We describe frequency locking of a diode laser to a two-photon transition of rubidium using the Zeeman modulation technique. We locked and tuned the laser frequency by modulating and shifting the two-photon transition frequency with ac and dc magnetic fields. We achieved a linewidth of 500 kHz and continuous tunability over 280 MHz with no laser frequency modulation.

Epsilon near zero (ENZ) materials exhibit strongly confined optical modes and plasmonic response around and beyond the ENZ wavelength (λENZ). In order to exploit the novel properties of ENZ materials for real-world applications, it is important to develop material platforms that offer continuous tuning of λENZ. We report octave span, controllable, and reversible tuning of λENZ from 1280 nm to 2900 nm in commercially available thin films of indium tin oxide (ITO), employing a low temperature annealing protocol. Electrical, spectroscopic, and optical measurements establish the physical basis of the observed tunability in free electron density by over an order of magnitude and quantify the real and imaginary components of the refractive index for ITO thin films. Excitation of surface plasmon polaritons (SPPs) in the metallic regime of ITO probes its infrared plasmonic response demonstrating continuous tunability of SPP frequency and crossover to the tunable ENZ plasmon mode in ultrathin films. Finally, dispersion tuning of optical fiber modes by optical coupling with a tunable λENZ platform is demonstrated by investigating modal interference in a tapered silica fiber in contact with various custom tuned ITO films.

Engineering modal dispersions of ultrathin, planar structures enables significant control over infrared perfect absorption (PA) and thermal emission characteristics. Herein, the optical response of ultrathin, low loss, epsilon‐near‐zero (ENZ) films on reflecting surfaces is simulated to investigate the wavelength and angular ranges over which they absorb and emit radiation most efficiently and identify the design parameters that tailor the ENZ mode dispersion of the system. A generic interference model is shown to elucidate the underlying physics of these ultrathin film absorption resonances, occurring well below the conventional quarter‐wavelength thickness limit. While the absorption is spectrally limited to wavelengths where the ENZ film is optically a dielectric with refractive index below unity, the angular spread is delimited by the material dispersion. Further, these resonant interferences are understood to arise from universal wave phenomena, realizable in simple planar structures having appropriate refractive index contrast, not restricted to ENZ materials. The results show that appropriate choice of material, film thickness and loss allows tailoring the modal dispersions, which enables precise directional control and wide tunability in spectral range (width ≈0.1–1.0 μm) of PA and thermal emission, paving the way towards efficient ENZ‐based infrared optical and thermal coatings.

We model the enhancement of near band edge emission from ZnO nanorods using plasmonic metal nanoparticles and compare it with emission enhancement from ZnO with semiconducting quantum dots. Selected CdSe quantum dots with absorption energies close to those of Ag and Au nanoparticles are chosen to construct model systems with ZnO to comprehend the role of ZnO’s intrinsic defects and plasmonic excitation in realizing the spectrally selective luminescence enhancement. Excitation wavelength dependent photoluminescence spectra along with theoretical models quantifying the related transitions and plasmonic absorption reveal that a complex mechanism of charge transfer between the ZnO nanorods and metal nanoparticles or quantum dots is essential along with an optimal energy band alignment for realizing emission enhancement. The theoretical model presented also provides a direct method of quantifying the relative transition rate constants associated with various electronic transitions in ZnO and their change upon the incorporation of plasmonic nanoparticles. The results indicate that, while the presence of deep level defect states may facilitate the essential charge transfer process between ZnO and the plasmonic nanoparticles, their presence alone does not guarantee UV emission enhancement and strong plasmonic coupling between the two systems. The results offer clues to designing novel multicomponent systems with coupled plasmonic and charge transfer effects for applications in charge localization, energy harvesting, and luminescence enhancement, especially in electrically triggered nanophotonic applications.

Nanoantenna-enhanced ultrafast emission from colloidal quantum dots as quantum emitters is required for fast quantum communications. On-chip integration of such devices requires a scalable and high-throughput technology. We report selfassembly lithography technique of preparing hybrid of gold nanorods antenna over a compact CdSe quantum dot monolayer. We demonstrate resonant and nonresonant gold nanorod antenna-enhanced radiative and anisotropic decay. Extensive simulations explain the mechanism of the decay rates and the role of antenna in both random and compact monolayers of quantum dots. The study could find applications in quantum dot display and quantum communication devices.