Methods and systems for coherent imaging and feedback control for modification of materials

Inventors

WEBSTER, Paul J. L. • Fraser, James M. • YANG, Victor X. D.

Assignees

IPG Photonics Corp

Abstract

Methods and systems are provided for using optical interferometry in the context of material modification processes such as surgical laser or welding applications. An imaging optical source that produces imaging light. A feedback controller controls at least one processing parameter of the material modification process based on an interferometry output generated using the imaging light. A method of processing interferograms is provided based on homodyne filtering. A method of generating a record of a material modification process using an interferometry output is provided.

Core Innovation

The invention relates to coherent imaging via inline coherent imaging with an imaging optical source that produces imaging light sharing at least one optical element comprising a mirror with a material processing beam source. A material processing beam is applied to at least one location of a material in a material modification process, while an optical interferometer produces an interferometry output using at least a component of the imaging light delivered to the material. The interferometry output simultaneously includes reflections of the imaging light from at least first and second optical path lengths to the material, and the interferometry output is based on a comparison of at least two optical path lengths to the material.

A detector receives the interferometry output and produces a detector output indicative of a characteristic of the material before, during, or after the material modification process. An image processor receives the detector output and tracks material geometry to establish a reference optical path length to the material. The disclosed approach includes inferring subsurface interfaces and depth-related indicators using interferometry outputs, including penetration depth and subsurface interface proximity.

The system supports tracking transitions from reference-path-only to sample-path-based signals and uses comparisons of speckle and interferograms to sense subsurface changes indicative of material modification progress. The invention further includes extracting depth efficiently using homodyne filtering with a pre-calculated synthesized interferogram correlated to measured interferograms using a threshold, and engineering sensitivity versus depth by selecting a zero optical path length difference point relative to a phase change region.

The interferometry-derived depth-related indicators are used to generate records and support control of material modification process parameters through interferometry-based feedback for monitoring and controlling material modification. Documented examples include sensing and monitoring of drilling perforation etch-rate and keyhole/welding breakthrough and refill after breakthrough, together with monitoring-related concepts such as keyhole stability and depth control verified with scanning OCT.

Claims Coverage

The document includes two independent claims: an apparatus claim and a method claim. Across both, the inventive coverage centers on inline coherent imaging combined with an interferometer that compares optical path lengths reflected from the material, and using the interferometry-derived detector output to track material geometry by establishing a reference optical path length to the material.

Both independent claims require inline coherent imaging with an interferometer that compares reflected optical path lengths to the material, producing a detector output indicative of material characteristics before, during, or after modification, and using image processing to track material geometry by establishing a reference optical path length.

Stated Advantages

Documented Applications