Extended Data Fig. 1: Measurement of VUV power.
From: Continuous-wave narrow-linewidth vacuum ultraviolet laser source
With the 710-nm beam shuttered, the PMT records a background count rate of 1.42(1) × 105 s−1. At t ≈ 3.5 s, the 710-nm beam is unshuttered and the count rate rises to 4.76(34) × 106 s−1. Control measurements verify that the background count is dominated by residual 375-nm stray light, that the PMT is insensitive at 710-nm and that it operates in the linear regime. Using the overall detection efficiency ηabs = 0.21(4) × 10−4 (Extended Data Table 1), we infer a VUV power of 290(60) nW at 148.4 nm.
