Oligomer-stabilized liquid crystal light valves

Abstract

The photochromic composition includes a first liquid crystal reactive mesogenic material having attached functional groups that enable crosslinking. A second liquid crystal reactive mesogenic material having attached functional groups and a different molecular weight than the first liquid crystal reactive mesogenic material is positioned to crosslink with the first liquid crystal reactive mesogenic material. For use in a light valve, at least one of a photo-alignment material and a rubbed LCD alignment material is in contact with the first liquid crystal reactive mesogenic material and the second liquid crystal reactive mesogenic material.

Description

[Technical Field]

[0001] Related Applications This disclosure is part of a non-provisional patent application claiming benefit of priority to U.S. Patent Application No. 63 / 427,306, filed November 22, 2022, which is incorporated by reference in its entirety.

[0002] This disclosure relates generally to the field of light valves and compositions for constructing light valves. More specifically, this application relates to oligomer-stabilized liquid crystal materials suitable for use in light valves. [Background technology]

[0003] Light modulators can be used to completely or partially block, redirect, or modulate laser light. For example, spatial light modulators (SLMs), also known as light valves (LVs), are a type of light modulator that can be used to impart information uniformly across an entire beam (1D modulation), to impart variation to a beam to form paralleled optical channels (2D modulation), or to impart variation to the volume of a pixel / voxel channel (3D modulation). The information imparted can be in the form of amplitude, phase, polarization, wavelength, interference, or quantum entanglement.

[0004] Industrial applications may require LVs to withstand high-fluence laser sources for extended periods of time. One commonly used light valve structure relies on liquid crystals with aligned molecules interposed between transparent glass or other suitable substrates. The liquid crystal molecules can be roughly aligned using mechanical techniques (e.g., rubbing) or by non-contact photoalignment. Photoalignment involves a set of chemicals that enable large-area non-contact liquid crystal (LC) alignment programming. Typically, a dichroic (i.e., polarization-sensitive) dye is coated onto the substrate by standard processing methods (e.g., spin or dip). The coated substrate is then exposed (usually perpendicular to the exposure polarization) to strongly polarized light (usually blue or sometimes UV wavelengths), which aligns the dye molecules to minimize absorption. This alignment places the orientation of the liquid crystal molecules at their interface and therefore in the bulk liquid crystal director field.

[0005] Unfortunately, photoalignment dyes tend to realign over time or with exposure to blue light after contacting the liquid crystal with the interface. There is a need for reliable compositions and construction techniques for the fabrication of liquid crystal-based light valves.

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

[0007] [Figure 1A] 1 illustrates example materials formed by combining various monomers into oligomers for use in stabilized liquid crystal devices. [Figure 1B] Illustrated are some example monomer units that combine to form oligomers as depicted in FIG. 1A. [Figure 2A] 1 illustrates an example transmissive light valve structure. [Figure 2B]1 illustrates an example reflective light valve structure. [Figure 3] 1 illustrates an additive manufacturing system capable of directing a light beam in one or two dimensions using a light valve containing stabilized liquid crystals. [Figure 4] 1 illustrates a method for operation of an additive manufacturing system capable of directing a light beam in one or two dimensions using light valves containing stabilized liquid crystals. [Figure 5] 1 illustrates an additive manufacturing system capable of directing a light beam in one or two dimensions using a light valve and switchyard system that includes stabilized liquid crystals. DETAILED DESCRIPTION OF THE INVENTION

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

[0009] As used herein, the term "polymer" should be understood to mean a molecule that includes different types of backbones of one or more repeating units (the smallest building blocks of a molecule) and includes known terms such as "oligomer," "copolymer," and "homopolymer." Furthermore, the term "polymer" should be understood to include not only the polymer itself, but also residues from initiators, catalysts, and other elements involved in the synthesis of said polymer, which residues are understood to be not covalently incorporated into the polymer. Furthermore, while said residues and other elements are typically removed during post-polymerization purification processes, they are typically mixed or intermingled with the polymer such that they typically remain with the polymer when transferred between containers or solvents or dispersion media.

[0010] The term "(meth)acrylic polymer" as used herein includes polymers obtained from acrylic monomers, polymers obtained from methacrylic monomers, and the corresponding copolymers obtained from mixtures of the above monomers.

[0011] The term "polymerization" refers to the chemical process of forming a polymer by linking together multiple polymerizable groups or polymer precursors (polymerizable compounds) containing such groups.

[0012] The terms "film" and "layer" include mechanically stable, self-supporting or free-standing films that are rigid or flexible, as well as coatings or layers on a supporting substrate or between two substrates.

[0013] Liquid crystal-based light valves or other optical devices can be formed from a variety of mesogenic materials. Mesogens are compounds that exhibit liquid crystal properties (i.e., as a disordered solid or an ordered liquid) and can assume a liquid crystal state (mesophase) intermediate between the crystalline solid state and the isotropic liquid state. The term "liquid crystal or mesogenic compound" can refer to a compound containing one or more calamitic (rod-like or plate-like / lath-like) or discotic (disk-like) mesogenic groups. The term "mesogenic group" refers to a group capable of inducing liquid crystal (LC) phase behavior. Compounds containing mesogenic groups need not exhibit LC phases themselves; they may also exhibit LC phase behavior only in mixtures with other compounds, or when the mesogenic compound or material, or their mixtures, are polymerized. For convenience, the term "liquid crystal" will be used hereafter to refer to both mesogenic and LC materials.

