WO2023099946A1

WO2023099946A1 - Pulsed laser beam shaping device for laser processing of a material transparent for the laser beam

Info

Publication number: WO2023099946A1
Application number: PCT/IB2021/061231
Authority: WO
Inventors: Orestas ULČINAS; Mindaugas MIKUTIS; Ernestas NACIUS; Antanas URBAS
Original assignee: Uab Altechna R&D
Priority date: 2021-12-02
Filing date: 2021-12-02
Publication date: 2023-06-08

Abstract

The invention relates to laser beam shaping devices, which can be used in the field of material processing, for example, for separating substrates of transparent media using laser pulses. Laser beam shaping device comprises a beam transforming element configured to convert an incident pulsed laser beam into two sub-beams and focusing means, that shapes focal spot or focal line in the form having transversally elongated cross section. The optical scheme of laser beam shaping device was simplified by reducing the number of optical elements required for forming two sub-beams, which have orthogonal polarizations and creating a non-diffracting beam. Said transforming element is configured to impose a pattern of light's Pancharatnam-Berry Phase wherein said transforming element comprises at least one metamaterial that is configured for imposing the evolution of the polarization state of the pulsed laser beam incident onto the transforming element.

Description

Pulsed laser beam shaping device for laser processing of a material transparent for the laser beam

Technical field of the invention

The invention relates to laser beam shaping devices, which can be used in the field of material processing, for example, for separating substrates of transparent media using laser pulses, wherein transparent media includes glasses, sapphire and semiconductor substrates and the like.

Background of the invention

Glasses and crystalline transparent materials find more and more applications in industry every year. This fact stimulates development of fabrication methods for these materials. Laser fabrication of transparent materials becomes one of main methods designed for semiconductor, microelectronics and micro-optics, MEMS and many more industries. This fabrication involves wide variety of applications that involve cutting, drilling, milling, welding, melting, etc. Among these processes, one that is of particular interest is cutting or separating different types of transparent substrates.

Despite of existing plethora of processes dedicated for this purpose, there still is a need for improvement in cutting and separating glass or other transparent substrates. It is of great interest to have a faster, cleaner, cheaper, more repeatable, and more reliable method of separating transparent substrates than what is currently practiced in the market. Accordingly, a need exists for alternative improved methods for separating glass substrates.

Methods of separating these substrates include forming a contour line in the transparent workpiece. Forming the contour line includes directing a pulsed laser beam oriented along a beam pathway and output by a beam source through an optical element such that the portion of the pulsed laser beam directed into the transparent workpiece generates an induced absorption within the transparent workpiece that produces a defect within the transparent workpiece. Most efficient way of forming separation contour lines is shaping the beam in such way that said defects are connected by cracks appearing in the volume of the workpiece and in between the defects. Such contour forming allows using larger distances between created defects, i.e. , in total, lesser number of the defects is required. Along with that, giving preferred direction of cracking that coincides with planned contour line improves smoothness of the separation surface because random cracks around defects are eliminated or, at least, significantly reduced. Consequential separation parts of the workpiece occurs due to release of the workpiece material by applying mechanical stress (bending, pressing), thermal shock (e.g., irradiating by CO2 laser as in US20180057390A1 T.Hackert et al., Laser cutting and processing of display glass compositions, 2015, cooling like in US8051679B2, A.Abramov et al., Laser separation of glass sheets, 2008 ) or chemical agitation (e.g., US10391588B2, E. Abbas Hosseini, Method and system for scribing brittle material followed by chemical etching, 2016, US10941069B2, Malte Kumkar, Processing a plate-like workpiece having a transparent, glass, glass-like, ceramic and/or crystalline layer , 2016).

