Refractive index of infrared-transparent polycrystalline alumina

Harris, Daniel C.; Johnson, Linda F.; Cambrea, Lee R.; Baldwin, Lawrence C.; Baronowski, Meghan; Zelmon, David E.; Poston, William; Kunkel, John D.; Parish, Mark V.; Pascucci, Marina R.; Gannon, J. L.; Wen, Tzu-Chien

doi:10.1117/12.2257580

Cited by 6 publications

(6 citation statements)

References 10 publications

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“…As discussed in our previous work, 1 transparent alumina is an ideal material for ballistic protection applications where visible or infrared wavelength transmission is required. [2][3][4] However, to achieve these favorable properties, alumina must be sintered to high densities (>99.99%TD) to eliminate light scattering due to porosity. 5 Even at high densities, the transparency of alumina is limited due the rhombohedral crystal structure being inherently birefringent.…”

Section: Introductionmentioning

confidence: 99%

Aligning α‐alumina platelets via uniaxial pressing of ceramic‐filled polymer blends for improved sintered transparency

et al. 2020

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Uniaxial warm pressing was used to align alumina platelet‐filled polyethylene‐based copolymer blends. The solids loading (30‐40 vol.%) and platelet diameter (1.2 and 11 μm) were varied to compare effects on viscosity, percent reduction, and final alignment. All ceramic‐filled thermoplastic polymer blends exhibited pseudoplastic behavior. Crystallographic alignment of green body samples was quantified by the orientation parameter (r) and grain misalignment angle (full width at half maximum, FWHM) obtained from rocking curve analysis. Blends with 11 μm diameter platelets displayed a higher temperature sensitivity constant, better flow properties, and higher alignment compared to blends with 1.2 μm diameter platelets. Optimal samples produced with blends containing 30 vol.% of 11 μm diameter platelets demonstrated an alignment of r = .251 ± .017; FWHM = 11.16° ± 1.16°. A sample with optimal alignment was hot‐pressed to transparency and obtained an in‐line transmission of 70.0% at 645 nm. The final alignment of this pre‐aligned hot‐pressed sample (r = .254 ± .008; FWHM = 11.38° ± 0.54°) improved when compared to a non‐pre‐aligned sample (r = .283 ± .005; FWHM = 13.40° ± 0.38°).

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Section: Introductionmentioning

confidence: 99%

Aligning α‐alumina platelets via uniaxial pressing of ceramic‐filled polymer blends for improved sintered transparency

et al. 2020

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“…Transparent alumina is a candidate for protection applications, such as nose cones, radomes, and ballistic blast shields. [1][2][3] Alumina can reach optical transparency at high relative densities. 4 However, alumina is birefringent due to its anisotropic rhombohedral crystal structure, causing light scattering at the grain boundaries and limiting transparency.…”

Section: Introductionmentioning

confidence: 99%

“…However, they used an equiaxed-morphology alumina powder in their studies, 22,[37][38][39] as have all other studies aiming to produce transparent alumina. [1][2][3][4][5][6][8][9][10][11][12][13][14][15][16][17][18][19][20][21] To the extent of the author's knowledge, there have been no reported attempts to hot-press platelet-morphology alumina powder to transparency.…”

Section: Introductionmentioning

confidence: 99%

Hot‐pressing platelet alumina to transparency

et al. 2019

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Alumina powder with a platelet morphology was hot-pressed to transparency with preload pressures of 0-8 MPa, maximum temperatures of 1750-1825°C, maximum pressures of 2.5-80 MPa, and isothermal hold times of 1-7 hours. Optical transmission (in-line and total), as well as optical losses (backward/forward scattering and absorption), of the hot-pressed samples were measured and related to the microstructure. Higher hot-pressing temperatures increase the in-line transmission. A gray discoloration of the samples (indicative of high absorption) was minimized by heat treating the powder in air prior to hot pressing and reducing the preload pressure. Maximum pressures above/below 10 MPa increased porosity, which decreased inline transmission and increased backward/forward scattering. Lower densities at higher pressures are attributed to a pore-swelling phenomenon. Increasing isothermal hold time decreased porosity, which increased in-line transmission and reduced backward/forward scattering. Best optical properties with an in-line transmission of 65.3% at 645 nm (0.8 mm thick) were achieved by hot-pressing heat-treated platelet alumina powder with a preload pressure of 0 MPa, maximum temperature of 1800°C, maximum pressure of 10 MPa, and an isothermal hold time of 7 hours. This high inline transmission, despite its large grain size (65 µm), is attributed to crystallographic orientation of the platelets during hot pressing.

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“…Alumina's dielectric function is taken from Malitson and Dodge [30], while noble gold is obtained from P. B. Johnson and R. W. Christy [31]. The whole structure is illuminated with plane electromagnetic waves of propagation constant K directed in negative z-axis.…”

Section: Resultsmentioning

confidence: 99%

An Ultrahigh Narrowband Absorber Close to the Information Communication Window

Ali¹,

Iqbal²,

Ullah³

et al. 2021

Preprint

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In this paper, we demonstrate a plasmonic ultrahigh narrowband perfect absorber, which realizes an absorption intensity of up to 99.99% in the near-infrared electromagnetic spectrum regime. Different dimensional effects on absorption properties are studied using computer simulation technology (CST) with finite element method (FEM) solver. For both transverse electric (TE) and magnetic (TM) polarization, the absorber shows high stability over a wide range of incident angles. This ultrahigh absorption is attributed to synergy effect of magnetic resonance and surface plasmon resonance. Furthermore, the sensitivity goes to 300 nm/RIU for various refractive indices of different analytes. Our proposed absorber working wavelength is very close to the communication window of information, therefore, except for remarkable sensing abilities, it can also be well utilized in optoelectronic applications like optical switching, amplifiers, and all-optical plasmonic modulators.

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Refractive index of infrared-transparent polycrystalline alumina

Cited by 6 publications

References 10 publications

Aligning α‐alumina platelets via uniaxial pressing of ceramic‐filled polymer blends for improved sintered transparency

Aligning α‐alumina platelets via uniaxial pressing of ceramic‐filled polymer blends for improved sintered transparency

Hot‐pressing platelet alumina to transparency

An Ultrahigh Narrowband Absorber Close to the Information Communication Window

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