend AO techniques to systems with diffractive surfaces, considerations need to be made for additional components of the measured phase that are attributable to diffraction from the object and are not a part of the extrinsic aberration. For example, light reflected from a diffractive surface of an optical storage disk contains an additional phase due to the diffracted orders from the grating-like structure of the data tracks. In this work, a modified Gerchberg algorithm is presented as a viable method of phase retrieval to detect the total aberration, and correction for extrinsic aberrations is shown for light reflected from a grating. An experimental microscope system demonstrates successful AO correction, thus verifying simulation results.

Superflexibility of ITO Electrodes via Submicron Patterning.

Indium tin oxide (ITO) is the premier choice for transparent conductive electrodes in optoelectronic devices despite its inherent brittleness. Here we report the fabrication of a grating-like structure that obviates ITO's mechanical limitations while retaining its resistivity and optical qualities. ITO nanopatterned films exhibited a resistivity <1.3 × 10-3 Ω cm, which surpassed all previously reported values for flexible ITO, with a normal transmission >90% across the whole visible spectrum range. We demonstrate the nanopatterned ITO retains extraordinary flexibility and durability on heat-sensitive substrates, accommodating cyclic bending to a curvature diameter of at least 3.2 mm for over 50 cycles of compressive and decompressive flexing without significant deterioration of its resistivity or optical properties. Moreover, 2-dimensional extrapolation shows that multiaxial bending is also feasible while maintaining mechanical flexibility, durability, and optical transparency.

Circularly polarized reflection from the scarab beetle Chalcothea smaragdina: light scattering by a dual photonic structure.

Helicoidal architectures comprising various polysaccharides, such as chitin and cellulose, have been reported in biological systems. In some cases, these architectures exhibit stunning optical properties analogous to ordered cholesteric liquid crystal phases. In this work, we characterize the circularly polarized reflectance and optical scattering from the cuticle of the beetle Chalcothea smaragdina (Coleoptera: Scarabaeidae: Cetoniinae) using optical experiments, simulations and structural analysis. The selective reflection of left-handed circularly polarized light is attributed to a Bouligand-type helicoidal morphology within the beetle's exocuticle. Using electron microscopy to inform electromagnetic simulations of this anisotropic stratified medium, the inextricable connection between the colour appearance of C. smaragdina and the periodicity of its helicoidal rotation is shown. A close agreement between the model and the measured reflectance spectra is obtained. In addition, the elytral surface of C. smaragdina possesses a blazed diffraction grating-like surface structure, which affects the diffuse appearance of the beetle's reflected colour, and therefore potentially enhances crypsis among the dense foliage of its rainforest habitat.

Role of Surface Mode on Light Out-Coupling Characteristics of waveguide in Three Dimensional Photonic Crystals

The radiation pattern and out-coupling efficiency of light from the end surface of interlayer (oblique) waveguides in stacked-stripe 3-D photonic crystals are numerically investigated. It is shown that the coupling to the surface mode of the 3-D photonic crystal decreases the out-coupling efficiency to free-space modes down to 60%, whereas the reflection at the surface is negligibly small. The efficiency can be improved to 90% by introducing a 2-D grating-like structure to create a surface-mode gap, where surface modes are prohibited.

Interference phenomenon with mobile displays

A simple experiment is presented in which the spacing and geometric pattern of pixels in mobile displays is measured. The technique is based on optical constructive interference. While the experiment is another opportunity to demonstrate wave interference from a grating-like structure, this can also be used to demonstrate concepts of solid state physics such as direct and reciprocal lattice vectors.

Implications of transient changes of optical and surface properties of solids during femtosecond laser pulse irradiation to the formation of laser-induced periodic surface structures

The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon wafer surfaces by linearly polarized Ti:sapphire femtosecond laser pulses (pulse duration 130 fs, central wavelength 800 nm) is studied experimentally and theoretically. In the experiments, so-called low-spatial frequency LIPSS (LSFL) were found with periods smaller than the laser wavelength and an orientation perpendicular to the polarization. The experimental results are analyzed by means of a new theoretical approach, which combines the widely accepted LIPSS theory of Sipe et al. with a Drude model, in order to account for transient (intra-pulse) changes of the optical properties of the irradiated materials. It is found that the LSFL formation is caused by the excitation of surface plasmon polaritons, SPPs, once the initially semiconducting material turns to a metallic state upon formation of a dense free-electron-plasma in the material and the subsequent interference between its electrical field with that of the incident laser beam resulting in a spatially modulated energy deposition at the surface. Moreover, the influence of the laser-excited carrier density and the role of the feedback upon the multi-pulse irradiation and its relation to the excitation of SPP in a grating-like surface structure is discussed.

