WO2024184323A1

WO2024184323A1 - A nuclear fusion system for producing energy and a method for ignition of a nuclear fusion process

Info

Publication number: WO2024184323A1
Application number: PCT/EP2024/055625
Authority: WO
Inventors: Regina GUMENYUK; Marco ORNIGOTTI
Original assignee: Tampere University Foundation Sr
Priority date: 2023-03-09
Filing date: 2024-03-04
Publication date: 2024-09-12

Abstract

A system for ignition of a nuclear fusion process comprises a laser source (101) configured to direct a laser beam (102) to a fuel system (103) of the nuclear fusion process The laser source is configured to generate the laser beam such that the laser beam is an orbital angular momentum OAM carrying laser beam. The laser beam carrying the OAM is capable of generating, via the inverse Faraday effect, a strong axial magnetic field in plasma, whose magnitude grows as a square of an OAM parameter indicative of vorticity of the laser beam. The strong axial magnetic field is, in turn, capable of accelerating particles and collimating and guiding a particle beam to ignite the nuclear fusion process. Furthermore, the laser beam carrying the OAM lowers electron thermal conductivity thus allowing a near- adiabatic compression at a lower implosion velocity, and enhances plasma confinement during the nuclear fusion process.

Description

A nuclear fusion system for producing energy and a method for ignition of a nuclear fusion process

Field of the disclosure

The disclosure relates to generally to nuclear fusion. More particularly, the disclosure relates to a method for ignition of a nuclear fusion process. Furthermore, the disclosure relates to a nuclear fusion system for producing energy.

Background

Nuclear energy can be released by a nuclear fusion process where light atomic nuclei are fused to form heavier atomic nuclei, releasing energy E=Amc² where Am is a nuclear mass defect taking place in the fusion process and c is the speed of light in vacuum. This released energy can be approximately 10 MeV per each fusion reaction.

In many nuclear fusion systems, fuel material which has been compressed by laser beams cannot be self-triggered because compressing laser pulses do not possess enough intensity and energy. A fuel system of a nuclear fusion system may comprise for example deuterium + tritium “DT” fuel material. To ignite a nuclear fusion process in the fuel system, an additional high intensity, ultrashort laser pulse can be introduced for generating and accelerating a particle beam to achieve sufficient ignition energy. Typically, protons or ions are considered as the best option for particles of the above-mentioned particle beam. When such a particle beam enters a fuel system, the particle energy is rapidly deposited in a small volume and, as a corollary, ignition of the nuclear fusion process takes place.

In the above-described ignition scheme, it can be challenging to generate a particle beam such that the particle beam possesses properties leading to efficient ignition of a nuclear fusion process. Typically, the challenges are mainly related to a large energy spread and divergence of a particle beam. The divergence of a particle beam can be reduced by a sufficiently strong magnetic field which collimates and guides the particle beam so that sufficient particle energy is deposited in a sufficiently small volume and thereby ignition of a nuclear fusion process takes place. The required magnetic field can be generated by a solenoidal coil driven by a pulsed laser, or the required magnetic field can be generated by a self-generated toroidal magnetic field at a rear side of a foil target on which a laser beam is directed. An inconvenience related to the solenoidal coil is that the solenoidal coil is typically destroyed after one shot. Correspondingly, an inconvenience related to the foil target is that the foil target is typically destroyed after one shot.

Summary

The following presents a simplified summary to provide a basic understanding of some aspects of various embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts in a simplified form as a prelude to a more detailed description of exemplifying and non-limiting embodiments.

In this document, the word “geometric” when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a planar or non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional.

In accordance with the invention, there is provided a new nuclear fusion system for producing energy. The nuclear fusion system comprises:

- a fuel system comprising fuel material of a nuclear fusion process, e.g. deuterium + tritium “DT” fuel material, and

- an ignition system comprising a laser source configured to ignite a nuclear fusion process within the fuel system.

The above-mentioned laser source is configured to direct a laser beam to the fuel system comprising the fuel material of the nuclear fusion process, wherein the laser source is configured to generate the laser beam such that the laser beam is an orbital angular momentum “OAM” carrying laser beam i.e. an 0AM laser beam. In this document, the orbital angular momentum “OAM” means the internal i.e. intrinsic orbital angular momentum of a laser beam.

