Exciting nitrogen atoms

[Rootje]

Hi all!

 

I'm just working on a concept, and i need to know something - is it possible to excite nitrogen atoms in the air by use of a laser (or a pair of lasers) at a specific frequency, so that the atom emits the excess energy in the form of visible light of predefined color? And if so, what direction is that light emitted in or is that random?

 

Thanks!

[YT2095]

as far as I know, Nitrogen taken to excited energy states (ionisation) has several bands in it`s spectra. there`s no clear color definition, but many are around the 600 and the 640 nm region, the higher levels are in the UV range and are widely spread from the dark blue to the invisible UV. this is using Electrical stimulation, as for Lasers??? I`de rather not comment, it`s not an area I know too much about, but I hope some of that`s usefull to you

[pulkit]

I am thinking stimulated radiation, because this sounds awfully similar to it.

 

Simulated radiation is the phenomenon behind the generation laser beams itself using half silvered mirorrs, and causing a population inversion in a group of atoms.

[Rootje]

Well, its not exactly my area of expertise either, hence the question

I always tought every atom has very specific frequencies of light they emit creating a fingerprint-like fraunhoffer spectrum, because of the limited amount of allowed energy states an electron can be in. Are bands created when you deal with paired atoms like nitrogen?

[Rootje]

I am thinking stimulated radiation' date=' because this sounds awfully similar to it.

 

Simulated radiation is the phenomenon behind the generation laser beams itself using half silvered mirorrs, and causing a population inversion in a group of atoms.[/quote']

 

Yes, i thought so too. But i never heard of a Nitrogen laser, i don't know if this gas is fit for the job ...

[pulkit]

There are Nitrogen - Helium lasers. Gases are in ratio 3:1 or 1:3 (don't remember exactly)

I know coz I used one.

It gives out red coloured light.

Frequency is somewhere b/w 550 and 600 nm (again don't remember exactly)

[Rootje]

There are Nitrogen - Helium lasers. Gases are in ratio 3:1 or 1:3 (don't remember exactly)

I know coz I used one.

It gives out red coloured light.

Frequency is somewhere b/w 550 and 600 nm (again don't remember exactly)

 

 

Cool. But how does that work, isn't it the helium that emits the stimulated radiation and the nitrogen serving as a source of spontaneus emission with the right frequency for the helium? Im taking a wild guess here ..

[pulkit]

I knew when I had to give a viva ....lol !

 

Unfortunately I don't remember now, you can always use google. Its not all that difficult a concept. Again it uses partially silvered mirrors and stimulated emission.

 

Also its quite a powerful laser. I performed a single slit diffraction experiment with it.

[pulkit]

OOPs !!

 

Made a massive mistake, it wasn't a Nitrogen-Helium laser, it was a Neon-Helium one.

 

I am really sorry ,I had a memory lapse of sorts ... (

[Rootje]

OOPs !!

 

Made a massive mistake' date=' it wasn't a Nitrogen-Helium laser, it was a Neon-Helium one.

 

I am really sorry ,I had a memory lapse of sorts ... ([/quote']

 

Nevermind, Google was a good place to look. N2-lasers do exist, they emit UV-light with wavelength 350 nm or so. But i don't think that's very useful for me, i want to excite them in mid-air and make them emit red light.

[YT2095]

the 350`s out the question for N2 360 to 350 is ok though, as is 335nm.

at lower levels you`ll not get a good red without carefull calibration, 640 ios about at middle band as you`ll get, it`s deep red and into in the IR range, the one above it will be yellow/green at about 600 nm.

 

as for "fingerprints" you`re quite correct, the spectral lines are indeed indicative of certain excited elements, I`ve just given you a FEW of the major ones for Nitrogen

 

they`re all middle-band approximate values also

[swansont]

And if so' date=' what direction is that light emitted in or is that random?

[/quote']

 

In your scenario whatever light is emitted will be somewhat random. The actual pattern will depend on the polarization of the incoming light and whether there is anything special about the nitrogen's orientation, but it will not be in a beam as with the original laser.

[pulkit]

What are the conditions for stimulated emission to occur ?

 

Would it be possible in this case to create a population inversion ?

[YT2095]

not without MEGA (perhaps even Giga) power, and even so, without containment it would at best be localised and random, as explained by Swansont. laser ablation of gas is VERY difficult!

 

it would be much easier to do this electricaly as opposed to conversion of photons for the energy, but even so, it would still require containment for the desired effect

[swansont]

What are the conditions for stimulated emission to occur ?

 

Would it be possible in this case to create a population inversion ?

 

Generally speaking, you can't get a population inversion by photon absorption alone for a system like that - the limit is 50% in the excited state, at least for simple atom structures. (anything that can be made to look like a two-level system) If you get complex systems you can do it - that's how pumped lasers work, e.g. dye lasers, and Nd-YAG and similar ones.

 

You need to be able to excite to a state where relaxation goes through another channel, so that inversion can occur, and have the right combination of states with appropriate lifetimes. The problem with that is that strong emission and strong absorption are coupled - if the atom absorbs strongly, the atom will tend to decay back to the original state.

 

One way around that is two-photon absorption. The atom wouldn't be able to decay back to the ground state, and would have to go through different states.

[swansont]

not without MEGA (perhaps even Giga) power' date=' and even so, without containment it would at best be localised and random, as explained by Swansont. laser ablation of gas is VERY difficult!

 

it would be much easier to do this electricaly as opposed to conversion of photons for the energy, but even so, it would still require containment for the desired effect [/quote']

 

The problem, as pulkit implied, is inversion. After you get that all you need is a pair of mirrors containing the gain medium. You will then get stimulated emission to swamp the spontaneous emission, and the stimulated photons all go along the axis of the mirrors.