Polarization-sensitive speckle spectroscopy of scattering media beyond the diffusion limit

“…Controllable changes in the coherence length of the probe light can also be provided using a slow modulation of the pumping current in the laser diode in the vicinity of the laser generation threshold [28]. At certain conditions, this approach makes it possible to tune the coherence length of emitting radiation within the range from several tens of micrometers to several millimeters.…”

Section: Introductionmentioning

confidence: 99%

Band-Limited Reference-Free Speckle Spectroscopy: Probing the Fluorescent Media in the Vicinity of the Noise-Defined Threshold

et al. 2020

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A method of reference-free speckle spectroscopy based on the statistical analysis of intensity spatial fluctuations of the spectrally-selected multiple-scattered fluorescence radiation is examined in the case of the finite-band spectral selection of fluorescence light emitted by the laser-pumped random medium, and detection conditions far from the ideal case. Intensity fluctuations are recorded during point-to-point scanning of the surface of a random multiple-scattering medium, which is characterized by the dependences of the second- and third-order statistical moments of intensity on the wavelength of detected spectrally selected light. In turn, the statistical moments of intensity fluctuations are determined by the average propagation path of fluorescent radiation in the medium. This makes it possible to analyze the features of the light-medium interactions at a scale of the order of the transport mean free path of radiation propagation in the medium. Depending on the spectral selection conditions, the method is applicable for characterizing micro- or nano-structured fluorescent layers with thicknesses from tens of micrometers to several millimeters. In the examined case, the finite-band spectral selection results in the values of coherence length of the detected fluorescence radiation compared with the ensemble-averaged absolute value of the path-length difference between the stochastically interfering and spectrally selected partial contributions to the fluorescence field. In addition, non-ideal detection conditions (usage of a multimode optical fiber in the light-collecting unit) cause additional strong damping of the detected speckle intensity fluctuations. These factors lead to a remarkable suppression of spatial fluctuations of the fluorescence intensity in the course of spatially- and spectrally-resolved surface scanning of the laser-pumped probed random medium. Nevertheless, with appropriate procedures of the intrinsic noise reduction and data correction, the obtained spectral dependencies of the normalized third-order statistical moment of the band-limited fluorescence intensity clearly indicate the fluorescence propagation features in the probed multiple-scattering random media (such as a strong influence of the scattering strength and multiple self-absorption–re-emission events on the average propagation path of light in the medium).The possibilities of noise reduction and data correction in the case of applying the band-limited reference-free spectroscopic instrumentation with low spectral and spatial resolution are illustrated by the experimental results obtained using the Rhodamine-6G-doped and continuous wave (CW)-laser-pumped layers of the densely packed titania and silica particles.

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“…This result suggests that only two scattering events are needed to randomize the polarization, so j͞l ‫ء‬ , 2. We note that most earlier methods for determining this depolarization rate relied on computation of the scattering cross section by use of Mie theory, 2,4,5,8,12 which is diff icult to apply in the case of irregularly shaped or densely packed scatterers. 21 For broadband waves, the evolution of the spectral content of the radiation can be another useful quantity for distinguishing the ballistic from the diffusive regime.…”

mentioning

confidence: 99%

Spectral shifts as a signature of the onset of diffusion of broadband terahertz pulses

2004

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We describe measurements of polarization dynamics as a probe of multiple scattering of photons in a random medium by use of single-cycle terahertz pulses. We measure the degree of polarization and correlate it directly with the single-scattering regime in the time domain. We also measure the evolution of the temporal phase of the radiation and show that the average spectral content depends on the state of polarization. In the case of broadband radiation, this effect can be used to distinguish photons that have been scattered a few times from those that are propagating diffusively.

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Polarization-sensitive speckle spectroscopy of scattering media beyond the diffusion limit

Cited by 18 publications

References 58 publications

Polarization recovery through scattering media

Polarization recovery through scattering media

Band-Limited Reference-Free Speckle Spectroscopy: Probing the Fluorescent Media in the Vicinity of the Noise-Defined Threshold

Spectral shifts as a signature of the onset of diffusion of broadband terahertz pulses

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