Thin film multilayer filters for solar EUV telescopes

Abstract

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.

Reflective aperiodic multilayer filters for metrology at XUV sources

“…Besides absorptive filters that block wider spectral ranges, XUV monitoring and metrology is making use mainly of periodic multilayer mirrors for selective reflection [5][6][7][8][9][10][11] of a desired, narrowband wavelength interval. However, with periodic layers, the shape of the spectral transmission peak is fixed due to the periodicity of the layer stack.…”

Исследование оптических, механических и термических свойств свободновисящих пленок на основе нанокомпозитных материалов MoSi-=SUB=-2-=/SUB=-N-=SUB=-x-=/SUB=- и ZrSi-=SUB=-2-=/SUB=-N-=SUB=-y-=/SUB=-

“…Свободновисящие пленочные структуры активно используются в качестве абсорбционных фильтров и защитных пленок в оптических схемах и приборах, работающих в мягком рентгеновском (МР) и экстремальном ультрафиолетовом (ЭУФ) спектральных диапазонах (λ = 1−100 nm) [1][2][3]. Такие пленки пропускают излучение на рабочих длинах волн в МР и ЭУФ диапазонах и подавляют внеполосовое (фоновое) излучение, высшие порядки дифракции в спектральных приборах, а также защищают нижележащую поверхность от попадания пылинок и иных загрязнений (например, защищают поверхность маски-фотошаблона в установках проекционной ЭУФ литографии).…”

Spontaneous formation of highly periodic nano-ripples in inclined deposition of Mo/Si multilayers

“…Multilayer (ML) coatings composed of dozens of nanometer thick alternating layers of high and low Z-materials are widely used in X-ray optics due to their high X-ray reflectivity. Multilayer-based optical components such as Xray mirrors, 1,2 zone plates, 3,4 multilayer Laue lenses, 5 spectral purity filters, 6,7 and multilayer diffraction gratings [8][9][10] are of great importance for extreme ultraviolet (EUV) lithography, X-ray imaging, high resolution X-ray spectroscopy, and X-ray astronomy.…”