Abstract

We performed high-resolution Fourier-transform infrared (FTIR) spectroscopy of a polymethyl methacrylate (PMMA) sphere of unknown size in the Mie scattering region. Apart from a slow, oscillatory structure (wiggles), which is due to an interference effect, the measured FTIR extinction spectrum exhibits a ripple structure, which is due to electromagnetic resonances. We fully characterize the underlying electromagnetic mode structure of the spectrum by assigning mode numbers to each of the ripples in the measured spectrum. We show that analyzing the ripple structure in the spectrum in the wavenumber region from about $3000{\mathrm{cm}}^{-1}$ to $8000{\mathrm{cm}}^{-1}$ allows us to determine both the unknown radius of the sphere and the PMMA index of refraction, which shows a strong frequency dependence in this infrared spectral region. While in this paper we focus on examining a PMMA sphere as an example, our method of determining the refractive index and its dispersion from infrared extinction spectra is generally applicable for the determination of the index of refraction of any transparent substance that can be shaped into micron-sized spheres.

© 2016 Optical Society of America

Observation of Mie ripples in the synchrotron Fourier transform infrared spectra of spheroidal pollen grains

R. Blümel, R. Lukacs, B. Zimmermann, M. Bağcıoğlu, and A. Kohler
J. Opt. Soc. Am. A 35(10) 1769-1779 (2018)

Determining the size and refractive index of microspheres using the mode assignments from Mie resonances

Thomas C. Preston and Jonathan P. Reid
J. Opt. Soc. Am. A 32(11) 2210-2217 (2015)

Mechanism of the Photoinduced Refractive Index Increase in Polymethyl Methacrylate

M. J. Bowden, E. A. Chandross, and I. P. Kaminow
Appl. Opt. 13(1) 112-117 (1974)

Interference structure of the Mie extinction cross section

Petr Chýlek and Jiyu Zhan
J. Opt. Soc. Am. A 6(12) 1846-1851 (1989)

Determination of refractive indices of Mie scatterers from Kramers–Kronig analysis of spectral extinction data

Jerry C. Ku and James D. Felske
J. Opt. Soc. Am. A 3(5) 617-623 (1986)