Method for marking by means of laser pulses

Abstract

The invention relates to a method (1) for introducing a marking (3) into a layer by means of a laser beam (11) generated by a laser generator (9), wherein the marking (3) has a plurality of pixels (BP) in at least a first path (29) connecting the pixels (BP), the laser beam (11) is guided along the first path (29) connecting the pixels (BP) on the layer (5) by means of at least one movable deflection mirror (15, 17) of a deflection device (13), a movement of the laser beam (11) through the deflection device (13) is carried out continuously, and to generate one of the pixels (BP) of the marking (3) during the continuous movement through the deflection device (13) a pulse train (33) of two or more successive laser pulses (31) of the laser beam (11) is generated.Furthermore, the invention relates to a marking device (7), a layer (5) with a marking (3), the use of a layer (5) for a security document (65) and a computer program.

Description

Subject of the invention

[0001] The invention relates to a method for introducing a marking, which may also include a contrast and / or surface change through structuring, into a layer of a security document using a laser beam generated by a laser generator. The marking comprises a plurality of pixels in at least one first path connecting the pixels. Furthermore, the invention relates to a marking device, a security document, the use of a layer for a security document, and a computer program. Background of the invention

[0002] To increase the forgery security of security documents, especially valuable documents, various features and processes are used to make replication or falsification more difficult or even impossible. A security document is typically composed of several layers, preferably bonded together by lamination. The data is embedded within the material under a preferably transparent cover layer to protect against tampering. This can be achieved by laser personalization of the otherwise finished data carrier. Another method involves providing the data carrier with a preferably transparent cover layer after personalization.

[0003] A valuable or security document can be tampered with by removing the cover layer and, after manipulating the underlying data, applying a new cover layer. Holograms can be used to protect the document from tampering, as described, among others, in documents WO 2017 109 119 A1, DE 10 2007 042 386 A1, EP 2 738 624 B1 and EP 1 475 678 B1. For this purpose, a special hologram film is appropriately exposed and applied to the data carrier. Another method for increasing the forgery security of security documents, according to EP 1 970 211 A1, is to laser-mark narrow sides of the document to create an optical connection between the layers. If the different layers are separated, the marking applied to the sides is damaged. Reproducing this damaged marking is technically challenging, making it difficult to forge the document.

[0004] Furthermore, microstructuring of the surface of a security document can be performed, making any tampering with the cover layer detectable. DE 10 2018 106 430 A1 discloses a security element for use as a layer for a security document, which has a structure comprising structural elements with dimensions of less than 200 micrometers. Furthermore, the document discloses a method for producing such a security element, wherein the structure is created by means of laser radiation and / or by local foaming and / or by means of high-resolution 3D printing technology. A disadvantage of the known methods for producing microstructuring, however, is that the processing time for producing the microstructuring is comparatively long.When creating a large-area microstructure with the smallest possible structural elements or pixels, it is often necessary to apply multiple laser pulses to a single location on the layer, which significantly increases processing time. To create small pixels, conventional methods guide the laser beam to a specific position on the layer using a deflection device with movable deflection mirrors. A laser generator, which generates the laser beam, then applies a corresponding number of laser pulses to the layer after positioning. The laser beam is then moved to the next position on the layer where a pixel is to be created. This process is also known as "jump and shoot."

[0005] Since security documents, such as identity documents, are often produced in very large quantities, even a slight increase in processing time is associated with high production costs.

[0006] US 10,391,586 B1 discloses a method for marking a workpiece made of aluminum covered by an oxide layer, comprising: irradiating the aluminum through the oxide layer with a plurality of pulse trains of optical pulses, wherein each irradiated location of the workpiece receives at least one pulse train of consecutive optical pulses.

[0007] WO 2014 / 106517 A1 discloses a method for producing a security element for security papers, value documents and other data carriers, in which a substrate is provided at least in some regions with a laser-sensitive recording layer, which is exposed in a first partial region to a first laser radiation with first laser parameters and in a second partial region to a second laser radiation with different second laser parameters in order to produce a target appearance.

[0008] WO 2013 / 017738 A1 discloses a method for producing markings on a web comprising cellulose fibers and a fluorescent substance, comprising forming a first altered portion of the web by directing a laser beam onto the web to reduce the fluorescence of the web at the location of the first altered portion. Description of the invention

[0009] Where the term value and / or security document or security element is used in the description and claims of the present application, this shall be understood to mean, for example, a passport, identity card, driving license, an access control card or other ID card, a vehicle registration document, vehicle registration certificate, visa, check, means of payment, in particular a banknote, a check, bank, credit or cash payment card, customer card, health card, chip card, a company ID card, proof of authorization, membership card, gift or shopping voucher, waybill or other proof of authorization, tax stamp, postage stamp, ticket, (gaming) token or another document.A security element can also be, for example, a sticker, adhesive label (for example for article security) or the like, which has the marking produced using the method according to the invention and which can be permanently connected to a precursor product of a valuable and / or security document or another article, for example with a product to be marked whose authenticity is to be guaranteed, in order to form the valuable and / or security document or this marked article. This article can, for example, be an example from a limited series of similar products, the uniqueness of which is documented by means of a numbering. This numbering can be realized by individualizing the security element provided with the security feature. The valuable and / or security product can also be, for example, a smart card.The valuable and / or security document can be in ID 1, ID 2, ID 3, or any other standardized or non-standardized format, for example, in booklet form, similar to a passport-like item, or in card form. A valuable and / or security product is generally a laminate of multiple document layers that have been precisely bonded together under heat and increased pressure. These products must meet standardized requirements, for example, according to ISO 10373, ISO / IEC 7810, and ISO 14443. The product layers consist, for example, of a carrier material suitable for lamination.

[0010] The valuable and / or security product and / or the layer can be formed from a polymer selected from a group comprising polycarbonate (PC), in particular bisphenol A polycarbonate, polyethylene terephthalate (PET), and derivatives thereof, such as glycol-modified PET (PETG), polyethylene naphthalate (PEN), polyvinyl chloride (PVC), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), polyimide (PI), polyvinyl alcohol (PVA), polystyrene (PS), polyvinylphenol (PVP), polypropylene (PP), polyethylene (PE), thermoplastic elastomers (TPE), in particular thermoplastic polyurethane (TPU), acrylonitrile-butadiene-styrene copolymer (ABS), and derivatives thereof, and / or paper and / or cardboard and / or glass and / or metal and / or ceramic. Furthermore, the valuable and / or security product and / or the layer can also be made from several of these materials, preferably from PC or PC / TPU / PC. The polymers can be either filled or unfilled.In the latter case, they are preferably transparent or translucent. If the polymers are filled, they are opaque. The value and / or security document is preferably produced from 3 to 12, preferably 4 to 10 layers, wherein at least one of the layers has a marking produced according to the method according to the invention. A laminate formed in this way can finally be coated on one or both sides with the protective or covering varnish or with a film. The film can in particular be a volume hologram, a film with a surface hologram (for example, a cinemagraphic element), or a scratch-resistant film. Overlay layers formed in this way protect a security feature arranged underneath and / or impart the document the required abrasion resistance.

