Effects of phosphor-based LEDs on vertical scanning interferometry

High-power phosphor-based LEDs are replacing conventional white-light sources for vertical scanning interferometry, but the spectrum of the phosphor-based LED is different from that of the conventional light source. The phosphor-based LED has two peaks in its spectrum, while the conventional light source has only one peak in the Gaussian distribution. In this Letter, we investigate the effects of phosphor-based LEDs on vertical scanning interferometry. Our result shows that the use of a phosphor-based LED changes the fringe contrast function significantly, such that measurement repeatability decreases. We propose and demonstrate that a constraint on the input to the existing reconstruction algorithm improves the repeatability of the vertical scanning interferometer with a phosphor-based LED.