Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05G—X-RAY TECHNIQUE
  • H05G2/00—Apparatus or processes specially adapted for producing X-rays, not involving X-ray tubes, e.g. involving generation of a plasma
  • H05G2/001—X-ray radiation generated from plasma
  • H05G2/003—X-ray radiation generated from plasma being produced from a liquid or gas
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05G—X-RAY TECHNIQUE
  • H05G2/00—Apparatus or processes specially adapted for producing X-rays, not involving X-ray tubes, e.g. involving generation of a plasma
  • H05G2/001—X-ray radiation generated from plasma
  • H05G2/008—X-ray radiation generated from plasma involving a beam of energy, e.g. laser or electron beam in the process of exciting the plasma

Definitions

• the present invention relates to the generation of light pulses.
• the present inven tion relates to a gas cell for generating high harmonics in a pulsed laser system of high repeti tion rate and high average power, an assembly comprising such a gas cell, as well as a kit and a method to assemble the gas cell assembly.
• EUV extreme ultraviolet
• gas is introduced into the light path from appropriate nozzles with the same frequency as the repetition rate of the excitation source, or the suitable gas is kept at the desired pressure in a light cell arranged within the light path.
• EUV systems need to be operated in vacuum to reduce unwanted absorption, however, the gas used for high harmonic generation flows into the vacuum chamber and decreases the efficien cy of the system in both optical and vacuum technical senses.
• the use of intermittent nozzles is widespread in such systems - as opposed to gas cells, in case of which the gas flows continuously through the light beam transmission openings of the cells.
• the invention is further based, partially, on the recognition that the higher average power achieved by the increasing repetition rate and the unaltered pulse energy poses a completely new problem when using gas cells, namely the overheating of the gas cells.
• the problem of warming of the high-harmonic-generating gas cell did not even arise, as it was so low that it actually did not significantly affect the op eration of the gas cell and its mechanical integrity. Accordingly, for the time being, no solu tions are available to a person skilled in the art for the cooling of a high-harmonic-generating gas cell.
• WO2011139303 A2 discloses a system for generating EUV pulses, wherein an infrared pulsed laser of high repetition rate (above 100 kHz) and high average power (50-500 W) is used as primary source, by means of which, in a first step, sec ond harmonics of the pulses are generated and then the thus obtained pulses are used to gen erate high harmonics in a gas cell, i.e., the EUV pulses to be used are generated.
• an infrared pulsed laser of high repetition rate (above 100 kHz) and high average power (50-500 W) is used as primary source, by means of which, in a first step, sec ond harmonics of the pulses are generated and then the thus obtained pulses are used to gen erate high harmonics in a gas cell, i.e., the EUV pulses to be used are generated.
• a further object of the present invention is to provide a gas cell in which a homogeneous gas space of extensive and optionally variable size (length) can be formed, wherein the pressure and density conditions within said gas space can be varied and adjusted over a wide range.
• a yet further object of the present invention is to provide a gas cell assembly that can be asVISd from easily and economically manufacturable components and allows easy usage of the gas cell according to the invention.
• the object of the gas cell assembly ac cording to the invention is to provide a modular arrangement wherein a series of gas cells (i.e., at least two gas cells) can be easily applied or the individual gas cells can be replaced quickly (either due to wear or changing the generation process parameters) without breaking the vacuum system, i.e., a gas cell assembly which allows an easier operation of the beam lines exploiting the gas cell according to the invention.
• FIG. 1A and IB illustrate a first exemplary embodiment of a gas cell according to the invention in various perspective views
• FIG. 1C is a cross-sectional view of the first exemplary embodiment of a gas cell accord ing to the invention shown in Figures 1 A and IB;
• FIGS. 2A and 2B illustrate an exemplary embodiment of a base element of a gas cell as sembly according to the invention accomplished by using the exemplary embodiment of a gas cell according to the invention shown in Figures 1 A- 1C in different perspective views;
• FIG. 3A is a perspective view of an exemplary embodiment of a closure element used in the gas cell assembly according to the invention.
