How to color only with light ?

Cold bone chilling winds, blinding blizzards and a vast open expanse of ice cover. Antarctica. A researchers paradise. The rising and setting of the sun controls many of our daily rituals, from when we eat breakfast in the morning to when we wind down at night. But what happens to us if the sun never rises? Or if it never sets? It’s an annual occurrence for residents who live in Antarctica, when summer can bring months of almost constant sun and winter can blend into one long period of darkness. Absolute bliss.

Let’s go 8400 Km north from the cold bitterly environment to the sun kissed beach paradise of the Rio de Janeiro, sun bathing and listening to “Copacabana” on the beach with the warm waters washing beneath the feet. A fun paradise.

Think Jungle. Another paradise in South America is the great Amazon rain forest. Residents of which include the tiny insects to the apex predators. But one captured my attention – “The Blue Morpho Butterfly”, nature’s mind blowing spectacle.

Wait, enough about nature and forests and butterflies. Aren’t we supposed to talk about how to color with light?

So, let’s begin this incredible story about light.

Yes, I love to study light.

Take any ordinary piece of clear transparent plastic found in your homes. I know that every home has a plastic bag filled with a lot of plastic bags. So, you took your plastic, let’s continue.

😀

I want to show you how to add color to a transparent piece of plastic without adding anything to it, no dyes, paint, nothing except holes.

Shocked!!! Me too.

But first, Let’s  discuss about light.

Light – It is a form of electromagnetic radiation. It is a combination of electric and magnetic fields perpendicular to each other where the fields are continuously changing. The light, as every wave has a wavelength. The wavelength of visible light varies from 400 to 800 nano-meters.

 

To imagine a nano meter – take a millimeter of a millimeter and divide that in half. That is about 500 nano meters, the wavelength of green light.

It is tiny but it not that tiny. And nature has actually figured out a way to take advantage of the size of light. Remember the butterfly from Amazon forest. It has a blue iridescent shiny wings. Nobody actually knows why it adapted to such a color. That beautiful iridescent blue color isn’t created by a pigment but it is created by the structure of its scales.

What!

If you were to zoom in on this butterfly we would see all these little sort of gratings and holes within these gratings that trap the light and reflect out the blue light.

If you take the butterfly and expose it to the path of direct light then you see only the brown grating structures because the wings are transparent.

The light is not able to reflect of the wings, it is not blue anymore.

Fascinating, right!

:-O

So, what are the implications of coloring transparent plastic using light ?

Scientists are secretly working with the government to create similar hole structures to be used in security devices on bank notes, credit cards, identity cards and tickets. The holes are about 100 nano meters deep and 100 nano meters in diameter.

Each of the image in this contains about 500 million holes. These holes create a 3D grading that allow for light to reflect and refract to create those brilliant colors.

Don’t confuse with holograms. Again, lot to explain in holograms. That’s a story for another day. Let’s not kill the cat.

But, how do they creates such small holes ?

You must be thinking that the nano pin used to punch nano holes must break off. No, it does not, because it has low aspect ratio, i.e. the ratio of height to width is low. And these nano pins have a low aspect ratio of 200 nano meters to 400 nano meters, essentially the ratio of 1:2, which is incredibly strong.

This is the same principle that you have definitely seen. Remember the bubbles formed by soap. Don’t you see a rainbow color on the soap film.

Holes of different thickness creates different colors.

Simple concepts, but the applications are creative. Imagine one day your notes and tickets are embedded with this simple image by the help of a special 3D printer. These applications can stop counterfeiters. So, clean money.

So many applications of light.

Light is the connection between us and the universe. Through light we can look at the stars and the existence of the universe itself. The age and the size of the cosmos are written in light. The story of light has many beginnings and no ending, its heroes come from many times and places.

A simple butterfly, light and some plastic has the power to change the world.

To light,

Vishal

Just a normal guy obsessed with light.