Pulse width modulation for adjusting laser power in measuring upconversion excitation threshold

Abstract Solid-state lasers are usually used as excitation light sources for measuring the upconversion luminescence spectra. But the output power of this kind of laser usually jitters at unsaturated output circumstances, leading to unstable luminescence intensity and affecting the accuracy of excitation threshold measurement. Herein, pulse width modulation was used for adjusting the power of a 532 nm solid-state laser for measuring the upconversion threshold. The average output power of lasers can be adjusted by changing the pulse width at a constant pulse frequency. The stability is significantly higher than that of the output power using current modulation. The excitation threshold estimated by this method is similar to that of the continuous light excitation. Pulse width modulation is expected to be applied to other lasers in power modulation and will play an important role in fluorescence detection and imaging.