| 1. |
- Cai, Yangjian, et al.
(författare)
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Analytical formula for a decentered elliptical Gaussian beam propagating in a turbulent atmosphere
- 2007
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Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 271:2, s. 509-516
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Tidskriftsartikel (refereegranskat)abstract
- Analytical formulas for the average intensity and decentered parameter of a decentered elliptical Gaussian beam (DEGB) propagating in a turbulent atmosphere are derived in a tensor form. The propagation properties of a DEGB in a turbulent atmosphere are investigated in detail, and found to be different from that in free space. Furthermore, as an application example, we investigate the propagation of a decentered elliptical flat-topped beam (DEFB) by expressing its electric field as a finite sum of DEGBs in a turbulent atmosphere. The properties of a DEGB or a DEFB in a turbulent atmosphere are closely related with the beam's parameters and the structure constant of the turbulent atmosphere.
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| 2. |
- Cai, Yangjian, et al.
(författare)
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Average intensity and spreading of an elliptical Gaussian beam propagating in a turbulent atmosphere
- 2006
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 31:5, s. 568-570
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Tidskriftsartikel (refereegranskat)abstract
- An analytical formula for the average intensity of an elliptical Gaussian beam (EGB) propagating in a turbulent atmosphere is derived. The spreading properties of an EGB in a turbulent atmosphere are studied. It is found that an EGB will eventually become a circular Gaussian beam in a turbulent atmosphere. This interesting phenomenon is quite different from the propagation of an EGB in free space. The evolution properties are closely related to the parameters of the beam and the turbulent atmosphere
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| 3. |
- Cai, Yangjian, et al.
(författare)
-
Coherent and partially coherent dark hollow beams with rectangular symmetry and paraxial propagation properties
- 2006
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Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 23:7, s. 1398-1407
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical model is proposed to describe coherent dark hollow beams (DHBs) with rectangular symmetry. The electric field of a coherent rectangular DHB is expressed as a superposition of a series of the electric field of a finite series of fundamental Gaussian beams. Analytical propagation formulas for a coherent rectangular DHB passing through paraxial optical systems are derived in a tensor form. Furthermore, for the more general case, we propose a theoretical model to describe a partially coherent rectangular DHB. Analytical propagation formulas for a partially coherent rectangular DHB passing through paraxial optical systems are derived. The beam propagation factor (M-2 factor) for both coherent and partially coherent rectangular DHBs are studied. Numerical examples are given by using the derived formulas. Our models and method provide an effective way to describe and treat the propagation of coherent and partially coherent rectangular DHBs.
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| 4. |
- Cai, Yangjian, et al.
(författare)
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Coincidence fractional Fourier transform implemented with partially coherent light radiation
- 2005
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Ingår i: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION. - 1084-7529. ; 22:9, s. 1798-1804
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Tidskriftsartikel (refereegranskat)abstract
- We introduce the coincidence fractional Fourier transform (FRT) implemented with incoherent and partially coherent light radiation. Optical systems for implementing the coincidence FRT are designed. The results show that the visibility and quality of the coincidence FRT of an object are closely related to the light source's transverse size, coherence, and spectral width. As an example, we numerically study the coincidence FRT of a single slit. (c) 2005 Optical Society of America.
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| 5. |
- Cai, Yangjian, et al.
(författare)
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Coincidence subwavelength fractional Fourier transform
- 2006
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Ingår i: Optical Society of America. Journal A. - 1084-7529 .- 1520-8532. ; 23:4, s. 835-841
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Tidskriftsartikel (refereegranskat)abstract
- The coincidence subwavelength fractional Fourier transforms (FRTs) with entangled photon pairs and incoherent light radiation are introduced as an extension of the recently introduced coincidence FRT. Optical systems for implementing the coincidence subwavelength FRTs are designed. The width of the coincidence subwavelength FRT pattern is two times narrower than the width of the coincidence FRT. The coincidence subwavelength FRT with partially coherent light radiation is also studied numerically. Differences between the coincidence subwavelength FRT with entangled photon pairs and that with incoherent light radiation are discussed.
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| 6. |
- Cai, Yangjian, et al.
(författare)
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Lensless imaging with partially coherent light
- 2007
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 32:3, s. 205-207
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Tidskriftsartikel (refereegranskat)abstract
- Based on the fourth-order correlation of light, lensless imaging with incoherent or partially coherent light is investigated theoretically by use of classical optical coherence theory. A novel lensless optical system for implementing imaging is proposed. The visibility and quality of the image are influenced by the coherence and transverse size of the light source. The results suggest useful imaging applications in x-ray, gamma-ray, or other wavelengths where no effective lens is available, and they have potential applications in optical metrology and holography.
