Probing compositional engineering effects on lead-free perovskite-inspired nanocrystal thin films using correlative nonlinear optical microscopy.

We introduce the use of correlative third-harmonic generation and multiphoton-induced luminescence microscopy to investigate the impact of manganese (Mn) doping on bismuth (Bi)-based perovskite-inspired nanocrystal thin films. The technique was found to be extremely sensitive to the microscopic features of the perovskite film and its structural compositions, allowing the unambiguous detection of compositionally different emitters in the perovskite film and manipulation of their nonlinear optical responses. Our work unveils a new way to investigate, manipulate, and exploit perovskite-inspired functional materials for nonlinear optical conversion at the nanoscale.

Surface and optical properties of phase-pure silver iodobismuthate nanocrystals.

The study of surface defects is one of the forefronts of halide perovskite research. In the nanoscale regime, where the surface-to-volume ratio is high, the surface plays a key role in determining the electronic properties of perovskites. Perovskite-inspired silver iodobismuthates are promising photovoltaic absorbers.

Lead-Free Cesium Titanium Bromide Double Perovskite Nanocrystals.

Double perovskites are a promising family of lead-free materials that not only replace lead but also enable new optoelectronic applications beyond photovoltaics. Recently, a titanium (Ti)-based vacancy-ordered double perovskite, CsTiBr, has been reported as an example of truly sustainable and earth-abundant perovskite with controversial results in terms of photoluminescence and environmental stability. Our work looks at this material from a new perspective, i.

Maskless fabrication of plasmonic metasurfaces in polymer film using a spatial light modulator.

We demonstrate a high-speed optical technique to fabricate plasmonic metasurfaces in a polymer film. The technique is based on a programmable spatial light modulator, which is used to spatially control the photoreduction sites of gold ions in a polyvinyl alcohol film doped with a gold precursor. After irradiation, annealing was used to induce the growth of nanoparticles, producing plasmonic microstructures.

Unveiling structured domains of persistent luminescent microparticles using second-harmonic generation microscopy.

We introduce the use of second-harmonic generation microscopy to investigate individual persistent luminescent microparticles that are either embedded in glass or as prepared. Three-dimensional mapping of the second-harmonic generation from monoclinic dysprosium- and europium-doped strontium aluminates, a popular persistent luminescent material, allows us to unambiguously visualize and reveal for the first time the presence of micrometer-sized structured domains from such microparticles. The technique was found to have high potential for studying noninvasively a wide range of individual persistent luminescent entities that are embedded in a variety of glass matrices.

Plasmonic mode conversion in individual tilted 3D nanostructures.

We investigate mode conversion in 3D asymmetric nanocones using angle-dependent linear optical spectroscopy and second-harmonic generation microscopy supported by corresponding simulations. The results prove the efficient excitation of the plasmonic out-of-plane mode that enhances the electric near-field at the sharp tip. Furthermore, we introduce two advanced fabrication processes including either etch mask transfer by tilted etching into a metallic layer or tilted electron-beam lithography followed by tilted evaporation and lift-off.

Resonant harmonic generation in AlGaAs nanoantennas probed by cylindrical vector beams.

We investigate second- and third-harmonic generation from individual AlGaAs nanoantennas using far-field mapping with radially- and azimuthally-polarized cylindrical vector beams. Due to the unique polarization structure of these beams, we are able to determine the crystal orientation of the nanoantenna in a single scanning map. Our method thus provides a novel and versatile optical tool to study the crystal properties of semiconductor nanoantennas.

Demonstration of longitudinally polarized optical needles.

Longitudinally polarized optical needles are beams that exhibit ultra-long depth of field, subwavelength transverse confinement, and polarization oriented along the longitudinal direction. Although several techniques have been proposed to generate such needles, their scarce experimental observations have been indirect and incomplete. Here, we demonstrate the creation and full three-dimensional verification of a longitudinally polarized optical needle.

Collective Effects in Second-Harmonic Generation from Plasmonic Oligomers.

We investigate collective effects in plasmonic oligomers of different symmetries using second-harmonic generation (SHG) microscopy with cylindrical vector beams (CVBs). The oligomers consist of gold nanorods that have a longitudinal plasmon resonance close to the fundamental wavelength that is used for SHG excitation and whose long axes are arranged locally such that they follow the distribution of the transverse component of the electric field of radially or azimuthally polarized CVBs in the focal plane. We observe that SHG from such rotationally symmetric oligomers is strongly modified by the interplay between the polarization properties of the CVB and interparticle coupling.

Nonlinear microscopy using cylindrical vector beams: Applications to three-dimensional imaging of nanostructures.

The three-dimensional (3D) optical fields that arise from the focusing of cylindrical vector beams (CVB) with radial and azimuthal polarizations provide new sources of contrast for optical microscopy of nano-objects. So far, these demonstrations have been restricted to two-dimensional transversal scanning, i.e.

Nonlinear imaging of nanostructures using beams with binary phase modulation.

We demonstrate nonlinear microscopy of oriented nanowires using excitation beams with binary phase modulation. A simple and intuitive optical scheme comprising a spatial light modulator gives us the possibility to control the phase across an incident Hermite-Gaussian beam of order (1,0) (HG mode). This technique allows us to gradually vary the spatial distribution of the longitudinal electric fields in the focal volume, as demonstrated by second-harmonic generation from vertically-aligned GaAs nanowires.

