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We report on the results of development, fabrication, and analysis of broadband Mo/Si multilayer mirrors for spectroheliographs at the KORTES solar observatory, which operate in the spectral bands of 17–21 and 28–33 nm. The advantages of the stack approach are demonstrated. The results of measurements of reflection characteristics of mirrors are considered.

The use of field emission cathodes in X-ray tubes requires the placement of the cathode assembly with a small gap from the anode, and this hampers the output of radiation. The greatest difficulties arise in the generation of a relatively soft spectrum with wavelengths of 1–10 nm: in this case, the accelerating voltage does not exceed several kilovolts and the interelectrode gap does not exceed several hundred microns. In this work, the possibility of using submicron films based on beryllium as through-type anodes for emitting the BeKα line (λ = 11.4 nm) and the accompanying bremsstrahlung spectrum is experimentally demonstrated. In particular, the characteristic radiation of a tube with a field emission blade-type cathode and a Be-film anode, introduced into a grazing incidence grating spectrometer, was detected. The characteristics of beryllium films necessary for designing high-power X-ray tubes of this type are determined.

We describe the method for increasing the efficiency of holographic diffraction gratings (HDGs) intended for operation in the X-ray wavelength range. We describe the procedure of processing of HDG surface for reducing the amplitude and roughness of grooves. For reducing the groove amplitude, we have used Xe ions with an energy of 600 eV, while ion polishing was performed with Ar ions having an energy of 800 eV. It is shown that, after ion polishing, the diffraction efficiency of the grating at a wavelength of 4.47 nm increases by almost four times.

The latest experimental results of studying beryllium-containing multilayer mirrors are reviewed. The mirrors are of interest for projection nanolithography, solar astronomy, X-ray microscopy, and other applications. It is shown that for a number of ranges beryllium-containing multilayer mirrors outperform the world analogues in their X-ray optical characteristics.

The influence of thermal action on X-ray optics performance and structure of films and transition regions in multilayer Mo/Be mirrors optimized for a reflection maximum in the interval 11.2–11.4 nm at normal incidence has been considered. The annealing temperature reached 300°C and the annealing time was 1 and 4 h. It has been shown that after thermal annealing in vacuum for 1 h at 300°C, the reflection coefficient rises; however, when the annealing time grows to 4 h, it drops. Grains in molybdenum films become finer, and the profiles of transition regions change from exponential to linear. The period of multilayer mirrors has remained the same under all annealing conditions.

The smoothing effect of thin silicon films used as buffer layers in multilayer Be/Al mirrors optimized for wavelengths longer than 17.1 nm has been investigated. The objects of investigation have been near-normal incidence (an angle of incidence of 88°) and grazing incidence (33.5°) mirrors. This effect has been observed in multilayer Be/Si/Al mirrors with periods of up to at least 29 nm. For normal incidence mirrors optimized for a wavelength of 17.14 nm, a record-high value of the peak reflection coefficient, 62.5%, has been achieved at spectral selectivity λ/Δλ = 59. The temporal stability of the mirrors has been studied.

Mo/Y multilayer mirrors designed to operate in the range of 9–11 nm are considered. The dependence of the internal stress of such mirrors on the molybdenum fraction is studied for the first time. It is shown that structures with zero stress are characterized by a reflection coefficient of about 6%. The experimentally obtained maximum reflection coefficient (30%) corresponds to a stress of –160 MPa. The influence of a buffer layer of boron carbide on the internal stress and reflectance factor of the Mo/Y mirrors is investigated. A Cr/Y structure is proposed for compensation of elastic deformations of the substrate in manufacturing highly reflective Mo/Y multilayer mirrors.

