Light valve system with clearance maintenance system

Abstract

The light valve may include a liquid crystal layer having a first side and a second side. The first substrate is positioned in contact with a first side of the liquid crystal layer, wherein the first substrate has a first semiconductor layer. The second substrate is positioned in contact with the second side of the liquid crystal layer, wherein the second substrate has a second semiconductor transparent electrode layer and a second semiconductor layer. A plurality of laser transparent aperture support structures are positioned within the liquid crystal layer to contact both the first substrate and the second substrate to create a stable and uniform gap under the action of liquid crystal surface tension applied to the thin and compliant substrate.

Description

Related Applications

[0001] This disclosure is part of a non-provisional patent application claiming priority benefit of U.S. Patent Application No. 63 / 580,158, filed September 1, 2023, which is hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0002] The present disclosure relates generally to the operation of liquid crystal light valves with high power capability suitable for additive manufacturing. More specifically, precise positioning of first and second substrates relative to a liquid crystal material is described. BACKGROUND

[0003] High power laser systems capable of operating at high fluence for long periods of time are useful for additive manufacturing and other applications. Such high power lasers can use a light valve to provide a patterned beam. For example, a light valve (LV) is a type of spatial light modulator that can be used to uniformly impress information across a beam (1D modulation), provide variations across a beam to form parallelized optical channels (2D modulation), or provide variations across a volume of pixel / voxel channels (3D modulation). The information imparted on the read beam can be in the form of amplitude, phase, polarization, wavelength, coherence, or quantum entanglement.

[0004] One type of light valve is a spatial light modulator (SLM), a light valve that uses a refractive material to impart a spatially varying modulation to a light beam. The SLM generally helps to modulate the intensity of the light beam. Alternatively, a cross polarizer can be used to convert a phase modulation to an amplitude modulation. However, devices can also be fabricated that modulate the polarization or phase of the light beam or both the intensity and phase simultaneously. Advantageously, the images created by electronically addressed spatial light modulators can be created and changed electronically.

[0005] A light valve or other spatial light modulator can include a light refracting liquid crystal layer between two transparent substrates or facing at least one transparent substrate in a reflective design. Maintaining a uniform gap thickness is important to achieve spatially uniform transmittance of a light beam through a liquid crystal based electro-optic device. Carefully polished and planarized, thick and rigid substrates can be used to assemble a liquid crystal cell that can maintain rigidity and gap thickness. The larger the area, the thicker the substrate must be to maintain a flat surface in an inherently self-supporting manner for gap control and to avoid sagging. Unfortunately, particularly in larger format light valves, thick substrates cannot easily compensate for stresses, warping, or deformation, resulting in non-uniform gap thickness across the aperture and reduced light valve performance. Moreover, there can be a lack of availability of suitable substrate materials with the required thickness. Methods and structures of operation are needed to improve or maintain light valves used in conjunction with high power lasers or in large format sizes. BRIEF DESCRIPTION OF DRAWINGS

[0006] Non-limiting and non-exhaustive embodiments of the present disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures unless otherwise specified.

[0007] Figure 1A Parts of a transmissive light valve with laser-transparent aperture support structures are shown; Figure 1B Parts of a reflective light valve with laser-transparent aperture support structures are shown; FIG. 1C shows a method of forming a light valve with laser-transparent aperture support structures; Figure 2 A block diagram of an additive manufacturing system based on high fluence light valves is shown, which supports a beam dump, light valves, and heat engines; Figure 3 An additive manufacturing system based on high fluence light valves is shown; Figure 4 Another embodiment of an additive manufacturing system based on high fluence light valves is shown; and Figure 5 Another embodiment of an additive manufacturing based on high fluence light valves is shown, which incorporates a switchyard method for recycling and further use of waste heat energy. DETAILED DESCRIPTION

[0008] In the following description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the present disclosure can be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the concepts disclosed herein, and it is to be understood that modifications can be made to the various disclosed embodiments without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense.

[0009] In the following disclosure, a light valve can include a liquid crystal layer having a first side and a second side. A first substrate is positioned in contact with the first side of the liquid crystal layer, where the first substrate has a first semiconductive layer. A second substrate is positioned in contact with the second side of the liquid crystal layer, where the second substrate has a second semiconductive transparent electrode layer and a second semiconductive layer. A plurality of laser-transparent aperture support structures are positioned within the liquid crystal layer to contact both the first substrate and the second substrate. Additionally, in some embodiments, separate and distinct laser-transparent aperture support structures are not required, where the first substrate and the second substrate are thin and flexible enough to allow surface tension provided by the liquid crystal layer to maintain a substantially uniform gap that varies by less than a micron or so.

[0010] In some embodiments, the first substrate further includes a first semiconducting transparent electrode layer positioned in contact with the first semiconducting layer to form a transmissive light valve.

[0011] In some embodiments, the first substrate further includes a reflective layer positioned in contact with the first semiconducting layer to form a reflective light valve.

[0012] In some embodiments, the liquid crystal layer has a thickness of less than 100 microns, less than 10 microns, or less than 5 microns.

[0013] In some embodiments, each substrate has a thickness of less than 1 mm.

[0014] In some embodiments, each substrate includes at least one of a wide bandgap semiconducting material or a super wide bandgap semiconducting material.

[0015] In some embodiments, the plurality of laser-transparent aperture support structures includes at least one of a spacer ball, a spacer, and a post positioned within the liquid crystal layer and sized to maintain a uniform gap between the first substrate and the second substrate.

[0016] In some embodiments, the first substrate and the second substrate, and the liquid crystal layer are attached to form a monolithic block.

[0017] In some embodiments, the first substrate and the second substrate, and the liquid crystal layer have a CTE that matches within 10% of each other.

[0018] In some embodiments, a method of forming a light valve includes providing a liquid crystal layer having a first side and a second side. A plurality of laser-transparent aperture support structures can be applied or otherwise positioned within the liquid crystal layer. A first electrode can be positioned on a first semiconducting layer to form a first substrate. The first semiconducting layer can be attached to the first side of the liquid crystal layer. A second transparent electrode can be positioned on a second semiconducting layer to form a second substrate, and the second semiconducting layer is arranged to contact the second side of the liquid crystal layer.

