Scattering, absorption and radiative transfer (optics)

Scattering, absorption, and radiative transfer are fundamental concepts in optics that describe how light interacts with matter. Here's a brief overview of each concept: ### Scattering Scattering refers to the deflection of light rays from a straight path due to interaction with particles or irregularities in a medium. When light encounters small particles (like dust, air molecules, or water droplets), it can be redirected in various directions.

Scattering, absorption, and radiative transfer are key concepts in various fields including atmospheric science, astrophysics, climatology, and optics. Here’s a brief overview of each concept and the role of codes used to model these phenomena: ### 1. Scattering **Definition**: Scattering refers to the process by which particles deviate from a straight trajectory due to non-uniformities in the medium through which they are traveling.

The absorption cross section is a measure of the likelihood of a particle (such as a photon) being absorbed by a target, which can be an atom, molecule, or any medium. It quantifies the effective area that a particular absorber presents to incoming radiation, correlating the physical properties of the absorber with its ability to absorb electromagnetic radiation.

Analytical light scattering is a technique used to study the size, shape, and distribution of particles, macromolecules, or colloids in a solution by measuring the scattering of light as it interacts with these particles. This method is based on the principle that when a beam of monochromatic light (usually from a laser) passes through a sample, the light is scattered in different directions by the particles present in the solution.

Anomalous diffraction theory is a concept in the field of wave optics and scattering theory, primarily applicable to the interaction of electromagnetic waves, such as light, with small particles. The term "anomalous" refers to the deviations from the standard diffraction patterns predicted by classical diffraction theory (e.g., Rayleigh diffraction) when the size of the scattering objects is comparable to the wavelength of the incident light.

Backscatter refers to the phenomenon where radiation, particles, or waves that are emitted or transmitted from a source are reflected or scattered back toward the source or in other directions. It can occur in various contexts, including physics, telecommunications, and imaging systems. Here are a few specific contexts in which backscatter is commonly discussed: 1. **Physics and Particle Physics**: In particle physics, backscatter refers to the deflection of particles, such as electrons or photons, when they collide with matter.

Coherent Anti-Stokes Raman Spectroscopy (CARS) is a nonlinear optical technique used to obtain information about the vibrational modes of molecules. It is primarily employed in fields such as chemistry, biology, and materials science to probe molecular structures and dynamics.

The Ewald–Oseen extinction theorem is a fundamental result in the field of electromagnetism, particularly in the study of light scattering and the interaction of light with small particles. The theorem addresses how the incident light field is affected when it encounters a particle, specifically regarding the scattering of light by the particle.

Forced Rayleigh scattering (FRS) is a technique used to analyze the properties of materials by probing them with light. It is an extension of the classical Rayleigh scattering phenomenon, which refers to the scattering of light by small particles. In classical Rayleigh scattering, the incident light interacts with particles in a medium, leading to scattered light whose characteristics depend on the size, shape, and composition of those particles.

Forward scatter refers to the phenomenon where light, or other forms of electromagnetic radiation or particles, are scattered in a direction that is close to the direction of the incoming beam. This is often studied in various scientific fields, including optics, astrophysics, and particle physics. In the context of light scattering, forward scatter typically occurs when light interacts with small particles or molecules. The degree of forward scatter can provide information about the size, shape, and composition of the particles.

Frequency Selective Surfaces (FSS) are structures designed to selectively reflect, transmit, or absorb electromagnetic waves at specific frequencies while allowing other frequencies to pass through. They are often composed of periodic arrays of conductive elements, such as patches or slots, arranged on a dielectric substrate. FSS is commonly used in various applications, including: 1. **Radar Systems**: To control electromagnetic wave propagation and enhance signal quality.

The Gaunt factor is a dimensionless quantity that arises in the field of astrophysics and plasma physics, particularly in the context of radiative transfer and the calculation of opacity in stellar atmospheres and hot plasmas. It quantifies the effect of electron scattering on the intensity of radiation in a medium.

Geometric albedo is a measure of the reflectivity of a celestial body, such as a planet, moon, or asteroid, as observed from a specific geometrical configuration. Specifically, it defines the ratio of the brightness of the object when illuminated by a light source (usually the Sun) to the brightness of a flat, fully reflective surface (like a perfect diffuser) under the same illumination conditions.

Goniophotometry is a measurement technique used to assess the luminous and color distribution of light emitted from a source or reflected from a surface. The term is derived from "gonia," meaning angle, and "photometry," which refers to the measurement of light intensity. In goniophotometry, light measurements are taken at various angles, typically using a goniophotometer, which is an instrument that allows for precise positioning of the light source and the measurement device.

A hail spike is a weather phenomenon associated with severe thunderstorms. It occurs when large hailstones are expelled from a thunderstorm, often resulting in a radar signature that appears as a spike on Doppler radar images. This spike typically indicates the presence of significant hail, often larger than one inch in diameter, within the storm. Hail spikes are formed when strong updrafts within a thunderstorm carry moisture and ice particles upwards to higher altitudes, where temperatures are below freezing.

