A cleaning device and method for controlling a laser focus inside a fluid beam (2). The cleaning device (1) includes a fluid assembly (9) arranged to produce the fluid beam (2). The fluid assembly (9) includes an enclosure (10) with a fluid inlet port (11), an outlet orifice (12),and a fluid flow path (13) between the fluid inlet port (11) and the outlet orifice (12). The enclosure (10) includes a laser input port (24). The cleaning device (1) further includes an optical assembly (20) including a laser beam optic arrangement (23) configured to direct a first laser beam (5) through the laser input port (24) and further through the outlet orifice (12) and to focus the first laser beam (5) inside the fluid beam (2), and a sensing arrangement (26) configured to emit a sensing signal (28) through the outlet orifice (12), to receive a reflected signal (29), and to determine length data of the fluid beam (2) based on the reflected signal (29). The optical assembly (20) is further arranged to regulate the laser beam optic arrangement (23) based on the determined length data in order to control the focus of the first laser beam (5).