Abstract
A high-resolution PSL system and method incorporating one or more of the following features with a standard PSL system using a SLM projected digital image to form components in a stereolithographic bath: a far-field superlens for producing sub-diffraction-limited features, multiple spatial light modulators (SLM) to generate spatially-controlled three-dimensional interference holograms with nanoscale features, and the integration of microfluidic components into the resin bath of a PSL system to fabricate microstructures of different materials.
Claims
1. A holographic projection micro-stereolithography (PSL) system, comprising: a bath containing a photosensitive resin; and at least two light projection systems, each projection system comprising a light source; and a spatial light modulator (SLM) adapted to produce a digital image when illuminated by the light source, wherein the at least two light projection systems are arranged to holographically interfere said digital images in the photosensitive resin to volumetrically cure select regions thereof in a holographic interference pattern.
2. The holographic projection micro-stereolithography (PSL) system of claim 1, wherein each light projection system further comprises a reduction lens, and a far-field superlens (FSL) contactedly interfacing the photosensitive resin, said FSL including a dielectric layer and a metal grating layer, and wherein the FSL is arranged to convert a far-field image produced by the SLM and reduced by the reduction lens into a near-field image for volumetrically curing the select regions of the photosensitive resin.
3. A holographically-controlled volumetric curing method of photosensitive resin, comprising: providing a bath containing a photosensitive resin, and at least two light projection systems, each light projection system comprising a light source and a spatial light modulator (SLM) adapted to produce a corresponding digital image when illuminated by the light source; activating the light projection systems to produce the digital images; and directing the digital images of the light projection systems to holographically interfere in the photosensitive resin so as to volumetrically cure select regions thereof in a holographic interference pattern.
4. The method of claim 3, wherein each light projection system further comprises a reduction lens, and a far-field superlens (FSL) contactedly interfacing the photosensitive resin, said FSL including a dielectric layer and a metal grating layer, and wherein the FSL is arranged to convert a far-field image produced by the SLM and reduced by the reduction lens into a near-field image for volumetrically curing the select regions of the photosensitive resin.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawings, which are incorporated into and form a part of the disclosure, are as follows.
[0028] FIG. 1 is a flow diagram schematically illustrating the optical path taken in a first exemplary embodiment of the present invention for producing sub-diffraction-limited features.
[0029] FIG. 2 shows a schematic view of a second exemplary embodiment of the present invention incorporating a far-field superlens in the optical path of the PSL to produce sub-diffraction-limited features of 3D micro- and nano-structures in a layer-by-layer stereo lithographic fabrication process.
[0030] FIGS. 3A-C show schematic views of three exemplary methods of superlens-liquid interfacing.
[0031] FIG. 4 shows a schematic view of another exemplary embodiment of the present invention showing multiple projection systems producing a structure based on a digital hologram generated by multiple SLMs arranged around a photosensitive resin bath for patterning 3D nanostructures without periodicity.
[0032] FIG. 5 shows an isometric illustration of three dynamically configurable masks corresponding to three interfering beams which produce a hologram of a complex 3D structure in a photosensitive resin bath to fabricate the 3D structure in a single snapshot/exposure.
[0033] FIG. 6 shows a schematic view of an exemplary microfluidic system of the present invention for injecting multiple types of photosensitive resins into a hath vessel of a PSL system.
[0034] FIG. 7 is a top view of an exemplary bath vessel of a PSL having three injection ports and three outlet ports of an integrated microfluidic system.
[0035] FIG. 8 is a schematic view of another exemplary embodiment of the system of the present invention incorporating multiple SLMS for 3D holographic stereolithography and a microfluidic system for using multiple materials.
DETAILED DESCRIPTION
[0036] Turning now to the drawings, FIG. 1 shows a flow diagram generally illustrating the primary components and the optical path of a first exemplary embodiment of a PSL system 10 of the present invention to produce three-dimensional structures (e.g. meso- or micro-scale) with sub-diffraction-limited features. As shown in FIG. 1, the system 10 generally includes a light source 11, such as for example a UV LED array, which produces electromagnetic radiation (hereinafter light) of a given wavelength, (e.g. 350 nm for UV). The system also includes a SLM 12 which functions as a dynamically configurable mask to produce a two-dimensional pattern/image from the light. The two dimensional image produced from the SLM 12 is then reduced by a reduction lens 13, and projected onto an FSL 14 which is positioned adjacent a photosensitive resin bath 14. The reduced two dimensional image from the SLM (i.e. far field image), is converted by the FSL 14 into a different two-dimensional image (i.e. near-field image) having sub-diffraction-limited features, i.e. features which exist below the diffraction limit. The near-field image then selectively cures local regions within the resin bath 14.
