APPARATUS AND METHOD FOR GUIDING CHARGED PARTICLES

Abstract

An apparatus for guiding, in particular directing or accelerating, charged particles (50), comprising: a substrate (110) having a surface (115); an optically thinner layer (120) formed on the surface (115); an inhomogeneous channel (130) which is formed by two mutually opposite delimiting structures on a side of the layer (120) that is opposite the substrate (110); and a radiation device which is designed to generate at least one pulsed laser beam (140) and inject the at least one pulsed laser beam (140) into the channel (130) from a side that is opposite the optically thinner layer (120). The layer (120) for the laser beam (140) is optically thin, and the delimiting structures have a high optical density in comparison with the layer (120). The delimiting structures are designed to guide the particles (50) by means of the laser beam (140) in the channel (130) and alternatingly focus them along the channel (130) and in at least one direction perpendicular to the channel (130).

Claims

1. An apparatus for guiding charged particles (50), comprising a substrate (110) having a surface (115); a layer (120) on the surface (115); an inhomogeneous channel (130) formed by two mutually opposite delimiting structures on a side of the layer (120) that is opposite the substrate (110); a radiation device which is designed to generate at least one pulsed laser beam (140) and inject the at least one pulsed laser beam (140) into the channel (130) from a side that is opposite the layer (120), wherein the layer (120), for the at least one laser beam (140), is optically thin and the delimiting structures have a high optical density in comparison with the layer (120), and wherein the delimiting structures are designed to guide the particles (50) by means of the at least one laser beam (140) in the channel (130) and thereby alternatingly focus them along the channel (130) and in at least one direction perpendicular to the channel (130).

2. The apparatus according to claim 1, wherein the two delimiting structures of the channel (130) comprise a plurality of acceleration elements (132) which are arranged quasi-periodically in order to achieve focusing via a non-homogeneous phase relation.

3. The apparatus according to claim 2, wherein the delimiting structures comprise a plurality of grounding paths (152), and the acceleration elements (132) are each electrically connected to a separate grounding path (152) in order to divert particles (50) escaping from the channel (130) into the relevant acceleration element (132) away from the channel (130).

4. The apparatus according to claim 2, wherein at least one acceleration element (132) has an elliptical base surface.

5. The apparatus according to claim 2, wherein the layer (120) comprises silicon dioxide and the acceleration elements (132) and the substrate (110) each comprise silicon, and/or wherein the surface (115) is designed to reflect the at least one injected laser beam (140) in order to thereby generate a symmetrical alternating field in the channel (130) and thus guide the particles (50) in the channel (130).

6. The apparatus according to claim 1, wherein the radiation device is designed to inject only one pulsed laser beam (140) perpendicularly or obliquely into the channel (130) from a side that is opposite the layer (120) in order to generate a focusing field which is symmetrical in two directions transversely to the channel (130).

7. A particle accelerator comprising an apparatus according to claim 1, wherein the charged particles (50) are in particular electrons and the radiation device has an optical system to shape the at least one pulsed laser beam (140) and direct said beam perpendicularly or obliquely onto the surface (115).

8. A method for producing an apparatus for guiding charged particles (50), comprising a substrate (110) having a surface (115), a layer (120) formed on the surface (115), an inhomogeneous channel (130) which is formed by two mutually opposite delimiting structures on a side of the layer (120) that is opposite the substrate (110), and comprising a radiation device which is designed to generate at least one pulsed laser beam (140) and inject the at least one pulsed laser beam (140) into the channel (130) from a side that is opposite the layer (120), the method comprising the following steps: providing (S110) a structure with a sequence consisting of an upper layer, the layer (120) and the substrate (110), wherein the layer (120) for the laser beam has a small optical density in comparison with the etching layer; and etching (S120) only the upper layer, thereby forming the delimiting structures of the channel (130).

