WO2022010977A2 - Systèmes et procédés de fabrication additive - Google Patents

Systèmes et procédés de fabrication additive Download PDF

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Publication number
WO2022010977A2
WO2022010977A2 PCT/US2021/040626 US2021040626W WO2022010977A2 WO 2022010977 A2 WO2022010977 A2 WO 2022010977A2 US 2021040626 W US2021040626 W US 2021040626W WO 2022010977 A2 WO2022010977 A2 WO 2022010977A2
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WIPO (PCT)
Prior art keywords
laser
laser beam
optical
manufacturing
light valve
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PCT/US2021/040626
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English (en)
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WO2022010977A3 (fr
Inventor
Kenneth L. Marshall
Stavros G. Demos
Tanya Kosc
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University Of Rochester
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Priority claimed from US16/923,055 external-priority patent/US20210046586A1/en
Application filed by University Of Rochester filed Critical University Of Rochester
Priority to US18/004,120 priority Critical patent/US20230264420A1/en
Publication of WO2022010977A2 publication Critical patent/WO2022010977A2/fr
Publication of WO2022010977A3 publication Critical patent/WO2022010977A3/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/0006—Working by laser beam, e.g. welding, cutting or boring taking account of the properties of the material involved
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/20—Direct sintering or melting
    • B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/36—Process control of energy beam parameters
    • B22F10/368—Temperature or temperature gradient, e.g. temperature of the melt pool
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/38—Process control to achieve specific product aspects, e.g. surface smoothness, density, porosity or hollow structures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/40—Radiation means
    • B22F12/44—Radiation means characterised by the configuration of the radiation means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
    • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0648—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising lenses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0652—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising prisms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/066—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms by using masks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/08—Devices involving relative movement between laser beam and workpiece
    • B23K26/082—Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/34—Laser welding for purposes other than joining
    • B23K26/342—Build-up welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/20—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B29C64/264—Arrangements for irradiation
    • B29C64/277—Arrangements for irradiation using multiple radiation means, e.g. micromirrors or multiple light-emitting diodes [LED]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y30/00—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y50/00—Data acquisition or data processing for additive manufacturing
    • B33Y50/02—Data acquisition or data processing for additive manufacturing for controlling or regulating additive manufacturing processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/36—Process control of energy beam parameters
    • B22F10/362—Process control of energy beam parameters for preheating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • B29C64/141—Processes of additive manufacturing using only solid materials
    • B29C64/153—Processes of additive manufacturing using only solid materials using layers of powder being selectively joined, e.g. by selective laser sintering or melting
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • LC's Liquid crystals
  • LC's have anisotropic optical properties that make them ideal materials from which to construct either passive or active devices that offer polarization, phase, or intensity control.
  • LC's are commonly associated with the display industry, they are useful in a wide variety of other applications, including in various laser systems for spectral and polarization control of the laser beam.
  • LC circular polarizers and wave plates have been key components in the near-infrared portion of the 351-nm, 1-ns, 40-TW OMEGA laser at the Laboratory for Laser Energetics (LLE) for over 30 years.
  • the laser induced damage threshold (LIDT) of the material (or optical component) is a key factor in determining the suitability and performance parameters for most optical materials incorporated in such laser systems. Because the utilization of lasers is continuously expanding into an increasing number of applications, there is a growing need for optical components suitable for higher average power and/or peak intensity systems. As the constituent optical materials and optical components represent a limit (damage threshold) on how much energy they can handle, increasing the power output of laser systems requires an accompanying increase in their clear aperture. An additional growing need is associated with attaining a high quality spatially tailored distribution of the laser energy within the laser beam profile, including the ability to control the spatial distribution of the beam amplitude and/or phase. Optical devices that can offer this capability are typically referred to generically as "light valves". For high peak or average laser beam power applications, such light valves must be able to withstand the transmitted power of the laser beam while maintaining performance and beam profile characteristics for the application-specific time durations.
  • a laser energy delivering system for an additive manufacturing includes: an optical light valve; a writing and erasing sub-system configured to repeatedly write and erase patterns in the optical light valve; a first laser beam, the optical light valve configured to spatially modulate an intensity of the first laser beam based on a pattern written into the optical light valve; a second energy beam, the second energy beam not being spatially modulated by the optical light valve; and a manufacturing material; in which the manufacturing system is configured to apply the modulated first laser beam and the non-modulated second energy beam to the manufacturing material to increase temperature in a build area to at least a first temperature that is at or above the melting temperature of the manufacturing material.
  • the system may be configured to apply the non-modulated second energy beam to the manufacturing material to increase temperature in a non-build area to a second temperature that is below the melting temperature of the manufacturing material.
  • the system may be configured to apply the modulated first laser beam and the non- modulated second energy beam to the manufacturing material to increase temperature in the non-build area to the temperature below the melting temperature of the manufacturing material.
  • the system may be configured to simultaneously apply the first laser beam and the second energy beam to both the build area and the non-build area.
  • the difference between the first and second temperatures may be 5% or more.
  • the increased temperature in the build area may spatially vary.
  • the system may also include a third laser beam, and a second optical light valve configured to spatially modulate an intensity of the third laser beam, the system may be configured to apply the modulated third laser beam to the manufacturing material to increase temperature in a portion of the build area to third temperature that is above the first temperature.
  • the second energy beam may be a second laser beam.
  • the first laser beam may have a first pulse duration that is shorter than the pulse duration of the second laser beam.
  • the system may be configured such that:
  • W > 2(Dt 1 ) 1/2 in which W is a required precision length for an object to be manufactured from the manufacturing material, D is a thermal diffusivity property of the manufacturing material, and ti is the first pulse duration.
  • the system may be configured such that:
  • the first pulse duration may be 10 ns or less and the second pulse duration may be longer than 10 ns.
  • the second energy beam may have a fluence that is higher than the fluence of the first laser beam.
  • the fluence of the second energy beam may be at least 80 % of the total fluence applied on the material comprised of the first and the second fluence.
  • the cross-sectional area of the second energy beam may be at least as large as the cross- sectional area of the first laser beam.
  • the system may also include a third laser beam, the third laser beam not being spatially modulated by the optical light valve, the system configured to apply the third laser beam to the manufacturing material at an angle that is non-normal to an upper surface of the manufacturing material.
  • the third laser beam may be configured to decrease a surface roughness attribute of the manufacturing material.
  • the optical light valve may be an all-optical light valve including a photoalignment layer that is not electrically conductive.
  • a laser additive manufacturing system may include: a particulate manufacturing material or material mixture; a first laser beam; and a second laser beam, the manufacturing system configured to apply the second laser beam to the manufacturing material at an angle that is non-normal to an upper surface of the manufacturing material; wherein the manufacturing system may be configured to apply the first laser beam and the second laser beam to the manufacturing material to increase temperature in a build area of the manufacturing material to at least a first temperature that is at or above the melting temperature of the manufacturing material; wherein the manufacturing system may be configured to apply the second laser beam to the manufacturing material to decrease a surface roughness attribute of the manufacturing material.
