Investigation of the laser-sustained plasma of a Xenon lamp driven by an annular beam

Higher brightness UV light sources based on laser-sustained plasma (LSP) finds critical applications in high-resolution optical inspection and measurement. An annular beam focused with a low F-number is proposed for the first time to investigate its effect in realizing high-brightness LSP compared with Gaussian beams. We experimentally verified that the annular laser beam sustained a nearly laterally symmetric plasma with a longitudinal length less than 600 µm plasma length, where the length-width ratio was four times smaller than that driven by a TEM₀₀ Gaussian beam. Theoretical analysis further explored that the annular beam's transmission path could limit the plasma's longitudinal growth, like a “reservoir”. Furthermore, the “reservoir” effect is favorable for effectively increasing the plasma temperature and the effective power ratio of UV from 8% to 15%. This work paves a novel way of generating high-brightness UV sources by spatial manipulation of infrared pumping beam.