Fig. 5: Pulse sequence for the spin echo experiments.
In the beginning, both the I (71Ga) and the S (75As) nuclear magnetizations are saturated by comb pulses comprised of 32 \(\pi /2\)-pulses. After the time interval \(\tau _{{{\mathrm{L}}}}\) for the buildup of the nuclear magnetizations, the spin-echo sequence for the I-spins is applied (P1 and P2). The S-spins are optionally flipped (P3) concurrently with the P2 pulse. An Oldfield echo sequence with the ratio of the P1/P2 pulse widths of 1:2 was used to minimize the distortion of the echo signal due to the quadrupolar effect. The P1/P2 pulse widths were adjusted such that the phase of the echo remains unchanged during the echo decay processes. In the light illumination experiments, the light (826 nm, σ+) was continuously applied during this sequence.
