Mónica Fernández-Perea

The soft x-ray instrument for materials studies at the linac coherent light source x-ray free-electron laser.

The soft x-ray materials science instrument is the second operational beamline at the linac coherent light source x-ray free electron laser. The instrument operates with a photon energy range of 480-2000 eV and features a grating monochromator as well as bendable refocusing mirrors. A broad range of experimental stations may be installed to study diverse scientific topics such as: ultrafast chemistry, surface science, highly correlated electron systems, matter under extreme conditions, and laboratory astrophysics. Preliminary commissioning results are presented including the first soft x-ray single-shot energy spectrum from a free electron laser.

Temporal cross-correlation of x-ray free electron and optical lasers using soft x-ray pulse induced transient reflectivity.

The recent development of x-ray free electron lasers providing coherent, femtosecond-long pulses of high brilliance and variable energy opens new areas of scientific research in a variety of disciplines such as physics, chemistry, and biology. Pump-probe experimental techniques which observe the temporal evolution of systems after optical or x-ray pulse excitation are one of the main experimental schemes currently in use for ultrafast studies. The key challenge in these experiments is to reliably achieve temporal and spatial overlap of the x-ray and optical pulses. Here we present measurements of the x-ray pulse induced transient change of optical reflectivity from a variety of materials covering the soft x-ray photon energy range from 500eV to 2000eV and outline the use of this technique to establish and characterize temporal synchronization of the optical-laser and FEL x-ray pulses.

Absolute pulse energy measurements of soft x-rays at the Linac Coherent Light Source

This paper reports novel measurements of x-ray optical radiation on an absolute scale from the intense and ultra-short radiation generated in the soft x-ray regime of a free electron laser. We give a brief description of the detection principle for radiation measurements which was specifically adapted for this photon energy range. We present data characterizing the soft x-ray instrument at the Linac Coherent Light Source (LCLS) with respect to the radiant power output and transmission by using an absolute detector temporarily placed at the downstream end of the instrument. This provides an estimation of the reflectivity of all x-ray optical elements in the beamline and provides the absolute photon number per bandwidth per pulse. This parameter is important for many experiments that need to understand the trade-offs between high energy resolution and high flux, such as experiments focused on studying materials via resonant processes. Furthermore, the results are compared with the LCLS diagnostic gas detectors to test the limits of linearity, and observations are reported on radiation contamination from spontaneous undulator radiation and higher harmonic content.

Development and calibration of mirrors and gratings for the soft x-ray materials science beamline at the Linac Coherent Light Source free-electron laser.

This work discusses the development and calibration of the x-ray reflective and diffractive elements for the Soft X-ray Materials Science (SXR) beamline of the Linac Coherent Light Source (LCLS) free-electron laser (FEL), designed for operation in the 500 to 2000 eV region. The surface topography of three Si mirror substrates and two Si diffraction grating substrates was examined by atomic force microscopy (AFM) and optical profilometry. The figure of the mirror substrates was also verified via surface slope measurements with a long trace profiler. A boron carbide (B4C) coating especially optimized for the LCLS FEL conditions was deposited on all SXR mirrors and gratings. Coating thickness uniformity of 0.14 nm root mean square (rms) across clear apertures extending to 205 mm length was demonstrated for all elements, as required to preserve the coherent wavefront of the LCLS source. The reflective performance of the mirrors and the diffraction efficiency of the gratings were calibrated at beamline 6.3.2 at the Advanced Light Source synchrotron. To verify the integrity of the nanometer-scale grating structure, the grating topography was examined by AFM before and after coating. This is to our knowledge the first time B4C-coated diffraction gratings are demonstrated for operation in the soft x-ray region.

Triple-wavelength, narrowband Mg/SiC multilayers with corrosion barriers and high peak reflectance in the 25-80 nm wavelength region

We have developed new, Mg/SiC multilayer coatings with corrosion barriers which can be used to efficiently and simultaneously reflect extreme ultraviolet (EUV) radiation in single or multiple narrow bands centered at wavelengths in the spectral region from 25 to 80 nm. Corrosion mitigation was attempted through the use of Al-Mg or Al thin layers. Three different multilayer design concepts were developed and deposited by magnetron sputtering and the reflectance was measured at near-normal incidence in a broad spectral range. Standard Mg/SiC multilayers were also deposited and measured for comparison. They were shown to efficiently reflect radiation at a wavelength of 76.9 nm with a peak reflectance of 40.6% at near-normal incidence, the highest experimental reflectance reported at this wavelength for a narrowband coating. The demonstration of multilayer coatings with corrosion resistance and multiple-wavelength EUV performance is of great interest in the development of mirrors for space-borne solar physics telescopes and other applications requiring long-lasting coatings with narrowband response in multiple emission lines across the EUV range.

Demonstration of multilayer reflective optics at photon energies above 0.6 MeV

Focusing optics operating in the soft gamma-ray photon energy range can advance a range of scientific and technological applications that benefit from the large improvements in sensitivity and resolution that true imaging provides. An enabling technology to this end is multilayer coatings. We show that very short period multilayer coatings deposited on super-polished substrates operate efficiently above 0.6 MeV. These experiments demonstrate that Bragg scattering theory established for multilayer applications as low as 1 eV continues to work well into the gamma-ray band.

Review of substrate materials, surface metrologies and polishing techniques for current and future-generation EUV/x-ray optics

This manuscript presents a review of recent advances in EUV/x-ray substrate specification, fabrication and metrology for photolithography, synchrotron sources, free-electron laser sources, solar physics and astronomy. Highlights from ultra-low- expansion glass substrates, silicon and silicon carbide substrates are presented. Selected emerging substrate materials and fabrication technologies are also discussed.

Hard x-ray/soft gamma-ray telescope designs for future astrophysics missions

We present several concept designs of hard X-ray/soft λ-ray focusing telescopes for future astrophysics missions. The designs are based on depth graded multilayer coatings. These have been successfully employed on the NuSTAR mission for energies up to 80 keV. Recent advances in demonstrating theoretical reflectivities for candidate multilayer material combinations up to 400 keV including effects of incoherent scatter has given an experimental base for extending this type of designs to the soft λ-ray range. At the same time, the calibration of the in-flight performance of the NuSTAR mission has given a solid understanding and modelling of the relevant effects influencing the performance, including optical constants, roughness, scatter, non-uniformities and figure error. This allows for a realistic extension for designs going to much higher energies. Similarly, both thin slumped glass and silicon pore optics has been developed to a prototype stage which promises imaging resolution in the sub 10 arcsecond range. We present designs based on a 20 m and 50 m focal lengths with energy ranges up to 200 keV and 600 keV.

In-band and out-of-band reflectance calibrations of the EUV multilayer mirrors of the atmospheric imaging assembly instrument aboard the Solar Dynamics Observatory

Experimental multilayer reflectance data on flight mirrors and witnesses for three extreme ultraviolet (EUV) channels of the Atmospheric Imaging Assembly (AIA) instrument aboard NASA’s Solar Dynamics Observatory are presented and compared to theoretical models. The relevance of these results to the performance of the AIA instrument is discussed.

Recent Advances in Multilayer Reflective Optics for EUV/X-Ray Sources

This paper discusses the development of (i) corrosion-resistant multilayers for the 25–80 nm region (ii) multilayer mirrors for the first 0.5-NA Micro-Exposure Tools at 13.5 nm and (iii) multilayer mirrors for the soft gamma-ray range.