Welcome to my kitchen. Today I’m going to attempt to make something
that is really vital for the Webb Telescope’s ability to see.
So, let’s give it a go! But first I have to make some distilled
water.
music
It’s a salt crystal!
Why Does
Webb Use Salt Lenses?
Who doesn’t love salt? It has a long and important
history. Since it was once the only way to preserve food,
it also dictated trade routes. It was one of the most coveted and expensive minerals.
Today, we rely heavily on salt to keep
our roads safe, and salty snacks at the best!
Webb needs salt.
Not this tasty kind, but as a lens.
So there are different types of lenses. Mirrors are a reflective lens
that bend the light. And then there are transmissive lenses that allow light to pass
through them. Here’s the kicker, visible light, it behaves
differently than infrared light.
So glass absorbs infrared light.
But salt doesn’t.
The type of salt in here is sodium chloride, or NaCl. And even though
it’s the most common type of salt on Earth, it is not the only kind.
Salts are more than something you sprinkle on your food.
A salt is a combination of two things. A positively charged element,
usually a metal from groups 1 or 2; and a negatively charged halide
usually from groups 16 or 17. They get their charge
by either gaining or losing a negatively charged electron.
Webb uses three kinds of salt lenses
lithium fluoride, barium fluoride
and zinc selenide.
Making these lenses happens to be pretty tricky.
I’ve been growing this one, now for about three weeks
and it’s only this size, right here.
The lithium fluoride lenses that Webb uses
have to be absolutely perfectly grown.
be optically useful, it needs to be completely clear
unlike my homegrown crystal over here, and be molecularly
consistent. That means the structure of the molecules
are absolutely the same everywhere. Then they have to be cut, and polished.
Considering what these lenses will do
they are sure worth their weight in salt.
music