[0011] Where the term "pattern" is used in the description and claims of this application, it is understood to mean any two-dimensional arrangement of at least one structure or pixel on a layer. A pattern can have any abstract or figurative form and, for example, consist of lines, surfaces, even in any combination, or alternatively of characters, such as alphanumeric characters, or represent images, such as a photo of the document owner or representations of specific objects. Any other information can also be represented graphically.

[0012] The object of the present invention is to provide a method which, compared to the prior art, enables a faster and / or simpler introduction of a marking, wherein the marking preferably offers increased security against counterfeiting compared to the prior art.

[0013] The invention solves the problem in a first aspect with the method defined in claim 1.

[0014] The invention utilizes the finding that the necessary acceleration times required for decelerating and accelerating the deflection mirrors can be reduced or avoided if the deflection mirrors of the deflection unit are moved continuously. Thus, with continuous movement of the deflection mirrors, in contrast to the previously described "jump and shoot" principle, no or only minimal inertial forces of the deflection device need to be overcome, which can significantly increase the processing speed when applying the marking. By generating a pulse sequence of two or more laser pulses, the laser beam needs to be guided less frequently, preferably only once, over the first path connecting the image points. Thus, the method according to the invention can also shorten processing times required for repeatedly guiding the laser beam along the first path connecting the image points.Preferably, the laser beam is guided only once along the first path connecting the pixels on the layer by means of the movable deflection mirrors of the deflection device. However, the laser beam can preferably also be guided multiple times along the first path. Preferably, the marking is a security marking. Furthermore, the layer is preferably a layer of a valuable and / or security document. Particularly preferably, the method is a method for generating a security marking in a layer for a valuable and / or security document.

[0015] The pattern thus created is preferably an individualized or personalized pattern containing individualized or personalized information. For example, the pattern can match or correspond to an image of the cardholder embedded in a layer beneath the pattern.

[0016] It should be understood that an image point does not necessarily have to be created by adding material, as is the case with conventional printing processes, for example. It can also be provided that a material forming the layer is locally modified or removed, thereby changing the optical impression. The laser generator is the device that generates the laser beam. The terms laser or laser beam refer to the electromagnetic wave generated by the laser generator. Preferably, a focusing device is arranged between the deflection device and the layer, which focuses the laser beam onto and / or into the layer of the material to be processed. Particularly preferably, the focusing device is a planar field focusing device. Preferably, the deflection device guides the focal point of the laser beam along the first path.

[0017] It should be understood that when guiding the laser beam along the first path, the laser beam does not have to strike the layer continuously. Thus, the laser beam preferably only strikes the layer when a laser pulse of the pulse sequence is generated. The continuous movement of the deflection mirrors then guides a theoretical point of impact of the laser beam, which is preferably the focal point, along the path onto and / or into the designated layer of the material to be processed.

[0018] According to a first preferred embodiment, the laser pulses are ultrashort laser pulses. Ultrashort laser pulses preferably have a pulse duration of less than 10 picoseconds (10 ps), in particular less than 1 ps. Particularly preferably, the ultrashort laser pulses have a pulse duration in a range from 100 femtoseconds (100 fs) to 900 fs, further preferably from 100 fs to 800 fs, particularly preferably from 200 fs to 600 fs. Micro- or nano-laser structures, in particular, can be manufactured comparatively easily using ultrashort laser pulses. The use of ultrashort laser pulses enables the precise manufacture of structural elements and / or the efficient generation of pixels. In particular, ultrashort laser pulses minimize or prevent thermal or mechanical damage to the structural elements during processing. With a suitable selection of the processing parameters, virtually melt-free and / or carbonization-free processing with high precision is possible.

[0019] Preferably, the laser pulses are generated with an oscillator frequency, measured between two consecutive laser pulses of the pulse train, which has a value in a range from 100 kHz to 100 MHz. A pulse train of several laser pulses in very short succession can also be referred to as a laser burst. Preferably, an oscillator frequency of the laser pulses of the pulse train is constant. However, it can also be provided that the oscillator frequency is varied between several laser pulses. The oscillator frequency describes a time interval between two consecutive laser pulses. The higher the oscillator frequency, the shorter the time interval between the consecutive laser pulses of the pulse train. For an oscillator frequency range of 100 kHz to 100 MHz, the time interval between two consecutive laser pulses is 10 microseconds (10 µs) to 10 nanoseconds (10 ns).The deflection device's movable deflection mirrors move the point of impact, at which the focused laser pulses or the focused laser beam strike and / or enter the relevant layer of the material to be processed, along the path. Even if the laser beam is moved along the path at a very high speed, the point of impact of two consecutive laser pulses of the laser beam moves only slightly due to the oscillator frequency according to the invention. For example, the time interval between two consecutive laser pulses at an oscillator frequency of 50 MHz is only 20 ns, with the point of impact moving imperceptibly or barely perceptibly to the human eye. The effects caused by the laser pulses on the layer are perceived as a single pixel of the marking.Due to the preferred oscillator frequency, one pixel of a marking can be generated using multiple laser pulses, even though the deflection device is continuously moved. It should be understood that with an oscillator frequency value within the preferred range, more than two laser pulses can be used to generate one pixel, for example 3, 4, 5, or more. Furthermore, the continuous movement of the laser beam can achieve a particularly preferred feature effect. If the laser beam is moved, the generated markings preferably overlap, whereby a special microstructure and / or microscopic shape of the pixels can be achieved, which then serves as a special security feature. For example, the pixel generated using the laser pulses can be oval.This ovality can then be used to verify the authenticity of the document, since it cannot be created using conventional methods such as the "jump and shoot" process.

[0020] In a preferred embodiment, the laser generator comprises a laser oscillator and a downstream amplifier, wherein the oscillator frequency corresponds to an oscillation frequency of the laser oscillator. This allows for particularly simple control of the laser generator. The ultrashort laser pulses are generated in the laser oscillator by mode locking and amplified to the desired power in a downstream amplifier. The laser amplifier can preferably be based on Yb fiber technology or Yb InnoSlab technology. The pulses are temporally stretched before amplification and temporally compressed again after amplification. Disk laser amplifiers are also used.

