Complex refractive indices in the ultraviolet and visible spectral region for highly absorbing non-spherical biomass burning aerosol

Biomass burning aerosol is a major source of PM2.5, and significantly affects Earth's radiative budget. The magnitude of its radiative effect is poorly quantified due to uncertainty in the optical properties of aerosol formed from biomass burning. Using a broadband cavity-enhanced spectrometer with a recently increased spectral range (360–720 nm) coupled to a size-selecting aerosol inlet, we retrieve complex refractive indices of aerosol throughout the near-ultraviolet and visible spectral region. We demonstrate refractive index retrievals for two standard aerosol samples: polystyrene latex spheres and ammonium sulfate. We then retrieve refractive indices for biomass burning aerosol from 13 controlled fires during the 2016 Missoula Fire Science Laboratory Study. We demonstrate that the technique is highly sensitive to the accuracy of the aerosol size distribution method and find that while we can constrain the optical properties of brown carbon aerosol for many fires, fresh smoke dominated by fractal-like black carbon aerosol presents unique challenges and is not well-represented by Mie theory. For the 13 fires, we show that the accuracy of Mie theory retrievals decreases as the fraction of black carbon mass increases. At 475 nm, the average refractive index is 1.635 (±0.056) +0.06 (±0.12)i, and at 365 nm, the average refractive index is 1.605 (±0.041) +0.038 (±0.074)i.

The Fabrication of a UV Notch Filter by Using Solid State Diffusion

One of the methods used to obtain notch filters involves one or several gradient index layers. In this method, the indices are decreased and then increased step by step to create a sinusoidal-like gradient layer. This paper reports a sinusoidal-like gradient layer fabrication method based on solid state diffusion. Al2O3/MgO/Al2O3 (AMA) was deposited by electron beam evaporation and then post-annealed at 800 °C for 4 h. Through inner diffusion, the MgO layers became a low refractive index material with a porous structure (the average refractive index was 1.55) such that the MgAl2O4 spinel was formed as an inhomogeneous layer with an average refractive index of 1.69. This allowed simply using a structured multilayer, (Al2O3/MgO)8 Al2O3, and post-annealing to form a sinusoidal-like gradient layer for a UV notch filter.

Theory of Dispersion Reduction in Plastic Optical Gratings Fiber

In this paper, we have proposed a way for reducing the dispersion level in plastic optical grating fiber by optimizing the grating-coupling strength (ξ) numerically. The effects of average refractive index (δn) and temperature (T) variation on the dispersion properties are investigated. Results show that, for reducing the dispersion level, the ξ parameter should be optimized and the amplitude of the δn needs to be reduced. Also results show that the dispersion due to the wavelength shift induced by the temperature variation will be eliminated by operating at high ξ value.

Large area light propagation in quasi-zero average refractive index materials

In this paper the experimental results show near-infrared light collimation through large area (2 x 2 mm) nanopatterned material with refractive index quasi-zero on the average. This quasi-zero refractive index is obtained alternating photonic crystals strips with effective refractive index neff = –1 and air strips (n = 1). Layers optically annihilate each other, verifying the optical antimatter concept theoretically proposed by Pendry et al [J. Phys.: Condens. Matter 15, 6345 (2003)].