Blaze Angle Research Articles

Fabrication of angle-gradient echelle grating on metallic glass using shaped vibration cutting with time-varying trajectory

In order to solve the problem of narrow band coverage of traditional infrared gratings, a new type of diffraction grating is invented and named as angle-gradient echelle grating. The blaze angle of the grating gradually changes along the direction of the grating grooves, which can be regarded as etching countless sub-gratings with different blaze angles on a grating, breaking the limitation of the number of blaze angles of traditional gratings. In addition, in order to solve the processing problem of angle-gradient echelle grating, a new processing method, shaped vibration cutting (SVC) with a time-varying trajectory is developed. By exploring the influence of different processing parameters on the grating processing results, a suitable processing plan was proposed. Eventually, angle-gradient echelle grating with blaze angles varying from 30° to 55° and surface roughness of as low as 20 nm was fabricated on metallic glass, a material that is difficult to machine.

A Polarization‐Insensitive and Adaptively‐Blazed Meta‐Grating Based on Dispersive Metasurfaces

AbstractThe diffraction efficiency of blaze gratings is optimized only at a specific frequency due to a fixed blaze angle, resulting in reduced and variable diffraction efficiencies over the working frequency band. Additionally, blazed gratings demonstrate polarization dependence due to their groove structures and the interaction of light with their surfaces. Consequently, designing gratings with constant diffraction efficiencies across a wide frequency bandwidth while maintaining polarization independence remains a challenge. Here, a design paradigm of dispersion engineerable meta‐grating inspired by orthogonal harmonic oscillations (OHO) is presented. Utilizing the OHO model, the phase dispersion of a metasurface can be precisely controlled, which applies to any unit cell featuring two orthogonal electromagnetic resonances. As a proof of concept, a polarization‐insensitive meta‐grating is showcased, where the blazed angle adapts with the incident frequency, ensuring broadband performance. In the experiment, the adaptively‐blazed grating measured an optimized and constant diffraction efficiency of ≈80% over the working wavelength range, i.e., 8.7–12.2 µm. The difference in diffraction efficiency between the two perpendicular linear polarization states remains within 4.6%. The proposed paradigm paves the way for meta‐device design based on precise dispersion engineering, which has potential applications in spectrometers, broadband beam forming and steering, hyperspectral imaging, etc.

Blaze-angle led dark-blue iridescence and superhydrophobicity features of non-morpho Euploea midamus butterfly wing scale

We report on backlit iridescent blue structural coloration as well as superhydrophobicity in a non-morpho butterfly of Euploea midamus (blue-spotted crow) belonging to the Lepidoptera order. Select forewing and hindwing parts were characterized by employing optical microscopy, field emission electron microscopy, UV–vis-NIR spectrophotometry, and an advanced contact angle meter. As substantiated from variable incident angle reflectance spectra and chromaticity plots, the apparent visual effect is most pronounced in the forewing case and at an incident angle of 30–40°, with reflectance peak maxima positioned at ~ 412 nm and 478 nm. Additionally, the forewing scale of this butterfly acts as an anti-reflection filter (< 460 nm) for p-polarized light, showing greater polarization anisotropy in the lower wavelength region. Numerical simulationand microstructure-based analytical calculations with blaze angle grating effects have been considered to elucidate the observed dark-blue iridescence at large. Moreover, both the forewing and hindwing of the butterfly exhibit the ‘lotus effect’, with a contact angle as high as of ~ 150°, low contact angle hysteresis (16° and 13°) as well as low roll-off angles (10° and 7°) to favor self-cleaning action. Theoretical calculations attributing to dual roughnesses would encompass micro-textured and nanoscale asperities within the wing scale interface. The scope of the bifunctional features including optical and dewetting responses in natural systems would provide valuable insights and clues for biomimetics, particularly in nanophotonic and nanocoating applications.

Fabrication of a high-quality, small blaze angle grating for visible short-wave infrared hyperspectral cameras

This study outlines the development of a low line density, small blaze angle grating, optimized for a visible to short-wave infrared hyperspectral camera. An analysis of grating specifications was conducted to meet the precise requirements of this application, particularly focusing on the stringent tolerance limits for the blaze angle. A specialized ruling tool adjustment device was designed to adhere to these exacting blaze angle tolerances. The grating groove shape was examined using atomic force microscopy (AFM), and the theoretical diffraction efficiency of the grating was calculated based on these observations. Additionally, laser-based methods were employed to measure the actual diffraction efficiency of the grating, while interferometry was used to assess the grating’s diffraction wavefront. The test results demonstrate our capability to fabricate high-quality gratings with a low line density and small blaze angles that are suitable for advanced hyperspectral imaging applications.