Third-harmonic generation imaging of three-dimensional microstructures fabricated by photopolymerization.

We demonstrate the capability of polarized third-harmonic generation (THG) for high contrast imaging of three-dimensional microstructures fabricated by photopolymerization. Using circular polarization of fundamental light, background-free optically-sectioned THG images were obtained from laser-written photopolymerized microstructures. The technique has great potential for simple and noninvasive characterization of photopolymerized devices, which typically show poor contrast in conventional light microscopy.

Sub-micron scale patterning of fluorescent silver nanoclusters using low-power laser.

Noble metal nanoclusters are ultrasmall nanomaterials with tunable properties and huge application potential; however, retaining their enhanced functionality is difficult as they readily lose their properties without stabilization. Here, we demonstrate a facile synthesis of highly photostable silver nanoclusters in a polymer thin film using visible light photoreduction. Furthermore, the different stages of the nanocluster formation are investigated in detail using absorption and fluorescence spectroscopy, fluorescence microscopy, and atomic force microscopy.

Second-harmonic generation imaging of semiconductor nanowires with focused vector beams.

We use second-harmonic generation (SHG) with focused vector beams to investigate individual vertically aligned GaAs nanowires. Our results provide direct evidence that SHG from oriented nanowires is mainly driven by the longitudinal field along the nanowire growth axis. Consequently, focused radial polarization provides a superior tool to characterize such nanowires compared to linear polarization, also allowing this possibility in the native growth environment.

Polarized THG microscopy identifies compositionally different lipid droplets in mammalian cells.

Cells store excess lipids as two major compounds, triacylglycerols (TAGs) and cholesteryl esters (CEs), inside lipid droplets (LDs). The degree of lipid ordering is considered to play a major role in the mobility and enzymatic processing of lipids in LDs. Here, we provide evidence that polarized third-harmonic generation (THG) microscopy distinguishes between native TAG- and CE-enriched LDs in cells due to the different ordering of the two lipid species.

Direct laser writing of photostable fluorescent silver nanoclusters in polymer films.

Metal nanoclusters consist of a few to a few hundred atoms and exhibit attractive molecular properties such as ultrasmall size, discrete energy levels, and strong fluorescence. Although patterning of these clusters down to the micro- or nanoscale could lead to applications such as high-density data storage, it has been reported only for inorganic matrices. Here we present submicron-scale mask-free patterning of fluorescent silver nanoclusters in an organic matrix.

Three-dimensional winged nanocone optical antennas.

We introduce 3D optical antennas based on winged nanocones. The antennas support particle plasmon oscillations with current distributions that facilitate transformation of transverse far-field radiation to strong longitudinal local fields near the cone apices. We characterize the optical responses of the antennas by their extinction spectra and by second-harmonic generation microscopy with cylindrical vector beams.

Third- and second-harmonic generation microscopy of individual metal nanocones using cylindrical vector beams.

We demonstrate third- (THG) and second-harmonic generation (SHG) microscopy of individual silver nanocones using tightly focused cylindrical vector beams (CVBs). Although THG is expected to be a weaker process than SHG, the yield for THG with radial polarization was higher than for SHG. We also found an excellent correlation between the imaging properties of THG and SHG, suggesting that both are governed by the same overall features of the individual nanocone.

Second-harmonic generation imaging of metal nano-objects with cylindrical vector beams.

We introduce an imaging technique based on second-harmonic generation with cylindrical vector beams that is extremely sensitive to three-dimensional orientation and nanoscale morphology of metal nano-objects. Our experiments and second-harmonic field calculations based on frequency-domain boundary element method are in very good agreement. The technique provides contrast for structural features that cannot be resolved by linear techniques or conventional states of polarization and shows great potential for simple and cost-effective far-field optical imaging in plasmonics.

Optical trapping and surgery of living yeast cells using a single laser.

We present optical trapping and surgery of living yeast cells using two operational modes of a single laser. We used a focused laser beam operating in continuous-wave mode for noninvasive optical trapping and manipulation of single yeast cell. We verified that such operational mode of the laser does not cause any destructive effect on yeast cell wall.

Tracking the emergence of defect in light emitting semiconductor diodes with two-photon excitation microscopy and spectral microthermography.

We demonstrate a multifunctional optical technique for tracking the evolution of defects in live 605 nm LEDs. Photocurrent images, electroluminescence, and spectral reflectance maps are simultaneously acquired and utilized to evaluate LED performance at different injection currents. Free-carrier density profiles in the active region are constructed from photocurrent images that are generated via two-photon excitation (2PE) at 800 nm.

Spectral microthermography for component discrimination and hot spot identification in integrated circuits.

We demonstrate an efficient and versatile spectral microthermography technique for identifying hot and cold spots in the active layer of a biased integrated circuit. Hot (cold) spots are regions where heat accumulates more rapidly (slowly) than the average rate of the entire active layer. Knowledge of the hot and cold spot locations is crucial in assessing the thermal integrity of a layer structure because hot spots are locations were defects are more likely to develop.