Synthetic wavelength scanning interferometry for 3D surface profilometry with extended range of height measurement using multi-colour LED light sources

Abstract

We report a three-dimensional surface profilometry with extended range of height measurement using synthetic wavelength scanning interferometry without any tunable filters, wavelengthtuning lasers, or grating elements. Here, we have used inexpensive multiple color light emitting diodes (LEDs) and operate them sequentially one by one or combination of two or more colors simultaneously to generate synthetic wavelength light source for illumination. Multiple color LED light source was synthesized and entire visible range from violet to deep red color was covered. A wide range of synthetic wavelengths were obtained. Experiments were performed on industrial objects and interferograms were recorded using Mirau type interferometer. Five step phase shifting algorithm was used to recover the phase maps which can be further utilized for 3D height measurement of the specimen. A simple phase subtraction method was used to reconstruct the phase map at synthetic wavelength thus extending the range of step-height measurement. The present system provides extended range of height measurement from subwavelength to tens of wavelengths. Experimental results of 3D-surface profile measurements of a Si-IC chip and a standard step object are presented. The present system does not require expensive multiple color filters or any wavelength scanning mechanism along with a broadband light source.

The Influence of the Wavelength of Laser Light on the Non-Contact Measurement of the Roughness of Shiny Cut Surfaces on Stainless Steel A304 Material

“…For example, some materials may have better visibility or contrast with other colors of light, which can lead to more accurate and reliable roughness measurements. The use of other wavelengths may bring advantages for certain applications, such as improved resolution when measuring finer structures or a better ability to penetrate the surface [26].…”