9. A method for guiding charged particles (50) in an apparatus for guiding charged particles (50), the apparatus comprising a substrate (110) having a surface (115), a layer (120) formed on the surface (115), an inhomogeneous channel (130) which is formed by two mutually opposite delimiting structures on a side of the layer (120) that is opposite the substrate (110), and a radiation device which is designed to generate at least one pulsed laser beam (140) and inject the at least one laser beam (140) into the channel (130) from a side that is opposite the layer (120), the method comprising the following steps: injecting (S210) the at least one laser beam (140) into the channel (130) from a side that is opposite the layer (120), wherein the surface (115) brings about a reflection of the at least one laser beam (140); thereby guiding (S220) the particles (50) in the channel (130); and alternatingly focusing (S230) the particles (50) along the channel (130) and in at least one direction perpendicular to the channel (130).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The embodiments of the present invention will be better understood from the following detailed description and the accompanying drawings of the various embodiments, which should not, however, be interpreted as limiting to the disclosure of the specific embodiments, but only serve the purpose of explanation and understanding.

[0037] FIG. 1 shows two views of an embodiment of an apparatus for guiding charged particles according to the present invention.

[0038] FIG. 2 shows a further view of the embodiment from FIG. 1.

[0039] FIG. 3 illustrates further details for the embodiment from FIG. 2.

[0040] FIG. 4 illustrates the embodiment according to FIG. 1 with grounding paths.

[0041] FIG. 5 shows further views of the embodiment according to FIG. 4.

[0042] FIG. 6 illustrates a field strength in the cross section of a channel for an embodiment.

[0043] FIG. 7 shows steps of an embodiment of a method for producing an apparatus for guiding charged particles.

[0044] FIG. 8 shows steps of an embodiment of a method for guiding charged particles.

DETAILED DESCRIPTION

[0045] FIG. 1 shows two views a, b of an embodiment of an apparatus for guiding charged particles 50 according to the present invention. View a on the left of the figure shows a cross section through a substrate 110 with a reflective surface 115. An optically thin and electrically insulating layer 120 is formed on the surface 115. Furthermore, an inhomogeneous channel 130 can be seen in cross section, which is formed on a side of the electrically insulating layer 120 that is opposite the substrate 110. The channel 130 is formed by two delimiting structures, each of which is designed here as a row of elliptical cylinders as acceleration elements 132. Grounding lines for the delimiting structures are not shown in this figure. Also not shown is a radiation device that generates a pulsed laser beam 140, for which a direction of incidence is indicated by a vertical arrow. The laser beam 140 radiates into the channel from a side that is opposite the electrically insulating layer 120, and here in particular vertically, onto the optically thin layer 120. The laser beam 140 penetrates the optically thin layer 120. The surface 115 brings about a (partial) reflection of the laser beam 140, and the channel 130 is designed in such a way that the laser beam 140 and the reflection in the channel 130 produce an electromagnetic alternating field which, in view a, guides, i.e. in particular directs and/or accelerates, the particles 50 with a flight direction that runs vertically onto the cross-sectional plane shown. In addition, the channel 130 is designed such that the electromagnetic alternating field is suitable for alternatingly focusing the particles 50 in the direction of the channel 130 and in at least one direction perpendicular to the channel 130 (for example orthogonally to the direction of incidence of the laser beam 140 and to the direction of the channel 130).

[0046] View b on the right of the figure shows a perspective view of the channel 130. In the present embodiment, the channel 130 is delimited or formed on the optically thin layer 120 by the large number of acceleration elements 132 which comprise silicon and have an elliptical base surface. The acceleration elements 132 form a delimitation of the channel 130 by their arrangement in two rows, with two acceleration elements 132 facing each other in pairs. There is a refractive index contrast between the acceleration elements 132 and the optically thin layer 120, i.e. said elements have a higher optical density or a higher refractive index than the layer 120. A difference in a refractive index of the acceleration elements 132 and a refractive index of the layer 120 can be of a factor of 1.5 or more. The distances between the acceleration elements 132 are adapted to a speed of the particles 50 along the channel 130; the length of the individual cell λ.sub.g=βλ (for example the distance between two acceleration elements 132 in a row) is determined by the relative speed β=v/c of the particle speed v in relation to the speed of light c and by a wavelength λ of the injected laser light 140.

