1：Experimental Design and Method Selection:

The study uses laser-induced fluorescence (LIF) technique to measure the density distribution of ground-state copper atoms in a vacuum arc extinction scenario. The principle involves exciting copper atoms with a laser at 324.8 nm and capturing fluorescence at 510.6 nm using an ICCD camera. The experimental circuit includes a main loop and a commutation loop to force the arc to current zero.

2：8 nm and capturing fluorescence at 6 nm using an ICCD camera. The experimental circuit includes a main loop and a commutation loop to force the arc to current zero. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: The experiments are conducted using cylindrical contacts made of CuCr25 and CuCr50 materials with a diameter of 40 mm and a gap length of 15 mm in a demountable vacuum chamber pumped below 5 × 10^{-4} Pa.

3：List of Experimental Equipment and Materials:

Key equipment includes a dye laser (Quantel, wavelength

4：8 nm, pulse width 5 ns, frequency 10 Hz, energy 5 mJ), an ICCD camera (Andor iStarDH334T, 1024 × 1024 pixels), a band-pass filter (center wavelength 32 nm, bandwidth 84 nm), capacitors (C

3 100 mF, C2: 2 mF), inductor (L1: 0.1 mH), thyristor, high-voltage probe, Hall-current sensor, oscilloscope, and vacuum chamber with quartz windows.

5：1 mH), thyristor, high-voltage probe, Hall-current sensor, oscilloscope, and vacuum chamber with quartz windows. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The main capacitor is charged to 50 V and the reverse capacitor to 100 V. A vacuum arc is initiated by a trigger electrode, and after 5 ms, the thyristor is triggered to force current zero. The laser is fired at specific time intervals (from 125 μs to 375 μs with 25 μs steps) after arc extinction, and the ICCD captures fluorescence signals with a 50 ns exposure time.

6：Data Analysis Methods:

The fluorescence intensity is analyzed to determine the relative density distribution of copper vapor, assuming proportionality between fluorescence photons and ground-state atom density. Temporal evolution is plotted to observe decay patterns.