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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 22 — Oct. 25, 2010
  • pp: 22826–22832
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Generalized Stokes parameters of three-dimensional stochastic electromagnetic beams

Zhangrong Mei  »View Author Affiliations


Optics Express, Vol. 18, Issue 22, pp. 22826-22832 (2010)
http://dx.doi.org/10.1364/OE.18.022826


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Abstract

The generalized Stokes parameters of 2D stochastic electromagnetic beams are developed to the 3D case, which can be addressed as certain linear combinations of the 3 × 3 cross-spectral density matrix in terms of the nine Gell-Mann matrices. Using the electromagnetic Gaussian Shell-model source as an example, we investigate their precise propagation laws of coherence properties and polarization properties with the help of the 3D generalized Stokes parameters. Some numerical examples and detailed comparisons of the obtained results with the 2D case are made. It is shown that 3D generalized Stokes parameters are required for the exact description of stochastic electromagnetic beams.

© 2010 OSA

1. Introduction

Most measure of the degree of coherence of light field was introduced within a scalar representation [1

1. F. Zernike, “The concept of degree of coherence and its application to optical problems,” Physica (Utrecht) 5(8), 785–795 (1938). [CrossRef]

]. The definition of the degree of coherence was later refined and generalized in several ways [2

2. L. Mandel and E. Wolf, “Spectral coherence and concept of cross-spectral purity,” J. Opt. Soc. Am. 66(6), 529 (1976). [CrossRef]

4

4. A. Luis, “Degree of coherence for vectorial electromagnetic fields as the distance between correlation matrices,” J. Opt. Soc. Am. A 24(4), 1063–1068 (2007). [CrossRef]

]. The polarization properties of electromagnetic beams are important in a great variety of optical phenomena. Normally, the polarization statistics of electromagnetic beams at a point in space are described either by use of the coherent matrix or the two-dimensional (2D) Stokes parameters [5

5. C. Brosseau, Fundamentals of Polarized Light: A Statistical Optics Approach (Wiley, New York, 1998).

]. Recently, a general theory was presented by Wolf, known as the unified theory of coherence and polarization or the cross-spectral density matrix, made it possible to characterize the correlations between two mutually orthogonal spectral components of electric field at a pair of points in a plane perpendicular to the axis of the beam [6

6. E. Wolf, “Correlation-induced changes in the degree of polarization, the degree of coherence, and the spectrum of random electromagnetic beams on propagation,” Opt. Lett. 28(13), 1078–1080 (2003). [CrossRef] [PubMed]

]. The Stokes parameters were also generalized from one-point quantities to two-point counterparts [7

7. O. Korotkova and E. Wolf, “Generalized stokes parameters of random electromagnetic beams,” Opt. Lett. 30(2), 198–200 (2005). [CrossRef] [PubMed]

]. The 2D generalized Stokes parameters can be expressed in terms of the 2×2 cross-spectral density matrix of the field and can be also used to study both the coherent properties and the polarization properties of random electromagnetic beams. However, the 2D formulism is not adequate for the description of the statistics properties of arbitrary electromagnetic beams, such as the nonparaxial random electromagnetic beams, since three orthogonal components of vectorial field are present [8

8. T. Setälä, M. Kaivola, and A. T. Friberg, “Degree of polarization in near fields of thermal sources: effects of surface waves,” Phys. Rev. Lett. 88(12), 123902 (2002). [CrossRef] [PubMed]

10

10. T. Setälä, K. Lindfors, and A. T. Friberg, “Degree of polarization in 3D optical fields generated from a partially polarized plane wave,” Opt. Lett. 34(21), 3394–3396 (2009). [CrossRef] [PubMed]

]. Consequently, the degree of coherence and the degree of polarization of the three-dimensional (3D) random electromagnetic beams must be extracted directly from the 3 × 3 cross-spectral density matrix of the field or from the 3D generalized Stokes parameters. In this Letter, we expand the 2D generalized Stokes parameters to the 3D case and investigate the statistics properties of 3D stochastic electromagnetic beams.

2. Theoretical analyses

The 2D generalized Stokes parameters can be expressed in terms of the 2 × 2 cross-spectral density matrix W2D(r1,r2,ω) of the field and the four Pauli matrices σi(i=0,1,2,3)in a simple manner as follows
Si,2D(r1,r2,ω)=tr[W2D(r1,r2,ω)σi],
(1)
where W2D(r1,r2,ω)=[<Eα*(r1,ω)Eβ(r2,ω)>],   (α,β=x,y), tr stands for trace. The 2D generalized Stokes parameters can be expanded in the linear combination of the four elements of the 2 × 2 cross-spectral density matrix [8

8. T. Setälä, M. Kaivola, and A. T. Friberg, “Degree of polarization in near fields of thermal sources: effects of surface waves,” Phys. Rev. Lett. 88(12), 123902 (2002). [CrossRef] [PubMed]

].

