Fundamental Principles of Optics.

04-REFRACTIVE INDEX

The refractive index (or refraction index) of an Optical Medium is a dimensionless number that gives the indication of the Light Bending ability of that medium.

The relative refractive index of an optical medium 2 with respect to another reference medium 1 (n21) is given by the ratio of velocity of light in medium 1 to that in medium 2.

This can be expressed as follows:

n21  :  v1/v2

If the reference medium 1 is vacuum, then the refractive index of medium 2 is considered with respect to vacuum. It is simply represented as n2 and is called the absolute refractive index of medium 2.Thomas Young (1807) has first used, and invented, the name "index of refraction". Refractive Index is generally denoted by the symbol µ. The concept of refractive index applies across the full electromagnetic spectrum from X-Rays to Radio Waves. 

For Lenses, a lens made from a high refractive index material will be thinner, and hence lighter, than a conventional lens with a lower refractive index. Such lenses are generally more expensive to manufacture than conventional ones.

05-REFLECTION

Reflection is the change in direction of a bundle of rays or of a wavefront at an interface between two different media so that the bundle of rays / wavefront returns into the medium from which it originated.

Common examples include the reflection of light against a mirror surface, acoustic and water waves. Apart from Visible Light, Reflection is observed with many types of electromagnetic waves.

Optical Reflection could be either specular (a mirror surface based) or diffused (photonic energy reflects, but image may not be seen) as per the nature of the interfacing surface. 

A mirror provides the most common model for specular light reflection, and typically consists of a glass sheet with a metallic coating where the significant reflection occurs.

Reflection also occurs at the surface of transparent media, such as water or glass.

The laws of reflection:

The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane. The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal. The reflected ray and the incident ray are on the opposite sides of the normal.

06-REFRACTION

Refraction is the bending of light as it passes from one transparent medium into another.

This bending is useful for focusing / diverging the light beam by lenses, magnifying glasses, prisms, rainbows and even by our eyes to form images. Refraction is the redirection of a wave / bundle of rays as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium.

The extent of redirection is determined by the change in wave velocity and the initial direction of wave propagation relative to the direction of change in wave velocity. Refraction of light can be seen in many places in our everyday life. It makes objects under a water surface appear closer than they really are.

Rainbows & Mirages appear due to Refraction of Light (when it travels from one media to another).

Refraction can be defined / understood in many ways. Light slows as it travels through a medium other than vacuum (such as air, glass or water). This is not because of scattering or absorption. This slowing is because, the passage of light waves (or photons) cause other electrically charged particles such as electrons, to oscillate. The oscillating electrons emit their own electromagnetic waves which interact with the original light waves. The resulting "combined" wave has wave packets that pass an observer at a slower rate. Thus, the light wave has effectively been slowed. When light returns to a vacuum and there are no electrons nearby, this slowing effect ends and its velocity returns to c.

Another way to explain the Refraction is:

When light enters a slower medium at an angle, one side of the wavefront is slowed before the other. This asymmetrical slowing of the light causes it to change the angle of its travel. Once light is within the new medium with constant properties, it travels in a straight line again.

Conclusion

In this week's blog, we delved into the fascinating world of optics and photonics, exploring the concepts of refractive index, reflection, and refraction. We learned how light behaves as it interacts with different materials, and how these fundamental principles are the building blocks of the incredible field of optics.

But the journey into the enchanting realm of light is far from over! In our upcoming blogs, we will take a deeper dive into the mysteries of Understanding and Manipulating Light. We'll be learning about captivating insights into Snell's Law, where we unravel the secrets of light bending and how it shapes our vision of the world.

And that's not all! We'll then set our sights on the wonders of Lenses and Mirrors, revealing how these optical elements can bend, focus, and shape light, leading to an array of applications that have revolutionized everything from telescopes to microscopes.

Get ready to embark on an optical adventure like never before, as we continue to explore the profound mysteries and cutting-edge technologies that lie at the heart of optics and photonics. Stay tuned for more captivating discoveries and knowledge that will illuminate your understanding of light! See you next week!