Pump-and-Probe Experiments

The optical laser system in the laser hutch

The optical laser system in the laser hutch

The extremely bright pulses of extreme-ultraviolet radiation and soft X-rays from FLASH can be as short as few 10 femtoseconds. These ultra-short pulses can be used to explore the temporal evolution of various processes such as atomic motion, phase transitions, expansion of hot plasmas, and chemical reactions.

To measure events happening in femtoseconds or picoseconds, researchers mainly utilize the so-called pump-and-probe technique. Two short pulses are required: The pump pulse starts the reaction, while the probe pulse investigates the state of the system after a defined time delay. This experiment is repeated several times with increasing time delays. Putting together all these experiments gives a "molecular movie"

FLASH offers 3 different options for pump-probe experiments:

  • XUV-XUV: Both the pump and the probe pulse originate from the FEL itself by splitting the pulse in two and delaying one of them by sending it on a longer path. This option is available at the PG2 and the BL2 beamline.
  • Optical/ IR – XUV: An alternative and much more flexible approach is to use an ultra-short pulse from an optical laser as the pump source. With an optical laser, it is much easier to change the wavelength, the polarization, and the angle of incidence, or to expand the pump delay from the femtosecond range up to several nanoseconds. In addition many processes, especially in biochemistry, are rather initiated by optical than XUV light. more details
  • A THz beamline, delivers naturally synchronized THz and IR pulses for pump probe experiments to BL3. more details