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Here
ω
tj
,
ω
lj
are frequences of resonances and nulls of dielectric permittivi-
ty. Dielectric permittivity being equal to one occurs for the so-called unitary
polaritons, whose frequences
ω
u
can be obtained from the relation
ε
∞
j
=5
Y
j
−
1
(
ω
2
lj
−
ω
2
u
)
(
ω
2
tj
−
ω
2
u
)
= 1
.
If frequence
ω
0
of the exciting radiation coincides with frequency
ω
u
of unitary polaritons (
ω
0
=
ω
u
), the synchronism conditions (4), (5)
are satisfied automatically. The exciting laser radiation insertion into a
straight quartz fiber makes it possible to obtain a high spectral intensity
of the exciting radiation along the entire length of the material. The usage
of Bragg mirrors
15
is the supplementary conditions for increasing the
radiation intensity. If the length of the optical fiber is large enough, the
probability of conversion processes increases. In certain pumping modes
the processes of both spontaneous and stimulated photon-axion conversion
can occur. In the second block of the experimental pattern (see Fig. 4,
d
),
in the similar quartz optical fiber the axion-photon conversion occurs.
The adjustment of the exciting laser radiation frequence to the unitary
polariton frequencies provides the fulfilment of synchronism conditions
for the processes of photon-axion conversion and inverse processes in the
diagrams being considered.
The additional opportunity to improve the efficiency of photon-
axion conversion can be implemented using three-dimensional photonic
crystals as a conversion medium [21–29]. In these crystals unitary photons
(polaritons) are present in infrared, visible and ultraviolet regions of the
spectrum. The view of the dispersion curves in an artificial opal calculated
for silica globules of 250 nm in diameter is shown in Fig. 5. As it can be
seen in the picture the group velocities of unitary polaritons (point
U
) can
have abnormally low values. It results in changing the probability of the
spontaneous radiation processes [30] and lowering the thresholds of the
relating stimulated processes [31, 32].
To illustrate the photonic crystals capabilities we developed a basic
scheme of the device (Fig. 6) detecting axions which arise inside the
Sun or in the center of the Earth. A photonic crystal (artificial opal) is
inserted into a steel container placed in a magnetic field, in which the
axion-photon conversion processes occur resulting from the solar axion
transformation into unitary polaritons (see Fig. 5). The detector registers
them in the direction opposite to the axions scattering direction due to the
refractive index of unitary polaritons
n
=
−
1
(Fig. 5). A similar detector
can be designed on the basis of ruby crystals or dielectric crystals with
rare-earth elements.
14
ISSN 1812-3368. Herald of the BMSTU. Series “Natural Sciences”. 2014. No. 6