[0047] Deviations 137 of the acceleration elements 132 from distances on the order of magnitude λ.sub.g cause jumps in the phase of laser light 140 for particles 50. The alternating phase focusing pattern APF is implemented in this way. The phase jumps for particle focusing shape the electron dynamics according to the alternating-phase focusing (APF) method known from the specialist literature.

[0048] FIG. 2 shows a further view of the embodiment from FIG. 1. A pulse of the injected laser beam 140 is shaped in such a way that it guides the particles 50 in the channel 130 and at the same time forms them into bunches, so that the particle bunches do not disperse and do not strike the delimiting structures or the acceleration elements 132.

[0049] As an alternative to the embodiment shown here with only one laser beam 140, a plurality of laser beams can also be used. For example, two laser beams can enter the channel 130 at the same angle, each inclined by 45° with respect to the optically thin layer 120. In this way, an alternative electromagnetic alternating field, which deflects particles in a vertical direction, for example, can also be formed.

[0050] FIG. 3 shows further details of the embodiment from FIG. 1.

[0051] The figure shows, in a part 1, a longitudinal section through the substrate 110, the electrically insulating layer 120, and the channel 130. An electric field strength in the longitudinal direction of a pulse of the laser beam 140 is shown in arbitrary linear units. The pulses of the laser beam 140 penetrate the electrically insulating layer 120 and are in particular at least partially reflected on the surface 115. As a result, the electromagnetic alternating field in the channel 130 is symmetrized in a direction vertical to the insulating layer 120. In the simplest case, the exact shape of the pulses is a plane wave (Gaussian ellipsoid pulse); the fronts of the pulses are optionally matched to the movement of the particles, i.e. tilted in an adapted manner, with the phase fronts remaining parallel to the electron beam axis. The pulses can also have an inhomogeneous intensity distribution in the direction along the channel 130. Methods for generating pulsed laser light with an at least partially adjustable intensity distribution and with inclined pulse fronts in the laser device are known in the specialist literature.

[0052] In a part 2, the figure shows a cross section through the substrate 110, the electrically insulating layer 120 and the channel 130 which qualitatively reproduces the thickness ratios. In embodiments, the apparatus is formed in particular on a silicon-on-insulator (SOI) wafer. Such a wafer comprises, for example, an electrically insulating layer 120 (cladding) between two layers of silicon, one of which serves as substrate 110 (bulk) and in the other (device layer) of which the channel 130 is formed by lithographic methods. The device layer or the acceleration elements 132 can be, for example, 220 nm above the insulating layer 120; a thickness of the insulating layer 120 may be approximately 3 μm, and the substrate 110 can have a thickness of approximately 725 μm. A temporal full width at half maximum (FWHM) for pulses of the laser beam 140 can be in the range of approximately 800 to 1000 fs, and can also be somewhat shorter in the case of inclined pulse fronts. Light can take approximately 14 fs to pass through the insulation layer; the laser beam reflected on the surface 115 then re-enters the channel as a reflected beam approximately 28 fs after it has entered the electrically insulating layer. In contrast, light can require around 8.2 ps to pass through the silicon layer of the substrate; a disturbance of the electromagnetic alternating field in the channel by a further reflection on an underside of the substrate 110 thus only reaches the channel well after the laser pulse has decayed and after the electron pulse has passed.

[0053] In a part 3, the figure shows an enlarged view of the cross section from part 2 in the region of the electrically insulating layer 120. Two acceleration elements 132 can be seen here which border the channel 130 and form a gap for the particles 50.

[0054] In a part 4, the figure shows an example of a section through a synchronous field strength e.sub.1 of the electromagnetic alternating field as can be generated by the laser beam 140 and its reflection in the channel 130. The synchronous field strength as a function of the transverse position (x, y) is defined as follows:

[00001]$e_1\left(x,y\right)=\frac{1}{{\lambda }_g}{\int }_{-{\lambda }_g/2}^{{\lambda }_g/2}{E}_z\left(x,y,z\right)e^{i\frac{2\pi z}{\beta \lambda }}dz,$

[0055] where E.sub.z(x, y, z) is the electric field in the direction of the channel at the location z along the channel in the frequency range for a frequency that passes through c/λ with the wavelength λ and the speed of light c. β=v/c is a relative speed of the particles, formed by the particle speed v in relation to the speed of light c.

