Two Color Pump-Probe Dichroism and Birefringence Measurements in Atmospheric Molecules

The experimental study of the laser induced alignment of linear atmospheric molecules naturally present into the air using an ultra-short (femtosecond temporal range) and ultra-intense (TW center dot cm(-2) fluence range) linearly polarised laser pulse is described. The measurements are conducted under a two-color pump-probe configuration using an IR pump beam and a blue probe pulse (red-blue configuration), which interacts with the molecules after they have been exposed to the IR alignment pulse. The optical birefringence and dichroism polarimetric signals have been both strictly measured into the same experimental conditions into this two-color configuration. A balanced detection permits the heterodyne signal to be got directly. Under the short and intense laser pulse exposure, the molecules present into the atmospheric air (under standard room temperature conditions) aligne, and periodic transient revivals are observed (field free alignment approach into non-adiabatic conditions). The results obtained are in accordance with those obtained in the red-red configuration and confirm the approach proposed as relevant for atmospheric sensing.