We have set up a time-resolved spectroscopy experiment with a temporal resolution on the order of tens of femtoseconds. This setup has been enhanced by incorporating three optical parametric amplifiers, allowing us to independently tune the pump and probe pulses over a spectral range from 250 nm to 20 microns. In the visible spectrum, we can even achieve a sub-10 fs temporal resolution. The experimental setup also includes a cryostat, enabling us to control the sample temperature between 6 K and 300 K. We use this experiment to track the real-time motion of atoms and electrons. In particular, we can control and selectively excite atomic vibrations, known as coherent phonons. These studies aim to understand how the elementary motion of atoms and electrons contributes to transport properties and photoinduced phase transitions.

One illustrative example is LaVS₃, a quasi-two-dimensional material composed of alternating atomic layers, LaS and VS₂, whose crystal structures are incommensurate along one of the crystallographic directions. This incommensurability generates localized energy states where electrons can be excited by a laser pulse with a wavelength centered at 1.2 µm. This excitation leads to a reduction in the material’s conductivity, a behavior distinct from that observed with other pump wavelengths. Thus, it becomes possible to modulate the conductivity of LaVS₃ with a laser pulse in just a few hundred femtoseconds, paving the way for the development of ultrafast switches for future electronics.