Figure 2
(a) Pulse-timing diagram employed in our experiments. Pulses are given as
. rf-field strengths were
(
pulse width) and
for pulsing and cyclic adiabatic inversion, respectively. A 0.5 s off-resonance (
) irradiation prior to the experiment and a two-step phase cycle (indicated by
) eliminated spurious rf-cantilever couplings. The repetition delay between scans was 30 s [
28]. The triangular frequency modulation used for cyclic adiabatic inversion had a depth of 200 kHz in all experiments, and its rate matched the cantilever eigenfrequency of typically 850 Hz. (b) Schematic drawing of the cantilever oscillations and the detected output of the lock-in amplifier (dashed line), which is then integrated over
. (c) Experimental setup. A cylindrical iron magnet (
) of 1 mm diameter (
) produced approximately planar surfaces of constant field (sensitive slices, dashed shape) perpendicular to the static field axis (
, 250 MHz proton frequency). The field gradient at
was
. Typical cantilever parameters were
,
and
(
with feedback). The 4 turn,
inner diameter coil was wound from
thick copper wire.
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