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1.IntroductionOptical beams with zero central intensity, which are called dark-hollow beams (DHBs), have recently attracted a lot of attention both experimentally and theoretically, due to their unique properties and useful applications in atomic optics, optical communication, optical trapping, and other fields.1–4 Meanwhile, a rich variety of methods have been used to generate various DHBs, such as the transverse mode selection method,5 the geometrical optical method,6 optical holographic method,7 the computer-generated hologram method,8 and the hollow optical fibers method.9 In theory, several models have been proposed to describe DHBs, such as the best-known beam (also known as a doughnut beam), high-order Bessel beams, hollow Gaussian beams,10–12 etc. In 2012, Sun et al. introduced a new mathematical model called hollow sinh-Gaussian (HsG) beams to depict DHBs.13 Their propagation characteristics in free space were also studied. On the other hand, fractional Fourier transform (FrFT) as the generalization of a conventional Fourier transform, was first proposed as a new mathematical tool for solving physics problems by Namias in 1980.14 Its subsequent potential applications in optics were first explored in 1993 by Mendlovic, Ozaktas, and Lohmann.15–17 Since then FrFT has become an active research subject in optics and has found wide application in signal processing, optical image encryption, beam shaping, and beam analysis.18–23 Recently, much work has been done concerning their FrFT for various types of beams that frequently used in modern optics.24–34 However, to the best of our knowledge, no results have been reported until now about the propagation properties of the newly proposed HsG beams in the FrFT optical system. In this work, we derived the analytical expression for HsG beams propagating through a paraxial optical system and used it to investigate its propagation properties in the FrFT optical system. The paper is structured as follows, In Sec. 2, a propagation analytical expression for HsG beams through a paraxial optical system is derived. In Sec. 3, evolution of HsG beams’ intensity distributions in the FrFT system and their dependent influences on several parameters are discussed in detail and numerically illustrated by using the derived equations. Finally, the mail results obtained are summarized in Sec. 4. 2.Fractional Fourier Transform of Hollow Sinh-Gaussian BeamsFrom an optical point of view, three kinds of optical systems for performing FrFT are proposed15–17 and are shown in Fig. 1, which are the Lohmann I system, the Lohmann II system, and the quadratic graded index (GRIN) medium system, respectively. Here, is the standard focal length, with being the fractional order, and is the axial distance between the input and output planes along the optical axis in the GRIN medium. According to matrix optics, the transfer matrix for Lohmann I optical system can be expressed as For a Lohmann II optical system, the corresponding transfer matrix can be described by For the GRIN medium system, the transfer matrix with quadratic index variation , can be written as35 In Eq. (3), denotes the radius of the GRIN medium. Obviously, Eqs. (1), (2), and (3) have the same form when and . Hence, the above-mentioned three optical systems have the same transfer matrix and they are equivalent for performing FrFT. In a cylindrical coordinate system, the electric field of the HsG beams in the original plane () is defined by13 In Eq. (4), () denotes the order of the HsG beams and is a constant related to the beam power. Obviously, for , the beam governed by Eq. (4) is the conventional fundamental