Motional stark effect in high magnetic fields: A new technique for sub-doppler spectroscopy

We have observed transitions between Rydberg states of He with sub-Doppler resolution, using a novel technique. Ordinary Doppler line shapes, observed at low magnetic fields, are completely altered at high fields by the quadratic Stark effect induced by velocity-dependent electric fields arising from atomic motion transverse to the magnetic field. The high-field line shape has an abrupt cutoff, corresponding to v0 atoms, whose slope is primarily limited by the homogeneous linewidth.