7  EP 3 800 002 A1 8  running surface, of a rail of a railway track, wherein the system is configured to be mounted on a train which can run on the track and to treat the surface while the train is, preferably runs, on the track. [0047] Inanembodiment,the system(e.g.a respective cover means) is configured to at least partly, preferably substantially, enclose a head section of the rail during operation. [0048] A particularly advantageous embodiment pro- vides a train for treating, in particular cleaning, at least one rail, preferably two rails, of a railway track on which the train can run, wherein the train is provided with at least one beam delivery system as described above, preferably at least one respective system for each rail to be treated. In particular, the system can be arranged for treating an upper side of the rail (i.e. a rail surface that directly contacts a train wheel during operation). [0049] Another particularly advantageous embodi - ment provides a transport system for operating a train service, wherein the transport system comprises a rail- way track or a network of railway tracks and at least one train as described above for treating one or more rails of the railway track or the network of railway tracks. [0050] Another aspect of the invention provides beam delivery method, comprising: transmitting at least one laser beam through a respective at least one beam passage of a shield; at least partly focusing the at least one laser beam on the at least one beam passage; and providing a fluid flow through the at least one beam pas- sage. [0051] Such a method can provide the above-men- tioned advantages. [0052] In an embodiment, a method of treating, in par- ticular cleaning, at least one rail, preferably two rails, of a railway track, is provided, the method comprising: pro- viding, on the track, a train as described above; and per- forming a beam delivery method as described above, wherein the atleastone laserbeamispreferably directed at the at least one rail, in particular at a running surface of said rail. [0053] In an embodiment,the method furthercompris- es removing liquid, e.g. rain water, from the at least one rail, in particular from the running surface of said rail, by a flow of gas, e.g. air. [0054] In an embodiment,a method ofoperatingatrain service is provided, wherein the method comprises: pro- viding a transport system as described above; and pre- forming a methodas described above fortreatingatleast one rail of a railway track of the transport system. [0055] The invention will be explained further with ref- erence to exemplary embodiments and drawings. In the drawings: Fig.1a schematicallyshows a cross sectionalofpart ofa beamdeliverysystemaccording toa non-limiting embodiment of the invention; Fig.1b shows a crosssection overline II-IIofFig.1 ; Fig. 1c shows an isometric view of a geometry of a laser beam and an optics system of the beam deliv- ery system according to an embodiment; Fig. 2 shows a diagrammatic representation of the beam delivery of Fig. 1; Fig. 3a shows a partly opened side view of a beam delivery system according to a further embodiment; Fig. 3b shows a partly opened isometric view of the beam delivery system of Fig. 3a; Fig. 3c shows a top view of a beam delivery area provided byan example ofthe beamdeliverysystem as in Fig. 3a; Fig. 4 shows a cross section of a nozzle of a beam passage of a beam delivery system, in detail, ac- cording to an embodiment; Fig. 5a shows a side view of a system for operating a train service according to an embodiment, without showing a cover means; and Fig.5b shows a schematiccross-section ofoperation of the system over line V-V of Fig. 5a, with a cover means. [0056] The drawings are schematic. In the drawings, similar or corresponding elements have been provided with similar or corresponding reference signs. [0057] Figures1a,1b,2depicta beamdeliverysystem 2, configured to carry out a laser treatment (i.e. laser beam cleansing) of a surface of an object 20. The object 20 tobe treatedcan beorbe part of manydifferenttypes of objects, made of many different materials, as will be appreciated by the skilled person. Thus, the invention is not limited to treatment of railway parts or rails (i.e. the embodiment described below). [0058] The system 2 comprises a laser device 22 (see Fig.2) for generating the laser beam 8,to be transmitted through an open laser beam passage 6 of a shield 4 by an optics assembly 10. The laser device 22 can be con- figured in various ways; good results can be achieved e.g.in case the laser device includes atleast one pulsed laser, in particular having a laser wavelength of about 1064 nm. It is preferred that the laser device 22 is con- figured togenerateacollimated (high power)laserbeam. [0059] The shield 4 as such can also be configured in various ways. It is preferred that the shield 4 is durable and sturdy, in particular robust against incoming debris. [0060] In the embodimentofFigures 1,2,a singlelaser beam passage 6isprovided in the shield4 (fortransmis- sion of a single laser beam). Alternatively, as shown in Figures 3, 5, the shield 4 can be provided with a plurality of, e.g. two, beam passages 6, 6’ which are associated with a respective plurality of laser beams 8, 8’. [0061] In orderto provide good beamdelivery,the sys- tem (i.e. its optics assembly) is configured to focus the laserbeam8 onto the surface ofthe object20 tobe treat- ed (see Figs. 1a, 1c). In this example, advantageously, the beam 8 is only partly focused onto that surface, as follows from fig. 1b, i.e. no point focus is applied. [0062] Also, as follows from Figure 1b, 1c, the system (i.e. optics assembly 10) is also configured to focus the 5