[0021] Preferably, a scanning speed at which the laser beam is moved along the first path has a value of 10 m / s or greater. The scanning speed is indirectly proportional to the processing time required to create the marking. Increasing the scanning speed therefore reduces the processing time, which can reduce manufacturing costs for the marking or a layer comprising the marking. Preferably, the scanning speed has a value of 10 m / s to 30 m / s. If the laser beam is moved over the layer at a scanning speed of 10 m / s, the point of impact moves approximately 0.2 micrometers (0.2 µm) along the path in a period between two consecutive laser pulses of 20 ns, which corresponds to an oscillator frequency of 50 MHz.A distance of 0.2 µm between two impact points is imperceptible to the human eye, resulting in only a single perceivable pixel. However, more than two laser pulses can be generated at a scanning speed of 10 m / s or greater. For example, pixels with impact point shifts of 1 µm, which occur at a scanning speed of 10 m / s and an oscillator frequency of 50 MHz with six laser pulses, are still perceived as a single pixel.

[0022] In a preferred embodiment of the method, the total energy of the pulse sequence is distributed substantially evenly across the laser pulses of the pulse sequence. A uniform distribution of the total energy of the pulse sequence across the laser pulses enables particularly simple and cost-effective control of the method. The fluence (energy density) describes the energy of a laser pulse that impinges on the surface to be processed. High reproducibility of the individual laser pulses preferably produces a particularly uniform marking.

[0023] The energy of a laser pulse in the pulse sequence preferably has a value of 10 microjoules (10 µJ) or less. The total energy introduced into the material forming the layer with the pulse sequence influences the marking effect caused by the pulse sequence. Particularly at high oscillator frequencies, successive laser pulses can achieve a combined effect. For example, a total energy of a pulse sequence greater than 10 µJ can carbonize the material forming the layer and / or cause particularly high material removal. The pulse sequence preferably has a total energy of 10 µJ to 100 µJ, more preferably 10 µJ to 80 µJ, more preferably 10 µJ to 60 µJ, and particularly preferably 20 µJ to 40 µJ.

[0024] According to a preferred development, the fluence of an incident laser pulse in the pulse sequence has a value that is less than or equal to ten times the threshold fluence of the material forming the layer. Fluence is a measure of the energy input per unit area of ​​the layer. The threshold fluence describes the fluence, i.e., the energy per unit area of ​​the layer, that must be applied by the laser pulses in order to ablate the material forming the layer. The higher the fluence of incident laser pulses, the greater the material ablation per laser pulse. However, the ablation efficiency does not follow a linear progression, so that a standardized ablation rate, measured as ablated material per applied energy, has a maximum.It has been shown that this maximum removal efficiency lies essentially in a range of five to ten times the threshold fluence, so that particularly efficient marking or material removal can be achieved with a fluence of the incident laser pulses in the preferred range. Preferably, the fluence has a value in a range of five to ten times the threshold fluence of the material forming the layer.

[0025] Preferably, the number of laser pulses in the pulse sequence generated to create the respective pixel can be varied. For example, a first pulse sequence can comprise only two laser pulses, while a second pulse sequence can then comprise three or more laser pulses. By varying the number of laser pulses, the perceived strength of the marking produced can preferably be varied. Alternatively or additionally, the intensity of the laser pulses can also be varied. For example, the amount of material removed by the laser pulses could be increased, so that a marking is also more clearly perceptible. Furthermore, the blackening of the material forming the layer, which is caused by the laser pulses, can also be greater if more laser pulses and / or laser pulses of higher intensity are applied.

[0026] In a preferred embodiment, a modulation frequency, measured between two consecutive pulse sequences, has a modulation frequency value in a range from 1 kHz to 1 MHz. The modulation frequency and the scanning speed determine a distance between adjacent pixels, measured along the first path. At the same scanning speed, a higher modulation frequency corresponds to a smaller distance between the pixels, which can increase the security against counterfeiting of the marking. A modulation frequency in the preferred range results in a particularly good combination of security against counterfeiting and processing time. Furthermore, by increasing the modulation frequency and the scanning speed while maintaining the same distance between the pixels, the required processing time can be reduced. The distance between consecutive pixels is determined from the quotient of the scanning speed divided by the modulation frequency.It should be understood that pulse sequences do not necessarily have to be generated strictly at a single modulation frequency; rather, two consecutive pulse sequences can also be generated at an integer fraction of the modulation frequency. For example, if an empty dot is to be positioned between two consecutive visible pixels, which is optically invisible or optically indistinguishable from the material forming the layer, the pulse sequences generating the two visible pixels are generated at half the modulation frequency. Furthermore, the time interval between two consecutive pulse sequences can be completely arbitrary.

[0027] In a preferred embodiment, the laser beam is moved along the first path by a beam advance value in a range from 0.01 µm to 100 µm, particularly preferably by a value of 1 µm, in a period between a first laser pulse and a last laser pulse of the pulse sequence. The beam advance value describes a distance from the centers of visible effects caused by the laser pulses. A beam advance value in the particularly preferred range is not perceptible to the human eye, thus enabling particularly precise marking. Furthermore, a marking produced with a pulse sequence with a beam advance value in the claimed range can serve as a special security feature.

[0028] The image points are preferably created by removing material from a material forming the layer, whereby a laser bore with a bore depth is created by removing material. The layer can also comprise a plurality of materials. The image points are then preferably created by uniformly removing material from the materials forming the layer. However, it can also be provided that only a portion of the materials forming the layer is removed and / or that the materials are removed in different quantities. The bore depth along a bore axis is preferably measured perpendicular to a surface of the layer. However, it can also be provided that the bore depth is measured transversely to the first path and parallel to a beam direction of the laser beam. The laser bore is preferably a blind hole. This means that the laser bore preferably does not extend completely through the layer.

[0029] According to a preferred embodiment, the material is removed without carbonization. Material is removed without carbonization if a material surrounding the image point is not carbonized. Carbonization describes a blackening of the carbon contained in the material forming the layer. If material is removed without carbonization, it can advantageously be achieved that the marking is only perceptible from certain optical viewing axes. If, for example, the viewing axis is parallel to the depth of a laser bore and the material forming the layer is translucent, the marking cannot be perceived visually or can only be perceived with great difficulty. If, on the other hand, the viewing axis is inclined to the bore axis, the marking becomes perceptible, whereby a particularly high security effect can be achieved with a marking produced in this way.

