RESUMO
We report the observation of terahertz (THz) electric field induced conductivity modulation in sub-wavelength gold plasmonic media. Through all-THz pump-probe time-resolved transmission spectroscopy, we demonstrate that the presence of induced surface charges influences near-field mediated light propagation. The phenomenon is ascribed to the enhanced metal conductivity due to enhanced surface density of conduction electrons. The surface induced charge dynamics are revealed via phase-dependent time-resolved signatures. The phenomenon is a prelude to a wide class of ultrafast active THz plasmonic devices and paves the way for plasmonic field effects devices, similar to semiconductor ones.
RESUMO
Pluripotent stem cells have the capacity to divide indefinitely and to differentiate into all somatic cells and tissue lines. They can be genetically manipulated in vitro by knocking genes in or out, and therefore serve as an excellent tool for gene function studies and for the generation of models for some human diseases. Since 1981, when the first mouse embryonic stem cell (ESC) line was generated, many attempts have been made to generate pluripotent stem cell lines from other species. Comparative characterization of ESCs from different species would help us to understand differences and similarities in the signaling pathways involved in the maintenance of pluripotency and the initiation of differentiation, and would reveal whether the fundamental mechanism controlling self-renewal of pluripotent cells is conserved across different species. This report gives an overview of research into embryonic and induced pluripotent stem cells in the rabbit, an important nonrodent species with considerable merits as an animal model for specific diseases. A number of putative rabbit ESC and induced pluripotent stem cell lines have been described. All of them expressed stem cell-associated markers and maintained apparent pluripotency during multiple passages in vitro, but none have been convincingly proven to be fully pluripotent in vivo. Moreover, as in other domestic species, the markers currently used to characterize the putative rabbit ESCs are suboptimal because recent studies have revealed that they are not always specific to the pluripotent inner cell mass. Future validation of rabbit pluripotent stem cells would benefit greatly from a validated panel of molecular markers specific to pluripotent cells of the developing rabbit embryos. Using rabbit-specific pluripotency genes may improve the efficiency of somatic cell reprogramming for generating induced pluripotent stem cells and thereby overcome some of the challenges limiting the potential of this technology.
Assuntos
Células-Tronco Pluripotentes , Coelhos , Animais , Diferenciação Celular/genética , Linhagem Celular , Quimera , Células-Tronco Embrionárias/citologia , Imuno-Histoquímica/veterinária , Células-Tronco Pluripotentes Induzidas/citologia , MicroRNAs/fisiologia , Modelos Animais , Técnicas de Transferência Nuclear/veterinária , Células-Tronco Pluripotentes/citologia , Coelhos/genética , Fatores de Transcrição/fisiologiaRESUMO
A versatile optical setup for all-terahertz (THz) time resolved pump-probe spectroscopy was designed and tested. By utilizing a dual THz pulse generator emitter module, independent and synchronized THz radiation pump and probe pulses were produced, thus eliminating the need for THz beam splitters and the limitations associated with their implementation. The current THz setup allows for precise control of the electric fields splitting ratio between the THz radiation pump and probe pulses, as well as in-phase, out-of-phase, and polarization dependent pump-probe spectroscopy. Since the present THz pump-probe setup does not require specialized THz radiation optical components, such as phase shifters, polarization rotators, or wide bandwidth beam splitters, it can be easily implemented with minimal alterations to a conventional THz time domain spectroscopy system. The present setup is valuable for studying the time dynamics of THz coherent phenomena in solid-state, chemical, and biological systems.
Assuntos
Fenômenos Ópticos , Análise Espectral/instrumentação , Semicondutores , Fatores de TempoRESUMO
We present a new class of plasmonic photoconductive THz emitters based on a complementary Sierpinski gasket fractal geometry. Due to the presence of sub-wavelength perforations on the surface of the antenna, these antennae operate in the plasmonic regime. By utilizing the unique self-similar and space filling of the tailored fractal surface and the plasmonic surface current spatial distribution, photoconductive THz emitters exhibiting superior performance (~80% increase in the emitted THz radiation power) to conventional bow-tie and Sierpinski gasket THz emitters are demonstrated. It is shown that the self-similarity of the surface plasmon current present on the antenna surface is responsible for this emission enhancement.
Assuntos
Iluminação/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Desenho Assistido por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Fractais , Radiação TerahertzRESUMO
We present the application of THz plasmonics in imaging dielectric objects embedded in metal-filled media. By exploiting the time domain information from the transmitted pulse, signatures of the objects were observed. To enhance the low quality images acquired through THz time domain spectroscopy, a super-resolution image processing technique was applied. It is shown that pulse arrival time and phase magnitude information compared to the integrated instantaneous power of the transmitted pulse provides more detailed images of the embedded object.
RESUMO
We present a material composite consisting of randomly oriented elements governed by non-resonant interactions. By exploiting near-field plasmonic interaction in a dense ensemble of subwavelength-sized dielectric and metallic particles, we reveal that the group refractive index of the composite can be increased to be larger than the effective refractive indices of constituent metallic and dielectric parent composites. These findings introduce a new class of engineered photonic materials having customizable and atypical optical constants.