In-situ and non-destructive focus determination device for high-precision laser applications

A non-destructive, in-line, and low-cost focusing device based on an image sensor has been developed and demonstrated. It allows an in situ focus determination for a broad variety of laser types (e.g. cw and pulsed lasers). It provides stringent focusing conditions with high numerical apertures. This approach does not require sub-picosecond and/or auxiliary lasers, or high fluences above damage thresholds. Applications of this system include, but are not limited to the laser-illumination of micro-electrodes, pump-probe microscopy on thin films, and laser ablation of small samples without sufficient surface area for focus determination by ablation. An uncertainty of the focus position by an order of magnitude less than the respective Rayleigh length could be demonstrated.