Exploring the structural color of micro-nano composite gratings with FDTD simulation and experimental validation.

The significance of micro-nano composite gratings (MNCGs) resides in their applications, including optical devices, sensors, and diffractive elements, which drive research interest in their diffraction characteristics. This study investigates both the diffraction characteristics of MNCGs and the factors that influence them by employing both Finite-Difference Time-Domain (FDTD) methods and experimental validation. The initial focus lies in deciphering the differences in diffraction characteristics between micro-gratings (MGs) and MNCGs by analyzing the coupling effects, diffraction order, color distribution, and intensity variation. Additionally, this research emphatically investigates five aspects to discover the influencing factors of MNCG's diffraction characteristics, such as the height, groove angle of MGs and the period, blaze angle, and height of nano-gratings (NGs). Results show that the structural coloration and saturation of MNCG surpass that of MG. NG plays the actual spectral role, and a reduction in the period of NG leads to enhanced splitting light capability of the white light. The optical detection tests validated the simulation results. The present study reveals the diffractive properties of MNCGs, providing technical insights for the design and processing of optically variable devices.

Advanced low blaze angle x-ray gratings via nanoimprint replication and plasma etch.

We developed a new method of making ultra-low blaze angle diffraction gratings for x-ray applications. The method is based on reduction of the blaze angle of a master grating by nanoimprint replication followed by a plasma etch. A master blazed grating with a relatively large blaze angle is fabricated by anisotropic wet etching of a Si single crystal substrate. The surface of the master grating is replicated by a polymer material on top of a quartz substrate by nanoimprinting. Then a second nanoimprinting is performed using the 1st replica as a mold to replicate the saw-tooth surface into a resist layer on top of a Si grating substrate. A reactive ion etch is used to transfer the grating grooves into the Si substrate. The plasma etch provides reduction of the groove depth by a factor defined by the ratio of the etch rates for the resist and Si. We demonstrate reduction of the blaze angle of a master grating by a factor of 5 during fabrication of a 200 lines/mm blazed grating with a blaze angle of 0.2°. We investigated the quality and performance of the fabricated low blaze angle gratings and evaluate process accuracy and reproducibility. The new blaze angle reduction method preserves the planarity of the optical surface of the grating substrate and at the same time provides improvement in the grating groove quality during the reduction process.

Anomalous absorption in TM polarization light by echelle gratings.

Echelle grating plays an essential role in spectral analysis due to its broadband blaze, high dispersion, and high resolution; however, its absorption properties have received no attention. In this paper, we investigate the effect of parameters including incident wavelength, incident angle, and blaze angle on the absorption properties of the Al echelle grating. Based on calculations by the boundary integral equation method, we observe that the Al grating with a large blaze angle has an absorption enhancement effect on TM-polarized waves, and its intensity increases as the incident angle approaches the pseudo-Brewster angle (maximum absorption over 87%). In particular, this absorption enhancement effect is present in the wideband and somewhat generalizable to other metallic materials. In addition, the potential physical mechanisms underlying the absorption enhancement of the echelle grating are analyzed in detail through the electric field distribution. The resonance between the grating anomaly and the pseudo-Brewster effect results in the appearance of surface plasmon polariton and strong absorption. These findings will bring new understanding to the study of echelle gratings in case of high energy loss when the light incidents with a high angle for high resolution and will also show potential applications in electromagnetic stealth, photothermal conversion, and photodetection.

Study of Coherent Smith–Purcell Radiation in the Terahertz Region Using Ultra-Short Electron Bunches

Smith–Purcell radiation (SPR) can be generated nondestructively, providing valuable applications in light sources and beam monitors. Coherent SPR is expected to enable single-shot measurements of very short bunch lengths on the fs scale. Since the reconstruction of the longitudinal bunch shape from the coherent SPR is based on the reliable SPR spectrum, a more detailed understanding of the properties of the radiation is important in this context. Employing a 100 fs ultrashort electron bunch at the t-ACTS test accelerator, the spectrum, angular distribution, and polarization of the produced coherent SPR were measured in the terahertz frequency region and compared with a model calculation. In addition to the widely known surface current model evaluation, the effect of the geometrical shading effect on induced currents on metal surfaces was evaluated using 3D numerical calculations. The obtained SPR characteristics are also presented. In the evaluation of the grating with a shallow blaze angle, it was found that the shading effect has a non-negligible effect on the generated SPR intensity; the measured angular distribution and polarization results were in good agreement with this result.