Creating cracks directed along desired cut line efficiently occurs by producing defects elongated along said cut line. It is obvious that material response to energy placed in the body of the workpiece will have the form equal or close to the form of the zone of energy accumulation, i.e., shape of the focal area of the laser beam delivery optics. There are several methods for shaping laser beam to achieve focal points or lines that are elongated in the plane transversal to direction of light propagation. EP2965853B1 , V.Matylitsky and F. Hendricks, Processing of material using elongated laser beams, 2014, presents a method for creating contour line consisting of cracks that spread along with long axis of elliptical focal spot of focusing optics comprising cylindrical lens. This method enables achieving cracks significantly longer than long axis of the ellipse in the focal plane. Main shortcoming of presented method is small size of the focal zone in direction of light propagation that causes necessity of making several paths on different depths into material to achieve cracking over entire thickness of the workpiece. This means extending time of fabrication and raises additional requirements to positioning accuracy that shall enable placing contours of different depths on exactly same cutting surface. More efficient way of producing cracks over entire cut surface is using focal lines instead of focal spot. Non-diffracting, more precisely, quasi non-diffracting beams (QNDB) can be focused inside the workpiece with the intensity nearly constant through entire thickness, which enables forming cracks along desired separation surface. Scientific papers presented possibility to create elongated damages by QNDB. Meyer et al. in Single-shot ultrafast laser processing of high-aspect-ratio nanochannels using elliptical Bessel, Optics Letters, vol.42, No 21, 4307-4310, 2017, suggested a method for shaping a QNDB by blocking part of its spatial spectrum in Fourier plane resulting in quasi-Mathieu beam in focal line. This method supposes significant loss of the energy proportional to blocked area of the spatial spectrum. Zhikun Yang et al. in Research on the special bottle beam generated by asymmetric elliptical Gaussian beams through an axicon-lens system, Optics and Lasers in Engineering v. 126, 105899, 2019 suggested another way for creating quasi-Mathieu beam that employs elliptical Gaussian beams. This method requires additional elements for shaping incident beam from axisymmetric form to one having elliptical cross section. Dudutis et al. in Aberration-controlled Bessel beam processing of glass, Opt. Express, v.26, iss.3 3627-3637, 2018 presented a possibility to use an elliptically shaped quasi-Bessel beam that is formed by tilted axicon in glass fabrication. This method, however, creates QNDB having uniform elliptical cross section in relatively short range. Experimental results presented in said paper show that efficient cracking of the glass is achieved only in ~1/3 of the Bessel zone formed by tilted axicon. Starting with EP3922793B1 , M.K.Bhuyan et al., High speed laser processing of transparent materials, 2013, many methods were developed that enable forming free form cut surface by means of QNDB. Relevant to present invention, there are US10882143B2 M.Kumkar et al., System for asymmetric beam shaping, 2014, that presents a principle for forming asymmetric QNDB by means of spatial light modulator or diffractive optical element and US10620444B2, M.Kumkar et al., Diffractive optical beam shaping element, 2014, that presents design of diffractive optical element suited for above purpose. However, most of the asymmetric beams described in above inventions do not have transversal shape, which would enable crack formation along desired cut line. Only example of the shape resulting in transversally elongated damage of the target is Mathieu beam, which was created by phase mask that requires blocking significant part of the beam incident to optical scheme and, therefore, relates to significant loss of the energy. Along with that, the beam presented in said invention consists of many beamlets elongated perpendicularly to the desired contour line while only envelope of said set of beamlets is elongated in direction of the said line. Said shape requires very precise balancing of the energy among beamlets inside the envelope otherwise undesired cracks appear along said beamlets and, therefore, make roughness of the separation surface much higher. US10047001B2, J. A. West, G/ass cutting systems and methods using non-diffracting beams, 2015, presents system that uses diffractive element in the path of QNDB formation that results in forming multiple QNDB’s in the glass volume located along desired contour line. However, having adjacent perforations of glass made by QNDB does not necessarily create cracks along symmetry plane of those adjacent perforations. The matter is that each perforation is surrounded by own plurality of cracks while cracks from neighboring perforations often enhance each other in direction perpendicular to the axis of said multiple QNDB’s and not in direction of desired contour.

