We report on our efforts in design and construction of a compact Extreme Ultraviolet (EUV)-pump-probe microscope. The goal is the observation of formation of nanostructures, induced by a femtosecond (fs)-laser pulse. The unique interaction processes of fs-laser radiation with matter open up new markets in laser material processing and, therefore, are actively investigated in the last decade. The resulting "sub 100 nm"-structures offer vast potential benefits in photonics, biotechnology, tribological surface design, plasmonic applications and production of nanoparticles. Focused fs-laser radiation causes a local modification resulting in nanostructures of high precision and reproducibility. However the formation dynamics is not well understood. Research in this field requires high temporal and spatial resolution. A combination of fs-laser and EUV-microscope provides a tool for "in situ"-observation of the formation dynamics. As exemplary structures to be investigated, we use nanojets on thin gold films and periodic surface structures (ripples) on dielectrics. In the future, the EUV-pump-probe microscope can become a versatile tool to observe physical or biological processes. Microscopy using EUV-light is capable of detecting structures on a scale down to several tens of nanometers. For detailed investigations a compact EUV-microscope has been realized utilizing OVI Balmer-alpha radiation at 17.3 nm coming from a discharge produced oxygen plasma. As optical elements a grazing incidence elliptical collector and a zone plate with a width of outermost zone of 50 nm and a spectral filter to avoid chromatic aberrations are used. The detector is a fast gated microchannel plate with a pore size of 2 microns contacted by a low impedance transmission line. The expected spatial resolution of the setup is better than 100 nm and the time resolution is better than 1 ns. The newly developed EUV-microscope is a powerful tool for a wide field of investigations that need high time and spatial resolutions simultaneously
Research in ultrafast nanoscale phenomena requires high spatial and temporal resolution detectors. Optical imaging microscopes achieve high time resolution but low spatial resolution and scanning microscopes vice versa. Extreme ultraviolet imaging microscopy closes this gap but demands a suited two dimensional detector for efficient use of photons and simultaneously enabling fast gating. We use a micro-channel plate photoelectron multiplier together with a phosphor screen as a detector. We pulse the operation voltage of the electron-multiplier for 1.25 ns. Only during that time the detector is highly sensitive to extreme ultraviolet light. A custom built impedance-transformer delivers high currents into the plates' capacitance. This leads to a short charging time and ensures a narrow temporal sensitivity window. We analyzed the following attributes of the detector system: - Temporal behavior is measured by femtosecond illumination with high harmonics generation radiation at different relative delays. The sensitivity curve has a width of 2 ns. Electronic timing jitter is below 150 ps. - Spatial resolution is determined by mapping the shadow of a sharp edge on the detector. The smearing gives information about the modulation transfer function. The resolution limit according to the Rayleigh criterion is at 12 lp/mm or a minimum resolvable pitch of 80 µm. - Spectral sensitivity of the detector is calibrated for extreme ultraviolet wavelengths ranging from 1 nm to 30 nm at the PTB facility at the BESSY2 synchrotron. In summary the detector provides a spatial resolution down to 80 nm and a time resolution shorter than 2 ns using a discharge produced plasma EUV source and a zone plate based microscope with a magnification of ~ 1000x. This is a highly interesting combination and will help to investigate a variety of short time processes in nanoscience
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