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Fabrication of Tuned Lipss-Based Metallic Polarization Gratings
Abstract
Surface nanostructuring has received increasing attention in recent years due to the wide range of applications in which it offers advantages. Particularly, Laser-Induced Periodic Surface Structures (LIPSS) have proven useful for surface functionalization. LIPSS are periodic formations generated in most materials when irradiated with linearly polarized radiation. The orientation of these structures is directly linked to the polarization of the incident light, while other parameters of their morphology such as period and depth can be controlled with the number of pulses, fluence, wavelength and pulse duration of the incident light.
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Laser texturing is an emerging technology for generating surface functionalities on basis of optical, mechanical, or chemical properties. Taking benefit of laser sources with ultrashort (fs) pulse durations features outstanding precision of machining and negligible rims or burrs surrounding the laser-irradiation zone. Consequently, additional mechanical or chemical post-processing steps are usually not required for fs-laser surface texturing (fs-LST). This work aimed to provide a bridge between research in the field of tribology and laser materials processing. The paper reviews the current state-of-the-art in fs-LST, with a focus on the tribological performance (friction and wear) of specific self-organized surface structures (so-called ripples, grooves, and spikes) on steel and titanium alloys. On the titanium alloy, specific sickle-shaped hybrid micro-nanostructures were also observed and tribologically tested. Care is taken to identify accompanying effects affecting the materials hardness, superficial oxidation, nano- and microscale topographies, and the role of additives contained in lubricants, such as commercial engine oil.
We employ a femtosecond light sheet generated by a cylindrical lens to rapidly produce high-fidelity nano-structures over large area on silicon surface. The Fourier analysis of electron microscopy images of the laser-induced surface structures reveals sharp peaks indicating good homogeneity. We observed an emergence of second-order spatial periodicity on increasing the scan speed. Our reliable approach may rapidly nano-pattern curved solid surfaces and tiny objects for diverse potential applications in optical devices, structural coloring, plasmonic substrates and in high-harmonic generation.
Highly regular laser-induced periodic surface structures (HR-LIPSS) have been fabricated on surfaces of Mo, steel alloy and Ti at a record processing speed on large areas and with a record regularity in the obtained sub-wavelength structures. The physical mechanisms governing LIPSS regularity are identified and linked with the decay length (i.e. the mean free path) of the excited surface electromagnetic waves (SEWs). The dispersion of the LIPSS orientation angle well correlates with the SEWs decay length: the shorter this length, the more regular are the LIPSS. A material dependent criterion for obtaining HR-LIPSS is proposed for a large variety of metallic materials. It has been found that decreasing the spot size close to the SEW decay length is a key for covering several cm2 of material surface by HR-LIPSS in a few seconds. Theoretical predictions suggest that reducing the laser wavelength can provide the possibility of HR-LIPSS production on principally any metal. This new achievement in the unprecedented level of control over the laser-induced periodic structure formation makes this laser-writing technology to be flexible, robust and, hence, highly competitive for advanced industrial applications based on surface nanostructuring.
We study the fabrication of photonic surface structures in single crystal diamond by means of highly controllable direct femtosecond UV laser induced periodic surface structuring. By appropriately selecting the excitation wavelength, intensity, number of impinging pulses and their polarization state, we demonstrate emerging high quality and fidelity diamond grating structures with surface roughness below 1.4 nm. We characterize their optical properties and study their potential for the fabrication of photonic structure antireflection coatings for diamond Raman lasers in the near-IR.
The precise control over the interaction between cells and the surface of materials plays a crucial role in optimizing the integration of implanted biomaterials. In this regard, material surface with controlled topographic features at the micro- and nano-scales has been proved to affect the overall cell behavior and therefore the final osseointegration of implants. Within this context, femtosecond (fs) laser micro/nano machining technology was used in this work to modify the surface structure of stainless steel aiming at controlling cell adhesion and migration. The experimental results show that cells tend to attach and preferentially align to the laser-induced nanopatterns oriented in a specific direction. Accordingly, the laser-based fabrication method here described constitutes a simple, clean, and scalable technique which allows a precise control of the surface nano-patterning process and, subsequently, enables the control of cell adhesion, migration, and polarization. Moreover, since our surface-patterning approach does not involve any chemical treatments and is performed in a single step process, it could in principle be applied to most metallic materials.