[0037] It is appreciated that the photosensitive resin bath contains a liquid, such as a liquid photosensitive monomer or resin, which is formed into a component when illuminated with the projected beam. In particular, the liquid converts to solid upon exposure to output of the superlens. Example material types include hexandiol diacrylate (HDDA), polyethylene glycol diacrylate (PEGDA), tBA-PEGDMA (a shape memory polymer), POSS-diacrylate, and there could also be nanoparticles in the liquid such as gold, copper, or ceramics. The photosensitive resin may also be loaded with ceramic, metal, or other particles to generate components of different materials. In this case, after initial stereolithographic fabrication, the parts can be sintered to remove the polymer and density the functional material of interest. This usually shrinks the part by some controllable amount. It is also notable that by varying the intensity of the UV light, various porosity/density structures can be generated resulting in graded density materials. This could be combined with the superlens or holographic projection to generate graded density structures with <100 nm features.
[0038] FIG. 2 shows a second exemplary embodiment of the PuML system of the present invention having a light source 26 (shown as a UV source) which illuminates a SLM 28 via a beam splitter 27, and a reduction lens 25 which projects the image onto a FSL 30. The SLM is shown connected to a computer 29 which dynamically controls the SLM to produce various digital masks, such as masks i, j, and k. It is appreciated that the two-dimensional image formed by the SLM are not the actual part or features, rather they are the far-field image calculations corresponding to the desired near-field images to be produced by the FSL 30 which are then used to selectively cure portions of the photosensitive resin, as previously described in the Summary. As shown in FIG. 2, the FSL is positioned to contactedly interface directly with the photosensitive resin at a liquid surface 22. The resin is shown contained in a stereolithographic bath vessel 21, which is open at the top. A z-axis stage 23 and 24 is also provided for lowering the part (such as 31) as each layer is fabricated. The z-axis stage 23, 24 is also shown connected to the computer 29 so as to be controlled by the computer as each level is completed.
[0039] FIGS. 3A-C show three different embodiments by which the FSL may interface with the photosensitive liquid resin. Although the FSL is characterized as far-field, this is only referring to one side of the lens. When a SLM-produced two-dimensional image is projected onto the FSL from the far-field, the FSL then generates near-field sub-wavelength features in the liquid monomer resin bath. Also, in order to have the required surface plasmons for the lens to work, the thin film of silver must have an interface with a dielectric material. It is appreciated that the FSL itself must be maintained in close proximity to the photosensitive liquid. However, it may not be desirable to use the liquid resin/monomer as the dielectric material since the fabricated features may simply stick to the FSL. FIG. 3A in particular shows an FSL 42 having a dielectric layer 43 and a metal grating layer 44 interfaced with the photosensitive resin 40 at a liquid surface 41. In particular, the metal grating layer 44 is shown without an intermediate dielectric material separating it from the resin, and instead directly contacts the photosensitive resin. And incoming light (e.g. the projected image) is shown at 45. FIG. 3B shows a second embodiment of the FSL 46 also having a dielectric layer 49 like FIG. 3A, but now also having an intermediate solid dielectric layer 48 which is formed (e.g. coated) over the metallic grating layer 47. The coating may be a very thin layer, e.g. <100 nm to provide the metal dielectric interface. Example material types may include PMMA, PDMS, glass, etc. And in FIG. 3C, another embodiment is shown having a dielectric layer 51, and where another liquid 52 (such as an oil) is used as the dielectric interlayer. As shown in the figure, a thin layer of the liquid dielectric 52 will remain in contact with the FSL 50 due to surface tension effect. Similar to the solid dielectric, the liquid dielectric interlayer provides the metal dielectric interface. In this case, the liquid 52 fills voids in the grading via surface tension effects and can provide a very thin layer, it also prevents cored components from sticking to the FSL. Example material types may include mineral oil, and other oils. The FSL may be held in placed on top of the liquid surface by conventional mounting hardware known in the art or, for example, on a motion stage to ensure good positioning. Furthermore, the FSL may be placed to cover the free liquid surface (in whole or in part).
[0040] FIG. 4 shows a second exemplary embodiment of the system 80 of the present invention, with multiple electromagnetic radiation projection systems 81-83 together stereolithographically producing a three-dimensional structure 85 based on a digital hologram generated by the multiple projection systems. The structures may be aperiodic structures, designed features, or even fully 3D holograms. In particular, the projection systems 81-83 each have integrated SLMs (not shown) to produce digital masks, and are arranged around a photosensitive resin hath vessel 83 to produce a 3D holographic interference pattern in liquid resin for patterning 3D nanostructures without periodicity. The vessel 83 is shown as with optically transparent walls so that projections systems 82 and 83 may illuminate from the sides. The projection system 81 illuminates from the top through the open top side of the vessel 83 where the liquid level 84 is shown. A stage 86 (such as a z-axis stage) may also be provided where the holographically produced structure may be positioned.
