Abstract: We describe an apparatus for producing a three-dimensional workpiece, the apparatus comprising: a process chamber for receiving a material from which the three-dimensional workpiece is producible using an additive layer manufacturing technique, wherein the process chamber comprises a translucent window; an irradiation device for irradiating, through the translucent window, the material for producing the three-dimensional workpiece; and an enclosure arranged between the translucent window of the process chamber and the irradiation device, wherein at least a part of the enclosure is translucent for an irradiation beam stemming from the irradiation device to travel from the irradiation device through the enclosure to the material for producing the three-dimensional workpiece, wherein the enclosure comprises an inlet and an outlet, and wherein the apparatus is configured to control a flow of a fluid through the enclosure via the inlet and the outlet.