403 research outputs found
Design of infrared microspectrometers based on phase-modulated axilenses
We design and characterize a novel axilens-based diffractive optics platform
that flexibly combines efficient point focusing and grating selectivity and is
compatible with scalable top-down fabrication based on a 4-level phase mask
configuration. This is achieved using phase-modulated compact axilens devices
that simultaneously focus incident radiation of selected wavelengths at
predefined locations with larger focal depths compared to traditional Fresnel
lenses. In addition, the proposed devices are polarization insensitive and
maintain a large focusing efficiency over a broad spectral band. Specifically,
here we discuss and characterize modulated axilens configurations designed for
long-wavelength infrared (LWIR) in the m--12~m wavelength range and
in the m--6~m mid-wavelength infrared (MWIR) range. These devices
are ideally suited for monolithic integration atop the substrate layers of
infrared focal plane arrays (IR-FPAs) and for use as compact
microspectrometers. We systematically study their focusing efficiency, spectral
response, and cross talk ratio, and we demonstrate linear control of
multi-wavelength focusing on a single plane. Our design method leverages
Rayleigh-Sommerfeld (RS) diffraction theory and is validated numerically using
the Finite Element Method (FEM). Finally, we demonstrate the application of
spatially modulated axilenses to the realization of compact, single-lens
spectrometer. By optimizing our devices, we achieve a minimum distinguishable
wavelength interval of at and
at . The proposed devices add
fundamental spectroscopic capabilities to compact imaging devices for a number
of applications ranging from spectral sorting to LWIR and MWIR phase contrast
imaging and detection
Enhanced Nonlinearity of Epsilon-Near-Zero Indium Tin Oxide Nanolayers with Tamm Plasmon-Polariton States
Recently, materials with vanishingly small permittivity, known as
epsilon-near-zero (ENZ) media, emerged as promising candidates to achieve
nonlinear optical effects of unprecedented magnitude on a solid-state platform.
In particular, the ENZ behavior of Indium Tin Oxide (ITO) thin films resulted
in Kerr-type nonlinearity with non-perturbative refractive index variations
that are key to developing more efficient Si-compatible devices with
sub-wavelength dimensions such as all-optical switchers, modulators, and novel
photon detectors. In this contribution, we propose and demonstrate enhancement
of the nonlinear index variation of 30 nm-thick ITO nanolayers by silicon
dioxide/silicon nitride (SiO2/SiN) Tamm plasmon-polariton structures fabricated
by radio-frequency magnetron sputtering on transparent substrates under
different annealing conditions. In particular, we investigate the linear and
nonlinear optical properties of ITO thin films and resonant photonic structures
using broadband spectroscopic ellipsometry and intensity dependent Z-scan
nonlinear characterization demonstrating enhancement of optical nonlinearity
with refractive index variations as large as in the non-perturbative regime.
Our study reveals that the efficient excitation of strongly confined
plasmon-polariton Tamm states substantially boost the nonlinear optical
response of ITO nanolayers providing a stepping stone for the engineering of
more efficient infrared devices and nanostructures for a broad range of
applications including all-optical data processing, nonlinear spectroscopy,
sensing, and novel photodetection modalities
Shaping, imaging and controlling plasmonic interference fields at buried interfaces
Filming and controlling plasmons at buried interfaces with nanometer (nm) and
femtosecond (fs) resolution has yet to be achieved and is critical for next
generation plasmonic/electronic devices. In this work, we use light to excite
and shape a plasmonic interference pattern at a buried metal-dielectric
interface in a nanostructured thin film. Plasmons are launched from a
photoexcited array of nanocavities and their propagation is filmed via
photon-induced near-field electron microscopy (PINEM). The resulting movie
directly captures the plasmon dynamics, allowing quantification of their group
velocity at approximately 0.3c, consistent with our theoretical predictions.
Furthermore, we show that the light polarization and nanocavity design can be
tailored to shape transient plasmonic gratings at the nanoscale. These results,
demonstrating dynamical imaging with PINEM, pave the way for the fs/nm
visualization and control of plasmonic fields in advanced heterostructures
based on novel 2D materials such as graphene, MoS, and ultrathin metal
films.Comment: 16 pages, 5 figures, 3 supplementary figure
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