Two-color light-emitting-diode source for high-precision phase-shifting interferometry
We describe a two-color light-emitting-diode source that provides intense, uniform, and highly stable illumination with a wavelength precision sufficient for multiwavelength phase-shifting interferometry applications. The source has feedback-stabilized intensity and junction temperature sensing for wavelength compensation. It has a theoretical mean time between failure of more than 30,000 h, and the two colors provide a step measurement capability of greater than 2.5 μm. Measurements made with this source in an interferometric microscope show subangstrom repeatability.