The novel field-resolved microscopy scheme of Quantum-probe Field Microscopy (QFIM) utilized fluorescence quanta to images local THz-electric waveforms [1]. In this contribution, we discuss the basis of the ultrafast microscopy scheme and the recovery of multi-Terahertz signals from fluorescence data. We elaborate fundamental aspects of time-domain sampling of electric waveforms and different strategies to recover response functions of systems under investigation.
[1] M.B. Heindl, et al., “Ultrafast imaging of terahertz electric waveforms using quantum dots”, Light: Science & Applications 11, 2022.
In this contribution, we present a novel type of sub-cycle field-resolved microscopy of Terahertz electric near-fields inside micro- and nanostructures. The “Quantum-probe Field Microscopy” (QFIM) scheme is based on fluorescence microscopy of semiconductor Quantum-dot luminescence and harnesses the Quantum-confined Stark effect for recording stroboscopic “movies” of ultrafast resonant and propagating THz-excitations. The scheme is compatible with strong local driving field strengths, sub-micrometer resolution and sub-cycle sampling of multi-THz waveforms. We discuss experimental implementations, recent results and future prospects of this versatile microscopy scheme.
We utilised thermal and UV-assisted Nanoimprint Lithography (NIL) i.e. thermal and UV-assisted to produce plasmonic coloration, and compare their ability for scalable fabrication. Several designs are presented and we show the generated colors are dependent on their geometry and the direction of polarisation of incident illumination. Finally, we demonstrated UV-NIL for consistent production of large-area (0.6×0.4 cm2) plasmonic color with extended color gamut.
Optical nano-antennas have been the focus of intense research recently due to their ability to manipulate electromagnetic radiation on a subwavelength scale, and there is major interest in such devices for a wide variety of applications in photonics, sensing, and imaging. Significant effort has been put into developing highly compact, novel, next-generation light sources, which have great potential in realizing efficient sub-wavelength single photon sources and enhanced biological and chemical sensors. We have developed a number of innovative optical antenna designs including elements of chiral metasurfaces for enabling circularly polarized emission from quantum sources, new designs derived from Radio Frequency (RF) elements for quantum source enhancement and directionality, and nanostructures for investigating plasmonic dark-modes that have the ability to significantly reduce the Q-factor of nano-antennas. A challenge, however, remains the development of a scalable nanofabrication technology. The capacity to mass-produce nano-antennas will have a considerable impact on the commercial viability of these devices, and greatly improve research throughput. Here we present recent progress in the development of scalable fabrication strategies for producing of nano-antennas and antenna arrays, along with slot based plasmonic optical devices.
Optical nano-antennas have become a hot topic in photonics research recently due to their ability to manipulate electromagnetic radiation on the subwavelength scale. Of particular interest is the application of optical nano-antennas to enhancement of quantum sources such as semiconductor Quantum Dots (QD) and Nitrogen Vacancy (NV) centers in nano-diamond. Much like their Radio Frequency (RF) cousins, optical nano-antennas are able to enhance and direct radiation from a localized source in the near-field of the antenna to the far-field. The work reported here exploits RF antenna designs by applying them to the development of optical nano-antennas for enhancement of multiple semiconductor QDs. In particular, the Vee antenna design, commonly used in improvised military RF applications, is utilized in this work as an optical nano-antenna to enable the selective excitation of two different color QDs via polarization control. The Vee antenna has two bright resonant modes in the visible spectrum, typically spectrally separated by approximately 50 nm, which are excited by orthogonal polarizations of the excitation field. Using these two resonant modes of the Vee antenna, two different color QDs can be selectively enhanced. The Vee antennas are fabricated with E-beam Lithography using aluminum as the antenna material on a multilayer SiO2/Al/glass substrate. The Vee antenna design consists of two dipole antennas, orientated at 90° to each other, where the gap between the antennas and the thickness of the SiO2 spacer layer is used to tune the spectral separation of the orthogonal resonances.