Gaussian beam with a beam waist of . However, for , a new kind of HsG beam is obtained. As defined by Eq. (4), the amplitude of the HsG beam is determined by the beam’s order and waist size . In order to visualize the shape of HsG beams, a preliminary demonstration is shown in Fig. 2 for HsG beams with different orders [Fig. 2(a)] and with different waist sizes [Fig. 2(b)], respectively. All curves in Fig. 2 have been normalized to their peak intensity value. It is apparent from Fig. 2 that the irradiance profile of the HsG beam presents a single bright ring, and the central dark size increases as and increase. Therefore, one can control the intensity distribution of HsG beams by choosing and . On the other hand, Eq. (4) can be rewritten in the form with the coefficients given by where is a binomial coefficient. Equation (5) indicates that the ’th order HsG beam can be generated in a laboratory by the superposition of several decentered Gaussian beams with the same waist width , whose centers are located at positions , respectively.Within the framework of the paraxial approximation, the propagation of any laser beam through an optical system can be described by the generalized Huygens-Fresnel diffraction integral, known as Collins integral formula, which takes the following form in a cylindrical coordinate system:36,37 In Eq. (7), and are the electric fields in the input and output planes, respectively. , and , are the radial and azimuthal angle coordinates in the input and output planes, respectively. is the axial distance between the input and output planes along the optical axis. is the wave number related to the wavelength by . , , , and are the transfer matrix elements of the optical system between the input and output planes, respectively. Substituting Eqs. (5) and (6) into Eq. (7), and recalling the following integral equation: we can transform Eq. (7) asExpand the exponential part into a Taylor series and use the integral equation of the hypergeometric Kummer function to evaluate the beams. When and , the integral equation will take the following form:38 In Eq. (10), stands for the -order Bessel function of the first kind, denotes the gamma function, and is the confluent hypergeometric function, respectively. After tedious but straightforward integration, we obtain a result as follows: Equation (11) is the general propagation and transformation for HsG beams through a paraxial optical system, which provides a convenient and powerful tool for treating the propagation and transformation of HsG beams. Substituting Eq. (1) or (3) into Eq. (11), one obtains the analytical expression for the hollow HsG beams propagating through the FrFT optical system. Then the corresponding intensity distribution reads as In the following, we investigate the HsG beam’s intensity distribution evolution in the FrFT system. 3.Numerical Simulations and AnalysisAccording to the analytical expressions obtained in Sec. 2, in the following, we numerically investigate the properties of HsG beams propagating through the FrFT system. In the following discussion, influence factors of HsG beam order and the fractional transform order on the evolution of the beam’s intensity distribution in the FrFT optical system are considered. Without loss of generality, we choose the calculation parameters of HsG beams as , , and , 3, 5, 9. Figure 3 depicts the normalized intensity distribution of HsG beams in several FrFT planes. For convenience of comparison, we choose the HsG beams of three different orders (i.e., , 3, 5, 9). It can be seen from Figs. 3(a) and 3(b) that HsG beams maintain their dark-centered distribution when the fractional order is low, and low-ordered