The principles of the holographic lithography technique are reviewed, and the ability in the formation of structures with different periods by the holographic lithography technique in SZ2080 is demonstrated. The influence of laser exposure, phase shift between interfering laser beams, and the used laser wavelength on the structures fabricated by the four-beam interference technique has been studied. It is shown that by using the interfering beams with a different phase is it possible to reduce the period of the structure root 2 times compared to the four interfering beams of the same phase. Fabrication of micro-structures by the holographic lithography technique can be realized via multi-photon and single-photon polymerization processes. The structures created by these two techniques are compared. Finally, in the experiments with the five-beam interference, the double-period effect was observed by adding the zero-order beam with a low intensity. The fabricated periodic microstructures have the potential to be used as a scaffold for cell growth and micro-optics.
Laser-induced periodic surface structures (LIPSS) can be reliably produced with ultrashort (<10ps) laser pulses given fluence near the ablation threshold. Neat, parallel, uniform structures are harder to reproduce. Electrodynamic models show a field at normal incidence interacts with the surface resulting in periodicity in intensity along the surface in the direction of the incident E-field producing ridges and toughs on the surface orthogonal to the E-field. A completely smooth surface offers nothing to perturb the eventual periodic feature formation but is very difficult to achieve: we have demonstrated that simply avoiding surface roughness components near the frequency and direction of the emergent features significantly improves uniform feature production. An appropriate unidirectional polishing process can be realised using an inexpensive spinning cloth wheel. By using a cylindrical lens we were also able to process stainless steel surfaces at 5mm2.s−1 so indicating useful industrial potential.
The surface morphology of a Niobium sample, irradiated in air by a femtosecond laser with a
wavelength of 800 nm and pulse duration of 100 fs, was examined. The period of the
micro/nanostructures, parallel and perpendicularly oriented to the linearly polarized fs-laser beam, was studied by means of 2D Fast Fourier Transform analysis. The observed Laser-Induced Periodic Surface Structures (LIPSS) were classified as Low Spatial Frequency LIPSS (periods about 600 nm) and High Spatial Frequency LIPSS, showing a periodicity around 300 nm, both of them perpendicularly oriented to the polarization of the incident laser wave. Moreover, parallel high spatial frequency LIPSS were observed with periods around 100 nm located at the peripheral areas of the laser fingerprint and overwritten on the perpendicular periodic gratings. The results indicate that this method of micro/nanostructuring allows controlling the Niobium grating period by the number of pulses applied, so the scan speed and not the fluence is the key parameter of control. A discussion on the mechanism of the surface topology evolution was also introduced.
We report on the fabrication of laser-induced periodic surface structures in Cr films upon high repetition rate fs laser irradiation (up to 1 MHz, 500 fs, 1030 nm), employing beam scanning. Highly regular large-area (9 cm2) gratings with a relative diffraction efficiency of 42% can be produced within less than 6 min. The ripple period at moderate and high fluences is 0.9 μm, with a small period of 0.5 μm appearing at lower energies. The role of the irradiation parameters on the characteristics of the laser-induced periodic surface structures (LIPSS) is studied and discussed in the frame of the models presently used. We have identified the polarization vector orientation with respect to the scan direction as a key parameter for the fabrication of high-quality, large-area LIPSS, which, for perpendicular orientation, allows the coherent extension of the sub-wavelength structure over macroscopic distances. The processing strategy is robust in terms of broad parameter windows and applicable to other materials featuring LIPSS.
The polarization state of an ultrafast laser is dynamically controlled using two Spatial Light Modulators and additional waveplates. Consequently, four states of polarization, linear horizontal and vertical, radial and azimuthal, all with a ring intensity distribution, were dynamically switched at a frequency ν = 12.5Hz while synchronized with a motion control system. This technique, demonstrated here for the first time, enables a remarkable level of real-time control of the properties of light waves and applied to real-time surface patterning, shows that highly controlled nanostructuring is possible. Laser ablation of Induced Periodic Surface Structures is used to directly verify the state of polarization at the focal plane.