Кремниевые решетки с блеском для мягкого рентгеновского и экстремального ультрафиолетового излучения: влияние формы профиля штриха и случайной шероховатости на дифракционную эффективность

The effect of the groove profile shape and random roughness of the reflecting facet of five silicon diffraction gratings (1°-4° blaze angle, period 0.4, 1.4, 2, and 4 μm, various coatings) operating in the soft X-ray and extreme ultraviolet radiation ranges on the outflow of the diffraction efficiency from working orders is studied. Diffraction gratings were fabricated by wet etching of Si(111) vicinal wafers and characterized by atomic force microscopy to determine the shape of the groove profile and roughness. The diffraction efficiency of gratings operating in classical and conical diffraction mounts was calculated based on realistic groove profiles by computer simulation using the PCGrateTM code and taking into account the scattering intensity using Nevot-Croce or Debye-Waller corrections or using the Monte Carlo method (rigorously). The effect of the groove profile shape and roughness on the diffraction efficiency of the fabricated Si gratings is shown.

Low line density blazed gratings with low blaze angles

Gratings installed in synchrotron beamlines and instruments have standard line densities ranging from ~300 L/mm up to 2400 L/mm with blaze angles from 0.3° to 2°. For FEL beamlines lower line densities and lower angles are required. To manufacture these in the required high quality poses some challenges with regard to the ruling process and the ion etching process. Our investigation and process results will be described here. Additionally, first results of the process on a grating substrate are demonstrated.

Blazed gratings with both controllable blaze angle and anti-blaze angle fabricated by using a twice oblique ion beam etching method.

A twice oblique ion beam etching method is proposed to fabricate triangular blazed gratings that have controllable both blaze angle and anti-blaze angle. The anti-blaze angle is controlled by first obliquely etching the photoresist mask to obtain an asymmetrical trapezoidal grating, one sidewall of which then evolves into the anti-blaze facet in the second etch step. The blaze angle is controlled by obliquely etching the asymmetrical trapezoidal grating to obtain a triangular blazed grating. We show the key process steps of the method by fabricating a blazed grating with the blaze angle of 20.9° and the anti-blaze angle of 89.0°. The method is verified not only to increase the anti-blaze angle to near 90°, but also have a good tolerance against over-etching.

Ultra-Precision Cutting and Characterization of Reflective Convex Spherical Blazed Grating Elements.

In this work, based on the diffraction principle of reflective blazed grating, the structure size of the convex spherical blazed grating unit is determined, the machining accuracy of the convex spherical blazed grating is formulated, the effects of tool nose radius and Poisson burr on the diffraction efficiency of the convex spherical blazed grating are analyzed, and the performances of cutting convex gratings with microcrystalline aluminum RSA6061 and RSA6061+ chemically plated NiP for two workpiece materials are compared. A convex spherical blazed grating with a radius of curvature R = 41.104 mm, substrate diameter 14 mm, grating density 53.97 line/mm, and blaze angle of roughly 3.8° is turned by a four-axis ultra-precision machining system by adjustment of the cutting tool, workpiece material, and cutting parameters, as well as modification of the layouts of the blazed grating on the convex sphere. The results of the testing of convex spherical blazed grating elements in both layouts show that the size error of the grating period is close for both layouts, the size error of grating height is smaller in the equal-along-arc layout, the blaze angle error in the equal-along-projection layout is only 0.74%, and the average roughness of the blazed surface is less than 5 nm to meet the processing quality requirements of the reflective convex spherical blazed grating. The greater the blaze angle accuracy of the blazed grating, the higher its diffraction efficiency, so the grating element with an equal-along-projection layout has a higher diffraction efficiency than the grating element with an equal-along-arc layout. RSA6061+ chemically plated NiP material is superior to RSA6061 material in Poisson burr height and blazed surface roughness, which is more suitable for Offner-type imaging spectrometers in the spectral range 0.95–2.5 μm (SWIR).

