DIFFUSION OR PROJECTION SCREEN

Abstract: A light diffusing screen comprises a sheet (20) of material having one surface provided with a ribbed structure comprising a series of parallel first ribs or grooves (5), of angular or lenticular profile. The major surface of each said first rib or groove (5) is provided with fine structure or texture comprising an array of generally parallel ribs or grooves (7), substantially narrower than the first ribs or grooves (5) and running across the first ribs or grooves (5). The screen may be manufactured by laser machining of a workpiece raster fashion using a pulsed laser.

Description: Title: "Diffusion or projection screen" THIS INVENTION relates to light-diffusion or projection screens, for example for off-axis illumination or viewing screens for visual displays, such as LCD displays, or for rear projection screens or front projection screens and/or to light diffusing screens for other purposes, for example for diffused lighting or for privacy purposes. It is an object of the present invention, in one of its aspects, to provide an improved off-axis light diffusion screen, that is to say a diffusing screen which will diffuse collimated light directed onto the diffuser from one side thereof in such a way that the diffused light emanating from the diffuser has a polar distribution with a maximum along an axis which is angularly displaced from the direction along which the collimated light is directed. Such a diffuser is of utility, for example, in projection applications, where the off-axis effect allows observers viewing a projection screen to perceive a projected image at maximum brightness without the observers themselves being in the way of the light projected towards the screen or, for example, as a means of allowing an LCD display to be viewed in ambient light, in such a way that the observer's head may conveniently be located in a position, in relation to the screen, in which it does not interfere with light incident on the screen at the angle appropriate for optimum viewing of the screen by the observer. Other possible applications of such a diffuser will be evident to those skilled in the art. According to one aspect of the invention, there is provided a light diffusing screen comprising a sheet of material having one surface provided with a ribbed structure comprising a series of parallel first ribs or grooves, of angular or lenticular profile and wherein a surface of each said first rib or groove is provided with fine structure or texture comprising an array of generally parallel ribs or grooves, substantially narrower than said first ribs or grooves and running across said first ribs or grooves, generally perpendicular to the direction in which said first ribs or grooves run. According to another aspect of the invention, there is provided a method of manufacturing a light-diffusing screen, comprising laser-machining a surface of workpiece sheet, and either utilising the workpiece as the light-diffusing screen, or deriving said light-diffusing screen from the workpiece in one or more additional steps. In a preferred embodiment, an off-axis light diffusing screen, as herein defined, comprises a sheet of light transmitting or reflecting material having one surface provided with a ribbed Fresnel structure of saw-tooth profile, comprising a series of parallel V-section grooves, each having a short wall generally perpendicular to the plane of the sheet and a long wall or flank inclined obliquely to the plane of the sheet, and wherein the surface of each said long wall or flank is provided with fine structure or texture comprising an array of generally parallel ribs extending perpendicular to the direction in which the respective furrow or groove runs. According to another aspect of the invention there is provided a method of manufacturing an off-axis diffusing screen, as herein defined, comprising providing a workpiece sheet and laser-machining a surface of the sheet to produce a series of parallel similar V-section grooves or furrows such that the surface is provided with a ribbed Fresnel structure of saw-tooth profile, by effecting relative displacement between a machining laser beam and said workpiece sheet in a scanning raster comprising a series of parallel lines, in each of which a respective said V-section groove is formed by erosion of the workpiece material and wherein variation in the depth of erosion across the breadth of each said groove is produced by arranging that the spot of laser light where the laser beam strikes the workpiece varies in its dimension parallel with the line scan, with position across the breadth of the resulting groove during each such major scan a minor scan, so that the rate of removal of material and thus the machining depth, increases progressively from one edge of the groove to the other. The workpiece may comprise a transparent or translucent sheet apt to form said diffusing screen directly, or the workpiece is used as an embossing or moulding tool, or used as an intermediary in producing an embossing or moulding tool, and the diffusing screen may be moulded or embossed by such embossing or moulding tool. It will be understood that the Fresnel profile referred to is adopted in order to afford the off-axis characteristic described. However, where such characteristic is not required, the diffusing screen or the tool for forming the same