HsG beams lose their original dark-centered distribution more quickly than high-ordered ones when the value of increases [see Fig. 3(c)]. Eventually all beams evolve into a peak-centered distribution with some side lobes located sideways [see Fig. 3(e)]. Furthermore, higher-ordered HsG beams have sharper center-peaked distributions. This indicates that in order to reshape the HsG beams, one can choose reasonable optical parameters for HsG beams in the optical FrFT system. Figure 4 shows the normalized intensity distribution of HsG beams in different planes in the GRIN medium. In Fig. 4, we choose ; hence, the GRIN medium is equivalent with the Lohmann I and Lohmann II optical systems for performing FrFT. Obviously, in our case, the planes , 1.38, 1.57, 1.76, and 3.06 m in the GRIN medium are, respectively, equivalent to , 0.88, 1.0, 1.12, and 1.95 in the FrFT optical system. Furthermore, one can find from Fig. 4 that the intensity distribution is symmetrical about (i.e., ). Figure 5 shows the evolution of the normalized on-axis intensity distribution of HsG beams of several orders in the FrFT planes versus the fractional order . It is obvious from Fig. 5 that the dependence of the normalized on-axis intensity on the fractional order is periodic, and the period is 2. The on-axis intensity has a maximum value when and a minimum value when . 4.ConclusionsIn this work, we have derived the analytical expression for HsG beams propagating through a paraxial optical system and used it to investigate its propagation properties in the FrFT optical system. Several influencing parameters of both the HsG beams and the FrFT optical system are discussed in detail. Results show that the FrFT optical system provides a convenient way for modulating HsG beams: HsG beams maintain their dark-centered distribution when the fractional order is low, and low-ordered HsG beams lose their original dark-centered distribution more quickly than high-ordered ones when the value of increases. Eventually, all HsG beams’ intensities evolve into peak-centered distributions with some side lobes located sideways. Furthermore, our results also show that HsG beam intensity distribution versus the fractional order is periodical and the period is 2. The results obtained in this work are valuable for the HsG beam shaping. AcknowledgmentsThis work is supported by the National Science Foundation of China (Grant No. 11274273 and 61263010), the Jiangxi Provincial Natural Science Foundation of China (Grant No. 20142BAB212003), the Scientific Project of Jiangxi Education Department of China (Grant No. GJJ14397), and the East China Jiaotong University Startup Outlay for Doctor Scientific Research (Grant No. 09132007). ReferencesT. Kugaet al.,
“Novel optical trap of atoms with a doughnut beam,”
Phys. Rev. Lett., 78
(25), 4713
–4716
(1997). http://dx.doi.org/10.1103/PhysRevLett.78.4713 PRLTAO 0031-9007 Google Scholar
Y. B. OvchinnikovI. ManekR. Grimm,
“Surface trap for Cs atoms based on evanescent-wave cooling,”
Phys. Rev. Lett., 79
(12), 2225
–2228
(1997). http://dx.doi.org/10.1103/PhysRevLett.79.2225 PRLTAO 0031-9007 Google Scholar
H. Itoet al.,
“Laser spectroscopy of atoms guided by evanescent waves in micron-sized hollow optical fibers,”
Phys. Rev. Lett., 76
(24), 4500
–4503
(1996). http://dx.doi.org/10.1103/PhysRevLett.76.4500 PRLTAO 0031-9007 Google Scholar
F. E. S. VetelinoL. C. Andrews,
“Annular Gaussian beams in turbulent media,”
Proc. SPIE, 5160 86
–97
(2004). http://dx.doi.org/10.1117/12.507774 PSISDG 0277-786X Google Scholar
X. WangM. G. Littman,
“Laser cavity for generation of variable-radius rings of light,”
Opt. Lett., 18
(10), 767
–768