In analogy with the 2D case, the 3D generalized Stokes parameters in terms of 3 × 3 cross-spectral density matrix W3D(r1,r2,ω) of the field and the nine Gell-Mann matrices λj(j = 0,1,…,8) [12

12. X. Du, D. Zhao, and O. Korotkova, “Changes in the statistical properties of stochastic anisotropic electromagnetic beams on propagation in the turbulent atmosphere,” Opt. Express 15(25), 16909–16915 (2007). [CrossRef] [PubMed]

] can be expressed to the following form
Sj,3D(r1,r2,ω)=tr[W3D(r1,r2,ω)λj],
(2)
where W3D(r1,r2,ω)=[<Eα*(r1,ω)Eβ(r2,ω)>],   (α,β=x,y,z), which satisfy the relation Wαβ*(r1,r2,ω)=Wβα(r1,r2,ω). The above relation (2) can be expanded in the form
S0,3D(r1,r2,ω)=Wxx,3D(r1,r2,ω)+Wyy,3D(r1,r2,ω)+Wzz,3D(r1,r2,ω),
(3a)
S1,3D(r1,r2,ω)=Wxy,3D(r1,r2,ω)+Wyx,3D(r1,r2,ω),
(3b)
S2,3D(r1,r2,ω)=i[Wyx,3D(r1,r2,ω)Wxy,3D(r1,r2,ω)],
(3c)
S3,3D(r1,r2,ω)=Wxx,3D(r1,r2,ω)Wyy,3D(r1,r2,ω),
(3d)
S4,3D(r1,r2,ω)=Wxz,3D(r1,r2,ω)+Wzx,3D(r1,r2,ω),
(3e)
S5,3D(r1,r2,ω)=i[Wxz,3D(r1,r2,ω)Wzx,3D(r1,r2,ω)],
(3f)
S6,3D(r1,r2,ω)=Wyz,3D(r1,r2,ω)+Wzy,3D(r1,r2,ω),
(3g)
S7,3D(r1,r2,ω)=i[Wyz,3D(r1,r2,ω)Wzy,3D(r1,r2,ω)],
(3h)
S8,3D(r1,r2,ω)=3[Wxx,3D(r1,r2,ω)+Wyy,3D(r1,r2,ω)2Wzz,3D(r1,r2,ω)]/3.
(3i)
The above definitions of 3D generalized Stokes parameters conveniently lead to the S 0,3D(r, ω)being equal to the spectral density of the field, the spectral degree of coherence of the field at a pair of point being given by the formula

μ3D(r1,r2,ω)=S0,3D(r1,r2,ω)/(S0,3D(r1,r1,ω)S0,3D(r2,r2,ω)).
(4)

The spectral degree of polarization at point r and frequency ω, P3D(r,ω), of the random electromagnetic beams that has three vector components can written in terms of the 3D generalized Stokes parameters as [11

11. A. Luis, “Polarization distribution and degree of polarization for three-dimensional quantum light fields,” Phys. Rev. A 71(6), 063815 (2005). [CrossRef]

]

P3D(r,ω)=32(j=18Sj,3D2(r,ω))1/2/S0,3D(r,ω).
(5)

Let us now consider an electromagnetic Gaussian Shell-model source, the elements of its cross-spectral density matrix in the source plane are given by the expressions [12

12. X. Du, D. Zhao, and O. Korotkova, “Changes in the statistical properties of stochastic anisotropic electromagnetic beams on propagation in the turbulent atmosphere,” Opt. Express 15(25), 16909–16915 (2007). [CrossRef] [PubMed]

]
Wαβ(0)(ρ10,ρ20,ω)=AαAβBαβexp(ρ1024σα2)exp(ρ2024σβ2)exp(|ρ20ρ10|22δαβ2),
(6)
where the coefficients Aα,Aβ,Bαβ and the variances σα2,σβ2,δαβ2 are independent of position but may depend on frequency, the transverse vector ρ(x,y).

