EXTRACTING THE 2-PHOTON POLARIZATION-RATIO OF THE N-]3S TRANSITION IN ACETALDEHYDE FROM MPI MEASUREMENTS

The ratio of signals for circularly and linearly polarized light obtained by multiphoton ionization of acetaldehyde at 3633.8 Å has been measured under a wide variety of experimental conditions. Laser flux was found to strongly affect the ratio, with measured values ranging from 0.02 to 0.77. Pressures up to 50 atm of added second gas at low acetaldehyde pressure and low flux increased the ratio by a factor of two. At absorber pressures of several hundred Torr, there is a dramatic increase in the polarization ratio compared to that at <1 Torr, possibly due to resonance energy transfer in the Rydberg state. A theoretical treatment based on a population rate equation model of MPI indicates that useful two-photon absorption polarization ratios may be obtained only at very high added gas pressure and low laser flux. © 1980 American Institute of Physics.