Sensitive in situ method to measure the rate of neutral free radical production by photodeionization of negative ion beams

Photoelectron-current measurement by low-frequency electromodulation probe (PMMP) is proposed as a sensitive method to determine the rate G r of neutral free radical production by the photodeionization of negative ion beams (PDINIB). The PMMP method was employed to evaluate the production rate in a trial surface-processing apparatus developed in the author’s laboratory utilizing a steady-flux refined beam of neutral free radicals produced by the PDINIB procedure. A 63 Cu − negative ion beam of kinetic energy E i varied up to 15 keV was irradiated with a 514.5 nm visible light beam from a 25 W cw Ar + ion laser. The detection limit of the production rate by the measurement setup was 6×10 9 /s under the conditions that E i =15 keV, the negative ion beam current I i =4 μA, and the laser power P=6 W. Based on the results of these basic experiments, furthermore, the photodeionization efficiency defined by eG r /I i where e is the elementary electric charge was estimated to be 27±6% under the conditions that E i =15 keV, I i =40 μA, and P=18 W.