10 / 18
pulses 10 ns long during the transition from the first excited metastable
level of chromium ions (Cr
3+
) to the ground state:
2
E
→
4
A
. This
transition is characterized by a very low oscillator power. The frequencies
of longitudinal and transverse electromagnetic waves coincide, i.e., the
wavelength of a unitary polariton coincides with the wavelength (
λ
= 694
.
3
nm) of laser transition (Fig. 3). Thus, the active medium of a ruby laser
that produces radiation with frequency
ω
0
, can be directly used to carry out
the photon-axion conversion. The basic diagram of an experimental setup
for this purpose is shown in Fig. 4,
a
. The axions with frequency
ω
0
=
ω
0
must arise in the ruby crystal, placed in a magnetic field in the laser cavity
with two end mirrors. After penetrating nontransparent wall
8
in the second
cavity, the inverse process must occur: axion-photon conversion with the
generation wave length of 694.3 nm. Radiation detector
6
is intended for
the second radiation detection with frequency
ω
0
, which conincides with
the frequency of ruby lasing.
Two more possible setups for the photon-axion conversion in ruby
crystals are presented in Fig. 4,
b
,
c
. In the pattern shown in Fig. 4,
b
, the
radiation from a ruby laser is delivered to a laser cell placed in a magnetic
field with the other two rubies and an opaque wall. As the source of the
exciting radiation, in the diagram shown in Fig. 1.
c
, the laser is used with
the wavelength that corresponds to the absorption of the ruby, which results
in the intensive photoluminescence in sample
2
, placed in a similar laser
cell. The probability of photon-axion and axion-photon conversions in case
of using this active medium (a ruby crystal) should be significantly higher
than in vacuum (see Fig. 1), as the group velocity of unitary polaritons
must be much less than the speed of light in vacuum (see Fig. 3). Under
these conditions, the conditions are improving both to reduce the threshold
of transition from a spontaneous conversion to a stimulated conversion and
to increase the intensity of the signal registered by the detector.
The experimental pattern shown in Fig. 4,
d
is also considered to be
promising for the photon-axion realization. The radiation from laser
9
is
delivered to optical fiber
14
made of quartz fiber doped with erbium ions
Er
3+
. This material as well as the ruby crystals are used as an active
medium. Radiation generation in an erbium fiber-optic laser is fulfilled in
the resonance transition with the wavelength
λ
= 1480
nm.
In the optical fiber absorbtion spectrum there are five resonance
transitions in the infrared and visible spectral ranges, corresponding to
the excited states of an erbium ion Er
3+
. The dielectric function as a
function of frequency can be presented in the form of Kurosawa relation:
ε
(
ω
) =
ε
∞
j
=5
Y
j
−
1
(
ω
2
lj
−
ω
2
)
(
ω
2
tj
−
ω
2
)
.
12
ISSN 1812-3368. Herald of the BMSTU. Series “Natural Sciences”. 2014. No. 6