[0014] In general, liquid crystalline properties arise because mesogenic compounds can be composed of both rigid and flexible segments. The rigid segments align the mesogenic components in one direction, while the flexible segments provide mobility to the mesogens. In many embodiments, the flexible segments are based on alkyl chains, which allow movement and prevent crystallization. The combination of rigid and flexible chains induces structural orientation and fluidity between the liquid crystal moieties. In some embodiments, this combination of structural orientation and fluidity can be controlled by stabilizing the liquid crystal orientation with polymerizable or crosslinkable liquid crystal compounds or moieties known as reactive mesogens (RMs). For example, including reactive mesogens as stabilizing polymerizable components in LC mixtures, i.e., polymer-stabilized liquid crystals (PSLCs), can improve the rigidity of the liquid crystal material in light valves and its resistance to laser fluence-based reorientation. In one embodiment, polymer stabilization can be achieved using RMs or monomeric materials that adopt the LC director field alignment in solvents that are miscible with the liquid crystal. In effect, the monomers are liquid crystals that allow for some degree of crosslinking of other liquid crystal materials. Using only small amounts of this material (e.g., roughly 1 part in 40 to 50 moles), the liquid crystal and monomer mixture is polymerized (usually by a UV curing process) into a fixed structure or liquid crystal network that provides strong, covalently fixed orientation to the surrounding LC solvent.

[0015] In some embodiments, polymer-stabilized liquid crystal devices allow for faster switching at the expense of high scattering. Chain-extended (oligomeric) liquid crystals mixed with low-molecular-weight liquid crystal mixtures allow for a more flexible liquid crystal polymer network after polymerization due to the lower cross-linking density and reduced scattering cross-section with equivalent mesogen content, reducing scattering in the switched state. This can be achieved with both positive and negative dielectric monomers, and monofunctional mesogenic and non-mesogenic monomers may also be used. Furthermore, oligomeric and low-molecular-weight liquid crystals can be chemically matched to improve miscibility, for example, by using selective fluorination reactions, and scattering can be reduced by reducing the refractive index mismatch.

[0016] Advantageously, polymer-stabilized liquid crystal devices can be utilized in many applications, including, but not limited to, liquid crystal displays (LCDs), light valves (LVs), electrically or optically switchable LC cells, or optical shutters. Other applications include, but are not limited to, optical, electro-optical, or electronic devices or components, such as optical retardation films, polarizers, compensators, beam splitters, reflective films, alignment layers, color filters, polarization-controlled lenses for autostereoscopic 3D displays, RM lenses and IR-reflective films for window applications, autostereoscopic 3D displays, organic light-emitting diodes (OLEDs), optical data storage devices, and window applications.

[0017] FIG. 1A illustrates a configurable LC crystalline material 100 with reactive mesogens that can be specifically tailored for solubility and functionality. As shown, the core compound member 102A can have calamitic (rod-like or plate-like / lath-like) or discotic (disk-like) mesogenic groups and can be relatively rigid. The core compound member 102A can include, but is not limited to, a cyclic group, such as an aromatic ring, an aliphatic ring, or a heterocyclic ring. Examples of aromatic rings include a benzene ring and a naphthalene ring. Examples of aliphatic rings include a cyclohexane ring. Examples of heterocyclic rings include a pyridine ring, a pyrimidine ring, a thiophene ring, a 1,3-dioxane ring, and a 1,3-dithiane ring. Optionally, one or more side groups can be attached to the mesogenic core compound member 102A; these end and side groups are typically selected from, for example, carbyl or hydrocarbyl groups, polar groups such as halogen, nitro, hydroxy, or polymerizable groups.