[0056] A cross in a central region of the image represents a point of symmetry of the field strength profile and, at the same time, a central position of the corpuscular ray aligned at a right angle to the plane of the drawing. The horizontal axis shows distances in nm from this position; the vertical axis shows a height in nm above the electrically insulating layer 120. A scale next to the image indicates a size of the field strength, normalized to the incident field strength. The exact shape of the potential profile depends on the nature of the acceleration elements or individual cells 132 and can be adapted to a transverse phase space distribution of the particles 50 at the position of the depicted cross section in the channel.

[0057] FIG. 4 shows in particular grounding paths 152 in the embodiment from FIG. 1. Each acceleration element 132 is connected to a grounding structure 155 via a separate grounding path 152 and is grounded in this way. The grounding paths 152 are formed on the side of the layer 120 that is opposite the substrate 110 outside the channel 130. The grounding paths 152 are also designed to sufficiently divert particles 50, which have diverged from their trajectory or the channel 130 and strike acceleration elements 132, away from the channel 130. The acceleration elements 132 and, in the embodiment shown, the grounding paths 152 are made of a material that is optically dense for the laser beam 140, while the layer 120 is optically thin and almost transparent for the laser beam. A large optical contrast is advantageous here; the optical density or a refractive index of the acceleration elements 132 can be, for example, higher than the optical density or a refractive index of the layer 120 by a factor of 3 or more. The optically thin layer 120 is also electrically insulating.

[0058] An inserted image 5 shows an enlargement of the channel 130 on the electrically insulating layer 120 with acceleration elements 132 and the grounding paths 152 extending therefrom. Another inserted image 6 shows a cross section through the structure with a qualitatively represented thickness ratio of the substrate 110, optically thin layer 120, and structures of the channel 130.

[0059] By means of embodiments of the depicted apparatus, scalable and in particular length-scalable accelerators, for example for electrons as particles 50, are implemented which bring about multiplication of the energy e.g. from 20 keV to 60 keV or even to 1 MeV or a corresponding acceleration of the electrons when the length of the channel 130 is less than approximately 2 cm.

[0060] FIG. 5 shows further views of the embodiment from FIG. 4. An upper part of the figure shows a perspective view, in the direction of the channel 130, of the substrate no, the optically thin layer 120, and the structures of the channel 130 with the grounding paths 152. A lower part of the figure shows a detail of the cross section from the inserted image 6 in FIG. 3 in an enlarged view. This part shows the optically thin layer 120 and the structures of the channel 130 thereon with acceleration and focusing elements 132, grounding paths 152, and the grounding structure 155 for the grounding of the acceleration elements 132 via the grounding paths 152.

[0061] FIG. 6 shows three profiles a, b, c for a synchronous field strength e.sub.1 of the electromagnetic alternating field in the channel 130 (not shown here) as can be generated by the laser beam 140 and its reflection in the channel 130. A cross in a central region of each of the profiles a, b, c represents a point of symmetry of the respective field strength profile and, at the same time, a central position of the corpuscular ray aligned at a right angle to the plane of the drawing. The horizontal axis shows distances in nm from this position in each case; the vertical axis shows a height in nm above the electrically insulating layer 120 in each case. A scale next to the image in each case indicates the amplitude of the synchronous field strength normalized to the incident laser field strength, which moves a particle 50 in the direction of the cross of the relevant profile and thus alternatingly focuses in all three spatial directions. The three profiles a, b, c correspond to three increasing values of the relative speed β=v/c of the particle speed v in relation to the speed of light c. When the particles accelerate along the channel 130, this corresponds to three ascending positions along the channel 130 at the same time. A field strength profile can be calculated for each relative speed β. A drift of the point of symmetry marked by the cross in one of the depicted profiles can be compensated for by suitable adaptation of the acceleration elements 132, and a variation in the position of the point of symmetry in the cross section along the channel can thereby be prevented or minimized. The exact shape of the field strength profile depends on the nature of the acceleration elements 132 or the individual cells each formed by two acceleration elements 132 and a speed of the particles 50.

