Combining spectroscopic ellipsometry with transmission spectroscopy to derive accurate optical constants for organic materials

Michael O. Yokosuk; Thomas E. Tiwald; Danielle L. Saunders; Thomas A. Blake; Timothy J. Johnson; Tanya L. Myers

doi:10.1117/12.2588323

12 April 2021 Combining spectroscopic ellipsometry with transmission spectroscopy to derive accurate optical constants for organic materials

Michael O. Yokosuk, Thomas E. Tiwald, Danielle L. Saunders, Thomas A. Blake, Timothy J. Johnson, Tanya L. Myers

Author Affiliations +

Proceedings Volume 11749, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XXII; 117490S (2021) https://doi.org/10.1117/12.2588323
Event: SPIE Defense + Commercial Sensing, 2021, Online Only

Abstract

A method for deriving the optical constants of organic powdered materials in the mid-infrared spectral range is introduced using both variable angle spectroscopic ellipsometry and transmission spectroscopy. The approach uses pressed pellets of the powder and is applied to organic solids, which have both strong and weak infrared absorption features. Many powders have significant voids and do not press into smooth, homogenous pellets. To account for pellet non-idealities and to accurately measure both n and k, three different forms of pellets were pressed and measured: A pure analyte pellet, a mixed analyte/KBr pellet with a large analyte percentage, and a KBr transmission pellet with only a small analyte percentage. Using all three pellets in a multi-sample analysis involving both ellipsometric and transmission data, the complex refractive index (n/k) values can be derived for many organic compounds. This method is illustrated to calculate the optical constants for anhydrous lactose from 6000-400 cm^-1. The transmission measurements improve the spectral fitting of weak absorption features, and the multi-sample analysis enables a better determination of the significant void space that is present in the pure pellet, leading to lower values for both n and k if not properly accounted for in the multi-oscillator model used to fit the ellipsometric data.

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Citation Download Citation

Michael O. Yokosuk, Thomas E. Tiwald, Danielle L. Saunders, Thomas A. Blake, Timothy J. Johnson, and Tanya L. Myers "Combining spectroscopic ellipsometry with transmission spectroscopy to derive accurate optical constants for organic materials", Proc. SPIE 11749, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XXII, 117490S (12 April 2021); https://doi.org/10.1117/12.2588323

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