2 research outputs found
Anapoles in Free-Standing IIIāV Nanodisks Enhancing Second-Harmonic Generation
Nonradiating
electromagnetic configurations in nanostructures open
new horizons for applications due to two essential features: a lack
of energy losses and invisibility to the propagating electromagnetic
field. Such radiationless configurations form a basis for new types
of nanophotonic devices, in which a strong electromagnetic field confinement
can be achieved together with lossless interactions between nearby
components. In our work, we present a new design of free-standing
disk nanoantennas with nonradiating current distributions for the
optical near-infrared range. We show a novel approach to creating
nanoantennas by slicing IIIāV nanowires into standing disks
using focused ion-beam milling. We experimentally demonstrate the
suppression of the far-field radiation and the associated strong enhancement
of the second-harmonic generation from the disk nanoantennas. With
a theoretical analysis of the electromagnetic field distribution using
multipole expansions in both spherical and Cartesian coordinates,
we confirm that the demonstrated nonradiating configurations are anapoles.
We expect that the presented procedure of designing and producing
disk nanoantennas from nanowires becomes one of the standard approaches
to fabricating controlled chains of standing nanodisks with different
designs and configurations. These chains can be essential building
blocks for new types of lasers and sensors with low power consumption
Polar Second-Harmonic Imaging to Resolve Pure and Mixed Crystal Phases along GaAs Nanowires
In this work, we report an optical
method for characterizing crystal
phases along single-semiconductor IIIāV nanowires based on
the measurement of polarization-dependent second-harmonic generation.
This powerful imaging method is based on a per-pixel analysis of the
second-harmonic-generated signal on the incoming excitation polarization.
The dependence of the second-harmonic generation responses on the
nonlinear second-order susceptibility tensor allows the distinguishing
of areas of pure wurtzite, zinc blende, and mixed and rotational twins
crystal structures in individual nanowires. With a far-field nonlinear
optical microscope, we recorded the second-harmonic generation in
GaAs nanowires and precisely determined their various crystal structures
by analyzing the polar response for each pixel of the images. The
predicted crystal phases in GaAs nanowire are confirmed with scanning
transmission electron and high-resolution transmission electron measurements.
The developed method of analyzing the nonlinear polar response of
each pixel can be used for an investigation of nanowire crystal structure
that is quick, sensitive to structural transitions, nondestructive,
and on-the-spot. It can be applied for the crystal phase characterization
of nanowires built into optoelectronic devices in which electron microscopy
cannot be performed (for example, in lab-on-a-chip
devices). Moreover, this method is not limited to GaAs nanowires but can
be used for other nonlinear optical nanostructures