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Using simulation by means of the finite difference method in the time domain (FDTD), we demonstrated that focal spots of different shape with respect to both intensity and energy flux form upon tight focusing of a Gaussian linearly polarized beam containing an optical vortex by a Fresnel zone plate and upon focusing of a Gaussian beam by a spiral zone plate. The most significant differences are observed for the topological charge equal three. The energy flux upon focusing of a Gaussian beam by a Fresnel zone plate has a ring distribution, while the distribution of intensity and energy flux upon beam focusing by a spiral zone plate has three local maxima, which corresponds to the spiral-zone-plate order. The petal structure of intensity (and the energy flux) changes to a ring distribution at a certain distance from the focus. [ABSTRACT FROM AUTHOR]

Presented here is a constructive solution to the challenge of utilizing the diffraction phenomenon for mitigating noise around roadside objects caused by the movement of vehicles on transportation routes. In contrast to existing prototypes, the innovation of the proposed solution lies in the creation of an active system that concentrates and directs oscillations originating from transportation sources. This active system, centered around sound absorption and reflection, establishes protective barriers and focuses on sound vibrations. The incorporation of diffraction effects within the Fraunhofer zones, along with the utilization of Fresnel lenses, directs attention towards these vibrations. The technical objective of harnessing the diffraction phenomenon for noise reduction around roadside objects involves demonstrating the feasibility of using a Fresnel zone plate (FZP) tailored for a specific oscillation frequency. This plate should demonstrate the ability to effectively manipulate sounds of varying frequencies while retaining its diffractive focusing capabilities. The intrinsic frequency characteristics of diffractive elements cannot be eliminated due to the inherent nature of sound diffraction. Consequently, it is imperative to thoroughly investigate and account for these properties. A groundbreaking discovery has been made, confirming the phenomenon of noise concentration originating from transportation sources. This revelation suggests that when a FZP is employed at frequencies other than its designed frequency, the concentration of oscillations remains. However, only the focal point of concentration shifts. Through experimentation, it has been established that the same FZP can be employed for varying wavelengths within a range of approximately ±20% while adhering to diffraction conditions. The feasibility of employing the thin lens formula to focus oscillations following the passage through a FZP has been substantiated. This solution also delves into the principal focusing, frequency, and shaping characteristics of the diffractive elements within FZPs. Furthermore, a computed estimation of the acoustic field scattered by a diffraction grating is compared against experimental data. This validates the approach and its efficacy in practical scenarios. The potential of harnessing the diffraction phenomenon to concentrate and regulate noise from transportation sources, thereby safeguarding roadside objects, is presented as a promising avenue for exploration.

Lift-off processing is a common method of pattern transfer for different nanofabrication applications. With the emergence of chemically amplified and semi-amplified resist systems, the possibilities for pattern definition via electron beam lithography has been widened. We report a reliable and simple lift-off process for dense nanostructured pattern in CSAR62. The pattern is defined in a single layer CSAR62 resist mask for gold nanostructures on silicon. The process offers a slimmed down pathway for pattern definition of dense nanostructures with varied feature size and an up to 10 nm thick gold layer. The resulting patterns from this process have been successfully used in metal assisted chemical etching applications. [ABSTRACT FROM AUTHOR]

Metal assisted chemical etching is a promising method for fabricating high aspect ratio micro- and nanostructures in silicon. Previous results have suggested that P-type and N-type silicon etches with different degrees of anisotropy, questioning the use of P-type silicon for nanostructures. In this study, we compare processing X-ray zone plate nanostructures in N and P-type silicon through metal assisted chemical etching with a gold catalyst. Fabricated zone plates were cleaved and studied with a focus on resulting verticality, depth and porosity. Results show that for high aspect ratio nanostructures, both N and P-type silicon prove to be viable alternatives exhibiting different etch rates, but similarities regarding porosity and etch direction.

