We explore the application of structured vortex laser beams, or shaped light with orbital angular momentum (OAM), in the diagnosis of cell and cell cultures and the quantitative characterization of biological tissues. To examine the conservation of spin and orbital angular momenta during propagation, we constructed a Mach-Zehnder-like interferometer, equipped with a spatial light modulator (SLM), to generate Laguerre-Gaussian (LG) beams with varying momenta. As the LG beam traverses tissue samples, its interference with a reference plane wave is captured by a camera. Our findings reveal that the OAM of the LG beam is maintained through both normal and cancerous tissue samples, exhibiting a distinct phase shift – or twist of light – which is significantly more sensitive (up to ~1000 times) to changes in the tissue's refractive indices compared to conventional methods. We conclude that leveraging OAM in biomedical diagnosis presents exciting prospects for both groundbreaking biological research and enhanced clinical applications.
SignificancePhase retardation of circularly polarized light (CPL), backscattered by biological tissue, is used extensively for quantitative evaluation of cervical intraepithelial neoplasia, presence of senile Alzheimer’s plaques, and characterization of biotissues with optical anisotropy. The Stokes polarimetry and Mueller matrix approaches demonstrate high potential in definitive non-invasive cancer diagnosis and tissue characterization. The ultimate understanding of CPL interaction with tissues is essential for advancing medical diagnostics, optical imaging, therapeutic applications, and the development of optical instruments and devices.AimWe investigate propagation of CPL within turbid tissue-like scattering medium utilizing a combination of Jones and Stokes–Mueller formalisms in a Monte Carlo (MC) modeling approach. We explore the fundamentals of CPL memory effect and depolarization formation.ApproachThe generalized MC computational approach developed for polarization tracking within turbid tissue-like scattering medium is based on the iterative solution of the Bethe–Salpeter equation. The approach handles helicity response of CPL scattered in turbid medium and provides explicit expressions for assessment of its polarization state.ResultsEvolution of CPL backscattered by tissue-like medium at different conditions of observation in terms of source–detector configuration is assessed quantitatively. The depolarization of light is presented in terms of the coherence matrix and Stokes–Mueller formalism. The obtained results reveal the origins of the helicity flip of CPL depending on the source–detector configuration and the properties of the medium and are in a good agreement with the experiment.ConclusionsBy integrating Jones and Stokes–Mueller formalisms, the combined MC approach allows for a more complete representation of polarization effects in complex optical systems. The developed model is suitable to imitate propagation of the light beams of different shape and profile, including Gaussian, Bessel, Hermite–Gaussian, and Laguerre–Gaussian beams, within tissue-like medium. Diverse configuration of the experimental conditions, coherent properties of light, and peculiarities of polarization can be also taken into account.
SignificanceThe study of the effect of aging on the optical properties of biological tissues, in particular polarization, is important in the development of new diagnostic approaches.AimThis work aims to provide a comprehensive analysis of the factors and mechanisms that contribute to the alteration of skin polarization properties caused by aging, using polarization-sensitive hyperspectral imaging measurements and Monte Carlo simulation.ApproachOur investigation involved both experimental studies of in vivo human skin of volunteers of different ages and computational modeling that accounted for changes in the absorption and scattering properties of the skin model. Specifically, we analyzed alterations in the degree of linear polarization (DOLP) to better understand the impact of aging on skin polarization properties.ResultsA statistically significant increase in the DOLP was found for the elderly group. At the same time, there was no correlation between changes in polarization and the calculated blood volume fraction parameter for different ages. According to the simulation results, it was also found that a change in the scattering properties of biological tissues has a more significant effect on the change in polarizing light compared to the change in absorption.ConclusionsThe results of the work prove that the sensitivity of polarization imaging to age- or pathological-related skin changes may be primarily due to changes in scattering, which in turn is associated with changes in the collagen fibers of the dermis. The proposed technique shows promise for in vivo non-invasive real-time assessment of age-associated skin changes and can also be extended to monitor changes associated with the development of age-related pathologies.
In turbid tissue-like scattering medium the conventional polarised light, scattered multiple number of times, is depolarised, and the depolarisation rate depends strongly on the size and shape of scattering particles, as well as on the number of scattering events. In fact, the structure of light can be more complicated when the polarisation of light across the laser beam can be radially or azimuthally polarised and carry orbital angular momentum (OAM). We use both conventional polarisation and shaped light with OAM for characterisation of biological tissues and their structural malformations associated with dangerous diseases, including cancer, dementia, diabetes and other.
The roles of birefringence and scattering of polarized light are considered in the visual perception of Haidinger's and Boehm’s brushes, both entopic phenomena. To simulate the phenomena, we developed and employed a theoretical polarization-based computational model that imitated the optical system geometry of the human eye. Using this model, we demonstrated that Haidinger's brushes originate because the structured organization of Henle's fibre layer, which act as the analyser to the polarized light, causes birefringence. Because of the radial orientation of these fibres, Haidinger's brushes appear perpendicular to the orientation of the incident linear polarization of light. Additionally, the results of Monte Carlo-based modelling confirm that Boehm’s brushes, which are perceived outside the macula region, are the product of low-order scattering of polarised light in the superficial layer of the retina. Understanding of these phenomena, in terms of their formation and appearance, is essential for basic and clinical studies on visual perception, including the development of advanced ophthalmic tools for assessing macular and retina functions.
Thorough analysis of the plasmonic phenomena requires proper account for such effects as size dependent plasmon resonance shifts and intensity changes observed in metal nanoparticles, especially in systems with small feature sizes. Recent theoretical advances, including Generalized Nonlocal Optical Response (GNOR), allow to accurately resolve these effects within the classical electromagnetics, paving the way for implementation of efficient low cost computational techniques. We present a new GNOR-based numerical scheme of the flexible Discrete Sources Method for analysis of light scattering by single plasmonic nanoparticle in the layered medium with rigorous account for both substrate-particle interaction and nonlocal effects.
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