9  EP 3 800 002 A1 10  laser beam 8 on the elongated beam passage 6 (i.e. a respective focus is located in the passage 6); again, no point focus is applied (as follows from the additional fo- cusing onto the object 20 to be treated). [0063] In particular(see Figures 1a,1b), the opticsas- sembly 10 is configured to partly focus the laser beam 8 on a first focal plane P1 which has an intersection with the atleastone beampassage 6.Inthe presentexample, the first focal plane P1 extends in parallel with and coin- cides with the shield 4. [0064] The optics assembly 10 is further configured to partly focus the laser beam 8 on a second focal plane P2, located externally of the system, the second focal plane P2 extending ata distancefromthe firstfocalplane P1 and which is in particular spaced away from the at least one beam passage 6. In the present example, the second focal plane P2 extends in parallel with the first focalplane P1.As followsfrom the drawings,the second focal plane P2 is located at an opposite/outer side  of shield 4, to coincide with the surface of the object 20 to be treated during operation. In a preferred embodiment, the system is configured to maintain focus, e.g. utilizing autofocus and respective autofocus components, as will be appreciated bythe skilled person,in orderto maintain focus onto the object20 in case of variation ofa distance between thatobjectand the beamdeliverysystem2 dur- ing operation. [0065] The optics assembly can be configured in var- ious ways to achieve the double focusing of the laser beam. As is shown in the drawings, the optics assembly 10 can comprise e.g. at least a first optical unit 28, e.g. a lens or a mirror or a set of lenses and/or mirrors, to provide a partial focus onto the first focal plane P1. In this example the first optical unit 28 is configured for fo- cusing the laser beam 8 with respect to a first spatial direction D1 (which extends in parallel with the first focal plane P1). A main focal length of the first optical unit substantially corresponds to a distance S1 between the first optical unit 28 and the respective beam passage 6 (see Figure 1b). [0066] Further there is provided a second optical unit 30,e.g.a lensora mirrorora setoflenses and/ormirrors, forfocusing the laserbeam8 partlyonto the second focal plane P2, with respect to a second spatial direction D2 (thatisinparallelwith the second focalplane P2).A main focal length of the second optical unit substantially cor- responds to a distance S2 between the second optical unit 30 and a respective treatment area A that is located in the second focal plane P2. [0067] It is preferred that the first spatial direction D1 is substantially transverse to the secondspatialdirection D2. It is also advantageous in case each, of the first and second optical units 28, 30 is configured to produce a respective line focus. To that aim, for example, the re- spective optical unit 28, 30 can including a substantially cylindrical lens (as in the drawings) or cylindrical mirror, i.e. cylindrical optics, as will be appreciated by the skilled person. [0068] In the presentexamples,each laser beam pas- sage 6,6’isan elongated slit/aperture.A lengthL ofeach laserbeam passage6 (seefigure 3c)can e.g. be atleast three times, preferably at least four times, more prefer- ably at least five times, larger than a width W of said passage 6. [0069] It follows that in particular, the present optics assembly 10 is configured to at least partly, preferably substantially, conform the laser beam 8 (i.e. its shape, viewed incross-section)tothe respectivebeampassage 6. In other words, the laser beam passage 6, in particular a respective relatively narrow width W thereof, can e.g. be dimensioned to conform to a respective beam width of the incoming respective laser beam 8, in particular a beam width in the range from the 1/e2 beam width BW1 to the 99.99% intensity beam width BW2. [0070] Advantageously, as follows from the drawings, the system (e.g. a housing 48 or wall structure thereof) includes several inner spaces 14, 16 or chambers, through which the beam 8 passes from the laser device 22 to the respective beam passage in the shield 4. A first inner space 14 is provided, bounded by the external shield 4, and a second inner space 16 that includes the optics 28, 30, wherein the first and second inner space 14, 16 are separated, e.g. by an intermediate wall 15. [0071] The beampassage 6 providesa respective fluid connection 18 from the first space 14 into the external space 19 (i.e. externally of the shield 4 c.q. system 2). [0072] A protective transparent gas-tight internal shield 50 is located between the first and second inner space14,16,the transparentgas-tightshield(e.g.made of glass, optical glass) allowing passage of the laser beam8 fromthe second innerspace16 into the firstinner space 14. [0073] The presentsystem 2 isconfigured to emitgas, e.g. a jet of gas, preferably towards the treatment area A, in particular via the laser beam aperture 6, to prevent or reduce chances of entry of debris into the system. [0074] The present example is provided with means 12 for providing a fluid flow F through the outer laser beampassage 6,inthiscase fromthe firstinternalspace 14 to the environment 19 [0075] In particular, the means 12 for providing a fluid flow F through the beam passage 6 are configured to providea fluid pressure gradientbetween opposite sides ofthe shield 4,in particulara fluid pressuregradientalong the beam passage 6. To this aim, such means 12 can include e.g. a pump of pumping system 12, a fan, venti- lator(incase the fluid Fisgas orair)orthe-like,configured to provide a positive, higher pressure in the first inner space 14 with respect to ambient (atmospheric) pres- sure. Alternatively, such means can be configured for sucking ambient air into the system, i.e. for providing a lower internal pressure in the first inner space 14 with respect to ambient pressure. [0076] In a preferred embodiment, the means 12 for providing a fluid flow F through the laser beam passage 6 are configured such that the provided fluid flow F is 6