(1993). http://dx.doi.org/10.1364/OL.18.000767 OPLEDP 0146-9592 Google Scholar
R. M. HermanT. A. Wiggins,
“Production and uses of diffractionless beams,”
J. Opt. Soc. Am. A, 8
(6), 932
–942
(1991). http://dx.doi.org/10.1364/JOSAA.8.000932 JOAOD6 0740-3232 Google Scholar
H. S. Leeet al.,
“Holographic nondivergjng hollow beam,”
Phys. Rev. A, 49
(6), 4922
–4927
(1994). http://dx.doi.org/10.1103/PhysRevA.49.4922 PLRAAN 1050-2947 Google Scholar
C. PatersonR. Smith,
“Higher-order Bessel waves produced by axicon-type computer-generated holograms,”
Opt. Commun., 124
(1–2), 121
–130
(1996). http://dx.doi.org/10.1016/0030-4018(95)00637-0 OPCOB8 0030-4018 Google Scholar
S. Marksteineret al.,
“Coherent atomic waveguides from hollow optical fibers: quantized atomic motion,”
Phys. Rev. A, 50
(3), 2680
–2690
(1994). http://dx.doi.org/10.1103/PhysRevA.50.2680 PLRAAN 1050-2947 Google Scholar
V. I. BalykinV. S. Letokhov,
“The possibility of deep laser focusing of an atomic beam into the Å-region,”
Opt. Commun., 64
(2), 151
–156
(1987). http://dx.doi.org/10.1016/0030-4018(87)90042-3 OPCOB8 0030-4018 Google Scholar
J. ArltK. Dholakia,
“Generation of high-order Bessel beams by use of an axicon,”
Opt. Commun., 177
(1–6), 297
–301
(2000). http://dx.doi.org/10.1016/S0030-4018(00)00572-1 OPCOB8 0030-4018 Google Scholar
Y. CaiX. LuQ. Lin,
“Hollow Gaussian beams and their propagation properties,”
Opt. Lett., 28
(13), 1084
–1086
(2003). http://dx.doi.org/10.1364/OL.28.001084 OPLEDP 0146-9592 Google Scholar
Q. Sunet al.,
“Hollow sinh-Gaussian beams and their paraxial properties,”
Opt. Express, 20
(9), 9682
–9691
(2012). http://dx.doi.org/10.1364/OE.20.009682 OPEXFF 1094-4087 Google Scholar
V. Namias,
“The fractional order Fourier transform and its application to quantum mechanics,”
J. Inst. Math. Appl., 25
(3), 241
–265
(1980). http://dx.doi.org/10.1093/imamat/25.3.241 JMTAA8 0020-2932 Google Scholar
D. MendlovicH. M. Ozaktas,
“Fractional Fourier transforms and their optical implementation: I,”
J. Opt. Soc. Am. A, 10
(9), 1875
–1881
(1993). http://dx.doi.org/10.1364/JOSAA.10.001875 JOAOD6 0740-3232 Google Scholar
H. M. OzaktasD. Mendlovic,
“Fractional Fourier transforms and their optical implementation: II,”
J. Opt. Soc. Am. A, 10
(12), 2522
–2531
(1993). http://dx.doi.org/10.1364/JOSAA.10.002522 JOAOD6 0740-3232 Google Scholar
A. W. Lohmann,
“Image rotation, Wigner rotation, and the fractional Fourier transform,”
J. Opt. Soc. Am. A, 10
(10), 2181
–2186
(1993). http://dx.doi.org/10.1364/JOSAA.10.002181 JOAOD6 0740-3232 Google Scholar
R. G. DorschA. W. Lohmann,
“Fractional Fourier transform used for a lens-design problem,”
Appl. Opt., 34
(20), 4111
–4112
(1995). http://dx.doi.org/10.1364/AO.34.004111 APOPAI 0003-6935 Google Scholar
M. A. KutayH. M. Ozaktas,
“Optimal image restoration with the fractional Fourier transform,”
J. Opt. Soc. Am. A, 15
(4), 825
–833
(1998). http://dx.doi.org/10.1364/JOSAA.15.000825 JOAOD6 0740-3232 Google Scholar
Y. Zhanget al.,
“Beam shaping in the fractional Fourier transform domain,”
J. Opt. Soc. Am. A, 15
(5), 1114
–1120
(1998). http://dx.doi.org/10.1364/JOSAA.15.001114 JOAOD6 0740-3232 Google Scholar
X. XueH. WeiA. G. Kirk,
“Beam analysis by fractional Fourier transform,”
Opt. Lett., 26
(22), 1746
–1748
(2001). http://dx.doi.org/10.1364/OL.26.001746 OPLEDP 0146-9592 Google Scholar
H. M. OzaktasZ. ZalevskyM. A. Kutay, The Fractional Fourier Transform with Applications in Optics and Signal Processing, John Wiley & Sons, Chichester
(2001). Google Scholar
X. WangD. Zhao,
“Simultaneous nonlinear encryption of grayscale and color images based on phase-truncated fractional Fourier transform and optical superposition principle,”
Appl. Opt., 52
(25), 6170
–6178
