Real-time, nonintrusive oxidation detection system for the welding of reactive aerospace materials.

We describe the development of a real-time nonintrusive monitor to detect degradation of a gas shield condition during laser welding by use of on-axis spectrally resolved detection of light emitted from the workpiece. Failure of gas shielding to the point at which there is a risk of contamination from the air is revealed by the marked increase in the intensity of a spectral feature around 426 nm. To avoid unwanted sensitivity to the overall intensity of the radiation, the intensity at 426 nm is normalized by that at 835 nm, where the spectrum is insensitive to gas shielding.

Beam quality after propagation of Nd:YAG laser light through large-core optical fibers.

Laser beam characteristics are altered during propagation through large-core optical fibers. The distribution of modes excited by the input laser beam is modified by means of mode coupling on transmission through the fiber, leading to spatial dispersion of the profile and, ultimately and unavoidably, to degradation in the quality of the delivered beam unless the beam is spatially filtered with consequent power loss. Furthermore, a mismatch between the intensity profile of a typical focused high-power laser beam and the profile of the step-index fiber gives rise to additional beam-quality degradation.

Preparation of Fiber Optics for the Delivery of High-Energy High-Beam-Quality Nd:YAG Laser Pulses.

Recent improvements in design have made it possible to build Nd:YAG lasers with both high pulse energy and high beam quality. These lasers are particularly suited for percussion drilling of holes of as much as 1-mm diameter thick (a few millimeters) metal parts. An example application is the production of cooling holes in aeroengine components for which 1-ms duration, 30-J energy laser pulses produce holes of sufficient quality much more efficiently than with a laser trepanning process.