Selection of an aligned subset of sample molecules by an exciting light beam. The selected subset will have an orientation distribution that is determined by the electric vector of the beam. If the beam is linearly polarized a uniaxial sample with a known orientation distribution will be produced. Also, the set of remaining molecules will be aligned with a known orientation distribution (residual anisotropy).
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 399 (https://doi.org/10.1351/pac200779030293)