(The phase of the arbitrary waveform generator sets the phase of the molecular signal.)

Complete phase control is demonstrated on a single MW transition (10 – 00 ) for propyne. By changing the phase on the linear frequency sweep by steps of p/4, the phase of the free induction decay molecular signal (shown above) is changed by the same amount. Notice the brown and black lines at phase = 0 and 2p have the identical phase.

In this case, there are multiple MW transitions within the bandwidth of our broadband FTMW; therefore, the free induction decay (FID) exhibits multiple frequencies. By tuning the phase of the arbitrary waveform generator to 0 (red trace) and p(blue trace), we can control the phase of the molecular FID (shown above).