We introduce a fast and cost-effective technique to fabricate large-area periodically nanopatterned metal samples and apply this technique to create reflective nano-grid wave plates for optical wavelengths. The technique makes use of azo-polymer-based interference lithography and a special imprint method that enables creating large-area metal nanopatterns with high vertical walls. We fabricate and experimentally test a gold nano-grid wave plate that operates as reflective λ/4-plate for λ = 604 nm and λ/2-plate for λ = 997 nm.
Nondiffracting Bessel beams have been recently applied to single shot ultrafast laser processing of high aspect ratio nanochannels. We review the principles and benefits of nondiffracting Bessel beams for material processing, and we compare experimental results with numerical simulations. We show how the stationarity of nonlinear propagation of ultrafast laser pulses allows high aspect ratio material processing.
The coupled-wave method formulated by Moharam and Gaylord [J. Opt. Soc. Am. 73, 451 (1983)] is known to be slowly converging, especially for TM polarization of metallic lamellar gratings. The slow convergence rate has been analyzed in detail by Li and Haggans [J. Opt. Soc. Am. A 10, 1184 (1993)], who made clear that special care must be taken when coupled-wave methods are used for TM polarization. By reformulating the eigenproblem of the coupled-wave method, we provide numerical evidence and argue that highly improved convergence rates similar to the TE polarization case can be obtained. The discussion includes both nonconical and conical mountings.
We report the first full numerical analysis of polarization gratings PGs, and study their most general properties and limits by using the finite-difference time-domain FDTD method. In this way, we avoid limiting assumptions on material properties or grating dimensions e.g., no paraxial approximations and provide a more complete understanding of PG diffraction behavior. We identify the fundamental delineation between diffraction regimes thin versus thick for anisotropic gratings and determine the conditions for 100% diffraction efficiency in the framework of the coupled-wave and Q parameters. Diffraction characteristics including the efficiency, spectral response, and polarization sensitivity are investigated for the two primary types of PGs with linear and circular birefringence. The angular response and finite-grating behavior i.e., pixelation are also examined. Comparisons with previous analytic approximations, where applicable, show good agreement.
We report on a four-mirror reflective wave-plate system based on a phase-shifting mirror (PSM) for a continuous variation of elliptical polarization without changing the beam position and direction. The system presented and characterized here can replace a conventional retardation plate providing all advantages of a PSM, such as high damage-threshold, large scalability, and low dispersion. This makes reflective wave-plates an ideal tool for ultra-high power laser applications. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3694659]
We theoretically investigate optical birefringence originating from subwavelength structures in intrinsic birefringent media. Assuming alternating layers of isotropic and anisotropic materials, the propagation of optical waves is simulated on the basis of the finite difference time domain method. Optical polarization changes throughout the structure reveal the birefringence of the layered structure as a whole. In addition, the birefringence is also analyzed on the basis of effective medium theory. The results indicate that the optical birefringence of the structure as a whole can be modified by the magnitude and direction of the intrinsic birefringence of the anisotropic layers. This theoretical prediction will be useful for micro- and nanofabrication in optical devices.
An efficient way to generate nanoscale laser-induced periodic surface structures (LIPSS) in rutile-type TiO(2) with frequency-converted femtosecond laser pulses at wavelengths around 400 nm is reported. Extended-area structuring on fixed and moving substrates was obtained by exploiting the line focus of a cylindrical lens. Under defined conditions with respect to pulse number, pulse energy and scanning velocity, two types of ripple-like LIPSS with high and low spatial frequencies (HSFL, LSFL) with periods in the range of 90 nm and 340 nm, respectively, were formed. In particular, lower numbers of high energetic pulses favour the generation of LSFL whereas higher numbers of lower energetic pulses enable the preferential creation of HSFL. Theoretical calculations on the basis of the Drude model support the assumption that refractive index changes by photo-excited carriers are a major mechanism responsible for LSFL. Furthermore, the appearance of random substructures as small as 30 nm superimposing low spatial frequency ripples is demonstrated and their possible origin is discussed.
