Camera-based speckle noise reduction for interferometric non-incremental shape measurement

Laser Doppler sensors enable 3d shape measurements of fast rotating objects [1]. Several speckles with equal frequency but random phases are generated [2]. This leads to disturbances in the power spectra, which result in systematic deviations of the estimated Doppler frequency and limit the achievable measurement uncertainty of the shape. For reducing the speckle noise, a novel separate speckle detection method by using a camera instead of a photo detector is investigated. Numerical simulations and physical experiments demonstrate that this method allows to decrease the measurement uncertainty by the order of one magnitude. This enables a reduction of the measurement uncertainty for interferometric non-incremental 3d shape measurements below 100 nm and with high temporal resolution. [1] P. Günther, T. Pfister, L. Büttner, J. Czarske, “Laser Doppler distance sensor using phase evaluation, ” Opt. Exp. 17, 2611-2622(2009). [2] Robert Kuschmierz, Nektarios Koukourakis, Andreas Fischer, Jürgen Czarske,“ On the speckle number of interferometric velocity and distance measurements of moving rough surfaces, ” Opt. Lett. 39, 5622-5625(2014).