Ultrafast Pump-Probe Experiment for Quantum Materials

Ultrafast pump-probe technique provides a powerful tool to investigate the electronic properties of solid materials under excitation. Two laser pulses, a pump and a probe, are employed with a delay. The pump pulse excites electrons within the material, driving it into a transient excited state, while the probe pulse interrogates the sample after a controlled delay. By monitoring changes in the probe's reflectivity as a function of pump-probe delay, we gain insights into the material's transient behavior. To enhance data collection, we incorporated a rapid-scanning mirror stage into the design. The stage scans a range from -3 ps to 3 ps or -33 ps to 33 ps. We successfully detected transient reflectivity signals from indium phosphide, the reference sample, confirming that the pump-probe system works. Our current efforts extend this methodology to complex materials, including Fe-doped NbS2, for which we obtained preliminary data with an 800-nm pump and a 1150-nm probe. Future work will incorporate temperature-dependent measurements to examine oscillations and other thermally activated processes at room temperature. We focus on Fe-doped NbS₂ because at low temperature it may host coherent oscillations of the charge-density wave (CDW) amplitude mode, while above the CDW temperature it has a non-reciprocal phonon dispersion.