[0019] In some embodiments, an additive manufacturing system includes a laser system and a powder bed. A light valve is positioned to pattern light received from the laser system and direct the patterned light to the powder bed. In such embodiments, the light valve includes a liquid crystal layer having a first side and a second side. A first substrate is positioned in contact with the first side of the liquid crystal layer, where the first substrate has a first semiconducting layer. A second substrate is positioned in contact with the second side of the liquid crystal layer, where the second substrate has a second semiconducting transparent electrode layer and a second semiconducting layer. A plurality of laser-transparent aperture support structures are positioned within the liquid crystal layer to contact both the first substrate and the second substrate.

[0020] In some embodiments, a light valve forming part of an additive manufacturing system can form a two-dimensional light pattern.

[0021] Figure 1A One embodiment of a transmissive light valve with high fluence or high power capability is shown that is suitable for use in additive manufacturing systems or other applications that use energy fluences greater than 2 Joules / cm 2 , kilowatt scale power, tens of Joules of energy over multiple cm 2 areas. In one embodiment, transmissive light valve system 100A includes a liquid crystal layer 104A. Liquid crystal layer 104A is positioned between a first substrate layer 102A(i) and a second substrate layer 102A(ii). In some embodiments, liquid crystal layer 104A, as well as first substrate layer 102A(i) and second substrate layer 102A(ii), can combine to form a monolithic block that resists delamination or layer separation and has matching CTEs and refractive indices between and within the layers that sandwich 104A. In some embodiments, first substrate layer 102A(i) and second substrate layer 102A(ii) can have their respective coefficients of thermal expansion (CTEs) matched to within 10%, 5%, or 1% of each other. Further, first substrate layer 102A(i) and second substrate layer 102A(ii) can have their CTEs matched to within 10%, 5%, or 1% of each other and of liquid crystal layer 104A.

[0022] Advantageously, the closely matched CTEs of liquid crystal layer 104A with first substrate layer 102A(i) and second substrate layer 102A(ii) each facilitate uniform expansion of transmissive light valve system 100A when heated by a laser. Similar and mostly transparent materials can be selected for first substrate layer 102A(i) and second substrate layer 102A(ii) to provide balanced light absorption and heating between the layers so that the layers experience the same temperature rise to minimize thermal mechanical strain and stress cycles, fatigue, and damage, thereby extending the device lifetime.

[0023] In some embodiments, the light-induced semiconductor excitation level in the photoconductor layer can also be balanced or closely matched to less than 1 percent in order to produce a more tightly coupled electric field applied to the liquid crystal from top to bottom, which can improve the spatial resolution of the patterning. In various embodiments, the substrates can be thin enough to be compliant and self-regulating when a fluid liquid crystal layer is stacked between the substrate layers. Gap uniformity can be achieved at least in part via the inward force through the liquid applied surface tension between the 2 substrates.

[0024] In some embodiments, first substrate layer 102A(i) can be formed from a first transparent electrode layer and a first wide bandgap or super wide bandgap semiconductor layer. Similarly, second substrate layer 102A(ii) can be formed from a second transparent electrode layer and a second wide bandgap or super wide bandgap semiconductor layer.

[0025] The thickness requirement of the substrate layers depends on one or more of the surface tension of the liquid crystal layer, the target gap thickness, the stiffness of the material, the surface shape, and the local geometry. In various examples, the thickness of the substrate layers is less than 1 mm. For example, the substrate thickness of each of the first substrate layer 102A(i) and the second substrate layer 102A(ii) can be in the range of 300 pm - 1000 pm. The resulting intrinsic interfacial tension pulls the two layers together compared to thicker substrate layers. In some embodiments, gap uniformity can be achieved by using hole support structures 106A (e.g., support spacers or spacing balls) within the liquid crystal layer. The hole support structures can be formed from silica or polymer microspheres or other support structures, e.g., polymer posts or other inorganic layers that counteract the surface tension. In one embodiment, the polymer posts or other inorganic layers can be produced by photolithography and then etched by reactive ion etching or other etching processes. In one example, the spacing structures are transparent to the laser, thus not affecting the operation of the light valve system.

[0026] The support fluid gap with surface tension can exert a uniform gap thickness under passive conditions, but can also maintain gap uniformity under dynamic loading conditions, preventing gap collapse or separation, thus maintaining device performance during operation. Additionally, in some embodiments, a separate and distinct laser-transparent hole support structure is not required, where the first and second substrates are thin and flexible enough to allow the surface tension provided by the liquid crystal layer to maintain a substantially uniform gap that varies by less than a micron or so.

[0027] The interfacial tension induced between the two substrate layers 102A(i) and 102A(ii) is a function of the gap thickness, the gap area, and the surface tension properties of the liquid crystal layer 104A. According to the power spectrum of the spatial surface non-uniformity and the local geometry, as well as the stiffness of the non-flat surface regions of the substrates, the non-uniformity can be eliminated as they are pulled towards abutting the hole supports 106A. In devices with thin substrate layers 102A(i) and 102A(ii) for high power laser applications, where the heat generated in the liquid crystal layer 104A or adjacent substrates can induce mechanical deformation and lead to stress-induced birefringence, maintaining a uniform thickness of the liquid crystal layer 104A can mitigate dynamic loading issues.

[0028] The use of hole support structures 106A within the liquid crystal layer 104A between the first substrate layer 102A(i) and the second substrate layer 102A(ii) helps to provide a uniform thickness of the liquid crystal layer 106A. Additionally, the hole support structures 106A can mitigate spatial surface non-uniformities of the first substrate layer 102A(i) and the second substrate layer 102A(ii) to achieve gap uniformity, which reduces the constraints on the flatness required to produce the substrate layers, or can reduce the substrate thickness required to maintain flatness. Gap uniformity can occur with non-flat substrates, as long as any surface non-uniformities of the first substrate layer 102A(i) and the second substrate layer 102A(ii) are locally compensated. For example, the holes can have a curved shape, but under the action of surface tension in all areas of the gap liquid crystal applied between the two substrates, have a uniform gap maintained by the spacer balls.

