Angle-of-incidence dependence of calcium fluoride reflectivity

Alfred Kahan, Donald E. Mccarthy

Room-temperature reflectivity measurements of CaF2 in the fundamental-lattice-vibration region were obtained between frequencies 200 to 650 cm-1 and angles of incidence ranging from near normal to 78°. Based on the method of classical oscillator analysis, the near-normal reflectivity is fitted by a two-resonance-frequency model and the corresponding dispersion parameters and optical constants are calculated. From these and the Fresnel equations, the reflectivity curves for non-normal angle of incidence are computed and compared with experimental results. It is concluded that the optical constants calculated from the reflectivity at normal angle of incidence can be applied to predict the behavior at non-normal angle of incidence. The angular dependence of the reflectivity is not significant until about 40°. The over-all effect is an increase in reflectivity and, as a consequence, a widening of the sideband on the high-frequency side of the transverse optical mode of vibration. In addition, some of the advantages and disadvantages of classical oscillator theory are commented on. © 1966 The American Physical Society.

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Materials
Curve 1
Temperature Range, K: ~298 Wavelength Range, µm: 17.9-50.0 Geometry θ θ' ω': 15° 15° Composition (weight percent), Specifications, and Remarks: Crystal polished to a plate-glass finish and flat to five fringes; aluminum mirror reference standard.
Curve 2
Temperature Range, K: ~298 Wavelength Range, µm: 15.4-28.6 Geometry θ θ' ω': 15° 15° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 3
Temperature Range, K: ~298 Wavelength Range, µm: 15.4-28.6 Geometry θ θ' ω': 60° 60° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 4
Temperature Range, K: ~298 Wavelength Range, µm: 15.4-28.6 Geometry θ θ' ω': 45° 45° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 5
Temperature Range, K: ~298 Wavelength Range, µm: 15.4-28.6 Geometry θ θ' ω': 75° 75° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.
Curve 6
Temperature Range, K: ~298 Wavelength Range, µm: 15.4-28.6 Geometry θ θ' ω': 70° 70° Composition (weight percent), Specifications, and Remarks: Above specimen and conditions.