Fig. 3: Atomic-scale tracking of hot carrier dynamics.

a A series of anti-Stokes spectra measured as a function of the delay between the pump and the probe pulses. Pump pulse parameters: λ ~ 830–870 nm, pulse duration ~ 30 fs, power ~ 5.8 mW (72 pJ). Probe pulse parameters: λ ~ 715–750 nm, pulse duration ~ 30 fs, power ~ 2.6 mW (32 pJ). STM was operated in the constant current mode with a tunneling current of 8 nA and a bias of 100 mV. b Representative anti-Stokes spectra from the measurement shown in (a) at different delays between pump and probe pulses, as annotated on top of each spectrum. c Spectral intensity variation of the anti-Stokes spectra at ~ 665 nm (hot carrier, dashed red curve) and at ~ 640 nm (FWM, dashed blue curve) as a function of the delay between pump and probe pulses, indicated by horizontal dashed red and blue lines in (a) respectively. The gray curve represents the duration of the probe pulse (see “Methods”). An exponential fit (solid red curve) of the temporal cross-cut reveals a relaxation time of ~ 149 fs. d Simulated anti-Stokes spectra as a function of the delay between the pump and the probe pulses. The parameters of the pump and probe pulses used in the simulations are identical to the experimental ones. e Temporal cross-cut at 665 nm from the simulation shown in (d) (horizontal dashed green curve). A relaxation time of ~ 112 fs is estimated from the exponential fit of the temporal cross-cut (solid red curve). f Variation of the measured relaxation times of the anti-Stokes signal as a function of various wavelengths. The top x-axis represents the energy shift of the anti-Stokes signal with respect to the central wavelength (~ 735 nm) of the probe pulse. The error bars indicate the standard deviation from the fit.