  • the system may be configured to spatially modulate an intensity of the first laser beam.
  • the system may be configured to apply the first laser beam to the manufacturing material at a normal angle.
  • the system may be configured to apply pulses of the first and second laser beams to the manufacturing material simultaneously or to apply at least some pulses of the first laser beam before pulses the second laser beam.
  • the manufacturing system may also include: a third laser beam; an optical light valve configured to spatially modulate an intensity of the first laser beam based on a pattern written into the optical light valve; and a writing and erasing sub-system configured to write and erase patterns in the optical light valve; wherein the second and third laser beams are not modulated by the optical light valve.
  • the optical light valve may be an all-optical liquid crystal light valve including a photoalignment layer that is not electrically conductive.
  • the manufacturing system may be configured to apply the modulated first laser beam and the non-modulated second and third laser beams to the manufacturing material to increase temperature in a build area of the manufacturing material to at least a first temperature that is at or above the melting temperature of the manufacturing material and to increase temperature in a non-build area of the manufacturing material to a second temperature that is below the melting temperature of the manufacturing material.
  • the pulse durations of the first and second laser beams may be shorter than pulse duration of the third laser beam.
  • the system may also include an additional laser beam, and the manufacturing system may be configured to apply the additional laser beam to the manufacturing material at an angle that is non-normal to an upper surface of the manufacturing material and that is different from the angle of the second laser beam.
  • a laser additive manufacturing system may include: an all optical liquid crystal beam shaper; an all optical writing and erasing sub-system configured to write, erase, and rewrite a plurality of optical patterns in the optical liquid crystal beam shaper; a laser beam source that produces a known and repeatable intensity profile on the locations of the all optical liquid crystal beam shaper; laser beam transport and imaging optics configured to project the image of the optical patterns in the optical liquid crystal beam shaper onto an unprocessed material layer; and a beam steering mechanism configured to control the position of the projected laser beam optical patterns on to the unprocessed material layer.
  • the all optical liquid crystal beam shaper may include: a first alignment layer that is photoswitchable and is located on an inner surface of the first transparent substrate; a second alignment layer having a fixed alignment state and is located on an inner surface of a second transparent substrate; a liquid crystal material contained between the two alignment layers and transparent substrates; and a polarizer that reflects a first polarization state and transmits a second complimentary polarization state.
  • the photoswitchable alignment layer comprises at least one from the group of materials including PESI-F, SPMA:MMA 1:5, SPMA:MMA 1:9, or SOMA:SOMA-p:MMA 1:1:6.
  • the fixed alignment layer may be either an inherently permanently aligned layer produced by rubbing or other physical processes or a write-once photoalignment layer that has been permanently oriented using polarized UV light with a maximum wavelength of 380 nm.
  • the fixed alignment layer may be a buffed Nylon 6/6 or a write-once photoalignment material.
  • the first and second transparent substrates may be any optical material that exhibits practically no absorption during operation of the system.
  • the liquid crystal material of the beam shaper may include partially saturated liquid crystals, fully saturated liquid crystals, partially fluorinated liquid crystals, or per-fluorinated liquid crystals.
  • the liquid crystal material of the beam shaper may include phenylcyclohexanes, cyclo- cyclohexanes, or a material including per-fluorinated alkyl side chains.
  • the all optical writing and erasing sub-system may be configured such that writing an optical pattern into the photoswitchable alignment layer causes a localized change in configuration of the liquid crystals, such that a laser beam passing through the liquid crystal beam shaper undergoes a localized change in polarization state.
  • the optical writing and erasing sub-system may include: a coherent or incoherent light source with an operating wavelength less than 500 nm and matched to a peak absorption wavelength of the photoswitchable alignment material; the light source may be coupled to either (i) a spatial light modulator configured to write an optical pattern on the photoswitchable alignment layer; or (il) an optical system that provides a raster-scanned light spot configured to write the optical pattern on the photoswitchable alignment layer.
  • the optical writing and erasing sub-system may be configured to erase the written optical pattern by application of (i) incident light of wavelength less than 500 nm and having a different polarization state than the incident light used to write the optical pattern, or (ii) application of visible light.
  • the laser beam source may operate at a wavelength that is larger than 500 nm
  • the laser beam transport and imaging optics may include: (i) fixed optical elements to control beam divergence, beam direction and beam polarization state and/or, (ii) adaptive optical elements to reduce or eliminate beam wavefront distortions and/or, (iii) active optical elements to control the location of beam direction or compensate for drifting during system operation.
  • the optically transparent substrates, the photoswitchable alignment layer, the fixed alignment layer, and the liquid crystal mixture may have an N-on-1 laser induced damage threshold using small beam damage testing configuration exceeding: (i) 40 J/cm 2 at 1053 nm and 1500 ps pulse width or (ii) 5 J/cm 2 at 1053 nm and 100 ps pulse width or (iii) 1 J/cm 2 at 1053 nm and 10 ps pulse width or (iv) 0.8 J/cm 2 at 1053 nm and 0.6 ps pulse width.
  • the photoswitchable alignment layer and the fixed alignment layer may be electrically non-conductive.
  • the liquid crystals may have an absorption edge of less than 330 nm.
  • Figure 1 illustrates an example of an additive manufacturing system.
  • Figure 2 illustrates an example of a multi-beam additive manufacturing system.
  • Figure 3 illustrates an example of an irradiation configuration for a multi-beam additive manufacturing system.
  • Figure 4 illustrates another example of an irradiation configuration for a multi-beam additive manufacturing system.
  • Figure 5 illustrates another example of an irradiation configuration for a multi-beam additive manufacturing system.
  • Figure 6 illustrates another example of a multi-beam additive manufacturing system.
  • Figure 7 illustrates another example of an irradiation configuration for a multi-beam additive manufacturing system.
  • Figure 8 illustrates another example of an irradiation configuration for a multi-beam additive manufacturing system.
  • Figure 9 shows an example of an optically addressable light valve.
  • Figure 10 shows an example of a photoswitchable command surface.
  • Figure 11 shows examples of photoswitchable LC alignment materials.
  • Figures 12(A) and (B) show the chemical structure of the poly(estermide) PESI-F.
  • Figure 13 shows an example of PESI-F synthesis.
  • Figure 14 shows the chemical structure of SPMA:MMA.
  • Figure 15 shows an example of SPMA:MMA synthesis.
  • Figure 16 shows the chemical structure of SOMA:SOMA-PMMA (1:1:6).
  • Figure 17 shows an example of SOMA:SOMA-PMMA (1:1:6) synthesis.
