A sample-scanning confocal optical microscope for cryogenic operation

A sample-scanning confocal optical microscope for single-molecule imaging and spectroscopy working at superfluid helium temperature, liquid nitrogen, and room temperature is described. An optical resolution of 800 nm full width at half maximum as well as a detection efficiency of ≈3.5% are achieved. The sample scanner features an exceptionally large scan range of 23 μm at 1.8 K. A position sensor allows for continuous observation of the scanner motion and for a correction of piezoelectric hysteresis and creep at 77 K and at room temperature. Coarse positioning of the sample in x-y is achieved by an inertia drive with high reproducibility and nanometer precision. We demonstrate combined high–resolution confocal imaging and spectroscopy of single molecules at 1.8 K.