Abstract: The present invention provides an apparatus 100, 200, 300, 900 and a method 400 for machining a workpiece 101 with a laser beam 102. In particular, the apparatus 100, 200, 300 comprises a nozzle 103 for generating a pressurized fluid jet 104, and at least one optical element 105 configured to couple the laser beam 102 into the fluid jet 104. The apparatus 100, 200, 300 also includes a hermetic enclosure 106 surrounding the nozzle 103 and the at least one optical element 105. The hermetic enclosure 106 includes an upper part 107 provided with an interface unit 108, and a lower part 109 removably attached to the upper part 107 by means of the interface unit 108. The lower part 109 comprises an exit aperture 110 for outputting the fluid jet 104 towards the workpiece 101, wherein the exit aperture 110 and the fluid jet 104 are coaxially aligned.