Disalignment collision cross sections of the neon levels 2p 4 and 2s 2 obtained by mode crossing

Alignment destroying collision cross sections of the Ne levels 2p ₄ and 2s ₂ were measured by investigation of the zero-field mode crossing resonances of a multimode He/Ne-laser operating on the 3s ₂→2p ₄ (λ=633nm) and 2s ₂→2p ₁ (λ=1.52μm) Ne transitions respectively. The measurements were carried out with the aid of a small sample cell which was placed inside the laser cavity and filled with pure Neon or a mixture of the He and Ne. Comparison of the measured cross sections concerning the 2p ₄ level with corresponding Hanle effect measurements shows that in multimode operation velocity changing collisions do not produce an additional broadening of the mode crossing resonances. The alignment destroying cross section is almost temperature independent in the case of He collisions; it decreases, however, with increasing temperature in the case of Ne. Due to the allowed dipol transition between the 2s ₂ and the ground state of Ne, radiation trapping and resonance interaction takes place if the gas filling contains Ne. The effect on the mode crossing resonance width is investigated.