In US10730783B2, R.K.Akarapu et al., Apparatuses and methods for laser processing transparent workpieces using non-axisymmetric beam spots, 2016, one particular embodiment (Fig. 4) utilizes aspheric QNDB forming element that is radially offset relatively to beam pathway, which results in asymmetric transversal shape of QNDB. However, offsetting beam forming element causes up to 4 times energy loss when considering non-diffracting part of the beam behind that element. Another embodiment (Fig. 5A and 5B) presented in above invention applies partial blocking of the beam incident to optical assembly. The blocking can be sector (5A) or slit (5B). It is obvious that blocking part of the incident beam causes significant losses of pulse energy while the shape of QNDB downstream from aspheric optics comprises sequence of maxima positioned in the row. Such distribution does not cause straight line damages or cracks that would be suitable for successful separation of the workpiece.

Most of existing solutions for efficient separating glass, sapphire, semiconductor substrates and their likes by laser light utilize focal zones that are transversally elongated in direction of desired separation line. Optical schemes that provide beam forms suitable for said elongation employ number of elements that must be precisely centered on optical axis of beam forming optics. Any misalignment of elements influences size and shape of elongation of the focal zone when rotating beam shaper aiming to produce free form separation line. This variation of elongation causes irregularity of cutting line, which, consequentially, results in higher roughness of the cut surface

Solution closest to present invention is described in US10730783B2, R.K.Akarapu et al., Apparatuses and methods for laser processing transparent workpieces using non-axisymmetric beam spots, 2016, as embodiment of Figs. 25, 28. In this embodiment, a QNDB is created from Gaussian beam with circular polarization and spatial spectrum of the QNDB is manipulated in Fourier plane of optical assembly. Manipulation is done by means of sectorial quarter-wave plate SQWP that comprises two equal segments with fast axes of these making right angle. Due to this manipulation, beam parts passing different segments are de-cohered and, therefore, build transversally asymmetric focal line. As a result, damages created in the workpiece are elongated in the direction perpendicular to the symmetry axis of SQWP. Rotating SQWP around the axis of the beam leads to equivalent rotation of the damages in the workpiece. This embodiment presents efficient shaping of the beam that enables forming focal line elongated transversally to direction of propagation and said line creates damages of controllable direction that demonstrate cracks oriented along desired cut contour.

However, known method and apparatus applies double conversion of polarization - first, original linear polarization of laser beam is converted to circular one by means of quarter-wave plate and second, after forming QNDB by means of aspheric optics, SQWP is employed to create two sub-beams of linear polarization oriented perpendicularly between these sub-beams. This method requires at least five elements along laser beam path that shall be precisely centered to achieve desired result. Such optical assembly is sensitive to axial deviations of each element and, therefore, repeatability of the form and direction of the damage and consequential cracks in the workpiece depending on rotational position of SQWP is hard to achieve. As the consequence, the cleanness or roughness of the cut surface may change depending on the direction of the axis of asymmetric focal line. In known optical systems and in the event of forming transversally elongated Gaussian focus, at least two elements are required: 1 ) beam splitter and 2) a lens. At least three elements are used for the event of forming QNDB with transversally elongated shape: 1 ) Bessel beam forming element (refractive or reflective axicon or diffractive/phase element emulating its behavior), 2) element manipulating spatial spectrum of Bessel beam and 3) focusing lens.

Technical problem to be solved

Present invention aims to simplify optical scheme of laser beam shaping device by reduction of number of elements along with improving repeatability of the damages created by laser beam shaping device in the workpiece to be processed. Disclosure of the essence of the invention

In order to solve the above problem, according to the proposed pulsed laser beam shaping device for laser processing of a material transparent for the laser beam, comprising a beam transforming element configured to convert an incident pulsed laser beam into two sub-beams, spaced apart one another and having orthogonal polarizations with respect to each other, and focusing means, located downstream from the transforming element that shapes focal spot or focal line in the form having transversally elongated cross section, wherein said transforming element is configured to impose a pattern of light’s Pancharatnam-Berry Phase wherein said transforming element comprises at least one first metamaterial that is configured for imposing the evolution of the polarization state of the pulsed laser beam incident onto the transforming element while said metamaterial is located in two adjacent homogeneous zones connected over single flat surface and each of those zones acts as a half-wave plate while the angle between fast axes of said half-wave plates is equal to 45°.

