Water Vapor Absorption of 266-nm Nanosecond Laser Pulses with Linear and Circular Radiation Polarization

An increase of 50% in the amplitude of the photoacoustic signal generated when water vapor absorbs pulses of circularly polarized laser radiation at 266 nm relative to the signal for linearly polarized radiation is reported. The effect observed is associated with different dissociation efficiency of H2O molecules as a result of one- and two-photon absorption of linearly and circularly polarized radiation.