A device for adjusting a predetermined focus position Z of a laser beam in a laser processing system comprising: an adjustment unit for adjusting the focus position z, characterised in that the device further comprises a calculation unit arranged to calculate a time-dependent value z t of a focus position z based on a first parameter, a second parameter, and a third parameter; and a control unit arranged to adjust the predetermined focus position Z of the laser beam by means of the adjustment unit based on the time-dependent value z t of the focus position z, wherein the first parameter indicates a laser power dependent focus shift A, wherein the second parameter indicates a time constant τ of a focus position change due to a temperature-induced refractive power change of at least one optical element of a laser beam optics by the factor of 1/e, and wherein the third parameter indicates a current laser power P at a time t, wherein the calculation unit is further arranged to calculate the time-dependent value z t of the focus position z based on a further parameter indicating a magnification m of the laser beam optics, wherein the calculation unit is arranged to calculate the time-dependent value z t of the focus position z using the following equation: z t ΔP t = A ⋅ m 2 ⋅ ΔP ⋅ 1 − e − t / τ wherein ΔP=P-P 0, and wherein P 0 indicates a reference laser power, and wherein a time t=0 is defined as the time at which a change in the laser power ΔP≠0 occurs, or wherein the calculation unit is arranged to compute the time-dependent value z t of the focus position z using the following equation: z t ΔP t = ∑ i = 1 N A i ⋅ m 2 ⋅ ΔP ⋅ 1 − e − t / τ i wherein ΔP=P-P 0, and wherein P 0 indicates a reference laser power, and wherein a time t=0 is defined as the time at which a change in the laser power ΔP≠0 occurs, and wherein N is a natural number, or wherein the calculation unit is arranged to calculate the time-dependent value z t of the focus position z using the following equation: z t ΔP t = ∑ i = 1 N A i ⋅ m 2 ⋅ ΔP ⋅ 1 − e − t / τ i + ∑ j = 1 M B j ⋅ m 2 ⋅ t j wherein ΔP=P-P 0, and wherein P 0 indicates a reference laser power, and wherein a time t=0 is defined as the time at which a change in the laser power ΔP≠0 occurs, and wherein N is a natural number, and wherein M is a natural number, and wherein B is a coefficient of the power j. an adjustment unit for adjusting the focus position z, characterised in that the device further comprises a calculation unit arranged to calculate a time-dependent value z t of a focus position z based on a first parameter, a second parameter, and a third parameter; and a control unit arranged to adjust the predetermined focus position Z of the laser beam by means of the adjustment unit based on the time-dependent value z t of the focus position z, wherein the first parameter indicates a laser power dependent focus shift A, wherein the second parameter indicates a time constant τ of a focus position change due to a temperature-induced refractive power change of at least one optical element of a laser beam optics by the factor of 1/e, and wherein the third parameter indicates a current laser power P at a time t, wherein the calculation unit is further arranged to calculate the time-dependent value z t of the focus position z based on a further parameter indicating a magnification m of the laser beam optics, wherein the calculation unit is arranged to calculate the time-dependent value z t of the focus position z using the following equation: z t ΔP t = A ⋅ m 2 ⋅ ΔP ⋅ 1 − e − t / τ wherein ΔP=P-P 0, and wherein P 0 indicates a reference laser power, and wherein a time t=0 is defined as the time at which a change in the laser power ΔP≠0 occurs, or wherein the calculation unit is arranged to compute the time-dependent value z t of the focus position z using the following equation: z t ΔP t = ∑ i = 1 N A i ⋅ m 2 ⋅ ΔP ⋅ 1 − e − t / τ i wherein ΔP=P-P 0, and wherein P 0 indicates a reference laser power, and wherein a time t=0 is defined as the time at which a change in the laser power ΔP≠0 occurs, and wherein N is a natural number, or wherein the calculation unit is arranged to calculate the time-dependent value z t of the focus position z using the following equation: z t ΔP t = ∑ i = 1 N A i ⋅ m 2 ⋅ ΔP ⋅ 1 − e − t / τ i + ∑ j = 1 M B j ⋅ m 2 ⋅ t j wherein ΔP=P-P 0, and wherein P 0 indicates a reference laser power, and wherein a time t=0 is defined as the time at which a change in the laser power ΔP≠0 occurs, and wherein N is a natural number, and wherein M is a natural number, and wherein B is a coefficient of the power j.