The propagation of each of the elements of the cross-spectral density matrix of the electric field at a pair of points r1 and r2 (the position vector specifies by r(ρ,z)) in the half space z>0 can be treated by the generalized Rayleigh-Sommerfeld formulas [13

13. K. Duan and B. Lü, “Partially coherent vectorial nonparaxial beams,” J. Opt. Soc. Am. A 21(10), 1924–1932 (2004). [CrossRef]

]:

Wαβ(r1,r2,ω)=(zλ)2Wαβ(0)(ρ10,ρ20,ω){exp[ik(R2R1)]}/R22R12d2ρ10d2ρ20,   (α,β=x,y),
(7a)
Wαz(r1,r2,ω)=zλ2[Wαx(0)(ρ10,ρ20,ω)(x2x20)+Wαy(0)(ρ10,ρ20,ω)(y2y20)]                        ×{exp[ik(R2R1)]}/R22R12d2ρ10d2ρ20                (α=x,y),
(7b)
Wzz(r1,r2,ω)=1λ2[Wxx(0)(ρ10,ρ20,0)(x1x10)(x2x20)+2Wxy(0)(ρ10,ρ20,0)(x1x10)             ×(y2y20)+Wyy(0)(ρ10,ρ20,0)(y1y10)(y2y20)]{exp[ik(R2R1)]}/R22R12d2ρ10d2ρ20.
(7c)

On substituting from Eq. (6) into Eq. (7), we obtain the elements of the cross-spectral density matrix of a stochastic electromagnetic beam in the output plane as follows:
Wαβ(r1,r,2ω)=AαAβBαβz2{exp[ik(r2r1)]/r12r22}exp(Fαβ)/Pαβ,         (α,β=x,y),
(8a)
Wαz(r1,r,2ω)=Aαzexp[ik(r2r1)]r12r22{AxBαxJαxPαxexp(Fαx)AyBαyJαyPαyexp(Fαy)}                             (α=x,y),
(8b)
Wzz(r1,r,2ω)=exp[ik(r2r1)]/(r12r22){Ax2Qxxexp(Fxx)/Pxx +Ay2Qyyexp(Fyy)/Pyy                        +AxAy(Bxy+Bxy)Qxyexp(Fxy)/Pxy},
(8c)
where
Fαβ=k[C1αβρ22/r22+C2αβρ12/r12kfαβ2(x1x2+y1y2)/(r1r2)]/Pαβ,
(8d)
Qxy=(1i/(2C1xyr))x1y2+ikfxy2y2Gxy(x)/Pxy+Hxy(x)Gxy(y)2kfxy2C1xyGxy(x)Gxy(y)/Pxy2,
(8e)
Qαα=(1i2C1ααr1)α1α2(ifαα2kα2Pαα+Hαα(α))Gαα(α)2C1ααkfαα2Pαα2(Gαα(α))2+fαα2Pαα,
(8f)
and fj=1/(kσα),fαβ=1/(kδαβ), Cjαβ=kfαβ2/2+kfj2/4i(1)j/(2rj),  (j=1,2), Pαβ=4C1αβC2αβk2fαβ4,Hαβ(γ)=2iC1αβγ1/Pαβ+γ1/(Pαβr1),Jαγ=2iC1αγGαγ(γ)/Pαx+γ2,Gαβ(γ)=γ2/r2kfαβ2γ1/(2C1αβr1), (γ=x,y).

On substituting from Eq. (8) into Eq. (3), the nine generalized Stokes parameters of a stochastic electromagnetic beam can be obtained as linear combinations of the nine elements of the 3 × 3 cross-spectral density matrix, then can be used to study both the coherence properties and the polarization properties of the 3D stochastic electromagnetic beams.

3. Numerical calculation results and comparative analyses

We apply the preceding analysis to illustrate how the statistical properties of the 3D stochastic electromagnetic beams change upon propagation in free space and compare the results with that of the 2D case. In the following figures, we use the wavelength λ and Rayleigh distance specified by zR = πσ 2/λ to normalize the corresponding transverse and longitudinal distances. Figure 1
Fig. 1 The spectral density of a stochastic electromagnetic beam in the plane z = 15zR, The source is assumed to be a Gaussian Shell-model source with Ax = 1.5, Ay = 1, Bxy = 0.3exp(/6), Byx = 0.3exp(-/6), (a) f 1 = f 2 = 0.005, fxx = fyy = fxy = fyx = 0.015, (b) f 1 = f 2 = 0.2, fxx = fyy = fxy = fyx = 0.45.
is the spectral density of a 3D stochastic electromagnetic beam in the plane z = 15zR for different parameters fj and fαβ value. For the convenience of comparison the corresponding 2D results are also given in the figures, which are represented by the dashed lines. One can see from Fig. 1 that when the value of parameters fj and fαβ is very small, the spectral density of 3D beams coincide with the 2D results quite well, so that for this case the 2D results hold true and the z component is very small and can be negligible. However, for the large values of parameters fj and fαβ, the difference between the 3D results and 2D results become obvious, the longitudinal component also become large and cannot be neglected. Figure 2
Fig. 2 The contour graphs of the spectral densityof a stochastic electromagnetic beam in the plane z = 15zR. The source parameters are the same as in Fig. 1(b). (a) S 0, 2D, (b) S 0, 3D.
is the contour graphs of the spectral density S 0,2D and S 0,3D of a stochastic electromagnetic beam in the plane z = 15zR when the value of parameters fj and fαβ is larger. From Fig. 2(a), we can see when the results were considered 2D case, the spectral density distribution S 0,2D is axially rotational symmetry. However, when we consider 3D field distribution, shown as Fig. 2(b), the spectral density distribution S 0,3D loses their circular symmetry and become inclined elliptical symmetry due to the existence of the longitudinal component.

