Relaxation of the 6p 2P03/2 metastable state in a self-terminating thallium laser

We present the results of an experimental study of a Tl vapour/Ar mixture as an active medium. Under optical excitation of thallium to the 6d ²D_3/2 state, we have achieved lasing at λ = 1.3 μm (7p ²P⁰_1/2 – 7s²S_1/2 transition) and 535 nm (7s ²S_1/2 – 6p²P⁰_3/2) through cascade transitions from the 6d ²D_3/2 state to the upper laser levels. The electron deexcitation rate of the 6p²P⁰_3/2 metastable state is no slower than 1.5 × 10^-8 cm³ s^-1, meaning that this process cannot prevent self-terminating laser action at the 7s ²S_1/2 – 6p²P⁰_3/2 transition under electron-beam pumping at pulse repetition rates up to 100 kHz.