FIG. 6.

(a) Matching condition of the NOVEL pulse sequence in a DPNO/BzP sample at 270 K. The enhancement was measured as a function of the microwave field strength. The spin lock pulse is fixed to 100 ns, whereas the length of the flip pulse is adjusted to give a 90° tip angle. The matching occurs at ω_1S = ω_0I. (b) ¹H spectra with (red) and without (blue) DNP. For the DNP enhanced spectrum, the sample was polarized for 10 s with a 16 ns flip pulse followed by a 100 ns spin lock pulse. The repetition time was 40 μs. The off spectrum was obtained with 10 s of recovery time. The enhancement in signal intensity was ε = 165. The intensities were normalized to the μw off signal. (c) DNP buildup time constant T_B using NOVEL pulse sequence and the spin-lattice relaxation time constant T₁. Reduction in the buildup time constant results in a sensitivity gain of $\epsilon {\left(T_1/T_B\right)}^{1/2}=230$.