Minimising the focus spot size from a 15 watt laser diode array

Abstract

Laser diodes emit strongly divergent beams. Most applications, however, require a collimated or focused beam. Optical systems using miniature lenses are often employed for laser diodes, where the beam is coupled into a fibre optic. In the present case, a laser diode array (15 W, CW) was connected to a fibre bundle, comprising 1 meter length of 23 fibres. The beam spot size was minimised using a simple imaging system. The performance of two optical systems was critically evaluated. The first system focused the beam from the fibre bundle directly onto the workpiece, and the second coupled the beam into a smaller diameter GRIN fibre optic. A single fibre beam delivery system offers significant advantages over the fibre bundle in applications that require high beam irradiances, for example, cutting or welding. The output beam quality is higher with a beam irradiance profile that is better suited for obtaining smaller focused spot sizes. The change in spot size due to repositioning of the optical components in each system was quantified by implementing an image processing system. This comprised a CCD-camera, frame grabber and Optimus, the image processing software. The correlation between the launch conditions of the non-symmetrical irradiance distribution into the fibre bundle and the resulting distribution in the near field output of the graded-index fibre will be presented.Laser diodes emit strongly divergent beams. Most applications, however, require a collimated or focused beam. Optical systems using miniature lenses are often employed for laser diodes, where the beam is coupled into a fibre optic. In the present case, a laser diode array (15 W, CW) was connected to a fibre bundle, comprising 1 meter length of 23 fibres. The beam spot size was minimised using a simple imaging system. The performance of two optical systems was critically evaluated. The first system focused the beam from the fibre bundle directly onto the workpiece, and the second coupled the beam into a smaller diameter GRIN fibre optic. A single fibre beam delivery system offers significant advantages over the fibre bundle in applications that require high beam irradiances, for example, cutting or welding. The output beam quality is higher with a beam irradiance profile that is better suited for obtaining smaller focused spot sizes. The change in spot size due to repositioning of the optical components in...