Multilayer Mirrors Research Articles

Darwinian Philosophy as Optimization Method for Design High Reflection Mirror Include New Merit Function

In this paper we proposes the philosophy of the Darwinian selection as synthesis method called Genetic algorithm ( GA ), and include new merit function with simple form then its uses in other works for designing one of the kinds of multilayer optical filters called high reflection mirror. Here we intend to investigate solutions for many practical problems. This work appears designed high reflection mirror that have good performance with reduction the number of layers, which can enable one to controlling the errors effect of the thickness layers on the final product, where in this work we can yield such a solution in a very shorter time by controlling the length of the chromosome and optimal genetic operators . Result shows that the construction of multilayer high reflection mirror using in this approach can be considered as a master stone for design another type of filters with most complicated performance, and it is difficult designing in other approach The experiment results demonstrate that our approach is a powerful technique. It is enable to locate the global optimum optimal automatically with high confidence without need for a good starting design.

Data quality in laboratory convergent-beam X-ray total scattering

Measurement of laboratory atomic pair distribution function data has improved with contemporary X-ray sources, optics and detectors, with acquisition times of the order of minutes for ideal samples. This paper examines resolution effects in pair distribution function data obtained using a convergent-beam configuration and an Ag X-ray tube from standard silicon powder and from 10 nm BaTiO3 nanocubes. The elliptical multilayer X-ray mirror reflects a non-trivial X-ray spectrum and introduces resolution effects not commonly treated in ordinary parafocusing divergent-beam laboratory diffraction. These resolution effects are modeled using the fundamental parameters approach, and the influence this has on interpretation and modeling of the resulting reduced atomic pair distribution function data is demonstrated.

Influence of silicon interlayers on the structural and reflective X-ray characteristics of Ni/Ti multilayer mirrors

The influence of Si interlayers on the microstructure of the films and boundaries and on the reflective characteristics of Ti/Ni multilayer mirrors has been studied using X-ray reflectometry and diffractometry. We established that these Si interlayers perform different functions at different interfaces. An Si interlayer at an Ni-on-Ti interface acts as a diffusion barrier. An Si interlayer at a Ti-on-Ni interface mainly acts as a smoothing layer with a slight diffusion barrier effect. The largest increase in the reflectance, from 62 to 65.7%, at a wavelength of 1.54 Å, is observed when Si interlayers are deposited on both boundaries. The reason for the increase in reflectivity is the decrease in the widths of the transition layers from 6.5 Å on Ni and 7.5 Å on Ti, to 6.0 Å on Ni and 5.0 Å on Ti, respectively. Here, we explain this through the `barrier' effect of Si interlayers, which results in less mixing of film materials at the interfaces. Data on the reflectance of Ni/Ti multilayer mirrors in the spectral range of the `water window' at a wavelength of 27.4 Å are presented for the first time. The maximum reflectivity for an Ni/Ti multilayer mirror at a grazing angle of 7.2° was about 56%.

Single-stack multilayer infrared mirrors with selectable higher-order interference peaks

A concept for the design of single-stack multilayer mirrors with multiple reflection peaks is presented. Its realization in the infrared is demonstrated by the sputter deposition of TiO2/Al2O3 bilayers on sapphire and HastelloyX substrates and corresponding reflection measurements. Even or odd higher-order interference peaks are selected by adjusting the optical thicknesses of the individual layers. The peak positions are very well reproduced by multiple scattering calculations. With the HastelloyX substrate, a potential application for high temperatures and aggressive atmospheres, e.g., in aircraft turbines, is addressed. A design for matching up to three turbine gas emission bands (CO2, H2O) is proposed.

Effects of interface-engineering on the internal structure and reflective characteristics of Cr/Sc multilayer mirrors.

Record reflectivity's of REXP=23.8% at 3.14 nm and RCALC=30.8% at 3.12 nm have been obtained for Cr/Sc mirrors. Such increases in reflection are the result of decreases in mixing of the system layers with each other due to the use of interface-engineering methods - passivation of the already deposited Cr layer with nitrogen before deposition of the subsequent Sc layer. However, it has been found that adding additional B4C layers to such a system leads to a decrease in reflectivity.