[0018] The core compound member 102A may be connected to a relatively flexible tail 104A, which may be composed of a long hydrocarbon chain. Tail 104A may include, but is not limited to, alkyl groups having 1 to 40 carbon atoms, alkoxy groups having 1 to 40 carbon atoms, acyl groups having 2 to 40 carbon atoms, alkoxycarbonyl groups having 2 to 40 carbon atoms, acyloxy groups having 2 to 40 carbon atoms, alkoxycarbonyloxy groups having 2 to 40 carbon atoms, alkylthio groups having 1 to 20 carbon atoms, amino groups having 1 to 40 carbon atoms, acylamino groups having 2 to 40 carbon atoms, and alkoxycarbonylamino groups having 2 to 40 carbon atoms. These flexible substituents may be further substituted with other substituents. Examples of the substituent include an alkyl group (e.g., methyl, ethyl, isopropyl, tert-butyl), an alkenyl group (e.g., vinyl, allyl, 2-butenyl, 3-pentenyl), an alkynyl group (e.g., propargyl, 3-pentynyl), an aryl group (e.g., phenyl, p-methylphenyl, naphthyl), a substituted or unsubstituted amino group (e.g., unsubstituted amino, methylamino, dimethylamino, diethylamino, anilino), an alkoxy group (e.g., methoxy, ethoxy, butoxy), an aryloxy group (e.g., phenyloxy, 2-naphthyloxy), an acyl group (e.g., acetyl, benzoyl, formyl, pivaloyl), an alkoxy group (e.g. ...methylamino, dimethylamino, diethylamino, anilino), an alkoxy group (e.g., methylamino, dimethylamino, diethylamino, anilino), an alkoxy group (e.g., methylamino, dimethylamino, diethylamino, anilino), an alkoxy group (e.g., methylamino, dimethylamino, diethylamino, anilino), an alkoxy group (e.g., methylamino, dimethylamino, diethylamino, anilino), an alkoxy group (e.g., methylamino, dimethylamino, diethylamino, anilino), an alkoxy group (e.g., methyl aryloxycarbonyl groups (e.g., phenyloxycarbonyl), acyloxy groups (e.g., acetoxy, benzoyloxy), acylamino groups (e.g., acetylamino, benzoylamino), alkoxycarbonylamino groups (e.g., methoxycarbonylamino), aryloxycarbonylamino groups (e.g., phenyloxycarbonylamino), alkylsulfonylamino groups (e.g., methanesulfonylamino), arylsulfonylamino groups (e.g., benzenesulfonylamino), sulfamoyl groups (e.g., sulfamoyl, N-methylsulfamoyl, N,N-dimethylsulfamoyl, N-phenylsulfamoyl), carbamoyl groups (e.g., unsubstituted carbamoyl, N-methylcarbamoyl, N,N-diethylcarbamoyl, N-phenylcarbamoyl), alkylthio groups (e.g., methylthio, ethylthio), arylthio groups (e.g., phenylthio), alkylsulfonyl groups (e.g., mesyl), arylsulfonyl groups (e.g., tosyl), alkylsulfinyl groups (e.g., methanesulfinyl), arylsulfinyl groups (e.g., benzenesulfinyl), ureido groups (e.g., unsubstituted ureido, 3-methyl-ureido, 3- phenylureido), phosphoramido groups (diethylphosphoramido, phenylphosphoramido), hydroxyl, mercapto, halogen atoms (e.g., fluorine, chlorine, bromine, iodine), cyano, sulfo, carboxyl, nitro, hydroxamic acid groups, sulfino, hydrazino, imino, heterocyclic groups, e.g., those containing heteroatoms such as nitrogen, oxygen, or sulfur (e.g., imidazolyl, pyridyl, quinolyl, furyl, piperidyl, morpholino, benzoxazolyl, benzimidazolyl, benzthiazolyl), and silyl groups (e.g., trimethylsilyl, triphenylsilyl). These substituents may themselves be further substituted.

[0019] The core compound members 102A (with tails 104A) may be linked to one another by linkers 106A, including, but not limited to, -O-, -S-, -CO-, -COO-, -OCO-, -S-CO-, -CO-S-, -O-COO-, -CO-NR-, -NR-CO-, -NR-CO-NR-, -NR-CO-O-, -O-CO-NR-, -OCH-, -CHO-, -SCH-, -CHS-, -CFO-, -OCF-, -CFS-, - It may contain SCF2-, -CH2CH2-, -(CH2)n1, -CF2CH2-, -CH2CF2-, -CF2CF2-, -CH=N-, -N=CH-, -N=N-, -CH=CR00-, -CY1=CY2-, -C≡C-, -CH=CH-COO-, -OCO-CH=CH- or a single bond, preferably -COO-, -OCO- or a single bond, more preferably -COO- or -OCO-.

[0020] The combination of liquid crystal portions 102A, 104A, and 106A described above may also include reactive functional groups 110A attached to the tail 104A. In one embodiment, these may include acrylate polymers functioning as monoacrylates or diacrylates. The functional groups may include, but are not limited to, secondary amines, thiols, epoxides, alkynes, hydroxyls, carboxylic acids, vinyls, and hydrosilanes. Advantageously, these functional groups may provide sufficient crosslinking to stabilize the liquid crystal material during high-fluence laser operation.

[0021] In some embodiments, a chain extender 120A may be provided to link similar or different liquid crystal materials 102A, 104A, and 106A. The chain extender may include, but is not limited to, the moieties previously described as linker 106A.

[0022] In one example, a chain extender 120A may be used to adjust the repeat number n and m. The chain extender may contain functional groups such as primary or secondary amines, thiols, epoxides (glycidyl), alkynes, hydroxyls, carboxylic acids, vinyls, and hydrosilanes. This allows for the construction of specific blocks, other two-dimensional or three-dimensional structures, or even random arrangements. In general, various combinations and permutations can be achieved by selecting specific liquid crystal materials and linking moieties to provide specific optical, thermal, and chemical stability. For example, appropriate liquid crystal oligomers can reduce operating voltage and improve (photo)alignment stability while maintaining high-speed operation in response to laser fluence.

[0023] In some embodiments, polymerization can be achieved, for example, by exposing the liquid crystal material to heat or actinic radiation. Actinic radiation refers to radiation such as UV, IR, or visible light; radiation such as X-rays or gamma rays; or radiation such as ions or electrons. In some embodiments, UV, IR, or visible lasers can be used. The curing time depends, at least in part, on the reactivity of the RM, the thickness of the coated layer, the type of polymerization initiator used, and the type of actinic radiation. The polymerization process is not limited to a single curing step. It is also possible to carry out polymerization in two or more steps by sequentially exposing the liquid crystal material film to two or more lamps of the same type or two or more different lamps. The curing temperatures of the different curing steps may be the same or different. The lamp power and dose from the different lamps may also be the same or different. In addition to the above conditions, the process steps may also include a heating step between exposure to different lamps. Preferably, polymerization is carried out in air, but polymerization in an inert gas atmosphere such as nitrogen or argon is also possible. The thickness of the liquid crystal polymer film according to the present invention is preferably less than 15 microns, very preferably less than 12 microns, and most preferably less than 10 microns.