[0029] The density of the support structures can be designed based on the substrate thickness, surface shape, substrate stiffness, and surface non-uniformities. For example, support structures such as spacer balls can be applied uniformly within the liquid crystal layer gap at a fixed number per unit area. Various methods can be used to apply the spacer balls, for example, controlled puffing / spraying, by spin coating a solvent solution dispersed with spacer balls, or using photolithographic techniques (e.g., photolithography or reactive ion exchange (RIE)) or a combination of techniques. The minimum required density of the spacer balls can be calculated by determining the force to pull the substrates together, for example, the spacer balls can be applied at a density of 1000 / cm 2

[0030] In operation, the addressing laser 101A(i) ("write light") causes a spatial pattern that can be transferred to a co-incident "read light" 101B(ii). In combination with polarizers, this image transfer process selectively results in blocking or transmitting laser light through the laser valve system 100A. The high fluence, high power, and high energy input light 101A(ii) is directed through the laser valve system 100A, spatially patterned, and becomes the output light 101A(iii). This light can be directed to heat a powder bed suitable for additive manufacturing.

[0031] Figure 1B An embodiment of a reflective light valve suitable for an additive manufacturing system is shown, which is suitable for an additive manufacturing system or for use in a system that has a fluence greater than 2 Joules / cm 2 ​Energy density use benefits from longer light valve lifetime for other applications. In one embodiment, the reflective light valve system 100B includes a liquid crystal layer 104B. The liquid crystal layer 104B is located between the first substrate layer 102B(i) and the second substrate layer 102B(ii). In some embodiments, the liquid crystal layer 104B and the first and second substrate layers 102B(i) and 102B(ii) can be combined to form a monolithic block that resists delamination or layer separation and has matching CTEs and refractive indices between and within the layers that sandwich 104B. In some embodiments, the first and second substrate layers 102B(i) and 102B(ii) can have their respective coefficients of thermal expansion (CTEs) matched to within 10%, 5%, or 1% of each other. Further, the first and second substrate layers 102B(i) and 102B(ii) can have their CTEs matched to within 10%, 5%, or 1% of each other and the liquid crystal layer 104A. The closely matched CTEs facilitate uniform expansion of the reflective light valve system 100B when heated by a laser, however, balanced light absorption and heating between the layers will be achieved for each layer if the same mostly transparent materials are used, so that the bottom and top layers experience the same temperature rise to minimize thermal mechanical strain and stress cycles, fatigue, and damage, thereby extending lifetime.

[0032] In some embodiments, the light-induced semiconductor excitation levels in the photoconductor layer can also be balanced or closely matched to less than 1 percent in order to produce a more tightly coupled electric field applied to the liquid crystal from top to bottom, which can improve the spatial resolution of the patterning. In various embodiments, the substrates can be thin enough to be compliant and self-regulating when fluid liquid crystal layers are stacked between the substrate layers. Gap uniformity can be achieved via surface tension applied by the liquid crystal layer material.

[0033] In some embodiments, the first substrate layer 102B(i) can be formed from a first transparent electrode semiconductor layer that includes a first wide bandgap or super wide bandgap photoconductor semiconductor and a reflective layer (e.g., a dielectric mirror or a doped semiconductor multilayer). In some embodiments, the second substrate layer 102B(ii) can be formed from a second semiconductor transparent electrode layer and a wide bandgap or super wide bandgap photoconductor semiconductor layer. In some embodiments, a plurality of orientation layers and anti-reflective layers can be monolithically formed on at least one of the first transparent electrode and photoconductor layer, the first transparent conductive electrode, the second transparent electrode and photoconductor layer, and the second transparent conductive electrode.

[0034] The thickness of the substrate layers depends on one or more of the surface tension of the liquid crystal layer, the target gap thickness, the stiffness of the material, the surface shape, and the local geometry. In various examples, the thickness of the substrate layers is less than 1 mm. For example, the substrate thickness of each of the first substrate layer 102B(i) and the second substrate layer 102B(ii) can be in the range of 300 pm - 1000 pm. The resulting intrinsic interfacial tension pulls the two layers together compared to thicker substrate layers. In some embodiments, gap uniformity can be achieved by using hole support structures 106B (e.g., support shims or spacer balls) within the liquid crystal layer. The hole support structures can be formed from silica or polymer microspheres or other engineered support structures, e.g., polymer posts or other inorganic layers that counteract the surface tension. In one embodiment, the polymer posts or other inorganic layers can be produced by photolithography and then etched by reactive ion etching or other etching processes. In one example, the spacing structures are transparent to the laser, so they do not affect the operation of the light valve system.

[0035] The support fluid gap with surface tension can apply a uniform gap thickness under passive conditions, but can also maintain gap uniformity under dynamic load conditions, preventing gap collapse or separation, thereby maintaining device performance during operation.

[0036] The interfacial tension induced between the two substrate layers 102B(i) and 102B(ii) is a function of the gap thickness, the gap area, and the surface tension properties of the liquid crystal layer 104B. According to the power spectrum of the spatial surface non-uniformity and the local geometry, as well as the stiffness of the non-flat surface regions of the substrates, the non-uniformity can be eliminated when they are pulled into abutment against the hole supports 106B. In devices with thin substrate layers 102B(i) and 102B(ii) for high power laser applications, where the heat generated in the liquid crystal layer 104B or adjacent substrates can induce mechanical deformation and cause stress-induced birefringence, maintaining a uniform thickness of the liquid crystal layer 104B can mitigate these dynamic load issues.

[0037] The hole support structures 106B within the liquid crystal layer 104B between the first substrate layer 102B(i) and the second substrate layer 102B(ii) help to achieve a uniform thickness of the liquid crystal layer 106B, but also can mitigate spatial surface non-uniformity of the first substrate layer 102B(i) and the second substrate layer 102B(ii) to achieve gap uniformity, which reduces the constraints on the flatness or thickness required to produce the substrate layers. Gap uniformity can occur with non-flat substrates as long as any surface non-uniformity of the first substrate layer 102B(i) and the second substrate layer 102B(ii) is locally compensated. For example, the holes can be curved, but have a uniform gap maintained by the spacer balls.

[0038] In Figure 1BIn the illustrated mode of operation, the addressing laser 101B(i) ("write light") causes a spatial pattern that can be transferred to the co-incident high fluence, high power, and high energy read light 101B(ii). In combination with the polarizer, this image transfer process selectively causes the reflected laser light through the laser valve system 100B to be blocked or transmitted as output light 101B(iii). This light can be directed to heat a powder bed suitable for additive manufacturing.

[0039] Figure 2 An example process of fabricating a high fluence, high power, and high energy reflective light valve is shown. Process 200 can include providing 202 a liquid crystal layer.

