Ponderomotive force exerted on a plasma by an infrared laser beam

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Abstract
The continuum and single particle approaches to the ponderomotive force in an underdense plasma are presented. The force density tends to expel the plasma out of a focused laser beam. Transient and steady‐state responses of the plasma to the ponderomotive force are studied, and the importance of α = (ωp2/ω2) 〈ε0(E2/2) 〉 /2neKT is emphasized. Experimental verifications are presented, obtained with a pulsed CO2 laser‐amplifier system (500 MW) irradiating an argon arc plasma (ne = 3×1014 cm−3, T=1.4 eV). Density changes are monitored by studying light emitted from the focal region, and the measured decrease in light intensity is consistent with the plasma density decrease expected for a value of α=0.37.