The beam transforming element further comprises a least one second metamaterial located downstream from the first metamaterial.

The second metamaterial is a metamaterial emulating a biprism configured for imposing divergence of said sub-beams.

The second metamaterial is a metamaterial which forms a non-diffracting beam.

The beam transforming element comprises two second metamaterials located sequentially downstream from the first metamaterial.

The focal spot or focal line with transversal cross section elongated in direction of the line connecting axes of sub-beams wherein longer dimension of said elongated cross section is 1 ,5 times or more bigger than shorter dimension.

The incident pulsed laser beam is a Gaussian beam.

Advantages of the invention

Present invention enables simplifying optical scheme of laser beam shaping device by reducing number of elements for forming two sub-beams, which have orthogonal polarizations with respect to each other and to create a non-diffracting beam, required for forming transversally elongated focal spot over entire non-diffracting region. This is achieved by means of combining several functions in one element. Due to manipulating Pancharatnam-Berry phase, incident laser beam is split into two sub-beams having perpendicular polarizations and same element later focuses the beam into Gaussian focal spot or quasi-Bessel zone.

Brief description of drawings

Fig.1 presents elements of suggested beam shaping device.

Fig.2 presents a picture of single nanostructure plurality of which build a metamaterial that introduces Panchratnam-Berry phase of the light passing through said metamaterial.

Fig.3 explains the mechanism of Pancharatnam-Berry phase appearance in the light travelling through a nanostructure presented in Fig.2.

Fig.4 presents design of suggested light transforming element intended for beam shaping.

Fig.5 presents calculated distribution of light intensity beyond the element valid for the event when the surface of connection of metamaterial zones (Fig.4) is located on the axis of laser beam.

Fig.6 presents measured distribution of light intensity beyond the element in the event when the surface of connection of metamaterial zones (Fig.4) is located on the axis of laser beam.

Fig.7 presents intensity of the light in Y direction measured along the vertical line shown in Fig.6.

Fig.8 presents intensity of the light in X direction measured along the horizontal line shown in Fig.6.

Fig.9 presents cross section of intensity in Rayleigh zone when focusing distribution from Fig.6 with spherical lens of 10 cm focal length.

Fig.10 presents cross section of intensity distribution beyond refractive axicon placed in the path of sub-beams. 10a presents a photograph of the beam, 10b demonstrates distribution of the intensity along long axis of the beam cross section, 10c presents distribution of the intensity along short axis of one.

Fig.11 presents phase (11a) and retardance (11 b) of metamaterial inscribed in the element that emulates refractive biprism. Fig.12 presents cross section of beam intensity in Rayleigh zone of spherical lens with focal length of 10 cm.

Fig.13 presents intensity cross section of quasi non-diffracting beam in Bessel zone formed by refractive axicon with apex angle of 176°

Fig. 14 presents embodiment of the invention in beam delivery module intended for use in laser microfabrication setups.

Fig. 15 presents application of beam delivery module in laser microfabrication.

Fig. 16 presents design of element combining beam transforming and focusing functionalities for the event when focusing is performed by an axicon.

Fig.17 presents design of element combining beam transforming and sub-beam divergence functionalities

Fig.18 presents design of element combining beam transforming, sub-beam divergence and focusing functionalities for the event when focusing is performed by an axicon

Fig.19 shows measured intensity distribution in Bessel zone of the axicon without placing the element of present invention in the beam path: a) distribution in XY plane; b) distribution in XZ plane; c) distribution in YZ plane; d) measured intensity along symmetry axis in XZ plane.

