While measuring the forces, it is basically possible to only acquire data from the trap steering unit, i.e. to evaluate the laser beam deflection. “This is not sufficient for quite a number of applications, however” explains Dr. Joost van Mameren, an application scientist at JPK. “If an analysis requires motion at constant speed, for example, we integrate a piezo-based three-axis nanopositioning system into our Nano-Tracker. This will prevent small interfering signals, which could arise with pure trap steering due to the motion caused when the optics are displaced. Furthermore, the positioning system provides the option of shifting the focus in the direction of the Z-axis, if required, in real-time. One should avoid manipulating the optics for this purpose, if at all possible, because measuring errors caused by interfering signals would then be inevitable. Moreover, the nanoposi tioning system enables the calibration of the optical tweezers to provide a higher positioning accuracy.” JPK chose the P-561.3CD nanopositioning system of the PIMars series from PI. “The parallel kinematics system operates with repeatability in the nanometer range at response times below one millisecond, and the travel range of 100x100x100 µm matches the requirements of our application perfectly. Moreover, it proves to be very reliable and convinces with its long service life”, Dr. van Mameren continues.