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arXiv:1709.06586 · Journal of Physics B Atomic Molecular and Optical Physics

Imaging interferometry of excitons in two-dimensional structures: can it detect exciton coherence

Heinrich Stolz, Maria Dietl, Rico Schwartz, Dirk Semkat

Published Dec 5, 2017• 2 citations
arXivHTMLPDF

Abstract

Abstract Using the theory of imaging with partially coherent light, we derive general expressions for different kinds of interferometric setups such as double slit, shift and mirror interference. We show that in all cases the interference patterns depend not only on the point spread function of the imaging setup but also strongly on the spatial emission pattern of the sample. Taking typical experimentally observed spatial emission patterns into account, we can reproduce, at least qualitatively, all the observed interference structures, which have been interpreted as signatures for spontaneous long range coherence of excitons, already for incoherent emitters (Butov et al 2002 Nature 418 751; Dubin et al 2006 Nat. Phys. 2 32). This requires a critical reexamination of the previous work.

DOI
10.1088/1361-6455/aa9f5d

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Abstract Using the theory of imaging with partially coherent light, we derive general expressions for different kinds of interferometric setups such as double slit, shift and mirror interference. We show that in all cases the interference patterns depend not only on the point spread function of the imaging setup but also strongly on the spatial emission pattern of the sample. Taking typical experimentally observed spatial emission patterns into account, we can reproduce, at least qualitatively, all the observed interference structures, which have been interpreted as signatures for spontaneous long range coherence of excitons, already for incoherent emitters (Butov et al 2002 Nature 418 751; Dubin et al 2006 Nat. Phys. 2 32). This requires a critical reexamination of the previous work.
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Nonlinear optical interactions are typically driven by coherent sources. Recently, however, incoherent sources have also been shown to offer new opportunities in nonlinear optics. Here we study the effects of the source incoherence in second harmonic generation. We derive and experimentally validate an analytic expression for the far-field coherence function at the second harmonic frequency, which is a generalization of the well-known van Cittert-Zernike theorem. Unlike the linear optics case, here the results depend not only on the source spatial distribution, but also on the nonlinear structure of the crystal. We further show, by performing Young's double-slit measurement, that the coherence at the second harmonic increases as the light propagates inside the nonlinear crystal. Our results establish nonlinearity as a degree of freedom for optical coherence, opening a new research area at the interface of statistical optics and nonlinear optics.
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