  • Figure 18 is a chart of laser induced damage thresholds at 1053 nm for various photoalignment materials.
  • Figure 19 shows examples of parallel-aligned, single-pixel LC devices fabricated using the spiropyran and spiroxazane photoswitchable copolymer alignment layers.
  • Figure 20 is a plot of the 1-on 1 and N-on-1 LIDT values for various LC materials as a function of the UV absorption edge at various pulse lengths.
  • the compound names and brackets identifying the saturated, unsaturated, and mixed materials in (a) apply to (b) through (d) as well.
  • Figure 21 shows N-on-1 LIDT values for saturated and unsaturated LC materials plotted as a function of pulse length.
  • the R 2 values of the fit lines range between 0.90 (E7) and 0.96 (PPMeOB/PPPOB, 1550C, and ZLI-1646).
  • Figure 22 charts the relative difference between N-on-1 LIDT's of saturated and unsaturated compounds as a function of pulse length. Data are normalized to results obtained for the unsaturated cyanobiphenyl LC mixture E7. At 10 ps there is a substantial increase in the difference between the LIDT of the two materials, which suggests a change in the mechanism for laser-induced damage.
  • Figure 23 is a chart quantifying the difference in intensity at the LIDT observed between successive test pulse lengths for both saturated and unsaturated materials.
  • Figure 24 illustrates certain electronic transitions leading to laser induced breakdown in LC materials.
  • Figure 25 charts LIDT and absorption edge for certain saturated and unsaturated LC materials.
  • Figure 26 charts LIDT results for saturated and unsaturated LC materials irradiated with 527-nm and 1.2-ns pulses.
  • Figure 27 charts the N-on-1 average LIDT values for nanosecond pulses at all three wavelengths as a function of each material's absorption edge, which enables direct comparison of the relative differences in LIDT arising from differences in the excitation process.
  • Figure 28 charts the average damage intensity for saturated and unsaturated materials for each tested pulse length and wavelength condition.
  • the mechanism for laser conditioning appears to have a minimum intensity of ⁇ 5GW/cm 2 .
  • the data also show a lower bound for the time scale ( ⁇ 50 ps) during which laser conditioning cannot take place.
  • Figure 1 schematically illustrates an example of a laser additive manufacturing system.
  • the system of Figure 1 includes an optical light valve 10 that spatially modulates the intensity of a laser beam 12. Spatial modulation is based on a pattern written into the optical light valve 10 by a writing / erasing sub-system 14. More specific examples of optical light valves and writing / erasing sub-systems are described in later sections below.
  • laser beam source 120 produces a laser beam 12 that typically may have a nearly uniform intensity profile l(x,y) and is impinging on the optical light valve 10.
  • the optical light valve 10 spatially modules the intensity of the laser beam 12 in accordance with the optical pattern written into the optical light valve 10 by the optical writing and erasing sub-system 14.
  • Laser beam transport and imaging optics 122 project the image of the optical patterns in the optical light valve onto the unprocessed material layer for additive manufacturing.
  • the laser beam transport and imaging optics 122 may include (i) fixed optical elements to control beam divergence, beam direction and beam polarization state and/or, (ii) adaptive optical elements to reduce or eliminate beam wavefront distortions and/or, (iii) active optical elements to control the location of beam direction or compensate for drifting during system operation
  • a beam steering mechanism 124 allows control of the position of the projected laser beam optical patterns onto the material layer.
  • a manufacturing material in this instance, a top layer of a powder bed or other particulate material
  • the spatially modulated laser beam such that the temperature of the material in a build area 16 is increased to be at or above the melting temperature of the material., and such that the temperature in a non-build area 18 is increased to a temperature that is below the melting temperature of the material.
  • the fluence and other aspects of the modulated laser beam will also be configured to change the viscosity to the material in the build area 16 to facilitate distribution of the melted material.
  • the optical light valve may be configured such that the contrast on beam rejection is on the order of 10% or less, or 5% or less (in other words, such that beam intensities in build and non-build areas differ by less than 10%, or less than 5%).
  • the system may be configured such that the difference in temperature increase between the non-build area and portions of the build area immediately adjacent to the non-build area is less than 10%, or less than 5%.
  • configuring the additive manufacturing system for small temperature differences between the build and non-build area may facilitate optimization of the mechanical properties, the surface texture, and enable embedding of tailored, localized residual stress in the part being built.
  • the modulation pattern written into the optical light valve 10 defines a keyhole shape so that the optical light valve modulates the cross- sectional portion of the laser beam outside of the keyhole (in this example, corresponding to the non-build area) to a lower intensity l 1 , and so that the optical light valve modulates the cross- sectional portion of the laser beam inside the keyhole (in this example, corresponding to the build area) so that it attains a nearly uniform intensity lo.
  • the modulation pattern may modulate beam intensity in both the build area and the non-build area.
  • the modulation pattern in the build area may be uniform (non-spatially varying) or non-uniform (spatially varying).
  • the modulation pattern in the non-build area may also be uniform (non-spatially varying) or non-uniform (spatially varying).
  • the system is configured to deposit additional powder layers on top of the exposed layer after laser exposure, which are each in turn exposed to the laser beam 12 after the pattern was refreshed by writing and erasing sub-system 14 to build additional layers of the product.
  • the writing and erasing sub-system 14 can repeatedly write and erase various modulation patterns into the optical light valve 10, in order to vary the cross- sectional shape of the particular layer of the product being built.
  • Figure 1 shows a single-beam additive manufacturing system.
  • Figure 2 schematically illustrates an example of a multi-beam additive manufacturing system.
  • the Figure 2 system includes a second energy beam 20 (which may be a second laser beam or other type of energy beam) in addition to a spatially modulated laser beam 12.
  • laser beam 12 has been spatially modified by an optical light valve (as in Figure 1) and second beam 20 has not passed through or been modulated by the optical light valve.
  • the combination of the spatially-modulated laser beam 12 and the second beam 20 are used to increase temperature in a non-build area of the material to a temperature that is below the melt- temperature, and to increase temperature in a build-area of the material to a temperature that is above the melt-temperature.
  • Spatially-modulated laser beam 12 and second energy beam 20 may have distinctly different temporal characteristics (pulse duration - t) that have been configured based on: (1) the diffusion properties (e.g. thermal diffusivity - D) of the material used, and (2) the required precision (e.g. tolerance - W) of the part being produced.
  • the pulse duration of the spatially modulated beam 12 can be set so that the thermal diffusion length is below the desired precision level [in other words, so that W>2(Dt 1 ) 1/2 ].
  • the pulse duration of the second beam 20 it is not necessary for the pulse duration of the second beam 20 to also be limited based on the desired precision level.
  • the second beam 20 can have a pulse duration (t 2 ) so that W ⁇ 2(Dt 2 ) 1/2 .
