The 667.7 nm optogalvanic effect signal in argon hollow cathode discharge

The optogalvanic signals (OGS) at 667.728 nm (the 1s(4)-2p(1)) Ar transition in pure Ar and He:Ar=1:1 mixture have been investigated with a low power diode laser in a longitudinal hollow cathode discharge. Qualitative explanation of the formation of the 667.7 nm Ar OGS is proposed. A simple model for explanation of the dependence of the 667.728 nn Ar OGS amplitude and sign along the cross-section of the discharge tube is applied. The OGS in pure Ar and He:Ar=1:1 mixture gas discharge are compared.