Optics · Cross-listed from physics.app-ph
Low-Cost Spectrophotometers: A Comparative Evaluation of Open-Source Architectures
Alex M. Rivera-Rivera, Daniela Martinez-Ortiz, François Quitin et al. (+4 more)
The rapid growth of low-cost and open-source spectrophotometers has created a need for systematic methodologies to evaluate and compare alternative instrument architectures. This study presents a comparative assessment of three representative open-source spectrophotometric platforms, encompassing discrete multispectral sensing and continuous-spectrum imaging approaches. Their performance was evaluated against a commercial Thermo Scientific Genesys 30 spectrophotometer in terms of spectral agreement, portability, implementation complexity, and cost. The results demonstrate that no single architecture is universally optimal; instead, each presents distinct trade-offs that determine its suitability for specific applications. Multispectral sensor-based systems offer compact, low-power solutions for field deployment, whereas imaging-based platforms provide spectral performance closer to laboratory-grade instrumentation. All hardware designs, firmware, and software developed in this work are released as open-source resources to support reproducibility and further development. The study highlights the importance of matching instrument architecture to application requirements and proposes a practical framework for the evaluation and selection of low-cost spectrophotometers, facilitating the adoption of open-source analytical tools for water quality monitoring and related applications.
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All authors Alex M. Rivera-Rivera, Daniela Martinez-Ortiz, François Quitin, Denis Terwagne, Stamatios C. Nicolis, Ernesto Altshuler, Alexandre Campo
Optics · Cross-listed from nlin.SI
Nonlinear Spectral Computing
Ludovica Falsi, Francesco Coppini and Claudio Conti
Many machine learning
algorithms rely on the
Fourier transform, which is also the inner core of many analog computing devices and, specifically, of optical computing. The square of the modulus of the
Fourier spectrum naturally maps onto pairwise interactions, as in the renowned Ising model, making it applicable to combinatorial optimization. Here we show how the nonlinear
Fourier transform, related to integrable nonlinear partial differential equations, significantly widens the computational capability and also enables a wide variety of computing gates. We study specifically the case of the nonlinear Schrödinger equation; we introduce an input composed by “
tokens”, i.e., batches of information encoded in a multi-step potential, and we show how the nonlinear spectral computing arising in the wave propagation not only generalizes combinatorial optimization to higher order problems, but also realizes boolean gates. In the weakly nonlinear regime, nonlinearity generates higher-order interactions as perturbative corrections to the pairwise terms. In the solitonic regime, the discrete nonlinear spectrum performs digital computation through
soliton generation. By using four input
tokens, we demonstrate the programmability of all 256 Boolean functions of three variables, including 3-SAT instances. Our results show that integrable nonlinear propagation provides an unprecedented single physical platform for higher-order and logical computation, opening the way to a rich variety of new
algorithms for analog computing, machine learning, and classical and
quantum information processing.
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Optics · Cross-listed from quant-ph
Energy-constrained two-way capacity bounds for noisy Gaussian channels
Stefano Pirandola
A gap between achievable rates and converse bounds persists for energy-constrained bosonic communication in the presence of excess noise. We derive a unified adaptive weak-converse bound for thermal attenuation, noisy amplification, and additive Gaussian noise under an unconditional mean transmitted-
photon-number constraint. The bound applies to arbitrary adaptive protocols with
quantum memories and constrains the two-way
quantum,
entanglement-distribution, private, and secret-key capacities. It vanishes throughout the
entanglement-breaking region and approaches the corresponding PLOB bound at infinite energy. At finite energy, it improves the evaluated Gaussian squashed-
entanglement and PLOB bounds in relevant parameter regimes, while comparison with hashing rates quantifies the remaining gap to achievability. The result provides a common energy-dependent
benchmark for noisy bosonic Gaussian channels and extends finite-energy converse methods beyond the
quantum-limited setting.
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Optics
Parametric amplifier mediated nonreciprocal phonon laser in non-Markovian optomechanical resonators
H. Yi, C. Cui, J. Luo et al. (+4 more)
Phonon lasers amplify mechanical vibrations, serving as key tools for coherent acoustics research and applications such as ultrasensitive sensing and information processing, which has been extensively studied in Markovian systems but remains unexplored in non-Markovian ones. In this paper, we propose the nonreciprocal
phonon laser in a coupled cavity system composed of nonlinear optomechanical resonator and degenerate optical parametric amplifier (DOPA) under the Markovian approximation. The mechanical gain and threshold power of the
phonon laser are influenced by Sagnac-Fizeau effects, which leads to the unidirectional
phonon laser and enhances the
phonon laser performance via DOPA. Moreover, we generalize the nonreciprocal
phonon laser to non-Markovian regimes. We find that non-Markovian effects can lead to the further enhancement of the
phonon laser at a lower
phonon laser threshold power with DOPA fixed. Our work reveals connections between low-power mechanical isolation and non-Markovian effects, offering a pathway to manipulate cavity optomechanical devices across a broader range of applications.
