The present invention discloses an improved laser apparatus (10), inscribed in a parallelepiped rectangle (R) defined by a longitudinal axis, X, a vertical axis, Y defining a plane P and a lateral axis, Z, comprising a mounting means (11) to mount the laser apparatus (10) on a window (2), preferably a multi-glazed window, mounted in situ. The laser apparatus (10) also comprises a laser device generating a laser beam (13) to treat a surface (211) of the window (2), an orientation means able to orientate the laser beam (13) defining a maximum decoatable surface on the coated surface (211) and a housing comprising an aperture to let the laser beam (13) going out of the housing. The laser apparatus (10) comprises a skirt (19) at least partially surrounding the aperture and in that the skirt (19) is opaque to the laser beam (13). The invention also relates to the associated method and use.