We present a simple method for measuring the ion flux from a molecular beam epitaxy (MBE) plasma cell in real time. A Langmuir probe was created by attaching the beam flux monitor to a picoammeter and measuring the current impinging upon the collector or filament wires. This provides a noninvasive, convenient, and direct measure of ion flux at the actual wafer position, yet requires no internal changes to the MBE machine. Quantitative measurements of maximum ion energies and relative ion fluxes are possible. Real-time feedback from this measurement allows rapid optimization of the plasma for the minimum ion flux. This method is applicable to GaN and related materials, but is particularly important for growth of dilute nitrides. This was one of the techniques which led to the longest wavelength GaInNAs(Sb) vertical cavity surface emitting lasers and continuous wave edge emitting lasers on GaAs to date. © 2005 American Vacuum Society.