Position and Mode Dependent Optical Detection Back-Action in Cantilever Beam Resonators

Optical detection back-action in cantilever resonant or static detection presents a challenge when striving for state-of-the-art performance. The origin and possible routes for minimizing optical back-action have received little attention in literature. Here, we investigate the position and mode dependent optical back-action on cantilever beam resonators. A high power heating laser (100 {\mu}W) is scanned across a silicon nitride cantilever while its effect on the first three resonance modes is detected via a low-power readout laser (1 {\mu}W) positioned at the cantilever tip. We find that the measured effect of back-action is not only dependent on position but also the shape of the resonance mode. Relevant silicon nitride material parameters are extracted by fitting the temperature-dependent frequency response of the first three modes to finite element (FE) simulations. In a second round of simulations, using the extracted parameters, we successfully fit the FEM results with the measured mode and position dependent back-action. Finally, different routes for minimizing the effect of this optical detection back-action are described, allowing further improvements of cantilever-based sensing in general

Imaging interferometry to measure surface rotation field

International audienceThis paper describes a polarized light imaging interfe-rometer to measure the rotation field of reflecting surfaces. This set-up is based on a home-made prism featuring a birefringence gradient. The arran-gement is presented before focusing on the home-made prism and its manufacturing process. The dependence of the measured optical phase on the rotation of the surface is derived, thus highlighting the key parameters driving the sensitivity. The system's capabilities are illustrated by imaging the rotation field at the surface of a tip-loaded polymer specimen

Real-Time Particle Mass Spectrometry Based on Resonant Micro Strings

Micro- and nanomechanical resonators are widely being used as mass sensors due to their unprecedented mass sensitivity. We present a simple closed-form expression which allows a fast and quantitative calculation of the position and mass of individual particles placed on a micro or nano string by measuring the resonant frequency shifts of the first two bending modes. The method has been tested by detecting the mass spectrum of micro particles placed on a micro string. This method enables real-time mass spectrometry necessary for applications such as personal monitoring devices for the assessment of the exposure dose of airborne nanoparticles

Vertical-cavity surface-emitting laser vapor sensor using swelling polymer reflection modulation

Vapor detection using a low-refractive index polymer for reflection modulation of the top mirror in a vertical-cavity surface-emitting laser (VCSEL) is demonstrated. The VCSEL sensor concept presents a simple method to detect the response of a sensor polymer in the presence of volatile organic compounds. We model the physics as a change in the top mirror loss caused by swelling of the polymer upon absorbing the target volatile organic compound. Further we show how acetone vapors at 82 000 ppm concentration can change the polymer coated VCSEL output power by 20 mu W