Apparatus and method for controlling laser processing of a remote material

Apparatus and method for controlling laser piercing of a remote material 10, the apparatus comprising; i) at least one laser 1 for emitting laser radiation 2; ii) a probe laser 3 (which may be a pulsed laser) for emitting a probe signal 4; iii) a beam delivery optics 5 configured to direct the laser radiation and the probe signal onto the material 10; iv) at least one detector 6 for detecting optical radiation 7 that is emitted by the material; v) and an electronic filter 8 for filtering an electronic signal 9 emitted by the detector in response to the detector detecting the optical radiation, the apparatus being characterized in that the probe laser is configured to be modulated by a modulation signal 13; and the electronic filter comprises a phase sensitive detector 14 which is configured to receive the modulation signal and to provide phase sensitive detection of the electronic signal, which can then be used to determine if piercing of the workpiece has taken place.