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All authors H. Yi, C. Cui, J. Luo, H. T. Cui, Yan-Hui Zhou, Cheng Shang, H. Z. Shen
Optics · Cross-listed from cs.CV
PolarScale: A Physics-Grounded Benchmark for Radiometrically Consistent RGB-to-Stokes Estimation
Beibei Lin, Tingting Chen, Xin Zhang et al. (+3 more)
Polarization imaging provides physical cues beyond intensity imaging but typically requires specialized hardware. Recent methods infer polarization from RGB-like inputs, yet predict only normalized Stokes components or relative descriptors, from which the radiometric scale needed for full Stokes reconstruction has been divided out. We introduce PolarScale, a
benchmark that makes this scale an explicit prediction and evaluation target. Built on existing trichromatic full-Stokes measurements, PolarScale takes the per-scene normalized total-intensity image $s_0$ (a scene-referred linear image, not a consumer sRGB photograph) and asks models to predict normalized Stokes components, AoLP/DoLP/DoCP, and a per-scene scale. Because the scale is divided out of the input, it is not physically identifiable; PolarScale therefore evaluates
dataset-conditioned semantic scale estimation against a constant-scale control, together with angular, self-consistency, and physical-bound metrics. Across seven restoration-based and generative backbones and three prediction strategies, the strongest restoration models estimate the scale with 3.6-4.3% mean relative error versus 5.7% for the constant control and violate physical bounds on fewer than 0.25% of pixels, whereas two generative baselines collapse to a near-zero scale; explicit descriptor supervision improves descriptor accuracy (23.66 vs. 18.88 dB PSNR for MAE). Predicted full-Stokes representations improve diffuse/specular separation, material segmentation, and glare classification, although in diffuse/specular separation the learned scale performs only on par with the constant control.
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All authors Beibei Lin, Tingting Chen, Xin Zhang, Wenhao Zhao, Dongjun Li, Zifeng Yuan
Optics
Perfect Bound States and non-Markovian Dynamics for Imperfect Giant Atoms in a Semi-Infinite Waveguide
T. Y. Liu, X. Y. Li, W. Y. Hu et al. (+3 more)
Bound states in structured reservoirs require exact interference conditions and are therefore sensitive to imperfections in the coupling geometry. In this paper, we study a two-level giant atom coupled at multiple points to a mirror-terminated semi-infinite waveguide. The exact atom-
photon bound state requires both cancellation of the outgoing radiation amplitude and dispersive matching to the atomic detuning. Generalized delay-equation dynamics, continued-pole spectra, and real-space
photon fields verify this criterion for coupling-strength, position, and coupling-phase imperfections. For representative realizations, retuning restores one-, two-, and three-root responses after strength errors and one- and two-root responses after position errors. The specified position-imperfect three-root configuration fails because its $2\pi$ root is no longer dark, consistent with a $58.77\%$ spectral mismatch. Ensembles of 1000 realizations at each error amplitude show near-unity target-state recovery for strength errors, unity recovery of the specified one- and two-root targets but no three-root recovery for position errors, and no nontrivial exact recovery for independent phase errors. Optimized phase-imperfect responses instead retain finite linewidths. Root matching with realization-dependent control retuning therefore constitutes a compensation procedure, rather than generic passive robustness against arbitrary disorder.
