Multipass wide-field phase imager.

Advances in optical imaging always look for an increase in sensitivity and resolution among other practicability aspects. Within the same scope, in this work we report a versatile interference contrast imaging technique, with high phase sensitivity and a large field-of-view of several mm2. Sensitivity is increased through the use of a self-imaging non-resonant cavity, which causes photons to probe the sample in multiple rounds before being detected, where the configuration can be transmissive or reflective. Phase profiles can be resolved individually for each round thanks to a specially designed single-photon camera with time-of-flight capabilities and true pixels-off gating. Measurement noise is reduced by novel data processing combining the retrieved sample profiles from multiple rounds. Our protocol is especially useful under extremely low light conditions as required by biological or photo-sensitive samples. Results demonstrate more than a four-fold reduction in phase measurement noise, compared to single round imaging, and values close to the predicted sensitivity in case of the best possible cavity configuration, where all photons are maintained until n rounds. We also find good agreement with the theoretical predictions for low number of rounds, where experimental imperfections would play a minor role. The absence of a laser or cavity lock-in mechanism makes the technique an easy to use inspection tool.

The new FAST module: A portable and transparent add-on module for time-resolved investigations with commercial scanning probe microscopes.

Time resolution is one of the most severe limitations of scanning probe microscopies (SPMs), since the typical image acquisition times are in the order of several seconds or even few minutes. As a consequence, the characterization of dynamical processes occurring at surfaces (e.g. surface diffusion, film growth, self-assembly and chemical reactions) cannot be thoroughly addressed by conventional SPMs. To overcome this limitation, several years ago we developed a first prototype of the FAST module, an add-on instrument capable of driving a commercial scanning tunneling microscope (STM) at and beyond video rate frequencies. Here we report on a fully redesigned version of the FAST module, featuring improved performance and user experience, which can be used both with STMs and atomic force microscopes (AFMs), and offers additional capabilities such as an atom tracking mode. All the new features of the FAST module, including portability between different commercial instruments, are described in detail and practically demonstrated.