[0030] Preferably, material removal occurs through sublimation of the material forming the layer. This allows for particularly detailed, precise marking. For example, particularly small pixels can be created by sublimating the material forming the layer. Furthermore, sublimation is particularly suitable for preventing carbonization of the material surrounding the pixel. Sublimation describes an immediate phase transition of the material from the solid phase to the gaseous phase.

[0031] According to a preferred embodiment, the laser bore has a substantially oval cross-section. Laser beams generally have a substantially round cross-section, so that conventional laser bores produced using such laser beams are also substantially round or cylindrical. An oval laser bore can preferably also be shaped like an elongated hole. The oval cross-section of the laser bore is preferably produced by moving the laser beam or the point of impact between successive laser pulses of the pulse sequence. However, it can also be provided to provide a laser beam with an oval cross-section. To produce a laser bore with an oval cross-section, several process parameters must be specifically controlled and coordinated with one another. This increases the complexity of carrying out the method and enhances security against forgery. The oval cross-section is particularly preferably elliptical.

[0032] Preferably, a short semi-axis of the oval cross-section is substantially transverse to the first path of the plurality of pixels. This allows the oval cross-section to be advantageously generated by appropriately controlling the oscillator frequency and the scanning speed.

[0033] Preferably, the laser hole has an aspect ratio, measured as the quotient of the hole depth and a maximum hole diameter, in a range of 0.05 to 5. The aspect ratio influences the visual perception caused by the laser hole. For example, laser holes with a high aspect ratio can appear higher in contrast than laser holes with a low aspect ratio. For example, the hole depth can have a value of 1 µm and the hole diameter a value of 20 µm, so that the laser hole has an aspect ratio of 0.05.

[0034] In a preferred embodiment, the perceived color intensity of the marking is varied by varying the bore depth and / or a maximum bore diameter of the laser bores. Preferably, the bore depth can be varied by varying the number of laser pulses generated to create the image point. Furthermore, the bore diameter of the laser bore can preferably be increased by increasing the pulse duration of the laser pulses and / or the energy of the laser pulses.

[0035] Preferably, the pixels have dimensions transverse to the direction of incidence of the laser beam of 200 µm or smaller, preferably 100 µm or smaller, particularly preferably 40 µm or smaller. The smaller the dimensions, the more difficult it is to counterfeit or tamper with the security element. On the other hand, the structural elements should preferably have dimensions larger than the wavelength of visible light, which is why, for example, structural elements with dimensions greater than 1 µm can be used.

[0036] According to a second aspect, the invention solves the problem mentioned at the outset with the marking device defined in claim 11.

[0037] In a first preferred embodiment, the laser generator comprises a laser oscillator and a downstream amplifier, wherein the laser is designed to provide a pulse train of laser pulses whose oscillator frequency corresponds to an oscillation frequency of the laser oscillator.

[0038] Preferably, the deflection device is designed to move the laser beam along a predetermined path at a scanning speed of 10 m / s or more, measured at the focal point of the laser beam or at the point of impact of the laser beam on the layer.

[0039] Preferably, the marking device forms a marking system with a layer to be marked. It should be understood that the marking system may also comprise other components in addition to the marking device and the layer.

[0040] It should be understood that the method according to the first aspect of the invention and the marking device according to the second aspect of the invention have identical and similar sub-aspects, as particularly set forth in the dependent claims. Therefore, for further embodiments of the marking system and their advantages, reference is also made in full to the above description of the first aspect of the invention.

[0041] According to a third aspect, the invention achieves the object mentioned above by means of the security document defined in claim 13. Preferably, a layer produced by the described method has laser holes with a non-circular cross-section.

[0042] In a fourth aspect, the invention solves the problem mentioned above by the use defined in claim 14.

[0043] According to a fifth aspect, the invention solves the problem mentioned above with the computer program defined in claim 15.

[0044] It should be understood that the method according to the first aspect of the invention, the marking device according to the second aspect of the invention, the security document according to the third aspect of the invention, the use according to the fourth aspect of the invention, and the computer program according to the fifth aspect of the invention have the same and similar sub-aspects, as particularly set forth in the dependent claims. Therefore, for further embodiments of the security document, the use, and the computer program, and their advantages, reference is also made in full to the above description of the first and second aspects of the invention. Description of implementation examples

[0045] Embodiments of the invention will now be described below with reference to the drawings. These are not necessarily intended to represent the embodiments to scale; rather, the drawings are schematic and / or slightly distorted where this is useful for explanation. With regard to additions to the teachings immediately apparent from the drawings, reference is made to the relevant prior art. It should be noted that various modifications and changes to the form and detail of an embodiment can be made, provided they fall within the scope of protection of the claims. The features of the invention disclosed in the description, in the drawings and in the claims can be essential for the further development of the invention, both individually and in any combination.Furthermore, all combinations of at least two of the features disclosed in the description, the drawings and / or the claims fall within the scope of protection of the claims. The general idea of ​​the invention is not limited to the exact form or detail of the preferred embodiments shown and described below, or to an object that would be more limited than the object claimed in the claims. In the case of specified dimensioning ranges, values ​​lying within the stated limits are also intended to be disclosed as limit values ​​and to be used and claimed as desired. For the sake of simplicity, the same reference numerals are used below for identical or similar parts or parts with identical or similar functions.Further advantages, features, and details of the invention will become apparent from the following description of the preferred embodiments and from the drawings. These show: . Figure 1 shows a schematic representation of a marking system having a marking device and a layer and executing the method according to the invention; Figure 2a shows a schematic representation of the steps of a first conventional method for producing a marking; Figure 2b shows a schematic representation of the steps of an embodiment of the method according to the invention for producing a marking; Figure 2c shows a schematic representation illustrating the production of multiple pixels of a marking using the method according to the invention; Figure 3 shows the production of a pixel of a marking in a schematic representation, wherein the pixel is produced by removing material from a material forming the layer using laser pulses; Figure 4 shows a schematic plan view of a layer in which a laser hole is produced; Figure 5 shows a security document in a partially sectioned and perspective view;Figure 6 shows a perspective view of a section of a layer having a marking; and Figure 7 shows a comparison of an intensity applied to the layer using a standard pulse with an intensity applied using a pulse sequence.