  • configuring the spatially-modulated beam 12 and second beam 20 in this manner will allow the bulk of the energy coupling and temperature increase to be provided by the long pulse second beam 20, with the spatially-modulated short pulse beam 12 providing the precision necessary to melt material only in the build area.
  • configuring the beams in this manner may lower the overall cost of the system (continuous wave lasers are typically less expensive than short pulse lasers). Additional advantages of this configuration may include providing for better heating of the material by allowing heat diffusion to uniformly heat the material, as well as limiting the energy of the spatially modulated beam to levels that will not damage the optical light valve.
  • the long pulse second beam may be operated at laser fluences that would exceed the damage threshold of the optical light valve.
  • the second beam 20 may provide a significantly larger (up to about one order of magnitude, 10X) amount of energy deposited on the material than would the spatially modulated beam 12.
  • the spatially-modulated laser beam 12 will have a shorter pulse duration (e.g. 10 ns or less) than the second beam 20 will have a longer pulse duration (e.g. 10 ns or longer).
  • the second beam 20's cross-sectional area is at least as large as the spatially modulated laser beam 12, and the two beams are applied to the build material simultaneously.
  • the cross-sectional areas of the two beams may be different, and the beams may be applied sequentially (e.g. the long pulse second beam 20 may be applied prior to the short pulse spatially modulated beam 12).
  • the second beam 20 may be spatially uniform in intensity. In other implementations, the intensity of the second beam 20 may spatially vary.
  • the second beam 20 can be comprised of light originating from one or more laser sources that are subsequently combined into a single laser beam.
  • the second beam 20 can be the same or different wavelength as the spatially-modulated laser beam 12.
  • the second beam 20 can be monochromatic or broadband light, or can be a non-light energy source.
  • the second beam 20 can be a non-laser source array.
  • the second beam 20 can be collimated or non-collimated [0091] While Figure 2 only shows a single spatially-modulated beam, one may also consider multiple modulated beam approaches such as when a pattern of significantly different temperatures are required within the build area.
  • a system may include, for example, two spatially- modulated beams, each modulated by a separate optical light valve, with the system configured to increase the temperature in one part of the build area to a first temperature at or above the material's melt temperature and to increase the temperature in another part of the build area to a second temperature that is even higher than the first temperature increase.
  • Figures 3-5 illustrate examples of irradiation configurations for a multi-beam additive manufacturing system including a spatially modulated short pulse laser beam 12 and one or more long pulse second beams 20.
  • both beams 12 and 20 have a nearly ninety- degree incident angle to the powder-bed target, and are combined together by a dichroic mirror or similarly functioning optical component downstream from beam 12 passing through the optical light valve (not shown).
  • spatially modulated laser beam 12 has a nearly ninety-degree incident angle to the powder bed target
  • second beam 20 has an acute incident angle to the powder bed target.
  • spatially-modulated laser beam 12 has a nearly ninety degree incident angle to the powder bed target
  • one second beam 20 has an first acute incident angle to the powder bed target
  • another second beam 20 has a second acute incident angle to the powder bed target from the opposite direction (or an obtuse incident angle when measured from the same direction).
  • the surface roughness on a material under deposition with laser assisted additive manufacturing can often be of great importance to the quality of the final part. That is because the roughness on a layer introduces mechanisms to generate additional roughness and other defects (porosity, stress etc.) during deposition of additional layers. It can therefore often be imperative to control roughness during the deposition of the material layer by layer. Described in this section is a new system and methodology for controlling roughness during laser assisted additive manufacturing using a large aperture light valve.
  • Figure 6 schematically illustrates an example of an additive manufacturing system that includes a third beam 22 in addition to the spatially modulated beam 12 and second beam 20 in which the third beam 22 is configured to reduce surface roughness of the material bed during additive manufacturing.
  • the third beam 22 is incident on the powder bed target at an acute angle.
  • the acutely incident beam 22 in Figure 6 will result in projections extending out of and depressions extending into the surface of the powder bed experiencing a higher exposure to the pulse of beam 22, which in turn will cause a higher amount of energy to be deposited in the projection or depression so that the projection or depression will experience a higher temperature above melting than relatively flat portions of the powder bed, thus helping to reduce or eliminate these surface imperfections and improve surface roughness.
  • This is achieved via two different mechanisms, which are activated based on the laser and material characteristics.
  • the higher temperature in the surface imperfection features will introduce a gradient in the melted material viscosity which in combination with other localized forces, such as surface tension and gravity, will help reduce the size of the surface features.
  • the increased localized laser fluence at the surface features can initiate laser ablation associated with explosive removal of material. This is achieved when a) the localized temperature is above the evaporation temperature initiating material superheating or b) the localized surface heating by the laser pulse initiates generation of stress waves that promote ejection of liquified material. In some implementations, it is preferable that the angle of incidence of beam 22 be less than 45 degrees.
  • Figure 7 illustrates an example of a three beam additive manufacturing system including a spatially-modulated beam 12 and second beam 20 that are combined and incident on the powder bed at a ninety-degree angle, with a third beam 22 incident at an acute angle to the powder bed for improving surface roughness of the powder bed.
  • Figure 8 illustrates another example of a three beam additive manufacturing system including a spatially-modulated beam 12 and second beam 20 that are combined and incident on the powder bed at a ninety-degree angle, with two additional beams 22 incident at acute angles to the powder bed for improving surface roughness of the powder bed.
  • the two additional beams 22 help to address shadowing effects from projections and depressions in the powder bed. For instance, a projection will not be illuminated on the opposite sides by a single additional beam 22, since a side of the projection will be in the shadow of its other side. By having two additional beams 22, shadowing effects may be reduced or completely eliminated.
  • the two additional beams 22 may be incident on the powder bed at different acute angles from one another, allowing for modification of an interference pattern between the two beams 22.
  • the additional beam(s) 22 may have pulse durations that are similar to that of the spatially-modulated beam 12, but, unlike beam 12, are not spatially-modulated. Short pulse beams may be preferable (in at least some implementations) for use as the third beam. In some cases, if the pulse duration of the additional beam is too long, heat diffusion may counteract or prevent the processes causing surface smoothing described above.
  • the additional beam(s) 22 may be configured to be incident on the target area during or immediately after the arrival of the pulse of beam 12.
  • Additional beam(s) 22 may be derived from the same source as the spatially-modulated beam 12.
  • Spatially modulated beam 12 and additional beam(s) 22 may either be coherent or incoherent relative to each other, and may (or may not) create an interference pattern at the area of overlap on the powder bed target.
  • OALV optically addressable light valves
  • the all-optical light valves described below employ specific classes of materials and optical arrangements allowing their use with high average power and/or peak intensity laser applications, such as for laser systems for additive manufacturing and directed energy applications, and for other laser applications.