Fig.20 shows measured intensity distribution in Bessel zone of an axicon in the event when element 4 is located upstream of said axicon: a) distribution in XY plane; b) distribution in XZ plane; c) distribution in YZ plane; d) measured intensity along symmetry axis in XZ plane.

Fig.21 presents measured intensity distribution in Bessel zone of an axicon placed downstream from element when rotating said element by following angles: a) 0; b) TT/4; C) TT/2; d) 3 TT/4; e) IT.

Fig.22 presents damages made in glass by focusing Bessel zone presented in Fig.18 at different angles of rotating the element.

Fig.23 presents damages made in glass by focusing Bessel zone depicted in Fig.19 as well as cutting line created be joining these damages. Fig.24 presents damages in glass made by focusing Bessel zone presented in Fig.20 as well as joined in cutting line ones by connecting cracks directed along elongation of the beam shape.

Fig.25 presents the feature cut in 2.135 mm thick glass by the beam shaped with element into Bessel zone as in Fig.17 and focused by optical scheme same as used in Fig.20.

Fig.26 presents side view on curved cut of Fig.22.

Detailed description of the invention

Manipulation of Pancharatnam-Berry (geometric) phase is powerful tool to achieve this goal. Following actions are to be performed to construct transversally elongated focal zone (Rayleigh zone of Gaussian focus or quasi non-diffracting beam). Linearly polarized axisymmetric pulsed light beam 2 on Fig.1 (e.g., TEMoo mode) of laser 1 with Gaussian intensity distribution 3 approaches the element 4, volume of which 5 or entry 6 or exit 7 surfaces contain laser inscribed nanostructures 10.

Said nanostructures comprise plates with modified features of the material. This modification can be induced microporosity of glassy material and said microporosity most efficiently emerges in fused silica. The plates are located periodically with the pitch p smaller than wavelength of inscribing light , namely p = A/2n where n is refractive index of the material. The orientation of the plates is perpendicular to polarization of inscribing light 11 on Fig.2. Said periodic structures act as half-wave plates with fast (extraordinary) axis 12 oriented perpendicularly to the orientation of the plates.

When light passes through an isotropic medium, the phase shift 6 named dynamic phase is introduced that depends on thickness of the medium d, refractive index n characteristic for wavelength of the light A Introduced phase is equal to:

2TT _

8 = —nd# (1) A.

Meanwhile, when light passes through birefringent medium like nanostructure presented in Figs.2-3, there are two terms of refractive index present, ordinary r?₀ and extraordinary r?_E that, as mentioned above, cause different phase shifts for ordinary and extraordinary components of the light, which results in total phase shift like below: First term in equation (2) represents dynamic phase the same as in equation (1 ) while second term 2(|> is called geometric or Pancharatnam-Berry phase.

In the case of linear polarization of impinging light, introduced Pancharatnam-Berry phase results in rotation of the polarization vector. Specifically, when linearly polarized light having polarization direction 13 traverses nanostructure 10 with fast axis directed in angle with relation to said polarization, direction of polarization vector of the light exiting that nanostructure rotates by the angle a = 26 as it is shown on Fig.3.

Plurality of such nanostructures, usually being ~2-4 pm in diameter and having various individual orientations, build a metamaterial that forms a pattern of light’s Pancharatnam-Berry Phase which results from the evolution of the polarization state while traversing this metamaterial.

In this invention, the beam transforming element 4 comprises two zones 15 and 16 in Fig.4 with inscribed metamaterials. Said zones are connected over flat surface 17. Inside of each zone, nanostructures have the same orientation and metamaterials built from ones act as half-wave plates while the angle between fast axes of these plates is |3 = TT/4