[0046] Figure 1shows a method 1 for introducing a marking 3 into a layer 5 of a security document 65, which method is carried out here by a marking device 7. The marking device 7 has a laser generator 9 designed to generate a laser beam 11. The laser beam 11 is emitted by the laser generator 9 and impinges on a deflection device 13 of the marking device 7, which here has a first movable mirror 15 and a second movable mirror 17. The deflection device 13 is a two-axis deflection device 19 designed to direct the laser beam 11 onto the layer 5. Furthermore, a focusing device 21 of the marking device 7 is arranged between the deflection device 13 and the layer 5, which focuses the laser beam on the layer 5.The laser generator 9, the deflection device 13, and the focusing device 21 are connected to a control unit 27, which is designed to control the components of the marking device 7. Together with the layer 5, the marking device 7 forms a marking system 200.

[0047] If the control unit 27 now controls the laser generator 9 accordingly, the latter generates the laser beam 11, which is then directed onto the layer 5 by means of the deflection device 13. The laser beam 11 is focused by the focusing device 21. By rotating the mirrors 15, 17 (indicated by arrows 27), the laser beam 11 can be moved on the layer 5, whereby a rotation of the first mirror 15 moves the laser beam 11 parallel to a Y-axis Y and a rotation of the second mirror 17 moves the laser beam 11 parallel to an X-axis X. The control unit 27 controls the mirrors 15, 17 such that the laser beam 11 is guided along a path 29 connecting several pixels BP of the marking 3. In this exemplary embodiment, the marking has a regular grid of pixels BP. However, any other regular and / or irregular patterns of pixels BP can also be generated.

[0048] When creating the marking 3, the deflection mirrors 15, 17 of the deflection device 13 are moved continuously, whereby the acceleration times required for accelerating and decelerating the first mirror 15 and the second mirror 17 can be minimized or avoided. Whenever the laser beam 11 is positioned over an image point BP of the marking 3 to be created, the control unit 27 controls the laser generator 9 such that it generates a pulse sequence 33 comprising several laser pulses 31. The laser beam 11 is therefore not generated continuously here, but only when an image point BP of the marking 3 is to be created. A theoretical point of impact 34 of the laser beam 11, which is defined by the respective position of the mirrors 15, 17 at a specific time, is, however, continuously guided along the path 29.

[0049] A first pixel BP1 is generated, for example, by means of the laser pulses 31 when the laser beam 11 is deflected by the deflection device 13 onto the Fig. 1 The laser beam 11 is guided to the first position P1 shown in FIG. Although the laser beam 11 continues to move during the generation of the laser pulses 31, the time interval between the laser pulses 31 is very short due to the high oscillator frequency 35, so that only one optically perceptible image point BP1 is generated. Preferably, sections of the image point BP generated by the individual laser pulses 31 of a pulse sequence 33 overlap.

[0050] Preferably, a focal point PF of the laser beam 11 lies on a side 23 of layer 5 facing the focusing device 21. However, it can also be provided that the focal point PF lies in layer 5 or on a side 25 facing away from the focusing device 21. Preferably, the focusing device 21 is an F-theta lens 37 or has an F-theta lens 37. It should be understood that the focusing device 21 can preferably also have multiple lenses and / or objectives.

[0051] In this embodiment, the laser generator 9 comprises a laser oscillator 39 and an amplifier 41. The laser oscillator 39 generates seed laser pulses 43, the energy of which is then increased by the amplifier 41, and these can then be emitted as laser pulses 31. The laser oscillator 39 generates the seed laser pulses 43 with an oscillation frequency of 45. A coupling device 47 of the laser generator 9 is designed to decouple seed laser pulses 43 and guide them to the amplifier 41. It should be understood that not every seed laser pulse 43 is amplified into a laser pulse 31.

[0052] Figure 2aIllustrates the steps of a first conventional method 300 designed to produce a marking 3 with multiple pixels BP. According to this first method, a laser beam 11 is guided by a deflection device 13 to a first position P1, at which a first pixel BP1 is to be produced (step S1.1). As soon as the laser beam 11 reaches the desired position P1, the deflection mirrors 15, 17 of the deflection device 13 are stopped (step S1.2), so that the focal point FP of the laser beam 11 remains stationary. Subsequently, to produce the first pixel BP1, multiple laser pulses 31 are successively applied to the layer 5 (steps S1.3 to S1.5). After the first pixel BP1 has been completely generated, the deflection mirrors 15, 17 of the deflection device 13 are accelerated and the laser beam 11 is moved along a path 29 connecting the pixels to a second position P2 of a second pixel BP2 to be generated (step S1.6).There, the laser beam 11 is stopped again by braking the deflection mirrors 15, 17 of the deflection device 13 (step S1.7). The second image point BP2 is then generated by applying several laser pulses 31 to the layer 5 (steps S1.8 to S1.10). This procedure is subsequently continued in an analogous manner until all image points BP of the marking 3 have been generated (step S1.11). The movement of the deflection device 13 is thus continuously interrupted within the scope of the known method 300, whereby the numerous interruptions in the movement increase the processing time required to generate the marking.

[0053] Figure 2bnow illustrates a first embodiment of the method 1 according to the invention. Here, too, the laser beam 11 is guided by the deflection mirrors 15, 17 of the deflection device 13 along the path 29 connecting the image points BP, but with a continuous movement. The continuous guidance of the laser beam 11 through the continuously moving deflection mirrors 15, 17 of the deflection device 13 is described in Figure 2bby means of the solid arrow 49. The arrow 49 shows, by way of example, the first position P1 of the first image point BP1 to be generated, the second position P2 of the second image point BP2 to be generated, and the position Pn of the nth image point BPn of the marking to be generated. The deflection device 13 guides the laser beam 11 along the path 29 at the scanning speed Vs. The scanning speed Vs describes the speed at which the point of impact 34 of the laser beam 11, which is preferably the focal point FP, is moved along the path 29 connecting the image points BP.