Monocapillary x-ray lenses (MXRLs) are mostly used as condensers in full-field transmission x-ray microscopy (TXM) based on synchrotron radiation or laboratory x-ray tubes. The performance of the condenser has a significant impact on the imaging quality of the TXM. In this paper, a procedure for the characterization of the MXRL as a condenser is presented. The procedure mainly includes two parts: optical measurement and x-ray tests. From the test results of the characterization procedure, it can be seen that a relatively high-performance condenser can be screened out from a series of MXRLs drawn by an electric furnace. This is also fed back to the manufacturing process, and therefore, the technology of manufacturing the condenser can be gradually optimized. Moreover, the method of characterizing the performance of the condenser designed for synchrotron radiation TXM by laboratory x-ray tubes is proposed to be used in this procedure, which effectively reduces the manufacturing time of high-performance condensers for synchrotron radiation TXM.

Lift-off processing is a common method of pattern transfer for different nanofabrication applications. With the emergence of chemically amplified and semi-amplified resist systems, the possibilities for pattern definition via electron beam lithography has been widened. We report a reliable and simple lift-off process for dense nanostructured pattern in CSAR62. The pattern is defined in a single layer CSAR62 resist mask for gold nanostructures on silicon. The process offers a slimmed down pathway for pattern definition of dense nanostructures with varied feature size and an up to 10 nm thick gold layer. The resulting patterns from this process have been successfully used in metal assisted chemical etching applications.

X-ray zone plates made from gold are common optical components used in X-ray imaging experiments. These nanostructures are normally fabricated using a combination of electron-beam lithography and gold electroplating with cyanide gold baths. In this study, we present a gold electroplating process in a miniaturized gold-suplphite bath. The miniaturization is enabled by on-chip reference plating areas with well defined sizes, offering a reliable way to control the height of the structures by carefully choosing the plating time at a given current density in accordance with a calibration curve. Fabricated gold zone plates were successfully used in X-ray imaging experiments with synchrotron radiation. Although gold electroplating of nanostructures is a well-established method, details about the actual process are often missing in the literature. Therefore, we think that our detailed descriptions and explanations will be helpful for other researchers that would like to fabricate similar structures. [ABSTRACT FROM AUTHOR]

The SHARP high-numerical aperture actinic reticle review project is a synchrotron-based, extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP emulates the illumination and imaging conditions of current EUV lithography scanners and those several generations into the future. An anamorphic imaging optic with increased mask-side numerical aperture (NA) in the horizontal and increased demagnification in the vertical direction has been proposed to overcome limitations of current multilayer coatings and extend EUV lithography beyond 0.33 NA. Zoneplate lenses with an anamorphic 4×/8× NA of 0.55 are fabricated and installed in the SHARP microscope to emulate anamorphic imaging. SHARP's Fourier synthesis illuminator with a range of angles exceeding the collected solid angle of the newly designed elliptical zoneplates can produce arbitrary angular source spectra matched to anamorphic imaging. A target with anamorphic dense features down to 50-nm critical dimension is fabricated using 40 nm of nickel as the absorber. In a demonstration experiment, anamorphic imaging at 0.55 4×/8× NA and 6 deg central ray angle (CRA) is compared with conventional imaging at 0.5 4× NA and 8 deg CRA. A significant contrast loss in horizontal features is observed in the conventional images. The anamorphic images show the same image quality in the horizontal and vertical directions.