The orbital angular momentum “OAM” of a laser beam is the component of the angular momentum of the laser beam that is dependent on a spatial distribution, rather than polarization, of the laser beam. The orbital angular momentum is an angular momentum independent of a location of the origin of a coordinate system, and it is associated with the helical, i.e. twisted, wavefront of the laser beam. The orbital angular momentum is characterized by a signed integer I, called an OAM parameter which defines the vorticity of the laser beam. A laser beam having the OAM parameter I, for example, is characterized by a l-folded helical wavefront, and the spatial intensity distribution of such a laser beam has the characteristic doughnut, i.e. ring, shape, with the dimension of the ring scaling with the square root of the OAM parameter I.

The laser beam carrying the OAM is capable of generating, via the inverse Faraday effect, a magnetic field having a strong axial component in plasma, such that magnitude of the axial magnetic field component grows as a square of the OAM parameter of the laser beam. In this document, the axial means a direction parallel with a propagation direction of the laser beam. The strong axial magnetic field component is, in turn, capable of accelerating particles and collimating and guiding a particle beam to ignite the nuclear fusion process in the fuel system. Thus, in conjunction with the invention, there is provided a more effective way to generate the magnetic field than in the known technologies mentioned in the backgroundsection of this document.

Furthermore, a magnetic field generated by a laser beam carrying the OAM lowers electron thermal conductivity thus allows a near-adiabatic compression of fuel material at a lower implosion velocity. In typical standard methods, the implosion velocity needs to be about 300 km/s, whereas an implosion velocity about 100 km/s can be sufficient when a magnetic field generated by a laser beam carrying the OAM is present.

Furthermore, a magnetic field generated by a laser beam carrying the OAM enhances plasma confinement during the nuclear fusion process, thus relaxing the Lawson criterion and reducing the convergence ratio, while maintaining sufficient areal density to support the fusion reactions in the central part of the laser beam.

In accordance with the invention, there is also provided a new method for igniting a nuclear fusion process. The method comprises directing a laser beam to a fuel system comprising fuel material of the nuclear fusion process, wherein the laser beam is an orbital angular momentum “OAM” carrying laser beam.

Exemplifying and non-limiting embodiments are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and nonlimiting embodiments when read in conjunction with the accompanying drawings.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of unrecited features.

The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

Brief description of the figures

Exemplifying and non-limiting embodiments and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figure 1 illustrates a nuclear fusion system according to an exemplifying and nonlimiting embodiment, figures 2a, 2b, 2c, 2d, and 2e illustrate OAM laser sources of systems according to exemplifying and non-limiting embodiments for igniting a nuclear fusion process, figures 3a, 3b, 3c, and 3d illustrate functionality of a system according to an exemplifying and non-limiting embodiment for igniting a nuclear fusion process, figures 4a and 4b illustrate nuclear fusion systems according to exemplifying and non-limiting embodiments, and figure 5 shows a flowchart of a method according to an exemplifying and non-limiting embodiment for igniting a nuclear fusion process.

Description of the exemplifying embodiments

The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated.

A photon with a helical phase front, so-called twisted photon, is said to carry orbital angular momentum “0AM”, which is an angular momentum distinct from the spin angular momentum “SAM”, i.e. , polarization, also carried by photons. At the heart of 0AM there is a phase singularity, around which the phase front winds an integer number of times, resulting in a topological structure on its wavefront with integer topological charge, i.e. the 0AM. At the location of the phase singularity, the phase of the photon is undefined, and polarization and amplitude must be zero, in order to compensate this divergence. This results in a dark center of the wave, sometimes referred as a “doughnut” intensity profile. Optical beams, or photons, carrying 0AM are typically described by Laguerre-Gaussian modes in the paraxial regime, and Bessel modes in the nonparaxial one.

Figure 1 illustrates a nuclear fusion system according to an exemplifying and nonlimiting embodiment. The nuclear fusion system comprises a fuel system 103 comprising fuel material that can be for example deuterium + tritium “DT” fuel material. The nuclear fusion system comprises an ignition system for igniting a nuclear fusion process in the fuel system 103. The ignition system is a system according to an exemplifying and non-limiting embodiment of the invention, wherein the system comprises a laser source 101 configured to generate an orbital angular momentum “0AM” carrying laser beam 102 to ignite the nuclear fusion process in the fuel system 103. The nuclear fusion system may further comprise a plasma generation laser source 104 configured to direct another laser beam 105 to the fuel system 103 to generate plasma within the fuel system 103. It is also possible that sufficient plasma generation is achieved with the 0AM laser beam 102 alone, and thus there is no need for the laser source 104. The 0AM laser beam 102 can be a laser pulse whose temporal duration can be for example from 10 fs to 100 ns. It is also possible that the 0AM laser beam 102 consists of two or more temporally successive laser pulses.

