Beamline setup
Optical probe:
As an alternative to the FEL probing, the TG can be probed by an ultrafast optical pulse at wavelength λlaser=785, 393 or 261 nm (see sketch); the installation of OPA and/or NOPA devices for probe pulses tunable in the UV-visible range, as well as a white-light supercontinuum source (450-720 nm) can be provided upon user request. The optical pulse can be a normal incidence (θlaser = 0°), i.e. at the bisector of the crossed FEL beams (opt. 1), or can be tuned in the ~40°-70° range (opt. 2, NOTE: in this case 2θ-values of 79° and 105.4° are not available), with variable angles possible upon request. A breadboard with a quite large space (~0.5 m2) is installed near the end-station to host optical setups requested by users. The optically probed transient grating diffracted signal is detected by an in-vacuum CCD (link detectors). A Faraday rotation setup is aditionally available for the optical probe, for detecting the transient optical transmission at normal incidence.
The optical laser can also be used to add a pump pulse in a EUV TG experiment, if needed, or in conventional pump-probe experiments, either as a pump or a probe.
Important note
Using the optical laser as a probe for the EUV TG, the diffraction conditions are not fulfilled for λexc < 45 nm, even exploiting the smallest value of 2θ (18.4°) and the larger angle / shorter wavelength (θlaser ~ 70° / λlaser ~ 260 nm) of the probing laser. This limits LTG to above ~ 150 nm (kTG < 0.04 nm-1). This limitation is relaxed using the mini-TIMER setup at DiProI, which enables a much larger range in λexc (i.e. down to ~ 7 nm), while keeping LTG ~ 190 nm.
