We use Anderson or vibration localization in coupled microcantilevers as an extremely sensitive method to detect the added mass of a target analyte. We focus on the resonance frequencies and eigenstates of two nearly identical coupled gold-foil microcantilevers. Theoretical and experimental results indicate that the relative changes in the eigenstates due to the added mass can be orders of magnitude greater than the relative changes in resonance frequencies. Moreover this sensing paradigm possesses intrinsic common mode rejection characteristics thus providing an alternate way to achieve ultrasensitive mass detection under ambient conditions.
Single pulse transmissivity and reflectivity of fused silica irradiated by tightly focused 90 fs laser pulses at a center wavelength of 800 nm are numerically and experimentally investigated to study the role of nonlinear photoionization and avalanche ionization processes in free electron generation. The laser beam inside fused silica is modeled with a ͑2+1͒-dimensional propagation equation which considers the effects of laser beam diffraction, group velocity dispersion, self-focusing, defocusing, and absorption due to the free electrons and nonlinear photoionization of the valence electrons. Comparison of our simulation to the experimental data reveals that the avalanche ionization coefficients are much smaller than some previously reported results and that avalanche ionization is of minor importance in generating free electrons in fused silica at the laser fluence levels considered in this study.
Nonequilibrium A 1g longitudinal optical phonon with a frequency of 1.84 THz in bismuth telluride ͑Bi 2 Te 3 ͒ is coherently excited by ultrafast pulses. Time-resolved reflectivity measurements show a distinct second harmonic vibration around 3.68 THz at room temperature caused by the nonlinearity of coherent phonon potentially related to the favorable crystal structure of Bi 2 Te 3. The scattering rate between A 1g coherent phonon and room temperature incoherent phonon is derived from the pump-fluence-dependent scattering rate of A 1g coherent phonon. It is also observed that energy coupling from photoexcited carriers to lattice through coherent phonon vibration is more efficient and faster at higher pump fluence.
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