Absorption Definition in Physics

Absorption Definition in Physics

In the realm of physics, absorption refers to the process by which a material or medium takes in and assimilates the energy carried by electromagnetic radiation. When a photon interacts with matter, its energy is transferred to the absorber, resulting in the conversion of electromagnetic energy into internal energy within the absorbing material. Thermal energy is a common form of absorber in this context. Importantly, the absorption of waves is not dependent on the intensity of the matter involved. In wave motion, absorption occurs when the energy of a wave is transferred to a medium as the wave passes through it.

Absorption in Physics

In physics, the term "absorb" describes a phenomenon that takes place when a wave encounters a medium and causes the molecules of the medium to vibrate, move, and change their positions. During this process, some of the energy carried by the wave is reduced as a result of the molecular vibrations, which effectively extract energy from the wave. As a consequence, less energy is reflected since the wave possesses minimal energy.

Let's consider an example of absorption. Black pavement serves as a suitable example as it absorbs energy from light. When light waves interact with black pavement, they are mostly absorbed, resulting in the pavement becoming hot. Only a small portion of the light waves are reflected back, which gives the pavement its black appearance. Conversely, if a white line is drawn on the black pavement, it will reflect more light since white does not absorb light waves to the same extent. Consequently, the white strip will be less hot compared to the other surfaces painted black.

Absorption in Laser Physics

In laser physics, absorption can occur within an optical substrate through various distinct methods. These methods involve electrons in discrete energy levels elevating the atoms within the optical medium to absorb radiative photons and transitioning to higher energy levels.

Following this process, the atoms begin to fluoresce, emitting radiation in the form of photons through spontaneous emission as the electrons return to lower energy levels.

Unintentional fluorescence contributes to energy loss and acts as a hindrance in signal detection, which can be detrimental in laser optics applications. Fluorescence is often isotropic, radiating in all directions, exacerbating the issue. The presence of impurities, such as rare-earth ions, is a significant cause of fluorescence.

For instance, UV grade fused silica demonstrates high transmittance in the UV and visible spectra but experiences dips in transmittance at 1.4 μm, 2.2 μm, and 2.7 μm due to absorption by hydroxide ion impurities. On the other hand, IR grade fused silica contains fewer hydroxide ions, resulting in higher transmission throughout the NIR spectrum.

The aforementioned explanation and example help to elucidate the concept of absorption and its operation in the context of lasers.

Absorption Spectrum Definition in Physics

An absorption spectrum refers to the electromagnetic spectrum in which a decrease in the intensity of radiation occurs at specific wavelengths or characteristic wavelength ranges associated with a particular absorbing substance. This decrease is manifested as dark lines or bands within the spectrum.

An absorption spectrum is generated when light passes through a cold, dilute gas. Atoms within the gas begin to absorb radiation at different frequencies. Since the re-emitted light is unlikely to be emitted in the same direction as the absorbed photons, dark lines or bands are created in the spectrum.

The absorption spectrum arises from the frequencies of light that are transmitted through the dark bands resulting from energy absorption by electrons transitioning from the ground state to higher energy states.

The study of absorption spectra can be challenging, but with regular practice, a comprehensive understanding of this topic can be achieved.

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