Multishot laser damage of multilayer dielectric mirrors in the near-infrared subpicosecond regime

The laser damage resistance of dielectric components of high-power laser facilities to laser irradiation depends significantly on the irradiation sequence. In the short pulse (fs) regime, it is known that continuous irradiation of these components leads to a reduction in the damage threshold, reflecting a laser fatigue effect. Conversely, in the long pulse (ns) regime, progressive irradiation of these components leads to an increase in the damage threshold, reflecting a laser conditioning effect. In this article, we experimentally evaluate the competition between the effects of laser fatigue and laser conditioning for multilayer dielectric components irradiated in the subpicosecond pulse regime in the infrared (∼1µm) through different test sequences. For this purpose, we implemented an original test sequence derived from an S-on-1 type protocol, which consists of irradiating the component until damage. By repeating this sequence at different set points, it was possible to estimate the progressive reduction in damage threshold with the number of laser irradiations and to compare it with that observed during the fluence ramps. Particular attention was also paid to the precise knowledge of the test beam irradiating the component, as a dependence of the beam surface on the test set point was highlighted.

Evaluation of an x-ray multilayer mirror for radiography at sub-1-keV photon energies.

An x-ray multilayer mirror on a spherical substrate designed for near-normal incidence with a photon energy of ∼738eV (F Heα) was procured and tested. This device is intended to be used for in-flight radiography of the shell in inertial confinement fusion experiments with cryogenic targets on the OMEGA laser at the Laboratory for Laser Energetics. Experiments in self-emission on a small (∼10J) laser system showed that the reflectivity of the mirror is high enough to record an image at laser energies as low as 0.1J. A second set of tests in backlighting geometry on a larger (kJ)-scale, short-pulse laser yielded usable radiographs with laser energies as low as 40J with a spatial resolution of ∼10μm.

Stress, reflectance, and stability of Ru/Be multilayer coatings with Mo interlayers near the 11 nm wavelength.

The stress, reflectance, and temporal stability of Ru/Be multilayer mirrors, both with and without Mo interlayers, were studied. A Ru/Be MLM was found to have zero stress at a Ru layer thickness-to-period ratio of γ ∼ 0.4. By adding Mo interlayers to both interfaces, it is possible to achieve a record-high reflectance (R > 71%) at a wavelength close to 11 nm while maintaining near-zero stress levels. A Ru/Be MLM with Mo interlayers at both interfaces also demonstrates high temporal reflectance stability. Ru/Be MLMs may be of interest for the next-generation projection lithography at a wavelength of 11.2 nm.

Investigation of an electrode-driven hydrogen plasma method for in situ cleaning of tin-based contamination

To prolong the service life of optics, the feasibility of in situ cleaning of the multilayer mirror (MLM) of tin and its oxidized contamination was investigated using hydrogen plasma at different power levels. Granular tin-based contamination consisting of micro- and macroparticles was deposited on silicon via physical vapor deposition (PVD). The electrode-driven hydrogen plasma at different power levels was systematically diagnosed using a Langmuir probe and a retarding field ion energy analyzer (RFEA). Moreover, the magnitude of the self-biasing voltage was measured at different power levels, and the peak ion energy was corrected for the difference between the RFEA measurements and the self-biasing voltage ( ). XPS analysis of O 1s and Sn 3d peaks demonstrated the chemical reduction process after 1 W cleaning. Analysis of surface and cross-section morphology revealed that holes emerged on the upper part of the macroparticles while its bottom remained smooth. Hills and folds appeared on the upper part of the microparticles, confirming the top-down cleaning mode with hydrogen plasma. This study provides an in situ electrode-driven hydrogen plasma etching process for tin-based contamination and will provide meaningful guidance for understanding the chemical mechanism of reduction and etching.

Emission of quasi-monochromatic ultrasoft X-ray of multilayer target in the Bragg direction under 5.7 MeV electron irradiation

Previously, it was experimentally shown that VUV radiation generated in a periodic structure of a multilayer X-ray mirror by relativistic electrons exhibits a quasi-monochromatic spectrum depending on the angle of inclination of the target and the direction of emission of radiation inside the radiation cone. Here, we present new experimental results regarding the properties of angular density of radiation. A comparison between the measured radiation intensity over a wide range of target inclination angles and theoretical calculations is provided.

Observation of quasi-Bragg scattering by Goebel mirrors

This paper reports the first observation of quasi-Bragg scattering from collimating Goebel mirrors in a real instrument. On the basis of the experimental data obtained and the numerical analysis performed, it is concluded that it is necessary to take into account the effect of quasi-Bragg scattering when constructing real devices with multilayer mirrors for use in X-ray diffractometry and in spectroscopy, especially for small-angle scattering with position-sensitive detectors.

