13  EP 3 800 002 A1 14  be configured to produce a point focus. [0089] Also, it should be observed that the system is optionally configured to focus the laser beam onto a tar- get area but that is not required. List of reference signs 2. Beam delivery system 4. Shield 6. Beam passage 8. Laser beam 10. Optics assembly 12. Means for providing a fluid flow through the at least one beam passage 14. First space 16. Second space 18. Fluid connection fromthe first spaceto the sec- ond space 20. Object to be treated 22. Laser 24. Constriction in a fluid flow path through beam passage 26. Convergent-divergent nozzle 28. First optical unit 30. Second optical unit 32. Vent 34. Running surface 35 Cover 36. Rail 38. Railway track 40. Train 42. Head section of the rail 44. Transport system 46. Air inlet 48. Housing 50. Protective gas-tight transparent shield A. Treatment area B. Main beam direction of the laser beam BW1. 1/e$^{2}$ beam width BW2. 99.99% intensity beam width D1. First spatial direction D2. Second spatial direction F. Fluid flow L. Length of the at least one beam passage M. Direction in which, during operation, an object to be treated moves with respect to the system P1. First focal plane P2. Second focal plane S1. Distance between the first optical unit and a treatment area S2. Distance between the second optical unit and the respective beam passage W. Width of the at least one beam passage [0090] - a shield (4) which includes at least one beam passage (6)fortransmission ofatleastone laser beam (8); - an optics assembly (10) configured to at least partly focus the at least one laser beam (8) on the at least one beam passage (6); and -means(12)forproviding a fluid flow (F)through the at least one beam passage (6), - the system (2) is configured to emit gas, e.g. a jetofgas,preferably towards a treatmentarea (A); and/or - during operation, a fluid flow of fluid flowing through the beampassage (6)is atleastpartial- ly, and preferably controllably, directed towards a by-product target area so that beam delivery by-products are at least partially urged towards the by-product target area by the fluid flow, wherein preferably, a direction from the beam passage to the by-product target area substan- tially corresponds to a movement direction (M) of an object to be treated with respect to the system (2), in case of such a movement. wherein the system is preferably configured for per- forming laser ablation using the at least one laser beam. 2. System according to claim 1, wherein the optics as- sembly (10) is further configured to at least partly focus the at least one laser beam (8) on a second focal plane (P2) which extends at a distance from the first focal plane (P1) and which is in particular spaced away from the at least one beam passage (6),wherein the second focalplane (P2)ispreferably at an opposite side of the first focal plane (P1) from theopticsassembly(10).whereintheoptics assem- bly (10) is configured to at least partly focus the at least one laser beam (8) on a first focal plane (P1) which hasan intersection withthe atleastonebeam passage (6), 3. System according to any of the preceding claims, including afirstinnerspace (14)and a separate sec- ond inner space (16), wherein the optics assembly is located in the first inner space (14), wherein the beam passage (6) bounds the second inner space (16). 4. System according to any of the preceding claims, wherein: 1. Beam delivery system (2), comprising: Claims 5. System according to any of the preceding claims, wherein: 8