[0040] One or more of the following can be used to apply 204 a plurality of hole support structures within the liquid crystal layer: controlled blow-spraying / spraying, dispersing a solvent solution with spacer balls by spin coating, or using photolithographic techniques (e.g., photolithography or reactive ion exchange (RIE)) or a combination of techniques. The minimum required density of the spacer balls can be calculated by determining the force that pulls the substrates together, for example, the spacer balls can be applied at a density of 1000 / cm2. The hole support structures can be formed from silica or polymer microspheres or other support structures, for example, polymer pillars or other inorganic layers that counteract surface tension. In one embodiment, the polymer pillars or other inorganic layers can be produced by photolithography and then etched by reactive ion etching or other etching processes. In one example, the spacer structures are transparent to the laser, thus not affecting the operation of the light valve system. 2

[0041] A first transparent electrode can be positioned 206 on a photoconductor layer including a first semiconductor layer having a wide bandgap, the first semiconductor layer contacting 208 the liquid crystal layer. In some embodiments, the first semiconductor layer can have a thickness of less than 1 mm. A second transparent electrode can be positioned 210 on a photoconductor layer including a second semiconductor layer having a wide bandgap, the second semiconductor layer contacting 212 the liquid crystal layer. In some embodiments, the first semiconductor layer can have a thickness of less than 1 mm.

[0042] In some embodiments, one or more anti-reflective coatings can be applied to the first semiconductor layer and the second semiconductor layer.

[0043] A wide range of lasers of various wavelengths can be used in conjunction with the described light valve system. In some embodiments, possible laser types include, but are not limited to: gas lasers, chemical lasers, dye lasers, metal-vapor lasers, solid-state lasers (e.g., fiber), semiconductor (e.g., diode) lasers, free electron lasers, gasdynamic lasers, "nickel-like" samarium lasers, Raman lasers, or nuclear-pumped lasers.

[0044] ​Gas lasers can include such as a helium-neon laser, argon laser, krypton laser, xenon ion laser, nitrogen laser, carbon dioxide laser, carbon monoxide laser, or excimer laser.

[0045] Chemical lasers can include such as a hydrogen fluoride laser, deuterium fluoride laser, COIL (chemical oxygen iodine laser), or Agil (all-gas iodine laser).

[0046] Metal-vapor lasers can include such as a helium-cadmium (HeCd) metal-vapor laser, helium-mercury (HeHg) metal-vapor laser, helium-selenium (HeSe) metal-vapor laser, helium-silver (HeAg) metal-vapor laser, strontium vapor laser, neon-copper (NeCu) metal-vapor laser, copper vapor laser, gold vapor laser, or manganese (Mn / MnCl2) vapor laser. Rubidium or other alkali metal vapor lasers can also be used. Solid-state lasers can include such as a ruby laser, Nd:YAG laser, NdCrYAG laser, Er:YAG laser, neodymium YLF (Nd:YLF) solid-state laser, neodymium yttrium vanadate (Nd:YVO4) laser, neodymium calcium oxyborate yttrium (Nd:YCa4O(BO3) 3 or simply Nd:YCOB, neodymium glass (Nd:glass) laser, titanium sapphire (Ti:sapphire) laser, thulium YAG (Tm:YAG) laser, ytterbium YAG (Yb:YAG) laser, ytterbium:2O3 (glass or ceramic) laser, ytterbium-doped glass laser (rod, slab / plate, and fiber), holmium YAG (Ho:YAG) laser, chromium ZnSe (Cr:ZnSe) laser, cerium-doped lithium strontium (or calcium) aluminum fluoride (Ce:LiSAF, Ce:LiCAF), praseodymium-doped 147 phosphate glass (147Pm +3 :glass) solid-state laser, chromium-doped alexandrite (chrysoberyl) laser, erbium-doped and erbium-ytterbium co-doped glass laser, trivalent uranium-doped calcium fluoride (U:CaF2) solid-state laser, divalent samarium-doped calcium fluoride (Sm:CaF2) laser, or F-center laser.

[0047] Semiconductor lasers can include such as the following laser medium types: GaN, InGaN, AlGaInP, AlGaAs, InGaAsP, GaInP, InGaAs, InGaAsO, GaInAsSb, lead salts, vertical-cavity surface-emitting lasers (VCSELs), quantum cascade lasers, hybrid silicon lasers, or combinations thereof.

[0048] Figure 2Use of a light valve such as disclosed herein in an additive manufacturing system 200 is shown. A laser source 202 directs a laser beam through a laser pre-amplifier and / or amplifier 204 into a light valve 206. After patterning, light can be directed into a print bed 210. In some embodiments, thermal or laser energy from the laser source 202, laser pre-amplifier and / or amplifier 204 or actively cooled light valve 206 can be actively or passively transferred to a heat transfer device, heat engine, cooling system and beam dump 208. The overall operation of the light valve based additive manufacturing system 200 can be controlled by one or more controllers 220 which can vary the laser power and timing.

[0049] In some embodiments, various pre-amplifiers or amplifiers 204 are optionally used to provide high gain to the laser signal, while optical modulators and isolators can be distributed throughout the system to reduce or avoid optical damage, improve signal contrast, and protect lower energy portions of the system 200. Optical modulators and isolators can include, but are not limited to, Pockels cells, Faraday rotators, Faraday isolators, acousto-optic reflectors, or volume Bragg gratings. The pre-amplifiers or amplifiers 204 can be diode-pumped or flashlamp-pumped amplifiers and configured as single-pass and / or multi-pass or cavity-type architectures. As will be appreciated, the term pre-amplifier is used here to indicate amplifiers that are not thermally limited relative to the laser amplifiers (i.e. they are smaller). The amplifiers will typically be positioned as the final units in the laser system 200 and will be the first modules susceptible to thermal damage, including but not limited to thermal fracture or excessive thermal lensing.

[0050] The laser pre-amplifiers can include single-pass pre-amplifiers available in systems that do not overly concern energy efficiency. For systems that are more energy efficient, multi-pass pre-amplifiers can be configured to extract many energies from each pre-amplifier 204 before entering the next stage. The number of pre-amplifiers 204 required for a particular system is defined by the system requirements and the stored energy / gain available in each amplifier module. Multi-pass pre-amplification can be achieved by angular multiplexing or polarization switching (e.g. using a waveplate or Faraday rotator).

