Abstract. A Pockels cell Q-switch has been operated in a manner analogous to a saturable absorber by initially keeping the cell partly open for the first 1000 or so double passes and then opening it completely at a pre-set resonator power. This then allows simple and reliable selection of a single longitudinal mode. A detailed discussion is given of the design considerations which lead to the correct choice of mode-selecting device. With three different devices, a TEM00 mode Nd:CaWO4 laser has produced 400 kW pulses in a single longitudinal mode with a shot-to-shot frequency stability of ∼ 0.01 cm−1.
