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  • Editor: Alan E. Willner
  • Vol. 37, Iss. 21 — Nov. 1, 2012
  • pp: 4446–4448
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Surface-plasmon enhanced optical activity in two-dimensional metal chiral networks

Kuniaki Konishi, Benfeng Bai, Yoshihiro Toya, Jari Turunen, Yuri P. Svirko, and Makoto Kuwata-Gonokami  »View Author Affiliations


Optics Letters, Vol. 37, Issue 21, pp. 4446-4448 (2012)
http://dx.doi.org/10.1364/OL.37.004446


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Abstract

We investigated the optical properties of a novel chiral metamaterial; two-dimensional metal chiral networks formed from metal ribbons deposited on a dielectric substrate. For zeroth-order transmitted light, sharp optical resonances were observed at spectral positions, which are determined by the surface plasmon resonance frequencies of the periodic metal structures. The experimental results are in excellent agreement with numerical calculations.

© 2012 Optical Society of America

Chiral media, which can exist in nature in two mirror-superimposable forms (e.g., left- and right-handed quartz crystals), are optically active; i.e., they can rotate the polarization plane of a propagating light wave clockwise or counterclockwise depending on the sense of chirality. In solids, optical activity is scaled as a/λ [1

1. L. Barron, Molecular Light Scattering and Optical Activity, 2nd ed. (Cambridge, 2004).

], where a is the crystal lattice parameter and λ is the light wavelength, and thus the effect is usually very weak. However, recent advances in nanotechnology have facilitated creation of artificial chiral structures that are often referred to as chiral metamaterials exhibiting a significant optical rotatory power [2

2. T. Vallius, K. Jefimovs, J. Turunen, P. Vahimaa, and Y. Svirko, Appl. Phys. Lett. 83, 234 (2003). [CrossRef]

13

13. M. Thiel, M. S. Rill, G. von Frymann, and M. Wegener, Adv. Mater. 21, 4680 (2009). [CrossRef]

]. In particular, chiral metamaterials possessing a strong optical activity open unique opportunities for a negative refraction [14

14. J. B. Pendry, Science 306, 1353 (2004). [CrossRef]

17

17. J. Zhou, J. Dong, B. Wang, T. Koschny, M. Kafesaki, and C. M. Soukoulis, Phys. Rev. B 79, 121104(R) (2009). [CrossRef]

], angular momentum conversion [18

18. Y. Gorodetski, N. Shitrit, I. Bretner, V. Kleiner, and E. Hasman, Nano Lett. 9, 3016 (2009). [CrossRef]

], and active polarization control, such as a terahertz polarization modulator [19

19. N. Kanda, K. Konishi, and M. Kuwata-Gonokami, Opt. Lett. 34, 3000 (2009). [CrossRef]

,20

20. J. Zhou, D. R. Chowdhury, R. Zhao, A. K. Azad, H.-T. Chen, C. M. Soukoulis, A. J. Taylor, and J. F. O’Hara, Phys. Rev. B 86, 035448 (2012).

] and an emitter of circularly polarized light [21

21. K. Konishi, M. Nomura, N. Kumagai, S. Iwamoto, Y. Arakawa, and M. Kuwata-Gonokami, Phys. Rev. Lett. 106, 057402 (2011). [CrossRef]

].

In order to design chiral metamaterials with enhanced rotatory power, it is important to identify the wavelength at which strong optical activity is observed. Planar chiral metamaterials usually consist of arrayed nanoentities, such as rosettes [2

2. T. Vallius, K. Jefimovs, J. Turunen, P. Vahimaa, and Y. Svirko, Appl. Phys. Lett. 83, 234 (2003). [CrossRef]

7

7. N. Kanda, K. Konishi, and M. Kuwata-Gonokami, Opt. Express 15, 11117 (2007). [CrossRef]

,16

16. E. Plum, J. Zhou, J. Dong, V. A. Fedotov, T. Koschny, C. M. Soukoulis, and N. I. Zheludev, Phys. Rev. B 79, 035407 (2009). [CrossRef]

