= Fourier transform microwave spectroscopy
= FTMW spectroscopy
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<Fourier transform microwave spectroscopy> excites gaseous <molecules> with a pulse of <electromagnetic radiation>, then records the emitted time-dependent <electric field>. A <Fourier transform> extracts transition <frequencies> from the decaying signal. In a cavity implementation, two facing mirrors form a resonator; tuned excitation, receiver electronics and digitization replace the molecule-counting readout of <molecular beam electric resonance>. The pulsed radiation prepares <quantum coherence> between rotational <quantum states>; it does not set the whole gas spinning at one classical <angular velocity>.
For documented laboratory context, <Evolution of Microwave Spectroscopy at the National Bureau of Standards (NBS) and the National Institute of Standards and Technology (NIST) by F. J. Lovas and others> (§5, printed pp. 280–282) describes the NIST cavity instrument, phase-locked sources, mirror tuning and detector-mixer modifications. That account explains one instrument family; it does not establish the electronics of every later commercial <spectrometer>.
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