Reststrahlen effect

The reststrahlen effect (German: “residual rays”) is a reflectance phenomenon in which electromagnetic radiation within a narrow energy band cannot propagate within a given medium due to a change in refractive index concurrent with the specific absorbance band of the medium in question; this narrow energy band is termed the reststrahlen band.

As a result of this inability to propagate, normally incident reststrahlen band radiation experiences strong-reflection or total-reflection from that medium.

The energies at which reststrahlen bands occur vary and are particular to the individual compound.

Numerous physical attributes of a compound will have an effect on the appearance of the reststrahlen band these include phonon band-gap, particle/grain size, strongly absorbing compounds, compounds with optically opaque bands in the infrared.

Appearance

Reststrahlen bands manifest in diffuse reflectance infrared absorption spectra as complete band reversal, or in infrared emission spectra as a minimum in emissivity.

Application

The reststrahlen effect is used to investigate the properties of semiconductors, it is also used in geophysics and meteorology.

See also

• Absorbance
• Emissivity
• Transmittance
• Reflectivity

References

• Elachi, C. et al. (2006) Introduction to the physics and techniques of remote sensing. John Wiley and Sons.
• Griffiths, P.R. (1983) Fourier transform infrared spectrometry. Science, 222, 297–302.
• Goldberg, A. et al. (2003) Detection of buried land mines using a dual-band LWIR/LWIR QWIP focal plane array. Infrared Physics & Technology, 44 (5–6), 427–437.
• Anderson, M. S. et al. (2005) Fourier transform infrared spectroscopy for Mars science. Rev. Sci. Instrum., 76 (3).