Figure 3
Fig. 3 The changes in the spectral degree of coherence along z-axis direction of a stochastic electromagnetic Gaussian Schell-model beam. The source parameters are the same as in Fig. 1 except for fxy = 0.6fxx. Pairs of field pointρ2=ρ1=(0.2mm, 0.2mm).
represents the changes in the spectral degree of coherence along z-axis direction of a stochastic electromagnetic Gaussian Schell-model beam when the pair of field points are located symmetrically with respect to the z-axis, i. e. ρ2 = -ρ1. The 3D results of spectral degree of coherence coincide with the 2D results quite well for the small values of parameters fj and fαβ, so that for this case the 2D results hold true. Whereas for the large values of parameters fj and fαβ, the initial spectral degrees of coherence exist obvious difference, but both of the 2D and 3D results tend to 1 with increasing propagation distance.

For vividly comparing the difference of P 2D and P 3D, three-dimensional distributions of spectral degree of polarization and corresponding contour graphs of 2D and 3D stochastic electromagnetic beams in the plane z = 15zR are plotted in Figs. 5
Fig. 5 There-dimensional distributions of spectral degree of polarization P 2D and corresponding contour graphs of a stochastic electromagnetic beam in the plane z = 15zR. fxy = 0.6fxx and the other source parameters are the same as in Fig. 4(d).
and 6
Fig. 6 As Fig. 5 but for P 3D, (a) Ax = 1.5, Ay = 1; (b) Ax = 1, Ay = 1; (c) Ax = 1, Ay = 1.5.
. It can be seen from Figs. 5 and 6 that the difference between P 2D and P 3D is very obvious. The 2D spectral degree of polarization P 2D is Gaussian distribution and axially rotational symmetry, but the 3D spectral degree of polarization P 3D is not Gaussian distribution and loses their circular symmetry. The P 3D first decreases to a minimum and then rises with increasing transverse coordinate. This is due to the existence of the longitudinal component of the 3D light field.

In summary of the results in Figs. 16, we conclude that the fj and fαβ are key parameters for determine the propagation behavior of 3D random electromagnetic beams. fj is proportional to the ratio of the wavelength to the beam width, and fαβ is proportional to the ratio of the wavelength to the correlation length. The large values of parameters fj mean the beam width that is comparable with or less than λ results in the beam nonparaxiality. The large values of parameters fαβ mean weak coherence that leads to the large divergence angle. Here, the longitudinal component must be taken into consideration.

4. Conclusions

Acknowledgments

This work was supported by the Zhejiang Provincial Natural Science Foundation of China (Y6100605) and Huzhou Civic Natural Science Fund of Zhejiang Province of China (2009YZ01).

References and links

1.

F. Zernike, “The concept of degree of coherence and its application to optical problems,” Physica (Utrecht) 5(8), 785–795 (1938). [CrossRef]

2.

L. Mandel and E. Wolf, “Spectral coherence and concept of cross-spectral purity,” J. Opt. Soc. Am. 66(6), 529 (1976). [CrossRef]

3.

J. Tervo, T. Setälä, and A. T. Friberg, “Degree of coherence for electromagnetic fields,” Opt. Express 11(10), 1137–1143 (2003). [CrossRef] [PubMed]

4.

A. Luis, “Degree of coherence for vectorial electromagnetic fields as the distance between correlation matrices,” J. Opt. Soc. Am. A 24(4), 1063–1068 (2007). [CrossRef]

5.

C. Brosseau, Fundamentals of Polarized Light: A Statistical Optics Approach (Wiley, New York, 1998).

6.

E. Wolf, “Correlation-induced changes in the degree of polarization, the degree of coherence, and the spectrum of random electromagnetic beams on propagation,” Opt. Lett. 28(13), 1078–1080 (2003). [CrossRef] [PubMed]

7.

