Ultra-narrow optical hole burning in ruby

Abstract

By applying a large magnetic field (∼3.5 T) along the crystal axis, the homogeneous line width of the 4A 2(− 1 2 ) → E(− 1 2 ) optical transition of Cr 3+ in dilute ruby is narrowed due to a suppression of Cr-Cr electron spin flipping. A hole width as narrow as 17.9 kHz (FWHM) is observed using a pump-probe technique. In contrast to earlier low field results which gave strictly Lorentzian line shapes, the high field line shape is Gaussian. Arguments are presented that suggest the line shape is determined by coherence rather than by dissipative effects. Achievement of the latter limit will require improvements in the long term frequency stability of the laser and an increase in sensitivity to allow pump-probe observations at low Rabi frequencies (<5 kHz).