Laser device for material processing, comprising - a source of a pulsed laser beam , - means for coupling out a portion of the radiation of the laser beam , - a detector system for the photodetection of two partial beams (16', 16") generated from the laser beam by radiation outcoupling and provision of corresponding first and second detection signals, wherein the detector system comprises a first detector element arranged in a propagation path of the first partial beam and a second detector element arranged in a propagation path of the second partial beam (16"), wherein the first detector element is operable according to the principle of single-photon absorption and the second detector element is operable according to the principle of two-photon absorption, and an evaluation unit linked to the detector system for evaluation of the first and second detection signals, characterized in that the evaluation unit is configured to calculate a quotient S Zpd /S Epf of the first and second detection signals of the first and second detector elements, wherein S Zpd describes a temporally averaged value of the second detection signal of the second detector element , and S Epf describes a temporally averaged value of the first detection signal of the first detector element ; and in response to a variation in the quotient S Zpd /S Epf , and assuming a constant pulse repetition rate f rep and a constant average power P ave , trace back to a variation in a spot size of the laser beam on a detection surface of the second detector element and/or in a pulse duration based on the following mathematical relationship: S Zpd / S Epd = c ∗ P ave / A Spot ∗ τ Puls ∗ f rep , wherein P ave describes an average radiation power of the laser beam , A Spot describes the spot size of the second partial beam (16") on the detection surface of the second detection element , τ Puls describes the pulse duration, f rep describes a pulse repetition rate and c describes a proportionality constant. - a source of a pulsed laser beam , - means for coupling out a portion of the radiation of the laser beam , - a detector system for the photodetection of two partial beams (16', 16") generated from the laser beam by radiation outcoupling and provision of corresponding first and second detection signals, wherein the detector system comprises a first detector element arranged in a propagation path of the first partial beam and a second detector element arranged in a propagation path of the second partial beam (16"), wherein the first detector element is operable according to the principle of single-photon absorption and the second detector element is operable according to the principle of two-photon absorption, and an evaluation unit linked to the detector system for evaluation of the first and second detection signals, characterized in that the evaluation unit is configured to calculate a quotient S Zpd /S Epf of the first and second detection signals of the first and second detector elements, wherein S Zpd describes a temporally averaged value of the second detection signal of the second detector element , and S Epf describes a temporally averaged value of the first detection signal of the first detector element ; and in response to a variation in the quotient S Zpd /S Epf , and assuming a constant pulse repetition rate f rep and a constant average power P ave , trace back to a variation in a spot size of the laser beam on a detection surface of the second detector element and/or in a pulse duration based on the following mathematical relationship: S Zpd / S Epd = c ∗ P ave / A Spot ∗ τ Puls ∗ f rep , wherein P ave describes an average radiation power of the laser beam , A Spot describes the spot size of the second partial beam (16") on the detection surface of the second detection element , τ Puls describes the pulse duration, f rep describes a pulse repetition rate and c describes a proportionality constant. <EOS>