Abstract
We investigated the experimental damage threshold of platinum coating on a silicon substrate illuminated by soft x-ray radiation at grazing incidence angle of 2 degrees. The coating was the same as the blazed grating used for the soft X-ray self-seeding optics of the Linac Coherent Light Source free electron laser. The irradiation condition was chosen such that the absorbed dose was similar to the maximum dose expected for the grating. The expected dose was simulated by solving the Helmholtz equation in non-homogenous media. The experiment was performed at 900 eV photon energy for both single pulse and multi-shot conditions. We have not observed single shot damage. This corresponds to a single shot damage threshold being higher than 3 J/cm(2). The multiple shot damage threshold measured for 10 shots and about 600 shots was determined to be 0.95 J/cm(2) and 0.75 J/cm(2) respectively. The damage threshold occurred at an instantaneous dose which is higher that the melt dose of platinum.
Highlights
In recent years, the advent of the Free Electron Laser (FEL) opened up the door to new classes of experiments, including dynamical studies of chemical and physical phenomenon, lens-less diffraction of periodic and non-periodic structures and the study of samples that are suffering radiation damage at third generation x-ray sources
In both direct seeding and High Gain Harmonic Generation (HGHG), the maximum photon energy is limited by the availability of an external seeding laser with enough power and with proper temporal characteristics at short enough wavelengths
For the soft X-ray self-seeding (SXRSS) project, the narrow bandwidth of the Spontaneous Emission (SASE) beam is selected by a diffraction grating based monochromator
Summary
The advent of the Free Electron Laser (FEL) opened up the door to new classes of experiments, including dynamical studies of chemical and physical phenomenon, lens-less diffraction of periodic and non-periodic structures and the study of samples that are suffering radiation damage at third generation x-ray sources. The Fermi@Elettra team employed a technique called High Gain Harmonic Generation (HGHG) [2] In this case, an external laser seeds the electron beam at a particular wavelength, but the radiation is amplified at a shorter wavelength. An external laser seeds the electron beam at a particular wavelength, but the radiation is amplified at a shorter wavelength In both direct seeding and HGHG, the maximum photon energy is limited by the availability of an external seeding laser with enough power and with proper temporal characteristics at short enough wavelengths. For the soft X-ray self-seeding (SXRSS) project, the narrow bandwidth of the SASE beam is selected by a diffraction grating based monochromator. The planned photon energy for the initial commissioning of the SXRSS was around 900 eV, and we decided to concentrate our studies on this particular value
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