Multilayer aluminum-based structures reflecting at λ(HeI) = 58.4 nm were studied. Spectral and angular dependences of the reflection coefficient of these coatings were determined using a laboratory reflectometer and at the ELETTRA and BESSY II synchrotrons. The optical characteristics of multilayer Ru/Al and Mo/Al mirrors with a protective MoSi2 layer were found to be stable: the absolute change in the reflection coefficient within 18 months of storage in air was no larger than 1.5%. The peak near-normal reflection coefficient for Mo/Al mirrors at 58.4 nm was R = 26.1% with FWHM Δλ0.5 = 10 nm of the reflection curve.

A set of multilayer X-ray mirrors for an upgraded version of the double-mirror monochromator installed on the VEPP-5 synchrotron of the Budker Institute of Nuclear Physics is fabricated, its constituent parts are optimized, and its X-ray optical characteristics are studied. Due to the use of seven subbands, for each of which an optimal pair of materials is chosen, the mirror set ensures high reflection coefficients—ranging from 10 to 75%— for a wide range of photon energies from 80 to 3000 eV and wavelengths from 0.413 to 15.48 nm. The principles of optimization of material pairs are reported. For the first time, multilayer mirrors based on the W/Be pair of materials are fabricated and studied.

With the aid of Mo/Be and Si/Mo interference mirrors, measurements of radiation intensity from laser plasma with Xe gas-jet target have been realized within a wavelength interval of 11–14 nm with a spectral resolution of 3–6 A. The results are compared with the spectrum formerly measured with the aid of a spectrograph. The ratio of intensities at wavelengths of 11.2 and 13.5 nm has been found to be about 10 under experimental conditions studied.

In this paper we investigated the influence of thin nanometer cap layers of aluminum nitride (AlN) and molybdenum disilicide (MoSi2) on the temporal stability of transmission and the ultimate strength of aluminum (Al) film filters. An increase in the stability of the optical characteristics and in the mechanical strength of Al films both with AlN and MoSi2 cap layers are shown in comparison with a monolayer Al film. The greatest efficiency was demonstrated in the case of Al with MoSi2 cap layers. The obtained results show that the presence of MoSi2 cap layers 2.5 nm thick on each side of an Al film significantly reduces (for example, by >4 times at the wavelength of 30.4 nm) the rate of film transmission loss in the extreme ultraviolet (EUV) range. In addition, the presence of cap layers can lead to a significant increase in the film's strength: the results of pressure bulge tests show that the Al with MoSi2 cap layers film can withstand an ultimate load 1.5 times greater than an Al monolayer film of comparable thickness. The carried-out bulge tests indicate that an increase in the strength of the Al thin film in the presence of MoSi2 cap layers may be due to the cap layers hindering crack initiation, which allows Al film to be plastically deformed. Acoustic tests of Al with MoSi2 cap layers filters indicate the possibility of their use as entrance filters on a supporting mesh with a mesh size up to 10 mm in solar telescopes.

It is shown that in the vicinity of 17 nm wavelength, Be can be used as an optically contrasting material with Al in periodic multilayer mirrors. At the same time, due to the low absorption of both Be and Al, we can expect a unique combination of reflective characteristics: record high peak reflectivity and spectral selectivity simultaneously. Although the theoretical reflectivity of a Be/Al multilayer is 78% at normal incidence and at the 17.14 nm wavelength, we recorded only 46% for a pure Be/Al structure. The introduction of 1 nm Si on top of the Be layers in each period increases the reflection up to 61% at normal incidence. The increase of the reflection coefficient of Be/Si/Al multilayer mirrors is conditioned by smoothing the interfaces from root-mean-square value of 1.3 nm in pure Be/Al structures to 0.6 nm in Si-containing samples. We suppose that the smoothing effect is connected with the amorphization of Al films in the presence of Si.

Multilayer Ag/Y mirrors intended for the spectral range of 9–11 nm have been investigated. The parameters of mirrors, specifically, the thicknesses of transition layers, have been determined. The efficiency of B4C and Si barrier layers has been demonstrated. It has been shown that the properties of structures like Ag/Y and Ag/Y with B4C and Si barriers layers have poor temporal stability. The highest reflection coefficient of 18% at a wavelength of 9.34 nm, has been observed for the Ag/Si/Y structure. The same structure has the best temporal stability.

