Time-dependence of the dipolar order. A cosine pulse with modulation frequency 5 kHz was used as the two-frequency pulse. The center frequencies of the cosine pulse were 0 kHz (cross), ±2 kHz (diamond), ±4 kHz (down triangle), ±6 kHz (up triangle), ±8 kHz (circle), and ±10 kHz (square). Open and filled symbols represent the positive and negative frequency offsets, respectively.