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# Preface! ✨

It’s your favorite material science & nanotechnology enthusiast! Time to explain more of the optical interactions between light and the transparency of aerogel!

I highly recommend you read the previous article to understand the fundamentals of optical depth and how it plays a huge role in the transparency of aerogels! 😃

Don’t worry, the article below is only 4 minutes long!

But for now, let’s cover more about what the single scattering albedo is all about!

# Single Scattering Albedo Explained! 💡

## Definitions! 🔑

Single-Scattering Albedo is used to define the scattering and absorption in a medium/material.

The equation for the single scattering albedo is shown below:

## ωλ = σ(s)/ β(e)

This may confuse some of you quickly, but let me explain each letter.

ω = Single-Scattering Albedo symbol.

σ(s) = The Scattering Coefficient.

β = The Extinction Coefficient.

The extinction coefficient (β(e)) is the sum of the absorption coefficient (β(a)) and the scattering coefficient (β(s)). This will lead to the extinction coefficient to look something like this:

## (β(a) + β(s) = β(e))

So if it helps, we can rearrange the single scattering albedo equation like this:

However, the output of “ω” can only be between 0 and 1.

• If “ω” is 0, the medium/material will absorb everything (particles, photons, etc.).
• If “ω” is 1, the medium/material will scatter everything (particles, photons, etc.).

The final main piece of information that I want to give you is that “ω” is being used for the scattering of light in transparent aerogels. In this case, we want to use the subscript “λ”. So when discussing aerogels, we will commonly use this to describe the single scattering albedo:

## ω(λ)

“λ” is the symbol for wavelengths of light. The unit to measure wavelengths of light is meter (m). But sometimes, we will often use nanometers to measure wavelengths of light (nm, m^-9).

# Closing Thoughts! 💭

We are 2/3 of the way complete with explaining the fundamental concepts of the theoretical equation proposed by MIT!

The last steps are Isotropicity, Rayleigh Scattering Equation, and the Beer-Lambert Law! ✌🏽

# Vocabulary! 📓

Optical Depth → The quantity of light that has been removed due to absorption, scattering, and reflection; τ.

TransparencyAll the light will pass through a material, and it won’t be reflected, absorbed, or scatter in a material.

Absorption The light is absorbed by the aerogel particles.

IsotropicA specific property of a medium/material is the same (or uniform) in all directions.

The Extinction Coefficient → A sum of the absorption coefficient and the scattering coefficient; β(e).

Single-Scattering Albedo Defines the scattering and absorption in a medium/material.

Absorption Coefficient(β(a))

Scattering Coefficient(β(s))

Wavelength Symbol → λ