• FIG. 3B shows an exemplary embodiment of the closure element, shown in Fig. 3 A, used in the gas cell assembly according to the invention in a sectional view parallel to a longitudi nal direction H within the plane of the refrigerant inlet and the refrigerant outlet;
• FIGS. 4A and 4B are a bottom view and a cross-sectional view, respectively, of the exem plary embodiment of the closure element of an exemplary embodiment of a gas cell according to the invention shown in Figures 1 A-1C;
• FIGs 5A and 5B illustrate, in an exploded perspective view, an exemplary embodiment of a gas cell assembly according to the invention accomplished by using an exemplary embodi ment of the gas cell illustrated in Figures 1A-1C, the base element illustrated in Figures 2 A and 2B, and the closure element illustrated in Figures 3 A and 3B;
• FIG. 6A, 6B and 6C illustrate another possible exemplary embodiment of a gas cell (im plemented with a lid having a sealing ring) according to the invention in two different per spective views and in cross-section, respectively;
• FIGS. 6E and 6D show a bottom view and a cross-section, respectively, of an embodiment of the closure element of an exemplary embodiment of the gas cell according to the invention shown in Figures 6A-6C;
• FIGS. 7A and 7B illustrate a possible further exemplary embodiment of a gas cell (with a reducing insert, and a locking tab) according to the invention in an exploded perspective view;
• FIG. 7C is a cross-sectional view of the second exemplary embodiment of a gas cell ac cording to the invention shown in Figures 7A and 7B;
• FIGS. 8A and 8B illustrate a possible further exemplary embodiment of a gas cell (with a motorized reducing insert) according to the invention in an exploded perspective view and in cross-section, respectively;
• FIGS. 9A and 9B illustrate an exemplary embodiment of the base element of a gas cell assembly according to the invention accomplished by using exemplary embodiments of a gas cell according to the invention illustrated in Figures 6A-6C or Figures 7A-7C or Figures 8A- 8B in various perspective views;
• FIG. 10A is a perspective view of another exemplary embodiment of the closure element used in a gas cell assembly according to the invention.
• Figure 10B shows an exemplary embodiment of the closure element used in the gas cell assembly according to the invention shown in Figure 10A in a sectional view parallel to the longitudinal direction H within the plane of the refrigerant inlet and the refrigerant outlet;
• FIGS 11 A-l 1C show the change in temperature over time in the gas cell assembly of the present invention during a prolonged continuous use (for several hours, even after a day) thereof.
• FIGS 1 A and IB illustrate an exemplary embodiment of a gas cell 1 according to the inven tion in two different perspective views.
• the gas cell 1 comprises at least one chamber 10 into which any gas suitable for generating high harmonic pulses, such as helium or neon, can be introduced via a gas inlet 13.
• the gas inlet 13 is preferably formed by a threaded hole to which a suitable gas source can be connected via a vacuum-compatible connector.
• the gas cell 1 is formed by a block of material, wherein the chamber 10 is formed by a cylindrical bore formed in said block of material by means of e.g. cutting or drilling.
• the gas cell 1 is made of a material with good thermal conductivity, which is also preferably workable by machining, for example a metal or a metal alloy, in particular, preferably copper.
• the gas cell 1 can, of course, also be formed of any other solid material with good thermal conductivity, preferably having a thermal conductivity of at least 50 W/(m K), more prefera bly at least 100 W/(m K), even more preferably at least 200 W/(m K), highly preferably at least 300 W/(m K).
• the block of the gas cell 1 can preferably also be made of aluminum or stainless steel. In addition to high machinability, these materials also have out standing resistance to galvanic corrosion, thus, significantly extend the lifetime of the gas cell 1
• the sealing between the gas connection (not shown in Figures 1A and IB; see e.g. Figure 5A) and the gas cell 1 preferably has got a suitably arranged sealing member, and particularly preferably, a surface portion of adequate surface quality assisting said sealing is formed on a surface of the gas cell 1 in contact with the sealing member, i.e. on the outer surface around the gas inlet 13.
• adequate surface quality refers to a degree of surface smoothness suitable for promoting vac uum sealing.
• the adequate surface quality is usually ensured by an additional working step (smoothing / polishing), since the finish of the gas cell achieved, for example by machining, generally does not provide a sufficiently smooth surface.
• the sealing member is preferably made of a vacuum-compatible fluoroelastomer, in particular an FKM rubber according to ASTM international standard D1418 and ISO 1629.
