White Light Interferometry Imager

This technology is an extended depth of field (EDOF) system that maintains high lateral resolution while extending the depth of field. It is based on white light interferometry but adds a feature where the interferometer scans through the different depths of an object to create a depth map.

Background:

White light interferometry offers a solution to the age-old trade-off in optics between depth of field and lateral field of view. Using white light interferometry, contrast fringes in interference images appear near zero optical path difference and best focus. By scanning through a range of height positions and integrating the resulting 3D data cube into a final 2D image, one can create a focused, full-color 2D object image. However, this process is both data collection and processing intensive. This project proposes a method to reduce both data collection time and the degree of post-processing needed to create a final focused image.

The relative phase between the signal and reference of the interferometer is not taken into account when examining the contrast fringes. The most accurate height measurements with height resolution on the order of 0.5 nanometers are from systems using best focus from contrast fringes and phase-shift data to correlate phase differences to surface height deltas. This project uses the contrast fringes for best focus measurements for height resolution on the order of microns.

Applications:

• Optical surface profilers (measurement tools using white light interferometry) are available from a number of optics companies, but data acquisition speeds are on the order of seconds. This project could reduce processing time to a fraction of a second.
• Currently, interferometric methods are used for ophthalmology but interest is growing in the medical community for non-invasive detailed surface measurement techniques.

Advantages:

• Leverages existing technology and improves efficiency
• Faster data collection and less post-processing
• Expand use of white light interferometry systems to industrial screening conditions requiring higher inspection rates

Status: issued U.S. Patent #11,910,104