Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXX Though new affordable high power laser technologies make possible many processing applications in science and industry, depth control remains a serious technical challenge. Here we show that inline coherent imaging, with line rates up to 312 kHz and microsecond-duration capture times, is capable of directly measuring laser penetration depth in a process as violent as kWclass keyhole welding. We exploit ICI's high speed, high dynamic range and robustness to interference from other optical sources to achieve fully automatic, adaptive control of laser welding as well as ablation, achieving micron-scale sculpting in vastly different heterogeneous biological materials.
The utility of a new laser interferometric technique, inline coherent imaging, for real time keyhole depth measurement during laser welding is demonstrated on five important engineering alloys. The keyhole depth was measured at 200 kHz with a spatial resolution of 22 mm using a probe beam, which enters the keyhole coaxially with the process beam. Keyhole fluctuations limited average weld depth determination to a resolution on the order of 100 mm. Real time keyhole depth data are compared with the weld depths measured from the corresponding metallographic crosssections. With the exception of an aluminium alloy, the technique accurately measured the average weld depth with differences of less than 5%. The keyhole depth growth rates at the start of welding are measured and compare well with order of magnitude calculations. The method described here is recommended for the real time measurement and control of keyhole depth in at least five different alloys.
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