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All authors T. Y. Liu, X. Y. Li, W. Y. Hu, T. Z. Luan, Cheng Shang, H. Z. Shen
Optics
Synthesizing free-electron wave functions by stimulated near-field interactions
Álvaro Rodríguez Echarri and Albert Polman
Stimulated electron-optical-near-field interactions imprint a coherent, phase-coherent modulation on the wave function of a free electron, of which the free-space dispersion subsequently converts into a train of attosecond density peaks. Light thereby becomes a tool for synthesizing the electron wave function itself, setting when, where, and how narrowly the electron density concentrates. Here we study
photon-induced near-field electron microscopy (PINEM) to gain control over that synthesis in two stages: first for a single PINEM interaction, whose design parameters we obtain in closed form, and then for multiple PINEM interactions acting in parallel, which extends the control across space and time. The design rules follow from decomposing the propagated density into temporal harmonics, which we classify into three: (i) the arrival time of the attosecond train, fixed by the optical phase of the coupling; (ii) the distance at which the train forms, set by diffraction at the point where all classical trajectories converge; and (iii) the pulse duration, fixed by the imprinted energy spread. We evaluate these parameters for a scanning-electron-microscope (SEM) configuration at 10~keV, where the compression completes within tens of micrometers from the interaction region, with results 20% better than previous approaches. Letting the electron then interact with several spatially separated near fields in parallel, normal to the trajectory, each pathway carrying its own coupling strength and optical phase, we show that retaining or erasing which-path information changes both the propagated density and the measurable energy spectrum, the latter providing in turn a measure of the mutual coherence of the driving fields. These results establish PINEM as a quantitative synthesis tool for free-electron wave functions in compact, low-voltage electron microscopes.
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Optics
Boosting the photon bunching of classical light via a modified Fabry-Pérot cavity
Lu Zhang, Dongxu Zhou, Hongzhi Zhang et al. (+1 more)
We proposed to boost the
photon bunching effect of classical light via a modified Fabry-Pérot cavity with one of the cavity mirrors being replaced by a spatial light modulator, through which multiple independent transverse modulations, each was to encode independently spatially correlated phase on the wave front of the light field, was cascaded in sequence in the longitudinal propagation direction in the cavity. The two-
photon bunching peak and the three-
photon bunching peak of the generated superbunching light field were measured to be $36.9\pm2.0$ and $\rm (2.46\pm0.12)\times10^{3}$, respectively, which, as compared to those of thermal light, were improved by one-order and three-order of magnitude, respectively. Correspondingly, the ghost image visibility reconstructed with the superbunching light was demonstrated experimentally to be improved by $\sim 40$ times as compared to that with the pseudo-thermal light. Such classical superbunching light field is of essential importance not only for fundamental physics but also for potential applications such as correlated imaging, ghost interference and nonlinear optics.
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All authors Lu Zhang, Dongxu Zhou, Hongzhi Zhang, Guoquan Zhang
Optics
In-line Dispersion Control of Femtosecond Laser Pulses by Multilayer Huygens' Metasurfaces
Anna Fitriana, Katsuya Tanaka, Roland Schiek et al. (+3 more)
Dispersion is a key limiting factor in ultrafast systems as it modifies the temporal structure of ultrashort optical pulses. Conventional dispersion compensation techniques, though widely used, rely on a combination of several bulky optical components and complex, long propagation paths, posing challenges for integration into compact photonic platforms. All-dielectric resonant metasurfaces operating in the Huygens' regime of spectrally overlapping electric and
magnetic dipolar resonances offer a promising route to low-loss dispersion control at the sub-wavelength scale; however, the achievable dispersion from a single layer remains fundamentally limited by its phase gradient and spectral bandwidth. Here, we experimentally demonstrate in-line dispersion control of femtosecond
laser pulses using a multilayer architecture of dielectric Huygens' metasurfaces, without requiring spatial separation of their spectral components, as typically employed in
Fourier-plane dispersion compensation schemes. The phase dispersion accumulates across stacked layers approaching a total of 8pi, corresponding to a maximum group delay dispersion of around 3969 fs2. This enables efficient compensation of the input chirp and results in a significant compression of femtosecond
laser pulses in the telecom wavelength range. Importantly, the metasurface stack functions as a single compact transmissive element, which is simply inserted into the beam path. Overall, our results establish a compact, scalable platform for integrated pulse compression and ultrafast dispersion engineering.