], crosses [8

8. M. Decker, M. Ruther, C. E. Kriegler, J. Zhou, C. M. Soukoulis, S. Linden, and M. Wegener, Opt. Lett. 34, 2501 (2009). [CrossRef]

,17

17. J. Zhou, J. Dong, B. Wang, T. Koschny, M. Kafesaki, and C. M. Soukoulis, Phys. Rev. B 79, 121104(R) (2009). [CrossRef]

], and U-shapes [10

10. M. Decker, R. Zhao, C. M. Soukoulis, S. Linden, and M. Wegener, Opt. Lett. 35, 1593 (2010). [CrossRef]

] that are isolated from one another. In these structures the resonant enhancement of the optical response is associated with localized Mie-type resonances of an individual nanoentity and the coupling between them. Because the shape of the individual nanoentities in chiral metamaterials is usually complicated, the analysis of their optical properties and identification of the resonances requires numerical calculations [4

4. A. V. Rogacheva, V. A. Fedotov, A. S. Schwanecke, and N. I. Zheludev, Phys. Rev. Lett. 97, 177401 (2006). [CrossRef]

10

10. M. Decker, R. Zhao, C. M. Soukoulis, S. Linden, and M. Wegener, Opt. Lett. 35, 1593 (2010). [CrossRef]

,17

17. J. Zhou, J. Dong, B. Wang, T. Koschny, M. Kafesaki, and C. M. Soukoulis, Phys. Rev. B 79, 121104(R) (2009). [CrossRef]

].

In periodic arrays of metal nanoparticles, propagating surface plasmon modes supported by interparticle coupling play an important role in determining the optical properties. Previously, by studying the dependence of resonance effects on the incident angle, we demonstrated the enhancement of optical activity using surface plasmon modes supported by interparticle coupling in two-dimensional (2D) arrays of chiral gammadion nanoparticles [22

22. K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 15, 9575 (2007). [CrossRef]

]. Moreover, we demonstrated that the propagating surface modes significantly enhance the optical activity in metallic and dielectric chiral structures [12

12. K. Konishi, B. Bai, X. Meng, P. Karvinen, J. Turunen, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 16, 7189 (2008). [CrossRef]

,22

22. K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 15, 9575 (2007). [CrossRef]

24

24. B. Bai, J. Laukkanen, A. Lehmuskero, and J. Turunen, Phys. Rev. B 81, 115424 (2010). [CrossRef]

]. In these cases, the observed resonances are well matched to the resonances predicted by the empty-lattice approximation [25

25. H. F. Ghaemi, T. Thio, D. E. Grupp, T. W. Ebbesen, and H. J. Lezec, Phys. Rev. B 58, 6779 (1998). [CrossRef]

,26

26. T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, Nature 391, 667 (1998). [CrossRef]

]. However, the relation between periodicity of chiral structure and the optical activity resonance still remains unclear.

The simplest structure that can support this type of propagating surface plasmon mode is a metal ribbon. Correspondingly, a planar structure consisting of metallic ribbons deformed in a chiral manner offers a new design concept for chiral metamaterials. In addition, the investigation of optical properties of planar chiral networks is also of fundamental importance. This is because the domination of propagation modes allows the description of the optical properties of a chiral network by drawing an analogy with the nearly free electron model in solid state physics. Thus, chiral networks emerge as counterparts of the planar arrays of chiral nanoentities with optical properties that can be described in the tight-binding model framework.

In this Letter we investigate the phenomenon of optical activity in planar, chiral metal networks. By measuring the dependence of the polarization state of the transmitted light on the periodicity of the structures at normal incidence, it was confirmed experimentally that the enhanced polarization rotation occurs at the wavelength of the surface plasmon resonance predicted by the empty-lattice approximation.

Figure 1 shows the fabricated chiral structures with a left and right sense of twist, designed to possess a fourfold rotational symmetry axis along the substrate normal. These samples were fabricated using electron beam lithography and reactive ion-etching processes. The metal film on a fused silica substrate consists of a 2 nm thin titanium adhesion layer and a 23 nm thick gold layer. A 10 nm thick over etching layer is under the titanium layer. The structures were manufactured with periods of 600 and 800 nm to investigate the dependence of the spectra on periodicity.

