Long-wavelength laser diode interferometer for surface flatness measurement

Modern phase-shifting interferometers grew out of a traditional need for high-precision evaluation of polished optical components. The technology is very mature now, enough so that it is reasonable to look for other applications of these instruments. Some important industrial applications have been found, particularly in the data storage industry. However, there are still many applications where the speed and high accuracy of phase-shifting interferometry would be very desirable, but the surface-finish requirements to generate visible-wavelength interference fringes are impractical. One way to increase the range of surface finishes compatible with interferometric analysis is to increase the source wavelength. Improvements in the reliability and affordability of 1.55-micrometers wavelength distributed-feedback laser diodes has opened up a new wavelength region for interferometric metrology. The 2.5X increase in wavelength when compared to HeNe-based interferometers is sufficient to a variety of important parts ordinarily considered too rough or distorted for visible-wavelength interferometry.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.