  • the approach uses an all-optical design (no conductive oxide electrodes, electrical interconnects, etc.) based on unique photoswitchable alignment layers and LC materials.
  • the photoalignment layers and LC materials used in the devices are exceptionally resistant to damage from high-intensity laser energy and provide the ability to reproducibly write, store, and erase high-resolution optical patterns with minimal loss of resolution and contrast after multiple write/erase cycles.
  • the LC materials incorporated into the device are preferably saturated materials (i.e., those that contain a minimum of carbon-carbon double bonds), even more preferably fully saturated materials.
  • saturated materials i.e., those that contain a minimum of carbon-carbon double bonds
  • fully saturated materials even more preferably fully saturated materials.
  • the lack of a delocalized p electron system minimizes the potential coupling with the intense optical field of the laser, completely eliminating third-order nonlinear optical reorientation of the LC molecular axis which, although known to occur in unsaturated LC materials, is slow (on the order of several seconds) and at best would produce some loss of alignment, which could be corrected easily by refreshing the written pattern with another optical write cycle.
  • the combination of strong, rewritable LC surface anchoring with a nearly nonexistent LC re-orientational response to strong incident laser fields allows the desired optical patterns to be written and maintained for a duration of time that could meet or exceed the requirements/specifications for the intended applications.
  • the novel photoalignment layers disclosed in this patent provide the ability to reproducibly write, store and erase high-resolution optical patterns with minimal loss of resolution and contrast after multiple write/erase cycles, and resistance to image-sticking and burn-in.
  • the ability to produce precise spatial shaping of the amplitude or phase of an incident high-energy laser beam is a key requirement fora number of applications in optics and photonics.
  • One example is in high-energy laser systems employing large-scale 1053 nm Nd:glass beamlines to either pre-compensate for spatial-gain variations or maximize the energy extraction using apodized high-order super-Gaussian beams.
  • Laser beam shaping in such systems has employed binary devices composed of distributions of opaque pixels with transmission equal to either 0 or 100%. These devices are typically in the form of a metal film deposited on a transparent glass substrate which, when positioned appropriately in the laser beam, produce a continuous beam profile after far-field Fourier filtering and re-imaging.
  • Metal-mask beam shapers are prepared using standard photolithographic processing techniques widely employed in the semiconductor fabrication industry and are relatively inexpensive to make, but have two key limitations: (1) a new mask must be generated if it is desired to change the shaping pattern (i.e., real-time manipulation of the spatial amplitude distribution is not possible); and (2) because the metal mask controls the beam shaping profile by spatially-distributed absorption of the near-IR laser energy by the metal pixels, the resistance of these devices to damage by the incident laser energy is very small ( ⁇ 200-700 mJ/cm 2 at 1053 nm, 1 ns pulse). As a result, these devices are limited to use only in low-fluence areas of the laser system.
  • An alternative method utilizes LC materials in either active (electric-field-driven control of the optical characteristics of the device) or passive (fixed optical properties, e.g. Dorrer et al., 2011).
  • Such LC materials and devices have demonstrated significant potential for both polarization control and beam-shaping of relatively high-power near IR lasers, and have an extended track record of proven performance in various locations in both the 60-beam, 40-TW OMEGA and 4 -beam, 4 petawatt Nd:glass laser systems in the Omega Laser Facility at the
  • LC-based devices include scalability to apertures of 200 mm or larger, cost effectiveness, high optical quality with low loss and high contrast, broad angular tolerance, ability to tune optical properties through LC material composition and, most importantly, a relatively high intrinsic laser damage resistance, as demonstrated with current generation materials.
  • the inventor has discovered that, by suitable tailoring of the LC material's molecular structure, the damage threshold can be increased significantly beyond current benchmark values, not only in the near infrared spectral range but also through the near ultraviolet spectral range (subject to consideration of the wavelengths that would write, rewrite, and/or erase the pattern written into the photoalignment layer).
  • Alignment layers in LC devices serve to establish a uniform alignment direction of the LC material throughout the bulk of the LC fluid layer, which significantly improves optical contrast and minimizes defects.
  • the LC molecules at the surface of the alignment layer are tightly bound in a particular orientation determined by the boundary conditions and the elastic deformation energy of the LC molecules, which in turn depends upon the particular surface treatment employed.
  • Commercially available LC devices are typically fabricated by rubbing (buffing) the alignment layer in a particular direction before device assembly to establish the molecular alignment direction of the LC.
  • a polyimide alignment layer is employed, although other polymers (e.g., Nylon 6/6) have also been used.
  • Photolithographic patterning of UV photosensitive LC alignment layers with linearly polarized UV light has been used to fabricate passive LC beam shaper devices with spatially varying molecular orientations.
  • These photoalignment materials have high near IR laser damage thresholds. Coupled with the ability to generate an almost infinite variety of binary and gray- scale apodization and beam-shaping profiles by the photoalignment process, the high laser- damage threshold, ease in processing flexibility, and the ability to scale to large apertures through conventional contact photolithography techniques make this type of device ideal for passive beam-shaping applications in high-fluence areas of high-power laser systems.
  • Active LC beam shaper devices provide "real-time”, spatially distributed amplitude and phase modulation of laser beams using matrix-addressed LC electro-optical spatial light modulators (SLM's).
  • SLM's matrix-addressed LC electro-optical spatial light modulators
  • One example of this type of device is the commercially available liquid crystal-on-silicon (LCOS) reflective SLM's for programmable beam shaping at high spatial resolution (typically 600 x 792 pixels) in low-fluence areas of high-peak-power lasers such as the 4 petawatt OMEGA EP laser and the Multi-Terawatt (MTW) laser at LLE.
  • LCOS liquid crystal-on-silicon
  • MTW Multi-Terawatt
  • the SLM image plane is captured using a near-field camera and the beam wave front is measured with a wave front sensor.
  • the 2-D near-field and wave front profiles are used to provide closed-loop feedback control of the SLM.
  • a computer program iteratively controls the
  • Matrix-addressed eiectro-optical LCOS-SLM devices allow for considerable flexibility for real-time beam shaping but the requirement for patterned metal-oxide conductive coatings on the inner cell surfaces makes device assembly complicated, and, most importantly, significantly reduces the amount of laser fluence that the device can handle before incurring permanent and catastrophic modification (damage).
  • the onset of damage is determined by the absorption and heating of a nanoscale region of a characteristic size reaching a critical temperature, which is applicable to indium tin oxide (ITO) films (exhibiting laser damage threshold at 1054 nm, 2.5 ns of about 250 mJ/cm 2 ) and also to conductive wide band-gap semiconductors (damage threshold on the order of 5 J/cm 2 ).
  • ITO indium tin oxide
  • the spatially distributed UV intensity induces a corresponding spatially distributed localized DC voltage that, when combined with the AC bias voltage across the ITO electrodes, causes the LC molecules in the illuminated areas to reorient and modulates the polarization of the 1053-nm incident laser beam.
