Figure 4.

f × λ-PADMR correlates near-IR PA with T₁ MR. (a) The PADMR signal magnitude, , shows strong signals when probing the 1000 nm PA (Figure 2) and driving the T_Z ↔ T_Y transition (642 nm pump wavelength, pump intensity ≈ 15 W/cm², f_mod^RF = 2.99 kHz, temperature ≈ 5–10 K). Slight asymmetry shows that the PA and MR spectral positions are correlated. (b) λ-PADMR spectra demonstrate shifting PA intensity as a function of f_Drive. They are slices taken from a global fit of the phase-optimized PADMR data (applied phase, ϕ = +34.2°; see SI section S1.2.5 for a discussion of the rephasing process). (c) The λ-PADMR basis spectra obtained by the fit. All are most intense near 1000 nm. A superimposed positive feature is seen at 850 nm when driven by 972 MHz RF and likely corresponds to a GSB (RF increases ground-state population). It shifts to bluer wavelengths with increasing f_Drive^RF. A similar shift is seen in a GSB near 740 nm, and pronounced shifts are seen when probing near the 600 nm PA (SI section S2.3.1).