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arXiv:1911.08466 · Physical Review Research

Photon-count fluctuations exhibit inverse-square baseband spectral behavior that extends to <1μHz

Nishant Mohan, Steven Bradley Lowen, Malvin Carl Teich

Published Feb 19, 2020• 5 citations
arXivHTMLPDF

Abstract

The authors demonstrate that a broad variety of light sources with markedly different optical spectra all exhibit slow photon-count fluctuations at baseband that display inverse-square spectral behavior at frequencies that extend to 1 $\ensuremath{\mu}$Hz. These fluctuations are unexpected and may appear in experimental schemes from optical coherence tomography to gravitational-wave detection

DOI
10.1103/physrevresearch.2.013170

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Abstract This study investigates photon-count fluctuation dynamics of two light sources, namely a spontaneous parametric down-conversion (SPDC) light source and a 780 nm attenuated laser diode (LD). White noise integral with customizable memory function is used to model the mean square displacements (MSDs) and the probability density functions (PDFs) for both light sources. This approach overcomes the limitation of monofractal scaling of fractional Brownian motion (fBm) model characterized by a single Hurst exponent. The memory function used has an exponential-tempered power-law relation, parametrized by μ and β, where β modulates the extent of memory parameter μ. Although optical losses and detector inefficiencies degrade photon statistics to Poissonian at post-detection, our findings reveal notable memory effects at higher mean photon counts, especially in the SPDC source with memory parameter μ ⪆ 1.00, compared to the classical LD, which remained relatively constant at μ ⪅ 1.00. Both light sources shared similar correction parameters β, which indicates they have identical photon-count fluctuations at short time but diverge significantly at longer time. This work highlights the need for models beyond fBm, capable of capturing complex MSD behaviors of photon-count fluctuations.