Fig. 1. Scanning electron microscope images of the metal chiral nanostructures. Gray areas correspond to the gold thin film. (a) Left twisted, 600 nm period; (b) right twisted, 600 nm period; (c) left twisted, 800 nm period; and (d) right twisted, 800 nm period.

Measurements were performed using polarization modulation with a tungsten lamp as the light source, as described in [22

22. K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 15, 9575 (2007). [CrossRef]

]. The transmission, polarization rotation, and ellipticity spectra were measured at normal incidence for zeroth-order transmitted light.

Nonideal focusing of the electron beam resulted in a slight nonequivalence of the X and Y axes of the manufactured nanostructures. In order to distinguish between the polarization effects originating from the chirality and the linear birefringence originating from the imperfection of the manufacturing process, measurements were performed at several inplane angles by rotating the sample [22

22. K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 15, 9575 (2007). [CrossRef]

]. At normal incidence, the polarization rotation Δ and the ellipticity H of the transmitted beam, as a function of the sample azimuth angle φ, can be described by [2

2. T. Vallius, K. Jefimovs, J. Turunen, P. Vahimaa, and Y. Svirko, Appl. Phys. Lett. 83, 234 (2003). [CrossRef]

,3

3. M. Kuwata-Gonokami, N. Saito, Y. Ino, M. Kauranen, K. Jefimovs, T. Vallius, J. Turunen, and Y. Svirko, Phys. Rev. Lett. 95, 227401 (2005). [CrossRef]

]:
(ΔH)=(θη)+(AB)sin(2φ+C),
(1)
where θ and η originate from the chirality and are measures of the circular birefringence and circular dichroism of the nanostructure, respectively. A and B originate from the nonequivalence of the X and Y axes, and are measures of the linear birefringence and dichroism, respectively [22

22. K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 15, 9575 (2007). [CrossRef]

].

Fig. 2. (a),(e) Transmission, (b),(f) polarization azimuth rotation θ, and (c),(g) ellipticity η spectra for metal chiral structures with a 600 nm period (a)–(c) and a 800 nm period (e)–(g). The red and blue lines refer to the results obtained with the left- and right-twisted gammadions, respectively. (d) Polarization rotation spectrum with the opposite incidence to the left-twisted sample with a 600 nm period (see the text). In the top of the both graphs, the black thin lines correspond to the value of the left-hand side of Eq. (2), N=mx2+my2. The blue and red thin lines are the dispersion-relation curves for the air–metal and metal–substrate interfaces, respectively, which correspond to the value of the right-hand side of Eq. (2). The circles indicate the wavelengths of the surface plasmon resonance.

In the framework of the empty-lattice approximation, the surface-plasmon resonance condition of a metal thin film with periodic structures is given by
λmx2+my2=Lεdεmεd+εm,
(2)
where εm and εd are the permittivities of the metal and the dielectric (air or substrate), respectively. λ is the wavelength of the incident light, L is the period of the structure, and mx and my are integers that define the diffraction orders for the 2D periodic structure [22

22. K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 15, 9575 (2007). [CrossRef]

]. The wavelengths of the surface plasmon resonance of the chiral structures with periods of 600 and 800 nm are indicated by circles in the dispersion curves presented in the top of Figs. 2(a) and 2(e), respectively. One can observe that the enhanced polarization rotation takes place at the wavelength of the surface plasmon resonance. Thus, in contrast to the chiral nanoparticles arrays [4

4. A. V. Rogacheva, V. A. Fedotov, A. S. Schwanecke, and N. I. Zheludev, Phys. Rev. Lett. 97, 177401 (2006). [CrossRef]

10

10. M. Decker, R. Zhao, C. M. Soukoulis, S. Linden, and M. Wegener, Opt. Lett. 35, 1593 (2010). [CrossRef]

,17

17. J. Zhou, J. Dong, B. Wang, T. Koschny, M. Kafesaki, and C. M. Soukoulis, Phys. Rev. B 79, 121104(R) (2009). [CrossRef]

], the optical activity resonance in planar chiral networks, which consist of coupled metallic ribbons and support propagating surface plasmon modes, is determined by the period rather than geometry of the structure. It indicates that the tuning of the optical activity resonance by only changing the periodicity in the case of such chiral network structures.

