Improved performance of an ultrastable measurement platform using a field-programmable gate array for real-time, deterministic control

Many precision measurement techniques (e.g. scanning probe microscopy, optical tweezers) are limited by sample drift. This is particularly true at room temperature in air or in liquid. Previously, we developed a general solution for sample control in three dimensions (3D) by first measuring the position of the sample and then using this position in a feedback loop to move a piezo-electric stage accordingly (Carter et al., Optics Express, 2007). In that work, feedback was performed using a software-based data acquisition program with limited bandwidth (<= 100 Hz). By implementing feedback through a field programmable gate array (FPGA), we achieved real-time, deterministic control and increased the feedback rate to 500 Hz - half the resonance frequency of the piezo-electric stage in the feedback loop. This better control led to a three-fold improvement in lateral stability to 10 pm (Delta f = 0.01-10 Hz). Furthermore, we exploited the rapid signal processing of FPGA to achieve fast stepping rates coupled with highly accurate and orthogonal scanning.