The direct optical monitoring of electron exchange on single plasmonic nanoparticles, involved in chemical reactions with gas molecules, is one of the main challenges in the heterogeneous catalysis and gas sensing fields.
Catalysts are substances that speed up reactions by providing an alternative pathway with lower activation energy than that required for the uncatalysed reaction. A lot of research, both fundamental and applied, has been carried out to investigate how catalysts work and to increase their efficiency.
The present work shows how the use of Dark Field Microscopy (DFM) coupled with surface plasmon spectroscopy, enables the direct observation of the kinetics of H2 gas interaction with single gold nanorods (NR) coupled with Pt nanoparticles (NPs) and/or with metal oxide matrices. The plasmonic particles, gold NRs, act as optical probes, and enable the monitoring of the electron exchange through the measurement of their surface plasmon resonance (SPR) band shift. To improve the redox reaction kinetics, the Au NRs have been coupled with Pt NPs and embedded also into a TiO2 or ZnO low scattering matrix. The Au NRs, the Pt, TiO2 and ZnO NPs have been synthetized by colloid chemistry. Several samples made of bare Au NRs, or Au NRs coupled with only Pt NPs or with Pt and TiO2 NPs or with Pt and TiO2 have been deposited by spin coating on silica substrates.
The longitudinal Au SPR band shift has been monitored by DFM looking at the variation of the scattering spectrum of a single Au NRs in the presence of H2. Time-resolved measurements have been also conducted at fixed wavelength in order to monitor the kinetics of the H2 reaction. With such measurements it was possible to elucidate the importance of the adsorbed oxygen and the TiO2 matrix on the H2 reaction with the Pt NPs.
The present paper introduces to the problems related with the application of silica shells to luminescent semiconductor nanocrystals, especially for bioanalytical applications. Two examples for the preparation of silica shells are presented: First, preparation of a very thin silica layer with simultaneous functionalisation and biological application. Second, a new preparation method for silica shells based on a sol-gel approach. In summary, it is shown, that --- despite of all problems --- high-quality silica coated nanocrystals can be prepared and are well suited for bioanalytical applications.
In this paper the dynamical response of cylindrical nanorods to ultrafast laser-induced heating is examined. Theoretical analysis predicts that both extensional and breathing vibrational modes of the rods should be excited by laser-induced heating. Analytical formulas for the frequencies of these modes are derived assuming that the length of the rods is much greater than their radii. Because the frequency of the fundamental extensional mode is much lower than that of the breathing mode, the extensional mode will dominate the response for a real experiment, i.e., for a finite-time heating/expansion process. The results of this model are compared to data from transient absorption experiments performed on gold nanorods with average aspect ratios (length / width) between 2.1 and 5.5, and widths on the order of 10-20 nm. The transient absorption traces show pronounced modulations with a period between 45 and 70 ps, which are only observed when the probe laser is tuned to the longitudinal plasmon band of the sample. The measured periods are in good agreement with the expected period for the extensional modes of the rods. The actual value of the measured period depends on the specific sample and probe laser wavelength. This occurs because the samples are polydisperse, and different length rods absorb in different regions of the spectrum. For rods with widths greater than 20 nm, the breathing mode can also be observed and, again, the measured periods are in good agreement with the theoretical calculations. The breathing mode is not observed for the thinner rods (~10 nm width) because in this case the period is comparable to the timescale for lattice heating in the experiment.
The acoustic vibrational modes of Au nanorods with aspect ratios between 2.1 and 5.5 have been investigated by timeresolved
spectroscopy. The results show that laser excitation launches a coherent vibrational motion which has a period that depends linearly on the length of the rod. Due to polydispersity in the samples, the measured period also depends on the probe wavelength (i.e., for a given sample different probe wavelengths interrogate different length rods). Analysis of the data potentially provides information about the elastic properties of these unique materials.
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