Laser beam for Pump-Probe

OPTICAL LASER PULSES FOR PUMP-PROBE EXPERIMENTS AT FERMI

The currently available pump-probe setups at all FERMI end-stations are based on the use of a portion of the infrared (IR) laser pulse generated by the FERMI Seed Laser Ti:sapphire amplifier, propagated to the Experimental Hall by a high-stability optical beam transport [1,2]. The IR laser beam is then delivered to a dedicated insertion breadboard at each end-station (one at a time), where the final beam manipulation, including polarization state adjustment, harmonic conversion, pulse compression, beam steering and focusing, as well as diagnostics and pointing stabilization, is performed.
Typical values of the main pulse parameters available at present:

Central wavelength, nm	784	392	261
Max Pulse Energy, mJ	0.75	0.1-0.2	0.02-0.05
Pulse Duration, fs (FWHM	80-250	80-120	120-170
Maximum Laser intensity on sample, W/cm2	> 5 1013
Typical jitter with respect to FEL pulse, fs (RMS)	< 10	< 10	< 10
Min Beam Diameter on sample, μm (1/e2)	80	80	80
Stability of beam position on sample, μm (RMS)	< 3	< 3	< 3

It is expected that the upgrade of the FERMI seed laser planned for spring 2016 would allow an increase of the available energy per pulse by a factor of 5, and a decrease of the optical laser pulse duration below 50 fs.

Photo of the Optical Laser manipulation and insertion breadboard of the TIMEX end-station

References

 P.Cinquegrana et al, Optical beam transport to a remote location for low jitter pump-probe experiments with a free electron laser, Physical Review ST-Accelerators and Beams 17 (2014), 040702
M.B.Danailov et al, Towards jitter-free pump-probe measurements at seeded free electron laser facilities , Optics Express 22 (2014), 12869-1287