Institute of Functional Interfaces

Microscopic imaging of biological samples using coherent soft X-rays from free-electron laser and synchrotron sources

  • chair:

    Gorniak, T. / Senkbeil, T. / Beckers, M. / Buck, A. / Alles, M. / Giewekemeyer, K. / Salditt, T. / Rosenhahn, A. (2012)

  • place:

    The 11th International Conference on Synchrotron Radiation Instrumentation, Lyon, France 9.-13. Juli, 2012

  • Date: 2012
  • Gorniak, T. / Senkbeil, T. / Beckers, M. / Buck, A. / Alles, M. / Giewekemeyer, K. / Salditt, T. / Rosenhahn, A. (2012): „Microscopic imaging of biological samples using coherent soft X-rays from free-electron laser and synchrotron sources“. In: The 11th International Conference on Synchrotron Radiation Instrumentation, Lyon, France 9.-13. Juli, 2012

Abstract

Coherent X-ray microscopy of hydrated biological samples – especially in the so-called water window of 284-540 eV – is of tremendous interest for life sciences due to the high contrast of organic matter with respect to the aqueous background. Especially freeelectron lasers can provide highly intense and coherent pulses, which allow single pulse imaging to overcome resolution limits set by radiation damage. We present the first holographic microscopy images of dehydrated biological material acquired in the water window with higher harmonic radiation provided by the free-electron laser FLASH.

In order to increase the photon flux we used high efficiency zone plates instead of pinholes to create the divergent light cone for holography. The results pave the way to the vision of holographic imaging of hydrated biological samples with single FEL pulses. We supplement single pulse imaging experiments by ptychographic imaging with synchrotron radiation at BESSY II. This method uses coherent diffraction imaging at different sample positions while maintaining a fixed spatial overlap between the fields of view. By introducing this spatial redundancy to the data an additional constraint for the iterative reconstruction algorithm is achieved.

This enhances the convergence of phase retrieval drastically. The spatial resolution of below 50 nm and the imaging properties were characterized using lithographic and biological test samples. We also show results on resonant imaging with chemical contrast caused by both, absorption and phase shifts, in the vicinity of core level absorption edges.