Broadband Mo/Si and Mo/Be multilayer stack-type mirrors for wavelength intervals of 11.1–13.8, 17–21, and 28–33 nm have been developed and fabricated. Uniform reflection of such structures can be implemented using few corrections of technological process.

The paper describes a multistage method of forming ultrasmooth substrates based on bulk beryllium. Such substrates are suggested to be used for multilayer extreme ultraviolet mirrors of spacecraft missions on solar corona investigations in the spectral range 17.1–58.4 nm. The technique for chemical nickel plating of the sample surface is described. The process parameters that provide the formation of an amorphous film with a thickness of about 100 microns are presented. The results of mechanical polishing are shown. The effective roughness of 1.3 nm is obtained, which is twice lower than one achievable for a nickel-free beryllium surface. The applicability of the ion beam figuring technique is demonstrated: the initial surface roughness of a nickel film after etching with Ar ions (E ion =200–800 eV) to a depth of 250 nm does not deteriorate. The amorphous silicon film deposition followed by ion polishing made it possible to reduce the microroughness (atomic force microscope frame 2×2 μm) to σ2×2=0.15 nm from the initial σ2×2=0.46 nm. The reflectivity of multilayer mirrors deposited on these substrates turned out to be close to the values obtained on “witnesses” (supersmooth silicon substrates). Moreover, for the Mg/MoSi2 mirror optimized for the wavelength λ=58.4 nm the values of the reflection coefficients of structures on the beryllium substrate and on the silicon “witness” were identical (about 28%).

Due to low density, high mechanical rigidity and thermal conductivity, ease of machining beryllium is one of the most promising materials for space mirrors, including for studies of the solar corona in the wavelength range of 13–30.4 nm. An obstacle to the widespread use of this material is its large surface roughness after mechanical polishing. In this paper, using samples of 200 nm thick beryllium films deposited on silicon substrates and polished bulk beryllium, we studied the main aspects of using ion-beam etching for finish polishing of beryllium. We present the results of investigation pertaining to the influence of the neon ion energy and angle of incidence on the beryllium films surface roughness. We measured the etching rates depending on the angle of incidence and energy of neon ions. We found that 400 eV is the optimal energy for neon ion etching ensuring slight surface roughness smoothing in the range of incidence angles of ± 40°. The deposition of 200 nm amorphous silicon films onto beryllium and their subsequent etching with the 800 eV argon ions improve the effective surface roughness integrated across the range of the spatial frequencies of 0.025–60 μm− 1, from σeff = 1.37 nm down to σeff = 0.29 nm. The effectiveness of the smoothing technology for X-ray applications has been confirmed by the results of the study of the reflective properties of the Mo/Si mirrors deposited on the substrate. The reflectivity at a wavelength of 13.5 nm increased from 2% for the substrates with the surface roughness of σeff = 2.3 nm (the roughness value corresponds to the as-prepared bulk Be substrates and is taken from the literature) up to 67.5% after the smoothing technology.

The efficiency of first-order diffraction on F1 glass echelle gratings for soft X-ray and extreme UV radiation can be significantly increased (by up to ten times) by etching the groove surface with a beam of neutralized Ar ions at 1250-eV energy. The processing was performed at normal incidence of ion beam on the surface of gratings, and the material thickness removed was on a level of 80–300 nm. A principle of optimization of the ion-beam etching process is proposed for solving particular tasks related to the planarization of microstructures with various lateral dimensions.