Design and Fabrication of Silicon-Blazed Gratings for Near-Infrared Scanning Grating Micromirror

Blazed gratings are the critical dispersion elements in spectral analysis instruments, whose performance depends on structural parameters and topography of the grating groove. In this paper, high diffraction efficiency silicon-blazed grating working at 800–2500 nm has been designed and fabricated. By diffraction theory analysis and simulation optimization based on the accurate boundary integral equation method, the blaze angle and grating constant are determined to be 8.8° and 4 μm, respectively. The diffraction efficiency is greater than 33.23% in the spectral range of 800–2500 nm and reach the maximum value of 85.62% at the blaze wavelength of 1180 nm. The effect of platform and fillet on diffraction efficiency is analyzed, and the formation rule and elimination method of the platform are studied. The blazed gratings are fabricated by anisotropic wet etching process using tilted (111) silicon substrate. The platform is minished by controlling etching time and oxidation sharpening process. The fillet radius of the fabricated grating is 50 nm, the blaze angle is 7.4°, and the surface roughness is 0.477 nm. Finally, the blazed grating is integrated in scanning micromirror to form scanning grating micromirror by MEMS fabrication technology, which can realize both optical splitting and scanning. The testing results show that the scanning grating micromirror has high diffraction efficiency in the spectral range of 810–2500 nm for the potential near-infrared spectrometer application.

Blazed grating enables highly decoupled optically variable devices fabricated by vibration-assisted diamond texturing.

Optically variable devices (OVDs) are well received for anti-counterfeiting and decorative applications. In this study, new strategies to develop highly decoupled OVDs were proposed and demonstrated based on the fast patterning of blazed gratings by vibration-assisted diamond texturing. A unique surface generation mechanism was revealed as a combined cutting and forming process. One facet of blazed grating is generated by the cutting motion defined by the tool tip trajectory. The other facet is formed by the tool flank face, which establishes the blaze angle. This process is able to generate high-resolution, structurally colored graphics by modulating cutting velocity to control the grating distribution. Due to the unique surface generation mechanism, the orientation of the created blazed gratings is intrinsically perpendicular to the cutting direction. Thus, it enables the flexible control of concentration directions of diffracted light by tuning the orientation of blazed gratings. We designed and demonstrated two types of highly decoupled OVDs based on vibration-induced blazed gratings. The orthogonal-type OVD utilizes the azimuth angle dependence of blazed gratings to encode two images in orthogonal cutting directions. The in-plane-type OVD utilizes the optimized diffraction efficiency of blazed gratings in a given diffraction order to encode two images in opposite cutting directions. The fabricated OVDs are presented and compared with optical simulation results based on an extended scalar diffraction theory.

Blazed Diffraction Gratings on Si --- First Results

Using direct laser lithography and wet etching of polished vicinal Si(111) wafers, a technology was developed and diffraction gratings 500 grooves/mm with a blaze angle of 4o were fabricated. The manufacturing process of a reflective Si-grating with the triangular profile (sawtooth) can be divided into four main steps: (1) obtaining a pattern of a protective mask for grooves etching; (2) anisotropic etching of grooves in KOH solution; (3) etching to smooth the grating profile and polish the surface of working facets; (4) coating to increase reflectivity. The samples obtained were characterized using scanning electron microscopy and atomic force microscopy methods to determine the shape of the groove profile and roughness: the shape turned out to be close to the ideal triangular, and the RMS roughness was less than 0.3 nm. Using PCGrateTM software and taking into account the measured real groove profile, the diffraction efficiency of gratings operating in classical and conical mounts in soft-X-ray and extreme ultraviolet radiation has been simulated. The obtained efficiency values are close to the record ones for the corresponding spectral range and the Au-coating of the grating. Keywords: diffraction grating, wet etching technology of Si, sawtooth groove profile, AFM, SEM, diffraction efficiency modelling.

Compact low-loss low-crosstalk echelle grating demultiplexer on silicon-on-insulator for CWDM

This letter reports on the design of an ultra-compact echelle grating (EG) demultiplexer in O-band for Coarse wavelength division multiplexing (CWDM) systems based on silicon-on-insulator (SOI) and proposes an optimization idea. The correlation between optical performance and design parameters of EG device is analyzed based on the theory of Finite-difference time-domain (FDTD), providing a more accurate optimization reference. Further optimization is achieved by secondary adjustment of the blaze angle of grating facets and the position of output waveguides according to the simulated field distribution. The device has four channels with channel spacing of 20 nm and a small footprint of only 140×100 µm2. The simulated insertion loss for all channels is lower than 2 dB with insertion loss uniformity of below 1dB, and the crosstalk is better than 40 dB.