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| 7. |
- Cai, Yangjian, et al.
(författare)
-
Lensless optical implementation of the coincidence fractional Fourier transform
- 2006
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 31:15, s. 2278-2280
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Tidskriftsartikel (refereegranskat)abstract
- A lensless optical system for implementing the coincidence fractional Fourier transform (FRT) is proposed. The conditions for the lensless optical system to implement the coincidence FRT with incoherent light and entangled photon pairs are discussed. The results offer a novel scheme for FRTs and thus suggest useful applications.
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| 8. |
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| 9. |
- Cai, Yangjian, et al.
(författare)
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Propagation of a hollow Gaussian beam through a paraxial misaligned optical system
- 2006
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Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 265:2, s. 607-615
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Tidskriftsartikel (refereegranskat)abstract
- Based on the generalized diffraction integral formula for treating the propagation of a laser beam through a paraxial misaligned optical system in the cylindrical coordinate system, we obtain an analytical formula for a hollow Gaussian beam passing through a paraxial misaligned optical system. Furthermore, we also obtain the approximate analytical formula for a hollow Gaussian beam passing through a paraxial circularly apertured misaligned optical system by expanding the hard aperture function into a finite sum of complex Gaussian functions. As a numerical example, the propagation properties a hollow Gaussian beam through a misaligned thin lens are studied numerically.
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| 10. |
- Cai, Yangjian, et al.
(författare)
-
Propagation of a partially coherent twisted anisotropic Gaussian Schell-model beam in a turbulent atmosphere
- 2006
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:4
-
Tidskriftsartikel (refereegranskat)abstract
- Analytical formulas are derived for the propagation of a partially coherent twisted anisotropic Gaussian Schell-model (TAGSM) beam in a turbulent atmosphere. Propagation properties of a TAGSM beam in a turbulent atmosphere are investigated in detail. It is found that a TAGSM beam will become a circular beam in a turbulent atmosphere, and low coherence and larger twist have an effect of anticircularization of the beam spot. The beam spot spreads more rapidly for lower coherence, larger twist, or stronger turbulence.
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| 11. |
- Cai, Yangjian, et al.
(författare)
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Propagation of hollow Gaussian beams through apertured paraxial optical systems
- 2006
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Ingår i: Journal of the Optical Society of America a-Optics Image Science and Vision. - 1084-7529. ; 23:6, s. 1410-1418
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Tidskriftsartikel (refereegranskat)abstract
- On the basis of the generalized Collins formula and the expansion of the hard-aperture function into a finite sum of complex Gaussian functions, an approximate analytical formula for a hollow Gaussian beam propagating through an apertured paraxial stigmatic (ST) ABCD optical system is derived. Some numerical examples are given. Furthermore, by using a tensor method, we derive approximate analytical formulas for a hollow elliptical Gaussian beam propagating through an apertured paraxial general astigmatic ABCD optical system and an apertured paraxial misaligned ST ABCD optical system. Our results provide a convenient way for studying the propagation and transformation of a hollow Gaussian beam and a hollow elliptical Gaussian beam through an apertured general optical system.
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| 12. |
- Cai, Yangjian, et al.
(författare)
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Propagation of partially coherent twisted anisotropic Gaussian Schell-model beams through an apertured astigmatic optical system
- 2006
-
Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 31:6, s. 685-687
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Tidskriftsartikel (refereegranskat)abstract
- By expanding the hard-aperture function into a finite sum of complex Gaussian functions, we derived an approximate analytical formula for a partially coherent twisted anisotropic Gaussian Schell-model (AGSM) beam propagating through an apertured paraxial general astigmatic (GA) optical system by use of a tenser method. The results obtained by using the approximate analytical formula are in good agreement with those obtained by using the numerical integral calculation. Our formulas avoid time-consuming numerical integration and provide a convenient and effective way for studying the propagation and transformation of a partially coherent twisted AGSM beam through an apertured paraxial GA optical system. (c) 2006 Optical Society of America.
