WO2015025174A1

WO2015025174A1 - Improvements in and relating to lenses

Info

Publication number: WO2015025174A1
Application number: PCT/GB2014/052578
Authority: WO
Inventors: Zengbo Wang
Original assignee: Bangor University
Priority date: 2013-08-22
Filing date: 2014-08-22
Publication date: 2015-02-26
Also published as: GB201315038D0; GB2537217A; GB201603139D0

Abstract

A lens (5) comprising a solid and transparent host material (6) containing therein a plurality of solid and substantially spherical or spheroid transparent particles (7) each fixed within the host material and collectively arranged therein to form a layer of such particles embedded immediately beneath a common surface (6A) of the host material such that a respective optical focus of each of the particles resides outside the host material.

Description

Improvements in and Relating to Lenses

FIELD OF THE INVENTION

The invention relates to lenses and in particular, though not exclusively, to optical lenses for use with light of optical wavelengths, such as for use in imaging, sensing or lithology.

BACKGROUND

In conventional optical microscopes, which employ "far-field" imaging, the imaging resolution is limited. The resolution limit is constrained because light in the far field cannot be imaged to a resolvable scale, cf, any smaller than:

2NA

where NA is the numerical aperture of the imaging optics employed and λ is the wavelength of the light employed. The fundamental reason for this resolution limit is the loss of evanescent waves in the

"far field" zone. Evanescent waves only exist at the boundary of two different media with different refractive indices. They decay dramatically within few wavelengths of distance. Therefore, these waves can only be detected in the region very close to the interface. The amplitudes of evanescent waves, which carry the sub-diffraction-limited information, fade away rapidly in at least one direction. The effect of the classical diffraction limit could be reduced or even eliminated when evanescent waves become significant. In classical optics, when the illumination and imaging lens (with a given N.A) are optimized, a resolution limit of about d=100nm of resolvable distance can be achieved. Resolution distances smaller than 100 nm may be achieved by utilizing the evanescent waves in the near-field.

The invention aims to provide an improved lens for use in near-field imaging. BRIEF DESCRIPTION

The invention at its most general is to use transparent particles (e.g. beads, "microspheres") immobilized in a transparent host medium to form a lens. The lens may be a flat, planar glass-slider-like structure, or may be flexible and pliant. The transparent particles may have a higher index of refraction than the host material. The transparent particles may occupy or form a layer or zone at/adjacent to a surface of the lens. A higher refractive index zone may thus be formed at e.g. the bottom by the particles/microspheres that can strongly bend the light rays and produce a shorter focal length and smaller focusing size, which may increase the imaging resolution of a microscope when used in conjunction with the conventional far-field objective lens of a microscope. In conventional optical microscopes, the imaging resolution is the same as the focus spot size. Thus, an object under study is required to be positioned exactly at the focal plane of the lens. The lens of the present invention is adapted to be able to operate in a near-field virtual imaging mode, in which an object located within the transparent particle focal length is viewable via the transparent particle (e.g. "microsphere") and magnified to form a virtual image which is then viewed via by conventional lens. The near-field light flows are strongly bent in a manner very different from the classical concept of straight light rays. Figure 1 illustrates the unusual light bending effect as well as the concept of near-field virtual imaging. The upper image shows theoretical flow lines of light (wavelength A=496nm) passing through and around a transparent spherical particle 1 of refractive index 1 .6 and a 2.0 micron diameter, as calculated according to Mie Theory. Only one half of the spherical particle is shown in a cross sectional plane containing the optical axis of the particle, flow lines being symmetrically mirrored about the optical axis in the lower (not shown) half of the particle. In addition to a tight focus 4 formed by the particle, some light paths 3 effectively diverge and this contributes to the occurrence of virtual imaging, as shown in the lower schematic diagram of Figure 1 .

The lower schematic diagram of Figure 1 shows the focal lengths of the transparent particle (^) and of the objective lens (f₂) of a microscope 2. Note the close proximity of the object to the transparent particle, within the focal length of both the transparent particle 1 and the objective lens 2. The bottom image shows the virtual imaging mechanism. This enables a virtual image to be formed which can provide a large magnification factor (M) and allows one to see objects smaller than the focus spot size. In other words, in the concept of near-field virtual imaging, imaging resolution (minimum object size we can see) is conceptually separated from lens focus size. Due to the unusual light bending 3 caused by the microsphere 1 , image resolution (r) of the virtual image can be smaller than focus spot size (d). It has been found that, approximately speaking: r « 2d/M , and M is the normalized field enhancement factor

produced by the particle in the focus formed by it. I_max is the maximum field intensity at focus, and /₀ is a normalising factor. Figure 2 shows (A) the theoretical (Mie Theory) Poynting Intensity distribution of parallel rays of incident light (upper arrows) light (wavelength A=600nm) focussed through a microsphere (white circle; central plane of symmetry) of 18 microns diameter and refractive index of 1 .9, together with (B) a magnified view showing the position of the focus relative to the microsphere. The focal length is found to be 14.04 microns, which equates to a back-focal length (portion of focal length outside the particle) of 5.04 microns. This is very close to the surface of the microsphere. Figure 3 shows the Poynting Intensity of light focussed 4 by the microsphere of Figure 2 along the optical axis (z) of the microsphere as measured from the centre (z=0) of the sphere. The peak intensity occurs at 14.04 microns along the optical axis - at 5.04 microns from the outer surface of the sphere. A larger sphere has been found to produce a longer back-focal length, e.g. 27.66 microns when the particle diameter is 76 microns. This is also very close to the surface of the microsphere. Smaller spheres provide more effective light bending and higher magnification, but at the cost of a less bright image and of presenting less field of view simply due to their smaller diameter. However, in order to achieve virtual imaging, and the image magnifications that follow, it is necessary to have an imaged object positioned within the focal length of the microsphere, and as close to the microsphere as possible to enhance object-to-particle evanescent wave coupling.

In a first aspect, the invention provides a lens comprising a solid and transparent host material containing therein a plurality of solid (e.g. substantially spherical or spheroidal) transparent particles (e.g. beads, such as "micro-beads") each fixed within the host material and collectively arrayed therein to form a layer of the particles which is embedded immediately beneath a common surface of the host material such that a respective optical focus (focal point) of each of the particles resides outside the host material. For example, the back focal length, or front focal length, of the transparent particles preferably exceeds the/any separation between the common surface and the surface part of the particles nearest to it. The "front focal length" (FFL) or "front focal distance" (FFD) may be considered to be the distance from the front focal point of the system to the vertex of the first optical surface. The "back focal length" (BFL) or "back focal distance" (BFD) may be considered to be the distance from the vertex of the last optical surface of the system to the rear focal point.

