Molecular-beam-stabilized argon laser

The frequency of a 5145-Å argon-ion laser has been locked to an absorption line in a molecular beam of I2. The drift of the laser frequency was less than 20 kHz or Δν/ν<3 × 10−11 for the duration of a run which lasted about 20 min. A molecular-beam external reference is attractive because transitions observed in the isolated conditions in the beam do not suffer shifts due to collisions or collisional broadening and, if the molecular beam is excited orthogonally, Doppler broadening can be virtually eliminated.