Figures 2a, 2b, 2c, 2d, and 2e illustrate 0AM laser sources of systems according to exemplifying and non-limiting embodiments for igniting a nuclear fusion process. Figure 2a shows an exemplifying case where the 0AM laser source comprises a source 206a for generating a transverse electro-magnetic “TEM” wave-mode laser beam 207a and a spiral phase plate 208 configured to convert the TEM wave-mode laser beam to an 0AM carrying laser beam 202a. The spiral phase plate 208 is a piece of transparent material such as glass, whose optical thickness increases with azimuthal position. The gradient of thickness is designed to satisfy the conditions for a particular wavelength and 0AM parameter. It is also possible to use a circularly polarized laser beam instead of the TEM wave-mode laser beam 207a.

Figure 2b shows an exemplifying case where the 0AM laser source comprises a source 206b for generating a TEM wave-mode laser beam 207b and a double pitchfork hologram 209 configured to convert the TEM wave-mode laser beam to an 0AM carrying laser beam 202b. The double pitch-fork hologram 209 can be for example a computer-generated hologram whose surface pattern is suitably designed to create phase singularities in the propagating beam, by creating phase dislocations in the phase front of the beam. It is also possible to use a circularly polarized laser beam instead of the TEM wave-mode laser beam 207b.

Figure 2c shows an exemplifying case where the 0AM laser source comprises a source 206c for generating a TEM wave-mode laser beam 207c and a spatial light modulator 210 configured to convert the TEM wave-mode laser beam to an 0AM carrying laser beam 202c. In the spatial light modulator 210, a required phase profile pattern to generate the 0AM laser beam is implemented with a liquid-crystal-based plate. By programming with the aid of a video interface of a computer, the phase profile pattern can be modified in a desired way in real-time. It is also possible to use a circularly polarized laser beam instead of the TEM wave-mode laser beam 207c.

Figure 2d shows an exemplifying case where the 0AM laser source comprises a source 206d for generating a circularly polarized laser beam 207d and a Q-plate

211 configured to convert the circularly polarized laser beam to an 0AM carrying laser beam 202d. The conversion functionality of the Q-plate 211 is based on spin- to-orbital angular momentum conversion by geometric phase effects within a liquid- crystal-based plate. Essentially, the conversion functionality of the Q-plate 211 is based on polarization anisotropy or symmetry breaking in suitably patterned structures.

Figure 2e shows an exemplifying case where the QAM laser source comprises a source 206e for generating a TEM wave-mode laser beam 207e and a twisted fiber

212 configured to convert the TEM wave-mode laser beam to an QAM carrying laser beam 202e. The twisted fiber 212 is a helically structured fiber where a core and a cladding are simultaneously twisted into a helical shape. This optical arrangement forces electromagnetic waves propagating in such fiber to follow helical trajectories around the core, thus producing azimuthal momentum and, therefore, the QAM. It is also possible to use a circularly polarized laser beam instead of the TEM wavemode laser beam 207e.

An QAM laser beam produced by any of the ways described above with reference to figures 2a-2e is advantageously amplified in plasma via non-linear interaction between electromagnetic radiation and the plasma.

It is to be noted that the technologies illustrated in figures 2a-2e for producing an orbital angular momentum “QAM” carrying laser beam, i.e. an QAM laser beam, are examples only, and embodiments of the invention are not limited to these exemplifying ways to produce an QAM laser beam, but different ways to produce an QAM laser beam are possible, too. Figures 3a, 3b, 3c, and 3d illustrate functionality of a system according to an exemplifying and non-limiting embodiment for igniting a nuclear fusion process. In figure 3a, a fuel system 303 that comprises fuel material, e.g. DT fuel material, is irradiated with an 0AM laser beam 302. Material of the fuel system 303 gets ionized and plasma 314 formation takes place. The plasma 314 can be generated by another laser beam or by the 0AM laser beam 302 only. Figure 3b schematically illustrates magnetic field generation in the plasma by the 0AM laser beam 302 via the inverse Faraday effect. In figure 3b, the magnetic field is schematically depicted with a dashed line 315. The magnetic field 315 has a strong axial component whose magnitude grows as the square of the 0AM parameter of the 0AM laser beam 302.