[0062] FIG. 7 shows steps of a method for producing an apparatus for guiding charged particles 50. The apparatus comprises a substrate 110 having a surface 115, an optically thin layer 120 formed on the surface 115, an inhomogeneous channel 130 which is formed by two mutually opposite delimiting structures on a side of the optically thin layer 120 that is opposite the substrate no, and a radiation device which is designed to generate at least one pulsed laser beam 140 and radiate said beam into the channel 130 from a side that is opposite the optically thin layer 120. The delimiting structures can in particular comprise a large number of acceleration elements 132. A high optical contrast between the delimiting structures or the acceleration elements 132 and the optically thin layer 120 is advantageous here; a refractive index of the acceleration elements 132 can be larger than a refractive index of the layer 120 by a factor of approximately 3. The method includes providing S110 a micro- or nanostructure, such as an SOI wafer, which has a sequence consisting of an etching layer (e.g. a device layer comprising silicon), the optically thin layer 120 (e.g. a cladding comprising glass or silicon dioxide), and the substrate 110 (e.g. a bulk also comprising silicon). Another step of the method includes etching S120 only the etching layer, whereby the channel 130 and the grounding paths 152 are formed.

[0063] In particular, the method advantageously does not include etching the optically thin layer 120. The optically thin layer 120 can represent an etch stop layer, i.e. when the upper etching layer is etched, the etching procedure automatically stops at the example oxide layer 120. In embodiments, the etching S120 takes place as a step in a method of photolithography or electron beam lithography; such methods are known in semiconductor technology. In particular, ready-made SOI wafers are already commercially available. This is important for carrying out focusing according to the APF method.

[0064] FIG. 8 shows steps of a method for guiding charged particles 50 in a channel 130 of an apparatus for guiding charged particles 50. The apparatus comprises a substrate no having a surface 115, an optically thin layer 120 formed on the surface 115, an inhomogeneous channel 130 which is formed by two mutually opposite delimiting structures on a side of the optically thin layer 120 that is opposite the substrate no, at least two grounding paths 152 formed on the side of the layer 120 that is opposite the substrate no, and a radiation device which is designed to generate at least one pulsed laser beam 140 and inject said beam into the channel 130 from a side that is opposite the optically thinner layer 120. The delimiting structures can in particular comprise a large number of acceleration elements 132. A high optical density contrast between the delimiting structures or the acceleration elements 132 and the optically thin layer 120 is advantageous here; a refractive index of the acceleration elements 132 can be larger than a refractive index of the layer 120 by a factor of approximately 3. The method comprises, as a step, injecting S210 the at least one pulsed laser beam 140 into the channel 130 by means of the radiation device from a side that is opposite the optically thin layer 120, the surface 115 reflecting the laser beam 140. As a result, a quadrupolar synchronous electromagnetic alternating field is formed in the channel 130. A second step comprises guiding S220, i.e. in particular accelerating and/or directing the particles 50 in the channel 130 by means of the electromagnetic alternating field. At the same time, focusing S230, in particular according to the APF method, of the particles 50 alternatingly along the channel 130 and in at least one direction perpendicular to the channel 130 is carried out.

[0065] The features of the invention disclosed in the description, the claims and the drawings may be essential for the realization of the invention either individually or in any combination.

LIST OF REFERENCE SIGNS

[0066] 50 charged particles [0067] 110 substrate [0068] 115 reflective surface [0069] 120 optically thin layer (low refractive index) [0070] 130 channel (vacuum) [0071] 132 acceleration and focusing element (optically dense, high refractive index) [0072] 137 deviation at regular (periodic or quasi-periodic) distances of the limiting elements to cause a phase jump [0073] 140 pulsed laser beam [0074] 152 grounding path (electrically conductive, e.g. same material as 132) [0075] 155 grounding structure (electrically conductive, e.g. same material as [0076] 132) [0077] S110, S120 steps of a method for producing an apparatus for guiding charged particles [0078] S210, S220, S230 steps of a method for guiding charged particles