The SHARP high-numerical aperture actinic reticle review project is a synchrotron-based, extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP emulates the illumination and imaging conditions of current EUV lithography scanners and those several generations into the future. An anamorphic imaging optic with increased mask-side numerical aperture (NA) in the horizontal and increased demagnification in the vertical direction has been proposed to overcome limitations of current multilayer coatings and extend EUV lithography beyond 0.33 NA. Zoneplate lenses with an anamorphic 4×/8× NA of 0.55 are fabricated and installed in the SHARP microscope to emulate anamorphic imaging. SHARP's Fourier synthesis illuminator with a range of angles exceeding the collected solid angle of the newly designed elliptical zoneplates can produce arbitrary angular source spectra matched to anamorphic imaging. A target with anamorphic dense features down to 50-nm critical dimension is fabricated using 40 nm of nickel as the absorber. In a demonstration experiment, anamorphic imaging at 0.55 4×/8× NA and 6 deg central ray angle (CRA) is compared with conventional imaging at 0.5 4× NA and 8 deg CRA. A significant contrast loss in horizontal features is observed in the conventional images. The anamorphic images show the same image quality in the horizontal and vertical directions.

An experimental set-up for hard X-ray off-axis Fresnel holography, based on a two-block Fresnel zone plates interferometer is proposed and analyzed. It is shown, that the suggested scheme provides a recording of the hologram and further numerical reconstruction of the image. The advantage of this scheme, compared with the earlier presented analogous scheme of on-axis holography, based on the three-block Fresnel zone plate interferometer is shown using numerical simulation. [ABSTRACT FROM AUTHOR]

X-ray zone plates made from gold are common optical components used in X-ray imaging experiments. These nanostructures are normally fabricated using a combination of electron-beam lithography and gold electroplating with cyanide gold baths. In this study, we present a gold electroplating process in a miniaturized gold-suplphite bath. The miniaturization is enabled by on-chip reference plating areas with well defined sizes, offering a reliable way to control the height of the structures by carefully choosing the plating time at a given current density in accordance with a calibration curve. Fabricated gold zone plates were successfully used in X-ray imaging experiments with synchrotron radiation. Although gold electroplating of nanostructures is a well-established method, details about the actual process are often missing in the literature. Therefore, we think that our detailed descriptions and explanations will be helpful for other researchers that would like to fabricate similar structures.

In this study, a new mechanism is proposed to develop a second virtual cathode (VC2). An axial vircator was simulated by adding a floating zone plate (ZP) inside the drift tube, which is designed at the dominant frequency of 3.42 GHz. The obtained results indicated that the floating ZP contributes to form a VC2 by using the drifting electrons as wall charges. The charge of a newborn VC2 interacts with electromagnetic (EM) waves generated from conventional VC1 to amplify its magnitude and the output power increases from 150 MW to 652 MW. Theoretical analysis indicates that the optimum synergy effects of these two VCs (VC1 and VC2) occur when the distance between them is the wavelength of EM waves, which agree well with simulation data. These results may demonstrate an important breakthrough in vircator research, introducing a new approach to use the drifting electrons to form a VC2 for power amplification.

We present a method for calculating a spectral multifocal diffractive lens that forms a given set of fixed-position foci at multiple operating wavelengths. It is based on minimizing a function represented as a squared absolute value of difference between the complex amplitudes of beams formed by the relief of a spectral lens at the given wavelengths and the complex transmission functions of multifocal lenses calculated for these wavelengths. As an example, we calculated zone plates that form three fixed foci at three and four operating wavelengths. The results obtained may find application in the development and creation of new multifocal contact and intraocular lenses with reduced chromatic aberrations.

In this paper, comprehensively utilizing the diffraction theory and electromagnetic resonance effect is creatively employed to design a multifunctional metasurface zone plate (MMZP) and achieve the control of polarization states, while maintaining a broadband achromatic converging property in a near-IR region. The MMZP consists of several rings with fixed width and varying heights; each ring has a number of nanofins (usually called meta-atoms). The numerical simulation method is used to analyze the intensity distribution and polarization state of the emergent light, and the results show that the designed MMZP can realize the polarization manipulation while keeping the broadband in focus. For a specific design wavelength (0.7 μm), the incident light can be converted from left circularly polarized light to right circularly polarized light after passing through the MMZP, and the focusing efficiency reaches above 35%, which is more than twice as much as reported in the literature. Moreover, the achromatic broadband focusing property of the MMZP is independent with the polarization state of the incident light. This approach broadens degrees of freedom in micro-nano optical design, and is expected to find applications in multifunctional focusing devices and polarization imaging.

