3  EP 3 800 002 A1 4  focal plane and which is in particular spaced away from the atleastone beampassage.Theconfiguration ispref- erably such that the second focal plane extends at an opposite side of the first focal plane, viewed from the respective optics assembly (and viewed from the shield aperture). The two spaced-apart focal planes preferably extendinparallelwitheachother,butthatisnotrequired. [0012] Thus, an asymmetric beam focus is achieved, using two mutually separate focal planes, providing sig- nificantadvantages overpriorartbeamdeliverysystems. Such combined focusing of the laser beam on two focal planes, which extend at a distance from each other, en- ables that the laser beam can travel through a relatively narrow respective beampassage,while atthe same time enabling that the laser beam can be sufficiently focused to provide a laser treatment, e.g. laser ablation, in an area, e.g. an ablation target area, which is spaced away from said beam passage (i.e. at the second focal plane). For example, the laser beam can be at least partly fo- cused on a treatment target area. [0013] It also follows that the beam passage can be spaced away from the treatment area,which can advan- tageously reduce the amount of by-products reaching the beam passage, as well as a speed at which such by- products reach said beam passage, taking into account speed loss due to e.g. friction and/or gravity. [0014] In an embodiment, the system includes a first innerspaceand a separate second innerspace,wherein the optics assembly is located in the first inner space, wherein the beam passage bounds the second inner space. [0015] The first inner space may be kept substantially free from by-products which may be present in and/or produced in the second space, so that for example an optical element may be arranged in contact with the first space,oratleastbeing located within the system,to keep the optical element substantially free from said by-prod- ucts. [0016] The separation can be significantly enhanced in case a fluid flow is induced in a direction from the first space to the second space (as will be explained below, e.g. by providing an overpressure in the first space with respect to a pressure in the second space). [0017] In an embodiment,during operation,a fluid flow of fluid flowing via the beam passage is at least partially, and preferably controllably, directed towards a by-prod- uct target area so that beam delivery by-products are at least partially urged towards the by-product target area by the fluid flow. [0018] Preferably, a direction from the beam passage to the by-product target area substantially corresponds to a movement direction of an object to be treated with respect to the system, in case of such a movement. more effectively by such a fluid. More generally, by thus directing the fluid flowtowards the by-producttargetarea, by-products can advantageously be urged away fromun- wanted areas outside said target area. A controllable di- rection enables easy and effective adaptation to varying situations andcircumstances,e.g.varying relative move- ment between object to be treated and system. [0020] In an embodiment,a means forproviding a fluid flow through the at least one beam passage are config- ured to provide a fluid pressure gradient between oppo- site sides of the shield (i.e. an inner side and an outer side), in particular a fluid pressure gradient along the at least one beam passage. [0021] Such a fluid pressure gradient may effect an advantageous fluid flow through the at least one beam passage, in particular in a direction from a higher pres- sure area to a lower pressure area. For example, the gradient may be realized by increasing a pressure on one side oftheshield,forexample inan afore-mentioned first (internal) space. Alternatively, the gradient may be realized by decreasing a pressurein an afore-mentioned second (internal)space (with respect to an external,am- bient pressure and/or with respect to a pressure in the first space). [0022] In an embodiment, the means for providing a fluid flow through the at least one beam passage are configured such that the respective fluid flow is substan- tially directed in a main beam direction ofthe laserbeam (i.e.in parallelwith a respectiveopticalaxis),forexample ata fluid flow velocityofatleast100m/s,morepreferably at least 200 m/s, for example about 250 m/s. [0023] Ithasbeen found thatsucha fluid flow cansub- stantiallylimitsaid by-productsfromtravelingthrough the beam passage, in particular substantially preventing such by-products from reaching the optics assembly. [0024] In an embodiment, the system further compris- es at least one laser for generating the at least one laser beam(usuallya collimatedlaserbeam),tobe transmitted via the beam passage by the optics assembly, wherein the at least one laser preferably includes at least one pulsed laser, for example having a laser wavelength of about 1064 nm. [0025] Such a laserisparticularlysuited forlasertreat- ment,in particularforlaserablation treatmentand/oroth- er high-power laser treatment. [0026] In an embodiment, the at least one beam pas- sage is elongated, wherein a length of the at least one beam passage is e.g. at least three times, preferably at leastfourtimes,morepreferably atleastfive times,larger than a width of said passage. For example, the beam passage can be a (narrow) slit. 3 [0019] In case of such a relative movement, by-prod- ucts produced due to the laser treatment process may have at least an initial velocity which at least partly cor- responds to the relative movement. By directing the fluid flow as described, by-products may thus be targeted [0027] The elongated beam passage can enable a substantially line focused laser beam to travel through the passage, in particular when the beam’s line focus is located in (coincides with) the beam passage. At the same time,a relativelysmallbeampassage can be used (i.e. providing only a relatively small open area) so that most incoming by-products willreach a surrounding part