Fig. 1. Calculated electron temperature T_e of silver for various incident laser fluences F according to Equation (2) with γ_e = 62.8 J m⁻³ K⁻², μ = 142 nm, and β = 0.15.

Fig. 2. Block diagram of the laser-electrochemical system. μWE: silver working microelectrode; CE: platinum counter electrode; fs-CPO: femtosecond chirped pulse oscillator; E: laser pulse energy; τ: pulse duration; OBJ: microscope objective; R: 1 MΩ resistor; DAQ: digital-to-analog converter output; φ: applied electrode potential; HPA: high pass amplifier; Δφ: transient voltage signal; OSC: digital storage oscilloscope.

Fig. 3. (a) Exemplary Δφ(t) transient voltage measurement averaged over 100 single laser pulses. τ = (55 ± 1) fs, F₀ = (64 ± 7) mJ cm^-2, ϕ = (–460 ± 40) mV vs. SHE. The inset enlarges the region around t = 0 and shows the extracted peak voltage change Δφ₀ = (19.7 ± 0.1) mV. (b) Comparison of Δφ(t) transient voltage measurements recorded at various laser peak fluences F₀.

Fig. 4. Imaginary part X of an exemplary impedance measurement corresponding to the Δφ(t) transient in Fig. 3.The solid line shows the constant phase element fit.

Fig. 5. Logarithmic plot of the emitted hot electron charge Q for two pulse durations, τ = (55 ± 1) fs (red circles) and τ = (213 ± 1) fs (blue stars), plotted over the applied electrode bias φ and peak laser fluence F₀. The gray surface is calculated from Eq. (5) but for a constant factor with γ_e = 62.8 J m⁻³ K⁻², μ = 142 nm, β = 0.15, and φ₀ = 3.41 eV at 0 V vs. SHE.

Fig. 6. Schematic electronic Fermi-Dirac distribution n on the metal and density of states (DOS) as function of the electronic energy ε of H₃O⁺ and H⁰.