In this way, a robust and re-useable lens is provided for optically viewing/imaging (virtual images) an object or sample under study in which the near-field coupling of object-to-lens evanescent light waves is permitted and which can be used in conjunction with conventional far-field optics to achieve sub-wavelength resolution. Preparation (such as plasmonic coating) of the object surface is not required in order to enable this coupling, and this provides versatility and broad applicability to the lens. The placement of the particles within the host material at or immediately close to a surface of the material permits the object under study to be placed against the common surface at very close proximity to one of the particles and within the focal length of the particle such that (a) an evanescent may pass from the object to the particle, and (b) the particle may support virtual image formation using the objective lens of a conventional "far-field" optical system (e.g. microscope) which in isolation is unable to couple to the evanescent wave. The host material is preferably sufficiently thin that it may be placed within the focal length of the objective lens of a microscope, or other imaging system, via which an object is to be studied and between the object under study and the objective lens. Embedding the transparent particles within the host material fixes them relative to the larger host material and protects them from the environment. This allows the lens to be reused many times and also allows it to be manipulated manually or mechanically to move the transparent particles relative to an object under study to allow adjustment/selection of the area of study on that object.

The embedded layer preferably extends substantially parallel to the common surface of the host material. The particles of the layer may be a monolayer, substantially one particle in thickness. The particles of the layer may be arrayed closely so that each one is immediately neighbouring at least one other (typically six others - e.g. forming a hexagonal close-packed monolayer), or may be separated and spaced, neighbour-to-neighbour (e.g. with a regular spacing, e.g. forming a regular or substantially uniform array).

A part of the surface area of each said particle of the embedded layer is preferably substantially tangential to the common surface of the host material and is not covered by the host material at the common surface. This allows closer proximity of each particle to a part of the object under study and permits better coupling of object-to-particle evanescent waves. For example, the embedded particles may be positioned to present a surface of closest approach to the common surface of the host material which touches, "kisses" or osculates the common surface from within the host material. In other embodiments, the particles may each present a locally flat surface area (e.g. formed by removal of a small sector of surface material from a spherical particle) which is exposed at the common surface. This too would enhance the coupling of object-to-particle evanescent waves. The value of the refractive index of the host material is preferably less than the value of the refractive index of the material of the transparent particles at optical wavelengths of light. This supports light focussing by the particles within the host material. The host material may have a refractive index value which is less than about 1 .5. The material may be glass or may be an elastomer such as a silicone elastomer (e.g. Polydimethylsiloxane, "PDMS"; refractive index = 1 .4).

The refractive index of the material of the particles may be at least about 1 .4 in value, more preferably a value in the range 1 .7 to 3.0 or more. For example, silica (Si0₂) particles may be used (e.g. refractive index about = 1 .5), or Al₂0₃ particles may be used (e.g. refractive index = 1 .76), or BaTi0₃ glass particles may be used (e.g. refractive index = 1 .9 to 2.0), or Ti0₂ particles may be used (e.g. refractive index = 2.4 to 3.0), or silica-titania composite material may be used (e.g. tunable refractive index = 1 .4 to 2.7). The transparent particles may individually have a width/diameter (or collectively have a mean width/diameter) which is less than 250 microns and more than 1 micron, or preferably less than about 150 microns, or preferably less than about 100 microns. The mean diameter of the transparent particles is preferably greater than about 2 microns. For example, smaller particles of mean diameter between 10 to 15 microns or between 2 microns and 10 microns (e.g. about 8, 5 or 3 microns) can provide higher magnification. Larger particles, for example with mean diameters between 40 to 50 microns, permit greater viewing area/aperture. The plurality particles may have a spread/variance of widths/diameters in practice, and preferably the variance is small in order that magnification is sufficiently consistent across the lens (i.e. as between different particles). The value of the standard deviation in the widths/diameters of the particles may be such that the diameter/width at least 60%, more preferably at least 70%, or yet more preferably at least 80%, or even more preferably at least 90% of the particles falls within one standard deviation of the mean width/diameter of the plurality of particles. The "width" of non-spherical particles may, for example, be considered to be the size of a selected one of its extreme (e.g. largest, or smallest) lateral dimensions. The host material may form a sheet and may be less than about 1 cm, or less than about

0.5cm or less than about 250 microns in thickness, or more preferably less than about 200 microns in thickness, or yet more preferably less than about 170 microns thick.

The lens may be plano-convex. The common surface may be the plane part of the plano- convex lens. The lens may include a sheet, slab, slide, web or film of host material comprising a plano-convex lens part positioned upon a surface of the sheet, slab, slide, web or film reverse to the common surface and extending across and in optical communication with one some or all of said transparent particles, such that the convex surface of the plano-convex lens part is presented outwardly of the lens.

The plano-convex lens material may be integrally formed with the host material or may be separately formed and attached or adhered thereto (e.g. using index-matching adhesive). The material of the plano-convex lens part is preferably substantially the same as the host material. The curvature of the plano-convex lens part may be 2-dimensional (e.g. cylindrical, e.g. radius of curvature extends within substantially only two dimensions) or 3-dimensional (e.g. spherical, e.g. radius of curvature extends in three dimensions). The radius of curvature of the planoconvex lens part may be substantially centred at or beyond the common surface (e.g. outside of the host material). This provides further improvement in imaging resolution and performance. The convex radius may be selected in accordance with the objective lens of a microscope the user is using.

The lens may include a coupling layer formed upon the common surface of the host material and comprising a transparent material having a refractive index which exceeds in value the refractive index of the host material at optical wavelengths of light. It has been found that providing such a relatively high refractive index layer over the common surface, which is the side of the lens intended to interface with the object under study, assists in better coupling object-to-lens evanescent waves. The lens may include such a coupling layer formed upon the common surface of the host material and comprising a transparent material having a refractive index which exceeds in value the refractive index of the material of the transparent particles at optical wavelengths of light.