(2013). http://dx.doi.org/10.1364/AO.52.006170 APOPAI 0003-6935 Google Scholar
Y. CaiQ. Lin,
“Fractional Fourier transform for elliptical Gaussian beams,”
Opt. Commun., 217
(1–6), 7
–13
(2003). http://dx.doi.org/10.1016/S0030-4018(03)01135-0 OPCOB8 0030-4018 Google Scholar
D. Zhaoet al.,
“Propagation of Hermite-cosh-Gaussian beams in apertured fractional Fourier transforming systems,”
Opt. Commun., 236
(4–6), 225
–235
(2004). http://dx.doi.org/10.1016/j.optcom.2004.03.047 OPCOB8 0030-4018 Google Scholar
D. Zhaoet al.,
“Propagation of flattened Gaussian beams in apertured fractional Fourier transforming systems,”
J. Opt. A: Pure Appl. Opt., 6
(1), 148
–154
(2004). http://dx.doi.org/10.1088/1464-4258/6/1/027 JOAOF8 1464-4258 Google Scholar
X. DuD. Zhao,
“Fractional Fourier transform of truncated elliptical Gaussian beams,”
Appl. Opt., 45
(36), 9049
–9052
(2006). http://dx.doi.org/10.1364/AO.45.009049 APOPAI 0003-6935 Google Scholar
Z. LiuD. Zhao,
“Coherence vortex properties of partially coherent flat-topped vortex beams,”
Appl. Phys. B, 106
(3), 691
–700
(2012). http://dx.doi.org/10.1007/s00340-011-4848-x APBOEM 0946-2171 Google Scholar
C. Zheng,
“Fractional Fourier transform for a hollow Gaussian beam,”
Phys. Lett. A, 355
(2), 156
–161
(2006). http://dx.doi.org/10.1016/j.physleta.2006.02.025 PYLAAG 0375-9601 Google Scholar
G. Zhou,
“Fractional Fourier transform of Lorentz–Gauss beams,”
J. Opt. Soc. Am. A, 26
(2), 350
–355
(2009). http://dx.doi.org/10.1364/JOSAA.26.000350 JOAOD6 0740-3232 Google Scholar
G. ZhouX. WangX. Chu,
“Fractional Fourier transform of Lorentz-Gauss vortex beams,”
Sci. China Ser. G, 56
(8), 1487
–1494
(2013). http://dx.doi.org/10.1007/s11433-013-5153-y SCSGCI 1672-1799 Google Scholar
D. Deng,
“Propagation of Airy beams through a hard-edged aperture,”
Appl. Phys. B, 107
(1), 195
–200
(2012). http://dx.doi.org/10.1007/s00340-012-4899-7 APBOEM 0946-2171 Google Scholar
B. TangC. JiangH. Zhu,
“Propagation of Bessel-Gaussian beams through a double apertured fractional Fourier transform optical system,”
J. Opt. Soc. Am. A, 29
(8), 1728
–1733
(2012). http://dx.doi.org/10.1364/JOSAA.29.001728 JOAOD6 0740-3232 Google Scholar
X. Luet al.,
“Experimental study of the fractional Fourier transform for a hollow Gaussian beam,”
Opt. Laser Technol., 56
(2), 92
–98
(2014). http://dx.doi.org/10.1016/j.optlastec.2013.07.023 OLTCAS 0030-3992 Google Scholar
J. N. McMullin,
“The ABCD matrix in arbitrarily tapered quadratic-index waveguides,”
Appl. Opt., 25
(13), 2184
–2187
(1986). http://dx.doi.org/10.1364/AO.25.002184 APOPAI 0003-6935 Google Scholar
S. A. Collins Jr.,
“Lens-system diffraction integral written in terms of matrix optics,”
J. Opt. Soc. Am., 60
(9), 1168
–1177
(1970). http://dx.doi.org/10.1364/JOSA.60.001168 JOSAAH 0030-3941 Google Scholar
S. WangD. Zhao, Matrix Optics, CHEP-Springer, Beijing
(2000). Google Scholar
A. ErdelyiW. MagnusF. Oberhettinger, Tables of Integral Transforms, McGraw-Hill, New York
(1954). Google Scholar
BiographyXun Wang received her MS degree from the Department of Physics in Dalian University of Technology, Dalian, China. She is currently an associate professor in the Department of Applied Physics at East China Jiaotong University, Nanchang, China. Her current research interests include optical wave propagation and transformation, physical optics, and information optics. Zhirong Liu received his PhD degree from the Department of Physics in Zhejiang University, Hangzhou, China. He is currently a lecturer in the Department of Applied Physics at East China Jiaotong University, Nanchang, China. His current research interests include optical physics, optical confinement and manipulation, and wave propagation and scattering. |