Temperature-dependent Dielectric Function Of Calcium Fluoride: From A Compact Functional Form To Atom-surface Interactions

Abstract

The optical properties of calcium fluoride (fluorspar, CaF2) are mainly determined by a strongly temperature-dependent giant infrared (IR) peak and a series of nearly temperature-independent ultraviolet (UV) peaks. We find that the temperature dependence of the IR peak can be modeled, to good accuracy, by a radiation-reaction improved coupled-oscillator model (RRCO model), with temperature-dependent parameters. For the UV peaks, we find a convenient functional form which covers both the real as well as the imaginary parts of the dielectric function and provides a comparison to first-principles calculations based on time-dependent density-functional theory. The result is a compact functional form for the dielectric function of undoped CaF2 applicable to wide frequency and temperature ranges (0 < h̄ω < 60 eV, 22 ◦C < T < 500 ◦C). With the help of the temperature-dependent dielectric function, we obtain temperature-dependent values of the short-range and long-range asymptotics of atom-surface interactions with CaF2, for hydrogen, as well as ground-state and metastable helium. The giant IR absorption peak of CaF2 is shown to lead to a delayed onset of the fully retarded Casimir-Polder limit in the long-range interaction regime. We present arguments supporting a more general applicability of the RRCO model to materials of general interest.

Department(s)

Physics

Comments

National Science Foundation, Grant PHY–2110294

International Standard Serial Number (ISSN)

2469-9969; 2469-9950

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2026 American Physical Society, All rights reserved.

Publication Date

01 Jan 2026

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