• an opening 12 is formed in each of the two opposite sides of the chamber 10 so that a light pulse directed into the chamber 10 through one of the openings 12 along an optical axis O leaves the chamber 10 and the gas cell 1 through the other opening 12 (along with high harmonics generated by the interaction between light and gas) after having passed the chamber 10. That is, the openings 12 are coaxial and in communication with one another.
• At least one cooling passage 14 is formed in the gas cell 1.
• at least one end of the cooling passage 14 is provided with a sealing groove 15 surrounding the cooling passage 14, which is adapted to receive a sealing ring, and preferably is substantially circular.
• the cooling passage 14 of the gas cell 1 is surrounded on a side opposite to its sealing groove 15 by a sur- face of adequate surface quality in at least a portion, which helps a sealing member arranged between the gas cell 1 and an adjacent element to provide a good seal when said sealing member is pressed to this portion of the gas cell 1.
• the gas cell 1 preferably comprises at least one recess 16 in each of its two opposite outer sides into which an adapter element with a shape complementary to that of the recess 16 can be inserted.
• the gas cell 1 comprises two recesses 16 in the form of a cylindrical bore each, the axis of which is perpendicular to the surface of the gas cell 1.
• the recess 16 can be polygonal or elongated in shape and / or extend axially at an acute angle to the surface - in such a case, a single recess and a single adapter element are sufficient to provide a displacement- and rotation-free connection of two members to be com bined.
• an undesired opening forms in the upper side of the gas cell 1, which should be closed to reduce the amount of gases flowing into the vacuum space. This can be done, for example, with a blind-flanged, cutting-edge sealing cap or by using gluing, soldering or cold-pressing techniques.
• a sealing flange In the embodiment of the gas cell 1 shown in Figures 1 A and IB, a sealing flange
• a suitably shaped cover lid can be clamped onto the sealing flange 17 by means of screws penetrating the cover lid and engaging with the threaded holes 18.
• Figure 1C shows an exemplary embodiment of a gas cell 1 according to the invention shown in Figures 1A and IB in cross-sectional view.
• the light pulse propagating along the optical axis O interacts with the gas arranged within the chamber 10 in the interaction space 11.
• the dimension of the interaction space 11 is substantially equal to the length of the optical axis O within the chamber 10, or it may be slightly larger or smaller depending on the pressure dif ference between the chamber 10 and the environment (vacuum), the size of the openings 12, i.e. how much gas flows out through the openings 12, and how large is the region around the focal point in which the intensity of the laser pulse is enough to generate high harmonics.
• a specific shape of the chamber 10 is essentially irrelevant from the point of view of the opera tion of the gas cell 1; it is the length of the chamber 10 along the optical axis what is essential, as it directly affects the dimension of the interaction space 11.
• the cylindrical shape of the chamber 10 is advantageous from the point of view of the simple production, since it can then be formed by a simple mechanical bore machining.
• each opening 12 is formed as a bore in such a way that said bore has a larger diameter wider bore section further away from the chamber 10 and a smaller diameter narrower bore section near the chamber 10.
• the advantage of this design is that the narrower bore section minimizes the amount of gas flowing out of the chamber 10, while the wider bore section allows the inser tion of reducing inserts to reduce, optionally, further the amount of gas flowing out of the gas cell 1 of a given dimension through the openings 12, if the inner diameter of the inserted re ducing insert is smaller than the diameter of the narrower section of the opening 12.
• the geometric parameters of the two openings 12 located at opposite sides of the chamber 10 may be identical or different. If the diameters of the bores forming the openings 12 vary along the optical axis O, the diameters of the wider bore sections are particularly preferably identi cal for the two openings 12, and hence, identical inserts, such as said reducing inserts, can be inserted into said openings 12. At the same time, a narrower bore section of an outlet side opening 12 may have a larger diameter than the narrower bore section of an opening 12 oppo site to it.
• the gas inlet 13 is in a lateral position, i.e. the gas is fed perpendicular to the longitudinal direction H and parallel to the optical axis O.
• the gas inlet 13 can also be formed at the bottom or top of the gas cell 1 (relative to the orientation shown in Figure 1C), in the latter case, essentially as part of the element closing the chamber 10.
• the design of the gas cell 1 according to the embodiment shown in Figures 1A, IB and 1C is also particularly advantageous as, making use of the gas cell 1, a gas cell assembly which comprises at least one, but preferably several gas cells 1 can be constructed.
