What is populaton inversion?

Question

seriously..how do you invert a population?

Answer 1

Population inversion is when there are more electrons in a given exited state then in the ground state. This effect is used for creating lasers. To create an inversion energy is pumped into a system to move to a higher energy state. This is usually a short lived state. The electron then quickly decays into a slightly lower long lived or metastable state. Since the energy being imputed is only of the strength to move electrons from the ground state to the higher state and because of the quantized nature of matter it does not effect the electrons in the metastable state. Soon there are more electrons in the metastable state then in the ground state. This is population inversion.
How this is used for lasers is that when you pass light through this material that has the proper energy to raise electrons from the ground state to the metastable state it actually causes more light to be admitted. This is because most of the electrons are already in the metastable state so that instead of lifting the electrons from the ground state they are more likely to bump the electrons out of the metastable state allowing them to "fall" to the ground state. The give the extra energy off as a photon of light.
This is where they got the name L.AS.E.R.or laser

Light
Amplification by
Stimulated
Emission of
Radiation

Answer 2

I guess, ur talking about Population Inversion in Lasers. If ur talking about Lasers, then here are the basics.
According to modren Atomic theory, basically different orbits of the electron revolving around a nucleus have different energy levels. Higher orbits have higher energies. So when an Electron jumps from a higher orbit to lower orbit, it emitts the difference in energy as radiation (photon). So if u first excite an Atom (make electron in it jump to higher orbit) and then before it jumps to the lower orbit, we make another photon (radiation packet) incident on it, then the electron would jump to lower orbit by emitting two identical photons. The two photons are of the same phase. These two can then be used to stimulate emission in other excited Atoms. In this way, if we can create a situation where we make a number of Atoms emitt radiation of the same phase and in the same direction, then we would have a radiation whhich is unidirectional and with lot of energy.
The process by which we make this happen is called Laser. LASER means Light Amplification by Stimulated Emision of Radiation.
But there is a problem. The average life of an excited Atom is very low. About 10^ -8 second. So before we can get a cascading effect of stimulated emissions, he Atoms would spontaneously emitt radiation. Which defeats our purpose.
So we have to find a way in which we make population of Atoms in excited state more than the population of Atoms in ground state (unexcited). This process is called Population Inversion.
Now, how do we do this? We choose a suitable substance like Chromium or Helium and Neon mixture. We excite the Atoms in it using radiation in such a way that they decay by spontaneous emission to an intermediate state called Meta Stable State (which is an intermediate electron orbit). Now this state is more stable and has more life. Thus Atoms remain in this state long enough for the cascading effect of stimulated Radiation can occur. And the process of exceiting most of the Atoms to this metastable state using radiation is called Optical Pumping, which is a method used to achive population inversion.
Now, we can make Stimulated Radiation to take place in this mixture where most Atoms are in Meta Stable State. And the we will have a cascading effect where more and more photons in the same phase stimulate emmission of radiation. And we can control the direction of Radiation build up using a pair of parallel mirrors facing each other , one of them partially silvered. And the intensity of Radiation builds up in a chosen direction until it is strong enough to penetrate the partiallly silvered and emerges as a very intense Radiation of Photons in the same phase. Thus the energy of the various Photons adds up making the Radiation very powerful.
This is basically the breif outline of LASER technology, though there are many types of Lasers and many different methods are used.

Answer 3

lol. Vasectomy. "Tying" of the male's Vas Deferens tubules to prevent sperm cells from escaping and populating.

Answer 4

It is a medical procedure more commonly known as a vasectomy.