Laser system and method for the spectral broadening of pulsed laser radiation

A method for the spectral broadening of pulsed laser radiation, the method comprising:

• generating pulsed laser radiation comprising laser pulses having pulse energies in a range of 1 mJ to 100 J and pulse durations in a range of 10 fs to 5 ps,
• changing a linear polarization state into a circular polarization state of the pulsed laser radiation for passing through a multipass cell, wherein the multipass cell comprises at least two mirrors and is filled with a filling gas having an optical nonlinearity, and wherein a plurality of intermediate focus zones is formed in the multipass cell,
• input coupling the pulsed laser radiation into the multipass cell, wherein the pulsed laser radiation passes through the plurality of intermediate focus zones and interacts nonlinearly with the filling gas in the intermediate focus zones, thereby causing a spectral broadening of the pulsed laser radiation in the intermediate focus zones,
• setting the pressure of the filling gas in a pressure range so that there is an ionization behavior of the filling gas in a form of multiphoton ionization,
• setting focus diameters in the intermediate focus zones so that a peak intensity of the pulsed laser radiation passing through the multipass cell is below an ionization threshold value of the filling gas, wherein the ionization threshold value of the filling gas is increased for circular polarized radiation as compared to linear polarized radiation,
• output coupling the spectrally broadened pulsed laser radiation out of the multipass cell, and
• changing the circular polarization state of the spectrally broadened pulsed laser radiation into the linear polarization state.