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All authors Anna Fitriana, Katsuya Tanaka, Roland Schiek, Thomas Perstch, Dragomir Neshev, Isabelle Staude
Optics · Cross-listed from cs.CV
RACE-FPP: A Robust AI-assisted Characterisation Enhancement for Fringe Projection Profilometry
Osman Ali, Xiangjun Kong, Tibebe Yalew et al. (+2 more)
Fringe Projection Profilometry (FPP) requires precise system characterisation to achieve reliable three-dimensional (3D) reconstructions; however, characterisation accuracy strongly depends on robust checkerboard feature localisation, which can deteriorate under challenging imaging conditions such as lens blur and characterisation target orientations. Existing deep learning-based corner detectors are typically assessed using detection metrics and camera reprojection error alone, without considering their wider impact on projector characterisation, camera-projector stereo characterisation consistency, or overall measurement accuracy. In this work, we introduce a complete FPP characterisation pipeline that incorporates deep learning-based corner detection into the standard camera characterisation workflow. We also characterise the projector by sampling phase values at the centres of the white squares in the characterisation target. Rather than treating corner detection as an isolated task, the proposed framework explicitly analyses how localisation errors propagate throughout the entire FPP characterisation chain. Performance is evaluated using detection metrics (e.g., precision and recall), camera and projector reprojection errors, and the camera and projector stereo characterisation. Across a mixed
dataset of clean and degraded images, the camera reprojection error is reduced from 1.237 pixels to 0.259 pixels, while the projector reprojection error is reduced by roughly 50%. Dimensional evaluation of reconstructed artefacts shows improved
geometric accuracy compared with those resulting from the conventional pipeline. Overall, the findings indicate increased robustness of system-level characterisation under challenging imaging conditions, thereby enabling more reliable industrial FPP measurements.
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All authors Osman Ali, Xiangjun Kong, Tibebe Yalew, Waiel Elmadih, Samanta Piano
Optics
Beyond Group Delay: Fundamental Limits of Achromatic Metasurfaces
Roman Buisine, Nicolas Kossowski, Adelin Patoux et al. (+3 more)
Achromaticity is one of the most demanding functionalities achievable with a metasurface because it requires reproducing the same optical response over a finite spectral bandwidth rather than at a single wavelength. Although previous studies established aperture-bandwidth limits based on temporal-delay considerations, the role of optical performance on these limits has remained unresolved. Here, we develop a rigorous theoretical framework that explicitly highlights how the optical performance sets the true aperture-bandwidth limit of single interface achromatic metasurfaces, quantifying the fundamental limits through the Strehl ratio. We identified two distinct operating regimes. In the first, the achromaticity conditions are exactly satisfied, guaranteeing diffraction-limited performance across the entire bandwidth. Surprisingly, the maximum achievable aperture in this regime is essentially independent of bandwidth and is instead governed by the ability of practical meta-atoms to simultaneously realize the required phase and dispersion. In the second regime, relaxing the required optical performance allows larger apertures at the cost of a fundamental trade-off between aperture, bandwidth, and optical performance. Numerical validation using a large library of high-transmission GaN meta-atoms confirms the theory and reveals the transition between these regimes. Our framework establishes the fundamental limits of achromatic metasurfaces, providing practical design rules for balancing aperture, bandwidth, and optical performance of achromatic metasurfaces.
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All authors Roman Buisine, Nicolas Kossowski, Adelin Patoux, Patrice Genevet, Rémi Colom, Samira Khadir
Optics · Cross-listed from quant-ph
Squeezed light from a semiconductor amplifier
Andrey S. Aleksandrov and Anatoly V. Masalov
The possibility of generating light in a squeezed
quantum state during saturated light amplification in a
semiconductor amplifier is theoretically analyzed. Due to four-wave mixing process during amplification, weak components of the spontaneous emission of the medium with symmetric frequency shifts relative to the strong amplified wave acquire the
quantum properties of two-mode squeezed light. The squeezing of quadrature components occurs in the range of frequency shifts of several GHz ($\sim$ the inverse relaxation time of the charge carrier density) and can reach 10 dB or more under optimal conditions. The formation of a two-mode squeezing phase facilitates the observation of the squeezing effect, in which a strong wave, playing the role of a local wave, exhibits quadrature noise suppression without additional homodyne detection.