Polarizing beam splitters that use the anisotropic spectral reflectivity (ASR) characteristic of high-spatial-frequency multilayer binary gratings have been designed, fabricated, and characterized. Using the ASR effect with rigorous coupled-wave analysis, we design an optical element that is transparent for TM polarization and reflective for TE polarization at an arbitrary incidence angle and operational wavelength. The experiments with the fabricated element demonstrate a high efficiency (97), with polarization extinction ratios higher than 220:1 at a wavelength of 1.523 m over a 20 angular bandwidth by means of the ASR characteristics of the device. These ASR devices combine many useful characteristics, such as compactness, low insertion loss, high efficiency, and broad angular and spectral bandwidth operations.
We propose an optical wave plate using a metal nano-grid. The wave plate operates in reflection mode. A single-mode truncated modematching theory is presented as a general method to design such nano-grid wave plates with the desired phase difference between the reflected TM and TE polarizations. This analytical theory allows angled incidence calculations as well, and numerical results agree-well with comprehensive finite-difference time-domain electromagnetic simulations. Due to the subwavelength path-length, the reflective wave plate is expected to have improved broad-band functionality over existing zero-order transmissive wave plates, for which an example is provided. The proposed wave plate is simple and compact, and it is amenable to existing nanofabrication techniques. The reflective geometry is especially promising for applications including liquid-crystal displays and laser feedback experiments.
A new concept of mechano-responsive colour-change is introduced in the present work that allows for turning flexible materials into an optical mechano-sensitive sensor. For this purpose diffraction gratings based on laser-induced periodic surface structures (LIPSS) are produced on ductile stainless steel surfaces (X2CrNiMo17–12–2) using a femtosecond laser (fs-laser). When the material is deformed, the increase of the lattice spacing in the diffraction grating leads to a mechano-responsive change of the initial structural colour in the direction of longer wavelengths. With increasing plastic deformation of the metal, the formation of tilted and twisted slip bands leads to a disappearance of the structural colours before the material fails. Using metal masters, the LIPSS can be transferred to elastomers by replica casting. For elastomers produced by replica casting, the mechano-responsive colour change is reversible. The mechanically induced colour change of LIPSS is of particular interest for the development of novel switches, safety devices, strain gauges, sensors, hazard classification and early detection of material failure.
Polarized light is a pervasive influence in our world-and scientists and engineers in a variety of fields require the tools to understand, measure, and apply it to their advantage. Offering an in-depth examination of the subject and a description of its applications, Polarized Light, Third Edition serves as a comprehensive self-study tool complete with an extensive mathematical analysis of the Mueller matrix and coverage of Maxwell’s equations. Links Historical Developments to Current Applications and Future Innovations This book starts with a general description of light and continues with a complete exploration of polarized light, including how it is produced and its practical applications. The author incorporates basic topics, such as polarization by refraction and reflection, polarization elements, anisotropic materials, polarization formalisms (Mueller-Stokes and Jones) and associated mathematics, and polarimetry, or the science of polarization measurement. New to the Third Edition: • A new introductory chapter • Chapters on: polarized light in nature, and form birefringence • A review of the history of polarized light, and a chapter on the interference laws of Fresnel and Arago-both completely re-written • A new appendix on conventions used in polarized light • New graphics, and black-and-white photos and color plates Divided into four parts, this book covers the fundamental concepts and theoretical framework of polarized light. Next, it thoroughly explores the science of polarimetry, followed by discussion of polarized light applications. The author concludes by discussing how our polarized light framework is applied to physics concepts, such as accelerating charges and quantum systems. Building on the solid foundation of the first two editions, this book reorganizes and updates existing material on fundamentals, theory, polarimetry, and applications. It adds new chapters, graphics, and color photos, as well as a new appendix on conventions used in polarized light. As a result, the author has re-established this book’s lofty status in the pantheon of literature on this important field.
We demonstrate that a stochastic optimization algorithm with a properly chosen, weighted fitness function, following a global variation of parameters upon each step can be used to effectively design reflective polarizing optical elements. Two sub-wavelength metallic metasurfaces, corresponding to broadband half- and quarter-waveplates are demonstrated with simple structure topology, a uniform metallic coating and with the design suited for the currently available microfabrication techniques, such as ion milling or 3D printing.