The thickness of the coupling layer is preferably less than the thickness of the host material and is preferably also thinner than the mean diameter of the particles in the embedded layer over which it extends. The thickness of the coupling layer is preferably substantially uniform, and is preferably no greater than about 250nm, and more preferably is no greater than about 200nm, or yet more preferably no greater than about 150nm, or even more preferably no greater than about 100nm. When a single layered structure of one material (or a multi-layered structure with few layers of differing materials), the thickness of the coupling layer may less than 80nm, or preferably less than about 50nm or yet more preferably less tan about 25 nm (e.g. about 20nm).

The material of the coupling layer may comprise a dielectric material. For example, Gallium Phosphide (GaP) may be used, which has a refractive index of about 3.6 at optical wavelengths. Other dielectrics may be used as desired. The coupling layer may comprise a multi-layered structure including one or more layers of dielectric material and one or more layers (or sub-layers) of metallic material arranged in alternating succession. For example, a metal sub-layer may be formed directly upon the common surface of the host material, and a dielectric sub-layer formed upon that first metal layer, followed by another layer of the metal, then a further layer of the dielectric etc, etc. Thus a multi-stack of metal-dielectric-metal- dielectric... etc may form the coupling layer. The order may be reversed, with a dielectric sublayer formed directly upon the common surface of the host material: dielectric-metal-dielectric- metal... etc. The metal layer(s) may be silver (Ag). The coupling layer, when a multi-layer structure, may be a meta-material providing a so-called "Superlens" or "Pendry" lens as known in the art (e.g. Manipulating the Near Field with Metamaterials.: Optics & Photonics News, September 2004. By John Pendry, and see references therein).

The host material is preferably a dielectric material. The material may be a glass or a plastics material, or may be an elastomer such as a silicone elastomer (e.g. Polydimethylsiloxane, "PDMS"; refractive index = 1 .4). Thus, the host material is preferably flexible or pliant. This permits the lens to be moulded or conformed to an irregular surface of an object, or generally presses against the object to enhance the proximity of the transparent particle layer of the lens and the object under study. The material of the transparent particles is preferably a dielectric material. For example, a glass material, such as silica (Si0₂) particles may be used (e.g. refractive index about = 1 .5), or Al₂0₃ particles may be used (e.g. refractive index = 1 .76), or BaTi0₃ glass particles may be used (e.g. refractive index = 1 .9 to 2.0), or Ti0₂ particles may be used (e.g. refractive index = 2.4 to 3.0), or silica-titania composite material may be used (e.g. tunable refractive index = 1 .4 to 2.7).

The transparent particles may be generally round (e.g. ball-like) and preferably substantially spherical in shape, or may be spheroidal (e.g. ellipsoidal). The particles may each present a locally flat surface area (e.g. formed by removal of a small sector of surface material from a spheroidal/spherical particle), and preferably that sector is presented to or is exposed at the common surface. In a second aspect, the invention provides a lens comprising a first lens element according to the lens of the invention in its first aspect (e.g. as described above), and a second lens element according to the lens of the invention in its first aspect (e.g. as described above), wherein the second lens element is arranged upon the common surface of the host material of the first lens element and extends substantially parallel thereto such that particles of the first lens element are in register with particles of the second lens element thereby to be in optical communication therewith. The width/diameter (e.g. the mean value of the plurality) of the transparent particles of the second lens element is preferably less than the width/diameter (e.g. the mean value of the plurality) of the transparent particles of the first lens element. The width/diameter (e.g. mean value) of the particles of the second lens element may be no more than about one half (e.g. no more than about one third, or no more than about ¼) of the value of the width/diameter (e.g. mean value) of the particles of the first lens element. The width/diameter (e.g. mean value) of the particles of the first lens element may be less than about 50 microns, and the width/diameter (e.g. mean value) of the particles of the second lens element may be less than about 10 microns. In this way, a cascade effect is provided whereby an image (e.g. virtual) of an object which is formed by transparent particles of the second lens element may, in turn, be images and magnified by the transparent particles of the first lens element. Further lens element(s) may be provided, each with transparent particles positioned in register with those of the preceding lens element in the cascade, each successive lens element having an embedded layer of transparent particles of smaller diameter (e.g. mean) than those of the preceding lens element.

The value of the refractive index of the material of the transparent particles of the second lens element is preferably greater than the value of the refractive index of the material of the transparent particles of the first lens element at optical wavelengths of light. For example, a glass material, such as silica (Si0₂) particles may be used for particles in the first lens element (e.g. refractive index about = 1 .5), and Al₂0₃ particles may be used (e.g. refractive index = 1 .76) for particles in the second lens element. For example, BaTi0₃ glass particles may be used (e.g. refractive index = 1 .9 to 2.0) for particles in a third lens element, if desired.

The thickness of the host material of the second lens element (and any successive lend element) may substantially match the width of particles of the second lens element (or the successive lend element, if any) such that the layer of particles of the second (and successive) lens element is embedded immediately beneath a respective common surface of the host material of the second (successive) lens element at each of two opposite sides thereof, and extends substantially parallel thereto. This permits the particles of the second (successive) lens element to attain very close proximity to both the object under study and the particles of the preceding (e.g. first) lens element, thereby to enhance both the object-to-lens and the lens- to-lens coupling of evanescent waves.

In a third aspect, the invention may provide a lens scanner apparatus comprising: a lens according to the invention as described in the first or second aspect above; a lens holder in which the lens is held permitting light to pass through the lens; a sample holder for holding a sample to be viewed through the lens; a position controller coupled to the lens holder to selectively move the lens holder relative to the sample holder to change the separation between the lens relative and the sample holder and/or to move the lens laterally over the sample holder thereby to permit the viewing of different parts of a sample when in the sample holder. The lens scanner apparatus may comprise an X-Y-Z stage in which the lens is held and with which it may be moved to/from or across an object/sample under study.

In a fourth aspect, the invention may provide a microscope comprising a lens according to the invention in either of the first and second aspect or comprising a lens scanner apparatus as described above in the third aspect of the invention. The thickness of the lens is most preferably less than the focal length of the objective lens of the microscope. Accordingly, a virtual image of an object under study may be formed by viewing the object through the objective lens of the microscope via the lens of the present invention.

