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Department Optics and Beamlines

Coherence and Wavefront Analysis

As a fourth-generation synchrotron light source, BESSY III will feature a multibend achromatic lattice, delivering synchrotron radiation with exceptional brightness and coherence in the soft to tender X-ray range. This high-precision radiation enables groundbreaking advances in nanoscale spectroscopy and microscopy.

Coherent radiation allows for detailed imaging of material boundaries and magnetic field configurations at the nanometer scale — structures that often remain invisible with other imaging techniques. It also enhances resolution and contrast in methods such as X-ray microscopy, X-ray holography, and phase-contrast imaging.

To fully harness this radiation, precise knowledge of coherence is essential — not only at the light source (the undulator) but also at the sample. Maintaining coherence throughout the entire beamline is crucial. Our goal is to identify factors affecting coherence preservation and develop strategies for its targeted control.

 

Types of Coherence

Spatial Coherence

  • Defines how well the wavefronts remain phase-synchronized across a surface.
  • High spatial coherence enables strong photon beam focusing and high photon density, both critical for imaging quality.

Temporal Coherence

  • Describes the consistency of wave phases over time.
  • Depends on the spectral width: a narrower bandwidth results in longer coherence length.

Due to the pulsed nature of synchrotron radiation, temporal coherence plays a secondary role. While individual pulses exhibit coherence, their discrete nature often makes temporal coherence less relevant in many applications.

Coherence (eng) - enlarged view
 

Research and Development for BESSY III

We collaborate with partners from various institutes to develop efficient, rapid coherence diagnostics for BESSY III. Our key focus areas include:

  • Advanced simulations to identify factors influencing coherence.
  • Long-term development of methods for real-time coherence monitoring during beam operation, ensuring optimal imaging results.

Wavefront analysis provides critical insights into coherence and optical surface quality along the beamline. As part of the EFRE-project MetrokX, we are pioneering new wavefront analysis techniques and active wavefront control methods to further optimize coherence within the beamline.

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