A novel adaptive focusing principle for scanning light stimulation systems down to 2μm resolution

A new principle to achieve optimal focusing conditions or rather the smallest possible beam diameter for scanning light stimulation systems is presented. It is based on the following three steps: First, a reference point is introduced on a CMOS sensor to adjust the beam diameter. The distance between the light focusing optic and the reference point is then determined using a laser displacement sensor. In a second step, this displacement sensor is used to obtain the topography of the sample under investigation. Finally, the actual measurement is conducted, using optimal focusing conditions in each measurement point on the sample surface. They are determined by the height difference between the CMOS sensor and the sample topography. This principle is independent of optical or electrical sample properties, the used light source or the selected wavelength. Furthermore, the samples can be tilted, rough, bent or of different surface materials. The described focusing principle can be applied to any scanning light stimulation system. Here, it is implemented using an optical beam induced current (OBIC) setup with a laser light source.