Beam stability and warm-up effects of Nd:YAG lasers used in particle image velocimetry

Abstract

The characteristics and causes of Nd:YAG laser warm-up transients and steady state beam stability effects are investigated in this study. Dynamic laser performance has a particularly noticeable impact on particle image velocimetry (PIV) and other laser-based flow visualisation techniques, where changes in beam pointing can influence the overlap between laser light sheets and thereby degrade the correlation of PIV image pairs. Despite anecdotal knowledge or experience of laser warm-up effects, they have not been formally documented or quantified to date for PIV applications. In this study, the nature of these laser transients are analysed and compared among a selection of typical PIV laser equipment. An investigation into the cause of these transients during the laser warm-up sequence is also presented. Furthermore, the degree of dual cavity transient coupling within a PIV laser system is analysed to determine a practical limit to the laser light sheet overlap that can be expected from PIV experiments. Finally, the results from this study inform a series of recommendations for PIV best practice, which aim to minimise the impact of laser transients on experimental data.

Study on noises influencing the accuracy of CNC machine straightness measurements methods based on beam position detection

“…There have been described many different turbulence spectrum models for refraction fluctuations [12,13] being a base for various numerical approaches [14,15]. Some tests were also described proving at least partial validity of those models for improvement of overall beam position stability in fibre [16], air [17] or vacuum [18] environments.…”