A novel self-switched high repetition rate HF(DF) laser

We present results obtained from a new class of self-switching, high repetition rate, HF (DF) laser. The laser utilises a magnetically stabilised longitudinal discharge, transverse to a high velocity gas flow. The gas mixture is pre-mixed, and consists of He, SF6 and H-2 (D-2) in the ratio 1000:9:2 at a total pressure of around 52 torr. A centrifugal fan recirculates the gas and provides a linear flow velocity of 80 ms(-1) in the gain region. Permanent magnets provide the stabilising magnetic field of similar to 1400 Gauss. This magnetic field ensures that the discharge and optic axes are co-linear. The discharge length is 30cm, and the gas flow channel 0.5cm in height. Conventional stable resonators were used to extract the laser energy. We show that the self-switching behaviour is a result of the negative I-V characteristic in the positive column of a constricted SF6 discharge, coupled with the current limitations imposed by the external electrical circuit. It is found that the switching frequency, and therefore lasing repetition rate, can be controlled via either the applied discharge current or the RC time constant for the external circuit. Higher discharge currents and shorter time constants both result in higher pulse repetition frequencies. We have demonstrated self-switched lasing at repetition rates from 400 Hz up to 17 kHz.