An optical arrangement for processing a workpiece, comprising: a fiber laser arrangement for emitting laser radiation, a fiber arrangement directly fiber-optically coupled to the fiber laser arrangement, which fiber arrangement has a transport fiber having a fiber core and having at least one fiber cladding (9b, 9c, 9d) surrounding the fiber core, in order to guide the laser radiation from the fiber laser arrangement in the direction of the workpiece to be processed, at least one coupling device (17, 17a-c) for coupling a portion of the laser radiation guided in the fiber arrangement into at least one fiber cladding (9b, 9c, 9d) of the transport fiber, characterized in that the fiber laser arrangement has a resonator having an active fiber, said resonator being formed between a first fiber Bragg grating and a second fiber Bragg grating, wherein a spectral bandwidth (Δλ FBG1) of the reflectivity of the first fiber Bragg grating has a magnitude at least 1.5 times that of a spectral bandwidth (Δλ FBG2) of the reflectivity of the second fiber Bragg grating, in that the optical arrangement comprises an actuator for acting on the second fiber Bragg grating for spectrally shifting the bandwidth (Δλ FBG2) of the reflectivity of the second fiber Bragg grating relative to the spectral bandwidth (Δλ FBG1) of the reflectivity of the first fiber Bragg grating, wherein the actuator is configured to generate a tensile stress and/or a compressive stress on the second fiber Bragg grating, in that the coupling device (17, 17a-c) has a spectral bandwidth (Δλ C; Δλ C1, Δλ C2, Δλ C3) of at least the same magnitude as the spectral bandwidth (Δλ L) of the laser radiation emitted by the fiber laser arrangement, and in that the fiber laser arrangement is configured, for the purpose of changing the beam profile (19a, b) of the laser radiation guided in the direction of the workpiece to be processed, to shift the spectral bandwidth (Δλ L) of the laser radiation relative to the spectral bandwidth (Δλ C; Δλ C1, Δλ C2, Δλ C3) of the coupling device (17, 17a-c) in that the bandwidth (Δλ FBG2) of the second fiber Bragg grating is shifted relative to the bandwidth (Δλ FBG1) of the first fiber Bragg grating such that the laser wavelength (λ L) emitted by the fiber laser resonator is tuned within the spectral bandwidth (Δλ FBG1) of the first fiber Bragg grating. a fiber laser arrangement for emitting laser radiation, a fiber arrangement directly fiber-optically coupled to the fiber laser arrangement, which fiber arrangement has a transport fiber having a fiber core and having at least one fiber cladding (9b, 9c, 9d) surrounding the fiber core, in order to guide the laser radiation from the fiber laser arrangement in the direction of the workpiece to be processed, at least one coupling device (17, 17a-c) for coupling a portion of the laser radiation guided in the fiber arrangement into at least one fiber cladding (9b, 9c, 9d) of the transport fiber, characterized in that the fiber laser arrangement has a resonator having an active fiber, said resonator being formed between a first fiber Bragg grating and a second fiber Bragg grating, wherein a spectral bandwidth (Δλ FBG1) of the reflectivity of the first fiber Bragg grating has a magnitude at least 1.5 times that of a spectral bandwidth (Δλ FBG2) of the reflectivity of the second fiber Bragg grating, in that the optical arrangement comprises an actuator for acting on the second fiber Bragg grating for spectrally shifting the bandwidth (Δλ FBG2) of the reflectivity of the second fiber Bragg grating relative to the spectral bandwidth (Δλ FBG1) of the reflectivity of the first fiber Bragg grating, wherein the actuator is configured to generate a tensile stress and/or a compressive stress on the second fiber Bragg grating, in that the coupling device (17, 17a-c) has a spectral bandwidth (Δλ C; Δλ C1, Δλ C2, Δλ C3) of at least the same magnitude as the spectral bandwidth (Δλ L) of the laser radiation emitted by the fiber laser arrangement, and in that the fiber laser arrangement is configured, for the purpose of changing the beam profile (19a, b) of the laser radiation guided in the direction of the workpiece to be processed, to shift the spectral bandwidth (Δλ L) of the laser radiation relative to the spectral bandwidth (Δλ C; Δλ C1, Δλ C2, Δλ C3) of the coupling device (17, 17a-c) in that the bandwidth (Δλ FBG2) of the second fiber Bragg grating is shifted relative to the bandwidth (Δλ FBG1) of the first fiber Bragg grating such that the laser wavelength (λ L) emitted by the fiber laser resonator is tuned within the spectral bandwidth (Δλ FBG1) of the first fiber Bragg grating.