The dependence of the magnetic field amplitude on the 0AM parameter of the 0AM laser beam indicates that the direction of the axial magnetic field component and/or its magnitude can be controlled by changing the sign of the 0AM parameter and/or its value, respectively. An 0AM laser pulse whose 0AM parameter is 10, for example will generate a 100 times higher axial magnetic field component than a standard Gaussian pulse. If power of the above-mentioned 0AM laser pulse is amplified to Terawatt “TW’ level, magnetic fields having multi-kilotesla “kT” magnetic flux densities can be generated. The axial magnetic field component accelerates and guides particles, such as protons and/or electrons and/or ions, which constitute a particle beam that ignites the nuclear fusion process in the fuel system 303.

Furthermore, the magnetic field 315 generated by the 0AM laser beam 302 lowers electron thermal conductivity and thus allows a near-adiabatic compression of the fuel material at a lower implosion velocity. In typical standard methods, the implosion velocity needs to be about 300 km/s, whereas an implosion velocity about 100 km/s can be sufficient for the near-adiabatic compression when the magnetic field 315 generated by the 0AM laser beam 302 is present.

In addition, the magnetic field 315 generated by the 0AM laser beam 302 can also enhance a confinement of a-particles during the nuclear fusion process, thus relaxing the Lawson criterion and reducing the convergence ratio, while maintaining sufficient areal density to support the fusion reactions in a central part of the 0AM laser beam. In figure 3c, the central part of the 0AM laser beam is a horizontally hatched area denoted with a reference 316. Figure 3d schematically depicts a situation in which the nuclear fusion process is active, and some a-particles are escaping from the area where the nuclear fusion process occurs.

An intensity distribution of the axial magnetic field component generated by the OAM laser beam 302, via the inverse Faraday effect, in the plasma can be approximated with the following mathematic equation:

where B is the magnetic flux density of the axial magnetic field component, r is a transversal distance from the center line of the OAM laser beam 302, a is the absorption coefficient of the plasma, P, T, COL, and wo are laser power, pulse duration, carrier frequency, and beam waist i.e. the beam size of the OAM laser beam 302, respectively, n_e is the electron plasma density, 1 is the OAM parameter, cr is the helicity of the OAM laser beam, equal to ±1 for circular polarization, and 0 for linear polarization, and (r) is the transverse intensity distribution of the OAM laser beam 302. In equation 1 , e means the absolute value of the electric charge of an electron.

The first term in the brackets in the above-presented equation is independent of the beam polarization, no cr in the first term. The first term indicates the quadratic dependence of the intensity of the axial magnetic field component on the OAM parameter 1. Moreover, by controlling the sign of the OAM parameter 1 one can regulate the direction of the axial magnetic field component corresponding to the first term in the brackets in the above-presented equation. The OAM laser beam is advantageously circularly polarized so that the helicity r is +1 when the OAM parameter 1 is positive and correspondingly cr is -1 when the OAM parameter 1 is negative to achieve a situation in which the first and second terms in the brackets have a same sign, i.e. the first and second terms in the brackets amplify each other.

The transverse shape of the OAM laser beam has a characteristic ring i.e. doughnut shape, which confines electromagnetic radiation into a ring of thickness equal to the beam size, i.e., wt), whose diameter scales with the square root of the OAM parameter, i.e. with /. This means that the axial magnetic field component will be generated in the region of the plasma, and that the axial magnetic field component can be experimentally controlled using the beam waist wt) and the 0AM parameter 1. The strong localization of the magnetic field in a ring-like structure will then allow for a better radial confinement of a-particles during the fusion process, as they will be forced to remain in the inner region of the 0AM laser beam. This reduces the escape of the a-particles illustrated in figure 3d.

Figure 4a illustrates a nuclear fusion system according to an exemplifying and nonlimiting embodiment. The nuclear fusion system comprises a fuel system 403a that may comprise for example deuterium + tritium “DT” fuel material. The nuclear fusion system comprises an ignition system for igniting a nuclear fusion process in the fuel system 403a. The ignition system is a system according to an exemplifying and nonlimiting embodiment of the invention, wherein the system comprises a laser source 401 configured to generate an 0AM laser beam 402 that bombards a surface of the fuel system 403a to ignite the nuclear fusion process in the fuel system 403a. The nuclear fusion system may further comprise a plasma generation laser source 404 configured to direct another laser beam 405 to bombard the surface of the fuel system 403a to generate plasma 414 in the vicinity of the above-mentioned surface of the fuel system 403a. It is also possible that sufficient plasma generation is achieved with the 0AM laser beam 402 alone, and thus there is no need for the laser source 404.