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| 13. |
- Cai, Yangjian, 1977-
(författare)
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Propagation of some coherent and partially coherent laser beams
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, we investigate the propagation of some coherent and partially coherent laser beams, including a dark hollow beam (DHB), an elliptical Gaussian beam (EGB), a flat-topped beam and a twisted anisotropic Gaussian Schell-model (TAGSM) beam, through a paraxial optical system or a turbulent atmosphere. Several theoretical models are proposed to describe a DHB of circular or non-circular symmetry. Approximate analytical formulas for a DHB and a partially coherent TAGSM beam propagating through an apertured paraxial optical system are derived based on the generalized Collins formula. Analytical formulas for a DHB, an EGB, a flat-topped beam and a partially coherent TAGSM beam propagating in a turbulent atmosphere are derived in a tensor form based on the extended Huygens-Fresnel integral formula. It is found that after a long propagation distance these beams become circular Gaussian beams in a turbulent atmosphere, and this is quite different from their propagation properties in free space. The conversion of any of these beams to a circular Gaussian beam becomes quicker and the beam spot in the far field spreads more rapidly for a larger structure constant of the turbulent atmosphere, a shorter wavelength and a smaller waist size of the initial beam. Lower coherence and larger twist have a stronger effect of anti-circularization of the beam spot. Our analytical formulas provide a convenient way for studying the propagation of various laser beams through a paraxial optical system or a turbulent atmosphere. The concept of coincidence fractional Fourier transform (FRT) with an incoherent or partially coherent beam is introduced, and the optical system for its implementation is designed. The coincidence FRT is demonstrated experimentally with a partially coherent beam, and the experimental results are consistent with the theoretical results.
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| 14. |
- Cai, Yangjian, et al.
(författare)
-
Propagation of various dark hollow beams in a turbulent atmosphere
- 2006
-
Ingår i: Optics Express. - 1094-4087. ; 14:4, s. 1353-1367
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Tidskriftsartikel (refereegranskat)abstract
- Propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry in a turbulent atmosphere is investigated. Analytical formulas for the average intensity of various DHBs propagating in a turbulent atmosphere are derived in a tensor form based on the extended Huygens-Fresnel integral. The intensity and spreading properties of the DHBs in a turbulent atmosphere are studied numerically. It is found that after a long propagation distance a dark hollow beam of circular or non-circular eventually becomes a circular Gaussian beam (without dark hollow) in a turbulent atmosphere, which is much different from its propagation properties in free space. The conversion from a DHB to a circular Gaussian beam becomes quicker and the beam spot in the far field spreads more rapidly for a larger structure constant, a shorter wavelength, a lower beam order and a smaller waist size of the initial beam.
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| 15. |
- Cai, Yangjian, et al.
(författare)
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Propagation of various dark hollow beams through an apertured paraxial ABCD optical system
- 2006
-
Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 357:1, s. 72-80
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Tidskriftsartikel (refereegranskat)abstract
- Propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry through an apertured paraxial ABCD optical system is investigated. Approximate analytical formulas for various DHBs propagating through an apertured paraxial optical system are derived by expanding the hard-aperture function into a finite sum of complex Gaussian functions in terms of a tensor method. Some numerical results are given. Our formulas provide a convenient way for studying the propagation of various DHBs through an apertured paraxial optical system.
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| 16. |
- Cai, Yangjian
(författare)
-
Propagation of various flat-topped beams in a turbulent atmosphere
- 2006
-
Ingår i: Journal of Optics. A, Pure and applied optics. - : IOP Publishing. - 1464-4258 .- 1741-3567. ; 8:6, s. 537-545
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of flat-topped beams with circular, elliptical and rectangular symmetries in a turbulent atmosphere is investigated. Analytical formulae for the average intensity of various flat-topped beams propagating in a turbulent atmosphere are derived in a tensor form. The formulae derived can easily be reduced to those for flat-topped beams propagating in free space (in the absence of turbulence). The propagation properties of flat-topped beams are studied in detail. We find that a flat-topped beam with circular or non-circular symmetry will evolve into a circular Gaussian beam in the far field under the influence of atmospheric turbulence, which is quite different to its properties in free space. Our method provides an effective and convenient way to analyse the propagation of various flat-topped beams in a turbulent atmosphere.
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| 17. |
- Hu, Li, et al.
(författare)
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Analytical formula for a circular flattened Gaussian beam propagating through a misaligned paraxial ABCD optical system
- 2006
-
Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 360:2, s. 394-399
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Tidskriftsartikel (refereegranskat)abstract
- Based on the generalized diffraction integral formula for treating the propagation of a laser beam through a misaligned paraxial ABCD optical system in the cylindrical coordinate system, analytical formula for a circular flattened Gaussian beam propagating through such optical system is derived. Furthermore, an approximate analytical formula is derived for a circular flattened Gaussian beam propagating through an apertured misaligned ABCD optical system by expanding the hard aperture function as a finite sum of complex Gaussian functions. Numerical examples are given.
