COL 10(Suppl.), S12601(2012) CHINESE OPTICS LETTERS June 30, 2012
Vectorial structure and beam quality of vector-vortex
Bessel–Gauss beams in the far field
Lina Guo (HHH|||AAA)
1,2
and Zhilie Tang (///)
1∗
1
School of Physics and Telecommunication Engineering, Laboratory of Quantum Information Technology,
South China Normal University, Guangzhou 510006, China
2
School of Electronics and Information, GuangDong Polytechnic Normal University,
Guangzhou 510665, China
∗
Corresponding author: tangzhil@scnu.edu.cn
Received August 25, 2011; accepted October 24, 2011; posted online May 9, 2012
The far-field analytical expressions for the electromagnetic fields of amplitude of vector-vortex beams
having a Bessel–Gauss (BG) distribution propagating in free space are obtained based on the vector
angular spectru m and the method of stationary phase. The far-field energy flux distributions and the
beam quality by the power in the bucket (PIB) in the paraxial and nonparaxial regimes are investigated.
The PIB of the vector-vortex BG beams depend on the ratio of th e waist width to wavelength and t he
polarization order. The analyses show that vector-vortex BG beams with low polarization order have
better energy focusability in the far field.
OCIS codes: 260.2110, 350.5500, 260.5430.
doi: 10.3788/COL201210.S12601.
In recent years, cylindrically vector beams, such as
radially polarized beams, have received lots of atten-
tion because of their interesting properties and practi-
cal applications
[1]
. Various methods to achieve such an
inhomogeneous polarization s tate of a laser beam have
been exploited by many researchers
[2]
. Many propaga-
tion resea rches are conducted within and beyond the
paraxial regime. The nonparaxial derivation of radi-
ally polarized beams is performed and analyzed by the
method of Rayleigh-Sommerfeld diffraction integrals
[3,4]
.
The paraxial propagation of radially polarized beams has
been dealt with as special cases of nonparaxial results
[4]
.
Also paraxial propagation of radially polarized b e ams is
analyzed by a q-parameter appro ach in Ref. [5]. The an-
alytical vectorial structures of radially polarized beams in
free space have been investigated in Ref. [6]. The far field
energy flux distribution and the beam quality of cylin-
drically polarized vector beam in the nonparaxial r e gime
have been pres e nted in Ref. [7]. Recently, vector-vortex
beams that have more than one rotation of the polariza-
tion have attracted increased interest
[8,9]
. Due to their
strange axial electric and magnetic field distributions,
vector-vortex beams may find interesting applications in
many areas like spectroscopy, high resolution microscopy,
optical tweezers, and quantum communication
[10]
.
In this letter, by means of the full vector angular spec-
trum of electromagnetic wave and the method of sta-
tionary phase, the analytical expres sions of the TE and
TM terms o f vector-vortex beams having a Bessel–Gauss
(BG) distribution are presented in the fa r field. The cor-
responding energy flux distributions of the TE term, the
TM term, and power in the bucket (PIB) are also inves-
tigated in the far field.
The electric fie ld distribution of a BG vector-vortex
beam at the z = 0 plane reads as
E
x
(x, y, 0) = E
0
J
n
(αr) exp
−
r
2
w
2
0
cos (nϕ) , (1a)
E
y
(x, y, 0) = E
0
J
n
(αr) exp
−
r
2
w
2
0
sin (nϕ) , (1b)
where E
0
is a constant, n is the polarization order of
vector-vortex beam which determines the s patial po-
larization pattern
[9]
, J
n
(·) is the nth order of Bessel
function of the first kind, w
0
is the beam waist width,
r =
x
2
+ y
2
1/2
and ϕ = arctan(y/x) are the radial and
azimuthal coordinates, respectively. Obviously, radially
polarized beam (n = 1) is n = 1 vector-vortex beams.
According to the vectorial structure of non-paraxial
electromagnetic beam
[11,12]
, an arbitrary polarized elec-
tromagnetic field can be expressed as the sum of two
terms
−→
E
TE
(
−→
r ) and
−→
E
TM
(
−→
r ), namely,
−→
E (
−→
r ) =
−→
E
TE
(
−→
r ) +
−→
E
TM
(
−→
r ) ,
−→
E
TE
(
−→
r ) =
Z Z
∞
−∞
1
b
2
[qA
x
(p, q) − pA
y
(p, q)]
(q
−→
e
x
− p
−→
e
y
) exp (ikm) dpdq,
−→
E
TM
(
−→
r ) =
Z Z
∞
−∞
1
b
2
[pA
x
(p, q) + qA
y
(p, q)]
p
−→
e
x
+q
−→
e
y
−
b
2
γ
−→
e
z
exp(ikm)dpdq, (2)
where
−→
r = x
−→
e
x
+ y
−→
e
y
+ z
−→
e
z
is the location vector;
m = px+qy +γz; b
2
= p
2
+q
2
; γ =
1 − p
2
− q
2
1/2
; k =
2π/λ with λ being the optical wavelength. A
x
(p, q, γ)
and A
y
(p, q, γ) are the x and y components of the vec-
tor angular spectrum, respectively, and are obtained by
Fourier transforming the x and y components of the ini-
tial electric field,
−→
A(p,q, γ) =
A
x
(p, q, γ)
A
y
(p, q, γ)
=
1
λ
2
Z
∞
−∞
Z
∞
−∞
E (x, y, 0) exp [−ik (px + qy)] dxdy
1671-7694/2012/S12601(4) S12601-1
c
2012 Chinese Optics Letters