| Home / lib / E_Engineering / EO_Optical devices / | ||
Cherrington B. Gaseous electronics and gas lasers (Pergamon, 1979)(KA)(600dpi)(T)(279s)_EO_.djvu |
|
Size 2.5Mb Date May 31, 2003 |
7.3.3 Three-body Attachment
In this case, the third body helps to conserve energy and momentum in the process...
Before we
begin, it should be pointed out that the expression for the electron temperature
that will be derived here assumes that electrons have a Maxwellian electron energy
distribution (which is usually only valid at high electron densities) and that
one-step ionization is the dominant electron source (which is not the typical sit-
situation) ...
As was mentioned in the previous section, an important property of the positive
column is that the voltage drop along a positive column is a function of the N R
product and is independent of the current...
In their results, they found that for plasma columns with identical values of
R N and E/N, the radial temperature distributions are identical and the electron
density distributions are similar...
The increased charge density and electron mobility in the central region then
tends to cause the current to increase in this region and leads to further gas
heating near the center...
Now, values of a in this range can indeed occur for recombination with molecular
ions (dissociative) and so constriction of the positive column can readily occur in
gases which contain large numbers of molecular ions...
In these cases, radiative decay
is usually the dominant loss process and the decay of the excited species is given
f x* = -ax* = -x*/t (9-D
where A is the atomic transition probability and t is the radiative lifetime of
the state...
Figure 9.2 shows a partial energy level diagram
for neon (not to scale) showing some relevant levels and some of the processes
involved in the excitation and de-excitation of the important species...
(9.10)
The cross section for metastable-metastable collisions is approximately
avr vr ~ 1«4 X 10 m ...
Since recombination is the dominant electron loss process in neon at these
pressures, and since Veatch and Oskam A970) have shown that dissociative recom-
recombination in neon preferentially populates the 2p and 3p levels, which radiatively
decay to the Is levels, it appears that many of the electrons lost by recombina-
recombination could result in the production of lS(...
Therefore,
dN9
dt R2 " N2/T2 " (N2"V B21 8(V) pv A0.15)
and dN
= Rl " VT1 + N2/T21 + CN2"V B21 gCv) Pv A0.16)
where 1 1 , 1
__ ss ——— -J- ——— #
n ., T2 T20 T21
Define
Ws = B21 g(v) pv = B21 8(V) Vc A0.17)
as the stimulated emission rate...
From equations A0.9) and A0.31)
hv
A0.37)
For a high gain medium, N~n » g~ N
A0.19), we obtain
os
and t2 > T-...
(.10.45)
In this equation
<a v > is the rate coefficient for electron impact
p e
excitation from the ground state,
<o...
Spontaneous light emission from Ne in a He-Ne mixture
as a function of discharge current (from White and
Gordon, 1963)
190 Gaseous Electronics and Gas Lasers
linearly with current...
for a (non-lasing) He-Ne discharge have been
made by White and Gordon A963) and are shown in Fig...
As it turns out, optimum pressures are of the
order of a few tens of microns, and the gain varies inversely with tube diameter...
A969) "Positive Column Population Calculations for the Evaluation
of Dispersive Effects in He-Ne Lasers," J...
Argon Ion Lasers
This discussion will be confined to argon ion lasers since these lasers have been
thoroughly studied...
The calculated efficiency of 2.1% com-
compared to the experimental value of 0.6% to 0.9% indicates, however, that the
analysis is not precise in all facets although it is certainly very good...
| © 2007 eKnigu | ||