Surface imaging using optically controlled microrods

We present an imaging technique using an optically trapped silica microrod probe controlled using holographic optical tweezers. The probe is raster scanned over a surface, allowing an image to be recorded in a manner analogous to scanning probe microscopy (SPM), with closed loop feedback control provided by high-speed CMOS camera image tracking. We demonstrate a proof of principle of this technique by imaging the surface of an oil droplet. We estimate the normal force exerted on the sample during imaging to be similar to 1 pN. The resolution is limited by the diameter of the microrod tip, thermal motion of the probe and the tracking accuracy. As our technique is not diffraction limited, there is scope for significant improvement by reducing the tip diameter, and position clamping to reduce unwanted thermal motion.