Evidence for light-induced kinetic effects due to velocity-selective heating or cooling

If velocity-selective optical excitation in a gas is followed by rapid collisional deexcitation, the result may be called velocity-selective heating. Through the temperature dependence of the transport coefficients, this process gives rise to a new type of kinetic effect. This is experimentally demonstrated using hot-band rovibrational excitation of CO₂ gas by a CO₂ laser tuned in the Doppler wing. Upon R- or P-branch excitation, rotational- to kinetic-energy conversion yields velocity-selective heating or cooling. This results in a light-induced flow for nonuniform illumination.