could be provided by forming, by laser machining, a plurality of grooves of substantially uniform depth along the direction of scan of the laser beam relative to the workpiece. As noted above, the material destined to form the diffusion screen may be directly acted on by the laser beam, but in practice the laser scanning technique will normally be used to form a master, from which, by known electrotyping or other techniques, an embossing tool or mould having a corresponding surface configuration may be produced, with the diffusing screen being produced by impressing plastics material, in a flowable condition, using the mould or embossing tool thus produced. More specifically, the master created by laser machining a plastics material, may have silver deposited by vacuum deposition on its machined surface and a layer of nickel may thereafter be applied by an electroplating technique onto the silver to form a nickel shim or mould to be used to replicate the original shape of the plastics master. In the replication process, a u.v. curable acrylic resin may be used, the uncured liquid resin being poured onto the nickel shim and thereafter cured by exposure to u.v. light. In this way volume production of diffusion screens in accordance with the invention is possible. However, to make small numbers of screens quickly and simply, it is possible to cast silicone rubber directly onto the laser-machined workpiece then produce replicates from the silicone rubber mould by casting with acrylic resin. Embodiments of the invention are described below by way of example with reference to the accompanying drawings in which :- FIGURE 1 is a perspective view, to a much enlarged scale, of a fragment of an off-axis diffusion screen embodying the invention, FIGURE 2 is a view, likewise to a much enlarged scale, showing the screen of Figure 1 in profile, FIGURE 3 is a diagrammatic perspective view illustrating a laser machining process forming a stage in the manufacture of the screen of Figures 1 and 2, FIGURE 4 is a diagrammatic perspective view to a larger scale than Figure 3 showing laser apparatus forming part of that illustrated in Figure 3, FIGURE 5 is a view similar to Figure 2 but showing an alternative profile, FIGURE 6 illustrates an aperture plate forming part of the apparatus shown in Figures 3 and 4, FIGURE 7 is a view similar to Figure 6, of a variant aperture plate which may be used in production of the profile shown in Figure 5, FIGURE 8 is a plan view of a preferred variant of the aperture plate of Figure 6, and FIGURE 9 is a schematic view in vertical section through part of a light diffuser in accordance with the invention. The screen illustrated in Figures 1 and 2 is characterised by a series of V- section or saw-tooth parallel grooves 5, each such groove extending longitudinally parallel with an axis 6, (shown in Figure 1) in the plane of the lower, flat surface of the screen, with the sloping or ramp surface of each such groove being characterised by fine surface detail texturing, in the form of a series of ribs or channels 7 of a width substantially less than the pitch of the saw-tooth grooves 5 illustrated in Figure 2, these smaller grooves 7 being to some degree irregular or random in structure but extending generally parallel with one another and perpendicularly to the longitudinal extent of the larger V- section grooves 5, that is to say parallel with an axis 8 indicated in Figure 1 lying in the plane of the lower surface of the screen and perpendicular to axis 6. By way of example, the pitch between the grooves 5, i.e. between the ramps of the Fresnel profile illustrated in Figures 1 and 2, may be of the order of 40 microns, whereas the smaller transverse grooves 7 may be around 5 microns wide, (i.e. may be arranged at approximately 5 microns pitch). The structure illustrated in Figure 1 may be produced by laser machining of a workpiece in the form of a sheet of, for example, plastics, by a laser, in a process illustrated highly schematically in Figures 3 and 4. By way of example, a plastics workpiece 20 in the form of a Mylar (polyester) sheet may be machined using a pulsed excimer laser pulsed at a pulse repetition rate of 20 to 120 Hz. The output power of such a laser may be 0.2 - 1.2 J/cm 2 . In Figure 3, the laser and its associated optics are indicated, for simplicity, at 26, Figure 3 showing no more of the laser apparatus than a housing illustrated schematically as a cylinder although it will be appreciated that the laser apparatus may have any convenient configuration. In Figure 3, the laser beam is illustrated diagrammatically in broken lines at 30. The workpiece 20, in the form of a Mylar sheet, may be mounted on a platform or bed (not shown) for indexing movement in the direction indicated by arrows 24 while the laser apparatus may be mounted for "line-scan" movement in the direction of arrows 22. Figure 4 shows, still schematically, but in rather greater detail, how the laser apparatus 26 may be arranged. The laser apparatus 26 is illustrated in Figure 4 as comprising a laser proper, represented at 28, directing a laser beam 30 through a first optical element or system 31 adapted to expand or diverge the beam (this expansion of the beam serves, inter alia, to avoid damage to the mask), then through an apertured plate 32 the image of the aperture in which is focused by a lens or optical system 34 onto