arXiv subjects

Amitrajit Nag

Publications and source records attributed to Amitrajit Nag.

3 recordsLinked to original sources

arXiv2025

Origin of the Fano interference and its tunability with near-field interactions in a guided mode-resonant metasurface

Asymmetric resonances emerging from the Fano interference are a well-known phenomenon in fields like atomic physics and grating optics, and they have recently started to gain interest in artificially engineered dielectric, metallic, or composite metasurfaces and metamaterials. The guided mode-resonant metasurface belongs to this class with grating-waveguide responses and shows asymmetric resonances. Here, we have theoretically studied the origin of the resonance, finding out the root of the Fano interference. We have followed the ab initio theory derived from the Feshbach formalism for the electromagnetic scattering. We have numerically simulated the metasurface to obtain different field parameters required for the ab initio theory; in this regard, we have used the multipole decomposition of the scattering fields for the induced moments. Motivated by our recent experiments, we have used a planewave and polarized dipole sources to excite the metasurface, and studied subsequent effects, like the resonance redshift and the resonance linewidth narrowing for the metasurface. These happened due to the change of the excitation, and we have numerically quantified them. The change of the excitation source bears the novelty of the work. Thus, it helps comprehend the experimental observations qualitatively. This work could help explain and explore possibilities to observe asymmetric resonances in metasurfaces for various excitation conditions, and the key results of resonance shift and linewidth narrowing could be significant for precision applications and fundamental optical studies.

physics.optics↗

arXiv2025

Non-monotonic temperature dependence of light-matter interaction in hyperbolic metamaterial due to interplay of electron-phonon scattering

Hyperbolic metamaterials (HMM) are artificially engineered materials that are congenial for light-matter interaction studies and nanophotonic applications with the hyperbolic dispersion of light propagating through them, which offers a large photonic density of states. We have explored HMM's broadband cavity-like modes and ultrasmall mode volumes, even though the system has lossy plasmonic constituents. The light-matter interaction properties of plasmonic materials strongly depend on different internal damping mechanisms. Temperature is a macroscopic parameter that controls these internal mechanisms and is reflected in their corresponding interaction behaviors. In this work, we investigated the light-matter interaction properties of the HMM system with temperature. We studied the HMM system weakly coupled to quantum emitters. This weakly coupled system shows a non-monotonicity in its broadband absorption and the emission from near-field coupling with quantum emitters. This is determined by the interplay between the electron-phonon and the phonon-phonon scatterings occurring in the metal nanowire array, effectively providing the damping with temperature. Theoretically, we confirmed the increased presence of the phonon-phonon scattering in nanowires compared to bulk metals, which plays an instrumental role in the observed light-matter interaction effects. This study could efficiently predict the use of the HMM in optics and photonics applications, with precise tuning and availability of control parameters with temperature. Also, this study could help identify the effect of increased phonon-phonon scattering in nanostructures and explore the possibility of quantifying and applying it by optical measurements.

physics.optics↗

arXiv2025

Unraveling cavity-like modes of two-dimensional broad band hyperbolic metamaterial and their coupling to quantum emitters

Hyperbolic metamaterials (HMM) are artificially engineered materials that exhibit hyperbolic dispersion of light propagating through them. These have been extensively studied for tailoring light propagation. Most studies use an effective medium approach that is extremely useful, though it misses out on properties that can arise from the microscopic details of the HMM. In particular, the HMM can have cavity-like modes, and it is important to understand such modes and their relevance in light propagation and coupling of HMM to quantum emitters. In this work, we bring out the cavity-like modes of the silver nanowire-alumina two-dimensional HMM, which remain on top of the broad response of the HMM. These modes define the characteristic reflection spectra. The observed resonances and their widths are in good agreement with our simulations. These well-defined modes occur even though the metallic part of the HMM has Ohmic losses. Then, we present experimental results on the coupling of quantum emitters to the cavity-like modes of the HMM. We present results for both steady-state and time-resolved photoluminescence. Using these, we extract the corresponding Purcell factors for radiative rate enhancement. Theoretical analyses of the experimental data allow the determination of the cavity coupling parameters and mode volumes. These experimental results are confirmed by the FDTD calculations for the HMM mode volume. This work elucidates the pathway to precise engineering for future applications of HMM modes in strong light-matter interactions.

physics.optics↗