Volume 14, Issue 13

Surface-enhanced infrared absorption (SEIRA) spectroscopy holds significant promise for chemical detection as it enables direct identification of distinct vibrational fingerprints of molecules. Traditionally, SEIRA has been exploited through the use of tailored metallic nanoantennas, which are burdened by high losses in the mid infrared and costly nanofabrication techniques. In this work, we introduce an alternative, simpler approach using self-assembled Cd(Zn)O nanoparticles as a SEIRA platform. We demonstrate enhancements of the vibrational absorption of several molecular bonds in polymethyl methacrylate and vanillin up to a factor of 4.3. Such enhancements scale linearly with the surface density of nanoparticles, which can be controlled through the growth conditions. Thanks to the tunability of our platform, we report extended sensing capabilities to high energies in the mid-IR, reaching as high as 3,800 cm −1 . All in all, we present a proof of concept for large-area, simple preparation, ready-to-sense surfaces that has the potential to be scaled up to become a prominent technology for mid-IR molecule sensing.

We studied dispersion in Rhodamine laser dyes in the Kretschmann geometry and found (i) multi-branch “staircase” dispersion curves in singly doped and double doped PMMA polymer, (ii) emergence of the new dispersion “fork” branch, (iii) unparallel dispersion and coupling in the mixture of two different dyes, and (iv) effect of high dye concentration on strong coupling without metal.

Recent studies have demonstrated that a laser can self-generate frequency combs when tuned near an exceptional point (EP), where two cavity modes coalesce. These EP combs induce periodic modulation of the population inversion in the gain medium, and their repetition rate is independent of the laser cavity’s free spectral range. In this work, we perform a stability analysis that reveals two notable properties of EP combs, bi-stability and a period-doubling cascade. The period-doubling cascade enables halving of the repetition rate while maintaining the comb’s total bandwidth, presenting opportunities for the design of highly compact frequency comb generators.

Ultra-silicon-rich nitride Bragg gratings provide a powerful platform for precise light manipulation in photonic chips. Their exceptionally high nonlinearity and strong grating-induced dispersion near the stop-band edges significantly reduce the power and length required for chip-scale light–matter interactions. Using computational methods, we theoretically investigate modulational instability, Fermi–Pasta–Ulam recurrence, and pattern formation in this platform within the framework of the Akhmediev breather. We assess their experimental feasibility and show that this platform can generate a high-quality pulse train at the output. We demonstrate that modulational instability can be triggered in the gratings as short as 1–2 mm, leading to Akhmediev breather formation. By analyzing the full dispersion profile, we identify pump wavelengths that generate new frequencies and show that the grating also can produce a comb-like discrete spectrum. Furthermore, we reveal that even with high loss, parametric amplification at the grating output is possible, highlighting its potential as a nonlinear platform for frequency comb generation, wavelength-multiplexed data transmission, and high-precision pulse processing.

Infrared windows-enabled infrared inspection has significant applications in both civilian and military domains. However, the static and indiscriminate transparency across the visible to infrared regions renders them vulnerable to potential laser damage. In this study, we construct a dynamic infrared optical switch based on a vanadium dioxide (VO 2 )–Al metasurface structure. The phase transition of VO 2 enables dynamic transmittance switching, while the Al metasurface confines this capability to specific wavelengths to mitigate unwanted interferences. The infrared switch transmits light within the 8–14 μm range only in its “ON” state, reflecting other wavelengths across the visible to infrared spectrum. The underlying physics is attributed to plasmon-induced extraordinary optical transmission combined with the reconfigurable metatronic properties of the VO 2 layer. Moreover, while maintaining excellent optical performance, we utilize full-wave simulations to enlarge the feature sizes of the Al metasurface structure to meet the demands for large-area fabrication. This advancement paves the way for practical applications of infrared switches, highlighting significant research implications for intelligent infrared windows and enhancing our understanding of light–matter interactions in reconfigurable photothermal devices.