The wavelength dependencies of the refractive indices of gold and titanium were obtained from ellipsometry measurements. It can be seen in Fig. 3 that the calculated transmission and polarization spectra at normal incidence reproduce the measured spectra presented in Fig. 2, both qualitatively and quantitatively. Such a correspondence between the calculated and measured spectra becomes possible due to the drastic improvement (in comparison with [3

3. M. Kuwata-Gonokami, N. Saito, Y. Ino, M. Kauranen, K. Jefimovs, T. Vallius, J. Turunen, and Y. Svirko, Phys. Rev. Lett. 95, 227401 (2005). [CrossRef]

]) of the fabrication quality.

Fig. 3. Calculated transmission, polarization rotation (θ), and ellipticity (η) spectra of the left-twisted samples with a period of 600 nm at normal incidence. The experimental data are also shown for comparison.

In conclusion, we have fabricated and characterized chiral metal networks composed of metal ribbons. We clearly observed, using samples with different periods at normal incidence, the optical activity of these chiral structures and demonstrated that resonant enhancement of the optical activity is associated with the surface plasmon resonance. A numerical simulation of the polarization effect reproduced the results of the experiment satisfactorily. The relative simplicity of the structures and the strong polarization effect observed open new prospects for the design of novel polarization modulation devices.

We are grateful to NTT-AT Corporation for the sample preparation. This research was supported by the Photon Frontier Network Program, KAKENHI (20104002), funding program for World-Leading Innovative R&D on Science and Technology (FIRST Program), the Special Coordination Funds for Promoting Science and Technology of the Ministry of Education, Culture, Sports, Science and Technology, Japan, the Academy of Finland (grant no. 134888), and the National Natural Science Foundation of China (11004119).

References

1.

L. Barron, Molecular Light Scattering and Optical Activity, 2nd ed. (Cambridge, 2004).

2.

T. Vallius, K. Jefimovs, J. Turunen, P. Vahimaa, and Y. Svirko, Appl. Phys. Lett. 83, 234 (2003). [CrossRef]

3.

M. Kuwata-Gonokami, N. Saito, Y. Ino, M. Kauranen, K. Jefimovs, T. Vallius, J. Turunen, and Y. Svirko, Phys. Rev. Lett. 95, 227401 (2005). [CrossRef]

4.

A. V. Rogacheva, V. A. Fedotov, A. S. Schwanecke, and N. I. Zheludev, Phys. Rev. Lett. 97, 177401 (2006). [CrossRef]

5.

E. Plum, V. A. Fedotov, A. S. Schwanecke, N. I. Zheludev, and Y. Chen, Appl. Phys. Lett. 90, 223113 (2007). [CrossRef]

6.

M. Decker, M. W. Klein, M. Wegener, and S. Linden, Opt. Lett. 32, 856 (2007). [CrossRef]

7.

N. Kanda, K. Konishi, and M. Kuwata-Gonokami, Opt. Express 15, 11117 (2007). [CrossRef]

8.

M. Decker, M. Ruther, C. E. Kriegler, J. Zhou, C. M. Soukoulis, S. Linden, and M. Wegener, Opt. Lett. 34, 2501 (2009). [CrossRef]

9.

J. K. Gansel, M. Thiel, M. S. Rill, M. Decker, K. Bade, V. Saile, G. von Freymann, S. Linden, and M. Wegener, Science 325, 1513 (2009). [CrossRef]

10.

M. Decker, R. Zhao, C. M. Soukoulis, S. Linden, and M. Wegener, Opt. Lett. 35, 1593 (2010). [CrossRef]

11.