In a fifth aspect, the invention may provide a method for manufacturing a lens comprising: providing a surface; arranging a plurality of solid and substantially spherical or spheroid transparent particles upon the surface; subsequently applying a liquid host material to the particles to embed the particles therein whilst the particles are upon the surface; subsequently solidifying the host material; and, separating the solidified host material and embedded particles from the surface. The arranging of the particles upon said surface may include: providing a fluid comprising a plurality of solid and substantially spherical or spheroid transparent particles mixed within a liquid; and, applying the fluid to the surface and evaporating the liquid from the fluid such that the particles remain arranged upon the surface. It has been found that the transparent particles tend to form a regular monolayer by self-assembly through the mutual attraction produced by lateral capillary forces in the liquid as it evaporates. Surprisingly regular, typically hexagonally closely-packed monolayers may be produced this way. Alternatively, the step of arranging of the particles on the surface may include a simple and cost-effective method of positioning and controllable movement of a microsphere by using a micropipette, such as a glass micropipette. The micropipette may retain a transparent particle at its tip by suction, in the manner of a pipette, and the tip of the pipette may be positioned as desired upon the provided surface and there released from the tip of the micropipette. The control of the position (relative to the provided surface) of the micropipette may be made via a mechanical stage to which the micropipette may be attached. The control of the mechanical stage may be automated. In this way a desired pattern (e.g. regular array) of transparent particles (micro- beads/spheres) may be made and then embedded in the liquid host material to provide the lens. The pattern or array of transparent particles may be any desired pattern, and may comprise transparent particles separated neighbour-to-neighbour, by a desired distance.

The method may include allowing particles to settle onto the surface within the liquid after the fluid is applied to the surface but before the liquid is evaporated. It has been found that the transparent particles tend to sink in the liquid and settle upon the surface as a layer at the base of the liquid, before it is evaporated.

The surface is preferably hydrophilic when the liquid comprises water. The surface is preferably substantially flat. Given that a liquid host material is applied to the particles, it may flow to surround and embed the layer particles whilst the host material is fluid. The layer of particles is positioned upon the provided surface, and the liquid host material applied to them upon that surface, may thus follow/match the provided surface in shape. The method may include the step, occurring between the steps of applying the liquid host material and solidifying the host material, comprising: pressing a second surface upon the liquid host material within which the particles are embedded thereby to sandwich the liquid host material and the particles between said surface and said second surface such that particles therein simultaneously contact both surfaces; subsequently solidifying the host material; separating the solidified host material and embedded particles from the surface and the second surface. The layer of particles positioned upon the provided surface, and the liquid host material applied to them upon that surface, may thus follow/match the provided surface in shape, as well as the second surface. The second surface is preferably substantially flat. Thus a thin sheet-like lens structure may be provided which is substantially as thick as the width/diameter of the transparent particles within it. This lens structure is most suitable for use as a second (or successive) lens element described above, in embodiments comprising two of more lens elements. In a further aspect, the invention may provide an apparatus for patterning a surface including: a lens as described above; a laser light source arranged to generate a laser light beam; a positioner for controllably positioning the laser light beam upon a surface of the lens for transmission through the lens for focussing by a said transparent particle thereof at a focal point of the transparent particle outside the lens for use in ablating or melting material of the surface when positioned at the focal point. The positioner may comprise a mechanical stage to which the laser light source is attached, the stage being arranged to controllably position the laser light source at a desired position over the lens to direct the laser light beam into the lens. Alternatively, the positioner may comprise one or more controllably tilting mirrors (e.g. mechanically/electrically controllable) arranged to receive the laser light beam and to direct the received beam by reflection from the mirror to a desired position upon the lens.

In a yet further aspect, the invention may provide a method for patterning a surface comprising: providing a lens as described above; providing a laser light source arranged to generate a laser light beam; controllably positioning the laser light beam upon a surface of the lens for transmission through the lens and focussing the laser light with a said transparent particle thereof at a focal point of the transparent particle outside the lens; ablating or melting material of the surface positioned at the focal point. The positioning may comprise a operating a mechanical stage to which the laser light source is attached, the stage being controlled to position the laser light source at a desired position over the lens to direct the laser light beam into the lens. Alternatively, the positioning may comprise the tilting of one or more controllably tiltable mirrors (e.g. mechanically/electrically controllable) arranged to receive the laser light beam and to direct the received beam by reflection from the mirror to a desired position upon the lens. BRIEF DESCRIPTION OF THE DRAWINGS

Examples of illustrative embodiments of the invention shall now be describes, to aid understanding, with reference to the accompanying drawings or which:

Figure 1 shows the flow of light through a microsphere (top half only, bottom half symmetrically identical) together with a schematic representation of virtual image formation that results when used with a conventional objective lens; Figure 2 shows (a) the intensity distribution of light focussed through a microsphere (central plane of symmetry) together with (b) a magnified view showing the position of the focus relative to the microsphere; Figure 3 shows the intensity of light focussed by the microsphere of Figure 2 along the optical axis (z) of the microsphere as measured from the centre (z=0) of the sphere. The peak intensity occurs at 14.04 microns along the optical axis - at 5.04 microns from the outer surface of the sphere; Figure 4 schematically shows the use of a lens of an embodiment of the invention in conjunction with an objective lens of a microscope, the non-transparent subject of study being illuminated from above, through the lens;

Figure 5 schematically shows the use of a lens of an embodiment of the invention in conjunction with an objective lens of a microscope, the non-transparent subject of study being illuminated from below, through the sample;

Figure 6 shows images of (a) an object comprising lines separated by 100nm as viewed non-confocally through a lens of an embodiment of the invention; (b) an object comprising lines separated by 100nm as viewed confocally through a lens of an embodiment of the invention; (c) an object comprising lines separated by 40nm as viewed confocally through a lens of an embodiment of the invention;

Figure 7 schematically shows a lens according to an embodiment of the invention selectively positionable above a sample under study;

Figure 8 schematically shows a lens according to an embodiment of the invention including a coupling layer on an outer surface for enhancing evanescent wave coupling into the lens;

Figure 9 schematically shows a lens according to an embodiment of the invention including a coupling layer on an outer surface comprising a meta-material forming a so-called "super-lens" of "Pendry lens"; Figure 10 schematically shows a lens according to an embodiment of the invention including a first lens element coupled to a second lens element, in which each lens element comprises a layer of in-register transparent micro-spheres embedded within a transparent host material; Figure 1 1 schematically shows a lens scanner according to an embodiment of the invention;

Figure 12 schematically shows a method for manufacturing a lens according to an embodiment of the invention;

Figure 13 schematically shows a variant of the method for manufacturing a lens according Figure 12; Figure 14 shows scanning electron microscope images of a monolayer of microspheres and the micro-pore pattern produced in a surface irradiated with a laser beam via the microspheres of the monolayer;

Figure 15A and Figure 15B schematically show surface patterning/texturing apparatus according to embodiments of the invention;

Figure 16 schematically shows the movement of the focal position of an objective lens of a microscope when used in conjunction with a lens of embodiments of the invention, in order to reach virtual image formation;

Figures 17a and 17b illustrate views of a lens according to an embodiment of the invention.