In this work, we develop a new design method based on fast Fourier transform (FFT) for implementing zone plates (ZPs) with bifocal focusing profiles. We show that the FFT of the governing binary sequence provides a discrete sequence of the same length, which indicates the location of the main foci at the ZP focusing profile. Then, using reverse engineering and establishing a target focusing profile, we are capable of generating a binary sequence that provides a ZP with the desired focusing profile. We show that this design method, based on the inverse fast Fourier transform (IFFT), is very flexible and powerful and allows to tailor the design of bifocal ZPs to achieve focusing profiles with the desired foci locations and resolutions. The key advantage of our design algorithm, compared to other alternatives presented in previous works, is that our method provides bifocal focusing profiles with an absolute control of the foci locations. Moreover, although we analyze the performance of this novel design algorithm for underwater ultrasonics, it can also be successfully extended to different fields of physics, such as optics or microwaves, where ZPs are widely employed.

High-aspect ratio silicon (Si) nanostructures are important for many applications. Metal-assisted chemical etching (MACE) is a wet-chemical method used for the fabrication of nanostructured Si. Two main challenges exist with etching Si structures in the nanometer range with MACE: keeping mechanical stability at high aspect ratios and maintaining a vertical etching profile. In this work, we investigated the etching behavior of two zone plate catalyst designs in a systematic manner at four different MACE conditions as a function of mechanical stability and etching verticality. The zone plate catalyst designs served as models for Si nanostructures over a wide range of feature sizes ranging from 850 nm to 30 nm at 1:1 line-to-space ratio. The first design was a grid-like, interconnected catalyst (brick wall) and the second design was a hybrid catalyst that was partly isolated, partly interconnected (fishbone). Results showed that the brick wall design was mechanically stable up to an aspect ratio of 30:1 with vertical Si structures at most investigated conditions. The fishbone design showed higher mechanical stability thanks to the Si backbone in the design, but on the other hand required careful control of the reaction kinetics for etching verticality. The influence of MACE reaction kinetics was identified by lowering the oxidant concentration, lowering the processing temperature and by isopropanol addition. We report an optimized MACE condition to achieve an aspect ratio of at least 100:1 at room temperature processing by incorporating isopropanol in the etching solution.

In this work, we analyze the effect of the distribution of transparent Fresnel regions over the focusing profile of Soret Zone Plates (SZP) based on binary sequences. It is shown that this effect becomes very significant in those fields where directional transducers are employed, such as microwaves or acoustics. A thorough analysis of both the SZP transmission efficiency and the focusing enhancement factor is presented. Moreover, experimental measurements are also carried out for a particular type of binary sequence, the Cantor ternary set, validating the theoretical model and demonstrating that the distribution of transparent Fresnel regions becomes a critical parameter in applications requiring directional emitters.

Zone plate reflectors for the highly directive broadside radiations are investigated in this letter, where we show that such a reflector could also function as a lens with endfire emissions when integrated with a dielectric phase compensation layer. More specifically, we employ additional dielectrics to collimate electromagnetic fields radiating through the radial direction of the original zone plate reflector, and obtain well-collimated beams as a lens without degrading the performances of the zone plate as a reflector. We practically implement the proposed design through drilling subwavelength holes with different sizes in a dielectric host medium, and the perforated zone plate demonstrates the functionalities of generating both broadside and endfire radiations in a broadband frequency range. [ABSTRACT FROM AUTHOR]

