UV-Vis-IR absorption

UV-Vis-IR absorption:

During the scattering of light, signal loss, or attenuation can also occur due to selective absorption of specific wavelengths, in a manner similar to that responsible for the appearance of the color. Primary material consideration both electrons and molecules as follow:

• At the atomic or molecular level, it depends on the frequencies of atomic or molecular vibrations or chemical bonds, how closely packed its atoms or molecules are, and whether the atom or molecules exhibit long-range ordering. These factors will determine a material's ability to transmit longer wavelengths in the infrared (IR), far IR, radio, and microwave ranges.
• At the level of electrons, it totally depends on whether the orbits of electrons are spaced or quantized so that they are allowed to absorb a quantum light (or photon) of a specific frequency or wavelength in the ultraviolet (UV) or visible ranges. This is the reason for the production of colors.

The design of any optically transparent device requires material selection based on knowledge of its properties and limitations. The observed characteristics of lattice absorption in the low-frequency regions (mid-IR to far-infrared wavelength range) define the long-wavelength transparency range of the material. They are the result of the interaction between the motion of thermally induced vibrations of the constituent atoms and molecules of the solid lattice and the incident light wave radiation. That's the reason why all materials are limited in the far-infrared (>10 µm) by limiting the regions of absorption due to atomic and molecular vibrations (bond-stretching).

It’s cause

Therefore the absorption of multi-phonon takes place when there are two or more phonons interacting together to produce an electric dipole moment with which the incident radiation can couple. These dipoles have the ability to absorb energy from the incident radiation, reaching a maximum coupling with the radiation when the frequency is equal to the fundamental vibrational mode of the molecular dipole (such as the Si–O bond) in the far-infrared, or on its harmonics. Precision optical polarizers are used during laser line beam splitter manufacturing by the optical products manufacturer.

Selective absorption of infrared (IR) light by a particular material occurs because the selected frequency of the light wave corresponds to the frequency (or an integer multiple of the frequency) at which the particles of that material vibrate. Since every type of molecule and atoms have different natural frequencies of vibration, they will selectively absorb different frequencies (or portions of the spectrum) of infrared (IR) light. Light waves are reflected and propagated because the frequencies of the light waves do not match the natural resonant frequencies of the vibrations of the objects.

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