[0024] The liquid crystal portions 102A, 104A, and 106A may also include a photo-alignment material, such as a representative dichroic (i.e., polarization-sensitive) dye, as shown for photo-alignment material 130A. Advantageously, the photo-alignment material mixed, coated, or otherwise in contact with the liquid crystal may be stabilized (link 132A), enabling use in high laser fluence applications. The photo-alignment material may include, but is not limited to, azobenzene, coumarin, cinnamate, anthracene, polyimide, or methacrylamide aryl. In some embodiments, the photo-alignment material may replace, in whole or in part, a conventional rubbed-alignment LCD material. The rubbed-alignment LCD material may be formed from a suitable mesogen, including, but not limited to, polyimide, polyamide, or polyvinyl alcohol. Like the photo-alignment material, the rubbed-alignment LCD material may also be advantageously stabilized by contact with various monomers combined into oligomers for use in stabilized liquid crystal devices. In some embodiments, the photo-aligned or rubbed-aligned LCD material may be coated onto a substrate, partially dried, cured, or otherwise processed, and then further treated with reactive mesogens as discussed in this disclosure to provide stabilizing oligomers suitable for use in liquid crystal devices.

[0025] Figure 1B illustrates specific examples of reactive mesogens suitable for use in accordance with the present disclosure. These may include, but are not limited to, 1B.I acrylic acid 6-[4'-(6-acryloyloxy-hexyloxy)biphenyl-4-yloxy]xyl ester (BAB6), 1B.II 1,4-bis[4-(3-acryloyloxypropyloxy)benzoyloxy]-2-methylbenzene (RM257), 1B.III 4,4'-bis{4-[6-(acryloyloxy)hexyloxy]benzoate}biphenylene (BABB6), and 1B.IV 4,4'-bis{4-[6-(methacryloyloxy)hexyloxy]benzoate}biphenylene (BMBB6). Other chemistries may include cyclohexyl groups and other common mesogenic cores, as well as mixtures thereof. Further details are discussed in Dierking, Ingo. "Polymer network-stabilized liquid crystals." Advanced Materials 12.3 (2000): 167-181. [Example]

[0026] In one example, an oligomer-stabilized liquid crystal electro-optical device may involve the use of the following materials and procedures.

[0027] material: E7 LCD (Merck) RM82 (1,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene) nBA (n-butylamine) DMPA (2,2-dimethoxy-2-phenylacetophenone, photoinitiator)

[0028] procedure In a small vial equipped with a stir bar, RM82 and nBA are added in a molar ratio of 2:1. The sealed vial is heated and stirred at 105°C for 16 hours. This is the oligomerization process.

[0029] In a second vial, add E7 liquid crystal along with 5 wt% RM82-nBA oligomer and 0.5 wt% DMPA. Mix the whole at 65°C.

[0030] This mixture may be "UV cured" after being infiltrated into an empty light valve or liquid crystal cell by exposure to 365 nm light.

[0031] Adjustable parameters: Molar ratio of monomer to linker (here RM82:nBA) Selection of oligomer composition (RM82, RM257, BAB6, etc.) Linker molecules and oligomerization methods (amine Michael addition, thiol Michael addition, etc.) Continuous phase liquid crystal (E7, E44, BL006, etc.)

[0032] The final properties of the device may depend on the time, temperature, and UV cure intensity.

[0033] Longer wavelength photoinitiators can be used (eg, BAPO) for compatibility with certain photoconductors.

[0034] Figure 2A shows 2 Joules / cm 2 Ultra-kW level output, large area cm 2 2 illustrates one embodiment of a transmissive light valve capable of high power output suitable for use in additive manufacturing systems or other applications, due to the light valve's long life when used at energy densities of tens of Joules of energy per second. In one embodiment, transmissive light valve system 200A includes a liquid crystal layer 204A, which may be formed from the reactive mesogens discussed herein along with photo-alignment materials. Liquid crystal layer 204A is located between first and second substrates 202A(i) and 202A(ii).

[0035] In operation, the addressed laser light 201A(i) can be combined with a polarizer to create a spatial pattern that selectively blocks or transmits laser light passing through the laser light valve system 200A. High fluence, high power, and high energy input light 201A(ii) is directed through the laser light valve system 200A and spatially patterned into output light 201A(iii). This light can be directed to heat a powder bed suitable for additive manufacturing, as described below with respect to Figures 3, 4, and 5.

[0036] Figure 2B shows 2 Joules / cm 2 2 illustrates one embodiment of a high-fluence, high-power, and high-energy reflective light valve suitable for use in additive manufacturing systems or other applications, due to the long lifetime of the light valve when used at energy densities above 202B. In one embodiment, the reflective light valve system 200B includes a liquid crystal layer 204B, which may be formed from the reactive mesogens discussed herein in conjunction with a photo-alignment material. The liquid crystal layer 204B is located between a first substrate 202B(i) and a second substrate 202B(ii).

