Optical constants of amorphous carbon in the mid-IR (2.5–25 μm, 4000-400 cm−1)

Laboratory measurements of the Fresnel reflectance are used to derive the real and imaginary indices of refraction of amorphous carbon in the 2.5–25 μm region. Comparisons to previously reported optical constants, derived from extinction measurements at these wavelengths, show both similarities and differences. The differences are likely due to the different samples studied. Wavelength-dependent calculated extinction coefficients Qext/a these values derived here are intermediate in value to previously reported Qext/a of other amorphous carbon samples. The overall spectral shape exhibits a λ−α behhavior with α = 1.05±0.05. However, more spectral structure is seen in the 18–25 μm region than has been reported previously.