In the drawings, like items are assigned like reference symbols.

DETAILED DESCRIPTION

Figure 4 schematically shows the use of a lens of an embodiment of the invention in conjunction with an objective lens of a microscope, the non-transparent subject of study being illuminated from above, through the lens.

The lens 5 comprises a solid and transparent host material 6 containing therein a plurality of solid and substantially spherical transparent beads/particles 7 (e.g. microspheres) each fixed within the host material. The beads 7 are collectively arranged within the host material to form a layer of beads embedded immediately beneath a common lower surface 6A of the host material such that the respective optical focal point of each of the beads resides outside the host material. A direction substantially perpendicular to the common surface 6A, which passes through the centre of an embedded bead, defines an optical axis of the bead. The beads are positioned within the host material of the lens such the focal length of a bead extends along its optical axis and its focal point resides thereon at a position outside the common surface 6A. This means that the object under study may be placed within the focal length of each of the beads 7 to permit virtual imaging to occur. The front focal length of each of the transparent beads extends beyond the common surface, and is able to contain the object under study, which may be a surface part of a sample 8. The "front focal length" (FFL) is here a reference to the distance from the front focal point of the beads to the vertex of the first optical surface of the bead in question. That is to say, the first optical surface of each bead, for receiving light from the object of study, may be placed close enough to that object such that the object is within the focal length of the bead in question. The embedded layer of beads extends substantially parallel to the common surface of the host material. The beads of the layer form a monolayer, one bead in thickness. The beads are shown schematically in Figure 4 and only a few are shown for clarity. Of course, in practice very many (e.g. thousands) of beads may form the monolayer. The beads of the layer are arrayed closely so that each one is immediately neighbouring six others thereby forming a hexagonal close-packed monolayer. In other embodiments, the beads may be separated and spaced, neighbour-to-neighbour e.g. with a regular spacing.

A part of the surface area of each bead of the embedded monolayer is substantially tangential to the common surface of the host material and is not covered by the host material at the common surface. A surface (of each bead) of closest approach to the common surface of the host material osculates the common surface from within the host material. The host material is a flexible and pliant silicone elastomer (e.g. Polydimethylsiloxane, "PDMS"; refractive index = 1 .4) formed as a flat, flexible and pliant sheet about 150 microns thick (shown schematically here) and is typically rectangular or square (but may be any desired shape) with a side of several cm in length (e.g. similar to the size of a microscope glass slide). The beads are BaTi0₃ glass beads (e.g. refractive index = 1 .9 to 2.0) of 18 microns mean diameter.

The lens is shown in Figure 4 in use with an objective lens 9 of a microscope (Olympus UMplane, x100 magnification, numerical aperture=0.9, or an objective lens from another manufacturer may be used such as with x50 or x100 magnification (or between those values) and a numerical preferably greater than 0.4). White light 10 illuminates the non-transparent sample 8 from above such that viewing is by reflected light. Figure 5 shows the same arrangement in used to study a transparent sample 1 1 permitting white light or laser light 10 to illuminate the sample from below and allowing imaging to occur via transmitted light. In either case, the light source can be white light source or a suitable laser source, and is not limited to white light. This has been confirmed experimentally. For example, a microscope has been employed with a 405 nm laser light source, not white light, to illuminate a sample as shown schematically in either of Figure 4 or Figure 5. However, the lens can operate with white light illumination if that desired. For many bio-applications, such as the imaging of biological samples, a certain wavelength of laser light may be desired as the illumination source in order to excite (e.g. fluorescence) the sample. Thus, the use of lasers as the illuminating light source may be desirable. White light has a broad wavelength spectrum, usually non-coherent. Laser light has sharp spectrum at certain wavelength, and is usually coherent.

Figure 6 shows an image of (a) an object comprising a grating having an array of scored lines separated by 100nm as viewed non-confocally through a lens of an embodiment of the invention, using reflected light (e.g. per Figure 4). Figure 6 also shows an image (b) the same object as viewed confocally through the lens of an embodiment of the invention. The grating lines are clearly seen. Figure 6(c) shows an image of on object comprising lines separated by 40nm as viewed confocally through a lens of an embodiment of the invention. The 40nm grating lines are clearly seen. A lens comprising separated spherical beads (or locally only a few beads) was used to provide these images, for clarity. It will be understood that neighbouring beads of the monolayer of breads of the lens also produce such views individually.

Figure 7 schematically shows a lens according to an embodiment of the invention selectively positionable above a sample under study. The vertical separation (d) of the lower surface of the lens may be adjusted to bring the object of study into the desired focus. A mechanical stage may be employed to achieve this as shown in Figure 1 1 , or the adjustment may be done manually by pressing the lens t the surface of the object to a lesser or greater extent (pressure) to reduce or increase d as required. Figure 8 schematically shows a lens according to an embodiment of the invention including a coupling layer 13 on the common outer surface for enhancing evanescent wave coupling into the lens. The lens includes a coupling layer formed upon the common surface of the host material and comprising a transparent film of Gallium Phosphide (GaP) which has a refractive index of about 3.6 at optical wavelengths. That refractive index exceeds in value the refractive index of the host material and the spherical beads at optical wavelengths of light. It has been found that providing such a relatively high refractive index layer over the side of the lens intended to interface with the object under study, assists in better coupling object-to-lens evanescent waves. The thickness of the coupling layer is about 20nm, i.e. less than the thickness of the host material and also thinner than the mean diameter of the particles in the embedded layer over which it extends.

Figure 9 schematically shows a lens according to an embodiment of the invention including a coupling layer 14 on the common surface comprising a meta-material forming a so- called "super-lens" or "Pendry lens". The coupling layer 14 comprises a multi-layered structure including one or more layers of dielectric material 16 and one or more layers of silver 15 arranged in alternating succession. The silver metal layer is formed directly upon the common surface of the host material, and a dielectric layer is formed upon that first silver metal layer. Another layer of the silver metal follows, then a further layer of the dielectric etc, etc. Thus a multi-stack of metal-dielectric-metal-dielectric... etc forms the coupling layer 14. This coupling layer enhances the coupling of evanescent waves into the spherical beads 7 of the lens.

