Now I'm just getting started on this page, but here is a brief explanation
of one process we will employ to cool our Rubidium vapor.
This primary process is called Optical Molasses. Below is an diagram of
Optical Molasses. Read the explantion below the diagram for an explanation
of the process.
To understand this diagram you must understand what a doppler shift is, that heat in a gas is a measure of how fast atoms are bouncing around, and what an atom's reasonant frequency is. Theese things in mind, here's an explanation:
Light is put into this system at a very specific frequency, represented here as green. On the top an atom is approaching the light source and as a result, it sees the light shifted towards a bluer frequency. Now, if the input frequency is set properly the atoms moving left will be shifted into a reasonant frequency which causes them to absorb most of the photons that hit them and then reemits them. As a simple consequence of conservation of momentum the atom experiences a strong force to the right.
On the bottom the atoms receding from the light see the input frequency shifted towards the red, which is farther away from resonance. So, instead of absorbing most of the light as above. Few of the photons incident upon them are absorbed and most simply pass by. As a result there is some kick to the right, however the effect is much smaller than in the previous case.
Keeping this in mind, you shoot laser light in from the top, bottom, left, right, forward, and backward. When this is done properly forces cancel out and the only force left is that which opposes motion. So no matter which way an atom tries to move, it is slowed down. And that in a nutshell is Optical Molasses.
Please keep an eye on these pages for far more info about this experiment.