Soft X-ray and EUV Microscopy
Microscopy using the soft x-ray (SXR) and extreme ultraviolet (EUV) radiation is a very promising technique in micro- and nano-structure imaging . It has many applications in life sciences. It can provide quality images of cells and their organelles and information on the chemistry of proteins and other bio-molecules . This is possible because of element specific light-matter interaction in the wavelength range of so called ‘water window’ between the absorption edges of oxygen and carbon from 2.3 – 4.4 nm . At water window water molecule is highly transparent while for proteins interaction cross-sections are significant for photon energies above K-absorption edge of carbon.
The prominent SXR and EUV radiation sources for tomographic microscopy are synchrotron accelerators [4, 5]. These sources are quite expensive and not accessible to everyone in typical research laboratories. Hence, there is a need for a compact, practical and less expensive source of SXR and EUV. The Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen with the Fraunhofer Institute for Laser Technology (ILT) houses compact SXR/EUV sources based on gas-discharge plasma. These sources were developed by Bergmann, K. et al [6, 7].
The optical setup of the compact transmission soft x-ray microscope with a gas-discharge source is shown in Figure 1. The sample two dimensional images of rat embryonic cells acquired with this setup are shown in Figure 2.
By rotating the sample, it is possible to acquire tomographic images. The three-dimensional images can be reconstructed from two-dimensional projection images using algorithms based on the principle similar to the one used in computed tomography x-ray machines.
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 Bergmann, K., Kupper, F., and Benk M. (2008). Soft x-ray emission from a pulsed gas discharge in a psedosparklike electrode geometry. J. Appl. Phys. 103, 123304-1 – 123304-8.
 Benk, M., Bergmann, K., Schafer, D., and Wilhein T. (2008). Compact soft x-ray microscope using a gas-discharge light source. Opt. Lett. 33 (20), 2359 – 2361.