The shift is from scanning to seeing it all at once. A team of researchers has built a microscope that records a full two-dimensional electronic spectrum at every pixel of a camera image in parallel, with no point-by-point raster scanning. The group is based at Università Cattolica del Sacro Cuore in Brescia, Italy, and works with KU Leuven, the University of British Columbia in Vancouver and Politecnico di Milano. They call the instrument 2DESM.
The trade-off it breaks
Two-dimensional semiconductors such as the transition-metal dichalcogenides are leading candidates for atomically thin optoelectronic and quantum technologies. Their optical response depends on local conditions that change across micrometre-scale structures: dielectric environment, strain, interfaces and defects. Conventional ultrafast spectroscopy averages over all of that, which hides where the measured dynamics come from.
Existing tools forced a choice. Pump-probe microscopy maps excited-state populations in space but is blind to quantum coherence, and it cannot tell the intrinsic linewidth of an optical transition from broadening caused by disorder. Two-dimensional electronic spectroscopy can make that distinction, but adding spatial detail has required tight focusing and slow raster scanning. 2DESM combines 2DES with widefield imaging. With no focusing objective in the excitation path, the pulses stay short and spectrally broad across the whole field of view.
Under the hood
Two ultrastable common-path interferometers built on translating birefringent wedges sit at the core. The first makes a pair of phase-locked pump pulses. The second, in the detection path, resolves the transmitted probe by wavelength while keeping the full image. A high-speed scientific camera synchronised with the pump modulation grabs around 3,000 frames per second. A two-dimensional Fourier transform along both delay axes then gives a complete 2D spectrum at each pixel.
The system reaches a temporal resolution of 38 femtoseconds, a spatial resolution of 1.05 micrometres and a spectral resolution of 50 meV. It runs from room temperature down to 4 kelvin in a custom cryogenic chamber.
First results on tungsten diselenide
To test it, the team imaged flakes of tungsten diselenide (WSe2) encapsulated in hexagonal boron nitride. The maps showed how the excitonic response varies across the sample and picked out regions with different dielectric environments. They also separated the intrinsic exciton decoherence time, a few tens of femtoseconds, from disorder-induced broadening at each location. Measurements at 300 kelvin and 20 kelvin captured the narrowing of the excitonic linewidth, and the matching rise in coherence time, as the sample cooled.
The catch is speed. One complete hyperspectral data cube takes about 10 hours to acquire, so faster acquisition is the main goal for the next generation. The team also plans to turn 2DESM on van der Waals heterostructures such as WSe2/MoS2 and on other quantum materials including MoSe2 and NiPS3. The work appears in Optica 13, 1861 (2026).
