Automatic real-time guidance of laser machining with inline coherent imaging

Abstract

Optical coherence imaging can measure hole depth in real-time ͑Ͼ20 kHz͒ during laser drilling without being blinded by intense machining light or incoherent plasma emissions. Rapid measurement of etch rate and stochastic melt relaxation makes these images useful for process development and quality control in a variety of materials including metals, semiconductors, and dielectrics. The ability to image through the ablation crater in materials transparent to imaging light allows the guidance of blind hole cutting even with limited a priori knowledge of the sample. Significant improvement in hole depth accuracy with the application of manual feedback from this imaging has been previously demonstrated ͓P. J. L. Webster et al., Opt. Lett. 35, 646 ͑2010͔͒. However, the large quantity of raw data and computing overhead are obstacles for the application of coherent imaging as a truly automatic feedback mechanism. Additionally, the high performance components of coherent imaging systems designed for their traditional application in biological imaging are costly and may be unnecessary for materials processing. In this work, we present a coherent imaging system design that costs less than a fifth of comparable commercial products. We also demonstrate streamlined image processing suited for automated feedback that increases processing speed by two orders of magnitude.

In situ morphology-based defect detection of selective laser melting through inline coherent imaging

“…The collection of sequential A-line measurements allows changes in sample morphology before, during, and after laser processing to be observed as a function of time and space. To reduce computational load, in this work, signal processing is performed through a single-step homodyne filtering technique (Webster et al, 2011) rather than the standard interpolation/Fourier transform technique typical to SD-OCT.…”

Laser process monitoring and automatic control at kHz rates through inline coherent imaging

“…Another key attraction of ICI is its exploitation of off-the-shelf photonic tools developed for other industries (such as telecommunications and machine vision) to significantly reduce instrument cost. Our most recent generation system had a component cost below $10k and, due to its portable design, can be easily integrated into most laser cutting/welding platforms [8].…”

Coaxial cavity injected OCT and fiber laser ablation system for real-time monitoring of ablative processes

“…This allows for high resolution, subsurface imaging (limited to penetration depth of OCT) right at the site of ablation activity. Using this data in a real-time feedback loop can be used to control depth of ablation (as demonstrated by Webster et al 5 The first report of OCT monitored ablation by Boppart et al 6 used soft tissue specimens. The first study showing in-situ, real time depth profiling during ablation was done by Webster et.…”