Extreme ultraviolet multilayer for the FERMI@Elettra free electron laser beam transport system

Abstract

In this work we present the design of a Pd/B₄C multilayer structure optimized for high reflectance at 6.67 nm. The structure has been deposited and also characterized along one year in order to investigate its temporal stability. This coating has been developed for the beam transport system of FERMI@Elettra Free Electron Laser: the use of an additional aperiodic capping layer on top of the structure combines the high reflectance with filter properties useful in rejecting the fundamental harmonic when the goal is to select the third FEL harmonic.

Pd/B_4C/Y multilayer coatings for extreme ultraviolet applications near 10 nm wavelength

“…However, Si/Mo has relatively low reflectance at wavelengths shorter than 12.4 nm wavelength (i.e., the Si L-edge), due to high optical absorption in the Si layers. Consequently, a variety of other multilayer material combinations have been investigated over the years for use at these shorter wavelengths [2][3][4][5][6].…”

Spectral tailoring of nanoscale EUV and soft x-ray multilayer optics

“…If the capping layers are designed such that for the unwanted wavelength, the antinode of the standing wave is very close to the absorbing layer (inside the capping structure), the absorption will be enhanced and a high suppression can be achieved. 20,21 This principle is very suitable to reject features adjacent to the peak wavelength. A high reflectance at 28.4 nm (Fe-XV line) with strong suppression at around 32.5 nm has been demonstrated using a periodic Mo/Si multilayer with a Mo/ Si capping layer structure, as shown in Figure 2.…”

Damage of multilayer optics with varying capping layers induced by focused extreme ultraviolet beam

“…On-top of the periodic stack, different aperiodic capping-layers (CL) were designed in order to improve the harmonics selection capabilities of the basic periodic structure using the optimization technique described previously. 16 The capping layer structures were optimized to increase the Fundamental Rejection Ratio (FRR), i.e., the ratio between the reflectance at the third harmonic (i.e., 13.5 nm) and the fundamental (i.e., 40.5 nm). In Table I, the capping-layer structures adopted in the experiment together with their experimental peak reflectance and FRR values measured at BEAR beamline in ELETTRA Synchrotron, Trieste, Italy are compiled.…”

“…Multilayer optics will be useful also to realize delay line systems able to split the beam and temporally shift one component with respect to the other. 16 The stability of nanostructured coatings for all different applications during experimental operation has been investigated by different authors. [17][18][19][20] This task is of particular importance when related to FEL applications, due to the high average and peak power densities of these sources.…”

“…24 Multilayers with high reflectance at third harmonics shall be used in the delay lines to control the temporal delay of the pulses. 4,15,16 In the present experiment the attention was focused on the resistance of capped multilayers, evaluating the influence of the top layers on the damaging process, measuring the respective damage thresholds, and providing a comparison between capped and standard Mo/Si periodic stacks. The coatings were exposed to an EUV beam from a laserproduced plasma with nanosecond pulse duration, which was tightly focused using a Schwarzschild objective.…”