Application of the synchronous detection to the identification of the characteristic lines of the neutral atoms sputtered and excited by a plasma

It is possible to excite by a Penning discharge the neutral atoms sputtered during the bombardment of a target by positive ions and thus to increase the sensibility of the ionoluminescence analysis method. However, the characteristic lines of the target elements may be masked by the discharge lines. In this paper an arrangement is described using a lock-in amplifier which permits to reduce the discharge lines. The results obtained with a duraluminium target show that it is possible to identify the characteristic target lines even when they are weak and near the discharge lines. The effect of the bombardment on the discharge induces a residual modulation of the stray lines on which their weakening depends. It is possible to diminish this effect by chosing the right conditions of discharge and for the insulator by adding a grid on the target. It would be possible to improve the efficiency of this detection (owing to the mechanism of ionoluminescence), if one could rigorously control the residual atomsphere to simultaneously obtain the optimum conditions of excitation, and a discharge spectrum without lines close to the characteristic lines of the sample. (T.G.)