M. Thiel, G. von Frymann, and M. Wegener, Opt. Lett. 32, 2547 (2007). [CrossRef]

12.

K. Konishi, B. Bai, X. Meng, P. Karvinen, J. Turunen, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 16, 7189 (2008). [CrossRef]

13.

M. Thiel, M. S. Rill, G. von Frymann, and M. Wegener, Adv. Mater. 21, 4680 (2009). [CrossRef]

14.

J. B. Pendry, Science 306, 1353 (2004). [CrossRef]

15.

S. Zhang, Y.-S. Park, J. Li, X. Lu, W. Zhang, and X. Zhang, Phys. Rev. Lett. 102, 023901 (2009). [CrossRef]

16.

E. Plum, J. Zhou, J. Dong, V. A. Fedotov, T. Koschny, C. M. Soukoulis, and N. I. Zheludev, Phys. Rev. B 79, 035407 (2009). [CrossRef]

17.

J. Zhou, J. Dong, B. Wang, T. Koschny, M. Kafesaki, and C. M. Soukoulis, Phys. Rev. B 79, 121104(R) (2009). [CrossRef]

18.

Y. Gorodetski, N. Shitrit, I. Bretner, V. Kleiner, and E. Hasman, Nano Lett. 9, 3016 (2009). [CrossRef]

19.

N. Kanda, K. Konishi, and M. Kuwata-Gonokami, Opt. Lett. 34, 3000 (2009). [CrossRef]

20.

J. Zhou, D. R. Chowdhury, R. Zhao, A. K. Azad, H.-T. Chen, C. M. Soukoulis, A. J. Taylor, and J. F. O’Hara, Phys. Rev. B 86, 035448 (2012).

21.

K. Konishi, M. Nomura, N. Kumagai, S. Iwamoto, Y. Arakawa, and M. Kuwata-Gonokami, Phys. Rev. Lett. 106, 057402 (2011). [CrossRef]

22.

K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 15, 9575 (2007). [CrossRef]

23.

B. Bai, Y. Svirko, J. Turunen, and T. Vallius, Phys. Rev. A 76, 023811 (2007). [CrossRef]

24.

B. Bai, J. Laukkanen, A. Lehmuskero, and J. Turunen, Phys. Rev. B 81, 115424 (2010). [CrossRef]

25.

H. F. Ghaemi, T. Thio, D. E. Grupp, T. W. Ebbesen, and H. J. Lezec, Phys. Rev. B 58, 6779 (1998). [CrossRef]

26.

T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, Nature 391, 667 (1998). [CrossRef]

27.

B. Bai and L. Li, J. Opt. A 7, 783 (2005). [CrossRef]

OCIS Codes
(240.6680) Optics at surfaces : Surface plasmons
(240.5440) Optics at surfaces : Polarization-selective devices

ToC Category:
Optics at Surfaces

History
Original Manuscript: July 3, 2012
Revised Manuscript: August 30, 2012
Manuscript Accepted: September 17, 2012
Published: October 23, 2012

Citation
Kuniaki Konishi, Benfeng Bai, Yoshihiro Toya, Jari Turunen, Yuri P. Svirko, and Makoto Kuwata-Gonokami, "Surface-plasmon enhanced optical activity in two-dimensional metal chiral networks," Opt. Lett. 37, 4446-4448 (2012)
http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-37-21-4446


