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Lamp-pumped thallium atomic line filter at 535.046 nm.

We present a new atomic line filter concept for the detection of frequency-doubled Nd:BEL laser radiation. Advantage is taken of the thallium 6(2)P(3/2) metastable energy level whose large lifetime can be preserved even in small vapor cells. The filter is pumped intermittently by a low-power spectral lamp and thereby combines the benefits of active and passive operation. Analysis of a proposed final design shows that simple engineering solutions exist, and excellent filter properties can be deduced. We have experimentally demonstrated the new operating principle in a preliminary setup.