Figure 4b illustrates a nuclear fusion system according to an exemplifying and nonlimiting embodiment. The nuclear fusion system comprises a fuel system 403b. In this exemplifying case, the fuel system 403b is arranged to constitute two elements 421 and 422. The element 421 is bombarded with an 0AM laser beam 402 and, as a corollary, the element 421 releases accelerated electrically charged particles 420 which, in turn, bombard a surface of the element 422 to ignite a nuclear fusion process in the element 422. The element 422 may comprise for example deuterium + tritium “DT” fuel material. The above-mentioned electrically charged particles 420 can be for example protons, electrons, or ions. The element 421 may comprise for example an aluminum foil in which case the electrically charged particles 420 are protons. Figure 5 shows a flowchart of a method according to an exemplifying and nonlimiting embodiment for igniting a nuclear fusion process. The method comprises directing 501 a laser beam to a fuel system that comprises fuel material of the nuclear fusion process, wherein the laser beam is an orbital angular momentum “0AM” carrying laser beam. Preparatory actions mentioned in figure 5 can be actions according to the prior art. Correspondingly, actions after the ignition may comprise actions according to the prior art. As described above with reference to figures 3c and 3d, the 0AM laser beam, which is a single laser pulse or consists of temporally successive laser pulses, is advantageously maintained during the nuclear fusion process after its ignition.

In a method according to an exemplifying and non-limiting embodiment, the laser beam is circularly polarized so that the helicity of the laser beam is +1 when the 0AM parameter of the laser beam is positive, and correspondingly the helicity of the laser beam is -1 when the 0AM parameter of the laser beam is negative.

A method according to an exemplifying and non-limiting embodiment comprises generating a transverse electro-magnetic “TEM” wave-mode laser beam and converting the TEM wave-mode laser beam to an 0AM carrying laser beam with a spiral phase plate. In a method according to this exemplifying and non-limiting embodiment, it is also possible to use a circularly polarized laser beam instead of the TEM wave-mode laser beam.

A method according to an exemplifying and non-limiting embodiment comprises generating a TEM wave-mode laser beam and converting the TEM wave-mode laser beam to an 0AM carrying laser beam with a double pitch-fork hologram. In a method according to this exemplifying and non-limiting embodiment, it is also possible to use a circularly polarized laser beam instead of the TEM wave-mode laser beam.

A method according to an exemplifying and non-limiting embodiment comprises generating a TEM wave-mode laser beam and converting the TEM wave-mode laser beam to an 0AM carrying laser beam with a spatial light modulator. In a method according to this exemplifying and non-limiting embodiment, it is also possible to use a circularly polarized laser beam instead of the TEM wave-mode laser beam.

A method according to an exemplifying and non-limiting embodiment comprises generating a circularly polarized laser beam and converting the circularly polarized laser beam to an OAM carrying laser beam with a Q-plate based on spin-to-orbital angular momentum conversion by geometric phase effects within a liquid-crystal- based plate.

A method according to an exemplifying and non-limiting embodiment comprises generating a TEM wave-mode laser beam and converting the TEM wave-mode laser beam to an OAM carrying laser beam with a twisted fiber being a helically structured fiber where a core and a cladding are simultaneously twisted into a helical shape. In a method according to this exemplifying and non-limiting embodiment, it is also possible to use a circularly polarized laser beam instead of the TEM wavemode laser beam. The specific examples provided in the description given above should not be construed as limiting the applicability and/or the interpretation of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.

Claims

What is claimed is:

1. A nuclear fusion system for producing energy, the nuclear fusion system comprising:

- a fuel system comprising fuel material of a nuclear fusion process (103), and

- an ignition system comprising a laser source (101 ) configured to ignite a nuclear fusion process within the fuel system, wherein the laser source of the ignition system is configured to direct a laser beam (102, 202a-202e) to the fuel system, characterized in that the laser source is configured to generate the laser beam such that the laser beam is an orbital angular momentum carrying laser beam.