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Optics
An Acousto-Optic Colorimeter
Pavel Aksentsev, Georgiy Lobarev, Sergey Korchagin et al. (+2 more)
Uniform color spaces and color-difference formulae rest on visual data obtained almost entirely with surface samples and conventional displays, whose primaries confine the measurements to a limited chromaticity range. The highly saturated region of color space is therefore the least measured part of human color perception, at the moment when
quantum-dot, microLED, and
laser displays have begun to operate inside it. Closing this gap requires stimuli more saturated than any fixed-primary device can produce, together with the stability and uniformity demanded by visual experiments. We present an acousto-optic colorimeter built for this purpose. A four-channel acousto-optic tunable filter selects narrow spectral components from a supercontinuum
laser over the calibrated range of 443–660~nm, with measured linewidths of 1.37–3.20~nm; the wavelength and radiance of every component are set electronically, so the primary set itself becomes an experimental variable. A compact diffuser–light-pipe homogenizer combines the selected components into a uniform observation field, and spectral feedback stabilizes their intensities. The calibrated primary set covered 95% of the area enclosed by the CIE 1964 $10^{\circ}$ spectral locus in the $x,y$ chromaticity plane. The calculated maximum luminance reached 1406~cd\,m$^{-2}$, with 328~cd\,m$^{-2}$ available at the gray Robertson chromaticity. Across an 18-mm observation field the mean spatial $\Delta E_{00}$ difference was 0.913, and five Robertson color centers reproduced under continuous feedback gave mean target errors of 0.34–1.26~$\Delta E_{00}$ over 10-min intervals. The instrument thus delivers calibrated, uniform, and stable highly saturated stimuli, and is intended to extend the empirical basis of color-difference measurement into the region where data are still absent.
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All authors Pavel Aksentsev, Georgiy Lobarev, Sergey Korchagin, Olga Polschikova, Egor Ershov
Optics · Cross-listed from astro-ph.IM
Optimizing Laguerre-Gaussian Mode Interferometry in Gravitational-Wave Detectors through Modal Degeneracy Breaking
Liu Tao, Eleonora Capocasa and Matteo Barsuglia
Higher-order Laguerre-Gaussian modes can reduce test-mass thermal noise in gravitational-wave interferometers, but their implementation is limited by degeneracy-induced coupling losses in realistic high-finesse cavities. We mitigate these losses by optimizing the mirror
curvature to break modal degeneracy. We develop a general framework for designing an axisymmetric corrective test-mass surface profile that lifts the degeneracy of the sixth-order Laguerre-Gaussian subspace while preserving an injected donut-shaped $\mathrm{LG}_{0,6}$ mode. Expanded in a
Fourier-Bessel basis, the profile is optimized to maximize the frequency splitting from the nearest unwanted mode while minimizing target-mode loss. For a Virgo-like Fabry-Perot arm cavity, the optimized profile separates the $\mathrm{LG}_{0,6}$ resonance from the nearest same-order resonance, $\mathrm{LG}_{1,4}$, by 2.04% of the free spectral range, reducing unwanted-mode gains below unity at the target-mode resonance and suppressing their resonant enhancement. The profile introduces negligible target-mode loss and improves robustness against astigmatism and realistic mirror surface distortions. Monte Carlo simulations with realistic mirror imperfections yield an average contrast defect of 368 ppm and an average reflected optical loss of 979 ppm, equivalent to a round-trip loss of approximately 3.5 ppm for the modeled cavity. These results substantially improve upon the central anti-reflective mirror mask approach based on selective loss engineering, bringing reflected optical loss within a factor of two of that obtained with the fundamental Gaussian mode under the same simulation conditions. This approach offers a route toward robust donut-shaped Laguerre-Gaussian modes in future precision interferometers with realistic imperfections.
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Optics · Cross-listed from physics.med-ph
A Multimodal Hyperspectral and Laser Speckle Imaging Platform for Simultaneous Monitoring of Spinal Cord Oxygenation, Perfusion and Metabolism
Junda Wang, Luca Giannoni, Ayse Gertrude Yenicelik et al. (+3 more)
Hyperspectral imaging (HSI) enables spatial mapping of haemoglobin oxygenation and cytochrome-c-oxidase (CCO) redox changes in exposed neural tissue. In this study, we present a technical upgrade of an existing HSI platform by the integration of
laser speckle contrast imaging (LSCI), enabling contemporaneous assessment of oxygenation, oxidative metabolism, relative perfusion and a derived relative oxygen metabolic index in exposed spinal cord in a rat preclinical model. The upgraded system (hNIR+) uses a shared optical path and a single camera to acquire HSI and LSCI images from the same field of view using a sequential acquisition workflow. Hyperspectral images are acquired at 11 discrete wavelengths (600, 630, 665, 784, 800, 818, 835, 851, 868, 881, and 894 nm) to estimate changes in oxygenated haemoglobin (HbO2), deoxygenated haemoglobin (HHb) and oxidized CCO (oxCCO). LSCI is implemented using 632.8-nm coherent illumination to generate relative blood-flow index (rBFI) maps. The LSCI subsystem was validated using a controlled blood-flow phantom, where the LSCI-derived inverse speckle contrast index showed a strong positive linear relationship with pump-controlled flow. The upgraded platform was then evaluated in proof-of-concept observations of the rat spinal cord under normoxia, hypoxia and recovery conditions. Representative
multimodal maps and ROI-based time-course analysis showed clear dynamic responses in HbO2, HHb, oxCCO and rBFI during oxygen challenges that were consistent with the expected physiological responses of the spinal cord during hypoxia, hyperoxia and subsequent recoveries. Overall, these results demonstrate that integrating LSCI into HSI extends the platform to
multimodal and simultaneous monitoring of haemodynamic-metabolic coupling.