the workpiece 20 to form an illuminated patch on the workpiece which is of the same configuration as the aperture in the plate 32. Thus, where it is desired, as in the preferred embodiment, to form grooves of a sawtooth form in profile, the plate 32 may be of the form illustrated schematically in Figure 6, with a triangular aperture so that the illuminated patch is of triangular shape with one side of the triangle (which side may be regarded as the base) extending parallel with the direction 22 in which the laser apparatus is scanned over the workpiece. As a result, regions of the workpiece over which the apex of this triangular patch passes during such a line scan are exposed to the laser light only briefly and are thus not much eroded whilst the regions of the workpiece which are passed over by the portion of the triangular patch of laser light bordering the base of the triangular patch, i.e. the side which is opposite to that apex are given a much longer exposure to laser light and are thus eroded more. It has been found, surprisingly, that aromatic, non-charring materials, can be "cut" cleanly in this way. As a result of the relative scanning and indexing movement of the workpiece relative to laser apparatus, as described, the workpiece is scanned repeatedly by laser beam, back and forth in the direction of the arrow 22, in the plane of the sheet, and at the end of each line scan, the workpiece 20 and its supporting table are indexed in the direction of arrow 24 by a distance corresponding to the pitch of the Fresnel sawtooth structure so that the workpiece is scanned in a scanning raster. It will be understood that if convenient, the line scan may be effected by moving the workpiece support apparatus rather than the laser and/or the indexing may be effected by moving the laser. Instead of moving the laser, it may be possible to deflect the laser beam by way of a system of scanning mirrors. The raster scanning movement of the laser beam relative to the workpiece results in the "machining" of a series of grooves, of the Fresnel profile as shown in Figures 1 and 2. As noted above, plastics workpiece 20 in the form of a Mylar (polyester) sheet is preferably machined using a pulsed excimer laser pulsed at a pulse repetition rate of 200 Hz. The output power of such a laser may be 60 watt and the pulse repetition rate 200 Hz. The applicants postulate that the ribs 7 result from the varying intensity of, or pulsed character of, the laser beam during the line scans of the scanning raster referred to. Whilst it would theoretically be possible to produce light-diffusing sheets directly by the laser machining process described, it is proposed, in practice, to use the machined workpiece thus produced as a "master" from which, for example, an embossing die having a corresponding surface structure can be produced by intermediate stages, known per se, such as electrotyping. Of course, a metallic workpiece, for example, could be utilised to form an embossing mould directly or a non-stick plastics workpiece, for example of PTFE, FEP or TEFZEL (R.T.M) could be utilised (machined using a laser light of an appropriate wavelength) and thereafter used as a mould for direct replication of plastics diffusive sheets, or at least of "daughter" moulds from which, in a manufacturing process, the off-axis diffuser product would be produced. A sheet of transparent plastics, for example, having the surface profile illustrated in Figure 1 and described above, acts, in effect, as a combination of diffuser with a thin Fresnel prism, the latter serving to impart an angular deflection or off-axis effect to a beam of collimated light directed therethrough, whilst the roughness of the major surfaces of the Fresnel facets acts to diffuse the light passing therethrough. Because the texturing of the major surfaces of the Fresnel facets is characterised as a series of fine grooves or corrugations 7 running perpendicular to the length of the Fresnel grooves 5, the surface texturing diffuses light preferentially in directions parallel with the Fresnel grooves 5. Thus, for example, if a screen as illustrated in Figures 1 and 2 were to be arranged in a vertical plane, with the grooves 5 running horizontally, a collimated light beam directed horizontally onto the screen, perpendicular to the major plane of the screen would be deflected upwardly or downwardly (depending on the orientation of the Fresnel structure) (hence off-axis) and would also be diffused, by reason of the surface texturing, and furthermore would be diffused more horizontally than vertically, (since the fine grooves 7 in this case run substantially vertically). That is to say, the diffuser possesses diffusive asymmetry. The extent of such asymmetry can be adjusted or "tailored" to some extent by deliberately forming the flanks of the saw-tooth Fresnel structure as convex (or concave) surfaces (neglecting the fine grooves 7) as illustrated in profile in Figure 5, so that light passing through each such flank is spread in a direction perpendicular to the grooves 5 by a lensing action of the flank. Such a quasi convex surface may be produced, by the method described with reference to Figure 3, by substituting, for the plate 32 of Figure 6, a plate 32 as illustrated in Figure 7, in which the slot 38 has one or both of its longer edges curved, so that the decrease in width of the resulting focused