If axisymmetric linearly polarized laser beam 1 in Fig.1 traverses element 4, two parallel sub-beams 9a and 9b (Figs.1 , 5 and 6) are formed downstream from the element. Sub-beams are linearly polarized, and polarization vectors of the subbeams are perpendicular to each other while distribution of light intensity in said sub-beams is reflectionally symmetric with respect to the plane 8 on Figs.5, 6. Distribution of the intensity in said sub-beams is characterized by elongation in direction parallel to symmetry plane 8 (19 on Fig.6). The length of cross section of the distribution is 2 times or more bigger than the width of it. FWHM of measured distribution of intensity l_L in Y direction along the line 19 in Fig.6, comprises 74 camera pixels (Fig. 7) while FWHM of intensity measured across the distribution in X direction and at the maximum of the curve on Fig.8, l_w comprises 33 camera pixels. This results in ratio l_L/l_w = 2.24 for presented case. When pair of beams 9a and 9b is focused by means of spherical lens, transversal cross section of the Rayleigh zone is elongated (Fig.9) in direction of line 19 connecting maxima of sub-beams 9a and 9b.

Creating quasi non-diffracting (Gauss-Bessel) beam (QNDB) by means of refractive axicon results in focal line with also elongated transversal cross section (Fig.10). The axicon used for this purpose can be refractive, reflective, diffractive, phase or geometric (Pancharatnam-Berry) phase element.

Elongation of the distribution, i.e., ratio of dimensions of long to short axes of transversal cross section can be manipulated by means of adding a biprism downstream from the beam transforming element. This biprism can be refractive, diffractive, phase or geometric (Pancharatnam-Berry) phase element.

Effect of adding a biprism with base angle of 2 mrad in the path of the light is presented in Figs.11-12. This effect applies for focusing the beam with spherical lens (Fig.11 - compare to Fig. 9) as well as creating QNDB by means of axicon (Fig.12 compare to Fig.10).

Description of embodiments

Example of potential embodiment of presented invention is presented in Fig.14. In this embodiment, linearly polarized laser beam 2 having axial symmetry 3 impinges on beam transforming Pancharatnam-Berry Phase element 4 co-located with element emulating a biprism 20, both are fastened in rotational holder 21. In some embodiments, said co-location can be achieved by inscribing two metamaterials in one element (Fig.17)., one with beam transforming function and second one introducing sub-beam divergence Two sub-beams with perpendicular polarizations 9a, 9b are formed beyond this pair of elements. Said sub-beams are focused by means of focusing element 22 that can be spherical or aspherical lens, Fresnel lens, refractive, reflective, diffractive, phase or geometric (Pancharatnam-Berry) phase axicon. In some embodiments, metamaterial 5 of element 4 and element 22 can be combined in one by inscribing two metamaterials providing functionality of element 4 and element 22 in one substrate (Fig.16). E.g., metamaterial like in Fig.4 can be inscribed in the substrate upstream to metamaterial emulating axicon in the same substrate, in some embodiments, three metamaterials can be inscribed in one element (Fig.18) providing beam transforming, sub-beam divergence and focusing functions. Focusing element builds an image 23 that has length in direction of light propagation equal to Rayleigh zone of the lens or equal to Bessel zone of the axicon. Said image is elongated in direction perpendicular to light propagation 24 while long axis of this elongation lies in plane crossing maxima of sub-beams 9a and 9b. 4f system is built from lenses 25,26 and aims to transpose the image by adjusting its size to dimensions of the workpiece in working zone 27. In some embodiments, spatial filters 28 may be applied to modify beam spatial spectrum in Fourier plane of 4f system, e.g., to block undesirable parts of the image or optical noise appearing in the system. All described elements are mounted in closed housing and build beam delivery system 29.

Possible application of beam delivery system in laser microfabrication device is presented in Fig 15. Laser 1 emits light beam 2 that is adjusted to the purpose of fabrication by means of the attenuator 30 constructed from rotatable half-wave plate 31 and polarizer 32. Rotating half-wave plate 31 with polarizer 32 downstream from it allows pre-defining energy of the laser pulse entering beam delivery system to correspond to fabrication demand. Beam size is adjusted to the size of working zone on beam shaping element 4 by means of adjustable Galilean telescope 33. Beam delivery system 29 prepares the image 27 with required size and energy to be placed in the workpiece 34 that is fastened on XYZ positioning system 35. Moving the workpiece in XYZ directions along with rotating the element by means of rotational holder 21 enables making free form 3D cuts in transparent materials.