Solar energy harvesting in the epicuticle of the oriental hornet (Vespa orientalis)

The Oriental hornet worker correlates its digging activity with solar insolation. Solar radiation passes through the epicuticle, which exhibits a grating-like structure, and continues to pass through layers of the exo-endocuticle until it is absorbed by the pigment melanin in the brown-colored cuticle or xanthopterin in the yellow-colored cuticle. The correlation between digging activity and the ability of the cuticle to absorb part of the solar radiation implies that the Oriental hornet may harvest parts of the solar radiation. In this study, we explore this intriguing possibility by analyzing the biophysical properties of the cuticle. We use rigorous coupled wave analysis simulations to show that the cuticle surfaces are structured to reduced reflectance and act as diffraction gratings to trap light and increase the amount absorbed in the cuticle. A dye-sensitized solar cell (DSSC) was constructed in order to show the ability of xanthopterin to serve as a light-harvesting molecule.

Moving electron density gratings induced in the beat-wave field of two counterpropagating laser pulses

The production and physical characteristics of moving electron density gratings (MEDGs) are investigated by analytical model and particle-in-cell (PIC) simulations. When the frequency difference of two counterpropagating pump pulses is equal to the electron plasma frequency, large amplitude electron plasma wave is resonantly excited in the plasma. As a result, electrons are excited to form a moving, gratinglike structure in the interfering region of pump pulses, while the ions keep at rest. The spatial period and velocity of the MEDG are obtained by solving the electron density modulation equation, which agrees well with one-dimensional PIC simulation results. When a short signal laser pulse is scattered on the MEDG, the frequency of the backscattering wave shifts due to the stimulated Raman scattering.

Nanoparticle image velocimetry at topologically structured surfaces

Nanoparticle image velocimetry (nano-PIV), based on total internal reflection fluorescent microscopy, is very useful to investigate fluid flows within approximately 100 nm from a surface; but so far it has only been applied to flow over smooth surfaces. Here we show that it can also be applied to flow over a topologically structured surface, provided that the surface structures can be carefully configured not to disrupt the evanescent-wave illumination. We apply nano-PIV to quantify the flow velocity distribution over a polydimethylsiloxane surface, with a periodic gratinglike structure (with 215 nm height and 2 mum period) fabricated using our customized multilevel lithography method. The measured tracer displacement data are in good agreement with the computed theoretical values. These results demonstrate new possibilities to study the interactions between fluid flow and topologically structured surfaces.

Investigation of microstructuring CuInGaSe2 thin films with ultrashort laser pulses

Microstructuring of CuInGaSe2 (CIGS) thin films by infrared ultrashort laser pulses is investigated in ambient air. A grating-like surface structure with a periodicity of 630 nm is generated by line scribing of linearly polarized 50 fs lasers. The formation condition of the gratings pattern is experimentally determined in terms of laser energy and scanning speed. It is found that the orientation of these laser-induced gratings is changed with different linear polarizations of the incident light. For circularly polarized light with either left or right circular polarization, however, similar well-defined surface gratings are produced. Both x-ray diffraction and Raman scattering analyses suggest that the lattice structure of the sample's surface is not disturbed by the laser treatments, but the concentration of Ga element can be modified by selecting the pulse width. In comparison with the untreated thin films, the measured optical transmittivity of the structured sample is reduced by 30% in the spectral region of 1–2 µm, indicating a significant change in the photoelectrical properties of the laser-treated CIGS surfaces.

Generation of an Axially Asymmetric Bessel-Like Beam from a Metallic Subwavelength Aperture

An electromagnetic nondiffractive Bessel-like beam from a subwavelength aperture is generated by placing a metallic circular gratinglike structure in front of the aperture. When the incident wave is linearly polarized, the beam is axially asymmetric. The beam possesses fluctuating, but approximately uniform, intensity distribution along its longitudinal axis. The full width at half maximum of the beam remains less than two wavelengths over nearly ten wavelengths. Our experimental results are in good agreement with the simulation results and analytical results.

Fabrication of grating-like polystyrene latex monolayer structure as three-dimensional calibration standards for scanning probe microscope

This paper illuminates the preparation of grating-like polystyrene latex monolayer structure, which can minimize the effects of the size deviation of spheres and the defect transfer on the accuracy as calibration samples for microscopes. The latex films are grown on freshly cleaved mica substrates by vertical deposition method. The concentration dependence of the structure and the topography of latex films is characterized by optical microscope, ultraviolet–visible transmission spectrum and scanning probe microscope. The origination of such a grating-like structure is also discussed.