Hapke parameters refer to a set of values used in the Hapke bidirectional reflection distribution function (BRDF), which is a mathematical model that describes how light is reflected off a rough surface (like that of a planetary body or a terrestrial material). The model is named after Bruce Hapke, who developed it to better understand and analyze the reflectance properties of planetary surfaces.

Hiding power, often referred to in the context of pigments and coatings, is a measure of a material's ability to obscure or conceal an underlying surface or color. It is particularly important in applications such as paint, where the effectiveness of the paint in covering a surface without requiring multiple coats is crucial for both aesthetic and economic reasons.

Hyper-Rayleigh scattering (HRS) is a nonlinear optical phenomenon that involves the scattering of light by molecules. Specifically, it refers to the scattering of light from a medium that exhibits a second-order nonlinear optical response. When a light wave interacts with a material, it can generate new frequencies through the nonlinear interaction of the electromagnetic field with the electronic structure of the molecules in that material.

Incoherent scatter refers to a type of scattering of electromagnetic waves, particularly radio waves, when they encounter particles in a medium, such as electrons in the ionosphere. This process is characterized by the lack of a clear correlation between the incident wave and the scattered wave, meaning that the scattering does not preserve the original phase of the incoming wave. Incoherent scatter is particularly significant in the study of the upper atmosphere and space weather.

Inelastic scattering is a process in which particles (such as photons, electrons, or neutrons) collide with a target and transfer some of their energy to the target during the interaction. This results in a change in the energy, momentum, or state of the incoming particles, as well as a change in the target particles.

The Kramers–Heisenberg formula is a fundamental result in the field of quantum mechanics and quantum electrodynamics (QED). It describes the scattering of photons by charged particles, particularly in the context of photon emission and absorption processes.

Kubelka–Munk theory is a mathematical model used to describe the light scattering and absorption properties of diffuse systems, particularly in relation to paints, pigments, and other similar materials. The theory, formulated by Paul Kubelka and Franz Munk in the 1930s, provides a way to understand how light interacts with multi-layered and heterogeneous materials.

Lambertian reflectance is a model used to describe the way a surface reflects light. It is based on the Lambertian surface concept, which assumes that the surface reflects light equally in all directions, regardless of the angle of incidence. This type of reflectance is characterized by its matte or diffuse appearance, meaning that the surface does not produce specular (mirror-like) highlights.

Light scattering by particles refers to the process where light waves encounter particles and are redirected in various directions. This phenomenon is critical in numerous fields, including physics, atmospheric science, and biology. The basic principles of light scattering involve the interaction of electromagnetic waves (light) with matter (particles).

Localized surface plasmons (LSPs) are collective oscillations of free electrons at the surface of metal nanoparticles, which occur in response to incident light or electromagnetic radiation. These oscillations are confined to the nanoparticle's surface and are characterized by their ability to create strong electromagnetic fields in the vicinity of the particle.

Near field and far field are terms commonly used in various fields, including physics, engineering, and telecommunications, to describe regions in relation to a source of waves, such as electromagnetic waves, sound waves, or other types of waves. ### Near Field The near field refers to the region close to the source of the wave where the behavior of the field is not specified by simple wave equations. In this zone, the wave typically does not propagate in the same way as it does in the far field.

Ocean color refers to the color of the ocean as perceived by the human eye, which results from the absorption and scattering of sunlight by water and various substances in the water. The color can vary widely depending on several factors, including: 1. **Water Depth**: In deep water, colors tend to appear darker and bluer, while shallow water may appear greener or brownish due to the presence of sediments and algae.

Ocean optics is a field of study that focuses on the interaction of light with water and its constituents, including phytoplankton, dissolved organic matter, sediments, and other materials present in the ocean. It encompasses various scientific disciplines, including physics, chemistry, and biology, to understand how light behaves in marine environments. Key aspects of ocean optics include: 1. **Light Propagation**: This involves understanding how light penetrates the ocean's surface, scattering and absorbing as it travels through water.

Optical conductivity is a fundamental property of materials that describes their ability to conduct electricity in response to an electric field oscillating at optical frequencies (typically in the range of terahertz to visible light). It reflects how well a material can transport electric charge when stimulated by electromagnetic radiation. Optical conductivity provides insight into a material's electronic structure and behavior, and it can be influenced by factors such as temperature, frequency of the light, and the presence of free carriers (like electrons) or bound charges.

Optical depth is a concept used in astrophysics and other fields to quantify how opaque a medium is to radiation, such as light. It provides a measure of how much a beam of light is attenuated as it passes through a medium, such as gas or dust.

The optical properties of water and ice are crucial in understanding their behavior in various environments, ranging from climate science to biology and engineering. Here are some key aspects: ### Optical Properties of Water 1. **Absorption**: - Water absorbs light in the ultraviolet (UV) and infrared (IR) regions. The absorption spectrum shows that water is relatively transparent in the visible range (400-700 nm), but it absorbs strongly in the UV and near-IR regions.