[0037] In operation, the addressing laser light 201B(i) creates a spatial pattern that selectively blocks or transmits laser light that reflects through the laser light valve system 200B. High fluence, high power, and high energy input light 201B(ii) is directed through the laser light valve system 200B, where it is spatially patterned and reflected as output light 201B(iii). This light can be directed to heat a powder bed suitable for additive manufacturing, as described below with respect to Figures 3, 4, and 5.

[0038] In another embodiment, as illustrated with respect to FIG. 3, an additive manufacturing system may be represented by various modules that form the additive manufacturing method and system 300. As can be seen in FIG. 3, the laser source and amplifier 312 may be constructed as a continuous or pulsed laser. In other embodiments, the laser source includes a pulsed electrical signal source, such as an arbitrary waveform generator, or a continuous laser source, such as a laser diode acting equivalently. In some embodiments, this may also be achieved via a fiber laser or fiber-delivered laser source modulated by an acousto-optic or electro-optic modulator. In some embodiments, a high repetition rate pulse source using a Pockels cell may be used to generate pulse trains of arbitrary length.

[0039] 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, gas dynamic lasers, "nickel-like" samarium lasers, Raman lasers, or nuclear pumped lasers.

[0040] The gas laser may include lasers such as a helium-neon laser, an argon laser, a krypton laser, a xenon ion laser, a nitrogen laser, a carbon dioxide laser, a carbon monoxide laser, or an excimer laser.

[0041] Chemical lasers may include lasers such as hydrogen fluoride lasers, deuterium fluoride lasers, COIL (chemical oxygen-iodine lasers), or Agil (all vapor phase iodine lasers).

[0042] Metal vapor lasers can include lasers such as helium-cadmium (HeCd) metal vapor lasers, helium-mercury (HeHg) metal vapor lasers, helium-selenium (HeSe) metal vapor lasers, helium-silver (HeAg) metal vapor lasers, strontium vapor lasers, neon-copper (NeCu) metal vapor lasers, copper vapor lasers, gold vapor lasers, or manganese (Mn / MnCl) vapor lasers. Rubidium or other alkali metal vapor lasers can also be used. Solid-state lasers include ruby ​​lasers, Nd:YAG lasers, NdCrYAG lasers, Er:YAG lasers, neodymium YLF (Nd:YLF) solid-state lasers, neodymium-doped yttrium orthovanadate (Nd:YVO4) lasers, neodymium-doped yttrium calcium oxoborate Nd:YCa4O(BO3)3 or simply Nd:YCOB, neodymium-glass (Nd:glass) lasers, titanium-sapphire (Ti:sapphire) lasers, thulium YAG (Tm:YAG) lasers, ytterbium YAG (Yb:YAG) lasers, ytterbium:2O3 (glass or ceramic) lasers, ytterbium-doped glass lasers (in rod, plate, or chip, and fiber), Holmium YAG (Ho:YAG) laser, Chromium ZnSe (Cr:ZnSe) laser, Cerium-doped Lithium Strontium (or Calcium) Aluminum Fluoride (Ce:LiSAF, Ce:LiCAF), Promethium-147 doped phosphate glass (147Pm+3:glass) solid-state laser, Chromium-doped Chrysoberyl (Alexandrite) 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.

[0043] The semiconductor laser may include laser medium types such as GaN, InGaN, AlGaInP, AlGaAs, InGaAsP, GaInP, InGaAs, InGaAsO, GaInAsSb, lead salt, vertical cavity surface emitting laser (VCSEL), quantum cascade laser, hybrid silicon laser, or combinations thereof.

[0044] As shown in FIG. 3 , additive manufacturing system 300 uses a laser that can provide one- or two-dimensional directed energy as part of energy patterning system 310. In some embodiments, one-dimensional patterning can be directed into linear or curved strips, rastered lines, spiral lines, or any other suitable shape. Two-dimensional patterning can include separate or overlapping tiles or images with varying laser intensity. Two-dimensional image patterns with non-square borders can be used, overlapping or interpenetrating images can be used, and images can be provided by two or more energy patterning systems. Energy patterning system 310 uses a laser source and amplifier 312 to direct one or more continuous or intermittent energy beams to beam-shaping optics 314. After shaping, if necessary, the beam is patterned by laser patterning unit 316, which can include a light valve system having a liquid crystal layer that can be formed from the reactive mesogens discussed herein along with a photo-alignment material. Typically, some energy can be directed to rejected energy processing unit 318 during the patterning process. The patterned laser energy is relayed by image relay 320 to article processing unit 340 as a two-dimensional image 322, which in one embodiment is focused near bed 346. Article processing unit 340 may include a cartridge or the like as described above. Article processing unit 340 has plates or bed 346 (with walls 348) that together form a sealed cartridge chamber containing material 344 (e.g., metal powder) dispersed by a powder hopper or other material dispenser 342. The dispersed powder may be fabricated or recycled, as discussed in this disclosure. The patterned energy directed by image relay 320 may melt, dissolve, sinter, fuse, alter crystalline structure, affect stress patterns, or otherwise chemically or physically modify the dispersed, dispensed material 344 to form a structure with desired properties.Control processor 350 may interface with various sensors, actuators, heating or cooling systems, monitors, and controllers to coordinate the operation of laser source and amplifier 312, beam shaping optics 314, laser patterning unit 316, and image relay 320, as well as any other components of system 300. As can be appreciated from the above, the connections may be wired or wireless, continuous or intermittent, and may include feedback capabilities (e.g., to allow adjustment of thermal heating in response to sensed temperature).

