Diode lasers have proved to be a valuable light source for laser-induced fluorescence (LIF) measurements for plasma science
since the early 1990s, and they have recently improved the state of the art of measuring ion flow from ion velocity distribution functions (ivdfs) at the
sheath–presheath boundary in single and
multiple ion species plasmas. In the case of a low temperature two ion species plasma (ArI + HeI), we were the first to show experimentally that ion species may reach the sheath edge flowing at a very different speed than that expected from the single species Bohm Criterion (ArII ions exceed the individual Bohm flow speed by almost a factor of 2 at the sheath edge). Simulation results are found to agree. Diode laser technology relevant to LIF measurements in multiple ion species plasmas is discussed with the aim of addressing outstanding problems in sheath formation in such plasmas.