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References

  1. L. Barron, Molecular Light Scattering and Optical Activity, 2nd ed. (Cambridge, 2004).
  2. T. Vallius, K. Jefimovs, J. Turunen, P. Vahimaa, and Y. Svirko, Appl. Phys. Lett. 83, 234 (2003). [CrossRef]
  3. M. Kuwata-Gonokami, N. Saito, Y. Ino, M. Kauranen, K. Jefimovs, T. Vallius, J. Turunen, and Y. Svirko, Phys. Rev. Lett. 95, 227401 (2005). [CrossRef]
  4. A. V. Rogacheva, V. A. Fedotov, A. S. Schwanecke, and N. I. Zheludev, Phys. Rev. Lett. 97, 177401 (2006). [CrossRef]
  5. E. Plum, V. A. Fedotov, A. S. Schwanecke, N. I. Zheludev, and Y. Chen, Appl. Phys. Lett. 90, 223113 (2007). [CrossRef]
  6. M. Decker, M. W. Klein, M. Wegener, and S. Linden, Opt. Lett. 32, 856 (2007). [CrossRef]
  7. N. Kanda, K. Konishi, and M. Kuwata-Gonokami, Opt. Express 15, 11117 (2007). [CrossRef]
  8. M. Decker, M. Ruther, C. E. Kriegler, J. Zhou, C. M. Soukoulis, S. Linden, and M. Wegener, Opt. Lett. 34, 2501 (2009). [CrossRef]
  9. J. K. Gansel, M. Thiel, M. S. Rill, M. Decker, K. Bade, V. Saile, G. von Freymann, S. Linden, and M. Wegener, Science 325, 1513 (2009). [CrossRef]
  10. M. Decker, R. Zhao, C. M. Soukoulis, S. Linden, and M. Wegener, Opt. Lett. 35, 1593 (2010). [CrossRef]
  11. M. Thiel, G. von Frymann, and M. Wegener, Opt. Lett. 32, 2547 (2007). [CrossRef]
  12. K. Konishi, B. Bai, X. Meng, P. Karvinen, J. Turunen, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 16, 7189 (2008). [CrossRef]
  13. M. Thiel, M. S. Rill, G. von Frymann, and M. Wegener, Adv. Mater. 21, 4680 (2009). [CrossRef]
  14. J. B. Pendry, Science 306, 1353 (2004). [CrossRef]
  15. S. Zhang, Y.-S. Park, J. Li, X. Lu, W. Zhang, and X. Zhang, Phys. Rev. Lett. 102, 023901 (2009). [CrossRef]
  16. E. Plum, J. Zhou, J. Dong, V. A. Fedotov, T. Koschny, C. M. Soukoulis, and N. I. Zheludev, Phys. Rev. B 79, 035407 (2009). [CrossRef]
  17. J. Zhou, J. Dong, B. Wang, T. Koschny, M. Kafesaki, and C. M. Soukoulis, Phys. Rev. B 79, 121104(R) (2009). [CrossRef]
  18. Y. Gorodetski, N. Shitrit, I. Bretner, V. Kleiner, and E. Hasman, Nano Lett. 9, 3016 (2009). [CrossRef]
  19. N. Kanda, K. Konishi, and M. Kuwata-Gonokami, Opt. Lett. 34, 3000 (2009). [CrossRef]
  20. J. Zhou, D. R. Chowdhury, R. Zhao, A. K. Azad, H.-T. Chen, C. M. Soukoulis, A. J. Taylor, and J. F. O’Hara, Phys. Rev. B 86, 035448 (2012).
  21. K. Konishi, M. Nomura, N. Kumagai, S. Iwamoto, Y. Arakawa, and M. Kuwata-Gonokami, Phys. Rev. Lett. 106, 057402 (2011). [CrossRef]
  22. K. Konishi, T. Sugimoto, B. Bai, Y. Svirko, and M. Kuwata-Gonokami, Opt. Express 15, 9575 (2007). [CrossRef]
  23. B. Bai, Y. Svirko, J. Turunen, and T. Vallius, Phys. Rev. A 76, 023811 (2007). [CrossRef]
  24. B. Bai, J. Laukkanen, A. Lehmuskero, and J. Turunen, Phys. Rev. B 81, 115424 (2010). [CrossRef]
  25. H. F. Ghaemi, T. Thio, D. E. Grupp, T. W. Ebbesen, and H. J. Lezec, Phys. Rev. B 58, 6779 (1998). [CrossRef]
  26. T. W. Ebbesen, H. J. Lezec, H. F. Ghaemi, T. Thio, and P. A. Wolff, Nature 391, 667 (1998). [CrossRef]
  27. B. Bai and L. Li, J. Opt. A 7, 783 (2005). [CrossRef]

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