The optical theorem is a fundamental concept in quantum mechanics and particularly in the field of scattering theory. It establishes a relationship between the total cross section of a scattering process and the forward scattering amplitude. In more detail, the optical theorem states that the imaginary part of the forward scattering amplitude (the amplitude for scattering at an angle of zero) is proportional to the total cross section for that scattering process.

The Oren–Nayar reflectance model is a widely used model in computer graphics that describes how light reflects off rough surfaces. It was introduced by Oren and Nayar in 1994 as an improvement over the traditional Lambertian reflectance model, which assumes perfectly diffuse reflection. The Lambertian model is straightforward and works well for smooth surfaces, but it fails to accurately represent the complex interaction of light with rough surfaces that have microfacets.

A phase curve in astronomy refers to a graphical representation that illustrates how the brightness (or flux) of a celestial body changes with its phase angle or with time. The phase angle is the angle between the observer, the celestial body, and the light source (usually the Sun). Phase curves are particularly useful for understanding the reflective properties, surface conditions, or atmospheric properties of planets, moons, asteroids, and comets.

The **radiative transfer equation (RTE)** is a fundamental equation that describes the propagation of radiation (such as light) through a medium. It considers the interactions of photons with matter, accounting for scattering and absorption processes, and is critical in understanding how light interacts with biological tissues.

Raman amplification is a process that utilizes the Raman effect to amplify light signals, primarily in optical fibers and other photonic devices. The Raman effect is a phenomenon where incident light interacts with the vibrational modes of molecular structures, causing a shift in the light's wavelength due to energy transfer between the photons and the molecules.

Raman scattering is an inelastic scattering process that occurs when light interacts with molecular vibrations, phonons, or other low-frequency excitations in a material. This phenomenon is named after the Indian physicist C.V. Raman, who, along with his colleague, discovered it in 1928. In simple terms, when a monochromatic light source, typically a laser, shines on a sample, most of the light is elastically scattered, meaning it retains its original energy (or wavelength).

The Rayleigh–Gans approximation is a theoretical framework used in scattering theory, particularly to analyze how electromagnetic waves scatter off small particles. It is an extension of the Rayleigh scattering theory, which applies primarily to particles whose size is much smaller than the wavelength of the incident light.

Rotating-polarization coherent anti-Stokes Raman spectroscopy (RP-CARS) is an advanced spectroscopic technique used to investigate molecular vibrations and dynamic processes at the nanoscale. It combines aspects of coherent anti-Stokes Raman scattering (CARS) and polarization techniques to provide enhanced contrast and sensitivity in the analysis of materials.

The scattering matrix method, often abbreviated as S-matrix method, is a powerful mathematical framework used in various fields of physics and engineering, particularly in quantum mechanics, optics, and wave propagation. This method is essential in analyzing how waves (or particles) scatter from obstacles or potential fields.

Scintillation in physics refers to the process by which certain materials emit flashes of light (or scintillation light) when they absorb ionizing radiation. This phenomenon is commonly observed in materials known as scintillators, which can be organic compounds, inorganic crystals, or even liquids. When a scintillator material is exposed to ionizing radiation (such as alpha particles, beta particles, or gamma rays), the incoming radiation interacts with the atoms of the scintillator, causing excitation and ionization.

Single-scattering albedo (SSA) is a parameter used in atmospheric science, particularly in the study of aerosols and clouds. It quantifies the fraction of incident light that is scattered by a particle (such as an aerosol droplet or cloud droplet) rather than absorbed. The concept is crucial for understanding how particles interact with sunlight and affect the Earth's energy balance and climate.

Subsurface scattering (SSS) is a phenomenon in optics that occurs when light penetrates the surface of a translucent material, interacts with its internal structures, and then exits the material at a different location. This effect is particularly significant in materials that are not completely opaque and allow light to scatter within their volume, such as skin, wax, marble, and plants.

Transport length typically refers to the effective length of a medium or system that affects the movement or transport of a particular quantity, such as mass, energy, or charge. The specific meaning can vary depending on the context in which it is used. Here are a few examples of how "transport length" might be applied in different fields: 1. **Physics**: In the context of particle transport, transport length may refer to the average distance that particles can travel before undergoing a scattering event or interaction.

An ultramicroscope is a specialized optical microscope that is used to observe objects that are smaller than the wavelength of visible light. This allows for the visualization of colloidal particles, bacteria, and other minute structures that cannot be effectively resolved with conventional light microscopy. The ultramicroscope operates on the principle of dark-field microscopy, where light is directed at an angle to the specimen, and only scattered light is observed.

The Umkehr effect, also known as the "Umkehr phenomenon," refers to a specific spectral phenomenon in atmospheric science relating to the absorption of solar radiation by atmospheric gases, particularly ozone. The term "Umkehr" is derived from the German word meaning "reversal." This effect occurs during the scattering and absorption processes of sunlight in the atmosphere, where the distribution of ozone alters the vertical profile of solar radiation.