Lead
halide perovskites have been widely explored in the field
of photovoltaics, light-emitting diodes, and lasers due to their outstanding
linear and nonlinear optical (NLO) properties. But, the presence of
lead toxicity and low chemical stability remain serious concerns.
Lead-free double perovskite with excellent optical properties and
chemical stability could be an alternative. However, proper examination
of the NLO properties of such a material is crucial to identify their
utility for future nonlinear device applications. Herein, we have
made use of femtosecond (fs) Z-scan technique to explore the NLO properties
of Cs2AgIn0.9Bi0.1Cl6 nanocrystals
(NCs). Our measurements suggest that under nonresonant fs excitation,
perovskite NCs exhibit strong two-photon absorption (TPA). The observed
saturation of TPA at high light intensities has been explained by
a customized model. Furthermore, we have demonstrated a change in
the nonlinear refractive index of the NCs under varying input intensities.
The strong TPA absorption of lead-free double perovskite NCs could
be used for Kerr nonlinearity-based nonlinear applications such as
optical shutters for picosecond lasers.
Silver nanowires have attracted considerable attention as subdiffraction limited diameter waveguides in a variety of applications including cell endoscopy and photonic integrated circuitry. Optical signal transport occurs by coupling light into propagating surface plasmons, which scatter back into light further along the wire. However, these interconversions only occur efficiently at wire ends, or at defects along the wire, which are not controlled during synthesis. Here, we overcome this limitation, demonstrating the visible laser light-induced fabrication of gold nanostructures at desired positions on silver nanowires, and their utility as efficient in/out coupling points for light. The gold nanostructures grow via plasmon-induced reduction of Au(III) and are shown to be excellent "hotspots" for surface-enhanced Raman scattering.
TERS is a powerful tool for nanoscale optical characterization of surfaces. However, even after 20 years of development, the parameters for optimal TERS tips are still up for debate. As a result, routine measurements on bulk or dielectric substrates remain exceptionally challenging. Herein we help to alleviate this by using electrical cutting to strategically modify silver nanowire TERS probes. Following cutting, the tips present a large, spherical apex and are often nanostructured with numerous nanoparticles, which we argue improve light collection and optical coupling. This doubles TERS signals on a highly enhancing, gap-mode substrate compared to our standard nanowire tips while maintaining a high reproducibility and resolution. More interestingly, on a dielectric substrate (graphene on SiO 2 ) the tips give ∼7× higher signals than our standard tips. Further investigations point to the nonlocal nature of the enhancement using standard, smooth TERS probes without gap-mode, making such nanostructuring highly beneficial in these cases.
We report a facile all-optical method for spatially resolved and reversible chemical modification of a graphene monolayer. A tightly focused laser on graphene under water introduces an sp 3 -type chemical defect by photo-oxidation. The sp 3 -type defects can be reversibly restored to sp 2 carbon centers by the same laser with higher intensity. The photoreduction occurs due to laser-induced local heating on the graphene. These optical methods combined with a laser direct writing technique allow photowriting and erasing of a well-defined chemical pattern on a graphene canvas with a spatial resolution of about 300 nm. The pattern is visualized by Raman mapping with the same excitation laser, enabling an optical read-out of the chemical information on the graphene. Here, we successfully demonstrate all-optical Write/Read-out/Erase of chemical functionalization patterns on graphene by simply adjusting the one-color laser intensity. The all-optical method enables flexible and efficient tailoring of physicochemical properties in nanoscale for future applications.
The potential of nonlinear optical microscopy for the label-free visualization of heterogeneities and defects in metal–organic frameworks is demonstrated.
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