A high-resolution laboratory reflectometer designed for operation in the soft x-ray (SXR) and extreme ultraviolet (EUV) ranges is described. High spectral resolution, up to 0.028 nm, in a wide spectral range is achieved due to the Czerny-Turner monochromator. A laser plasma generated by irradiating a solid-state target with a focused laser beam (wavelength 1.06 µm, pulse energy 0.5 J, duration 4 ns, and pulse repetition rate 10 Hz) is used as a source of SXR and EUV radiation. The goniometer allows the study of curved optical elements with an aperture up to NA = 0.5 and a diameter of up to 500 mm. The methods providing high efficiency of the optical system and spectral resolution in a wide range of wavelengths are described in detail. The problem of taking into account high orders in the recorded spectra of a laser plasma is discussed. A comparison of the measurement results with the described reflectometer and the optics beamline at the BESSY-II synchrotron is given.

A design strategy for the fabrication broadband grazing incidence mirrors in the wavelength range of 0.8–18 nm is proposed. Instead of high-density materials, we propose a bilayer coating consisting of the high-density material most suitable for the task coated with a thin film of low-density material. In the wavelength range of 4–18 nm, an increase of the reflection coefficients of such coatings by 10–20% compared with the single high-density layers traditionally used is theoretically expected. We also present an experimental demonstration of such advantageous properties based on a Cr-C bilayer film.

In the paper is studied the main aspects of using ion-beam etching for finish polishing. It is found that 400 eV is the optimal energy for neon ion etching ensuring slight surface roughness smoothing in the range of incidence angles of ± 40°. The deposition of 200 nm amorphous silicon films onto beryllium and their subsequent etching with the 800 eV argon ions improve the effective surface roughness integrated across the range of the spatial frequencies of 0.025-60 μm-1, from σeff=1.37 nm down to σeff=0.29 nm. The effectiveness of the smoothing technology for x-ray applications, confirmed by the results of the study the reflective properties of the Mo/Si mirrors deposited on the substrate. The reflectivity at a wavelength of 13.5 nm increased from 2% for the substrates with the surface roughness of σeff=2.3 nm (the roughness value corresponds to the as-prepared bulk Be substrates and is taken from the literature) up to 67.5% after the smoothing technology.

Al, with a passband in the wavelength range of 17–60 nm, and Zr, with a passband in the wavelength range of 6.5–17 nm, thin films on a support grid or support membrane are frequently used as UV, visible, and near-IR blocking filters in solar observatories. Although they possess acceptable optical performance, these filters also have some shortcomings such as low mechanical strength and low resistance to oxidation. These shortcomings hinder meeting the requirements for filters of future telescopes. We propose multilayer thin film filters on the basis of Al, Zr, and other materials with improved characteristics. It was demonstrated that stretched multilayer films on a support grid with a mesh size up to 5 mm can withstand vibration loads occurring during spacecraft launch. A large mesh size is preferable for filters of high-resolution solar telescopes, since it allows image distortion caused by light diffraction on the support grid to be avoided. We have investigated the thermal stability of Al/Si and Zr/Si multilayers assuming their possible application as filters in the Intergelioprobe project, in which the observation of coronal plasma will take place close to the Sun. Zr/Si films show high thermal stability and may be used as blocking filters in the wavelength range of 12.5–17 nm. Al/Si films show lower thermal stability: a significant decrease in the film’s transmission in the EUV spectral range and an increase in the visible spectrum have been observed. We suppose that the low thermal stability of Al/Si films restricts their application in the Intergelioprobe project. Thus, there is a lack of filters for the wavelength range of λ>17 nm. Be/Si and Cr/Si filters have been proposed for the wavelength range near 30.4 nm. Although these filters have lower transparency than Al/Si, they are superior in thermal stability. Multilayer Sc/Al filters with relatively high transmission at a wavelength of 58.4 nm (HeI line) and simultaneously sufficient rejection in the wavelength range near 30.4 nm (HeII line) have been fabricated. They are planned to be used in the project KORTES, whose telescopes will have an EUV channel at 58.4 nm.

