High resolution holography with table top extreme ultraviolet lasers

The development of tabletop extreme ultraviolet (EUV) lasers enabled the implementation of several experimental techniques like high-resolution imaging, nanolithography, mass spectroscopy, etc. in a small laboratory size environment. In this talk I will summarize results of high-resolution holographic imaging using a tabletop EUV laser. The approach we used was Fourier transform holography (FTH). FTH has the distinctive advantage that the image reconstruction process is straightforward. It can be numerically reconstructed by calculating the inverse Fourier transform of the interference pattern collected on the charge coupled device detector. The point reference source in FTH is typically obtained using a small pinhole located in the object plane. This usually limits the object size in order to match the amount of light to the intensity of the reference pinhole. In our experiments we utilized a setup in which this limitation was mitigated using a reference point source created with a Fresnel zone plate that split the laser beam to generate the illumination and reference waves. The pulsed illumination is generated by a tabletop EUV laser at 46.9nm wavelength, (750μm coherence length and 550μm coherence radius). Multiple shots and single shot holograms were acquired. A resolution of 128±33 nm was obtained for multiple shots holograms (accumulation of 20 shots). For single shot exposures, due to the lower signal-to-noise level the resolution was reduced to 159±58 nm. Three-dimensional imaging was also achieved by numerical refocusing the reconstructed image. A sequence of single shot holograms allowed for the composition of holographic movies of nano-scale oscillating cantilevers at megahertz frequencies. Also, holograms obtained at 13.9nm will be presented, in which we obtained a spatial resolution below 100nm.