This paper reports a novel optical head-disk interaction tester setup and experimental investigations into the effects of slider-disk interaction in nanometer spaced head-disk interface. The setup revealed quantitatively the lubricant induced change of slider-disk spacing before the slider enters its fully flying status. The setup was also applied to investigate the slider sinking process which is caused by the meniscus force when the slider starts to rest on disk surface. Results shows that such a setup has the advantage of quantitative characterization of slider-disk interface compared with acoustic emission method. Furthermore, the results also demonstrate its advantages in reflecting the actual interaction between slider, lube, and disk surface, compared with the current optical flying height testers.