Advantage of present invention can be demonstrated by comparing fabrication of the glass by means of QNDB created by an axicon without element of present invention with the results achieved when element 4 is implemented in beam delivery system. In the first case, axicon located in the beam path builds a QNDB having intensity distribution presented in Fig.19. Reduced image of that distribution is located in transparent workpiece for making damages that build cutting contours in said workpiece. In Fig. 23, we see result of laser pulses focused inside of the glass while single pulse energy increases from bottom to the top. One can see that, at high energies, cracks in the material surround focal point and these cracks have random orientations. This means that, if damages of low energy with no or little cracking are used for cutting, then these shall be placed next to each other (3-4 pm for the bottom row in Fig. 23) to build cutting line. Increasing pulse energy allows bigger distance between damages but, in this case, cracks propagating aside from the cutting line cause chipping of the edges and big roughness of the cut surface. Employing beam transforming element from this invention in beam delivery system depicted in Fig.15 allows efficient rotating of the elongated beam shape seen in Fig.20. Rotation of the element 4 by means of rotational holder 21 causes rotation of intensity distribution on the beam that follows orientation of the element regarding beam axis (see Fig.21. Consequentially, damages created in transparent material follow orientation of elongation of the shape like it is presented in Fig.22. Elongated damages cause cracking the material along direction of elongation in cross section of focused beam, which allows placing damages at significant distance from each other. For embodiment used to make damages in Fig.24, the distance between damages is 20 pm or more. Consequentially, it means that cutting speed increases compared to conventional quasi-Bessel beam at the same laser pulse repetition rate (compare Figs. 23 and 24). One of practical embodiments of present invention that utilizes beam delivery system as in Fig.15 was used for high-speed cutting of 2.135 mm thick glass with high precision. Figs 25 and 26 present top and side views of the cut in said glass. It is worth noting that focus line of the beam shape created by the element 4 being essence of this invention is quite homogeneous in the direction of light propagation. This results in homogeneous cut surface over entire thickness of the fabricated workpiece (Fig. 26).

Claims

1 . Pulsed laser beam shaping device for laser processing of a material transparent for the laser beam, comprising a beam transforming element configured to convert an incident pulsed laser beam into two sub-beams, spaced apart one another and having orthogonal polarizations with respect to each other, and focusing means, located downstream from the transforming element that shapes focal spot or focal line in the form having transversally elongated cross section, characterized in that said transforming element (4) is configured to impose a pattern of light’s Pancharatnam-Berry Phase wherein said transforming element (4) comprises at least one first metamaterial (5) that is configured for imposing the evolution of the polarization state of the pulsed laser beam incident onto the transforming element (4) while said first metamaterial is located in two adjacent homogeneous zones (15, 16 ) connected over single flat surface (17) and each of those zones acts as a half-wave plate while the angle between fast axes of said half-wave plates is equal to 45°.

2. Device of claim 1 , characterized in that the beam transforming element (4) further comprises at least one second metamaterial located downstream from the first metamaterial (5).

3. Device of claim 2, characterized in that that the second metamaterial is a metamaterial (20) emulating a biprism configured for imposing divergence of said sub-beams.

4. Device of claim 2, characterized in that the second metamaterial is a metamaterial (22) which forms a non-diffracting beam.

5. Device of claim 2, characterized in that the beam transforming element (4) comprises two second metamaterials (20) and (22) located sequentially downstream from the first metamaterial (5).

6. Device of claim 1 , characterized in that the focal spot or focal line with transversally cross section elongated in direction of the line connecting axes of subbeams wherein longer dimension of said elongated cross section is 1 ,5 times or more bigger than shorter dimension.

7. Device of claim 1 , characterized in that the incident pulsed laser beam is a Gaussian beam.