[0051] Alternatively, the pre-amplifier can include a cavity structure with a regenerative amplifier type configuration. While such a cavity structure can limit the maximum pulse length due to typical mechanical considerations (length of the cavity), in some embodiments, a "white cell" cavity can be used. A "white cell" is a multi-pass cavity architecture where each pass adds a small angular deviation. By providing an entrance and exit path, such a cavity can be designed to have a very large number of passes between the entrance and exit, allowing for large gain and efficient use of the amplifier. One example of a white cell is a confocal cavity, where the beam is injected slightly off-axis and the mirrors are tilted so that a circular pattern is created on the mirrors after multiple passes. By adjusting the injection angle and mirror angle, the number of passes can be varied.

[0052] The amplifiers are also used to provide sufficient stored energy to meet the system energy requirements while supporting sufficient thermal management to enable operation at the required repetition rate of the system, whether they are diode pumped or flashlamp pumped. Both the thermal energy and the laser energy generated during operation can be directed for heat transfer into a heat engine, cooling system, or beam dump 208.

[0053] The amplifiers can be configured as single pass and / or multi-pass or cavity type architectures. The amplifiers can include single pass amplifiers that are available in systems that do not overly concern energy efficiency. For systems that are more energy efficient, multi-pass amplifiers can be configured to extract much of the energy from each amplifier before entering the next stage. The number of amplifiers required for a particular system is defined by the system requirements and the stored energy / gain available in each amplifier module. Multi-pass pre-amplification can be achieved by angular multiplexing, polarization switching (waveplates, Faraday rotators). Alternatively, the amplifiers can include a cavity structure with a regenerative amplifier type configuration. As discussed with respect to the pre-amplifiers, the amplifiers can be used for power amplification.

[0054] In some embodiments, the thermal energy and laser energy generated during operation of the system 200 can be directed into a heat transfer device, heat engine, cooling system, and beam dump 208. Alternatively or additionally, in some embodiments, the beam dump 208 can be part of a heat transfer system to provide useful heat to other industrial processes. In still other embodiments, the heat can be used to power a heat engine suitable for generating mechanical, thermoelectric, or electrical power. In some embodiments, the waste heat can be used to increase the temperature of connected components. It can be appreciated that by adding more pre-amplifiers and amplifiers with appropriate thermal management and optical isolation, the laser flux and energy can be scaled in this architecture. By adjusting the performance by increasing the pump rate or changing the cooling efficiency, it is possible to adjust the heat dissipation characteristics of the cooling system.

[0055] Figure 3 An additive manufacturing system 300 is shown that can accommodate a light valve as described in this disclosure. As seen in Figure 3 the laser source and amplifier 312 can include a light valve and laser amplifier, as well as other components such as previously described. As Figure 3 shown, the additive manufacturing system 300 uses a laser capable of providing one- or two-dimensional directed energy as part of the laser patterning system 310. In some embodiments, one-dimensional patterning can be directed as linear or curved strips, raster lines, spiral lines, or any other suitable form. Two-dimensional patterning can include separate or overlapping tiles, or images with variations in laser intensity. Two-dimensional image patterns with non-square boundaries can be used, overlapping or interpenetrating images can be used, and images can be provided by two or more energy patterning systems. The laser patterning system 310 directs one or more continuous or intermittent energy beams to beam shaping optics 314 using the laser source and amplifier 312. After shaping, if necessary, the beam is patterned by a laser patterning unit 316, which includes a transmissive or reflective light valve, where typically some energy is directed to a waste energy handling unit 318. The waste energy handling unit can utilize heat provided by active cooling of the light.

[0056] The patterned energy is relayed by an image relay 320 into an article processing unit 340, in one embodiment as a two-dimensional image 322 focused near a bed 346. The bed 346 (with optional walls 348) can form a chamber containing material 344 (e.g., metal powder) dispensed by a material dispenser 342. The patterned energy directed by the image relay 320 can melt, fuse, sinter, amalgamate, change crystal structure, affect stress pattern, or otherwise chemically or physically alter the dispensed material 344 to form a structure with desired properties. A control processor 350 can be connected to various sensors, actuators, heating or cooling systems, monitors, and controllers to coordinate the operation of the laser source and amplifier 312, beam shaping optics 314, laser patterning unit 316, and image relay 320, as well as any other components of the system 300. As will be appreciated, the connections can be wired or wireless, continuous or intermittent, and include the ability for feedback (e.g., heating can be adjusted in response to sensed temperature).

[0057] In some embodiments, beam shaping optics 314 can include various imaging optics to combine, focus, diverge, reflect, refract, homogenize, adjust the intensity of, adjust the frequency of, or otherwise shape and direct one or more laser beams received from laser source and amplifier 312 toward laser patterning unit 316. In one embodiment, wavelength selective mirrors (e.g., dichroic mirrors) or diffractive elements can be used to combine multiple beams, each having a different optical wavelength. In other embodiments, multiple facet mirrors, microlenses, and refractive or diffractive optical elements can be used to homogenize or combine multiple beams.

[0058] Laser patterning unit 316 can include static or dynamic energy patterning elements. For example, laser beams can be blocked by a mask having fixed or moveable elements. To increase the flexibility and ease of image patterning, pixel addressable masking, image generation or transmission can be used. In some embodiments, the laser patterning unit includes addressable light valves, either alone or in combination with other patterning mechanisms to provide patterning. The light valves can be transmissive, reflective, or use a combination of transmissive and reflective elements. Dynamic modification of the pattern can be achieved using electrical or optical addressing. In one embodiment, a transmissive optically addressed light valve is used to rotate the polarization of light passing through the valve, with optically addressed pixels forming a pattern defined by a light projection source. In another embodiment, a reflective optically addressed light valve includes a write beam to change the polarization of a read beam. In certain embodiments, non-optically addressed light valves can be used. These can include, but are not limited to, electrically addressable pixel elements, moveable mirrors or micro-mirror systems, piezoelectric or micro-actuated optical systems, fixed or moveable masks or screens, or any other conventional system capable of providing high intensity light patterning.

[0059] Waste energy handling unit 318 is used to disperse, redirect, or utilize energy that is not patterned and passes through image relay 320. In one embodiment, waste energy handling unit 318 can include passive or active cooling elements that remove heat from both laser source, light valve, and amplifier 312 and laser patterning unit 316. In other embodiments, the waste energy handling unit can include a "beam dump" to absorb any beam energy that is not used in defining the laser pattern and convert it to heat. In still other embodiments, beam shaping optics 314 can be used to recycle the waste laser beam energy. Alternatively or additionally, the waste beam energy can be directed to article handling unit 340 for heating or further patterning. In certain embodiments, the waste beam energy can be directed to additional energy patterning systems or article handling units.

