Effects of the F-number on the generation condition of a diode-laser-sustained plasma

Abstract

A laser-sustained plasma (LSP) is a promising method for generating atmospheric-pressure plasmas. Although diode lasers are highly efficient, compact, and low-cost light sources for LSP, previous studies have reported that the laser power required for LSP generation is high, owing to the poor beam quality of diode lasers. In this study, we attempted to generate an LSP using a 4-kW-class diode laser with different F-numbers. The minimum laser power required for LSP generation strongly depends on the F-number. Comparing F1.2 and F2.0, F1.2 reduces the required power by approximately 2,840 W. The LSP temperature and length also strongly depend on the F-number, with the temperature increasing by approximately 5,000 K and the length increasing by approximately 1.4 times at F 1.2 compared with those at F 2.0.