| 1. |
- Schwenke, Jörg, et al.
(författare)
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Digital in-line holography on amplitude and phase objects prepared with electron beam lithography.
- 2012
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720. ; 247:2, s. 196-201
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication and characterization of amplitude and phase samples consisting of well defined Au or Al features formed on ultrathin silicon nitride membranes. The samples were manufactured using electron beam lithography, metallization and a lift-off technique, which allow precise lateral control and thickness of the metal features. The fabricated specimens were evaluated by conventional microscopy, atomic force microscopy and with the digital in-line holography set-up at the Lund Laser Centre. The latter uses high-order harmonic generation as a light source, and is capable of recovering both the shape and phase shifting properties of the samples. We report on the details of the sample production and on the imaging tests with the holography set-up.
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| 2. |
- Schwenke, Jörg
(författare)
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Towards ultrafast imaging with extreme ultraviolet light sources
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis reports experimental studies performed with two advanced coherent XUV sources with ultrashort pulse duration, high-order harmonic generation and seeded-free electron laser. High-order harmonic generation (HHG) is the generation of overtones of a fundamental laser pulse in a medium, e.g. noble gases. The emitted radiation has a high degree of transverse coherence, and pulse lengths in the attosecond regime can be achieved. We have applied the pulses to digital in-line holography, where we demonstrated imaging of micrometer-sized objects with single XUV pulses, and the reconstruction of the phase shifting properties of thin layers of material. A method to produce thin layers of arbitrary shape and thickness, on top of ultra-thin membranes, is presented. In another experiment, we used HHG pulses to eject electrons from a sample, to be imaged with a PEEM microscope. The experiment aims at combining the short temporal duration achievable with high-order harmonic generation, to the high spatial resolution of PEEM, in order to image electron density variations on prepared surfaces. A further experiment is proposed to use the XUV pulses from the HHG source to study the charge-carrier recombination processes in a wide-bandgap semiconductor. The short duration and high intensity of the XUV pulse allows us to create a transient phase grating and to probe the induced refractive index change at a variable time delay. Finally, we have also studied the feasibility to use HHG pulses as a seed laser for a seeded free-electron laser, by investigating the energy and pointing stability of the source. These studies are a preparation to implement an HHG setup at an existing seeded free-electron laser setup. The characterization of the emission of the seeded FEL is also presented. Here the coherence was tested in a double-slit experiment, and the polarization was determined with a linear polarizer.
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