• Figures 2A and 2B show a preferred embodiment of a base element 2 for use in the gas cell assembly according to the invention in various perspective views.
• the base element 2 is pref erably provided with recesses 26, preferably bores, for facilitating connection with the gas cell 1, into which suitable adapter elements, preferably dowel pins, can be inserted.
• suitable adapter elements preferably dowel pins
• the base element 2 when the gas cell 1 has two parallel cooling passages 14, the base element 2 is preferably provided with a passage 24 in the form of an elongated notch, into which passage 24, at one end of said passage 24, a refrig erant can enter from one of the cooling passages 14 of the gas cell 1 tightly connected to the base element 2, flow along a longitudinal direction of the passage 24 to the other end of said passage 24 and, from there, enter the other cooling passage 14 of the gas cell 1.
• the base element 2 comprises a groove 25 around the passage 24 for receiving a sealing member.
• the base element 2 is preferably provided with recesses 26 which are arranged in accordance with the respective recesses 16 of the gas cell 1 and have substantially the same dimensions.
• the base element 2 can be assembled with the gas cells 1 by means of the same adapter elements as the gas cells 1 them selves.
• the base element 2 has two recesses 26 formed by bores which are as far apart from each other as the bores forming the recesses 16 of the gas cell 1.
• the base element 2 further comprises openings 27 for receiving clamping elements.
• Said openings 27 may be formed as threaded or threadless through holes or blind holes.
• the base element 2 optionally, also comprises bores perpendicular to these holes, into which fastening elements can be inserted which engage with the respective surface portions of the clamping elements in order to fasten said clamping elements to the base element 2.
• the openings 27 are formed by threaded through holes into which threaded spindles, i.e. the threaded ends of screws, used as the clamping elements, can be screwed in.
• One or more gas cells of the gas cell assembly can preferably be mounted through the base element 2 to a fixed or movable support structure, preferably to an actuating mechanism with at least five degrees of freedom (translation along three axes and rotation about two axes).
• the base element 2 comprises a threaded fixing bore 28 and two recesses 29 which are suitable for receiving corresponding adapter elements.
• the size of the recesses 29 can be the same as that of the recesses 16 of the gas cell 1 or can be different.
• many other fastening techniques known to those skilled in the art can equally be used, preferably in the form of releasable bonds, especially frictional or form-fitting joints.
• FIG 3A is a perspective view of a preferred exemplary embodiment of a closure element 3 for use in the gas cell assembly according to the invention.
• the closure element 3 comprises at least one, preferably two refrigerant passages 34, which is/are arranged in such a way that by assembling the closure element 3 with the gas cell 1, the refrigerant can flow from the clo sure element 3 to the gas cell 1 and / or vice versa.
• the refrigerant passage 34 is in fluid communication with a refrigerant inlet 33a or a refrigerant outlet 33b formed in the closure element 3.
• the closure element 3 comprises two refrigerant passages 34 and a refrigerant inlet 33a in fluid communication with one of the refrigerant pas sages 34 and a refrigerant outlet 33b in fluid communication with the other refrigerant pas sage 34.
• Each refrigerant passage 34 is arranged to be in fluid communication with a cooling passage 14 of the gas cell 1 when the closure element 3 and the gas cell 1 are properly assem bled and clamped together.
• the closure element 3 is preferably designed to have as little weight as possible while performing its fixing and refrigerant flow functions. That is, if the closure element 3 is formed of, e.g., a rectangular block of material by means of mechanical processing (milling / machining), as illustrated in Fig. 3A, it is preferred to re move the corners of the rectangular block; thus, the exemplary embodiment of the closure element 3 concerned is substantially cross-shaped. Of course, a different design is also possi ble. In particular, if the openings 37 (see below) and / or the refrigerant inlet 33a and the re frigerant outlet 33b are arranged differently, the closure element 3 can be, for example, trian gular or Y-shaped.
• the closure element 3 further comprises openings 37 for receiving clamping elements.
• Said openings 37 may be formed as threaded or threadless through holes or blind holes.
• the clo sure element 3, optionally, also comprises bores perpendicular to these holes, into which fas tening elements can be inserted which engage with the respective surface portions of the clamping elements in order to fasten said clamping elements to the closure element 3.