[0045] In some embodiments, the beam shaping optics 314 can include a wide variety of imaging optics that combine, focus, diverge, reflect, refract, homogenize, intensity adjust, frequency adjust, or otherwise shape one or more laser beams received from the laser source and amplifier 312 and direct them toward the laser patterning unit 316. In one embodiment, multiple light beams, each having a different wavelength of light, can be combined using wavelength-selective mirrors (e.g., dichroics) or diffractive elements. In other embodiments, multiple beams can be homogenized or combined using polygonal mirrors, microlenses, and refractive or diffractive optical elements.

[0046] The laser patterning unit 316 may include static or dynamic energy patterning elements. For example, the laser beam may be blocked by a mask with fixed or movable elements. Pixel-addressable masking, image generation, or transmission may be used to increase the flexibility and ease of image patterning. In some embodiments, the laser patterning unit includes addressable light valves, alone or with other patterning mechanisms, to effect the patterning. The light valves may be transmissive, reflective, or use a combination of transmissive and reflective elements. The pattern may be dynamically altered using electrical or optical addressing. In one embodiment, a transmissive optically addressed light valve acts to rotate the polarization of light passing through the valve, forming a pattern of optically addressed pixels defined by a floodlight source. In another embodiment, a reflective optically addressed light valve includes a write beam to modify the polarization of the read beam. In certain embodiments, non-optically addressed light valves may be used. These may include, but are not limited to, electrically addressable pixel elements, movable mirror or micromirror systems, piezo or microactuated optical systems, fixed or movable masks or shields, or any other conventional system capable of providing high intensity light patterning. The light valve may include a light valve system liquid crystal layer that may be formed from the reactive mesogens discussed herein along with photo-alignment materials.

[0047] The rejected energy processing unit 318 is used to disperse, redirect, or utilize unpatterned energy, which circulates through the image relay 320. In one embodiment, the rejected energy processing unit 318 may include passive or active cooling elements to remove heat from both the laser source and amplifier 312 and the laser patterning unit 316. In other embodiments, the rejected energy processing unit may include a "beam dump" that absorbs and converts to heat any beam energy not used to define the laser pattern. In yet other embodiments, the rejected laser beam energy can be recycled using beam shaping optics 314. Alternatively, or in addition, the rejected beam energy can be directed to an article processing unit 340 for heating or additional patterning. In certain embodiments, the rejected beam energy can be directed to an additional energy patterning system or article processing unit.

[0048] In one embodiment, a "switchyard"-style optical system can be used. Switchyard systems are suitable for reducing wasted light in additive manufacturing systems caused by rejection of light not needed by the pattern being printed. Switchyards involve redirecting a complex pattern from its generation (in this case, a plane where a spatial pattern is imparted to a structured or unstructured beam) to its transport through a series of switching points. Each switching point can optionally change the spatial profile of the incident beam. Switchyard optical systems can be utilized, for example, but not limited to, laser-based additive manufacturing techniques in which a mask is applied to the light. Advantageously, in embodiments according to the present disclosure, wasted energy can be recycled either in a homogenized form or as patterned light used to maintain high power efficiency or high throughput rates. Furthermore, wasted energy can be recycled and reused to print more difficult materials, improving intensity.

[0049] The image relay 320 can receive the patterned image (either one-dimensional or two-dimensional) from the laser patterning unit 316, either directly or via a switching station, and direct it toward the article processing unit 340. In a manner similar to the beam shaping optics 314, the image relay 320 can include optics that combine, focus, diverge, reflect, refract, adjust the intensity, adjust the frequency, or otherwise shape and direct the patterned light. The patterned light can be directed using movable mirrors, prisms, diffractive optical elements, or solid optical systems that do not require substantial physical movement. One of the multiple lens assemblies can be configured to provide incident light with a magnification ratio using both a first set of optical lenses and a second set of optical lenses, with the second set of optical lenses being interchangeable from the lens assemblies. Rotation of one or more sets of mirrors mounted on the compensation gantry and a final mirror mounted on the build platform gantry can be used to direct the incident light from the precursor mirror to a desired location. The translational motion of the compensation gantry and build platform gantry also makes it possible to 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 allows for quick variation of the optical beam illumination size and intensity across positions in the build area for different materials while ensuring high system availability.

[0050] The material dispenser 342 (e.g., powder hopper) within the article processing unit 340 (e.g., cartridge) can disperse, remove, mix, provide gradients or variations in material type or particle size, or adjust material layer thickness. Materials can include metals, ceramics, glasses, polymer powders, other meltable materials capable of undergoing a heat-induced phase change from solid to liquid and vice versa, or combinations thereof. Materials can also include composites of meltable and non-meltable materials, where either or both components can be selectively targeted by an imaging relay system, melting the meltable component while leaving the non-meltable component, or undergoing a vaporization / disintegration / burning or otherwise destruction process. In certain embodiments, slurries, sprays, coatings, wires, strips, or sheets of material can be used. Undesired materials can be removed for disposal or recycling by using a jetting machine, a vacuum system, sweeping, vibrating, shaking, tilting, or inverting the bed 346.