[0041] Similarly, FIG. 5 shows an isometric illustration of three dynamically configurable masks 91-93 corresponding to three interfering beams which produce a hologram of a complex 3D structure 90 in a photosensitive resin bath to fabricate the 3D
[0042] structure in a single snapshot/exposure. The three masks are shown orthogonally oriented, such as on xyz-axes. However, as shown in FIG. 8, multiple projection systems need not be orthogonal to each other. It is appreciated that each of the projections systems may also incorporate a FSL to produce sub-diffraction limited features when holographically interfered with the near-field images from the other projection systems. The holographic lithography interferes light beams from multiple digital masks rather than lasers, and can provide individual pixel control. With this control, the interference pattern between the two or more beams can be changed in 3D space resulting in locally controlled features and aperiodic structures. In addition, true 3D holograms may be generated and projected into the photosensitive monomer to generate 3D structures (without the need for Z-stage adjustment).
[0043] FIG. 6 shows another exemplary embodiment of a microfluidic system 100 of the present invention, integrated with a larger PSL system (not shown) to enable materials flexibility, i.e. fabricating multi-materials components, with multiple materials in either the same layer or across layers. This allows a broad range of materials to be used with PSL to include metals, ceramics and a range of polymers. FIG. 6 shows in particular a PSL bath vessel 101 having a cylinder 102 and a piston 103. The top of the cylinder is open and contains a photosensitive resin. The top of the piston 103 is shown as the fabrication stage and is connected to a z-stage 104 for lowering/elevating the fabricated part, typically in a layer-by-layer process. The cylinder 102 walls may be optically transparent so as to enable illumination by image projectors (not shown). The system 100 is shown having an inlet 108 fluidically connected to at least two different photosensitive resin sources 106 to 107, which are connected to supply the vessel with different photosensitive liquids. A control valve 109 is shown connected to a computer 105 (or other controller) for controlling injection of resin into the bath vessel. An outlet port 110 is also shown for exhausting photosensitive liquid from the hath container, so that the vessel may be emptied of a first photosensitive liquid used to produce a first feature of a fabricated structure prior to tilling with a second photosensitive liquid used to produce a second feature of the fabricated structure. And a control valve 111 is also shown connected to the computer 105 for controlling flow out of the vessel.
[0044] FIG. 6 also shown a membrane 112 which may be positioned at the liquid surface, so as to enable laminar flow when resin is moved in and out of the vessel. The membrane is preferably optically transparent, as well as flexible so as to deform when fluid is moving in/out and eliminate liquid free surface disturbance. Optionally, the membrane may be gas permeable. Example material types include PDMS, glass, quartz, and other clear flexible polymers. It is notable that if an FSL is used, the membrane may or may not be used since the FSL would cover the free surface in place of the membrane. However, since the FSL is a thin film structure it can also be deposited on the membrane 112, such as in combination with radical inhibition layer.
[0045] FIG. 7 shows a top view of another embodiment of the microfluidic system integrated into the PSL of the present invention. In particular, a bath vessel 200 used in a PSL system and adapted to contain a photosensitive resin therein is shown having multiple inlet, and outlet ports 201-206 connected along its walls, and preferably near the liquid surface. The injection or inlet ports are indicated at 201-203, and the exhaust or outlet ports are indicated at 204-206. Each of the inlet ports are in fluidic communication with one or more different types of photosensitive resin reservoir or sources to provide the vessel basin 200 with the desired material. In one particular embodiment, each inlet port may be connected with a unique material, while in an alternative embodiment, each inlet port may be connected to each of the various types of resins available.
[0046] And FIG. 8 shows a combined system 300 having the features of a multiple projection system for 3D holographic fabrication and an integrated microfluidic system for multiple material delivery. In particular, three projection systems 321-322 are shown, which project two-dimensional images into the fabrication zone characterized by a bath vessel 301. Similar to FIG. 36, the system includes a PSL bath vessel 301 having a cylinder 302 and a piston 303. The top of the cylinder is open and contains a photosensitive resin. The top of the piston 303 is shown as the fabrication stage and is connected to a z-stage 304 for lowering/elevating the fabricated part, typically in a layer-by-layer process. The cylinder 302 walls may be optically transparent. And ports 308 and 310 are connected to the bath vessel and controlled by valves 309 and 311, respectively. Furthermore a computer 305 controls the z-stage 304 and the valves 309, 311. While not shown in FIG. 8, each of the projections systems 301-301 may incorporate a FSL such that the image projected into the fabrication zone is a near-field image. And similar to the membrane 112 of FIG. 6, FIG. 8 also shows a membrane 312 positioned at the liquid surface.
[0047] While particular embodiments and parameters have been described and/or illustrated, such are not intended to be limiting. Modifications and changes may become apparent to those skilled in the art, and it is intended that the invention be limited only by the scope of the appended claims.
