108 research outputs found
Observation of nonlinear bands in near-field scanning optical microscopy of a photonic-crystal waveguide
We have measured the photonic bandstructure of GaAs photonic-crystal
waveguides with high energy and momentum resolution using near-field scanning
optical microscopy. Intriguingly, we observe additional bands that are not
predicted by eigenmode solvers, as was recently demonstrated by Huisman et al.
[Phys. Rev. B 86, 155154 (2012)]. We study the presence of these additional
bands by performing measurements of these bands while varying the incident
light power, revealing a non-linear power dependence. Here, we demonstrate
experimentally and theoretically that the observed additional bands are caused
by a waveguide-specific near- field tip effect not previously reported, which
can significantly phase-modulate the detected field.Comment: 6 pages, 5 figure
Femtosecond spectral phase shaping for CARS spectroscopy and imaging
Coherent Anti-Stokes Raman Scattering (CARS) is a third-order non-linear optical process that provides label-free, chemically selective microscopy by probing the internal vibrational structure of molecules. Due to the resonant enhancement of the CARS process, faster imaging is possible compared to Raman microscopy. CARS is unaffected by background fluorescence, but the inherent non-resonant background signal can overwhelm the resonant signal. We demonstrate how simple phase shapes on the pump (and probe) beam reduce the background signal and enhance the resonant signal. We demonstrate chemically selective microscopy using these shaped pulses on plastic beads
Vibration transfers to measure the performance of vibration isolated platforms on site using background noise excitation
This article demonstrates a quick and easy way of quantifying the performance of a vibration-isolated platform. We measure the vibration transfer from floor to table using background noise excitation from the floor. As no excitation device is needed, our setup only requires two identical sensors (in our case, low noise accelerometers), a data acquisition system, and processing software. Background noise excitation from the floor has the additional advantage that any non-linearity in the suspension system relevant to the actual vibration amplitudes will be taken into account. Measurement time is typically a few minutes, depending on the amount of background noise. The (coherent) transfer of the vibrations in the floor to the platform, as well as the (non-coherent) acoustical noise pick-up by the platform are measured. Since we use calibrated sensors, the absolute value of the vibration levels is established and can be expressed in vibration criterion curves. Transfer measurements are shown and discussed for two pneumatic isolated optical tables, a spring suspension system, and a simple foam suspension system
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