2-state laser

[neptune]

Hi,

i have a query regarding theory of LASERS
as we all know 2-state lasers are impossible to build. yet i think we can create a Material with varying refractive index.
I am posting a pic here which shows material in two different condition.
when matter is excited such that electrons in base state are pumped to excited state we call this state of matter as perfect absorber of light as no. of e- in base state > no. of e- in excited state.

then when we further increase excitation energy we reach equilbrium state where no. of photon absorbed to excite e- = no. of photon released by spontenaus emmision (when e- looses energy), At this point photons become invisible to light. (of that perticular frequency)

so we can have material that changes refractive index when we vary its excitation energy

 

[Sceadwian]

That would be a variable frequency laser (which do exist although I'm not sure using the methods you suggest) I doubt the conditions for two stable and differing phase correct laser beams being generated from the same medium would be possible, or least practical if it were. What would be the point? Any further reflections or refraction would instantly destroy the phase correlation of the original phase matched beams. This isn't a problem with monochromatic lasers because being all the same wavelength they all change phase the exact same way through any given medium. Out side of a perfect vacuum there would be destructive interference in a very short period of time.

 

[neptune]

no i am not asking for variable freq. laser
Let me rephrase it. i want to have variable refractive index material.
my Proffesor has told me that at initial stage of laser start when we are starting to excite material through optical pumping, the material absorb one perticular frequency of light. this stage is called perfect absorption. photon is absorbed and e- is pumped to higher energy state.
when enough electrons are excited from base energy level to higher level then we reach equilbrium state, where rate of photon absorption to excite e- = rate of photon release when e- looses energy.
we can not have more e- in excited state then base state, therefore population inversion is not possible implying that 2 state laser is not possible.

so we can control photon absorption by controlling energy required to excite that material.
Laser action only takes place when we achieve population inversion
but i dont know weather enough photons will be realeased from resonating cavity of that laser

 

[Sceadwian]

Ahh, I see what you mean now, haven't the foggies clue, as far as I know you're the only laser enthusiast on this forum, probably a question better dedicated to a forum dedicated specifically to lasers.

 

[neptune]

ihmm. i will ask this in physics forum

 

[jpanhalt]

Let me rephrase it. i want to have variable refractive index material.

I believe liquid crystals can show variable refractive index. One way to demonstrate that is to apply an electric field (e.g., LCD's). Pressure and temperature are other ways to effect the change.

John

 

[ericgibbs]

ihmm. i will ask this in physics forum

hi,
Look up Kerr Cell it may give you some insight into a solution.

**broken link removed**