  • Liquid crystal materials exhibit properties of both fluids (inability to support a shear stress) and crystalline solids (ordered molecular orientation) and, in general, they partially orfully lack positional molecular order.
  • the two main classes of LC's, (thermotropic and lyotropic) are distinguished by the physical parameters that control over what conditions the liquid crystalline phase will appear (changing temperature or changing solution concentration, respectively).
  • the most common thermotropic LC materials consist of either rod-like (calamitic) or disk-like (discotic) molecules.
  • Calamitic LC materials can exhibit several different mesophases (e.g., nematic, smectic, and cholesteric phases) that differ depending on the molecular structure of the material and the degree of order of the mesophase.
  • mesophases e.g., nematic, smectic, and cholesteric phases
  • the directional molecular ordering characteristic in these mesophases gives rise to useful properties (e.g., optical and dielectric anisotropy) and are thus particularly suitable for optical applications.
  • Laser-induced damage is determined by the formation of an observable material modification, which requires the deposition of laser energy into the material.
  • the energy- coupling mechanisms are largely dependent on the electronic structure of the material, the presence of absorbing defects structures, and the associated excitation (laser) parameters.
  • defects may be intrinsic (such as related to molecular orientation and domain boundaries) or extrinsic (impurities, substrate defects or inclusions).
  • Figure 9 schematically shows an example of an optically addressable light valve design that does not require the use of electrically conductive coatings and that employs a photo- switchable alignment layer instead.
  • Figure 9 shows an all-optical liquid crystal beam shaper using a photo-switchable polymer, or "command surface,” as an alignment coating.
  • Incident low power UV light from a variety of sources (here, either an Hg/Xe lamp, LED source, or Ar+ laser) provides the "write” illumination to a liquid crystal on silicon (LCOS) device, whose image plane is focused onto the photoalignment layer within the beam shaper.
  • LCOS liquid crystal on silicon
  • Patterns produced on the LCOS are written, erased, and rewritten on the photoalignment layer using either alternating UV incident polarizations or serial applications of UV and visible light. Alternatively, patterns can be written and erased directly using a raster-scanned polarized UV laser source or in other manners.
  • the writing and erasing sub-system may include a coherent or incoherent light source with operating wavelength less than 500 nm and matched to the peak absorption wavelength of the photo-switchable alignment material, the light source coupled to either (i) a spatial light modulator configured to write an optical pattern on the photo-switchable alignment layer; or (ii) an optical system that provides a raster-scanned light spot configured to write the optical pattern on the photo-switchable alignment layer.
  • the writing and erasing sub- system may erase the optical pattern written into the optical light valve by: (i) application of incident light of wavelength less than 500 nm having a polarization state that is different from the polarization state used to write the optical pattern, or (ii) application of visible light.
  • the optical light valve shown in Figure 9 utilizes two different non-electrically conductive LC alignment layers located on each inner substrate surface that is in contact with the LC material.
  • one alignment layer is a buffed nylon 6/6 passive alignment layer, which has a fixed alignment state.
  • Such materials are currently used as alignment layers for LC waveplates in OMEGA and are known to have 1053 nm, 1 ns laser-damage threshold in the near- IR of 9 -14 J/cm 2 , depending on whether the coating is buffed or pristine (not buffed), respectively. See (1) Jacobs, S. D., Cerqua, K. A., Marshall, K. L., Schmid, A., Guardalben, M. J.
  • Options for a passive photoalignment layer include, without limitation, Nylon 6/6 (Poly(N,N'- hexamethyleneadipinediamide)), ROLIC ROP 203/2CP (a cinnamate photopolymer available from ROLIC Corp, Switzerland), Polymer 3 (a coumarin-based photoalignment layer material), and LIA- 01 (an azobenzene photoswitchable alignment layer available from DIC Corp, Japan).
  • the second substrate contains a photo-switchable "command surface" polymer alignment layer that undergoes a reversible change in molecular shape or orientation when exposed sequentially to low incident energy UV or visible light (or UV light with two different polarization states).
  • a photo-switchable "command surface" polymer alignment layer that undergoes a reversible change in molecular shape or orientation when exposed sequentially to low incident energy UV or visible light (or UV light with two different polarization states).
  • imaging techniques contact photolithography, laser raster-scanning, or projecting a pattern in the image plane of an
  • LCOS--SLM onto the coated surface using a polarized light source
  • spatially distributed alignment states can be written, erased, and re-written into this "all-optical" photo-switchable LC beam shaper, thereby duplicating the behavior of an electro-optical SLM or electrically-biased OALV without the need for conductive coatings.
  • incoherent or coherent UV sources Hg/Xe lamp, LED, argon-ion, or helium-cadmium laser
  • the alignment layers are coatings on the inner surfaces of transparent substrates.
  • the transparent substrates may be any optical material that exhibits little to no absorption during operation of the system.
  • the written state in these photo-switchable alignment layers requires no applied electrical or optical fields to remain stable for extended periods of time (weeks or longer) under normal ambient conditions, provided that background UV or visible light intensity remains below the threshold intensity required to change the orientation of the command surface.
  • This switching threshold is a function of the molecular structure of the command-surface material and can be controlled by molecular design to be as low or high as necessary to suppress switching by ambient effects. Write-erase times are dependent on the incident UV energy, and can be as fast as 10 ms.
  • the pendants on this photo-switchable command surface are switched optically between two different alignment states, which in turn redirects the orientation of the LC material in contact with the coating surface in response to wavelength of the polarized "write” (UV) or "erase” (visible) incident light.
  • Figure 10 shows an example of a photo-switchable command surface including azobenzene pendant groups.
  • the azobenzene groups in the elongated trans state (left) cause LC molecules to adopt an orientation parallel to the azobenzene long molecular axis, while azobenzenes in the bent cis state (right) switch the orientations of the LC to a near- parallel orientation to the substrate to minimize their free energy.
  • the resultant LC reorientation can occur either out of the substrate plane (top) or in the plane of the substrate (bottom). This change in orientation induces a change in the polarization, phase, or amplitude of an incident optical beam, depending on the optics in the system.
  • the outer surface of the substrate(s) may include anti-reflection (AR) coatings to minimize back-reflection and other stray light that could, in some instances, have a negative effect on the pattern writing process.
  • AR anti-reflection
  • the AR coatings may be designed to operate at the wavelength of the write illumination source, and, for the sections in which the near IR beam passes through the substrate, a second AR coating may be required with properties optimized for the near IR.