We review thin micro-optics components with nanostructured microreliefs intended to control the polarization and phase of laser light. These components include transmission and reflection subwavelength diffraction gratings characterized by spatially −varying groove directions and fill factors, with the microrelief period and depth remaining approximately unchanged. In the visible spectrum, the microrelief features may vary in size from dozens to hundreds of nanometers. Segmented diffractive micropolarizers for linear to radial/azimuthal polarization conversion and subwavelength microlenses for tightly focusing the laser light are discussed in detail. Examples of particular micropolarizers and microlenses fabricated in amorphous silicon films are also given.
Broadband reflective polarizers for liquid crystal displays (LCDs) are designed. The working principle is based on giant form birefringence generated by engineering the materials of the subwavelength gratings. The optical performances of the proposed polarizers are investigated by the finite difference time domain (FDTD) method. The proposed polarizers show an ultra-thin profile, high transmission, large extinction ratio and wide acceptable angle, all of which are highly desirable for high-efficiency ultra-thin LCDs. Finally, the fabrication tolerance of the proposed structure is discussed in detail.
We have investigated a four-Sector transmission Polarization Converter (4-SPC) for a wavelength of 633 nm, that enables the conversion of a linearly polarized incident beam into a mixture of linearly and azimuthally polarized beams. It was numerically shown that by placing a Fresnel zone plate of focal length 532 nm immediately after the 4-SPC, the incident light can be focused into an oblong subwavelength focal spot whose size is smaller than the diffraction limit (with width and breadth, respectively, measuring FWHM = 0.28. and FWHM = 0.45., where. is the incident wavelength and FWHM stands for full-width at half maximum of the intensity). After passing through the 4-SPC, light propagates in free space over a distance of 300 mu m before being focused by a Fresnel zone plate (ZP), resulting in focal spot measuring 0.42 lambda and 0.81 lambda. The focal spot was measured by a near-field microscope SNOM, and the transverse E-field component of the focal spot was calculated to be 0.42. and 0.59 lambda. This numerical result was verified experimentally, giving a focal spot of smaller and larger size, respectively, measuring 0.46 lambda and 0.57 lambda. To our knowledge, this is the first implementation of polarization conversion and subwavelength focusing of light using a pair of transmission micro-optic elements. (C) 2016 Optical Society of America
Materials with three-dimensional micro- and nanoarchitectures exhibit many beneficial mechanical, energy conversion and optical properties. However, these three-dimensional microarchitectures are significantly limited by their scalability. Efforts have only been successful only in demonstrating overall structure sizes of hundreds of micrometres, or contain size-scale gaps of several orders of magnitude. This results in degraded mechanical properties at the macroscale. Here we demonstrate hierarchical metamaterials with disparate three-dimensional features spanning seven orders of magnitude, from nanometres to centimetres. At the macroscale they achieve high tensile elasticity (>20%) not found in their brittle-like metallic constituents, and a near-constant specific strength. Creation of these materials is enabled by a high-resolution, large-area additive manufacturing technique with scalability not achievable by two-photon polymerization or traditional stereolithography. With overall part sizes approaching tens of centimetres, these unique nanostructured metamaterials might find use in a broad array of applications.
Picosecond direct laser interference patterning (ps-DLIP) is investigated theoretically and experimentally for the bulk metals copper, stainless steel and titanium. While surface texturing with nanosecond pulses is limited to feature sizes in the micrometer range, utilizing picosecond pulses can lead to sub-micrometer structures. The modelling and simulation of ps-DLIP is based on the two-temperature model and was carried out for a pulse duration of 35 ps at 515 nm wavelength and a laser fluence of 0.1 J/cm2. The subsurface temperature distribution of both electrons and phonons was computed for periodic line-like structures with a pitch of 0.8 μm. The increase in temperature rises for a lower absorption coefficient and a higher thermal conductivity. The distance, at which the maximum subsurface temperature occurs, increases for a small absorption coefficient. High absorption and low thermal conductivity minimize internal heating and give rise to a pronounced surface micro topography with pitches smaller than 1 μm. In order to confirm the computed results, periodic line-like surface structures were produced using two interfering beams of a Yb:YAG-Laser with 515 nm wavelength and a pulse duration of 35 ps. It was possible to obtain a pitch of 0.7 μm on the metallic surfaces.