[0051] In addition to material processing components, the article processing unit 340 may include components for fixing or supporting three-dimensional structures, mechanisms for heating or cooling chambers, auxiliary or support optics, and sensors, and control mechanisms for monitoring or adjusting material or environmental conditions. The article processing unit may, in whole or in part, support a vacuum or inert gas atmosphere to reduce unwanted chemical interactions and mitigate the risk of fire or explosion (especially for reactive metals). In some embodiments, mixtures of various pure substances or other atmospheres may be used, including Ar, He, Ne, Kr, Xe, CO2, N2, O2, SF6, CH4, CO, N2O, C2H2, C2H4, C2H6, C3H6, C3H8, i-C4H10, C4H10, 1-C4H8, cic-2, C4H7, 1,3-C4H6, 1,2-C4H8 ... Examples include those containing H6, C5H12, n-C5H12, i-C5H12, n-C6H14, C2H3Cl, C7H16, C8H18, C10H22, C11H24, C12H26, C13H28, C14H30, C15H32, C16H34, C6H6, C6H5-CH3, C8H10, C2H5OH, CH3OH, and iC4H8. In some embodiments, refrigerants or large inert molecules (including, but not limited to, sulfur hexafluoride) can be used. Enclosure atmosphere compositions can be used to have at least about 1% He by volume (or number density), along with a selected percentage of inert / non-reactive gases.

[0052] The control processor 350 can be connected to control any of the components of the additive manufacturing system 300 described herein, such as the lasers, laser amplifiers, optics, thermal control, build chamber, and manipulator devices. The control processor 350 can be connected to various sensors, actuators, heating or cooling systems, monitors, and controllers to coordinate operation. A variety of sensors can be used, including imagers, light intensity monitors, heat sensors, pressure sensors, or gas sensors, to provide information used for control or monitoring. The control processor can be a single central controller or, alternatively, can include one or more independent control systems. The control processor 350 is provided with an interface for inputting manufacturing instructions. The use of various sensors allows for various feedback control mechanisms to improve quality, manufacturing throughput, and energy efficiency.

[0053] One embodiment of the operation of a manufacturing system suitable for additive or subtractive manufacturing is illustrated in FIG. 4. In this embodiment, flowchart 400 illustrates one embodiment of a manufacturing process supported by the described optical and mechanical components, including the use of various optical diagnostic systems, etc., as previously described herein. In step 401, a powder of a generated or recycled material, as discussed in this disclosure, is formed. In step 402, the powder material is placed in a cartridge, bed, chamber, or other suitable support. In some embodiments, the material may be a metal sheet for laser cutting using subtractive manufacturing techniques, or a powder that can be melted, dissolved, fired, fused, altered crystal structure, affected stress patterns, or otherwise physically modified chemically or by additive manufacturing techniques to form a structure with desired properties.

[0054] In step 404, unpatterned laser energy is irradiated by one or more energy emitters, such as, 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, this unpatterned laser energy is patterned using a light valve system including a liquid crystal layer, which may be formed from the reactive mesogens discussed herein, along with a photo-alignable material, with energy that does not form part of the pattern processed in step 410 (this may include conversion to waste heat, reuse as patterned or unpatterned energy, or waste heat generated by cooling the laser amplifier in step 404). In step 412, the patterned energy, here forming a one-dimensional or two-dimensional image, is relayed toward the material. In step 414, the image is applied to the material either by ablation or additive construction of a portion of a three-dimensional structure. Information derived from applying patterned laser energy to the material can be used to identify or measure powder size or other desired characteristics (step 415). In additive manufacturing, these steps can be repeated until an image (or another image, and then the next image) has been applied to all desired areas of the top layer of material (loop 418). Once the application of energy to the top layer of material is complete, a new layer can be applied to continue building the three-dimensional structure (loop 416). These process loops continue until the three-dimensional structure is complete, where remaining excess material can be removed or recycled.

[0055] FIG. 5 illustrates one embodiment of an additive manufacturing system including a phase-change light valve system containing a liquid crystal layer that can be formed from the reactive mesogens discussed herein along with a photo-alignment material. As previously described with respect to FIG. 3, the switchyard system allows for two-dimensional patterned energy recycling. The additive manufacturing system 520 includes 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 to a rejected energy processing unit 522, which can include an active light valve cooling system. After building, the beam is typically two-dimensionally patterned by an energy patterning unit 530 with some energy directed to the rejected energy processing unit 522. The patterned energy is relayed by one of multiple image relays 532 to one or more article processing units 534A, 534B, 534C, or 534D, typically as a two-dimensional image focused near a movable or fixed-height bed. The bed is inside a cartridge containing a powder hopper or similar material dispenser. A patterned laser beam directed by an image relay 532 can melt, dissolve, sinter, fuse, alter crystal structure, affect stress patterns, or otherwise chemically or physically modify the dispersed material to form a structure with desired properties.

