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Room temperature terahertz generation is demonstrated in graphene under femtosecond optical excitation. This is induced by dynamical photon drag, which relies on the transfer of light momentum to the carriers by ponderomotive and magnetic forces.
A one-dimensional photonic crystal structure in a total-internal-reflection geometry has been developed for real-time, label-free specific protein binding detection. With the streptavidin-biotin system, an ultra low mass density detection limit 24 fg/mm2 was achieved.
A substantial improvement in the reconstruction of time-reversed THz fields is demonstrated by adapting a waveguide technique from ultrasouultrasound imagingnd imaging. Furthermore, a model based reconstruction method is considered as an alternative to time-reversal THz imaging.
Electron energy loss spectroscopy combined with spectral imaging in a transmission electron microscope is used to probe and map the energy distribution of the optical-frequency surface plasmons of coupled gold nanorods. Local field enhancement and spectral shift of the surface plasmon modes is observed when two nanoparticles are electromagnetically coupled.
We have observed third-harmonic generation by single nanorods in solution and investigated its excitation polarization dependence. Our findings demonstrate the possibility of using third-harmonic signals for correlation spectroscopy, in contrast to conventional fluorescence correlation spectroscopy.
Ultrafast optical pump - THz probe spectroscopy is used to measure the conductivity recovery dynamics in epitaxial graphene. The observed dynamics are insensitive to probe frequency, with recovery rates consistent with mid-IR measurements of carrier cooling.
We inject ballistic electric currents into epitaxial graphene at 300 K via quantum interference between phase controlled cross-polarized 3.2 mum and 1.6 mum 200- fs pulses. The transient currents are detected via the emitted terahertz radiation.
We demonstrate the use of a double-clad fiber probe to conduct two-photon excited flow cytometry in a live mouse. High detection efficiency of GFP-expressing cells is demonstrated, and the initial dynamics of injected circulating cells is observed.
We use a tightly focused ultrashort laser pulse to produce a third harmonic signal from an air-dielectric interface containing gold nanorods. When the fundamental frequency is resonant with the longitudinal plasmon of the nanorods, the third harmonic signal can be enhanced by more than 3 orders of magnitude.
Nondegenerate ultrafast mid-infrared pump-probe spectroscopy is used to study multilayer epitaxial graphene. By tuning the probe wavelength, we can determine the doping profile of the layers.
In this study, the nature of electronic transport in quantum cascade lasers (QCLs) has been extensively investigated using an ultrafast time-resolved, degenerate, pump-probe optical technique. Our investigations enable a comprehensive understanding of the gain recovery dynamics in terms of a coupling of the electronic transport to the oscillating intracavity laser intensity. In QCLs that have a lasing...
Ultrafast upconversion is employed to investigate pulse propagation in quantum cascade lasers. The authors have observed advances of the pulse peak to early times, pulse re-shaping, and evidence of a coherent contribution to pulse propagation.
Time-resolved mid-infrared upconversion based on sum-frequency generation was applied to measure the group-velocity dispersion in quantum cascade lasers; material, waveguide, and gain contributions were distinguished, and used to model the temporal pulse broadening.
We report the use of a dual-clad optical fiber for two-photon excited fluorescence correlation spectroscopy. The ability to detect nanoparticles has been demonstrated. This technique shows the potential of conducing FCS measurements invivo.
The excitation of surface plasmons on individual silver nanowires is studied by high-resolution electron energy loss spectroscopy in a transmission electron microscope, and the results are compared to ensemble optical spectra. The transverse and longitudinal modes of these nanostructures were selectively resolved, confirming the plasmon peak shift versus nanowire length.
Folate-targeted silver/dendrimer nanocomposites were developed and tested on a human oral epidermoid cancer cell line. We observed a reduced threshold in targeted cells for femtosecond-laser-induced optical breakdown, which leads to selective photodisruption of cancer cells.
Broadband THz generation is demonstrated using optical rectification in 6 mm GaP waveguides pumped by a high power, high repetition rate, ultrafast Yb-doped fiber amplifier. 150 muW THz radiation is obtained from 10 W pump power.
We report a novel sensor for label-free biomolecular assay using a one-dimensional photonic crystal in a total-internal-reflection geometry. This configuration creates a unique open biosensing interface for real-time detection with ultrahigh sensitivity.
We report a series of femtosecond pump-probe measurements on quantum cascade lasers operating below and above threshold; the gain recovery dynamics reveal how quantum stimulated emission drives the current through the cascade heterostructure, which we refer to as photon-driven transport.
Ultrafast mid-infrared pump-probe experiments are used to study gain dynamics and transport processes in quantum cascade lasers below and above threshold. We observe for the first time how stimulated emission drives the current through the cascade heterostructure.
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