Quantum-Probe Field Microscopy of Ultrafast Terahertz Excitations

TL;DR

This paper introduces Quantum-probe Field Microscopy (QFIM), a novel far-field imaging technique using quantum-dot probes to visualize ultrafast Terahertz electric fields with sub-wavelength spatial and sub-picosecond temporal resolution.

Contribution

The work presents a new quantum-dot based microscopy method capable of capturing ultrafast electric fields in the Terahertz regime with high spatial and temporal resolution.

Findings

Successfully visualized localized Terahertz excitations

Achieved sub-wavelength spatial resolution

Demonstrated sub-picosecond temporal resolution

Abstract

Rapid evolutions of microscopic fields govern the majority of elementary excitations in condensed matter and drive microelectronic currents at increasing frequencies. Beyond nominal "radio frequencies", however, access to local electric waveforms remains a challenge. Several imaging schemes resolve sub-wavelength fields up to multi-Terahertz (THz) frequencies - including scanning-probe techniques, electro-optic sampling or recent ultrafast electron microscopy. Yet, various constraints on sample geometries, acquisition speed and maximum fields limit applications. Here, we introduce ubiquitous far-field microscopy of ultrafast local electric fields based on drop-cast quantum-dot probes. Our approach, termed Quantum-probe Field Microscopy (QFIM), combines fluorescence imaging of visible photons with phase-resolved sampling of electric fields deeply in the sub-wavelength regime. We capture stroboscopic movies of localized and propagating ultrafast Terahertz excitations with sub-picosecond temporal resolution. The scheme employs field-driven modulations of optical absorption in colloidal quantum-dots via the quantum-confined Stark-effect, accessible via far-field luminescence. The QFIM approach is compatible with strong-field sample excitation and sub-micrometer resolution - introducing a route towards ultrafast field imaging in active nanostructures during operation.