• the openings 37 are formed by threadless through holes into which spindles with threads at least at their ends, used as the clamping elements, can be inserted in such a way that their heads rest on the surface of the closure element 3 and their threaded ends can be screwed into the threaded holes of the base element 2. Due to being applied in a vacuum space, the open ings 26 of the base element 2 and the openings 36 of the closure element 3 are preferably through holes, even if the lengths of the individual clamping elements do not necessarily re quire this.
• the base material of the components used in the gas cell assembly of the present invention is chosen expediently, with a view to avoid galvanic corrosion.
• Figure 4A shows a bottom view of an exemplary embodiment of a cover lid 4 of the gas cell 1 according to the invention.
• the cover lid 4 comprises a groove 45 for re DCving a sealing flange 17 formed on a top plate of the gas cell 1 and holes 48 for receiving fastening elements, such as screws, for connecting the cover lid 4 to the gas cell 1, said holes 48 are preferably threadless holes.
• FIG. 4B shows a cross-section of a possible exemplary embodiment of the cover lid 4 of the gas cell 1 according to the invention.
• a circular protrusion 46 is formed in the groove 45 of the cover lid 4 in such a way that when the cover lid 4 is placed on the gas cell 1, an edge 47 of the protrusion 46 rests on the upper surface of the sealing flange 17.
• the cover lid 4 gets pressed onto the gas cell 1, and thus, the sealing flange 17 and / or the protrusion 46 are elastically and / or plastically deformed in the vicinity of the edge 47.
• the cover lid 4 ensures a gas-tight sealing of the top plate of the chamber 10.
• Figures 5A and 5B are exploded perspective views of an exemplary embodiment of a gas cell assembly according to the present invention.
• the gas cell assembly comprises four gas cells 1 with chambers 10 of, optionally, different dimen- sions, and equipped with separate gas connections 9b, by means of which each gas cell 1 can be supplied with gas of different pressure and / or gas of different material quality.
• the chambers 10 of different dimensions provide different interaction lengths.
• the gas cell assembly may comprise more or less gas cells 1, two or more of which may have chambers of the same size.
• the embodiment shown in Figures 5A and 5B is for illustrative purposes only and is not to be construed as limiting any of the features of the gas cell assembly.
• the gas cell assembly comprises at least one, preferably several gas cells 1, a base element 2, as well as a closure element 3, which are designed in the manner discussed with reference to Figures 1A-1C, 2A-2B, 3A-3B and 4A-4B and arranged in succession along the longitudinal direction H in such a way that the cooling passages 14 of the gas cells 1 form one or more continuous flow paths with the refrigerant passages 34 of the closure element 3, and in the case of using several gas cells 1, with the cooling passages 14 of the adjacent gas cells 1, and, if two cooling passages 14 per gas cells 1 are used, preferably with the passage 24 of the base element 2.
• the gas cell assembly further comprises, if neces sary, a cover lid 4 for each gas cell 1, which can be fastened to the gas cells 1 by one or more fastening elements 8 to close the open top side of the chamber 10 of the gas cell 1.
• the fas tening elements 8 are, optionally, formed by screws which can be screwed into the threaded holes forming the openings 18 of the gas cells 1.
• adapter elements 6 are arranged in the recesses 16 of the gas cells 1, in the recess es 26 of the base element 2 and in the recesses 36 of the closure element 3 to facilitate precise fitting of the gas cell 1 to the base element 2, to the closure element 3 and, optionally, to the further gas cells 1.
• rubber sealing members optionally rubber rings, of suitable size are preferably arranged in the sealing grooves 15 of the gas cells 1 and in the sealing groove 25 of the base element 2 which ensure the tightness of the associated continuous flow path of the cooling passages 14, the passage 24 and the refrigerant passage 34 to the external vacuum space when the one or more gas cells 1, the base element 2 and the closure element 3 are clamped together.
• the recesses 16 of the gas cells 1, the recesses 26 of the base element 2 and the recesses 36 of the closure ele ment 3 are formed by identical bore holes, into which uniform adapter elements 6 are intro- quizd, which are formed as dowel pins in this case.
• clamping of the one or more gas cells 1, the base element 2 and the closure element 3 is performed by the clamp ing elements 7 passing through the openings 37, formed by threadless bore holes, of the clo sure element 3.