Doc. ID 253220) Diffraction gratings were discovered during the 18th century, and they are now widely used in spectrometry analysis, with outstanding achievements spanning from the probing of single molecules in biological samples to the analysis of solar systems in astronomy. The fabrication of high-quality diffraction gratings requires precise control of the period at a nanometer scale. The discovery of lasers in the 1960s gave birth to optical beam lithography in the 1970s. This technology revolutionized the fabrication of diffraction gratings by offering highly precise control of the grating period over very large scales. It is surprising to see that a few years after, the unique spectral properties of diffraction gratings revolutionized, in turn, the field of high-energy lasers. We review in this paper the physics of diffraction gratings and detail the interest in them for pulse compression of high-power laser systems.
A reflective waveplate with subwavelength grating structure of the photoresist was fabricated using two-beam interference technology. From the optical measurement, it is found that the phase retardation of the fabricated reflective element (period: 400 nm, fill factor: 0.5, depth: 280 nm) was almost the same as that of the transmission waveplate with the around twice deeper grating depth (period: 400 nm, fill factor: 0.5, depth: 450nm). This is because the optical length of the reflective element was twice of the transmissive one by using reflection. By changing the period and depth to 285nm and to 300 nm, respectively, it is also confirmed from the experimental result that the phase retardation of the reflective waveplate exceeded 150° for 450nm wavelength at the incident angle of 45°.
Two-photon polymerization (2PP) is a powerful tool for direct laser writing of micro-optical and photonic structures due to its flexibility in 3D structuring and sub-micrometer resolution. However, it can be time consuming to fabricate arrays of micro-optical devices and complex photonic structures. In this study, we propose to use predefined patterns (PPs) for parallel 2PP processing. A PP contains a multiple focal spot pattern optimized for the fabrication of certain microstructures. PP can be created by holographic laser beam modulation with a spatial light modulator (SLM). The quantity and position of the multiple foci can be flexibly and precisely controlled by predesigned computer generated holograms (CGHs). With these specially designed PPs, parallel fabrication of arbitrary distributed microlens arrays and 3D photonic structures is demonstrated. This method significantly improves throughput and flexibility of the 2PP technique and can be used for mass production of functional devices in micro-optics and photonics.
The femtosecond laser color marking stainless steel surfaces with different incident wavelengths were investigated theoretically and experimentally. It indicates that the spectral regions of the colors firstly increase and then reduce with increasing spatial periods of the ripples induced by laser irradiation. Additionally, the colors are gradually changed from blue to red due to the elongation of the diffracted light wavelengths. As a result, the color effects are distinctly different. This study offers a new controllable parameter to produce diverse colors, which may find a wide range of applications in the laser color marking, art designing and so on.
Ripples with a subwavelength period were induced on the surface of a stainless steel (301 L) foil by femtosecond laser pulses. By optimizing the irradiation fluence of the laser pulses and the scanning speed of the laser beam, ripples with large amplitude (∼150 nm) and uniform period could be obtained, rendering vivid structural colors when illuminating the surface with white light. It indicates that these ripples act as a surface grating that diffracts light efficiently. The strong dependence of the ripple orientation on the polarization of laser light offers us the opportunity of decorating different regions of the surface with different types of ripples. As a result, different patterns can be selectively displayed with structural color when white light is irradiated on the surface from different directions. More interestingly, we demonstrated the possibility of decorating the same region with two or more types of ripples with different orientations. In this way, different patterns with spatial overlapping can be selectively displayed with structural color. This technique may find applications in the fields of anti-counterfeiting, color display, decoration, encryption and optical data storage.
We describe S 4, a free implementation of the Fourier modal method (FMM), which has also been commonly referred to as rigorous coupled wave analysis (RCWA), for simulating electromagnetic propagation through 3D structures with 2D periodicity. We detail design aspects that allow S 4 to be a flexible platform for these types of simulations. In particular, we highlight the ability to select different FMM formulations, user scripting, and extensibility of program capabilities for eigenmode computations.