Recently, aspheric lenses have been developed to correct various aberrations and to produce optical elements with various functions. In particular, efforts have focused on fabrication miniaturized and compact elements that make the use of flat, diffractive optical elements such as zone plates to replace conventional lenses. Direct laser lithography is one of the typical methods used to manufacture such diffraction optical elements. By using a high magnification objective lens, it generates a laser beam with a spot size of less than 1 μm at the focal point. To produce a pattern, such as a diffraction grating, a chromium-coated surface is controllably exposed to this light. In this study, the process conditions for fabricating a zone plate using a direct laser lithography were studied by using an air-bearing type linear XY stage which can easily make various patterns including a zone plate array. The previous studies using a polar coordinate lithographic system have an advantage for fabricating the circular type zone plate because the system uses a rotational stage. It, however, is not proper to fabricate an array type diffractive optics element. In this study, we used a rectangular type lithographic system by using an XY stage and tested the fabrication issues such as a runout error. The optical performance of the zone plate array fabricated by the suggested method was also verified by experimental evaluation. [ABSTRACT FROM AUTHOR]

A novel type of zone plate (ZP), termed an inverse‐phase composite ZP, is proposed to gain a deeper focus than the standard diffraction‐limited depth of focus, with little reduction in spatial resolution. The structure is a combination of an inner ZP functioning as a conventional phase ZP and an outer ZP functioning with third‐order diffraction with opposite phase to the inner ZP. Two‐dimensional complex amplitude distributions neighboring the focal point were calculated using a wave‐optical approach of diffraction integration with a monochromatic plane‐wave illumination, where one dimension is the radial direction and the other dimension is the optical‐axis direction. The depth of focus and the spatial resolution were examined as the main focusing properties. Two characteristic promising cases regarding the depth of focus were found: a pit‐intensity focus with the deepest depth of focus, and a flat‐intensity focus with deeper depth of focus than usual ZPs. It was found that twice the depth of focus could be expected with little reduction in the spatial resolution for 10 keV X‐ray energy, tantalum zone material, 84 nm minimum fabrication zone width, and zone thickness of 2.645 µm. It was also found that the depth of focus and the spatial resolution were almost unchanged in the photon energy range from 8 to 12 keV. The inverse‐phase composite ZP has high potential for use in analysis of practical thick samples in X‐ray microbeam applications. A novel type of zone plate, i.e. an inverse‐phase composite zone plate, is proposed and examined with the aim of achieving deeper focus with little reduction in spatial resolution. [ABSTRACT FROM AUTHOR]

Focusing properties of high-numerical-aperture micro-Fresnel zone plates (FZP) have been rigorously investigated at the wavelength from deep ultraviolet to visible based on the combination of the vectorial angular spectrum theory and three-dimensional finite-difference time-domain method. New insights are found. The axial spot size evaluated by full-width-at-half-maximum is in direct proportion to the inverse of the total annulus number. Linearly negative focal shift phenomenon can be observed due to the wavelength dispersion over a finite range of tens of nanometers. A proper wavelength deviation can lead to the maximum focal intensity. A simple method has been demonstrated to probe either multi-focus or a light needle using a composite microstructure based on high-NA FZPs. The findings of this study expand the common understandings of the classic widely-used FZPs. [ABSTRACT FROM AUTHOR]

Zone plates are diffractive optics commonly used in X-ray microscopes. Here, we present a wet-chemical approach for fabricating high aspect ratio Pd/Si zone plate optics aimed at the hard X-ray regime. A Si zone plate mold is fabricated via metal-assisted chemical etching (MACE) and further metalized with Pd via electroless deposition (ELD). MACE results in vertical Si zones with high aspect ratios. The observed MACE rate with our zone plate design is 700 nm/min. The ELD metallization yields a Pd density of 10.7 g/cm 3 , a value slightly lower than the theoretical density of 12 g/cm 3 . Fabricated zone plates have a grid design, 1:1 line-to-space-ratio, 30 nm outermost zone width, and an aspect ratio of 30:1. At 9 keV X-ray energy, the zone plate device shows a first order diffraction efficiency of 1.9%, measured at the MAX IV NanoMAX beamline. With this work, the possibility is opened to fabricate X-ray zone plates with low-cost etching and metallization methods.