In addition, we compared the enhancements obtained from the SE, ASE, SSE and ISE at 70 K with the same ω $& (with EIK output ∼250 W instead of ~300 W used in Fig. ), and these results are tabulated in Table . The ASE is the most efficient pulse sequence at this relatively modest 𝜔 $& as Fig. suggests. Theoretically, when the microwave power is sufficient, the SSE that covers more electron spins should be more efficient than ASE. In practice, however, since the ASE uses a narrower and thus slower frequency chirp than the SSE, it achieves a higher with the same 𝜔 $& and becomes the more efficient approach for our conditions. Furthermore, the enhancement of the 10 mM sample was quickly measured at 90 K and 110 K without a full re-optimization, and an enhancement above 300 was obtained at these temperatures.