Testing aspherics by using the two-wavelength holographic interferometry (TWHI)

A discussion was made on the usage of two-wavelength holographic interferometry in testing the aspherics and evaluating the testing results. The TWHI uses the visible light as the working wavelength to accomplish the actual long-wavelength interferometry whose main advantage is its ability in meeting various requirements on the sensitivity, accuracy, and range of measurement by selecting suitable combination of wavelengths.