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| 18. |
- Huang, Ke, et al.
(författare)
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The confounding effect of snow cover on assessing spring phenology from space : A new look at trends on the Tibetan Plateau
- 2021
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 756
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Tidskriftsartikel (refereegranskat)abstract
- The Tibetan Plateau is the highest and largest plateau in the world, hosting unique alpine grassland and having a much higher snow cover than any other region at the same latitude, thus representing a “climate change hot-spot”. Land surface phenology characterizes the timing of vegetation seasonality at the per-pixel level using remote sensing systems. The impact of seasonal snow cover variations on land surface phenology has drawn much attention; however, there is still no consensus on how the remote sensing estimated start of season (SOS) is biased by the presence of preseason snow cover. Here, we analyzed SOS assessments from time series of satellite derived vegetation indices and solar-induced chlorophyll fluorescence (SIF) during 2003–2016 for the Tibetan Plateau. We evaluated satellite-based SOS with field observations and gross primary production (GPP) from eddy covariance for both snow-free and snow covered sites. SOS derived from SIF was highly correlated with field data (R2 = 0.83) and also the normalized difference phenology index (NDPI) performed well for both snow free (R2 = 0.77) and snow covered sites (R2 = 0.73). On the contrary, normalized difference vegetation index (NDVI) correlates only weakly with field data (R2 = 0.35 for snow free and R2 = 0.15 for snow covered sites). We further found that an earlier end of the snow season caused an earlier estimate of SOS for the Tibetan Plateau from NDVI as compared to NDPI. Our research therefore adds new evidence to the ongoing debate supporting the view that the claimed advance in land surface SOS over the Tibetan Plateau is an artifact from snow cover changes. These findings improve our understanding of the impact of snow on land surface phenology in alpine ecosystems, which can further improve remote sensing based land surface phenology assessments in snow-influenced ecosystems.
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| 19. |
- Lu, Xiang, et al.
(författare)
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Analytical formulas for a circular or non-circular flat-topped beam propagating through an apertured paraxial optical system
- 2007
-
Ingår i: Optics Communications. - : Elsevier BV. - 0030-4018 .- 1873-0310. ; 269:1, s. 39-46
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Tidskriftsartikel (refereegranskat)abstract
- Propagation of a flat-topped beam of circular or non-circular (rectangular or elliptical) symmetry through an apertured optical system is investigated. By expanding the hard aperture function as a finite sum of complex Gaussian functions, some approximate analytical propagation formulas are derived for a flat-topped beam of circular or non-circular (rectangular or elliptical) symmetry propagating through an apertured paraxial general astigmatic (GA) optical system or an apertured paraxial misaligned stigmatic (ST) optical system. The derived formulas are very fast to compute. The results obtained by using the approximate analytical expressions are in a good agreement with those obtained by direct numerical integration. The present analytical formulas provide a convenient and effective way for studying the propagation and transformation of a circular or non-circular flat-topped beam through an apertured general optical system.
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| 20. |
- Lu, Xingyuan, et al.
(författare)
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Phase detection of coherence singularities and determination of the topological charge of a partially coherent vortex beam
- 2019
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 114:20
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Tidskriftsartikel (refereegranskat)abstract
- In the theory of partial coherence, coherence singularities can occur in the spectral degree of coherence (SDOC): in case the fields at two different points are completely uncorrelated, the phase of the SDOC is undefined. For a partially coherent vortex beam, the detection of coherence singularities is linked to the measurement of topological charge, whose magnitude equals the number of ring dislocations in its far field amplitude. However, the phase distribution of coherence singularities is rarely mentioned in the literature and the amplitude distribution can hardly reflect the sign of topological charge. In this letter, we present a phase-analysis method for measuring the coherence singularities by introducing a movable perturbation at a certain point in an illumination window of a finite size. Using the proposed method, we measure experimentally the coherence singularities of a partially coherent vortex beam in the focal plane. From the results, the magnitude and sign of the topological charge can be determined simultaneously from the phase distribution of the coherence singularities. Our results can find application in information transmission.
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| 21. |
- Lue, Xiang, et al.
