Ammonia maser 2026-10-18
An ammonia maser uses an ammonia molecular beam, maser state selection and a maser cavity to obtain amplification or sustained microwave oscillation. In the 1954 experiment by James Power Gordon, Herbert Jack Zeiger and Charles Hard Townes, a quadrupolar static electric field focused upper-state molecules toward the cavity and deflected lower-state molecules away. The reported ammonia inversion transition lies near .[ref]
Molecular Microwave Oscillator and New Hyperfine Structure in the Microwave Spectrum of NH3 by James Power Gordon and others. pp. 282–283, Fig. 1 and Fig. 2 caption; 23 870 Mc/sec
Maser discovery experiment 2026-10-18
Ammonia gas entered a vacuum chamber through fine channels; the selected beam entered a cavity with input and output waveguides.[ref]
The Maser—New Type of Microwave Amplifier, Frequency Standard, and Spectrometer by James Power Gordon and others. pp. 1264–1265, Fig. 1, source and vacuum
With external microwaves swept across a molecular resonance, the 1954 experiment read an increase in transmitted power; with sufficient beam emission, it sustained oscillation.[ref]The 1955 readout mixed two maser signals with a local oscillator in a crystal detector, amplified them at an intermediate frequency, and combined them in a diode detector. An oscilloscope showed their beat frequency. Changing cavity tuning, source pressure or focuser field tested sensitivity; excessive detuning stopped oscillation.[ref]
The Maser—New Type of Microwave Amplifier, Frequency Standard, and Spectrometer by James Power Gordon and others. pp. 1266–1267, Experimental Results, heterodyne and controls
The beat tests relative frequency stability; it does not by itself establish an absolute frequency or an intrinsic linewidth independent of detector noise. Detuning also changes the field–molecule interaction, so the threshold model's constant cannot describe arbitrary tuning scans.