Slawka J. Pfauntsch

Broadband Mo∕Si multilayer transmission phase retarders for the extreme ultraviolet

Experimental results on aperiodic broadband transmission molybdenum/silicon multilayer phase retarders for the extreme ultraviolet range are presented. The broadband phase retarders were designed using a numerical method and made using direct current magnetron sputtering on silicon nitride membrane. The polarization properties of these aperiodic transmission phase retarders have been investigated using the soft x-ray polarimeter at BESSY-II. The measured phase shift was about 42° in the wavelength range of 13.8–15.5nm, and the corresponding s-component transmission (Ts) decreased from 6% to 2% with increasing wavelength.

Two approaches for irradiating cells individually: a charged-particle microbeam and a soft X-ray microprobe

Abstract We are developing two independent, but complementary microbeams for irradiating cells individually in vitro. Firstly, a charged-particle microbeam that uses a fine-bore glass capillary, combined with a transmission detector to precisely irradiate cells with exact numbers of energetic charge-particles and secondly, a soft X-ray microprobe that produces a very fine beam of carbon-K (278 eV) ultrasoft X-rays, focused to a spot size

Complete polarization analysis of extreme ultraviolet radiation with a broadband phase retarder and analyzer

The polarization state of the BESSY UE56/1-PGM beamline radiation in the broad wavelength range of 12.7–15.5nm was measured using a molybdenum/silicon transmission phase retarder and a reflection analyzer with aperiodic multilayer interference structures, which can broaden the spectral response of these optical elements. The characteristics of the circular polarized undulator radiation, as well as the polarization properties of the two polarizing elements, were determined by a complete polarization analysis. Furthermore, the polarization of the radiation as a function of the undulator shift setting was also measured at the wavelength of 13.1nm by use of the broadband phase retarder-analyzer pair.

Broadband multilayer polarizers for the extreme ultraviolet

Nonperiodic molybdenum/silicon broadband multilayer polarizers have been designed using numerical optimization algorithm and fabricated using direct current magnetron sputtering. Their performances have been characterized using the high precision eight-axis soft x-ray polarimeter at the BESSY facility. Different multilayers have measured s-polarized reflectivities of 27% at 13.1nm and higher than 15% over the wavelength range of 13–19nm. Nearly constant s reflectivity, up to 37%, is observed over the 15–17nm wavelength range, where the degree of polarization is more than 98%. Furthermore, these multilayer polarizers also show high s reflectivity and polarization over a broad angular range at fixed wavelength.

Extreme ultraviolet broadband Mo/Y multilayer analyzers

Broadband extreme ultraviolet molybdenum/yttrium aperiodic multilayer analyzers were designed for polarization experiments in 8.5–11.7nm wavelength range. The multilayer analyzers were made using direct current magnetron sputtering and characterized using the soft x-ray polarimeter at BESSY-II facility. Measured s reflectivities at the Brewster angle are 5.5% for a multilayer designed for 8.5–10.1nm wavelength range and 6.1% for one designed for 9.1–11.7nm. The multilayers also exhibit high polarization degree up to 98.79%. In addition, the multilayer was also measured over 38°–52° angular range at the fixed wavelength of 10.2nm and the mean s reflectivity is 6.2%.

Determination of the evolution of layer thickness errors and interfacial imperfections in ultrathin sputtered Cr/C multilayers using high-resolution transmission electron microscopy

The structures of ultrathin sputtered Cr/C multilayers were determined by high-resolution transmission electron microscopy. The evolution of layer thickness errors, interdiffusion and interfacial roughness were simulated using time series models. The results show that with increasing of interdiffusion and roughness the multilayer thickness ratio changes, thereby influencing the optical performance. All structural parameters show good correlation with and influence adjacent layers. The system errors of the deposition equipment can also be evaluated by the models.

Active microstructured arrays for x-ray optics

The UK Smart X-Ray Optics programme is developing the techniques required to both enhance the performance of existing X-ray systems, such as X-ray telescopes, while also extending the utility of X-ray optics to a broader class of scientific investigation. The approach requires the control of the inherent aberrations of X-ray systems using an active/adaptive method. One of the technologies proposed to achieve this is micro-structured optical arrays, which use grazing incidence reflection through consecutive aligned arrays of channels. Although such arrays are similar in concept to polycapillary and microchannel plate optics, they are more flexible. Bending the arrays allows variable focal length, while flexing parts of them provides adaptive or active systems. Custom configurations can be designed, using ray tracing and finite element analysis, for applications from sub-keV to several-keV X-rays. The channels may be made using deep silicon etching, which can provide appropriate aspect ratios, and flexed using piezo actuators. An exemplar application will be in the micro-probing of biological cells and tissue samples using Ti Kα radiation (4.5 keV) in studies related to radiation induced cancers.

Zone plate achromatic doublets

Zone plates as used in high resolution x-ray microscopy have focal lengths which are proportional to the x-ray energy. This means that in techniques such as elemental and chemical state mapping, which require images to be made at more than one energy, refocusing is required which can lead to loss of image registration. Using two zone plates, in a similar fashion to achromatic refractive lens doublets for visible light, it is possible to focus two x-ray energies to the same spot.

Progress on the development of active micro-structured optical arrays for x-ray optics

The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing active/adaptive micro-structured optical arrays (MOAs). These devices are designed to focus X-rays using grazing incidence reflection through consecutive aligned arrays of microscopic channels etched in silicon. The silicon channels have been produced both by dry and wet etching, the latter providing smoother channel walls. Adaptability is achieved using piezoelectric actuators, which bend the device and therefore change its focal distance. We aim to achieve a 5 cm radius of curvature which can provide a suitable focal length using a tandem pair MOA configuration. Finite Element Analysis (FEA) modelling has been carried out for the optimization of the MOA device design, consider different types of actuators (unimorph, bimorph and active fibre composites), and different Si/piezoelectric absolute and relative thicknesses. Prototype devices have been manufactured using a Viscous Plastic Processing Process for the piezoelectric actuators and dry etched silicon channels, bonded together using a low shrinkage adhesive. Characterisation techniques have been developed in order to evaluate the device performance in terms of the bending of the MOA channels produced by the actuators. This paper evaluates the progress to date on the actuation of the MOAs, comparing FEA modelling with the results obtained for different prototype structures.

Active microstructured x-ray optical arrays

The UK Smart X-Ray Optics consortium is developing novel reflective adaptive/active x-ray optics for small-scale laboratory applications, including studies of radiation-induced damage to biological material. The optics work on the same principle as polycapillaries, using configured arrays of channels etched into thin silicon, such that each x-ray photon reflects at most once off a channel wall. Using two arrays in succession provides two reflections and thus the Abbe sine condition can be approximately satisfied, reducing aberrations. Adaptivity is achieved by flexing one or both arrays using piezo actuation, which can provide further reduction of aberrations as well as controllable focal lengths. Modelling of such arrays for used on an x-ray microprobe, based on a microfocus source with an emitting region approximately 1μm in diameter, shows that a focused flux approximately two orders of magnitude greater than possible with a zone plate of comparable focal length is possible, assuming that the channel wall roughness is less than about 2nm.