(författare)
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Partially coherent circular and elliptical dark hollow beams and their paraxial propagations
- 2007
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Ingår i: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 369:1-2, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical model is proposed to describe a partially coherent dark hollow beam (DHB) of circular or elliptical symmetry. The characteristics of the partially coherent circular or elliptical DHB can be easily controlled by properly choosing the beam parameters. Based on the generalized Collins integral, analytical formulas for a partially coherent circular or elliptical DHB propagating through paraxial aligned and misaligned optical systems are derived. Some numerical examples are illustrated. Our model provides a convenient way to describe and treat the propagation of partially coherent circular and elliptical DHBs.
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| 22. |
- Peng, Xiaofeng, et al.
(författare)
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Self-reconstruction of twisted Laguerre-Gaussian Schell-model beams partially blocked by an opaque obstacle
- 2020
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Ingår i: Optics Express. - : The Optical Society. - 1094-4087. ; 28:21, s. 31510-31523
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Tidskriftsartikel (refereegranskat)abstract
- Twisted Laguerre-Gaussian Schell model (TLGSM) beams are a novel type of partially coherent beams, which carry the twist phase and the vortex phase simultaneously. In this paper, the self-reconstruction (SR) of the TLGSM beam partially blocked by an opaque obstacle and propagating through a thin lens focusing system is studied in detail. Implementing the pseudo-mode expansion method, we represent the TLGSM beam as a superposition of spatially coherent modes, which is applicable for calculating the cross spectral density (CSD) and spectral degree of coherence (SDOC) of such a beam using the Fourier transform. The numerical results reveal that the twist parameter, a measure of the strength of a twist phase, determines the characteristics of the SR. In the case of the topological charge of the vortex is positive, the SR capability of spectral density is significantly improved with the increase of the twist parameter. The physical mechanism behind these phenomena is analyzed in detail from the point view of mode expansion. Further, the dependence of the side ring intensity and SR capability of the SDOC on the twist parameter are also investigated. It is found that the SR capability and side ring intensity of the SDOC are simultaneously enhanced for a large twist parameter, providing an efficient way to determine the number of topological charge. Our study results may find application in communication and information recovery applications.
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| 23. |
- Peng, Xiaofeng, et al.
(författare)
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Twisted Laguerre-Gaussian Schell-model beam and its orbital angular moment
- 2018
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 26:26, s. 33956-33969
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that a light beam with vortex phase or twist phase carries orbital angular momentum (OAM), while twist phase only exists in a partially coherent beam. In this paper, we introduce a new partially coherent beam, named twisted Laguerre-Gaussian Schell-model (TLGSM) beam. This TLGSM beam carries both vortex phase and twist phase. Further, the evolutional properties of the spectral density and spectral degree of coherence (SDOC)] of the TLGSM beam passing through a paraxial ABCD optical system are explored in detail. Our results reveal that the vortex and twist phases' handedness significantly affects the evolution properties. When the twist phase's handedness is the same as that of the vortex phase, the beam profile maintains a dark hollow shape during propagation and the side rings in SDOC are suppressed; however, when the handedness of two phases is opposite, then the beam shape evolves into a Gaussian shape and the side rings in SDOC are enhanced. Furthermore. we obtain the analytical expression for the OAM of the TLGSM beam. It is found that the vortex phase's and twist phase's contributions to the OAM are interrelated, which greatly increases the amount of OAM. In addition, the OAM variation of the TLGSM beam passing through an anisotropic optical system is also explored in detail. Our results will be useful for information transfer and optical manipulations.
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| 24. |
- Wang, Fei, et al.
(författare)
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Experimental observation of coincidence Fractional Fourier transform with a partially coherent beam
- 2006
-
Ingår i: Optics Express. - 1094-4087. ; 14:16, s. 6999-7004
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Tidskriftsartikel (refereegranskat)abstract
- The coincidence Fractional Fourier transform (FRT) is implemented with a partially coherent light source experimentally. The visibility and quality of the coincidence FRT pattern of an object are investigated theoretically. The FRT pattern of an object is obtained by measuring the coincidence counting rate between the detected signals passing through two different optical paths. The experimental results are analyzed and found to be consistent with the theoretical results.
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| 25. |
- Xu, Zhiheng, et al.
(författare)
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Vortex Beams on Incoherent Background
- 2023
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Ingår i: 2023 Photonics North, PN 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- We introduce a novel class of structured random beams carrying orbital angular momentum on incoherent background. We confirm that such beams maintain their vortex structure in free space and manifest robust behavior against atmospheric turbulence as well.
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