JOURNAL DE PHYSIQUE IV. Colloque 0, supplkment au Journal de Physique 111, Vol. 1, dkembre 1991. EXPLOSIVE ABSORPTION EFFECT OF POWER C02 ...
JOURNAL DE PHYSIQUE IV Colloque 0, supplkment au Journal de Physique 111,Vol. 1, dkembre 1991
EXPLOSIVE ABSORPTION EFFECT OF POWER C02 LASER BEAM IN ATMOSPHERE
V.I. ZAKHAROV, VM.SHMELEV and A.I. NESTERENKO Laser-Test Diviswn, The SORUS Co. Ltd., Zarechny settL, "Takhov"104, Sverdlovsk reg. 624051, USSR
Rbstract-The interaction of a wide beam of intense 10.6 laser radiation
with
atmospheric
C02
is
studied.
pm and 9.4 pm The
spectroscopic effect of explosive absorption have been
threshold
obtained.
In
this effect the absorption coefficient of the atmosphere
increases
K)
of the beam
sharply
owing to
strong self-heating
(AT-700-1000
channe 1.
I. -1ntroduct ion. The
problem
of
the
transfer
of
power
laser
radiation
atmosphere over large distances with low losses is this purpose C02-laser
beams with diffraction
diameter is large are employed.
divergence
in C13.
actual
and
whose
In this case of weak removal of
from the propagation channel occurs and explosive absorption
the For
of
heat C02
laser radiation owing to thermal explose leading to sharp 'adarkening" of the atmosphere can arise. The mechanism of explosive absorption of resonance radiation in not
the
ground
between
the
of
number
the
absorption
state.
In
this case the positive feedback
occur
absorption at the resonanse transition and the increase on
of
molecules
vibration
theoretically in Refs.2,3 2.-Thermal
gases is possible when the absorbing level is
in
the
transitions
absorbing in
level.
molecules
Explosive
was
studied
and experimentally in Ref.4.
instability of power
Cog-laser
beam
channel
in
atmosphere. The purpose of this work is to determine
the possible thermal states
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:19917207
JOURNAL DE PHYSIQUE 1V
C7-776
of the C02 laser beam channel in the atmosphere,the conditions which thermal instability in
the
atmosphere
arises
and
under
explosive
absorption process develops. The
attenuation
of
radiation
determined by Bougier's
law
propagating
in
the
atmosphere
is
Im.t~Io expC-Kv (t)23.
The absorption coefficient K (t), because it is small for 10.6pm V 9.4pm radiation,depends on the time t and does not depend on coordinate z; 1gs.t) is the intensity
of
the
radiation
at
a
and the point
with the coordinate z at the time t; and Io is the starting intensity of laser beam.The
value of Kv(t)
in the range of 10.6
pm and 9.4pm
determined by the difference of the populations of the
states
is
(100)
and (001); (020) and (001) of COz:
where
0
L
the cross-section for absorption on the
transition
(100)-
(001) and oz is on the transition (020)- (001). PI simplified kinetic scheme of the relaxation process accopanying the
possage of intense 10.6~.
and 9.4~1radiation in atmospheric
air
is
given in Fig. 1.
v-V'
(020)
T-V
Fig.l.Kinetic
scheme of processes wich lead to a thermal explosion in
the channels of
X310.6pm
and
X=9.4pm
laser beams.
Reactions presented on Fig.1
indicates
the
existence
of
positive
feedback between intense absorption on the transit ions (100)(020)- (001) and an increase in the population
of
(100)
(001f,
and
(020)
levels as a result o f heating the atmosphere in the channel of
power
Con laser beam accompanying V-T relaxation of nitrogen and W n .
R qualitative analysis of
explosive
absorption
in
the
scheme
of
levels studied above can be performed with the help of one-mode model (see Ref.3.)
where
I
with the generalized relaxation time
CO -N 2
2
'
I
C02 -H
2
0 '
I
N2 -H
2
are the characteristic times of Fig. 1,
,for
?t
is the ratio
T
0 '
~
the
of the
I
~and-
N2-N 0
relaxation
concentrations
2
'~
processes of CO2
and
above,
Nn;
and
the atmosphere ~=4*10-*.Clssuming that the lower levels (100) and
(020) in COn is thermalized,in
the
one-mode
model
following system of two eguat ions (equation of
we
obtain
vibrational
the
kinetics
and the heat-balance equation) :
where j=l for 15.6pm coot,
transition CO
2
radiation and j=Z for 9.4pm,
r Z i correspond the
(ioo,
-
tooi)
,and
1-
the transition CO
4
(OW)
- C02
9
JOURNAL DE PHYSIQUE 1V
C7-778
with
the
initial conditions T=Ta
for t=O,and n=n for T=To,
To
is
~ the the temperature of the qas outside the beam of radiati o n; P - is and are the corresponding e ioo>~e