[0054] As soon as the laser beam 11 reaches the first position P1 of the first pixel BP1, a first pulse sequence 33.1 is generated by the laser generator 9 in the method according to the invention and applied to the layer 5 (step S2.1). Here, the pulse sequence 33 comprises a total of six laser pulses 31.1, 31.2, 31.3, 31.4, 31.5, and 31.6. The application of the laser pulses 31.1, 31.2, 31.3, 31.4, 31.5, and 31.6 is represented by the substeps S2.1.1, S2.1.2, S2.1.3, S2.1.4, S2.1.5, and S2.1.6. To generate multiple pixels BP of the marking 3, a pulse sequence 33 is generated whenever the laser beam 11 reaches a position along the path 29 where a pixel BP is to be generated. Examples shown here are a first pulse sequence 33.1 for generating a first pixel BP1, a second pulse sequence 33.2 for generating a second pixel BP2 (step S2.2), and an nth pulse sequence 33.n (step S2.3). The application of the laser pulses 31.7, 31.8, 31.9, 31.10, 31.11, 31.12 of the second pulse sequence 33.2 is represented analogously to the first pulse sequence 33.1 by the sub-steps S2.2.1, S2.2.2, S2.2.3, S2.2.4, S2.2.5, S2.2.6. It should be understood that pulse sequences 33.3 to 33.n are emitted to generate third pixels BP3 (not shown) through n-th pixels. After a single scanning of the laser beam 11 along the path 29 connecting the pixels BP, the marking 3 is completely generated, whereby the time required to generate the marking 3 can be significantly reduced compared to the conventional method 300.

[0055] According to this exemplary embodiment, the laser pulses 31 of the pulse sequence 33 are generated at a particularly high oscillator frequency 35 of, for example, 50 MHz and applied to the layer 5. Thus, there is a period of 20 ns between two consecutive laser pulses 31.1, 31.2 of the pulse sequence 33. In this example, a total period of 100 ns elapses between the generation of the first laser pulse 31.1 and the generation of the sixth laser pulse 31.6, resulting in a pulse sequence duration 36 of the first pulse sequence 33.1 of 100 ns.

[0056] The generation of the pulse sequence 33 takes place parallel to the arrow 49 or during the movement of the laser beam 11 through the deflection device 13. As indicated by the curly brackets in Figure 2bAs is illustrated, the period of time required to generate one of the pulse sequences 33 is much shorter than the total time required to generate the marking 3. The generation of an image point BP can therefore be illustrated as a point on the arrow 49 representing the guidance of the laser beam 11 along the path 29.

[0057] A period of time that elapses between the generation of two consecutive pulse sequences 33 is greater than the pulse sequence duration 36 for generating all laser pulses 31 of a pulse sequence 33. The period of time between consecutive pulse sequences 33 is determined by the modulation frequency 55. Here, the modulation frequency 55 has a value of 10 kHz, so that there is a time interval of 100 µs between the first pulse sequence 33.1 and the second pulse sequence 33.2. According to this exemplary embodiment, a time interval between consecutive pulse sequences 33 thus corresponds to a thousand times the pulse sequence duration 36 for generating the laser pulses 31 of a single pulse sequence 33. The oscillator frequency preferably has a value in a range from 40 MHz to 50 MHz and the modulation frequency has a value of up to 2 MHz, particularly preferably 1.5 MHz to 2 MHz.

[0058] According to this embodiment, the laser pulses 31 are ultrashort laser pulses 32 with a pulse duration 81 of less than 10 ps ( Figure 7). Due to the ultrashort pulse duration of the ultrashort laser pulses 32, the laser beam 11 is moved only imperceptibly along the path 29 during an ultrashort laser pulse 32. The oscillator frequency 35 is also so high that the movement of the point of impact 34 of the laser beam 11 along the path 29 between two consecutive pulses 31.1, 31.2 is very slight. Therefore, for example, all laser pulses 31.1, 31.2, 31.3, 31.4, 31.5, 31.6 of the first pulse sequence 33.1 impinge on the layer 5 at the essentially identical first position P1 along the path 29 and interact to generate the first image point BP1 of the marking 3. It should be understood that due to the continuous guidance of the laser beam 11 by means of the deflection device 13, respective impact points 34.1, 34.2, 34.3, 34.4, 34.5, 34.6 of the individual laser pulses 31.1, 31.2, 31.3, 31.4, 31.5, 31.6 of the first pulse sequence 33.1 are slightly offset from each other and yet cooperate to generate the first pixel BP1.

[0059] Figure 2cillustrates that pixels BP of the marking 3 can be arranged irregularly relative to one another. Preferably, the scanning speed Vc, with which the laser beam 11 is guided by the deflection device 13 along the path 29, is constant. Possible positions P1 to Pn for generating pixels then have a regular distance from one another. In this exemplary embodiment, the scanning speed Vc has a value of 10 m / s, so that two consecutive positions P1, P2 have a spatial distance of 1 mm along the path 29 at a modulation frequency 55 of, for example, 10 kHz. To generate a regular pattern of pixels BP, a pulse sequence 33 is generated whenever the laser beam 11 reaches a position P. However, it can also be provided that a pulse sequence 33 is not generated at each of the positions P. Thus, in Figure 2cA respective pulse sequence 33.1, 33.2, 33.5, 33.7 is generated only at the first position P1, at the second position P2, at a fifth position P5, and at a seventh position P7. The image points BP1, BP2, BP5, BP7 of the marking 3 generated by the pulse sequences 33.1, 33.2, 33.5, 33.7 are shown parallel to the arrow 49.

[0060] The pulse sequences 33 can therefore preferably also be generated with an integer fraction of the modulation frequency 55. In this exemplary embodiment, an interval 56 of the modulation frequency 55 lies between the first pulse sequence 33.1 and the second pulse sequence 33.2. In contrast, there are three intervals 56 between the second pulse sequence 33.2 and the fifth pulse sequence 33.5, and two intervals 56 of the modulation frequency 55 between the fifth pulse sequence 33.5 and the seventh pulse sequence 33.7. Generating the pulse sequences 33 with an integer multiple of the interval 56 or an integer fraction of the modulation frequency 55 enables a particularly simple method. However, it can also be provided that two consecutive pulse sequences 33 are spaced from one another as desired. In this way, for example, markings 3 with particularly individual patterns can be generated.

[0061] Figure 3illustrates a marking 3, which is created by removing material from a material 57 forming layer 5. According to this embodiment, the material removal is effected by sublimation of the material 57 forming layer 5, wherein a material 59 surrounding the pixel BP is free of carbonization. Polymer molecules contained in the surrounding material 59 are not carbonized. Figure 3a A first laser pulse 31.1 of the pulse sequence 33 strikes the material 57 of layer 5, creating a laser hole 61. The laser hole 61 extends substantially uniformly around the point of impact 34.1 of the first laser pulse, which is located at the tip of the arrow illustrating the first laser pulse 31.1.

