Abstract

It is well known that second harmonic generation (SHG) in atomic vapor is highly forbidden by symmetry.¹ Experimentally, however, with input laser pulses tuned to either one or two-photon resonances, appreciable amount of second harmonic generation in alkali vapor can be detected.^2,3 In nearly all cases, nanosecond pulses were used. It has been proposed that multiphoton ionization of the vapor followed by the electron separation from ions may lead to the creation of macroscopic dc electric field that breaks the inversion symmetry and gives rise to the second harmonic generation.^2–4 Some experimental results obtained with nanosecond lasers seem to support this proposed mechanism. To our knowledge, there exists no report on SHG by picosecond pulses with resonance excitation in atomic vapor. There is also the question whether the above mentioned dc-field-induced SHG mechanism can operate on the picosecond time scale.

© 1994 Optical Society of America