laser light patch on the workpiece with position along the direction of arrow 24, and thus the variation in the erosion rate of the workpiece with position along the direction of arrow 24 is similarly non-linear. It will be understood that, in the same way, a lenticular profile could be produced using a plate 32 having a slot 38 of concave or bi-concave profile, for example. Furthermore, it is contemplated that useful off-axis effects may be produced by orienting the slot 38 so that the "base" edge of the slot is angled with respect to arrow 22, for example, rather than parallel to arrow 22. In another form of the apparatus, the aperture plate has a slot 38a of the form shown in Figure 8, which is effectively a series of triangular slots arranged in a row, in series, base to apex, the row extending in the direction of arrow 24 when the plate is mounted in the apparatus. As a result of the form of slot 38a, in each scan of the workpiece 20 relative to the apparatus 26 in the directions of arrow 22 there are formed, instead of a single groove 5, a set of parallel grooves 5, the number of grooves 5 in such set corresponding to the number of individual triangular regions in the slot 38a. In this variant, at the end of each scan along the direction of arrow 22, the workpiece is indexed, relative to the apparatus 26, in the direction of arrow 24 by a distance corresponding to as many times the individual groove 5 pitch as there are grooves 5 in such a set of parallel grooves 5 as aforementioned. In order to avoid the appearance, in the finished product, of flat portions of the original upper surface of the workpiece 20, the aperture 38a is formed as a continuous slot having, in the arrangement illustrated, one straight longitudinal edge and an opposing serrated longitudinal edge, rather than having, in the plate 32, a series of discrete triangular apertures separated by opaque areas. After the laser-machining process, it may be necessary to clean or remove debris from the surface of the machined workpiece. One way of doing this is to subject the machined surface to reactive ion etching. It will be understood that variant forms of quasi-triangular aperture 38 discussed above with reference to Figure 7, for example, could also be used for a plurality of identical apertures arranged in a row in plate 32 or incorporated as respective portions of a single elongate slot in a manner similar to that described above with reference to Figure 8 above. Whilst the action of the screen described above has been described in terms of light transmission through the screen, it will be appreciated that since the effect is determined by surface configuration of the screen, similar effects can be afforded by making the screen from a light-reflecting, e.g. metallic, material, or by providing a light-reflecting coating to a sheet configured as described, either to the textured surface or to the opposite, planar, surface. There are various applications in which an off-axis asymmetric diffuser may be useful. One which the applicants have particularly in mind is in relation to LCD displays illuminated by ambient light where an asymmetric diffusive reflector may be utilised as a back-reflector for an LCD display to allow off- axis viewing or off-axis illumination of the display. On a larger scale such a screen may, as a light-reflecting screen, be used as a front projection screen, to allow efficient concentration of light from the image on screen in the viewing area, or, as a light transmitting screen, to be similarly used as a back-projection screen. It will be appreciated that in some applications, no net light deflecting or "off- axis" effect may be necessary. It is envisaged that, nevertheless, an effective technique for producing a diffuser having defined light diffusing characteristics, particularly in relation to degree of diffusive asymmetry, would be to form, by laser machining, a structure similar to that described with reference to Figures 1 and 2 herein, but adapted to provide a lenticular, rather than a saw-tooth profile, whereby a controlled amount of light "spread" by the quasi cylindrical lenses replacing the saw-tooth ramps will provide "diffusive" spread perpendicular to that favoured by the small scale grooves 7. Alternatively, a light diffuser of controlled asymmetry could be produced simply by forming a controlled distribution of grooves on the workpiece by scanning a machining laser beam across and along the workpiece to provide a controlled number and distribution of grooves in respective ones of two orthogonal directions in the plane of the workpiece sheet. The optical, particularly diffusive, performance of the screen derived from the workpiece can be controlled to some extent by selection of the shape and orientation of the aperture 38. The applicants have noted that the shape and orientation of the microgrooves 7 is primarily dependent on the shape and orientation of the trailing edge of the image, on the workpiece, of the aperture 38, i.e. the edge which passes last over a point on the workpiece during a line scan. Thus, where that trailing edge is straight and perpendicular to the direction of line scan, (for example, where the aperture has the shape of a right- angled triangle and is arranged so that, in the corresponding image of the aperture 38 on the workpiece, one of the sides including the right angle lies parallel