  • the components of the optical light valve (including the optically transparent substrates, the photo-switchable alignment layer, the fixed alignment layer, and the liquid crystal mixture) have an N-on-1 laser induced damage threshold using small beam damage testing configuration exceeding one or more of 40 J/cm 2 at 1053 nm and 1500 ps pulse width, 5 J/cm 2 at 1053 nm and 100 ps pulse width, 1 J/cm 2 at 1053 nm and 10 ps pulse width, and/or 0.8 J/cm 2 at 1053 nm and 0.6 ps pulse width.
  • new photo switchable alignment layer materials are needed whose molecular structures and switching mechanisms will provide (1) excellent near IR laser damage threshold; (2) the ability to reproducibly write, store and erase high-resolution optical patterns; (3) minimal loss of resolution and contrast after multiple write/erase cycles, and (4) be resistant to image- sticking and burn-in of previously written patterns.
  • the LC materials ideally will provide a similarly high damage threshold.
  • Photo-switchable Alignment Layer Materials for High-Power Laser Beam Shaping [0137] Several unique photo-switchable LC alignment polymer coatings have been developed based on azobenzene, spiropyran and spiroxazane photoactive pendants. Spiropyrans and spiroxazanes differfundamentallyfrom the azobenzene photo-switchable coatings in that photo- switching occurs due to a reversible photo-mediated ring opening/closing reaction upon absorption of UV and visible light rather than through photomechanical trans-cis isomerization, in which no chemical bonds are broken. [0138] The generalized schematic diagram for these new materials is shown in Figure 11.
  • Figure 11 shows a photo-switchable alignment material in which the chromophore containing appropriate terminal group (as shown, either azobenzene or spiropyran) is tethered to a polymer backbone by a flexible alkyl spacer chain.
  • a photo-switchable LC alignment material utilizing azobenzene as a chromophore
  • a reversible photomechanical trans-cis photoisomerization is employed.
  • spiropyran shown
  • spiroxazane chromophores a photo-mediated ring opening/closing reaction is employed.
  • Figure 12(A) shows the chemical structure of the poly(esterimide) PESI-F.
  • This material is an indolene polymer with azobenzene chromophores partially incorporated in the backbone and not through a flexible tether.
  • Figure 12(B) shows how the material switches in response to UV and visible light. Weglowski et al. (Opt. Commun. 400, 144 (2017)) reported these materials to be useful for fabrication of photochromic diffraction gratings, but, to the best of the inventor's knowledge, it had not been previously known prior to the inventor's discovery to use PESI-F in a photo-switchable LC alignment layer.
  • Figure 13 shows one example of how PESI-F may be synthesized, with an overall product yield of approximately 10%. [See A. Kozanecka-Szmigiel et al., Dyes Pigments 114, 151 (2015).]
  • These materials are methacrylate copolymers containing spiropyran chromophores with a NO 2 terminal group attached to a methacrylate backbone through a 6-carbon alkyl spacer.
  • the general molecular structure is shown in Figure 14.
  • Spiropyran copolymers with a ratio of one spiropyran monomer to five methacrylate backbone units (1:5) and a ratio of one spiropyran monomer to nine methacrylate backbone units (1:9) have been shown to be useful. To the best of the inventors' knowledge, it had not been previously known to use these spiropyran copolymers to function as LC alignment layers, either write-once or photo-switchable.
  • Figure 15 shows one example of how SPMA:MMA may be synthesized, with an overall product yield of approximately 10%. [See S. Friedle and S. W. Thomas, Angew. Chem., Int. Ed. 49, 7968 (2010).]
  • These materials are also methacryate copolymers, but in this case contain two different spiroxazane methacrylate monomer chromophores copolymerized with unsubstituted methacrylate monomers in a ratio of one pyridine-containing spiroxazane chromophore (SOMA) to one piperidine-containing spiroxazane monomer (SOMA-p) to six unsubstituted methacrylate monomers.
  • SOMA pyridine-containing spiroxazane chromophore
  • SOMA-p piperidine-containing spiroxazane monomer
  • Figure 17 shows one example of how SOMA:SOMA-PMMA (1:1:6) may be synthesized, with an overall product yield of approximately 10%.
  • Buffed alignment layers such as those used in the matrix addressed LCOS-SLM and OALV beam shapers of the prior art have the lowest 1053 nm laser damage thresholds of the group (buffed polyimide is not shown, as its 1053 nm laser damage threshold is ⁇ 1 J/cm 2) .
  • the ROLIC ROP 203/2CP, "Polymer 3" and LIA-01 are write- once photoalignment materials, while the three PAAD materials, PESI-F, SPMA-MMA (1:5), and SOMA:SOMA-PMMA (1:1:6) are photo-switchable.
  • FIG. 19 shows the first three single-pixel LC devices fabricated using the new spiropyran (SPMA:MMA 1:5 and SPMA:MMA 1:9) and spiroxazane (SOMA:SOMA-p:MMA 1:1:6) photo-switchable polymers viewed under crossed polarizers. Excluding fabrication defects, these photo-switchable alignment materials exhibit contrast, alignment uniformity, and write-state stability equivalent to or exceeding photoalignment materials of the prior art.
  • the white arrows in the photographs define the alignment direction of the LC material in the device. All samples were photographed between crossed polarizers.
  • Liquid Crystal Materials for High-Power Laser Beam Shaping [0148] Several nematic LC materials were selected to explore the effect of varying degrees of ⁇ -electron delocalization and electron density on their damage thresholds. The aim was to provide baseline measurements on the LIDT's of currently available LC's as a function of their chemical structure and extend the limited available knowledge on LC damage thresholds for nanosecond pulses at 1053 nm to both the sub-nanosecond and nanosecond pulse length regimes at 527 nm and 351 nm. Delocalized ⁇ -electrons are found in unsaturated (e.g., benzene- like) carbon rings with double bonds, and their presence shifts the electronic absorption edge toward longer wavelengths.
  • unsaturated e.g., benzene- like
  • LC materials with the highest degree of p-electron delocalization include the well-known cyanobiphenyl (two unsaturated hydrocarbon rings) LC materials such as 5CB (4-pentyl- cyanobiphenyl or K-15) and the eutectic mixture E7.
  • the ZLI-1646 mixture contains contain compounds with both saturated and unsaturated ring structures.
  • Pulse Length Dependence at 1053 nm The LIDT dependence at 1053 nm as a function of laser pulse duration was investigated at six different pulse lengths: 600 fs, 2.5 ps, 10 ps, 50 ps, 100 ps, and 1.5 ns.
  • the 1-on-1 and N- on-1 LIDT values plotted as a function of each material's UV-absorption edge (and therefore the linear absorption cross section) are shown in Figure 20.
  • the saturated materials have an absorption edge ⁇ 330-nm, and data for saturated and unsaturated materials can be differentiated easily.
  • the partially saturated LC mixture ZLI-1646 behaves more like a fully saturated material, suggesting that at least in this material, the unsaturated components, which one might expect to be the 'weak links', did not adversely affect the LC mixture's performance.