Fermi arcs are nontrivial surface states that exist in topological semimetals, which exhibit a variety of interesting effects, such as anomalous transport properties and chiral anomaly induced phenomena. Recently, the emerged Two-dimensional transition-metal dichalcogenide (TMDC) shows distinctive optical and electrical properties, makes it a promising platform for efficient modulation of Fermi arcs. By covering TMDC sheets on a photonic Dirac metamaterial (PDS), the quadrupole Dirac point splits into two triple degeneracy points (TDPs), each TDP share one Fermi arc. Through tuning the characteristics of TMDC layers, Fermi arcs and transmissions of PDS can be effectively modulated in multi-degrees of freedom. Unconventionally, we find the Fermi arcs may do not terminate at the degeneracy points but between the two type III TDPs. Fermi arcs with nonlocal effect are also investigated. Furthermore, topological transition from open (hyperbolic-like) to closed (elliptical-like) equi-frequency contours at TDP is also observed. Our findings may provide potential applications in flexible modulation of Fermi arcs with multiple functions.

Passive reflective metasurfaces can possess perfect absorption conditions: Singular scattering anomalies at which all impinging light is absorbed. Perfect absorption is a common yet powerful metasurface design option with applications in energy harvesting, sensing, and more. Less common is the inclusion of optical gain to the system, which can give rise to a singular condition for perfect amplification. We analyze absorption and amplification singularities in plasmon antenna metasurface etalons with gain with a simple transfer matrix model. Our etalon follows the Salisbury screen design: A metal ground plate spaced by dielectric medium from an array of resonant plasmonic scatterers. We include frequency dispersive models for gain media and discuss the limitations of time reversal symmetry arguments for relating gain singularity conditions (reflectivity poles) to the well-known perfect absorption conditions (reflectivity zeros) of metasurface etalons. We show that for metasurface etalons with both gain and loss, gain can induce both perfect absorption and gain singularities, and we describe topological constraints on their creation and annihilation. Our findings have implications for the fields of non-Hermitian photonics, parity-time symmetric scattering systems, and dynamically controllable active metasurface pixels.

A considerable part of the energy of the traditional terahertz metasurface sensor located in the substrate/dielectric layer, which cannot contact and interact with the analyte, resulting in energy loss and greatly limiting the sensitivity of the sensor. In addition, the strong absorption of THz wave by water makes it difficult for THz metasurface sensor to achieve the direct detection of aqueous solution. In this paper, a novel sandwich-type THz metasurface microfluidic sensor with high sensitivity for direct detection of aqueous solution is proposed and verified. Numerical simulation results show the proposed sensor has a perfect absorption peak with high Q -factor of 67.55 and high S of 0.534 THz/RIU at 1.85 THz. The proposed sensor not only can confine all the energy in microfluidic channel greatly improving the energy utilization and light–matter interaction, but also precisely controls the liquid thickness at 3.1 μm greatly reducing the absorption of THz wave, which provides the foundation for realizing the direct detection of aqueous solutions with high sensitivity. Na + aqueous solutions of different concentrations are selected as analytes to verify the performance and feasibility of the proposed novel sensor. The offset of Na + aqueous solution with concentrations of 50, 100, 300, 500, 1,000 and 1,500 mmol/L is 13, 22, 46, 60, 93 and 115 GHz, respectively (using pure water as reference). The experiment and simulation of the sensor are basically consistent, which fully verifies the high sensing performance of the designed device and its applicability to the direct sensing of aqueous solution.

In the strong light–matter coupling regime, the transmission properties of metasurfaces have a remarkable similarity to those of typical two-level systems. In this work, we explore the absorption spectra of a metasurface coupled to a quantum phonon bath using the time-dependent variational principle and the flexible multi-D2 Davydov trial states. In the weak light–matter coupling regime, phonon coupling has minimal impact on system dissipation. However, in the strong coupling regime, it significantly influences dissipation dynamics. Additionally, a phonon bath with a selected number of strongly coupled modes near the phonon center line substantially narrows the absorption spectrum linewidth by controlling dissipation through a few phonon channels. These findings demonstrate the critical role of the phonon bath in shaping metasurface transmission properties, offering a promising approach for the precise engineering of metasurfaces.