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Use of steady-state imaging setup for assessing the internal optical properties of non-spherical apple samples
摘要： The aim of this paper was to retrieve the absorption (μa) and reduced scattering (μ's) coefficients of whole apples which exhibit a complex shape. The effect of the local boundary curvature on the retrieved optical properties was investigated by means of numerical simulations and measurements carried out at the wavelength of 633 nm. A first attempt was made by performing Monte Carlo simulations on an apple-like spheroid model covered with a thin skin layer of thickness 80 μm. Monte Carlo data were then analyzed to depict the changes of photon densities, diffusively reflected images and optical properties as a function of the light source location over the surface of such target. Second, spatially-resolved backscattered images were acquired from 207 ‘Royal Gala’, and the values of μa and μ's were retrieved using an inverse algorithm to fit the scattering profiles with a diffusion theory model, in a selected fitting range of 2.8–10 mm. The results confirm the theoretical prediction and show that the absorption coefficient μa may be overestimated, while the reduced scattering coefficient μ's is slowly changed when the measurements are performed on these apple species. Finally, experiments carried out on 200 apples still show that μ's is negatively correlated to the fruit firmness with a correlation coefficient (r) of 0.63. The spatially-resolved technique provides an efficient means for measuring the optical properties of fruits, and may be also useful for assessing the apple firmness.
关键词： Diffusion theory,Optical properties,Light propagation,Imaging system,Apple firmness
更新于2025-09-19 17:15:36
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Fast 3D movement of a laser focusing spot behind scattering media by utilizing optical memory effect and optical conjugate planes
摘要： Controlling light propagation intentionally through turbid media such as ground glass or biological tissue has been demonstrated for many useful applications. Due to random scattering effect, one of the important goals is to draw a desired shape behind turbid media with a swift and precise method. Feedback wavefront shaping method which is known as a very effective approach to focus the light, is restricted by slow optimization process for obtaining multiple spots. Here we propose a technique to implement feedback wavefront shaping with optical memory effect and optical 4f system to speedy move focus spot and form shapes in 3D space behind scattering media. Starting with only one optimization process to achieve a focusing spot, the advantages of the optical configuration and full digital control allow us to move the focus spot with high quality at the speed of SLM frame rate. Multiple focusing spots can be achieved simultaneously by combining multiple phase patterns on a single SLM. By inheriting the phase patterns in the initial focusing process, we can enhance the intensity of the focusing spot at the edge of memory effect in with 50% reduction in optimization time. With a new focusing spot, we have two partially overlapped memory effect regions, expanding our 3D scanning range. With fast wavefront shaping devices, our proposed technique could potentially find appealing applications with biological tissues.
关键词： optical memory effect,biological tissues,turbid media,3D space,light propagation,feedback wavefront shaping
更新于2025-09-16 10:30:52
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Light propagation in inhomogeneous media, coupled quantum harmonic oscillators and phase transitions
摘要： this contribution has two main purposes. first, using classical optics we show how to model two coupled quantum harmonic oscillators and two interacting quantized fields. Second, we present classical analogs of coupled harmonic oscillators that correspond to anisotropic quadratic graded indexed media in a rotated reference frame, and we use operator techniques, common to quantum mechanics, to solve the propagation of light through a particular type of graded indexed medium. Additionally, we show that the system presents phase transitions.
关键词： inhomogeneous media,phase transitions,quantum harmonic oscillators,light propagation
更新于2025-09-11 14:15:04
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Efficient and quantitative analysis of photon density of states for two-dimensional photonic crystals with omnidirectional light propagation
摘要： Omnidirectional light propagation in two-dimensional (2D) photonic crystals (PCs) has been investigated by extending the formerly developed 2D finite element analysis (FEA) of in-plane light propagation in which the corresponding band structure (BS) and photon density of states (PDOS) of 2D PCs with complex geometry configurations had been calculated more accurately by using an adaptive FEA in real space for both the transverse electric (TE) and transverse magnetic (TM) modes. In this work, by adopting a wave-guiding theory under the consideration of translational symmetry, the omnidirectional PDOS corresponding to both the radiative and evanescent waves can be calculated efficiently based on the in-plane dispersion relations of both TE and TM modes within the irreducible Brillouin zone. We demonstrate that the complete band gaps shown by previous work considering only the radiative modes will be closed by including the contributions of the evanescent modes. These results are of general importance and relevance to the spontaneous emission by an atom or to dipole radiation in 2D periodic structures. In addition, it may serve as an efficient approach to identifying the existence of a complete photonic band gap in a 2D PC instead of using time-consuming three-dimensional BS calculations.
关键词： two-dimensional photonic crystals,radiative and evanescent waves,finite element analysis,photon density of states,omnidirectional light propagation
更新于2025-09-10 09:29:36
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Propagation of light from dipole source and generalization of Fresnel-Kirchhoff integral
摘要： The elementary system which can emit light is a dipole. Theoretical method of light propagation from point like dipole source is presented in this paper. The propagation is considered through two media divided by 3D arbitrary surface. Orientation of new formed dipole on surface segment is determined according to the refraction of incident wave-front electric ?eld strength on boundary surface. Generalized formulation of Fresnel-Kirchho? integral is derived for elementary dipole as a source and arbitrary surface dividing two media with arbitrary refraction indexes. This model shows that distribution of light depends on orientation of primary point like dipole source and curvature of 3D boundary surface. The model presented here can be used for extended surface or volume source of light, where each point of the source is point like dipole. In this way, the propagation of light wavefront could be modeled.
关键词： Dipole source,Light propagation,Di?raction
更新于2025-09-10 09:29:36
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Geometrical optics and geodesics in thin layers
摘要： The propagation of a light ray in a thin layer (film) within geometrical optics is considered. It is assumed that the ray is captured inside the layer due to reflecting walls or total internal reflection (in the case of a dielectric layer). It has been found that for a very thin film (the length scale is imposed by the curvature of the surface at a given point) the equations describing the trajectory of the light beam are reduced to the equation of a geodesic on the limiting curved surface. There have also been found corrections to the trajectory equation resulting from the finite thickness of the film. Numerical calculations performed for a couple of exemplary curved layers (cone, sphere, torus, and catenoid) confirm that for thin layers the light ray which is repeatedly reflected propagates along the curve close to the geodesic but as the layer thickness increases, these trajectories move away from each other. Because the trajectory equations are complicated nonlinear differential equations, their solutions show some chaotic features. Small changes in the initial conditions result in remarkably different trajectories. These chaotic properties become less significant the thinner the layer under consideration.
关键词： thin layers,geometrical optics,light propagation,geodesics,curved surfaces
更新于2025-09-04 15:30:14
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Rotary photon drag in a Mach-Zehnder-type Sagnac interferometer
摘要： We theoretically investigate rotary photon drag in a Mach-Zehnder type Sagnac interferometer using a four level N-type atomic medium. Splitting of a single pulse of light into two pulses is observed at high strength of the control field both in absorption and dispersion spectra. Group index, relativistic velocities and rotary photon drag are examined as a function of probe field detuning Δp. Rotation angles of ± 2, ± 3, ± 4 and ± 6 micro radians are achieved for the two beams propagating in clockwise and counter clockwise direction by varying values of the probe field detuning as 0γ, 0.5γ and 1.5γ, respectively. The results obtained show potential applications in sensing technology, optical fibre communication technology as well as in perfect lens formation.
关键词： Rotary photon drag,Light propagation,Polarization,Quantum coherence,Interferometry,Electromagnetically induced transparency
更新于2025-09-04 15:30:14