We theoretically propose two types of antireflection (AR) coatings for metals. One type consists of a single layer of a dielectric material having a high refractive index and is used for metals such as stainless steels in the infrared region. The other type consists of bilayers of absorptive and dielectric materials that are used in order to reduce the reflectance of high reflectivity metals such as Al in the visible region. In both types of AR coatings, FeSi2 plays an essential role. The bilayered AR concept has been applied to reduce the reflectance of wire grid (WG) polarizers made of Al. An FeSi2 layer, which serves as an absorptive layer, has been deposited by glancing angle deposition technique immediately on the top of Al wires covered with a thin SiO2 layer, which serves as a gap layer. For the optimum combination of the thicknesses of FeSi2 and SiO2, the reflectance reduces to lower than a few percent independent of the polarization, whereas the transmission polarization properties remain favorable. Because low reflectivity WG polarizers are completely composed of inorganic materials, they are useful for applications requiring thermal durability, such as liquid crystal projection displays.
Diffraction by a dielectric surface-relief grating is analyzed using rigorous coupled-wave theory. The analysis applies to arbitrary grating profiles, groove depths, angles of incidence, and wavelengths. Example results for a wide range of groove depths are presented for sinusoidal, square-wave triangular, and sawtooth gratings. Diffraction efficiencies obtained from the present method of analysis are compared with previously published numerical results. To obtain large diffraction efficiencies (greater than 85%) for gratings with typical substrate perinittivities, it is shown that the grating profile should possess even symmetry.
A new formulation of the Fourier modal method (FMM) that applies the correctrules of Fourier factorization for crossed surface-relief gratings is presented.The new formulation adopts a general nonrectangular Cartesian coordinate system, which gives the FMM greater generality and in some cases the ability to savecomputer memory and computation time. By numerical examples, the new FMM isshown to converge much faster than the old FMM. In particular, the FMM isused to produce well-converged numerical results for metallic crossed gratings.In addition, two matrix truncation schemes, the parallelogramic truncationand a new circular truncation, are considered. Numerical experiments showthat the former is superior.
The rigorous coupled-wave analysis technique for describing the diffraction of electromagnetic waves by periodic grating structures is reviewed. Formulations for a stable and efficient numerical implementation of the analysis technique are presented for one-dimensional binary gratings for both TE and TM polarization and for the general case of conical diffraction. It is shown that by exploitation of the symmetry of the diffraction problem a very efficient formulation, with up to an order-of-magnitude improvement in the numerical efficiency, is produced. The rigorous coupled-wave analysis is shown to be inherently stable. The sources of potential numerical problems associated with underflow and overflow, inherent in digital calculations, are presented. A formulation that anticipates and preempts these instability problems is presented. The calculated diffraction efficiencies for dielectric gratings are shown to converge to the correct value with an increasing number of space harmonics over a wide range of parameters, including very deep gratings. The effect of the number of harmonics on the convergence of the diffraction efficiencies is investigated. More field harmonics are shown to be required for the convergence of gratings with larger grating periods, deeper gratings, TM polarization, and conical diffraction.
A rigorous coupled-wave approach is used to analyze diffraction by general planar gratings bounded by two different media. The grating fringes may have any orientation (slanted or unslanted) with respect to the grating surfaces. The analysis is based on a state-variables representation and results in a unifying, easily computer-implementable matrix formulation of the general planar-grating diffraction problem. Accurate diffraction characteristics are presented for the first time to the authors’ knowledge for general slanted gratings. This present rigorous formulation is compared with rigorous modal theory, approximate two-wave modal theory, approximate multiwave coupled-wave theory, and approximate two-wave coupled-wave theory. Typical errors in the diffraction characteristics introduced by these various approximate theories are evaluated for transmission, slanted, and reflection gratings. Inclusion of higher-order waves in a theory is important for obtaining accurate predictions when forward-diffracted orders are dominant (transmission-grating behavior). Conversely, when backward-diffracted orders dominate (reflection-grating behavior), second derivatives of the field amplitudes and boundary diffraction need to be included to produce accurate results.