with the direction of line scan and the other of the sides including the right angle forms the trailing edge of that image), then the microgrooves 7 run perpendicular to the Fresnel grooves 5. If the trailing edge of the image of the aperture 38 is straight and inclined with respect to the direction of line scan, then the microgrooves 7 will be correspondingly inclined to the grooves 5. Likewise, if the aperture 38 has a semi-circular or crescent-shaped profile and is arranged so that in the corresponding image on the workpiece has an arcuate trailing edge, then the microgrooves 7 will be of arcuate shape. Similarly, if the laser light image of the aperture 38 on the workpiece has the form of an equilateral triangle with its leading edge perpendicular to the direction of line scan then the microgrooves 7 will have the form of 60° chevrons. (In this instance, of course, the larger scale grooves 5 would be of V-shaped profile). In embodiments of the invention the grooved or saw-tooth profiled surface of the diffuser produced as described above may be provided, as illustrated in Figure 9, with a transparent coating 50 intimately contacting the grooved surface of the substrate, referenced 20a, produced as described above and providing a flat optically smooth exposed surface 52 which thus forms one of two opposite flat surfaces of the resulting product. Where the diffuser is transmissive rather than reflective, such layer 50 is selected to have a refractive index significantly different from that of substrate 20a. Where the grooved surface of substrate 20a is arranged to be a light-reflective diffuser, the layer 50 may be, but need not be, of a different refractive index from the material of the substrate 20a (if the substrate 20a is indeed light-transmitting). The arrangement may be similar to that disclosed in GB-2314943 or WO00/41009, to which reference should be had. Examples of manufacture of diffusing screens in accordance with the invention are set out below by way of example :- In order to demonstrate the process as described it was decided to create two alternative prism-like structures incorporating light diffusing characteristics. The first, A, comprised an array of parallel grooves 5 generally of the form shown in Figure 2 defining a corresponding array of parallel prisms with a prism angle of 10° and a prism pitch of 50 μm; the second, B, comprised a similar arrangement of parallel grooves and prisms, but in which successive prisms had different prism angles such that the array comprised a repeating sequence of 3 prisms with prism angles of 8°, 12° and 16° each with a pitch of 30 μm, the sequence repeating every 90 μm. To create these arrays, chrome on quartz masks were first produced using standard electron beam lithography techniques 4 times the required size. The dimensions of the mask being of the same ratio as those required in the finished prism structure. The mask was then placed in the expanded beam of an excimer laser, the beam then reduced (x 4) such that the final dimensions were produced in the polyester workpiece. The laser beam and mask were then scanned across the workpiece as shown in Figure 4. The laser was operating at 50Hz and the progression rate was above 120 -•) μm/sec. The laser energy was about U/cm . The structures were then evaluated for their light deflecting and light scattering properties. The light deflection results confirming the prism angle are as follows: Light deflection was measured using the deflection of a light beam through the sample. The beam arriving inclined to the prism face at the prism angle but with the overall repeat prism structure perpendicular to the beam. Table 1 compares the calculated with the measured deflection of the laser beam. This result demonstrates the accuracy of the laser machining process. The light scattering of the microgroove substructure was examined under a microscope and the diffusion of the substructure measured separately. The substructure of -A- (single prism) was as represented in Figure 1. The grooves 7 had a width of about 3 μm. The scattering (diffusion) as measured using a goniometer was about 15° (full width, half maximum intensity). This data confirms that the structure both deflects light as determined by the prism angle and scatters light consistent with the size of the micro structure. Reference made herein to "Fresnel structure" or "Fresnel grooves" is not intended to signify that the corresponding structure necessarily has the properties of a lens rather than of a prism, and indeed, in the preferred embodiments described in which the grooves 5 are formed by rectilinear scanning, so that the grooves 5 are straight, the product will have the properties of a prism rather than a lens. In such a case the use of the name "Fresnel" is to be regarded as highlighting the fact that the structure is analogous to, although simpler than, a Fresnel lens. In the present specification "comprises" means "includes or consists of and "comprising" means "including or consisting of. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. A light diffusing screen comprising a sheet of material having one surface provided with a ribbed structure comprising a series of parallel first ribs or grooves, of angular or lenticular profile and wherein a surface of each said first rib or groove is provided with fine structure or texture comprising an array of generally parallel ribs or grooves, substantially narrower than said first ribs or grooves and running across said first ribs or grooves. 