On Oct 30, 2:51 am, William Asher wrote:
wrote in news:1193701240.948855.163970
@o3g2000hsb.googlegroups.com:

Why do CO2 laser's emit around 10um. They absorb in the continous
spectrum of the infrared. They have the bands of low emisison.
Therefore, energy is radiated around 10um which is not radiated at the
low emission bands, which makes the use of CO2 in a laser possible.
That CO2 amplifies these frequencies, means that it also absorbs these
frequencies. That is the process of a laser. To put the lasing
material in a container where the frequencies it emits are reflected
back into it, where they are absorbed and emitted which converts
energy into these specific frequencies.

KRoidRage:

What do you use to wipe the spittle off your screen?

The CO2 in a CO2 laser is excited collisionally from vibrationally
excited N2 molecules. The population inversion is not created by direct
radiation of CO2. The point of a CO2 laser is that the emission lines
are dictated by the vibrational levels of the excited N2 molecules, whose
energy just happens to match a vibrational energy level of the CO2
molecule. When the excited CO2 molecule emits the photon, it comes out
as a 10.6 (or 9.4, depending on the cavity) micron photon. If a
different vibrational energy level of the N2 molecule matched a different
energy level of the CO2 molecule, CO2 would lase quite happily at other
wavelengths. Anyway, the operating wavelength of a CO2 laser has nothing
to do with the continuous absorption spectrum of CO2 from the ground
state, it has everything to do with emission of photons from an excited
vibrational state.

More than that Bill it's emission from an excited state to an excited
state. In order to lase there has to exist a population inversion
between the two states, i.e. the upper state has a higher population
than the lower. If the lower state is a ground state that's very
difficult to do so usually a laser transition is between a relatively
long lived excited state to a lower excited state which has a short
lifetime, thus allowing an inversion to be built up before stimulated
emission takes place. In the case of the CO2 laser the first excited
state of the Asymmetric vibrational mode is excited collisionally by
symmetrically vibrating nitrogen (excited electrically but long lived
since it can't emit radiation). Stimulated emission then takes place
to either the first excited state of the CO2 symmetric mode (10.6
microns) or to the 2nd excited state of the bending mode (9.4 microns)
depending on the tuning of the laser cavity. The two lower levels
are rapidly depopulated by collisions (He added to improve this) thus
establishing an inversion. The absorption at 15 microns takes place
between the ground state and the rotational manifold of the 1st
excited state of the bending mode.





I don't really expect you to understand this, or look it up to see how it
shows you are basically psychotic and completely clueless, I just want to
press your buttons again.

--
Bill Asher