• each clamping element 7 is formed by a screw with a thread at one end thereof and a widening head at the other end thereof; the clamping elements 7 can be screwed into the openings 27 formed as threaded bore holes of the base element 2.
• assembling of the gas cell assembly with a support structure or an actuator mechanism, pref erably with an actuator mechanism with at least five degrees of freedom, is facilitated by adapter elements 61 inserted into the recesses 29, formed as holes, of the base element 2, while the gas cell assembly is fastened to said support structure or said actuator mechanism by a retaining bolt 81 which can be screwed into the fixing bore 28 formed in the base ele ment 2.
• the flow of refrigerant preferably water
• a refrigerant source connected to the refrigerant inlet 33a and the refrigerant outlet 33b via refrigerant con nections 9a.
• Each of the refrigerant inlet 33a and the refrigerant outlet 33b is preferably formed as a threaded hole, with which the refrigerant connections 9a are engaged through suitable screw threads.
• sealing members optionally rubber rings, are arranged therebetween.
• closure element 3 and / or the refrigerant connections 9a are provided around the refrigerant passages 34, the refrigerant inlet 33a and the refrigerant outlet 33b, as well as on their surfaces in contact with the sealing members, respectively, with surface portions of adequate surface quality facilitating the forming of seal ing.
• the gas cell assembly is supplied with gas for high harmonic generation by means of gas connections 9b, each of which is connected to the gas inlet 13 of the one or more gas cells 1.
• the gas inlet 13 is preferably formed as a threaded hole, with which the gas connection 9b is engaged through suitable screw threads.
• a sealing member optionally a rubber ring, is arranged between the gas cell 1 and the gas connection 9b.
• the surface of the gas cell 1 in contact with the sealing member around the gas inlet 13 and / or the surface of the gas connection 9b in contact with the sealing member is processed to have adequate surface quality.
• the threads of the threaded elements are not shown in the figures.
• the gas cell assembly can of course be accomplished in a number of other embodiments fall ing within the scope of protection defined; for example, the passage 24 connecting the two cooling passages 14 of the gas cells 1 can be arranged on the closure element 3 instead of the base element 2.
• the refrigerant inlet 33a, the refrigerant outlet 33b and the 34 refrigerant passages connected thereto can be moved to the 2 base elements.
• Another possibil ity is to provide only one cooling passage 14 in the gas cells 1 and to use such a base element 2 and closure element 3 with the thus obtained gas cells 1, wherein one of the refrigerant inlet 33a and the refrigerant outlet 33b with the associated connected refrigerant passage 34 is formed in either the base element 2 or the closure element 3, while the other of the refrigerant inlet 33a and the refrigerant outlet 33b with the associated connected refrigerant passage 34 is formed in the other of the base element 2 and the closure element 3 - here, there is a need to use neither the elongated passage 24 nor the sealing groove 25 surrounding the passage 24 in any of the base element 2 and the closure element 3.
• Figures 6A-6C show, for example, an embodiment of a gas cell 50 for use in the gas cell as sembly of the present invention, which is provided with mounting grooves 51 on its faces perpendicular to the longitudinal direction H to facilitate the assembling of the gas cell as sembly.
• the adjacent gas cells 51 can be easily disengaged.
• the gas cell 50 has one or more degassing holes 52 which, in the assembled state of the gas cell assembly, facilitate the escape of gases trapped in closed cavities that form be hind the adapter elements when the adapter elements are getting into their place. This acceler ates the degassing of the closed cavities of the gas cell assembly during vacuum pumping.
• Figures 6D and 6E show, in a bottom view and a cross-section, respectively, a cover lid 40 that can be used in conjunction with both embodiments of the gas cell 1, 50 to hermetically seal an undesired opening in the top side of the chamber 10.
• the cover lid 40 has a groove 45’ for receiving an elastic sealing member, preferably a circular sealing ring, in such a way that when said cover lid 40 is arranged on the top face of the gas cell 1, 50, the sealing ring rests on the top face of the gas cell 1, 50.
• the cov er lid 40 With retaining bolts pass ing through the holes 48 and screwed into the threaded holes 18 of the gas cell 1, 50, the cov er lid 40 can be clamped onto the gas cell 1, 50, and thus, the sealing member arranged be tween the cover lid 40 and the top face of the gas cell 1, 50 gets elastically deformed. As a result, the cover lid 40 provides a gas-tight sealing with the top side of the chamber 10.