Highly efficient ultra-low blaze angle multilayer grating.

We have developed an advanced process for blaze angle reduction of x-ray gratings for the soft, tender, and EUV spectral ranges. The process is based on planarization of an anisotropically etched Si blazed grating followed by a chemically selective plasma etch. This provides a way to adjust the blaze angle to any lower value with high accuracy. Here we demonstrate the reduction of the blaze angle to an extremely low value of 0.04°±0.004°. For a 100 lines/mm grating with a Mo/Si multilayer coating, the grating exhibits diffraction efficiency of 58% in the 1st diffraction order at a wavelength of 13.3 nm. This technique will be applicable to a wide range of uses of high efficiency gratings for synchrotron sources, as well as for Free Electron Lasers (FEL).

Optical anisotropy of self-organized gold quasi-blazed nanostructures based on a broad ion beam.

To circumvent elaborate conventional lithographic methods for realizing metallic nanostructures, it is necessary to develop self-organized nanofabrication methods for suitable template structures and their optical characterization. We demonstrate the potential of ion bombardment with impurity co-deposition to fabricate terraced or quasi-blazed nanostructure templates. Self-organized terraced nanostructures on fused silica were fabricated using Ar+ ion bombardment with iron impurity co-deposition and subsequent Au shadow deposition. The aspect ratios are enhanced threefold, and the range of nanostructure period variation is significantly increased with respect to that of conventional nanostructures realized by pure ion bombardment. We reveal the key features of the method via atomic force microscopy and optical characterization. Variable-profile quasiperiodic nanostructures with periods of 100-450 nm, heights of 25-180 nm, and blaze angles of 10°-25° were fabricated over an area of 20×40mm2, and these exhibited tunable and broadening optical anisotropy across the nanostructured area. Thus, the proposed method is a viable technique for rapid, cost-effective, and deterministic fabrication of variable nanostructure templates for potential optical applications.

Дифракционные решетки с блеском, получаемые на пластинах Si --- первые результаты

Using direct laser lithography and liquid etching of polished vicinal Si(111) wafers, a technology was developed and diffraction gratings 500 /mm with a blaze angle of 4° were fabricated. The manufacturing process of a reflective Si-grating of a triangular profile (sawtooth) can be divided into four main steps: (1) obtaining a pattern of a protective mask for etching grooves; (2) anisotropic etching of grooves in KOH solution; (3) etching to smooth the grating profile and polish the surface of working facets; (4) coating to increase reflectivity. The samples obtained were characterized using scanning electron microscopy and atomic force microscopy methods to determine the shape of the groove profile and roughness: the shape turned out to be close to the ideal triangular, and the root-mean square roughness was less than 0.3 nm. With the help of the PCGrate™ code, taking into account the measured real groove profile, the diffraction efficiency of gratings operating in classical and conical mounts in soft-X-ray and extreme ultraviolet radiation has been simulated. The obtained efficiency values are close to the record ones for the corresponding spectral range and the Au-coating of the grating.

Extending the working range for the flame photometric determination of alkali metals and calcium using the PAVLIN spectrometer

At the Novosibirsk Chemical Concentrates Plant, the determination of alkali metals and calcium in the range of 0.1–100 mg/l is carried out using atomic emission spectra excited in an air-acetylene flame and recorded in the range of 390–860 nm. When these elements are analyzed simultaneously in a wide range of concentrations, the accumulation time of the analytical signal (exposure) is determined by the minimum concentration of calcium. However, at this exposure, the highly sensitive lines of sodium and potassium do not provide the analysis in the entire concentration range, since at large values, the analytical signal goes into saturation. Other analytical lines of potassium and sodium in the above-mentioned operating spectral range have three to four orders of magnitude lower sensitivity. As a result, there may be a gap in the range of detectable concentrations. This paper provides a way to eliminate this gap. To evaluate the degree of correction of the recorded signal, the relative intensities of the spectral lines of potassium and sodium excited in an air-acetylene flame are calculated. Then, based on the calculation results, an optimal echelette diffraction grating with a blaze angle of 300 nm is selected, and a combination of filters is installed to equalize the recorded radiation. As a result, for sodium and potassium, for which the determination is carried out along two analytical lines, the calibration dependences have an overlap that includes at least two concentration values.