[0060] In one embodiment, a "switchyard" style optical system can be used. Switchyard systems are adapted to reduce light waste in additive manufacturing systems due to unwanted light that is wasted because of the pattern to be printed. Switchyard involves the redirection of a complex pattern from its generation (in this case, referring to the plane in which spatial patterns are imparted to a structured or unstructured beam) to its delivery through a series of switch points. Each switch point can optionally modify the spatial profile of the incident beam. Switchyard optical systems can be used, for example, but not limited to, in laser-based additive manufacturing techniques, where a mask is applied to the light. Advantageously, in various embodiments according to the present disclosure, discarded energy can be recycled in a homogenized form or as patterned light for maintaining high power efficiency or high productivity. Further, discarded energy can be recycled and reused to increase intensity to print more difficult to handle materials.

[0061] The image relay 320 can receive the patterned image (one or two dimensional) from the laser patterning unit 316 directly or through a switch station and direct it to the article processing unit 340. In a manner similar to the beam shaping optics 314, the image relay 320 can include optics for combining, focusing, diverging, reflecting, refracting the patterned light, adjusting the intensity of the patterned light, adjusting the frequency of the patterned light, or otherwise shaping and directing the patterned light. Moveable mirrors, prisms, diffractive optical elements, or solid state optical systems that do not require substantial physical movement can be used to direct the patterned light. One of a plurality of lens assemblies can be configured to provide the incident light with a magnification ratio, where the lens assembly has both a first set of optical lenses and a second set of optical lenses, and the second set of optical lenses is exchangeable from the lens assembly. Rotation of one or more sets of mirrors mounted on a compensation gantry and a final mirror mounted on a build platform gantry can be used to direct the incident light from the precursor mirror onto a desired location. Translational movement of the compensation gantry and the build platform gantry can also ensure that the distance of the incident light from the precursor mirror to the article processing unit 340 is substantially equal to the image distance. In effect, this enables the beam delivery size and intensity for different materials to be rapidly varied over the location of the build area while ensuring high availability of the system.

[0062] The article processing unit 340 can include a walled chamber 348 and a bed 344 (collectively defining a build chamber), and a material distributor 342 for distributing material. The material distributor 342 can distribute, remove, mix, provide gradations or variations of material type or particle size, or adjust the layer thickness of the material. The material can include metals, ceramics, glasses, polymeric powders, other meltable materials capable of undergoing a heat-induced phase change from solid to liquid back to solid, or combinations thereof. The material can also include composites of meltable and non-meltable materials, where either or both of the constituents can be selectively targeted by the imaging relay system to melt the meltable constituent while leaving or causing the non-meltable material to undergo evaporation / destruction / combustion or other destructive process along the non-meltable material. In certain embodiments, slurries, sprays, coatings, wires, ribbons, or sheets of the material can be used. Unwanted material can be removed for disposal or recycling by using a blower, vacuum system, sweeping, vibration, shaking, tilting, or inverting the bed 346.

[0063] In addition to material handling components, the article processing unit 340 can include components for holding and supporting 3D structures, mechanisms for heating or cooling the chamber, auxiliary optics or support optics, and sensors and control mechanisms for monitoring or regulating material or environmental conditions. The article processing unit can support a vacuum or an inert gas atmosphere, in whole or in part, to reduce unwanted chemical interactions as well as mitigate the risk of fire or explosion (particularly for active metals). In some embodiments, various pure other atmospheres or mixtures of other atmospheres can be used, including those containing Ar, He, Ne, Kr, Xe, C02, N2, 02, SF6, CH4, CO, N20, C2H2, C2H4, C2H6, C3H6, C3H8, i-C4H 10 , C4H 10 , 1-C4H8, cic-2, C4H7, 1,3-C4H6, 1,2-C4H6, C5H 12 , n-C5H 12 , i-C5H 12 , n-C6H 14 , C2H3Cl, C7H 16 , C8H 18 , C 10 H 22 , C 11 H 24 , C 12 H 26 , C 13 H 28 , C 14 H 30 , C 15 H 32 , C 16 H 34 , C6H6, C6H5-CH3, C8H 10 , C2H5OH, CH3OH, iC4H8. In some embodiments, a refrigerant or a large inert molecule (including but not limited to sulfur hexafluoride) can be used. An enclosure atmospheric composition with at least about 1% by volume (or by number density) of He and a selected percentage of inert / non-reactive gas can be used.

[0064] In certain embodiments, multiple article processing units or build chambers (each having a build platform that holds a powder bed) can be used in conjunction with multiple optical mechanical assemblies arranged to receive and direct one or more incident energy beams into the build chambers. Multiple chambers allow for simultaneous printing of one or more print jobs within one or more build chambers. In other embodiments, removable chamber sidewalls can simplify removal of printed objects from the build chamber, allowing for rapid exchange of powder material. The chamber can also be equipped with adjustable process temperature controls. In still other embodiments, the build chamber can be configured as a removable printer cartridge that can be positioned in proximity to the laser optics. In some embodiments, the removable printer cartridge can include a powder or support detachable connection to a powder supply. After a manufacturing project, the removable printer cartridge can be removed and replaced with a new printer cartridge.

[0065] In another embodiment, one or more article processing units or build chambers can have a build chamber held at a fixed height, while the optics are vertically movable. The distance between the final optics of the lens assembly and the top surface of the powder bed can be managed to be substantially constant by indexing the final optics upward by a distance equivalent to the powder layer thickness, while holding the build platform at a fixed height. Advantageously, larger and heavier objects can be more easily manufactured compared to a vertically moving build platform, as precise micron-level movement of a mass- varying build platform is not required. Generally, build chambers intended for use with metal powders having a volume greater than about 0.1 cubic meters - 0.2 cubic meters (i.e., greater than 100 liters - 200 liters or heavier than 500 kg - 1,000 kg) would benefit most from holding the build platform at a fixed height.

[0066] In one embodiment, a portion of a powder bed layer can be selectively melted or fused to form one or more temporary walls from the fused portion of the powder bed layer, thereby containing another portion of the powder bed layer on the build platform. In selected embodiments, fluid channels can be formed in the one or more first walls to enable improved thermal management.