Aluminum thin-film spectral filters are widely used in telescopes for space observations of the Sun in the extreme ultraviolet range of wavelengths. The main purpose of film filters is to block radiation in the UV, visible, and near-IR spectral ranges. In connection with the development of new projects for the observation of the Sun from close distances, the thermal stability of the entrance film filter is an important characteristic. In this paper, the thermal stability of Al films with 2.5 nm thick MoSi2 protective cap layers has been studied. MoSi2 was chosen as a coating material because MoSi2 caps effectively protect the Al film from oxidation and simultaneously increase the mechanical strength of the Al film. Vacuum annealing of MoSi2/Al/MoSi2 films was carried out at temperatures up to 300°C. It has been demonstrated that at an annealing temperature of more than 200°C for 24 h, a noticeable decrease in the blocking properties of the MoSi2/Al/MoSi2 film is observed in the visible wavelength range, which is caused by the appearance of semi-transparent crystalline silicon dendritic structures that are tens of micrometers in size in the film. In the annealed area of the film specimen, the intermetallic Al12Mo phase was detected by electron diffraction structure analysis, indicating a possible reason for the appearance of silicon atoms needed for dendrite growth as a result of the chemical interaction of Al and MoSi2. Due to the requirements for a high degree of visible radiation blocking (106 to 107 times), the appearance of even one dendritic structure significantly reduces the blocking properties of the film filter and is, therefore, not permissible. Based on the measurement of the transmission of MoSi2-2.5 nm/Al-72 nm/MoSi2-2.5 nm films at 633 nm for isothermal annealing at 200°C-250°C, the activation energy for the formation of dendritic structures (E=1.55±0.1 eV) was measured and the maximum permissible film temperature (130°C) at which dendritic structures did not appear during a 5-year mission was predicted.

We optimized the parameters of a laser-produced plasma source based on a solid-state Nd: YAG laser (λ = 1.06 nm, pulse duration 4 ns, energy per pulse up to 500 mJ, repetition rate 10 Hz, lens focus distance 45 mm, maximum power density of laser radiation in focus 9 × 1011 W/cm2) and a double-stream Xe/He gas jet to obtain a maximum of radiation intensity around 11 nm wavelength. It was shown that the key factor determining the ionization composition of the plasma is the jet density. With the decreased density, the ionization composition shifts toward a smaller degree of ionization, which leads to an increase in emission peak intensity around 11 nm. We attribute the dominant spectral feature centred near 11 nm originating from an unidentified 4d-4f transition array in Xe+10…+13 ions. The exact position of the peak and the bandwidth of the emission line were determined. We measured the dependence of the conversion efficiency of laser energy into an EUV in-band energy with a peak at 10.82 nm from the xenon pressure and the distance between the nozzle and the laser focus. The maximum conversion efficiency (CE) into the spectral band of 10–12 nm measured at a distance between the nozzle and the laser beam focus of 0.5 mm was CE = 4.25 ± 0.30%. The conversion efficiencies of the source in-bands of 5 and 12 mirror systems at two wavelengths of 10.8 and 11.2 nm have been evaluated; these efficiencies may be interesting for beyond extreme ultraviolet lithography.We optimized the parameters of a laser-produced plasma source based on a solid-state Nd: YAG laser (λ = 1.06 nm, pulse duration 4 ns, energy per pulse up to 500 mJ, repetition rate 10 Hz, lens focus distance 45 mm, maximum power density of laser radiation in focus 9 × 1011 W/cm2) and a double-stream Xe/He gas jet to obtain a maximum of radiation intensity around 11 nm wavelength. It was shown that the key factor determining the ionization composition of the plasma is the jet density. With the decreased density, the ionization composition shifts toward a smaller degree of ionization, which leads to an increase in emission peak intensity around 11 nm. We attribute the dominant spectral feature centred near 11 nm originating from an unidentified 4d-4f transition array in Xe+10…+13 ions. The exact position of the peak and the bandwidth of the emission line were determined. We measured the dependence of the conversion efficiency of laser energy into an EUV in-band energy with a peak at 10.82 nm from the xenon ...