All-optical measurement of nuclear-spin relaxation

Nuclear-spin relaxation rates are usually measured by pulsed radio frequency excitation of nuclear-spin transitions. When the number of spins is too small for direct detection with conventional nuclear-magneticresonance spectrometers, pulsed excitation may be combined with optical detection of the nuclear spins for increased sensitivity. Here we demonstrate that such measurements can also be done purely optically, without radio frequency fields. This is achieved by preparing nonthermal populations by optical hole-burning and time-resolved probing of the populations as a function of the decay time. Measurements of the nuclear-spin relaxation of Pr in the electronic ground state of Pr:YAlO3 show that the relaxation rates for the three transitions differ by a factor of 3.