  • the LIDT values determined in this work for three common commercial LC materials were higher than those determined for the same materials in 19SS, which we attributed to advances in chemical purification processes applied to commercial LC materials in general. Of notable significance are the data at 1.5 ns, where the LIDT values of saturated LC's approach those of bare fused silica.
  • the N-on-1 LIDT is lower than the 1-on-1 LIDT, an effect commonly referred to as "incubation.” Neither conditioning nor incubation is strongly observed at either 600 fs or 2.5 ps.
  • the average damage intensity changes by similar amounts in each increment for both saturated and unsaturated materials ( ⁇ 1.5x and ⁇ 2.5x, respectively).
  • the damage intensity changes by differing amounts for the two materials types. Specifically, between 2.5 ps and 10 ps, the change in the damage threshold intensity is lower for the saturated materials than for the unsaturated materials (1.7x and 2.6x, respectively). This difference is reversed between 10 ps and 50 ps, where the change in the damage threshold intensity is 2.9x and 1.8x for the saturated and unsaturated materials, respectively.
  • the excitation process is dependent on the electronic structure of the material and, as such, should depend strongly on the laser wavelength.
  • Nematic LC materials were tested using nanosecond laser excitation at 351-nm (third harmonic, 3w) and 527-nm (second harmonic, 2w) to compliment the results obtained at the fundamental 1053-nm (1w) wavelength presented above. This multiple-wavelength investigation aims to probe the correlation between the electronic structure of each material and its laser-induced damage behavior via altering the excitation photon energy.
  • the electronic excitation pathways in LC materials are generally known and involve a singlet ground state (S 0 ) and excited singlet (S 1 , S 2 ,...S n ) and triplet states.
  • the time scale of the transition from the singlet states to the corresponding triplet states during relaxation, or intersystem crossing, is typically > 1 ns, which has been confirmed for several unsaturated LC compounds [See (1) F.H. Loesel, M.H. Niemz, J.F. Bille, and T. Juhasz, "Laser-induced optical breakdown on hard and soft tissues and its dependence on the pulse duration: experiment and model," IEEE J Quant Elect, 32 (10), 1717 - 1722 1996; and (2) A. Oraevsky, L. B.
  • the accordingly modified Jablonski energy diagram in Figure 24 describes the electronic structure in LC materials involving a singlet ground state (S 0 ) and excited singlet (S 1 , S 2 ,...S n ) where the energy levels are defined as multiples of the energy of a 1053 nm photon used in this study. Transmission measurements for each material provided insight into which photon absorption order would be required to bridge the energy gap from S 0 -> S 1 .
  • the LIDT results shown in Figure 25 indicate that the laser-induced-damage thresholds under irradiation with 351-nm and 1-ns pulses follow the absorption edge of the LC materials, a trend that is particularly clear for the N-on-1 results. This behavior may be assigned in part to the order of the excitation process. As depicted in the schematic representation of the energy structure of the saturated and unsaturated materials shown in Figure 24 the highly unsaturated materials require 1-photon absorption forthe S 0 -> S 1 transition while saturated materials require a 2-photon absorption process. This difference is potentially responsible for the large difference in the LIDT ( ⁇ 20x-50x, depending on damage testing method) between the saturated and unsaturated materials. The results also show laser conditioning (N-on-1 LIDT > 1-on-1 LIDT) occurs in saturated materials.
  • ESA is a more effective energy-deposition mechanism, but is limited by the available excited-state electron population. Therefore, two general governing mechanisms that contribute to absorption of energy by the laser pulse can be considered: (a) direct absorption by ground-state electrons and (b) absorption by excited-state electrons involving only the singlet states.
  • the excited-state electrons can, in principle, undergo multiple absorption cycles by either reaching the higher excited state (S2) and returning to the Si state during the laser pulse to repeat the process or continuing with additional absorption toward higher excited states (S 2 -> S m ).
  • S2 higher excited state
  • S 2 -> S m Laser-induced damage experiments exploring pulse length scaling provide insight into energy-deposition mechanisms.
  • unsaturated materials require both linear absorption at 351 nm and 2-photon absorption at 527 nm, while for saturated materials, 2-photon absorption is necessary to populate the first excited state at both wavelengths. This key difference in the electronic excitation process is reflected in the corresponding difference in the LIDT values.
  • the laser conditioning mechanism is dictated by the time scale of photochemically-- induced reaction kinetics (e.g. volatilization of impurities or photochemically-induced reaction of the LC molecules with intrinsic or extrinsic impurities, breakdown products, or with each other to form more stable compounds (eg. oxygen bridge formation in biphenyls).

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Abstract

L'invention concerne des systèmes et des procédés de fabrication additive faisant appel à un modulateur de lumière optique conçu pour moduler spatialement l'intensité d'un faisceau laser, conjointement avec un sous-système d'écriture et d'effacement configuré pour écrire et effacer de manière répétée des motifs du modulateur de lumière optique de façon à varier de manière répétée la modulation spatiale du faisceau laser. Selon certains modes de réalisation, les systèmes et les procédés peuvent également faire appel à des faisceaux laser supplémentaires ou à d'autres sources d'énergie qui ne sont pas modulés spatialement par le modulateur de lumière optique. Selon certains autres modes de réalisation, les systèmes et les procédés peuvent faire appel à des faisceaux laser supplémentaires ou à d'autres sources d'énergie conçus pour réduire la rugosité de surface de la poudre ou d'un autre matériau utilisé pour la fabrication additive.
PCT/US2021/040626 2019-08-16 2021-07-07 Systèmes et procédés de fabrication additive WO2022010977A2 (fr)

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CN116945600A (zh) * 2023-08-04 2023-10-27 北京易加三维科技有限公司 粉末床熔融热塑性弹性体的表面处理方法

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11581691B2 (en) 2019-08-16 2023-02-14 University Of Rochester All-optical, optically addressable liquid crystal-based light valve employing photoswitchable alignment layer for high-power and/or large aperture laser applications
CN114574854A (zh) * 2022-02-28 2022-06-03 中国矿业大学 一种脉冲激光原位冲击辅助激光熔覆装置及使用方法
CN114574854B (zh) * 2022-02-28 2022-12-02 中国矿业大学 一种脉冲激光原位冲击辅助激光熔覆装置及使用方法
EP4254054A1 (fr) * 2022-04-01 2023-10-04 SLM Solutions Group AG Procédé de fonctionnement d'un système d'irradiation, système d'irradiation et appareil de production d'une pièce tridimensionnelle
CN116945600A (zh) * 2023-08-04 2023-10-27 北京易加三维科技有限公司 粉末床熔融热塑性弹性体的表面处理方法
CN116945600B (zh) * 2023-08-04 2024-02-23 北京易加三维科技有限公司 粉末床熔融热塑性弹性体的表面处理方法

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