Measuring and imaging nanomechanical motion with laser light

We discuss several techniques based on laser-driven interferometers and cavities to measure nanomechanical motion. With increasing complexity, they achieve sensitivities reaching from thermal displacement amplitudes, typically at the picometer scale, all the way to the quantum regime, in which radiation pressure induces motion correlated with the quantum fluctuations of the probing light. We show that an imaging modality is readily provided by scanning laser interferometry, reaching a sensitivity on the order of $$ , and a transverse resolution down to $$ . We compare this approach with a less versatile, but faster (single-shot) dark-field imaging technique.