[0062] In Figure 3ba second laser pulse 31.2 of the pulse sequence 33 strikes the material 57. In the process, a further portion of the material 57 of the layer 5 is sublimated and thus removed, increasing the drilling depth T1 of the laser drilling 61. Between the first laser pulse 31.1 and the second laser pulse 31.2, the laser beam 11 was moved slightly further along the path 29, so that a second impact point 34.2 of the second laser pulse 31.2 is slightly shifted along the path 29 to the first impact point 34.1 of the first laser pulse 31.1. Figure 3 The path 29, which connects the image points BP, runs to the right.

[0063] In an analogous manner, material removal is also carried out by means of the further laser pulses 31.3, 31.4, 31.5, 31.6 ( Fig. 3c to Fig. 3f), wherein the respective impact points 34.3, 34.4, 34.5, 34.6 are offset from one another. The hole depth T1 of the laser hole 61 increases with each incident laser pulse 31. After the sixth laser pulse 31.6 has been applied to the layer 5, the creation of the laser hole 61 is complete. The aspect ratio of the finished laser hole 61 is determined from a quotient T1 / D of the hole depth T1 and a maximum diameter D of the laser hole 61.

[0064] Due to the movement of the laser beam 11 along the path 29, the laser hole also has the Figure 3 The stepped profile shown here is barely noticeable or not noticeable, depending on its severity. Figure 4illustrates the method for creating the laser hole 61 in a view parallel to the hole depth T1. The first laser pulse 31.1 strikes the layer 5 at the first impact point 34.1 and vaporizes the material 57 forming the layer 5. This creates the approximately circular laser hole 61. Subsequently, the second laser pulse 31.2 is generated and strikes the layer 5 at the second impact point 34.2, increasing the hole depth T1. In the view shown, the movement of the impact point 34 is particularly clearly visible. Figures 4c to 4e illustrate the changing shape of the laser bore 61 due to the impact of the further laser pulses 31.3, 31.4, 31.5 at the impact points 34.3, 34.4, 34.5. Figure 4f shows the cross-section of the laser bore 61 after the material 57 of layer 5 has been removed by the impact of the sixth laser pulse 31.6 of the pulse sequence 33.

[0065] The laser hole 61 is thus in Figure 4ffinished and has an oval cross-section, which here corresponds to the shape of an elongated hole. A short semi-axis 63 of the laser bore 61 is transverse to the path 29 due to the displacement of the point of impact 34. The shape of the oval cross-section of the laser bore 61 is influenced by a scanning speed Vs, at which the laser beam 11 is guided by the deflection device 13 along the path 29, the oscillator frequency 35, and the pulse repetition time 36 of the laser pulses 31 of a pulse train 33. A marking 3 with laser bores 61 produced using the method 1 according to the invention is therefore particularly forgery-proof. However, it can also be provided that the oscillator frequency 35, the pulse repetition time 36 of the laser pulses 31, and the scanning speed Vc are selected such that the laser bore 61 has a substantially round cross-section. Furthermore, the laser bore 61 can also have an elliptical cross-section.Preferably, a cross-sectional shape of the laser bore 61 can be varied by varying a beam cross-section of the laser beam 11.

[0066] In Fig. 5 is shown, by way of example and not to scale, a section of a document body of a security document 65. The security document 65 has a front side 67 and a back side 69. The security document 65 is constructed from several layers 71 and comprises a preferably transparent cover layer 73, which here is layer 5 (see Fig. 1). At least one of the layers 71 and / or 73 can be configured as a foil. The layers are bonded together by lamination to form a document body. Beneath the cover layer 73 is the information characteristic of the security document 65, preferably personalized or individualized, such as a personal or individual text element and / or graphic representation and / or image, for example, a portrait.

[0067] A marking 3 is arranged on the front side 67 of the security document 65. This marking is essentially invisible when viewed perpendicular to the front side 67, thus allowing the underlying information to remain clearly visible. Generally, if the marking 3 is formed before the cover layer 73 is applied to the foil stack, it can also be arranged on the inner surface of the cover layer 73 with respect to the foil stack. One or more additional layers can also be applied to protect the marking 3.

[0068] When viewed from a gloss angle, i.e., from a flat angle, the marking 3 becomes visible as a matte surface. Preferably, the marking 3 is applied so as to precisely fit an underlying image element 77. Preferably, the marking 3 corresponds to the underlying information, preferably the image element 77. The marking 3 is therefore preferably an individual or personalized marking 3 and carries or encodes individual or personalized information that corresponds to the information of the underlying layer. Any manipulation of the surface or replacement of the cover layer 73 would thus be easily detectable. The marking 3 does not have to be arranged above, in particular congruent with, the image element 77, but can also be applied at a different location on the security document 65.For example, the layer 5 marked with the mark 3 may also be applied to the back 69 of the security document 65.

[0069] Figure 6 shows a section of a layer 5 provided with a marking 3. The marking 3 has a pattern of pixels BP embodied as laser holes 61. Preferably, the method 1 further optionally comprises one of the steps: filling the laser holes with a material that differs from the material forming the layer 5 and / or covering the marking 3 with a layer, a foil, and / or a film. For example, the laser holes 61 can be covered with a lacquer layer.

[0070] Figure 7illustrates the intensity of a pulse sequence 33 with three ultrashort laser pulses 32, which are applied to the layer 5 in the method 1 according to the invention for producing a marking 3, compared to a standard pulse 79, as can be used in a conventional method 300. The abscissa of the illustrated coordinate system describes a time axis ZA, while the ordinate represents a value of the intensity I.

[0071] In this exemplary embodiment, an intensity IKP of the ultrashort laser pulses 32.1, 32.2, 32.3 corresponds to approximately one-third of the intensity IS of the standard pulse 79. Thus, a sum of the intensities IKP of the ultrashort pulses 32 applied to the layer 5 during the pulse sequence 33 corresponds to the intensity IS of a standard pulse 79. A pulse duration 81 of the ultrashort laser pulses 32 and the standard pulse 79, as well as the modulation frequency 55, are also identical in this exemplary embodiment. By distributing the intensity I over several ultrashort laser pulses 32, an ablation efficiency of the pulse sequence 33 is greater than an ablation efficiency of the standard pulse IS. This means that more material 57 can be removed from the layer 5 using the pulse sequence 33 than with the standard pulse IS, whereby the overall energy requirement for creating the marking 3 can be reduced. List of reference symbols