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All authors Junda Wang, Luca Giannoni, Ayse Gertrude Yenicelik, Eleni Giama, Frederic Lange, Ilias Tachtsidis
Optics
Microfabrication of Paul wheel trap chip in fused silica by selective laser etching
Jakub Vejrosta, Lukáš Šilhan, Mojmír Šerý et al. (+3 more)
We present a rapid, mask-free fabrication workflow for the Paul wheel trap chip based on selective
laser etching (SLE) of fused silica. The complete process - femtosecond
laser writing, wet-chemical etching in KOH ($\sim$230 $\mu$m/h, releasing the trap geometry from a 500 $\mu$m wafer in approximately 2 h), RF magnetron sputtering of silver electrodes, and direct femtosecond
laser ablation for electrode patterning - is carried out in-house, bypassing photolithographic processing and custom shadow masks entirely. Nine chips per 4-inch wafer can be produced in a single working day, reducing the fabrication lead time by more than one order of magnitude relative to the outsourced CVD diamond design. The functionality of the fabricated wheel trap chip is confirmed by a proof-of-concept microparticle trapping demonstration, in which a single microparticle was confined continuously for 72 h at atmospheric pressure. This establishes SLE of fused silica as a rapid, economically accessible fabrication platform for Paul traps in levitated-optomechanics applications.
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All authors Jakub Vejrosta, Lukáš Šilhan, Mojmír Šerý, Tomáš Fořt, Oto Brzobohatý, Pavel Zemánek
Optics
Direct visualization of non-equilibrium heat extraction by a metasurface absorber
Shu Watanabe, Robert E. Simpson, Takuo Tanaka et al. (+1 more)
Metasurface heat absorption is conventionally characterized by far-field infra-red spectroscopy under
equilibrium conditions. The approach provides information on the surface emissivity but does not directly reveal heat transferred by electromagnetic absorption. To understand the resulting temperature change, however, the associated heat transfer must be considered. Here, we directly observe heat extracted by electromagnetic absorption using infrared thermography. By monitoring the cooling dynamics of a copper plate placed in contact with a metasurface-integrated thermoelectric device, we show that the copper plate cools faster than one placed on an unstructured planar surface (control). This result provides direct evidence of heat transfer from the adjacent solid to the metasurface; revealing a metasurface-mediated electromagnetic absorption heat transfer mechanism. These findings provide new insight into nonequilibrium thermal processes enabled by metasurface absorbers.
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All authors Shu Watanabe, Robert E. Simpson, Takuo Tanaka, Wakana Kubo
Optics
Crossover of magnetodipole and electrodipole contributions in the broadband magneto-optics of bismuth-substituted iron garnets
Nika Gribova
This work presents a comprehensive macroscopic electrodynamic framework isolating the magnetodipole (MD) and electrodipole (ED) contributions to the magneto-optical effects in bismuth-substituted iron garnet. By rigorously incorporating the dispersive
magnetic permeability tensor, the dominance of the MD mechanism in the terahertz (THz) gap is demonstrated. In the mid-infrared (MIR) to near-infrared (NIR) domain, a fundamental spectral crossover is revealed where the magnitudes of the MD and ED contributions exactly equalize, invalidating the widespread assumption that
magnetic contributions vanish uniformly at infrared frequencies. Furthermore, it is shown that interfacial phase shifts uniquely dictate how these competing mechanisms project onto observable rotation and ellipticity, yielding an inverted spectral hierarchy between transmission (Faraday) and reflection (polar and longitudinal Kerr) geometries. Most notably, the transverse Kerr effect for s-polarized light is established to be exclusively driven by the off-diagonal
magnetic permeability. While strictly zero under the conventional ED approximation, the s-polarized transverse Kerr effect emerges as a robust, free of the gyroelectric contribution probe of MD activity in the THz and MIR–NIR regimes, yielding a THz response two orders of magnitude larger than its p-polarized counterpart.
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