Subwavelength metallic and dielectric diffraction gratings which rotate the linear polarization of incident light by 90° are examined. Using rigorous diffraction theory in total-internal-reflection configuration, it is shown that full conversion from incident transverse electric field to transverse magnetic zero-order field can be achieved with both dielectric and metallic elements,
but dielectric gratings provide higher efficiency and are thus preferable. The fabrication aspects and constraints are discussed in detail and the behavior of the gratings over broad wavelength bands is presented.
Semiconductor surface damage, produced by a focused beam of ruby laser light, consisted of regular patterns of cracks and a system of parallel straight lines. The system of grooves (spacing of about 0.0001 cm) can be explained on the basis of diffraction effects at the focus of a lens. The regular crack patterns were related to the cleavage habits of the semiconductors by x-ray analysis. (Author)
We demonstrate optically thin quarter-wave plates built with metasurfaces that generate high-quality circularly-polarized light over a broad wavelength range for arbitrary orientation of the incident linear polarization. The metasurface consists of an array of plasmonic antennas with spatially varying phase and polarization response. Experimentally demonstrated quarter-wave plates generate light with a high degree of circular polarization (>0.97) from λ=5 to 12 μm, representing a major advance in performance compared to previously reported plasmonics-based wave plates.
A detailed investigation of the performance of the Fresnel rhomb is given, particular attention being paid to the effect of residual stress birefringence in the rhomb material and of films on the surfaces at which total internal reflection occurs. For glass and silica rhombs good agreement has been obtained between experimental results and theoretically computed phase retardations. The possibility of producing an achromatic quarter-wave system by depositing thin dielectric films on the reflecting surfaces of the rhomb is explored, measurements showing that the variation in phase retardation through the visible spectrum and near ultra-violet extending down to a wavelength of 330 nm can be kept to less than 0.4°.
Periodic line structures with a period of 167 nm and linewidths varying from 35 to 100 nm have been produced on polyimide by direct ablation with a KrF laser using an interferometric technique. Since ablation is a nonlinear process, the resolution can exceed that expected from the wavelength and numerical aperture of the system and the linewidth can be controlled by varying the laser fluence. This externally generated period of 167 nm prevents the spontaneous growth of periodic surface structures due to radiation remnants.
We present a novel reflective quarter-wave plate comprised of subwavelength meanderline elements. The device is operational over the long-wave infrared (LWIR) spectrum, with significant spectral and angular bandwidths. Power reflection is approximately 70% over the majority of the LWIR. Efficient conversion from a 45° linear polarization state into circular polarization is demonstrated from finite-element electromagnetic simulations and from broadband polarimetric measurements.
A subwavelength concentric ring metal grating for visible light (λ=632.8 nm) is designed and fabricated by electron-beam lithography to transform circularly polarized light into radially polarized light. Experimental results are compared to theoretical predictions and the advantages and disadvantages of the element with alternative methods are discussed.
We propose achromatic quarter-wave plates of a subwavelength grating structure. When the period of the grating structure is smaller than the wavelengths of the incident light, the structure is considered to be an optically anisotropic medium. The effective refractive indices strongly depend on the wavelengths, especially when the period is close to the wavelength. Using this feature, we can design a grating quarter-wave plate whose phase retardation is maintained at pi/2 for a wide wavelength range. A design method using the effective medium theory is described, and the wave plates designed were evaluated by numerical calculation with a rigorous electromagnetic grating theory. The calculation results led to the possibility of an achromatic quarter-wave plate whose retardation errors are smaller than 3 degrees for a +/-10% change in wavelength.
Laser-Induced Periodic Surface Structures— A Scientific Evergreen
- J Bonse
- S Höhm
- S V Kirner
- A Rosenfeld
- J Krüger
J. Bonse, S. Hohm, S. V. Kirner, A. Rosenfeld, J. Kruger, Laser-Induced Periodic
Surface Structures-A Scientific Evergreen, IEEE J. Sel. Top. Quantum Electron.
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Effective refractive index and composition of oxidized porous silicon films
- E Astrova
- V A Tolmachev
E. V Astrova, V.A. Tolmachev, Effective refractive index and composition of
oxidized porous silicon films, Mater. Sci. Eng. B. 69-70 (2000) 142-148.
doi:https://doi.org/10.1016/S0921-5107(99)00236-6.