A method of laser cutting a workpiece, wherein in particular a device (10; 100, 200; 300) for laser cutting with a cutting head is used; comprising the following steps: irradiating a process zone of the workpiece with a processing laser beam, cutting the workpiece in a cutting direction and producing a kerf; irradiating the process zone with a coherent illumination light beam, in particular with an illumination laser beam; and detecting at least a portion of the illumination light beam, which is reflected from the process zone; - wherein the illumination light beam is split into a first light beam and a second light beam; - wherein the first light beam is directed onto the process zone; - wherein the second light beam is directed onto a reference mirror; characterised in that - a radiation intensity of a superposition of at least a portion of the first light beam reflected from the process zone and at least a portion of the second light beam reflected from the reference mirror is acquired, and - a plurality of distances travelled by the reflected first light beam from the process zone is determined based on the acquired radiation intensity; wherein the plurality of distances travelled by the reflected first light beam from the process zone is determined by minimising phase shifts between the first light beam reflected from the process zone and the second light beam reflected from the reference mirror; and wherein depth information about the process zone is obtained using the determined plurality of distances travelled by the reflected first light beam from the process zone. wherein in particular a device (10; 100, 200; 300) for laser cutting with a cutting head is used; comprising the following steps: irradiating a process zone of the workpiece with a processing laser beam, cutting the workpiece in a cutting direction and producing a kerf; irradiating the process zone with a coherent illumination light beam, in particular with an illumination laser beam; and detecting at least a portion of the illumination light beam, which is reflected from the process zone; - wherein the illumination light beam is split into a first light beam and a second light beam; - wherein the first light beam is directed onto the process zone; - wherein the second light beam is directed onto a reference mirror; characterised in that - a radiation intensity of a superposition of at least a portion of the first light beam reflected from the process zone and at least a portion of the second light beam reflected from the reference mirror is acquired, and - a plurality of distances travelled by the reflected first light beam from the process zone is determined based on the acquired radiation intensity; wherein the plurality of distances travelled by the reflected first light beam from the process zone is determined by minimising phase shifts between the first light beam reflected from the process zone and the second light beam reflected from the reference mirror; and wherein depth information about the process zone is obtained using the determined plurality of distances travelled by the reflected first light beam from the process zone. irradiating a process zone of the workpiece with a processing laser beam, cutting the workpiece in a cutting direction and producing a kerf; irradiating the process zone with a coherent illumination light beam, in particular with an illumination laser beam; and detecting at least a portion of the illumination light beam, which is reflected from the process zone; - wherein the illumination light beam is split into a first light beam and a second light beam; - wherein the first light beam is directed onto the process zone; - wherein the second light beam is directed onto a reference mirror; - wherein the illumination light beam is split into a first light beam and a second light beam; - wherein the first light beam is directed onto the process zone; - wherein the second light beam is directed onto a reference mirror; characterised in that - a radiation intensity of a superposition of at least a portion of the first light beam reflected from the process zone and at least a portion of the second light beam reflected from the reference mirror is acquired, and - a plurality of distances travelled by the reflected first light beam from the process zone is determined based on the acquired radiation intensity; - a radiation intensity of a superposition of at least a portion of the first light beam reflected from the process zone and at least a portion of the second light beam reflected from the reference mirror is acquired, and - a plurality of distances travelled by the reflected first light beam from the process zone is determined based on the acquired radiation intensity; wherein the plurality of distances travelled by the reflected first light beam from the process zone is determined by minimising phase shifts between the first light beam reflected from the process zone and the second light beam reflected from the reference mirror; and wherein depth information about the process zone is obtained using the determined plurality of distances travelled by the reflected first light beam from the process zone.