Scattering of light

Light is a sort of energy that creates a vision in our eyes and helps us view different objects in our surroundings. Luminous objects are those that generate light on their own. The Sun, a light bulb, a tube light, glowworms, and so forth. Non-luminous items are those that reflect light from other sources. They don’t have their light source. For instance, consider the Moon, a tree, a table, and a painting. Light can take the form of a beam (reflection), a wave (interference), or a diffraction particle (diffraction) (photoelectric effect). We’ll start with a related notion before moving on to light Scattering or Scattering of light. 

Refraction

Refraction is the shift in the direction of a wave travelling through one medium to another. Light refraction is a well-known phenomenon, but other waves can also refract, such as sound and water waves. Because of refraction, we can even use optical equipment like magnifying glasses, lenses, and prisms. In addition, we can focus light on our retina due to light refraction.

Atmospheric Refraction: The refraction of light by different layers of the atmosphere is known as atmospheric refraction. The bending of light rays as they travel through layers of the earth’s atmosphere with various optical densities is known as atmospheric refraction. The optical densities of multiple gases and dust particles differ. Because of the varied optical densities of air, light from a star is refracted by the atmosphere at different altitudes. When an object fires light rays into the atmosphere, they pass through several layers of air with different densities and are refracted by them.

Scattering of light

Scattering of light is defined as when light travels from one medium to another, such as air or a glass of water, a portion of it is absorbed by the medium’s particles, followed by subsequent radiation in a specific direction. Light Scattering is the term for this phenomenon.

The particle size and wavelength of light impact the intensity of scattered light. Because of the waviness of the line and its interaction with a particle, smaller wavelengths and higher frequencies scatter more. If a line is wavy, it is more likely to collide with a particle. On the other hand, longer wavelengths have a lower frequency and are more straight, reducing the chances of colliding with a particle. Due to refraction and the entire internal reflection of light, the bending of multicoloured light can be seen in the afternoon. The wavelength of sunlight produces distinct colours in different directions. The scattering theory of Rayleigh explains the phenomenon.

State different types of Scattering of light

1. Elastic Scattering occurs when the incident and dispersed light beams have the same energy.

2. Inelastic Scattering: When the energy of the incident and dispersed beams of light vary, this is called Inelastic Scattering. There are four different types of Inelastic Scattering:

Scattering by Rayleigh’s phenomenon: Rayleigh scattering occurs when light reacts with particles in the environment that have a smaller diameter than the wavelength of the incoming radiation. When compared to shorter wavelengths, longer wavelengths scatter more readily. Small particles scatter light with shorter wavelengths, such as NO2 and O2 (blue and violet visible light). Red light scatters more in the atmosphere than blue light due to its longer wavelength. At sunrise and sunset, incoming sunlight travels a greater distance through the atmosphere. We only see the longer (red and orange) wavelengths due to the longer route scattering the short (blue) wavelengths.

Mie Scattering happens when the wavelength of electromagnetic radiation is the same as the size of air particles. Photons in the near-ultraviolet to mid-infrared areas of the spectrum are affected by Mie scattering. Mie scattering occurs mostly in the lower atmosphere when the sky is overcast, where larger particles are more common. Pollen, dust, and pollution are the main causes of Mie scattering. Mie Scattering, for example, makes the clouds appear white.

The Tyndall Effect describes how the earth’s atmosphere comprises various microscopic particles. These particles include smoke, minuscule water droplets, suspended dust particles, and air molecules. When a light beam collides with such little particles, its path becomes visible. For example, this phenomenon happens when a beam of sunlight enters a room filled with smoke and dust through a small hole. Light Scattering causes the particles to become visible. The Tyndall Effect is visual when sunlight passes through a dense forest canopy. In the mist, little water droplets scatter light. The size of scattering particles determines the hue of diffused light. Smaller particles can scatter light of shorter wavelengths, while larger particles can scatter light of longer wavelengths. If the scattering particles are white, the scattered light may appear white.

Raman Scattering: The Scattering of photons at higher energy levels by stimulating molecules is known as the Raman Effect. Since the photons are inelastically scattered, the incident particle’s kinetic energy is either lost or acquired, with Stokes and anti-Stokes components.

Rayleigh’s Scattering

Rayleigh scattering refers to the phenomenon of scattering of electromagnetic radiation by particles with a radius of less than a tenth of the wavelength of the light. The process was named after Lord Rayleigh, who described the phenomena in a paper published in 1871.

The angle through which the beam of Sun’s rays gets scattered by molecules of the constituent gases in the atmosphere varies inversely as the fourth power of the wavelength; thus, blue light, which is present at the short-wavelength end of the visible spectrum, will be scattered much more strongly than long-wavelength red light. Since the viewer sees only dispersed light in directions other than the Sun, the sunlit sky is blue. The Rayleigh rules also predict the variation of scattered light intensity with direction, with one of the results being that forward and backward scattering patterns are entirely symmetrical.

Some examples on Scattering of light

Let us now discuss some scattering of light examples :

The Rayleigh scattering of sunlight is responsible for the sky’s blue colour. The visible light from the Sun has a wavelength that ranges from 400 nanometers for blue to 800 nanometers for red. The molecules scatter the light from the Sun in the atmosphere as it travels through the atmosphere. Because the size of the molecules scattering light from the Sun is on the order of 10-10 m, which is much smaller than the wavelength of the incident light, Rayleigh Scattering of light holds true, and the intensity of the scattered light varies inversely as the fourth power of the wavelength of light. For example, because the wavelength of blue light is almost half that of red light, the intensity of scattered blue light is approximately 24 times that of red light. As a result, the sky seems blue, and the blue colour prevails.

Clouds are white because they are located in the lower section of the earth’s atmosphere. Dust, water droplets, ice particles, and other particles make up the clouds. Rayleigh scattering is not valid because the size of these particles is far bigger than the wavelength of the incident light. Instead, all of the incident sunlight’s wavelengths are spread nearly evenly. As a result, the scattering of light from the clouds contains all visible light wavelengths. When this light, which includes all visible light wavelengths, enters the observer’s eye, the viewer views clouds as white.

Conclusion

One of the most visible phenomena to the human eye, the sky is frequently photographed at sunrise and sunset for its beautiful clouds. Scattering of light has real-world uses in addition to theoretical principles and atmospheric studies. Before satellite imaging was used to forecast weather, people looked at the colours in the night sky to see if the next day would be pleasant. Light scattering knowledge is increasingly useful in determining which wavelengths of light should be used when carrying signals across optical fibres.

Furthermore, knowing Rayleigh and Mie scattering allows us to reduce the impact of bright skies on our natural body clocks.

As a result, studying light scattering allows us to understand our environment better and apply these concepts in real-life situations.