O. Korotkova and E. Wolf, “Generalized stokes parameters of random electromagnetic beams,” Opt. Lett. 30(2), 198–200 (2005). [CrossRef] [PubMed]

8.

T. Setälä, M. Kaivola, and A. T. Friberg, “Degree of polarization in near fields of thermal sources: effects of surface waves,” Phys. Rev. Lett. 88(12), 123902 (2002). [CrossRef] [PubMed]

9.

A. Luis, “Degree of polarization for three-dimensional fields as a distance between correlation matrices,” Opt. Commun. 253(1-3), 10–14 (2005). [CrossRef]

10.

T. Setälä, K. Lindfors, and A. T. Friberg, “Degree of polarization in 3D optical fields generated from a partially polarized plane wave,” Opt. Lett. 34(21), 3394–3396 (2009). [CrossRef] [PubMed]

11.

A. Luis, “Polarization distribution and degree of polarization for three-dimensional quantum light fields,” Phys. Rev. A 71(6), 063815 (2005). [CrossRef]

12.

X. Du, D. Zhao, and O. Korotkova, “Changes in the statistical properties of stochastic anisotropic electromagnetic beams on propagation in the turbulent atmosphere,” Opt. Express 15(25), 16909–16915 (2007). [CrossRef] [PubMed]

13.

K. Duan and B. Lü, “Partially coherent vectorial nonparaxial beams,” J. Opt. Soc. Am. A 21(10), 1924–1932 (2004). [CrossRef]

OCIS Codes
(030.1640) Coherence and statistical optics : Coherence
(260.0260) Physical optics : Physical optics
(260.5430) Physical optics : Polarization

ToC Category:
Coherence and Statistical Optics

History
Original Manuscript: August 24, 2010
Revised Manuscript: October 7, 2010
Manuscript Accepted: October 8, 2010
Published: October 13, 2010

Citation
Zhangrong Mei, "Generalized Stokes parameters of three-dimensional stochastic electromagnetic beams," Opt. Express 18, 22826-22832 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-22-22826


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References

  1. F. Zernike, “The concept of degree of coherence and its application to optical problems,” Physica (Utrecht) 5(8), 785–795 (1938). [CrossRef]
  2. L. Mandel and E. Wolf, “Spectral coherence and concept of cross-spectral purity,” J. Opt. Soc. Am. 66(6), 529 (1976). [CrossRef]
  3. J. Tervo, T. Setälä, and A. T. Friberg, “Degree of coherence for electromagnetic fields,” Opt. Express 11(10), 1137–1143 (2003). [CrossRef] [PubMed]
  4. A. Luis, “Degree of coherence for vectorial electromagnetic fields as the distance between correlation matrices,” J. Opt. Soc. Am. A 24(4), 1063–1068 (2007). [CrossRef]
  5. C. Brosseau, Fundamentals of Polarized Light: A Statistical Optics Approach (Wiley, New York, 1998).
  6. E. Wolf, “Correlation-induced changes in the degree of polarization, the degree of coherence, and the spectrum of random electromagnetic beams on propagation,” Opt. Lett. 28(13), 1078–1080 (2003). [CrossRef] [PubMed]
  7. O. Korotkova and E. Wolf, “Generalized stokes parameters of random electromagnetic beams,” Opt. Lett. 30(2), 198–200 (2005). [CrossRef] [PubMed]
  8. T. Setälä, M. Kaivola, and A. T. Friberg, “Degree of polarization in near fields of thermal sources: effects of surface waves,” Phys. Rev. Lett. 88(12), 123902 (2002). [CrossRef] [PubMed]
  9. A. Luis, “Degree of polarization for three-dimensional fields as a distance between correlation matrices,” Opt. Commun. 253(1-3), 10–14 (2005). [CrossRef]
  10. T. Setälä, K. Lindfors, and A. T. Friberg, “Degree of polarization in 3D optical fields generated from a partially polarized plane wave,” Opt. Lett. 34(21), 3394–3396 (2009). [CrossRef] [PubMed]
  11. A. Luis, “Polarization distribution and degree of polarization for three-dimensional quantum light fields,” Phys. Rev. A 71(6), 063815 (2005). [CrossRef]
  12. X. Du, D. Zhao, and O. Korotkova, “Changes in the statistical properties of stochastic anisotropic electromagnetic beams on propagation in the turbulent atmosphere,” Opt. Express 15(25), 16909–16915 (2007). [CrossRef] [PubMed]
  13. K. Duan and B. Lü, “Partially coherent vectorial nonparaxial beams,” J. Opt. Soc. Am. A 21(10), 1924–1932 (2004). [CrossRef]

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