2. A light diffusing screen according to claim 1 wherein said sheet of material is light transmitting. 3. A light diffusing screen according to claim 1 wherein said sheet of material is light reflecting. 4. A light diffusing screen according to claim 1 wherein said sheet of material is partly light transmitting and partly light reflecting. 5. A light diffusing screen, as herein defined, comprising a sheet of light- transmitting or reflecting material having one surface provided with a ribbed structure comprising a series of parallel V-section ribs or grooves, and wherein the surface of at least one wall or flank of each said rib or groove is provided with fine structure or texture comprising an array of generally parallel ribs extending transversely to the direction in which the respective V-section rib or groove runs. 6. A screen according to claim 5 wherein said parallel V-section grooves are of sawtooth form in section whereby said grooves form a ribbed Fresnel structure of saw-tooth profile, on said surface, each of said parallel V-section grooves having a short wall generally perpendicular to the plane of the sheet and a long wall or flank inclined obliquely to the plane of the sheet, and wherein the surface of each said long wall or flank is provided with said fine structure or texture comprising an array of generally parallel ribs extending transversely to the direction in which the respective V-section groove runs. 7. A light diffusing screen according to any preceding claim, wherein there is provided, over said ribbed surface of said sheet, and in intimate contact with said surface, a layer of transparent material, providing a flat surface on the outside of said layer remote from said ribbed surface of said sheet. 8. A light diffusing screen according to claim 7, wherein said sheet is light- transmitting and said layer of transparent material has a refractive index different from that of said sheet. 9. A method of manufacturing a light-diffusing screen, comprising providing a workpiece sheet and laser-machining a surface of the workpiece sheet, to produce a series of parallel grooves or ribs thereon, by scanning said surface with a laser beam in a scanning raster and either utilising the workpiece as the light-diffusing screen, or deriving said light-diffusing screen from the workpiece in one or more additional steps. 10. A method according to claim 9 wherein said laser machining is so carried out that said grooves or ribs have fine structure comprising a pattern of generally parallel fine ribs extending transversely to the longitudinal direction of the first- mentioned, larger- scale ribs or grooves. 11. A method of manufacturing an off-axis diffusing screen, as herein defined, comprising providing a workpiece sheet and laser-machining a surface of the sheet to produce a series of parallel similar V-section grooves or furrows such that the surface is provided with a ribbed Fresnel structure of saw-tooth profile, by effecting relative displacement between a machining laser beam and said workpiece sheet in a scanning raster comprising a series of parallel lines, in each of which a respective said V-section groove or set of V-section grooves is formed by erosion of the workpiece material and wherein variation in the depth of erosion across the breadth of each said groove is produced by arranging that the spot of laser light where the laser beam strikes the workpiece varies in its dimension parallel with the line scan, with position across the breadth of the resulting groove during each such line scan, so that the rate of removal of material and thus the machining depth, increases progressively from one edge of the groove to the other. 12. A method according to claim 1 1 wherein said spot of laser light is the image of an aperture in an aperture plate through which the laser beam passes before being focused by an optical system onto the workpiece. 13. A method according to claim 12 wherein said aperture plate has an array of such apertures so that a corresponding array of spots of laser light are formed upon said surface of the workpiece, whereby, during each said line scan, a set of such parallel first grooves is formed simultaneously, the workpiece being indexed, relative to the laser apparatus, by a distance corresponding to the pitch or width of such set of first grooves, at the end of each line scan. 14. A method according to any of claims 9 to 13 wherein said laser machining is carried out by a pulsed laser, which is repeatedly pulsed at a frequency large in relation to the scanning frequency, during each said line scan of said raster. 15. A method of manufacturing a light-diffusing screen, comprising laser- machining a surface of workpiece sheet, and either utilising the workpiece as the light-diffusing screen, or deriving said light-diffusing screen from the workpiece in one or more additional steps. 16. A light diffusing screen manufactured by the method of any of claims 9 to 15.

Inventors: CLABBURN ROBIN JAMES THOMAS, CLABBURN, ROBIN, JAMES, THOMAS
Applicants: CLABBURN ROBIN JAMES THOMAS, MICROSHARP CORP LTD, CLABBURN, ROBIN, JAMES, THOMAS, MICROSHARP CORPORATION LIMITED
Application year: 2000
Main classification: G03B21
IPC codes: G02B3, G02B5, G03B21, H04N5