Laser photodetachment diagnostics of negative ions in plasma

Our diagnostic scheme is based on laser induced photodetachment of the H- ion into an atom and a free electron, followed by detection of the free electron using a Langmuir probe. In this scheme an intense 'pump' laser pulse depletes, via photodetachment, the negative ion population within the test volume - the cylinder defined by the laser beam, with radius R. An excess electron density, equal to that of the destroyed H- ions, is created within the test volume, and measured using a probe. A determination of the H- temperature is obtained using two laser pulses delayed in time. (orig./AH)