• FIGS 7A-7C illustrate a further embodiment of a gas cell 60 for use in the gas cell assembly according to the present invention, wherein the undesired opening in the chamber 10 is closed by a bolt, in particular a stud bolt 63b, screwed into a threaded hole 63a formed in the upper section of the chamber 10.
• a bolt in particular a stud bolt 63b
• the sealing is provided by the form-fitting connection between the tapered surface of the stud bolt 63b and a flange formed in the upper section of the chamber 10.
• At least one sensor opening 62 is formed, preferably, as a blind hole, into which a suitable temperature sensor (not shown in the drawings) for monitoring the temperature within the chamber 10 can be arranged.
• the temperature sensor is connected to a suitable evaluating, processing and con trol unit (not shown in the drawings) which, based on the signal received from said tempera ture sensor, can intervene in the operation of the gas cell assembly if necessary.
• Figures 7A-7C also show a mechanism for restraining the dis placement and rotation of the gas cells 60 relative to each other, as well as to the base element and the closure element when said components are assembled together.
• Said mechanism re places the system of dowel pins and recesses, and is formed by recesses 66” with mating edg es 6” formed on a lateral side of the gas cell 60 along the longitudinal direction H and protru sions 66' with mating edges 6’ complementary to the shape of the mating edges 6”, said pro trusions 66’ being formed on an opposite lateral side of the gas cell 60 along said longitudinal direction H.
• the mating edges 6’, 6 have the same height, are preferably located in the cor ner regions of said lateral sides and are inclined with respect to the edges delimiting the cor ner regions.
• the number of protrusions 66’ with mating edges 6’ and the number of recesses 66” with mating edges 6” are at least two. This mechanism performs its matching function through the recesses 66” and protrusions 66’ of adjacent gas cells bearing against each other when the gas cell assembly is assembled.
• Figures 9A and 9B, as well as Figures 10A and 10B illustrate the displacement-free and rota tion-free assembling and / or mounting mechanism discussed in connection with the gas cells 60 for further preferred exemplary embodiments of the base element 20 and the closure ele ment 30, respectively.
• the base element 20 is preferably provided with recesses 26” having mating edges 6” in the comer regions of one of the lateral sides along the longitu dinal direction H (see Fig. 9A), while the closure element 30 is preferably provided with pro trusions 36’ having mating edges 6’ in the comer regions of one of the lateral sides along the longitudinal direction H (see Fig. 10 A), or vice versa.
• Figures 7A-7C illustrate a further embodiment of a gas cell 60 for use in the gas cell assembly according to the present invention, wherein reducing inserts 67 are arranged in the openings 12 of the gas cell which can be easily replaced in case of need.
• the object of using said reducing inserts 67 is to allow that the gas cell 60 be suitable for increases in pres sure within the interaction space or decreases in gas load within the gas space, and thereby increases in both the optical and the gas engineering efficiencies of the gas cell assembly without a need for re-manufacturing the gas cell 60.
• bores 12 of the gas cell 60 are drilled with a large diameter along their entire length, and preferably contain roundings at the inlets of the bores 12 and at the ends of the reducing inserts 67 in order to avoid damaging the bore / insert sliding surfaces when they are made of soft metals.
• the de sign of the internal bore system of the reducing inserts 67, except for the diameters of the smaller diameter bore sections, is fully identical with the design of the bores of the gas cells 1. That is, the bore 12 comprises a larger diameter wider bore section further away from the chamber 10 and a smaller diameter narrower bore section near the chamber 10.
• spacer plates 64 of various thicknesses are used. Fix ing of said reducing inserts 67 is performed through washers 68 with screws 69 that fit into threaded holes formed in the side wall of the gas cell 60.
• FIGS 8A and 8B illustrate a yet further embodiment of a gas cell 70 for use in the gas cell assembly according to the present invention, wherein fixing and moving one of the reducing inserts 67 of the gas cell 70, arranged preferably on that side of said gas cell 70 which is not illuminated, are performed by a commercially available actuator having an external electrical control, preferably by a so-called piezo linear 75 actuator.
• This embodiment allows the inter action length of the gas cell 70 to be varied without disrupting the vacuum system, and thus, enhances the benefits achievable through the modular design of the gas cell assembly of the present invention. In particular, it provides more freedom and flexibility as to the replacement of the members of a series of gas cells, primarily to change the process parameters of the high harmonic generation.
