Abstract

We have measured the two-photon cross section for the Q1 branch of the EF(v = 6) ← X(v = 0) transition in H₂, using techniques developed in this laboratory. The population of the excited EF level was determined using a calibrated fluorescence detection system to monitor B(v = 1) ← EF(v = 6) fluorescence at ~750 nm. Ions resulting from absorption of a third photon were collected on parallel wire electrodes and amplified with a calibrated charge-sensitive preamplifier. The temporal and spatial profiles of the laser pulses were characterized with a fast photodiode and a linear pyroelectric array, respectively. The 100-μm resolution of the pyroelectric array and the necessity to avoid saturation both dictate the use of a gently focused beam geometry. Our results (4.3×10⁻⁴⁷ cm⁴/s⁻¹ and 1.6 × 10⁻¹⁸ cm²) are in reasonable agreement with previous experiments and calculations, and we are currently working to upgrade our accuracy.

© 1987 Optical Society of America