Optimization of Cr/Sc-based multilayer mirrors for water window soft x-rays.

The development of efficient multilayer mirrors for the water window (a spectral region between absorption edges of carbon and oxygen, from 284 to 543 eV) remains a challenge. As the best candidate, the Cr/Sc multilayer provides maximum theoretical reflectivity of about 60% at near-normal incidence around the Sc L2,3 absorption edge (397 eV). However, the maximum measured peak reflectance published so far just slightly exceeds 20%. We report on a new (to the best of our knowledge) approach to design more efficient Cr/Sc-based multilayer coatings using the process of nitridation of chromium during deposition and adding boron carbide as a third material in the multilayer structure. We discuss our strategy of optimization of the CrN/B4C/Sc multilayer system based on experimental studies. The peak reflectance as high as 32% at 396 eV was measured with this type of coating, which is of main interest for various water window applications such as x-ray microscopy.

Ultrasmooth Ti/Al multilayer with a Ti seed layer for EUV applications

Al-base multilayers have attracted much interest in the extreme ultraviolet (EUV) optics field, but high roughness of this multilayer due to the Al film is still a big concern. Here, a strategy of the seed layer was proposed to reduce the surface roughness and intermixing layer thickness of the Al-base multilayer. Ti film is not only a seed layer, but also an absorption layer in this novel multilayer. An optimized Ti/Al multilayer film structure was designed to work at 21.1 nm, while investigating the use of Ti as a seed layer to reduce the roughness and enhance the peak reflectivity. The experimental results showed that the Ti seed layer effectively reduced the surface roughness and intermixing layer thickness and improved the reflectance. At 21.1 nm, the peak reflectance reached 39.6%, with a bandwidth of only 1.0 nm and an RMS roughness of 0.17 nm. Ti/Al multilayer also exhibits good stability. This multilayer has potential application in high-precision optics, such as corona detection, which requires extreme low light scattering of multilayer mirror.

Direct multiple monochromatic x-ray imaging with a pinhole array and a laterally graded multilayer mirror.

Multiple monochromatic x-ray imaging (MMI) is a technique for diagnosing the emission spectra of tracer elements in laser-driven inertial confinement fusion experiments. This study proposes an MMI method that combines a simple pinhole array with a laterally graded multilayer mirror. The method directly obtains multiple monochromatic x-ray images by regulating the multilayer thickness in different mirror positions to compensate for the energy-broadening effect. This paper presents a comprehensive design scheme, the multilayer fabrication and experimental verification of the gradient MMI imaging performance. The experimental results show that the method achieves monochromatic imaging with a spectral resolution of ∼70-90eV in several keV energy regions. This paper presents a practical diagnostic approach for directly and synchronously capturing the spatial, temporal, and spectral information of laser plasma x rays.

Development of a narrowband multilayer mirror for extracting a single order component from high harmonics in the 63–70 eV region

The Y/AlSi multilayer with narrowband performance was developed for extracting a single order component from high harmonics. We compared the performance and thermal stability of Y/AlSi with another EUV mirror, Zr/AlSi multilayer, which has shown promising performance in the EUV region. At near-normal incidence, the measured peak reflectances of Y/AlSi and Zr/AlSi multilayers are 43% and 52% at ∼63.8eV, and the energy bandwidths (FWHM) are 1.7 eV and 2.5 eV, respectively. The narrower bandwidth feature obtained in the Y/AlSi multilayer allows better suppression on adjacent high harmonic lines. After heating up to 200°C, there is no significant decrease in the reflectance of either multilayer. No decrease in reflectivity was observed after storage in air for one year.