Figure 10 schematically shows a lens according to an embodiment of the invention including a first lens element 5 coupled to a second lens element 19, in which each lens element comprises a layer of in-register transparent spherical beads (7, 17) embedded within a respective transparent host material (6, 18). The lens comprises a first lens element 5 substantially as described above with reference to Figures 4, 5 or 7, optically coupled to a second lens element 19 as described above except for the host material and the material and diameters of the spherical beads embedded therein. The second lens element is arranged upon the common surface of the first lens element and it extends substantially parallel thereto such that optical axes of the beads 7 of the first lens element are in register (coincident) with the optical axes of beads 17 of the second lens element. In this way substantially each bead of the first lens element is in optimal optical communication with an immediately adjacent bead of the second lens element via a common optical axis. The diameter (e.g. about 8 microns, being the mean value of the plurality) of the transparent beads 17 of the second lens element is less than the diameter (e.g. e.g. about 18 microns, being the mean value of the plurality) of the transparent beads 7 of the first lens element. In this way, a cascade effect is provided whereby an image (e.g. virtual) of an object which is formed by transparent beads of the second lens element may, in turn, be imaged and magnified by the transparent beads of the first lens element.

The value of the refractive index of the material of the transparent beads of the second lens element is greater than the value of the refractive index of the material of the transparent beads of the first lens element at optical wavelengths of light. For example, a glass material, such as silica (Si0₂) particles may be used for beads in the first lens element (e.g. refractive index about = 1 .5), and Al₂0₃ beads may be used (e.g. refractive index = 1 .76) in the second lens element, or BaTi0₃ glass particles may be used (e.g. refractive index = 1 .9 to 2.0) for beads in a second lens element, if desired.

The thickness of the host material 18 of the second lens element is substantially the same as the diameter of the beads of the second lens element 19 so that the layer of beads 17 of the second lens element is embedded immediately beneath a respective common surface of the host material of the second lens element at each of two opposite sides thereof. The layer of beads 17 extends substantially parallel thereto. This permits the beads 17 of the second lens element 19 to attain very close proximity to both the object under study and the beads 7 of the first lens element 5, thereby to enhance both the object-to-lens and the lens-to-lens coupling of evanescent waves. Figure 1 1 schematically shows a lens scanner 20 according to an embodiment of the invention. The lens scanner includes a lens 5, according to any embodiment described herein, and a lens mount/holder 21 in which the lens 5 is held permitting light to pass through both flat faces of the lens. The lens mount holds the lens at opposite peripheral edges of the lens so as to leave exposed the common surface (first optical surface) of the lens, and the layer of spherical beads 7 to face a sample (8, 1 1) under study, while simultaneously exposing the opposite surface (second optical surface) of the lens to face an objective lens 9 of a conventional microscope. A sample holder 23 is provided for holding or supporting a sample to be viewed through the lens. A position controller including a vertical stage 22 (Z-direction) and a horizontal stage (X-Y directions) is coupled to the lens holder to selectively move the lens holder relative to the sample holder to change the separation (Z-direction) between the lens relative and the sample holder (as shown by arrows) and to move the lens laterally (X-Y directions) over the sample holder thereby to permit the viewing of different parts of a sample when in the sample holder. The position controller 22 comprises an X-Y-Z stage (mico-stage, or nano-stage) in which the lens is held and with which it may be moved to/from or across an object/sample under study. The spatial resolution/accuracy of the movements possible by the stage may be several microns in magnitude or even sub-micron magnitudes (nanometres). In this way a fine control of focus may be provided, and the microspheres of the lens may be laterally moved to allow the fields of view of the transparent beads (e.g. microspheres) to range over the sample as desired. The thickness of the lens is less than the focal length of the objective lens 9 of the microscope. Accordingly, a virtual image of an object under study may be formed by viewing the object through the objective lens of the microscope via the lens 5.

Figure 16 schematically shows how the focal plane of the objective lens of the microscope may be moved relative to the transparent beads (e.g. microspheres) of the lens from a location within the lens (focus position 1), to a focal position at the surface of the sample under study (focal position 2), and further to a focal position under and potentially beyond the surface of the sample under study (focal positions 3, 4 and 5), in order to bring the virtual image of the sample surface into view. The photographs numbered 1 to 5 in Figure 16 correspond with views of a Blue-Ray DVD disk line structure (100nm line separation) as seen through a microsphere of 18 micron diameter. It can be seen how virtual image formation occurs at focal position 4.

Figure 12 schematically shows steps in a method for manufacturing a lens. The method for manufacturing a lens comprises: Step 1 : providing a clean and substantially flat and hydrophilic surface on a substrate 24, which is preferably chemically homogeneous. This may comprise providing a glass surface and washing it with a detergent (e.g. Decon 90 detergent), then rinsing the surface with deionized (Dl) water, and allowing to dry;

Step 2: arranging a plurality (e.g. hundreds, or thousands) of the transparent beads (e.g. microspheres) 7 upon the surface of the substrate by providing a fluid comprising the plurality of transparent beads (e.g. microspheres) mixed within distilled water 25 and, applying the fluid to the surface and evaporating the liquid from the fluid such that the particles remain arranged upon the surface. The transparent beads (e.g. microspheres) form a regular monolayer by self-assembly through the mutual attraction produced by lateral capillary forces in the deformed liquid as it evaporates. An hexagonally closely- packed monolayers is be produced this way. Evaporation may occur at room temperature or higher if desired;

Step 3: subsequently applying a liquid host material (e.g. Polydimethylsiloxane, "PDMS") to the monolayer of transparent beads (e.g. microspheres) to embed the beads therein whilst the beads are upon the surface. Subsequently solidifying the host material - this may be by curing the PDMS at a suitable curing temperature; and,

Step 4: separating the solidified host material and embedded transparent beads (e.g. microspheres) from the surface. This separated body is the lens which may then be arranging upon a surface of a sample for study. At step 2, the transparent beads (e.g. microspheres) are allowed to settle onto the surface of the substrate 24 within the water 25 after the fluid is applied to the surface but before the liquid is evaporated. This allows the transparent beads (e.g. microspheres) to sink in the liquid and settle upon the surface of the substrate as a layer at the base of the liquid, before it is evaporated. In preparing a PDMS pre-polymer, one may prepare silicone elastomer base and curing agent with ratio of 10:1 . The silicone elastomer base may be cured using a curing agent such as manufactured by Dow Corning, but others may be used. The mixed PDMS pre- polymer may be placed into a low-pressure environment (e.g. a vacuum chamber) if it is desired to de-gas the pre-polymer mixture to remove any bubbles there may be - which could cause optical interference in the finished lens. The degassed (if necessary) PDMS pre- polymer may then be cured. A curing temperature of about 80°C may be used. Due to the properties of PDMS, it can spread over the surface and inside the gaps between microspheres to wrap around microspheres. Curing may take about 30 minutes after which the liquid PDMS has become an elastic solid. The resulting lens is very deformable to match a surface shape it is applied to.

