DiProI Research

Pump & probe: stroboscopic experiments The single-shot CDI speckle pattern formed by the short femtosecond FERMI-FEL pulse is an excellent probe to monitor the evolution of the transient states of the sample. These can be followed, at variable delays after the excitation by a pump photon pulse, with time resolution on scales down to the pulse duration. Even before applying Fourier inversion methods, information on the induced dynamics or changes in the average size and size distribution of the microscopic building blocks is already coded in the intensities and dimensions of CDI patterns. The probe pulse will be provided either by a synchronized Ti:Sapphire user laser, tunable from the infrared to the near ultraviolet, or by a split-delay correlation system, separating the pump pulse from the probe FEL soft X-ray beam, providing a variable delay up to 1 ns. By splitting the pulse and simultaneously hitting an object from two directions, it is possible to explore stereo 3D imaging as well.

Time resolved experiments can be carried out impinging on sets of identical samples with pump & probe pulses with variable delays.

Resonant CDI and magnetic dichroism Resonant CDI at the atomic absorption edges in a single-shot mode, enabled by the full longitudinal coherence and tunability of the seeded FERMI-FEL pulses, adds elemental sensitivity. This selective "chemical" imaging, combined with the FERMI-FEL circular or linear polarization, extends the information to spin and orbital momentum: in non-destructive mode, with attenuated FEL beam, the difference between images obtained with photons of opposite chirality enhances the contrast related to the magnetic domain structure. Magnetic dichroism can be used to image magnetic domains thanks to variations in the response to circular light of different chirality.

Identical samples or integrating mode

Since the full power of focalized FEL pulses will destroy any sample, experiments planning to compare results from different shots need either to be performed using sets of identical samples or in an integrating mode with attenuated beam intensity.