Zn-Ti oxo cluster photoresists for EUV Lithography: Cluster structure and lithographic performance

Low reflectivity of multilayer mirror–induced low efficiency of existing extreme ultraviolet lithography (EUVL) has triggered the search for photoresists with heightened sensitivity. For this purpose, considerable research has focused on elements with high extreme ultraviolet (EUV) absorption, leading to considerable advancements. Solubility alteration, often resulting from ligand variations after exposure, is influenced by the cluster structure, markedly impacting lithography sensitivity. Herein, three Ti-based metal clusters, Ti6O4(OEt)8(OMc)8 (T-2), Zn2Ti4O4(OiPr)2(OMc)10 (TZ-1), and Zn4Ti2O2(OAc)2(OBu)2(OMc)10 (TZ-2), are designed and synthesized to elucidate the effects of the structure on lithography. These mixed metal–oxo clusters derived from Ti6O4(OR)8(OOCR)8 and stabilized by identical ligands exhibit structural diversity. The increase in the number of zinc atoms results in marked alterations in the oxo core, thereby triggering alterations in ligand coordination modes. These variations confer metal clusters with different solubility and lithographic properties. Analysis of the photochemical reaction mechanism and theoretical calculations reveal a reactive tridentate ligand coordination mode that considerably improves lithography sensitivity. Therefore, changing the ligand coordination mode by designing a mixed metal–oxo core holds promise for discovering new photoresists for EUV lithography.

Multistrip multilayer mirrors for sources based on inverse Compton scattering

A technique has been developed for calculating the periods of multi-strip multilayer mirrors for effective use with sources based on the inverse Compton effect. A model for constructing the multi-strip mirror is presented. The model has been developed in accordance with modern capabilities for creating multilayer X-ray mirrors. The reflection coefficients and fractions of the energy emitted by the source that are reflected are compared for total external reflection, for multilayer Goebel mirrors and for multi-strip mirrors. It is shown that the multi-strip design of multilayer mirrors proposed in the work is almost an order of magnitude superior to Goebel mirrors and to mirrors based on the total external reflection effect in terms of the efficiency of use of the source energy.

EUV Radiation in the Range of 10–20 nm from Liquid Spray Targets Containing O, Cl, Br and I Atoms under Pulsed Laser Excitation

The article describes the results of an investigation to determine the values of radiation intensities emitted by O-, Cl-, Br-, and I-containing liquid spray targets in absolute units in the wavelength range 10–20 nm when excited by pulsed laser radiation. The conversion coefficients of laser radiation into the EUV radiation are given for some wavelengths. The authors’ specially designed pulse extrusion liquid supply system was used to form the liquid spray targets. An Nd:YAG laser with λ = 1064 nm, τ = 8.4 ns, and Epulse = 0.8 J was used to excite the targets. Spectral measurements were made using a grazing incidence grating spectrometer–monochromator. The absolute intensities of a number of emission lines were also measured using a Bragg spectrometer based on a Mo/Be multilayer X-ray mirror, calibrated by both sensitivity and wavelength. The high values of absolute intensities of the liquid targets in the extreme ultraviolet wavelength range were demonstrated.

Structural and optical performance of NiV/Ti multilayer mirrors for Z-pinch plasma diagnostic at the wavelength region of 350-450 eV.

This Letter reports on investigations of novel, to the best of our knowledge, NiV(Ni93V7)/Ti multilayer mirrors for the operation in the wavelength region of 350-450 eV. Such mirrors are promising optical components for the Z-pinch plasma diagnostic. The NiV/Ti multilayers show superior structural and optical performance compared to conventional Ni/Ti multilayers. Replacing Ni with NiV in multilayers decreases interface widths and enhances the contrast of the refractive index between the absorber and spacer layers. The improvement of interface quality contributes to the enhancement in reflectance. Under the grazing incidence of 13°, a peak reflectivity of 25.1% at 429 eV is achieved for NiV/Ti multilayers, while 17.7% at 427 eV for Ni/Ti.

Narrowband Mg/SiC multilayer mirror working as high-harmonic selector at 30.4 nm wavelength

Multilayers (MLs) are a good choice for high-harmonic generation (HHG) sources for selecting single-wavelength radiation. MLs working around 30.4 nm with a significantly reduced bandwidth based on high Bragg order reflection have been designed and fabricated. The narrowband MLs were characterized using grazing incidence x-ray reflectometry, extreme ultraviolet reflectivity, and intrinsic stress measurements. The results indicate that Mg/SiC MLs designed with 3rd Bragg order have narrowest bandwidth of 0.71 nm (full width half maximum) with a spectral resolution (λ/Δλ) of 42, and reflectance of 30% under near normal incidence geometry. Based on these results, the simulation of narrowband MLs working at large incident angles demonstrates that 3rd Bragg order ML has a better spectral selectivity compared with 1st Bragg order ML for HHG sources.