Spin waves were first observed in spin polarized atomic hydrogen gas in the mid 1980's at
temperatures between 0.1 and 1.0 K via pulsed NMR. A description of these experiments and
their interpretation will be summarized. Later on spin waves have been produced in very
dilute helium 3-helium 4 mixtures from moving domain walls following a single 180 degree
pulse in a field gradient. Multiple echoes were observed, each one corresponding to a
different spin wave mode. In these experiments, the echoes appeared at intervals of
0.1 -1.0 seconds, depending on the values of the magnetic field gradient and the temperature.
The echoes are thought to be associated with geometric spin wave resonances as the domain
wall moves through the field gradient in the cell.