Pulsed laser based on a resonance–metastable level transition in mercury ion

The method of doubled pulses was used to achieve pulsed lasing due to the 5d¹⁰6p²P_3/2–5d⁹6s^{2 2}D_5/2 transition in the mercury ion (λ = 398 nm), similar to efficient lasing transitions in copper and gold atoms. Discharge tubes with inner diameters 4 and 8 mm and 30 cm long were used. They were filled with neon or helium as the buffer gases. There was a significant difference between lasing in the narrow and wide tubes. In the wide tube it was possible to observe lasing only when the delay between the pulses was short; the beam was not ring-shaped, contrary to what was found earlier for the narrow tube. Lasing was observed even when the delay between the two pulses was less than 5 μs, but lasing disappeared when heating of the tube became stronger as the pulse repetition frequency was increased. Possible population and inversion mechanisms were analysed.