Optical and thermal properties of spinel with revised (increased) absorption at 4 to 5 μm wavelengths and comparison with sapphire

Abstract

Infrared absorption of high-quality, commercial, polycrystalline MgAl 2 O 4 spinel is ∼40% greater in the range of 3.8 to 5.0 μm than the value predicted by the computer code OPTIMATR®, which has been used for window and dome design for more than 20 years. As a result, spinel and a-plane sapphire windows designed to support the same external pressure with the same probability of survival have approximately the same infrared absorptance in the range 3.8 to 5.0 μm. c-Plane sapphire has greater absorptance than spinel in the range 3.8 to 5.0 μm. Spinel has two weak absorption bands near 1.8 and 3.0 μm. At 1.064 μm, the laser calorimetric absorption coefficient of spinel is 10 to 50 times greater than that of sapphire. New measurements of specific heat capacity, thermal expansion, thermal conductivity, elastic constants, and refractive index (including dn∕dT ) of spinel are reported. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 05/26/2015 Terms of Use: http://spiedl.org/terms Optical Engineering 087113-2 August 2013/Vol. 52(8) Harris et al.: Optical and thermal properties of spinel with revised (increased) absorption. . . Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 05/26/2015 Terms of Use: http://spiedl.org/terms

Properties of an Infrared‐Transparent MgO:Y2O3 Nanocomposite

“…Transmission of 50:50 vol% MgO:Y 2 O 3 nanocomposite (M:Y) is similar to that of its constituents above 4 μm, but diverges at short wavelength. The absorption coefficient (α, cm −1 ) of M:Y in Table , measured by laser calorimetry at 4.85 μm, is five times less than that of spinel and ten times less than that of c ‐plane sapphire . The short wavelength cutoff of M:Y near 2 μm arises from optical scattering, not from absorption.…”

“…The light source was an Optical Parametric Oscillator laser from JP Innovations (Monroe, WA) tunable from 3.46 to 4.41 μm. Refractive index (±0.0001) of a polished 45° prism was measured at 22.5°C ± 0.3°C by the method of minimum deviation . Five measurements were made on a Moller–Wedel divided circle spectrometer at each wavelength.…”

“…For laser calorimetry, polished 10‐mm‐diameter disks were irradiated with known laser power and the temperature rise was measured . Specific heat capacities used to compute absorptance (fraction of radiant power absorbed) were MgO, 0.906; Y 2 O 3 , 0.452, and M:Y, 0.647 J (g·K) −1 at 295 ± 1 K. The slope of absorptance versus sample thickness (1, 2, and 3 mm) is the absorption coefficient.…”

Highly transparent Mg0.27Al2.58O3.73N0.27 ceramic fabricated by aqueous gelcasting, pressureless sintering, and post‐HIP

“…The densities of the HIP-DP and HIP-GC ceramics were 99.84% and 99.93%, respectively. The absorption coefficient is given by: 52 where T i is the transmittance of each sample and b i is their thickness. The average grain sizes of the HIP-DP and HIP-GC ceramics were about 59.9 ± 1.2 μm and 42.6 ± 0.8 μm, respectively, which were obtained by the linear intercept method.…”

“…4 In addition, we obtained the absorption coefficient by measuring the transmittance of MgAlON with thicknesses of 1.95 and 4.86 mm. The absorption coefficient is given by: 52 where T i is the transmittance of each sample and b i is their thickness.…”