Figure 13 schematically shows a variant of the method for manufacturing a lens according Figure 12. The method may include the step 3b, occurring between the steps 3 of applying the liquid host material and step 4 of solidifying the host material, comprising:

Step 3b: pressing a second flat substrate surface 28 upon the liquid host material within which the transparent beads (e.g. microspheres) are embedded thereby to sandwich the liquid host material and the transparent beads (e.g. microspheres) between two substrate surfaces (24, 28) such that transparent beads (e.g. microspheres) therein simultaneously contact both surfaces. Subsequently, the host material is solidified (e.g. cured) and separated (with its embedded bead mono-layer) from the surfaces of the two substrates (24, 28).

Thus a thin sheet-like lens structure 5 may be provided which is substantially as thick as the diameter of the transparent beads (e.g. microspheres) within it. This lens structure is most suitable for use as a second lens element 19 described above, in embodiments comprising two of more lens elements as shown in Figure 10.

In a further embodiment of the invention, the lens may be combined with a scanning laser light source for surface implementing nano-scale surface patterning. In the imaging mode described in embodiments above, the lens is positioned adjacent to the sample such that the part of the sample being imaged resides within focal length of the transparent beads (e.g. microspheres) of the lens thereby enabling formation, via a microscope objective lens, of a virtual imaging. Conversely, when used for surface patterning, one may simply position surface to be patterned at exact foci of the transparent beads (e.g. microspheres), as shown in Fig.2. This will enable each micro-sphere to focus incident laser light in sufficient intensity to form one ablate a hole in the surface being patterned. Collectively, the transparent beads (e.g. microspheres) of the layer of transparent beads 7 ablate a pattern of holes in the surface.

Figure 14 shows the effect. A pattern of nano-holes/pores can be generated - a respective one under each particle - to produce a pattern of holes or pores that matches the pattern of the layer of transparent beads (e.g. microspheres) each about 1 micron in diameter. A hexagonally close-packed monolayer of transparent beads (e.g. microspheres) 7 within the lens 5 focuses laser light input at the upper surface of the lens, at focal points just beyond the lower surface of the lens where the patterning target surface resides. The "upper" surface of the lens is the surface of the lens opposite to the one at which the transparent beads (e.g. microspheres) are embedded. Figure 14 shows a scanning electron microscope (SEM) image of a small part of the hexagonally-packed microsphere monolayer (shown at x10000 magnification) and a corresponding small part of the resulting patterned target surface and the hexagonal array of micro-pores 30 produced using the lens containing this monolayer. The patterned surface is shown at increasing magnifications of x6315, x20000 and x40000 (bottom to top images). The micro-pores are of the order of about 250nm in diameter.

In this application, most desirably, a suitably high-intensity laser(s) are employed as the illumination source. By controlling laser light fluence (light energy per unit area, e.g. milli J/cm²), one can generate different diameter nano-pores, as tabulated in the following table.

The manufacture of patterned surface microstructures, the laser used is preferably suitable for the material of the target object being patterned. The laser should be able to either melt or ablate the material. Examples of the some types of lasers used in laser surface patterning/texturing are Nd:YAG lasers, carbon dioxide lasers, and excimer lasers. The laser may be a pulsed laser (i.e. producing pulses of light). The laser may be controlled to produce one micro-hole/pore per laser pulse. Pulse repetition rates and pulse durations (e.g. με to fs) may be controlled to enable many micro-holes/pores to be created over short processing times (e.g. 1000s of micro-holes/pores produced per second). In order to produce the patterned microstructures on the material's surface, the laser beam position relative to the surface may be manipulated. The laser may be scanned over the lens to direct the laser beam to successive transparent beads (e.g. microspheres) within the lens for focussing the laser light with that local transparent bead (e.g. microsphere) at the local surface of the material being patterned. A mechanical apparatus (X-Y stage) may be used to move/scan the laser in controlled increments to scan it across the lens to produce the desired pattern. Figure 15A shows a schematic example of an apparatus 40 for surface patterning comprising a lens 5 of the present invention and a mechanically-scanned laser source 41 . Alternatively, control of the laser patterning may be by a beam-scanning system. For example, by reflecting the laser beam with a series of motorized mirrors, the laser beam may be moved to the desired position or contact point on the lens for focussing by a transparent bead (e.g. microsphere) there, to create a micro-pore in the underlying surface being patterned. Motorized mirrors such as a mirror galvanometer may be used and controlled to direct the laser beam to the desired contact point. Figure 15B shows a schematic example of an apparatus 45 for surface patterning comprising a lens 5 of the present invention and a fixed laser source 41 combined with a scanned mirror and collimating lens 46 (to ensure normal incidence at the lens 5) for scanning the laser beam contact point over the lens 5 of the invention at normal incidence.

Figure 17a schematically an embodiment of the invention in which the lens 50 is planoconvex. The lens includes a planar sheet, slab, slide, web or film 6 of host material comprising a plano-convex lens part 6B positioned upon a surface of the sheet, slab, slide, web or film reverse to the common surface 6A and extending across and in optical communication with transparent beads 7 of the lens. The convex surface of the plano-convex lens part is presented outwardly of the lens.

