Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOptical Response of Nanostructured Surfaces: Experimental Investigation of the Composite Diffracted Evanescent Wave Model
98
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Investigations of the optical response of subwavelength structure arrays milled into thin metal films has revealed surprising phenomena including reports of unexpectedly high transmission of light. Many studies have interpreted the optical coupling to the surface in terms of the resonant excitation of surface plasmon polaritons (SPPs), but other approaches involving composite diffraction of surface evanescent waves (CDEW) have also been proposed. We present here a series of measurements on very simple one-dimensional (1-D) subwavelength structures with the aim of testing key properties of the surface waves and comparing them to the CDEW and SPP models.
rate research
Read More
While conventional optical trapping techniques can trap objects with submicron dimensions, the underlying limits imposed by the diffraction of light generally restrict their use to larger or higher refractive index particles. As the index and diameter decrease, the trapping difficulty rapidly increases; hence, the power requirements for stable trapping become so large as to quickly denature the trapped objects in such diffraction-limited systems. Here, we present an evanescent field based device capable of confining low index nanoscale particles using modest optical powers as low as 1.2 mW, with additional applications in the field of cold atom trapping. Our experiment uses a nanostructured optical micro-nanofiber to trap 200 nm, low index contrast, fluorescent particles within the structured region, thereby overcoming diffraction limitations. We analyze the trapping potential of this device both experimentally and theoretically, and show how strong optical traps are achieved with low input powers.
We extend the recently developed classical theory for the optical response of a single-layer crystal to bilayers. We account for the interaction between the two atomic planes and the multiple reflections inside the crystals. We show how to define a global susceptibility meaningful for the bilayer crystal and how its expression varies compared to the single-layer case. We compute both the local and the macroscopic fields which allow us for a direct comparison with experimental data.
79 -
Sinuhe Perea-Puente
, Francisco J. Rodriguez-Fortu~non (Department of Physics
, Kings College London
2021
Spin-momentum locking of evanescent waves describes the relationship between the propagation constant of an evanescent mode and the polarization of its electromagnetic field, giving rise to applications in light nano-routing and polarimetry among many others. The use of complex numbers in physics is a powerful representation in areas such as quantum mechanics or electromagnetism; it is well known that a lossy waveguide can be modelled with the addition of an imaginary part to the propagation constant. Here we explore how these losses are entangled with the polarization of the associated evanescent tails for the waveguide, revealing a well-defined mapping between waveguide losses and the Poincare sphere of polarizations, in what could be understood as a polarization-loss locking of evanescent waves. We analyse the implications for near-field directional coupling of sources to waveguides, as optimized dipoles must take into account the losses for a perfectly unidirectional excitation. We also reveal the potential advantage of calculating the angular spectrum of a source defined in a complex, rather than the traditionally purely real, transverse wavevector space formalism.
Black phosphorus (BP) is an emerging two-dimensional semiconducting material with great potential for nanoelectronic and nanophotonic applications, especially owing to its unique anisotropic electrical and optical properties. Many theoretical studies have predicted the anisotropic optical properties of BP, but the direct experimental quantification remains challenging. The difficulties stem from the ease of BPs degradation when exposed to air in ambient conditions, and from the indirect nature of conventional approaches that are subject to large measurement uncertainties. This work reports a direct investigation of the birefringent optical constants of micrometer-thick BP samples with picosecond (ps) interferometry, over the wavelength range from 780 to 890 nm. In this ps-interferometry approach, an ultrathin (5 nm) platinum layer for launching acoustic waves naturally protects the BP flake from degradation. The birefringent optical constants of BP for light polarization along the two primary crystalline orientations, zigzag and armchair, are directly obtained via fitting the attenuated Brillouin scattering signals. A bi-exponential model is further proposed to analyze the BS signals for a random incident light polarization. The BP experimental results and the associated measurement sensitivity analysis demonstrate the reliability and accuracy of the ps-interferometry approach for capturing the polarization-dependent optical properties of birefringent materials.
Harmonic generation mechanisms are of great interest in nanoscience and nanotechnology, since they allow generating visible light by using near-infrared radiation, which is particularly suitable for its endless applications in bio-nanophotonics and opto-electronics. In this context, multilayer metal-dielectric nanocavities are widely used for light confinement and waveguiding at the nanoscale. They exhibit intense and localized resonances that can be conveniently tuned in the near-infrared and are therefore ideal for enhancing nonlinear effects in this spectral range. In this work, we experimentally investigate the nonlinear optical response of multilayer metal-dielectric nanocavities. By engineering their absorption efficiency and exploiting their intrinsic interface-induced symmetry breaking, we achieve one order of magnitude higher second-harmonic generation efficiency compared to gold nanostructures featuring the same geometry and resonant behavior. In particular, while the third order nonlinear susceptibility is comparable with that of bulk Au, we estimate a second order nonlinear susceptibility of the order of 1 pm/V, which is comparable with that of typical nonlinear crystals. We envision that our system, which combines the advantages of both plasmonic and dielectric materials, might enable the realization of composite and multi-functional nano-systems for an efficient manipulation of nonlinear optical processes at the nanoscale.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
