We theoretically investigate the fluorescence enhancement of a representative set of dye-molecules excited by three classes of nanoantennae, using a fully vectorial three-dimensional finite-difference time-domain (3D FDTD) method. Through these 3D FDTD calculations, in conjunction with analytic guidance using temporal coupled-mode (TCM) theory, we develop a design procedure for antennae assemblies that allow achieving fluorescence enhancements of 200-900 over the emission intensity in the bare dye molecule. The enhancement from these commercially available fluorochrome conjugates, namely, CFTM568, CFTM660R and CFTM790 are fully investigated using spherical-dimer, elliptical-dimer, and bowtie nanoantennae. These results demonstrate a method for rationally designing arbitrary metallic nanoparticle/emitter assemblies prior to their synthesis and assembly to achieve optimum fluorescence enhancement.
We report femtosecond laser cutting of ultrathin ferroelectric sheets. This process enables one to do rapid patterning
of microns-thick films of complex oxides such as LiNbO3, which are obtained via ion-beam exfoliation from
standard wafers. Cutting these fragile samples is extremely difficult using standard methods but can be done
effectively with ultrafast lasers. To achieve fast writing speed, we employ a high-repetition-rate amplified
Ti:sapphire laser system with a pulse peak power of ~100MW. Optimization of the depth and quality of cut were
determined as a function of laser pulse energy, crystallographic axes, optical polarization, and pre- and post-ablation
chemical treatments.
The nonlinear refractive index (n2) and two-photon absorption coefficient (β2), was determined for PbSe
nanocrystals (NCs) suspended in trichloroethylene (TCE) using a standard Z-scan technique with
femtosecond pulses over a range of wavelengths in the near-IR. For comparison, the n2 of PbS NCs in
chloroform was also measured. The exciton peaks of the NCs were tuned to telecommunications
wavelengths. The concentration of the solutions ranged from 4.5 mg/mL to 18.8 mg/mL.
We employ ultranarrow silicon-on-insulator (SOI) waveguides to demonstrate significant Raman gain using low CW pump powers from a diode laser. Starting with measurements based on spontaneous Raman scattering in nanowire SOI waveguides, we obtain the parameters necessary to develop a useful numerical modeling tool for our system. This work shows clearly the feasibility of an SOI-based low-loss, low-power, on-chip Raman amplifier in the silicon nanowire system. We have also developed a rigorous coupled wave model to examine temporal effects in our Raman system.
Solid state femtosecond lasers enable powerful new nonlinear optical spectroscopic characterization techniques for technologically relevant Column IV and III-V semiconductor interfaces and growth surfaces.
Using femtosecond pulses from a Kerr-lens Mode-Locked Ti:Sapphire laser to generate second harmonic from a series of native-oxidized Si(001)/SiO2 samples prepared with systematically varied etch- induced interfacial microroughness, we demonstrate rapid, noncontact, noninvasive measurement of Angstrom-level Si(001)/SiO2 interface roughness. These measurements were performed in air and correlated with atomic force microscopy (AFM) measurements. We also demonstrate in-situ second harmonic monitoring of Si epitaxy in two growth regimes: high temperature (approximately equals 925 K) ultra high-vacuum chemical vapor deposition (UHV-CVD) growth mode and a cyclic atomic layer epitaxy (ALE) growth mode. During UHV-CVD growth of Si on ALE-grown Si0.9Ge0.1(001), we observed interference of the second harmonic signals between the growing Si surface and the buried Si0.9Ge0.1(001) interface. In the ALE growth mode, we monitored several key stages during a full cycle of growth of a partial (approximately equals 0.42) Si monolayer on Si(001) from a disilane (Si2H6) precursor.
We demonstrate two complementary techniques: femtosecond ellipsometry and surface second harmonic generation, for characterization and diagnostics of semiconductor epilayers using unamplified femtosecond laser sources. Through femtosecond ellipsometry, we obtained the time-resolved change in the real and imaginary parts of the index of refraction in relaxed and strained Si1-xGex alloys. Through surface second harmonic generation in conjunction with the Kerr Lens mode-locked (KLM) Ti:Sapphire laser, we obtained surface second harmonic signals in Si(100) and Diamond(111) with an unprecedented signal-to-noise ratio.
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