2. A nuclear fusion system according to claim 1 , wherein the laser source (101 ) is configured generate the laser beam such that the laser beam is circularly polarized so that a helicity of the laser beam is +1 when an 0AM parameter of the laser beam is positive, and the helicity of the laser beam is -1 when the 0AM parameter of the laser beam is negative.

3. A nuclear fusion system according to claim 1 or 2, wherein the laser source comprises a source (206a) for generating a transverse electro-magnetic wave-mode laser beam (207a) or a circularly polarized laser beam and a spiral phase plate (208) configured to convert the transverse electro-magnetic wave-mode or circularly polarized laser beam to the orbital angular momentum carrying laser beam (202a).

4. A nuclear fusion system according to claim 1 or 2, wherein the laser source comprises a source (206b) for generating a transverse electro-magnetic wave-mode laser beam (207b) or a circularly polarized laser beam and a double pitch-fork hologram (209) configured to convert the transverse electro-magnetic wave-mode or circularly polarized laser beam to the orbital angular momentum carrying laser beam (202b).

5. A nuclear fusion system according to claim 1 or 2, wherein the laser source comprises a source (206c) for generating a transverse electro-magnetic wave-mode laser beam (207c) or a circularly polarized laser beam and a spatial light modulator (210) configured to convert the transverse electro-magnetic wave-mode or circularly polarized laser beam to the orbital angular momentum carrying laser beam (202c).

6. A nuclear fusion system according to claim 1 or 2, wherein the laser source comprises a source (206d) for generating a circularly polarized laser beam (207d) and a Q-plate (211 ) configured to convert the circularly polarized laser beam to the orbital angular momentum carrying laser beam (202d), a conversion functionality of the Q-plate being based on spin-to-orbital angular momentum conversion by geometric phase effects within a liquid-crystal-based plate.

7. A nuclear fusion system according to claim 1 or 2, wherein the laser source comprises a source (206e) for generating a transverse electro-magnetic wave-mode laser beam (207e) or a circularly polarized laser beam and a twisted fiber (212) configured to convert the transverse electro-magnetic wave-mode or circularly polarized laser beam to the orbital angular momentum carrying laser beam (202e), the twisted fiber being a helically structured fiber where a core and a cladding are simultaneously twisted into a helical shape.

8. A nuclear fusion system according to any one of claims 1 -7, wherein the nuclear fusion system comprises a plasma generation laser source (104) configured to direct a laser beam (105) to the fuel system to generate plasma within the fuel system.

9. A method for igniting a nuclear fusion process, the method comprising:

- directing (501 ) a laser beam to a fuel system comprising fuel material of the nuclear fusion process to ignite the nuclear fusion process within the fuel system, characterized in that the laser beam is an orbital angular momentum carrying laser beam.

10. A method according to claim 9, wherein the laser beam is circularly polarized so that a helicity of the laser beam is +1 when an 0AM parameter of the laser beam is positive, and the helicity of the laser beam is -1 when the OAM parameter of the laser beam is negative.

11. A method according to claim 9 or 10, wherein the method comprises generating a transverse electro-magnetic wave-mode laser beam or a circularly polarized laser beam and converting the transverse electro-magnetic wave-mode or circularly polarized laser beam to the orbital angular momentum carrying laser beam with a spiral phase plate.

12. A method according to claim 9 or 10, wherein the method comprises generating a transverse electro-magnetic wave-mode laser beam or a circularly polarized laser beam and converting the transverse electro-magnetic wave-mode or circularly polarized laser beam to the orbital angular momentum carrying laser beam with a double pitch-fork hologram.

13. A method according to claim 9 or 10, wherein the method comprises generating a transverse electro-magnetic wave-mode laser beam or a circularly polarized laser beam and converting the transverse electro-magnetic wave-mode or circularly polarized laser beam to the orbital angular momentum carrying laser beam with a spatial light modulator.

14. A method according to claim 9 or 10, wherein the method comprises generating a circularly polarized laser beam and converting the circularly polarized laser beam to the orbital angular momentum carrying laser beam with a Q-plate based on spin-to-orbital angular momentum conversion by geometric phase effects within a liquid-crystal-based plate.

15. A method according to claim 9 or 10, wherein the method comprises generating a transverse electro-magnetic wave-mode laser beam or a circularly polarized laser beam and converting the transverse electro-magnetic wave-mode or circularly polarized laser beam to the orbital angular momentum carrying laser beam with a twisted fiber being a helically structured fiber where a core and a cladding are simultaneously twisted into a helical shape.