A fluid jet apparatus for receiving a ribbon of parallel continuous filaments, then heating and spreading the filaments for deposit on a moving surface as a nonwoven web includes an adjustable diffuser connected to the outlet end of the jet. The diffuser comprises a pair of spaced plates, adjustable with respect to each other, mounted to the outlet end of the jet. The plates are arranged to form aspiration slots at one end between the jet and the plates. The slots open into a central converging passage formed by the plates for confining and diverting gas out the open sides of the diffuser. The particular structural arrangement of the plates with respect to the jet permits development of static pressure in the diffuser which in turn causes a large percentage of jet fluid to exit from the open edges of the diffuser, generally parallel to the moving laydown surface, while less fluid accompanies the filaments to the laydown surface to reduce web disturbance.