We report on the synchronization of two commercial picosecond Ti:sapphire lasers with unprecedented low temporal jitter between the pulse trains. Pulse jitter is reduced from a few picoseconds to 20 fs with a stability of several hours. The technology enabling the tight pulse synchronization is reviewed in this article. We demonstrate the usefulness of the synchronization scheme by applying the technique to coherent anti-Stokes Raman scattering ͑CARS͒ microscopy. It is shown that CARS images can be acquired with a significant improvement in signal-to-noise ratio. This level of performance brings the fluctuations of the CARS signal down to the fundamental photon shot-noise limit. We present detailed statistical analysis of the pulse jitter and CARS noise along with enhanced CARS vibrational images of polymer beads.
Femtosecond response and relaxation of the third-order optical nonlinearity in a newly developed poly (p-phenylene vinylene)/sol-gel silica composite are investigated by time-resolved forward wave degenerate four-wave mixing, Kerr gate, and transient absorption techniques using 60 fs pulses at 620 nm. Using a theoretical description of two- and four-wave mixing in optically nonlinear media, it is shown that the results obtained from simultaneous use of these techniques yield valuable information on the real and imaginary components of the third-order susceptibility. In the composite material investigated here, the imaginary component is derived from the presence of a two-photon resonance at the wavelength of 620 nm used for the present study. This two-photon resonance is observed as transient absorption of the probe beam induced by the presence of a strong pump beam. It also provides fifth-order nonlinear response both in transient absorption and in degenerate four-wave mixing. The fifth-order contributions are derived from the two-photon generated excited species which can absorb at the measurement wavelength and therefore modify both the absorption coefficient and the refractive index of the medium.
A plasmon-induced hot-electron photodetector based on silicon nanopillar array is developed. The nanostructure is fabricated by reactive ion etching with a monolayer of self-assembled polystyrene nanosphere in hexagonal close-packed lattice as the mask. Light absorption and hotelectron generation are mainly enhanced by the surface plasmon polaritons formed at the surface of the gold film on the nanopillar sidewalls. The photoresponse spans two telecom wavebands, viz. the range of 1250-1600 nm, and has a value of 2.5 mA W −1 at 1310 nm. The proposed silicon nanopillar-based hot-electron infrared detector has great potentials for device integration in silicon photonics relying on the economic large-area fabrication process.
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