Photon Beam Parameters

Optical laser available for pump-probe experiments

The currently available pump-probe setups at all FERMI end-stations are based on the use of the infrared (IR) laser pulse generated by one of the FERMI seed laser Ti:Sapphire amplifiers, propagated to the experimental hall by a high-stability optical beam transport. This IR laser beam, referred to as SLU,  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.
The typical values of the main pulse parameters available are summarized in the following table:

Central wavelength, nm	794(1)	392	261
Max Pulse Energy , mJ	2(2)	0.1-0.5	0.04-0.1
Compressed Pulse Duration ,  fs (FWHM)  (3)	55-65	60-90	100-170
Typical jitter with respect to FEL pulse, fs (RMS)	< 8
Min Beam Diameter on sample,   μm  (1/e2 )	50-80
Stability of beam position on sample, μm (RMS)	< 3
Maximum Laser intensity on sample , W/cm2	1-2 x 1014

 

Tunable pulses in the ranges 740-780 nm and 800-880  nm with an energy per pulse in the range 50-120 µJ can be made available, however need to be requested at the stage of proposal submission.
⁽¹⁾ On request can be adjusted to other values in the range 784-800 nm (and respectively the harmonics). When FEL1 is operated, the SLU wavelength can be remotely tuned in real time in this range.
⁽²⁾ Measured at the beamline optical breadboard.
⁽³⁾ Fundamental (IR) pulses with desired chirp value and sign can be provided. The harmonic pulse duration can be optimized for the needs of the experiment by the choice of nonlinear crystal length combination, within the limits imposed by the required harmonic pulse energy.  
 
As described here, both FEL-1 and FEL-2 allow one to implement pump-probe schemes in which both the pump and the probe are FEL pulses. The performance of these schemes is quite flexible and can be tailored based on user requirements. For more information and specific questions, users are invited to send a message to the address

Options providing an extension of the above parameters towards higher energy and shorter pulses, as well as the addition of new wavelength ranges by an OPA at some of the end stations, are expected to be available in the near future.

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