Patent Number: 
Section: abstract

For irradiating a layer (3) a radiation beam (7) is directed and focused to a spot (11) on the layer (3), relative movement of the layer (3) relative to the optical element (59) is caused so that, successively, different portions of the layer (3) are irradiated and an interspace (53) between a surface of the optical element (59) nearest to the layer (3) is maintained. Furthermore, at least a portion of the interspace (53) through which the radiation irradiates the spot (11) on the layer (3) is maintained filled with a liquid (91). By directing a gas flow (71-73) to a surface zone (74) of the layer (3), liquid (91) is reliably prevented from passing that surface zone (74), without causing damage to the layer (3). The liquid (91) is drawn away from the layer (3) in the vicinity of the surface zone (74).