Beamline description

Seed laser system

The laser system consists of an SAM mode-locked fiber laser oscillator and a regenerative amplifier. The passive mode-locked oscillator (FemtoFiber pro IR, Toptica Photonics) can generate pulses as short as 20 fs, that for this experiment has been set to about 12 nm FWHM at 780 nm, in order to match the bandwidth required by the regenerative amplifier (Legend HE, Coherent Inc.). The repetition rate of the oscillator is 80 MHz in order to allow synchronization.

The amplifier, in which the active medium is a sapphire crystal (Al₂O₃), doped with titanium ions (Ti³⁺), provides pulses of up to 2.5 mJ energy and about 100 fs (FWHM) duration; it has a repetition rate from 1 Hz to 1 kHz. The amplifier is also equipped with second and third harmonic generation stages in BBO crystals, in order to generate radiation at 390 nm (with 0.8 mJ of energy per pulse) and at 260 nm (with 0.3 mJ per pulse): in this way it is possible to perform the seeding at those wavelengths.

The laser system is located in the FEL back-end station, in a temperature-controlled room so as to minimize the thermal drifts of the optical alignment.

Top: SAM mode-locked fiber laser oscillator; Bottom: Ti:Sa regenerative amplifier.