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Thereby, the total probability of the conversion-reconversion process
will be
P
γ
→
γ
0
= (
P
γ
→
a
)(
P
a
→
γ
0
)
≈
10
−
28
.
(11)
Let us firstly analyze the spontaneous conversion-reconversion processes.
With the exciting radiation power of about 10Watts an argon laser
operates in continuous or quasi-continuous mode of generating visible
light (0.5
μ
m), but the number of excitatory quanta of light falling into the
first cavity per one second is
N
γ
≈
10
20
. Consequently, at the second cavity
output (Fig. 1), according to the relation (11), the number of the emerging
photons resulted from the process of conversion-reconversion during one
second is equal to
N
γ
0
≈
10
−
8
. It corresponds to the noise signals level
which is below the threshold of sensitivity of the current light radiation
detectors. The converted radiation intensity can be increased if the exciting
radiation energy increases up to many orders of the magnitude or when the
time of secondary radiation detection also increases, which significantly
complicates the experimental setup. Thus, the observation of the discussed
effect in the regime of the spontaneous conversion-reconversion processes
with the experimental setups, presented in Fig. 1, and continuous sources
of exciting radiation is unpromising.
For the stimulated conversion similarly to the SCS process (relations (6),
(7)) we obtain
P
γ
→
a
=
1
4
n
a
Q
4
π
ω
k
a
(
gB
0
l
)
2
F
2
(
q
)
.
The transition from the spontaneous radiation regime to the stimulated
one corresponds to the condition:
n
a
>
1
.
To estimate a value
n
a
we use the relation
n
a
=
1
4
Q
π
ω
k
a
(
gB
0
l
)
2
F
2
(
q
)
n
0
.
(12)
Here
n
0
is the number of quanta per a field mode of the exciting
radiation. To excite the stimulated processes of light scattering it is
necessary to use ultrashort (
10
−
8
s) or supershort (
10
−
10
s) pulses of
the exciting radiation [21–23]. Let us consider the case where the power
density of the excitation pulse is
10
12
W/сm
2
, and its durability is 100 ps.
This mode of operation, in particular, can be implemented for the second
optical harmonic of the solid-state YAG : Nd
3+
laser. Here the number of
quanta per one exciting radiation field mode is
n
0
≈
10
14
. According to
(12) we obtain
n
a
≈
1
, i.e. under these conditions the implementation of
the threshold behaviour of the stimulated radiation for conversion processes
may be expected.
10
ISSN 1812-3368. Herald of the BMSTU. Series “Natural Sciences”. 2014. No. 6