[0056] In this embodiment, the rejected energy processing unit has multiple components that allow for reuse of the rejected patterned energy. Coolant from the laser and amplifier source 512 can be directed to one or more of the power generator 524, the heating / cooling thermal management system 525, or the energy dump 526. Additionally, repeaters 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, repeater 528C can direct the patterned energy to an image repeater 532 for further processing. In other embodiments, the patterned energy can be directed by repeater 528C to repeaters 528B and 528A for insertion into the laser beam provided by the laser and amplifier source 512. Reuse of the patterned image is also possible through the use of the image repeater 532. The image may be redirected, reversed, inverted, sub-patterned, or otherwise transformed for distribution to one or more article processing units 534A-534D. Advantageously, recycling of patterned light can improve the energy efficiency of the additive manufacturing process, in some cases improving energy intensity directed to the bed or reducing production time. In some embodiments, information derived from applying patterned laser energy to material in one or more of the article processing units 534A-534D can be used to identify powder size or other desired characteristics.

[0057] References throughout this specification to "one embodiment," "an embodiment," "one example," or "an example" mean that a particular feature, structure, or characteristic described in connection with an embodiment or example is included in at least one of the embodiments of the disclosure. Thus, appearances of the phrases "in one embodiment," "in an embodiment," "one example," or "an example" in various places throughout this specification do not necessarily all refer to the same embodiment or example. Furthermore, particular features, structures, data, or characteristics may be combined in any suitable combinations and / or subcombinations in one or more embodiments or examples. Additionally, it should be understood that the figures provided herein are for illustrative purposes to persons skilled in the art, and that the drawings are not necessarily drawn to scale.

[0058] Many modifications and other embodiments of the present invention will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing description and the associated drawings. It is understood, therefore, that the present invention is not limited to the particular embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims. It is also understood that other embodiments of the present invention may be practiced in the absence of elements / steps not specifically disclosed herein.

Claims

1. a first liquid crystal reactive mesogenic material having attached functional groups that enable crosslinking; a second liquid crystal reactive mesogenic material having a functional group attached thereto and a molecular weight different from that of the first liquid crystal reactive mesogenic material, wherein the second liquid crystal reactive mesogenic material is crosslinked to the first liquid crystal reactive mesogenic material; at least one of a photo-alignment material and a rubbed LCD alignment material, which may be in contact with the first liquid crystal reactive mesogenic material and the second liquid crystal reactive mesogenic material; A photochromic composition comprising:

2. The photochromic composition of claim 1 , wherein the functional group is an acrylate.

3. 10. The photochromic composition of claim 1, wherein the functional group is at least one of a monoacrylate and a diacrylate.

4. a first transparent substrate and a second substrate; a liquid crystal material located between the first substrate and the second substrate, the liquid crystal material further comprising: a first liquid crystal reactive mesogenic material having attached functional groups that enable crosslinking; a second liquid crystal reactive mesogenic material having attached functional groups and a different molecular weight than the first liquid crystal reactive mesogenic material, wherein crosslinking is formed between the first liquid crystal reactive mesogenic material and the second liquid crystal reactive mesogenic material; and at least one of a photo-alignment material and a rubbed LCD alignment material that can contact the first liquid crystal reactive mesogenic material and the second liquid crystal reactive mesogenic material. Including a light valve.

5. 5. The light valve of claim 4, wherein the functional group is an acrylate.

6. 5. The light valve of claim 4, wherein the functional group is at least one of a monoacrylate and a diacrylate.

7. a light valve capable of patterning a light beam in two dimensions, the light valve comprising a first substrate and a second substrate; a liquid crystal material located between the first substrate and the second substrate, the liquid crystal material further comprising: a first liquid crystal reactive mesogenic material having attached functional groups that enable crosslinking; a second liquid crystal reactive mesogenic material having attached functional groups and a different molecular weight than the first liquid crystal reactive mesogenic material, wherein crosslinking is formed between the first liquid crystal reactive mesogenic material and the second liquid crystal reactive mesogenic material; and at least one of a photo-alignment material and a rubbed LCD alignment material that can contact the first liquid crystal reactive mesogenic material and the second liquid crystal reactive mesogenic material; a laser that can be directed at the light valve for patterning; Additive manufacturing systems, including:

8. 8. The light valve of claim 7, wherein the functional group is an acrylate.

9. 8. The light valve of claim 7, wherein the functional group is at least one of a monoacrylate and a diacrylate.

10. a light valve capable of patterning a light beam in two dimensions, the light valve comprising a first substrate and a second substrate; a liquid crystal material located between the first substrate and the second substrate, the liquid crystal material further comprising: a first liquid crystal reactive mesogenic material having attached functional groups that enable crosslinking; a second liquid crystal reactive mesogenic material having attached functional groups and a different molecular weight than the first liquid crystal reactive mesogenic material, wherein crosslinking is formed between the first liquid crystal reactive mesogenic material and the second liquid crystal reactive mesogenic material; and at least one of a photo-alignment material and a rubbed LCD alignment material that can contact the first liquid crystal reactive mesogenic material and the second liquid crystal reactive mesogenic material; a laser that can be directed against a light valve for patterning before being directed at the powder bed; 1. A powder bed additive manufacturing system comprising:

11. 11. The light valve of claim 10, wherein the functional group is an acrylate.

12. 11. The light valve of claim 10, wherein the functional group is at least one of a monoacrylate and a diacrylate.

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