The plano-convex lens material is integrally formed with the host material. In other embodiments the plano-convex lens may be separately formed and attached or adhered thereto (e.g. using index-matching adhesive). The curvature of the plano-convex lens part is 3- dimensional (e.g. spherical). The radius of curvature of the plano-convex lens part is substantially centred at or beyond the common surface 6A and outside of the host material. As is schematically shown in Figure 17a, light rays emanating from transparent beads not in optical communication with the plano-convex lens part may be subject to total internal reflection (TIR) when incident internally upon a bounding surface of the planar part of the lens at a critical angle for TIR. Such light is lost from the output of the lens. However, light rays emanating in the same orientation/angle from transparent beads that are in optical communication with the plano-convex lens part may avoid such total internal reflection (TIR). This is because the bounding surface of the lens they intercept is the convexly curved part of the plano-convex lens part when incident internally upon it. Due to that curvature, the angle of incidence upon it is less than the critical angle for TIR, and so the incident ray is transmitted through the convex surface of the lens as is shown schematically in Figure 17a.

Figure 17b shows a perspective view of a lens according to such an embodiment, illustrating the spherically convex shaping of the plano-convex lens part 6B outwardly presented from the planar sheet, slab, slide, web or film 6 of host material.

It is to be understood that the plano-convex lens features described above with reference to figures 17a and 17b, may also be applied to the embodiments of the invention as described above with reference to figures 8, 9 and 10 herein. In such embodiments, the plano-convex lens may be located upon the planar surface opposite/reverse to the common surface of the lens element 5 over which the coupling layer 13 (Figure 8), or the meta-material 14 (Figure 9), or the second lens element 19 (Figure 10) is located. Put in other words, the embodiment of figures 17a and 17b may also have applied to the common surface 6A thereof, any one of the coupling layer 13 (Figure 8), or the meta-material 14 (Figure 9), or the second lens element 19 (Figure 10).

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS:

1 . A lens comprising: a solid and transparent host material containing therein a plurality of solid and substantially spherical or spheroid transparent particles each fixed within the host material and collectively arranged therein to form a layer of such particles embedded immediately beneath a common surface of the host material such that a respective optical focus of each of the particles resides outside the host material.

2. A lens according to any preceding claim in which a part of the surface area of each said particle of the embedded layer is substantially tangential to said common surface of the host material and is not covered by said host material at said common surface.

3. A lens according to any preceding claim in which the value of the refractive index of the host material is less than the value of the refractive index of the material of the transparent particles at optical wavelengths of light.

4. A lens according to any preceding claim including a coupling layer formed upon said common surface of the host material and comprising a transparent material having a refractive index which exceeds in value the refractive index of the host material at optical wavelengths of light.

5. A lens according to any preceding claim including a coupling layer formed upon said common surface of the host material and comprising a transparent material having a refractive index which exceeds in value the refractive index of the material of the transparent particles at optical wavelengths of light.

6. A lens according to any of claims 5 and 6 in which the material of the coupling layer is a dielectric material.

7. A lens according to any of claims 5 and 6 in which the coupling layer comprises a multi- layered structure including one or more layers of dielectric material and one or more layers of metallic material arranged in alternating succession.

8. A lens according to any preceding claim in which the host material is a dielectric material.

9. A lens according to any preceding claim in which the material of the transparent particles is a dielectric material.

10. A lens according to any preceding claim in which the host material is flexible or pliant.

1 1 . A lens comprising: a first lens element according to the lens of any preceding claim; and, a second lens element according to the lens of any preceding claim; wherein the second lens element is arranged upon the common surface of the host material of the first lens element and extends substantially parallel thereto such that particles of the first lens element are in register with particles of the second lens element thereby to be in optical communication therewith.

12. A lens according to claim 1 1 in which the value of the refractive index of the material of the transparent particles of the second lens element is greater than the value of the refractive index of the material of the transparent particles of the first lens element at optical wavelengths of light.

13. A lens according to any of claims 1 1 and 12 in which the thickness of the host material of the second lens element substantially matches the width of particles of the second lens element such that the layer of particles of the second lens element is embedded immediately beneath a respective common surface of the host material of the second lens element at each of two opposite sides thereof, and extends substantially parallel thereto.

14. A lens scanner apparatus comprising: a lens according to any preceding claim; a lens holder in which the lens is held permitting light to pass through the lens; a sample holder for holding a sample to be viewed through the lens; a position controller coupled to the lens holder to selectively move the lens holder relative to the sample holder to change the separation between the lens relative and the sample holder and/or to move the lens laterally over the sample holder thereby to permit the viewing of different parts of a sample when in the sample holder.

15. A microscope comprising a lens according to any preceding claim or comprising a lens scanner apparatus according to claim 14.

16. A method for manufacturing a lens comprising: providing a surface; arranging a plurality of solid and substantially spherical or spheroid transparent particles upon the surface; subsequently applying a liquid host material to the particles to embed the particles therein whilst the particles are upon the surface; subsequently solidifying the host material; separating the solidified host material and embedded particles from the surface.

17. A method according to claim 16 in which the arranging of the particles upon said surface includes; providing a fluid comprising a plurality of solid and substantially spherical or spheroid transparent particles mixed within a liquid; applying the fluid to the surface and evaporating the liquid from the fluid such that the particles remain arranged upon the surface.

18. A method according to claim 17 including allowing particles to settle onto the surface within the liquid after the fluid is applied to the surface but before the liquid is evaporated.

19. A method according to any of claims 17 to 18 in which the surface is hydrophilic and the liquid comprises water.

20. A method according to any of claims 16 to 29 including the step, between applying the liquid host material and solidifying the host material: pressing a second surface upon the liquid host material within which the particles are embedded thereby to sandwich the liquid host material and the particles between said surface and said second surface such that particles therein simultaneously contact both surfaces; subsequently solidifying the host material; separating the solidified host material and embedded particles from the surface and the second surface.

21 . A method according to claim 20 in which the second surface is substantially flat.

22. A method according to any of claims 16 to 21 in which the surface is substantially flat.

23. Apparatus for patterning a surface including: a lens according to any of claims 1 to 13; a laser light source arranged to generate a laser light beam; a positioner for controllably positioning the laser light beam upon a surface of the lens for transmission through the lens for focussing by a said transparent particle thereof at a focal point of the transparent particle outside the lens for use in ablating or melting material of the surface when positioned at the focal point.

24. A method for patterning a surface comprising: providing a lens according to any of claims 1 to 13; providing a laser light source arranged to generate a laser light beam; controllably positioning the laser light beam upon a surface of the lens for transmission through the lens and focussing the laser light with a said transparent particle thereof at a focal point of the transparent particle outside the lens; ablating or melting material of the surface positioned at the focal point.