Device and method for stretching or compressing laser pulses

A shaping method for shaping laser pulses with a shaper unit with negative dispersion, including a first dispersive element, a second dispersive element and a mirror, wherein a beam path of the shaper unit includes a forward beam path from the first dispersive element via the second dispersive element to the mirror and a return beam path from the mirror via the second dispersive element to the first dispersive element, comprising the steps of

• in-coupling the laser pulses along the forward beam path and spatially separating spectral components of the laser pulses using the first dispersive element,
• parallelizing the spatially separated spectral components using the second dispersive element, wherein the spatially separated spectral components are deflected into a Fourier plane of the first and second dispersive elements,
• reflecting the laser pulses at the mirror along the return beam path back to the second dispersive element,
• spatially recombining the spectral components of the laser pulses at the second dispersive element, and
• parallelizing the recombined spectral components and out-coupling the laser pulses using the first dispersive element, wherein
• the laser pulses are subjected to a light modulation in the Fourier plane of the first and second dispersive elements,
• said shaping method further including the step of
• focusing the spatially separated spectral components of the laser pulses to the Fourier plane of the first and second dispersive elements with a focusing device being arranged at an input side of the forward beam path before the first dispersive element.