[0072] Proceedings 1 mark 3 layer 5 Marking device 7 Laser generator 9 laser beam 11 deflection device 13 First Mirror 15 Second Mirror 17 Two-axis deflection device 19 Focusing device 21 Focusing device facing side 23 Side facing away from the focusing device 25 Control unit 27 Train 29 laser pulse 31, 31.1, 31.2, 31.3, 31.4, 31.5, 31.6, 31.7, 31.8, 31.9, 31.10, 31.11, 31.12 Ultrashort laser pulse 32 Pulse sequence 33, 33.1, 33.2 Point of impact 34, 34.1, 34.2, 34.3, 34.5 Oscillator frequency 35 Pulse duration 36 F-Theta lens 37 Laser oscillator 39 amplifier 41 Seed laser pulse 43 Oscillation frequency 45 coupling device 47 Arrow 49 Modulation frequency 55 Modulation frequency interval 56 The layer forming material 57 Surrounding material 59 Laser drilling 61 Short semi-axis 63 Security document 65 front 67 back 69 Layers 71 Transparent top layer 73 Image element 77 Standard pulse 79 Pulse duration 81 Marking system 200 conventional methods 300 pixels BP, BP1, BP2, BP5, BP7, BPn Maximum diameter D Focus point FP intensity I Intensity of ultrashort laser pulses IKP Intensity standard pulse IS Positions of the pixels P1, P2, P3, P4, P5, P6, P7, P8, Pn Steps S# Depth of laser drilling T1 Scan speed vs Timeline ZA

Claims

1. Method (1) for introducing a marking (3) by means of a laser beam (11) generated by a laser generator (9) into a layer (5) of a security document (65), wherein the marking (3) comprises a plurality of pixels (BP) in at least a first path (29) connecting the pixels (BP), the laser beam (11) is guided by means of at least one movable deflection mirror (15, 17) of a deflection device (13) along the first path (29) connecting the pixels (BP) on the layer (5), characterized in that a movement of the laser beam (11) through the deflection device (13) takes place continuously, and for generating one of the pixels (BP) of the marking (3) during the continuous movement by the deflection device (13) a pulse sequence (33) of two or more subsequent laser pulses (31) of the laser beam (11) is generated.

2. Method (1) of claim 1, wherein the laser pulses (31) are ultrashort laser pulses (32), wherein the laser pulses (31) are preferably generated with an oscillator frequency (35), measured between the two subsequent laser pulses (31) of the pulse sequence (33), the oscillator frequency (35) having a value in a range from 100 kHz to 100 MHz.

3. Method (1) of any of the preceding claims, wherein a scanning velocity (Vs) at which the laser beam (11) is being moved along the first path (29), has a value of 10 m / s or higher.

4. Method (1) of any of the preceding claims, wherein a total energy of the pulse sequence (33) is substantially evenly distributed among the laser pulses (31) of the pulse sequence (33), wherein an energy of a laser pulse (31) of the pulse sequence (33) has preferably a value of 10 µJ or less.

5. Method (1) of any of the preceding claims, wherein a fluence of an impinging laser pulse (31) of the pulse sequence (33) comprises a value which is less than or equal to a tenfold value of a threshold fluence of the material (57) forming the layer (5).

6. Method (1) of any of the preceding claims, wherein a number of laser pulses (31) of the pulse sequence (33), which is generated for generating the corresponding pixel (BP), is varied.

7. Method of any of the preceding claims, wherein the laser beam (11) is moved in a time period between a first laser pulse (31.1) and a last laser pulse (31.n) of the pulse sequence (33) by a beam progression value in a range from 0.1 µm to 10 µm, particularly preferred by a value of 1 µm along the first path (29).

8. Method (1) of any of the preceding claims, wherein the generation of pixels (PB) takes place by material removal of a material (57) forming the layer (5), wherein by material removal a laser bore (61) with a bore depth (T1) is generated, wherein the material removal takes place preferably without carbonization and / or by sublimation of the material (57) forming the layer (5).

9. Method (1) of claim 8, wherein the laser bore (61) comprises a substantially oval cross section, wherein short half axis (63) of the oval cross section is preferably substantially transverse to the first path (29) of the plurality of pixels (BP).

10. Method (1) of claim 8 or claim 9, wherein the laser bore (61) comprises an aspect ratio (T1 / D), measured as quotient of the bore depth (T1) and a maximum bore diameter (D), in a range of 0.05 to 5.

11. Marking device (7) for introducing a marking (3), the marking (3) comprising a plurality of pixels (BP), into a layer (5) of a security document (65), the marking device (7) comprising: a laser generator (9) being configured for generating a laser beam (11), a deflection device (14) with at least one movable deflection mirror (15, 17) for guiding the laser beam (11) on the layer (5), and a control unit (27) being configured for controlling the deflection device (13) and the laser generator (9), wherein the control unit (27) is configured to control the deflection device (13) such that the at least one movable deflection mirror (15, 17) of the deflection device (13) for guiding the laser beam (11) along a first path (29) connecting the pixels (BP) executes a continuous movement, and to control the laser generator (9) such that the laser generator (9) for generating a pixel (BP) of the marking (3) during the movement of the at least one deflection device (15, 17) applies a pulse sequence (33) of two or more subsequent laser pulses (31) of the laser beam (11) on the layer (5).

12. Marking device (7) of claim 11, wherein the laser generator (9) comprises a laser oscillator (39) and a downstream amplifier (41), and wherein the laser generator (9) is configured to provide a pulse sequence (33) of laser pulses (31) whose oscillator frequency (35) corresponds to an oscillation frequency of the laser oscillator (39).

13. Security document (65), comprising a layer (5) with a marking (3), comprising a plurality of pixels (BP), producible by a method (1) with the steps: guiding a laser beam (11) by means of at least one movable deflection mirror (15, 17) of a deflection device (13) along a first path (29) that connects the pixels (BP) of the layer (5), wherein a movement of the laser beam (11) by the deflection device (13) takes place continuously, and generating a pulse sequence (33) of two or more subsequent laser pulses (31) of the laser beam (11) during the continuous movement of the deflection device (14) for generating one of the pixels (BP) of the marking (3).

14. Use of a layer (5) with a marking (3), comprising a plurality of pixels (BP), producible by a method (1) with the steps: guiding a laser beam (11) by means of at least one movable deflection mirror (15, 17) of a deflection device (13) along a first path (29) that connects the pixels (BP) of the layer (5), wherein a movement of the laser beam (11) by the deflection device (13) takes place continuously, and generating a pulse sequence (33) of two or more subsequent laser pulses (31) of the laser beam (11) during the continuous movement of the deflection device (14) for generating one of the pixels (BP) of the marking (3) in a security document (65).

15. Computer program, comprising commands that cause the marking device (7) of claim 11 or claim 12 to execute the method (1) defined in claims 1 to 10, when the computer program is executed on a computing unit.

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