Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                

Spatial coherence and the orbital angular momentum of light in astronomy

D. Hetharia, M. P. van Exter, and W. Löffler
Phys. Rev. A 90, 063801 – Published 1 December 2014
PDFHTMLExport Citation
Abstract
Authors
Article Text
  • ACKNOWLEDGMENTS
    • References

    Abstract

    The orbital angular momentum (OAM) of light is potentially interesting for astronomical study of rotating objects such as black holes, but the effect of reduced spatial coherence of astronomical light sources like stars is largely unknown. In a laboratory-scale experiment, we find that the detected OAM spectrum depends strongly on the position of the light-twisting object along the line of sight. We develop a simple intuitive model to predict the influence of reduced spatial coherence on the propagating OAM spectrum for, e.g., astronomical observations. Further, we derive equations to predict the effect of line-of-sight misalignment and the received intensity in higher-order OAM modes for limited-size detectors such as telescopes.

    • Figure
    • Figure
    • Figure
    • Figure
    • Received 28 April 2014
    • Revised 13 November 2014

    DOI:https://doi.org/10.1103/PhysRevA.90.063801

    ©2014 American Physical Society

    Authors & Affiliations

    D. Hetharia, M. P. van Exter, and W. Löffler*

    • Huygens–Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands

    • *loeffler@physics.leidenuniv.nl

    Article Text (Subscription Required)

    Click to Expand

    References (Subscription Required)

    Click to Expand
    Issue

    Vol. 90, Iss. 6 — December 2014

    Reuse & Permissions
    Access Options
    Author publication services for translation and copyediting assistance advertisement

    Authorization Required

    Log In
    Other Options
    ×

    Images

    • Figure 1
      Figure 1

      (a) The scheme: A spatially incoherent source of diameter d1 such as a star illuminates a region of space that modifies the OAM of light, for instance, a Kerr black hole. On earth, a telescope or interferometer with an effective diameter (baseline) of d2 is used to measure the OAM spectrum. (b) Laboratory-scale experimental setup. To simulate the star, we use a spatially incoherent light source (LED) illuminating the first aperture; the spiral phase plate (SPP) with charge Δℓ mimics the light-twisting object that modifies the OAM. A combination of phase-only spatial light modulation (SLM; see inset for an exemplary hologram) and imaging onto the core of a single-mode fiber (SMF) coupled to a photodiode (PD) is used to measure the OAM spectrum; the aperture d2 on the SLM corresponds to the telescope diameter.

      Reuse & Permissions
    • Figure 2
      Figure 2

      Measured OAM spectra [filled (red) circles; Pℓ versus ℓ] for different aperture sizes: (a), (c) d1=1800μm; (b), (d) d1=2800μm. (a), (b) Measured without the SPP; (c), (d) Measured with a Δℓ=2 SPP introduced L1=560 mm behind the source aperture d1. The experimental error is estimated from multiple measurements (10%) and the uncertainty in d1 (±50μm). Bars show the theoretical results (no fit parameters). Common parameters: d2=800μm,L2=315 mm.

      Reuse & Permissions
    • Figure 3
      Figure 3

      The detected mean OAM as a function of the aperture size d1 for Δℓ=1 and Δℓ=2 spiral phase plates placed L1=56 cm behind the first aperture (d2=800μm,L2=315). The experimental data (symbols) agree well with the theory [Eq. (2)] and the simple s-curve model.

      Reuse & Permissions
    • Figure 4
      Figure 4

      Detected normalized mean OAM for d1- and L1-dependent calculations (symbols), plotted as a function of the parameter F. Both calculations lie on an s-shaped curve that is nicely represented by the incomplete β function (curve). Inset: Calculated mean OAM as a function of detector displacement in multiples of Δx0=d1d2L2/L1, relative to the exact line-of-sight condition Δx=0.

      Reuse & Permissions
    ×

    Sign up to receive regular email alerts from Physical Review A

    Log In

    Cancel
    ×

    Search

    Article Lookup

    Paste a citation or DOI
    Enter a citation
    ×