[0067] In some embodiments, an additive manufacturing system can include an article processing unit or a build chamber having a build platform that supports a powder bed, the powder bed being tiltable, invertible, and shakable to substantially separate the powder bed from the build platform in a hopper. The powder material forming the powder bed can be collected in the hopper for reuse in later print jobs. The powder collection process can be automated, and a vacuum system or gas jet system can also be used to assist in powder removal and removal.

[0068] For some embodiments, the additive manufacturing system can be configured to readily process parts that are longer than the available build chamber. A continuous (long) part can be sequentially advanced in a longitudinal direction from a first zone to a second zone. In the first zone, selected particles of the particulate material can be consolidated. In the second zone, unconsolidated particles of the particulate material can be removed. A first portion of the continuous part can be advanced from the second zone to a third zone, while a last portion of the continuous part is formed within the first zone, and the first portion remains in the same position in a lateral direction and a transverse direction as the position occupied by the first portion within the first zone and the second zone. In effect, additive manufacturing and purging (e.g., segregation and / or re-use of unused or unconsolidated particulate material) can be performed in parallel (i.e., simultaneously) at different locations or zones on the part conveyor, without the need to stop for removal of particulate material and / or parts.

[0069] In another embodiment, additive manufacturing capacity can be increased by using an enclosure that limits the exchange of gaseous matter between the interior of the enclosure and the exterior of the enclosure. An airlock provides an interface between the interior and the exterior; where the interior has multiple additive manufacturing chambers, including chambers that support powder bed fusion. A gas management system maintains gaseous oxygen within the interior at or below a limit oxygen concentration, thereby increasing the flexibility of the types of powder that can be used and processes that can be performed in the system.

[0070] In another manufacturing embodiment, capacity can be increased by housing an article processing unit or build chamber within an enclosure, the build chamber capable of creating parts that weigh greater than or equal to 2,000 kilograms. A gas management system can maintain gaseous oxygen within the enclosure at a concentration that is below atmospheric levels. In some embodiments, a wheeled vehicle can transport parts from the interior of the enclosure through the airlock, as the airlock serves to buffer between the gaseous environment of the interior of the enclosure and the gaseous environment of the exterior of the enclosure, and to a location outside of both the enclosure and the airlock.

[0071] Other manufacturing embodiments involve collecting powder samples from a powder bed in real time. An ingester system is used for in-process collection and characterization of powder samples. Collection can be performed periodically, and the results of the characterization lead to adjustments to the powder bed fusion process. The ingester system can optionally be used for one or more of auditing, process adjustment, or behavior such as modifying printer parameters or verifying correct use of licensed powder materials.

[0072] A further improvement to additive manufacturing processes is described, which can be provided through the use of a manipulator device, such as a crane, hoist gantry, robotic arm, or similar device that allows for manipulation of parts that are difficult or impossible for humans to move. The manipulator device can grasp various permanent or temporary additively manufactured manipulation points on the part to enable repositioning or manipulation of the part.

[0073] A control processor 350 can be connected to control any of the components of the additive manufacturing system 300 described herein, including the laser, laser amplifier, optics, thermal controls, build chamber, and manipulator device. The control processor 350 can be connected to various sensors, actuators, heating or cooling systems, monitors, and controllers to coordinate operation. A wide range of sensors, including imagers, light intensity monitors, thermal sensors, pressure sensors, or gas sensors, can be used to provide information for use in control or monitoring. The control processor can be a single central controller, or alternatively, can include one or more independent control systems. The controller processor 350 is provided with an interface that allows input of manufacturing instructions. The use of a wide range of sensors allows for various feedback control mechanisms to improve quality, manufacturing yield, and energy efficiency.

[0074] Figure 4 One embodiment of the operation of a manufacturing system that supports the use of a light valve suitable for additive or subtractive manufacturing is shown. In this embodiment, a flowchart 400 illustrates one embodiment of a manufacturing process supported by the described optical and mechanical components. In step 402, a material is positioned in a bed, chamber, or other suitable support. The material can be a sheet of metal that is laser cut using subtractive manufacturing techniques, or a powder that is capable of being melted, fused, sintered, induced to change crystal structure, have a stress distribution pattern affected, or otherwise chemically or physically altered to form a structure with desired properties through additive manufacturing techniques.

[0075] In step 404, unpatterned laser energy is emitted by one or more energy emitters, including but not limited to solid state or semiconductor lasers, and then amplified by one or more laser amplifiers. In step 406, the unpatterned laser energy is shaped and modified (e.g., intensity modulated or focused). In step 408, the unpatterned laser energy is patterned by a light valve, where the portion of the energy that is not formed into a pattern is disposed of in step 410 (this can include use of a beam dump, as described with respect to FIG. 3). In step 412, the patterned laser energy is directed to the material in the build chamber. Figure 2 and Figure 3The disclosed beam dump provides for conversion to waste heat, recycling as patterned or unpatterned energy, or waste heat generated by cooling the laser amplifier in step 404. In step 412, the patterned energy now forming a one or two dimensional image is relayed toward the material. In step 414, the image is applied to the material, either subtractively processing or additively building a portion of the 3D structure. For additive manufacturing, these steps can be repeated (loop 416) until the image (or a different subsequent image) has been applied to all necessary areas of the top layer of the material. When the energy application to the top layer of the material is complete, a new layer can be applied (loop 418) to continue building the 3D structure. These process loops continue until the 3D structure is complete, at which point the remaining excess material can be removed or recycled.

[0076] Figure 5 is an embodiment of an additive manufacturing system that includes a light valve and a switchyard system that enables the reuse of patterned two-dimensional energy. Additive manufacturing system 520 has an energy patterning system with a laser and amplifier source 512 that directs one or more continuous or intermittent laser beams to beam shaping optics 514. Excess heat can be transferred into a waste energy disposal unit 522, which can include an active light valve cooling system. After shaping, the beam is two-dimensionally patterned by energy patterning unit 530, generally some energy is directed to waste energy disposal unit 522. The patterned energy is relayed by one of a plurality of image relays 532 toward one or more article processing units 534A, 534B, 534C, or 534D, typically as a two-dimensional image focused near a moveable or fixed height bed. The bed is within a cartridge that includes a powder hopper or similar material dispenser. The patterned laser beam directed by image relay 532 can melt, fuse, sinter, merge, change crystal structure, affect stress distribution patterns, or otherwise chemically or physically alter the dispensed material to form a structure with desired properties.

