Approaching attometer laser vibrometry

Theheterodyne two-beaminterferometer has been proven to be the optimal solution for laser-Doppler vibrometry (LDV) regarding accuracy and signal robustness. Thetheoretical resolution limit for a two-beaminterferometer of laser class 3R (up to 5 mW visiblemeasurement-light) is in the regime of a few femtometer per square-root Hertz and well suited to study vibrations in microstructures. However, some new applications of radio-frequency microelectromechanical (RF-MEM)resonators, nanostructures, and surface-nano-defect detection require resolutions beyond that limit. The resolution depends only on the photodetector noise and the sensor sensitivity to specimen displacements. The noise is already defined in present systems by the quantum nature of light for a properly designed optical sensor and more light would lead to an inacceptable influence like heating of the tiny specimen. Noise can only be improved by squeezed-light techniques which require a negligible loss ofmeasurement light which is impossible to realize for almost all technicalmeasurement tasks. Thus, improving the sensitivity is the only path which could make attometer laser vibrometry possible. Decreasing themeasurement wavelength would increase the sensitivity but would also increase the photon shot noise. In this paper, we discuss an approach to increase the sensitivity by assembling an additionalmirror betweeninterferometer and specimen to form anoptical cavity. A detailedtheoretical analysis of this setup is pre...

Source: Review of Scientific Instruments - October 13, 2016 Category: Physics Authors: C. Rembe, L. Kadner and M. Giesen Source Type: research