Robust, motion-free optical characterization of samples using actively-tunable Twyman–Green interferometry

Focal length characterization of the TFL used for the experiments

We characterized the focal length of the TFL as a function of the applied DC current \(I_\mathrm{DC}\) from the Optotune lens driver model 4i. For this purpose, we used a simple setup where a collimated beam was passed through the TFL. The location of the minimum focal spot was recorded for different input current \(I_\mathrm{DC}\) values to the TFL. The distance of the minimum focal spot from the TFL equalled the TFL focal length at each corresponding applied \(I_\mathrm{DC}\). For each applied \(I_\mathrm{DC}\), a CCD,…