Technique for frequency selective, sub-diffraction limited imaging of rare-earth ions in bulk crystals

We propose and demonstrate the principle of a sub-diffraction-limited optical imaging technique for rare-earth ion crystals that preserves the ions’ homogeneous line width. Our method uses a combination of applied electric field gradients and optical pumping to create a resonant nanoscopic volume within an otherwise non-resonant macroscopic crystal. We present the concept of the Stark activation technique and perform a demonstration in Pr³⁺: Y₂SiO₅ in which we create a 10 μm-thick absorption feature in a 1 mm thick crystal. By modeling the system we show that it is possible to increase the resolution of the technique to the 5 nm range for single Pr³⁺ ions. We also discuss the physical properties that will fundamentally limit the resolution of Stark activation. Because the proposed technique simultaneously achieves high spatial and high spectral resolution it is an enabling protocol to realize technology based on single rare-earth ions and harness short-range interactions in ensembles.