[0077] In this embodiment, the waste energy handling unit has multiple components to allow for the reuse of the wasted patterned energy. The coolant fluid from the laser amplifier and source 512 can be directed into one or more of the power generator 524, the heating / cooling thermal management system 525, or the energy dump 526. Additionally, the relays 528A, 528B, and 528C can transfer energy to the power generator 524, the heating / cooling thermal management system 525, or the energy dump 526, respectively. Optionally, the relay 528C can direct the patterned energy into the image relay 532 for further processing. In other embodiments, the patterned energy can be directed by the relay 528C to the relays 528B and 528A for insertion into the laser beam provided by the laser and amplifier source 512. The image relay 532 can also be used to reuse the patterned image. The image can be redirected, inverted, mirrored, sub-patterned, or otherwise transformed for distribution to one or more article handling units 534A-534D. Advantageously, the reuse of the patterned light can improve the energy efficiency of the additive manufacturing process and, in some cases, improve the energy intensity directed to the bed or reduce the manufacturing time.

[0078] Many modifications and other embodiments of the applications will come to mind to one skilled in the art to which these applications pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the applications are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. It is also to be understood that other embodiments of the applications can be practiced without the elements / steps explicitly disclosed here.

Claims

1. A light valve, comprising: A liquid crystal layer having a first side and a second side; A first substrate, the first substrate being positioned to contact the first side of the liquid crystal layer, wherein the first substrate has a first semiconductor layer; as well as A second substrate is positioned to contact the second side of the liquid crystal layer, wherein the second substrate has a second semiconductor transparent electrode layer and a second semiconductor layer. as well as Multiple laser-guided transparent hole support structures are positioned within the liquid crystal layer to contact both the first substrate and the second substrate.

2. The light valve according to claim 1, wherein, The first substrate further includes a first semiconductor transparent electrode layer, which is positioned to contact the first semiconductor layer to form a transmissive light valve.

3. The light valve according to claim 1, wherein, The first substrate further includes a reflective layer, which is positioned to contact the first semiconductor layer to form a reflective light valve.

4. The light valve according to claim 1, wherein, The liquid crystal layer is at least one of the following: a liquid crystal layer with a thickness of less than 100 micrometers, a liquid crystal layer with a thickness of less than 10 micrometers, or a liquid crystal layer with a thickness of less than 5 micrometers.

5. The light valve according to claim 1, wherein, The thickness of each substrate is less than 1 mm.

6. The light valve according to claim 1, wherein, Each substrate includes at least one of a wide-bandgap semiconductor material and an ultra-wide-bandgap semiconductor material.

7. The light valve according to claim 1, wherein, The plurality of laser transparent hole support structures include at least one of spacer spheres, gaskets, and pillars, wherein the spacer spheres, gaskets, and pillars are located within the liquid crystal layer and are sized to maintain a uniform gap between the first substrate and the second substrate.

8. The light valve according to claim 1, wherein, The first substrate, the second substrate, and the liquid crystal layer are attached to form a monolithic block.

9. The light valve according to claim 1, wherein, The CTE of the first substrate, the second substrate, and the liquid crystal layer is within 10% of each other.

10. A method of forming a light valve, comprising: A liquid crystal layer having a first side and a second side is provided; Multiple laser-guided transparent hole support structures are applied to the liquid crystal layer; The first electrode is positioned on the first semiconductor layer to form the first substrate; Make the first semiconductor layer contact the first side of the liquid crystal layer; The second transparent electrode is positioned on the second semiconductor layer to form the second substrate; and The second semiconductor layer is brought into contact with the second side of the liquid crystal layer.

11. The method according to claim 10, wherein, The first substrate further includes a first semiconductor transparent electrode layer, which is positioned to contact the first semiconductor layer to form a transmissive light valve.

12. The method according to claim 10, wherein, The first substrate further includes a reflective layer, which is positioned to contact the first semiconductor layer to form a reflective light valve.

13. The method according to claim 10, wherein, The thickness of the liquid crystal layer is less than 1 mm.

14. The method of claim 10, wherein, The thickness of each substrate is less than 1 mm.

15. The method according to claim 10, wherein, Each substrate includes at least one of a wide-bandgap semiconductor material and an ultra-wide-bandgap semiconductor material.

16. The method of claim 10, wherein, The plurality of laser transparent hole support structures include at least one of spacer spheres, gaskets, and pillars, wherein the spacer spheres, gaskets, and pillars are located within the liquid crystal layer and are sized to maintain a uniform gap between the first substrate and the second substrate.

17. The method according to claim 10, wherein, The first substrate, the second substrate, and the liquid crystal layer are attached to form a monolithic block.

18. The method according to claim 10, wherein, The CTE of the first substrate, the second substrate, and the liquid crystal layer is within 10% of each other.

19. An additive manufacturing system, comprising: Laser system; Powder bed; A light valve, positioned to pattern light received from the laser system and guide the patterned light to the powder bed, wherein the light valve further comprises: A liquid crystal layer having a first side and a second side; A first substrate, positioned to contact a first side of the liquid crystal layer, wherein the first substrate has a first semiconductor layer; and A second substrate, positioned to contact a second side of the liquid crystal layer, wherein the second substrate has a second transparent semiconductor electrode layer and a second semiconductor layer; and Multiple laser-guided transparent hole support structures are positioned within the liquid crystal layer to contact both the first substrate and the second substrate.

20. The additive manufacturing system according to claim 19, wherein, The light valve is capable of forming two-dimensional light patterns.

21. A light valve, comprising: A liquid crystal layer having a first side and a second side; A first substrate, the first substrate being positioned to contact the first side of the liquid crystal layer, wherein the first substrate has a first semiconductor layer; A second substrate is positioned to contact the second side of the liquid crystal layer, wherein the second substrate has a second semiconductor transparent electrode layer and a second semiconductor layer. And among them The liquid crystal layer contacts both the first substrate and the second substrate within a uniform gap.

22. The light valve according to claim 21, wherein, The liquid crystal layer is at least one of the following: a liquid crystal layer with a thickness of less than 100 micrometers, a liquid crystal layer with a thickness of less than 10 micrometers, or a liquid crystal layer with a thickness of less than 5 micrometers.

23. The light valve according to claim 21, wherein, The thickness variation of the uniform gap containing the liquid crystal layer is less than one micrometer.

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