Spiral spectrum of Airy–Schell beams through
non-Kolmogorov turbulence
Yun Zhu (朱云)
1,2
, Licheng Zhang (章里程)
2
, and Yixin Zhang (张逸新)
2,
*
1
School of IoT Engineering, Jiangnan University, Wuxi 214122, China
2
School of Science, Jiangnan University, Wuxi 214122, China
*Corresponding author: zyx@jiangnan.edu.cn
Received October 20, 2015; accepted January 25, 2016; posted online March 18, 2016
Based on the geometrical optics approximation, we analyze the effects of non-Kolmogorov turbulence on the
spiral spectrum of the orbital angular momentum (OAM) of Airy–Schell beams. Our numerical results of
Airy–Schell beams on the horizontal path show that the beam spreading due to diffraction is smaller for shorter
wavelengths, a smaller OAM quantum number, a larger radius of the main ring, and a higher arbitrary trans-
verse scale in weak turbulence. The oscillation frequency of the mode probability density of Airy–Schell beams
in the radial direction is much lower than that of Hankel–Bessel beams. The mode probability densities of
Airy–Schell and Hankel–Bessel beams are remarkably dependent on the wavelength and OAM quantum num-
ber. In order to improve the mode probability density, Airy–Schell beams with shorter wavelengths and lower
OAM quantum numbers may be the better choice, which is diametrically opposite to Hankel–Bessel beams. Our
research provides a reasonable basis for selecting light sources and precise tracking.
OCIS codes: 100.6640, 210.4770, 180.1790.
doi: 10.3788/COL201614.042101.
According to its exotic features, such as non-diffracting
[1]
,
self-accelerating
[2–4]
, and self-healing
[5,6]
in vacuum, more
and more attention has been paid to Airy beams. The
propagation properties of Airy beams in atmospheric tur-
bulence, such as scintillation
[7,8]
, evolution
[9]
, thermal
blooming
[10]
, beam wander
[11]
, average intensity distribu-
tion
[12]
, and average spreading
[13]
also have been carefully
investigated. But, as we know, there are almost no discus-
sions with respect to the effects of turbulence on the spiral
spectrum of the orbital angular momentum (OAM) modes
of Airy–Schell (AS) beams.
Considering the needs of precise tracking and significant
deviations from Kolmogorov’s model in certain atmos-
pheric experiments
[14]
, in this Letter, we discuss the radial
distribution of the mode probability density (MPD) and
crosstalk probability density (CPD) of the OAM modes
of AS beams in the horizontal path through the non-
Kolmogorov atmosphere in various situations. To reveal
the distinctive properties of the spiral spectrum of the
OAM of the AS beams in a turbulent atmosphere, we also
compare them with Hankel–Bessel (HB) beams
[15]
.
On account of the Gaussian-like Airy beam in
far-field region, for long-distance transmissions, both trun-
cated Airy and HB beams become spherical-like beams.
Based on the Retov approximation, in the weak fluc-
tuation region
[16]
, q ¼ z∕kρ
2
pl
< 1, where qΛ < 1, ρ
pl
is the
spatial coherence radius of a plane wave, k is the wave
number of light, and Λ ¼ 2z∕kW
2
is the Gaussian beam
parameter characterizing the spot size W at the receiver.
In the half-space z > 0, the complex amplitude of an Airy
beam is given by
Aiðr; φ; zÞ¼Ai
l
0
ðr; φ; zÞexp½ψ
1
ðr; φ; zÞ; (1)
where r ¼jrj, r ¼ðx; yÞ is the two-dimensional position
vector in the source plane, φ is the azimuthal angle,
and z is the propagation distanc e. ψ
1
ðr; φ; zÞ is the com-
plex phase of waves propagating through turbulence
and Ai
l
0
ðr; φ; zÞ is the normalized Airy-Gaussian model
at the z plane with the OAM quantum number l
0
in free
atmospheric turbulence. In the paraxial approximation,
Ai
l
0
ðr; φ; zÞ has the form
[17]
Ai
l
0
ðr; φ; zÞ¼−
ik
z
ω
0
ðr
0
− ω
0
a
2
ÞJ
l
0
krr
0
z
× exp
ik
r
2
2z
þ
a
3
3
expð−il
0
φÞ; (2)
where ω
0
is associated with the arbitrary transverse scale,
r
0
is the approximate radius of the main ring, and a is the
exponential truncation. J
l
0
ðkrr
0
∕zÞ denotes the l
th
0
order
Bessel function of the first kind.
For a paraxial beam, the second-order cross-spectral
density of the partially coherent case is defined by the stat-
istical average over the ensembles as the following
[16,18]
:
W ðr; r
0
; zÞ¼hEð r; φ; zÞE
ðr
0
; φ
0
; zÞi; (3)
where Eðr; φ; zÞ is the complex amplitude of the AS beams
and hirepresents the ensemble average of the source and
atmospheric turbulence. In free space, Ref. [
19] indicates
that the normalized correlation function of Gaussian–
Schell mode for any distance z is coincident with that
of the original plane (z ¼ 0). Based on the statistical inde-
pendence between the sources and the atmospheric turbu-
lence, the cross- spectral density of AS beams at any
distance z is written as
COL 14(4), 042101(2016) CHINESE OPTICS LETTERS April 10, 2016
1671-7694/2016/042101(5) 042101-1 © 2016 Chinese Optics Letters