Brescia, October 11 — The shift is clear: ultrafast spectroscopy just got a widefield upgrade. Researchers from Università Cattolica del Sacro Cuore in Brescia, KU Leuven in Belgium, the University of British Columbia in Vancouver, and Politecnico di Milano have unveiled a new microscope called 2DESM that captures a full two-dimensional electronic spectrum at every pixel of an image simultaneously, eliminating the need for slow point-by-point scanning.
The system was tested on tungsten diselenide (WSe₂), a two-dimensional semiconductor, and operates across a broad temperature range from room temperature down to four kelvin inside a custom cryogenic chamber. At the heart of the instrument are two ultrastable common-path interferometers built from translating birefringent wedges.
One interferometer, located in the excitation path, generates phase-locked pump pulses. The other, placed in the detection path, spectrally resolves the transmitted probe light while maintaining the full spatial image. A high-speed scientific camera, synchronized with pump modulation, records roughly three thousand frames per second.
Applying a two-dimensional Fourier transform along both delay axes then reconstructs a complete 2D spectrum for each pixel in the field of view. This design allows the team to distinguish intrinsic exciton decoherence — occurring on the scale of a few tens of femtoseconds — from disorder-induced inhomogeneous broadening at every spatial point.
By imaging hexagonal boron nitride-encapsulated WSe₂ flakes, they mapped how the excitonic response varies across the sample, linking these variations to local differences in dielectric environment, strain, interfaces, and defects. Measurements at both 300 kelvin and 20 kelvin showed that cooling narrows the excitonic linewidth and correspondingly increases coherence time, revealing temperature-driven changes in quantum behavior. Currently, acquiring a full hyperspectral data cube takes about ten hours, which the researchers identify as a key target for future speed improvements.
The breakthrough lies in overcoming a long-standing compromise: traditional pump–probe microscopy can map excited-state populations with spatial resolution but is blind to quantum coherence and cannot separate homogeneous from inhomogeneous broadening. Conversely, conventional two-dimensional electronic spectroscopy preserves coherence information but requires slow scanning to achieve spatial detail. 2DESM merges the strengths of both approaches by using widefield imaging to preserve broadband femtosecond pulses across the entire field of view, avoiding the need for focusing objectives in the excitation path that would limit bandwidth or pulse duration.
As a result, the technique establishes a direct, pixel-by-pixel connection between local nanoscale structure and the coherent electronic dynamics that govern performance in atomically thin optoelectronic and quantum devices. Watch this space — the next push will be to cut acquisition time from hours to minutes, bringing real-time coherent imaging of quantum materials closer to reality.