• the invention further relates to a kit for assembling the gas cell assembly, said kit comprises at least one, preferably a plurality of gas cells, a base element and a closure element chosen from the possible embodiments of the gas cell 1, 50, 60, 70, the base element 2, 20 and the closure element 3, 30 discussed above (naturally, in such a way that the components to be used are compatible with regard to the mechanism applied for their displacement- and / or rotation-free assembling), the kit also comprises suitable mounting elements, such as
• sealing members e.g. sealing rings, that fit into the sealing grooves 15 of the gas cells 1, 50, 60, 70;
• - clamping elements 7 such as e.g. screws / bolts, for clamping the components of the gas cell assembly together through being inserted into the openings 27 in the base element 2, 20 and the openings 37 in the closure element 3, 30.
• the kit optionally, also comprises
• cover lids 4, 40 for closing hermetically the top side of the chamber 10 of the gas cells 1, 50, 60, 70, and, if appropriate, fastening elements 8, preferably screws / bolts, for fastening said cover lids to said gas cells;
• fastening elements 81 e.g. retaining bolts, for fastening the base element 2, 20 to the support structure
• the following steps are performed: - providing at least one, preferably several gas cells, base elements and closure elements cho sen from the various embodiments of the gas cell 1, 50, 60, 70, the base element 2, 20 and the closure element 3, 30 discussed above in detail in such a way that said components are com patible with each other with regard to the mechanism applied for their displacement- and / or rotation-free assembling, and
• a sealing member such as a sealing ring
• the base element 2, 20 is fastened to the support structure by means of one or more fas tening elements 81, for example retaining bolts;
• the cover lids 4, 40 can be fitted after clamping of the gas cell assembly has been performed or the refrigerant connections 9a and the gas connections 9b can be connected before clamping of the gas cell assembly has been completed.
• a further advantage of the gas cell and the gas cell assembly according to the invention is modularity, i.e. it is possible to form gas cell assemblies of different purposes from given components. Moreover, to remove, replace and / or add additional components, an existing gas cell assembly according to the invention can be easily disassembled. For example, to sup ply a gas cell with different gas, it is sufficient to replace merely the corresponding gas con nection 9b or the gas source connected to said gas connection 9b.
• the temperature of the warmer parts of the gas cell assembly will exceed the ambient temperature of 20°C by at most about 1-2°C if water at the temperature of 20°C is passed through said gas cell assembly. If the laser arrangement is incorrectly set or gets maladjusted due to external interfering factors, the beam of the primary laser source may strike partly on the gas cell or the reducing insert, in which case the heat load may multiply.
• the gas cell assem bly according to the invention is still protected against catastrophic overheating.
• the gas cell(s), the base element and / or the closure element are equipped with temperature sensors that detect overheating of the gas cell assembly.
• Figures 11 A-l 1C show the change in temperature measured within a gas cell assembly according to the invention as a function of time during a relatively long operation of the gas cell assembly.
• the curves in Figures 11 A-l 1C illustrate the change in temperature of the hot spots of the gas cell assembly over time in experiments performed on three different days.
• a primary laser source with a repetition rate of 100 kHz and an average power of 100 W was used to generate high harmonics in high vacuum.
• the figures clearly show the slowly changing background temperature in the range of 20.0 to 21.5 degrees Celsius, which repre sents the evolution of the refrigerant temperature during the day.
• a sudden temperature in crease of 1.5 degrees Celsius on average which is observed when the laser source is switched on / off and varies slightly in accordance with to the current geometrical conditions, superim poses to this background temperature with a time constant of a few minutes.
• the operational experience clearly show that the gas cell assembly according to the in vention is capable of operating for a long time (even several days) without being overheated and a need for being shut down by means of a simple cooling which is provided by one or more continuous cooling passages formed within the interconnected modular components of the gas cell assembly.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Fuel Cell (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)

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• 2019
  • 2019-06-30 HU HUP1900238A patent/HU231453B1/hu unknown
• 2020
  • 2020-06-30 EP EP20851334.1A patent/EP3991524A2/de active Pending
  • 2020-06-30 WO PCT/HU2020/050028 patent/WO2021058989A2/en unknown

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