Product Code: ICA10_P119

Focal Plane Considerations for Fiber Laser Wide Field Processing
Authors:
Mark Brodsky, SPI Lasers LLC; Santa Clara CA USA
Jack Gabzdyl, SPO Lasers UK Limited; Southampton
Presented at ICALEO 2010

Scan heads now are replacing processing traditionally done with fixed head optics using X-Y tables One reason is that fiber lasers offer opportunities to direct intense energy through scan heads over wide marking fields now exceeding 200mm square. Additionally the availability of fiber lasers with increased divergence provides a better application of consistent power across a large mark. This is especially useful for applications such as anneal marking, remote welding, and vapor pressure cutting. These applications require careful control of the spot size across the entire marking field because higher mode lasers, while better for processing, require different set-up to single-moded lasers.

Scan head processing can exhibit variations in linearity of spot size when the beam is directed through f-theta flat field focusing lenses. Many traditional fixed head focusing tricks will no longer work with such lenses. Any move outside the focal plane to change power density (to create a favorable processing condition) is fraught with danger. Additionally, the quality of input collimation can provide a user with a false reading of the optimal working plane. Such variation in input to the scan head can mis-lead users to confuse the best focus, (at one point in the field), with the most consistent working distance, ( as measured across the entire field). This interaction of optimal input, focus, and working distance will be demonstrated by studies with both 40W nanosecond pulsed and 400W CW fiber lasers. Specific examples of material differences with anneal marking, cutting, and welding will be presented and differences between higher-moded and single-moded lasers will also be discussed. This paper will provide experimental evidence for why care must be taken in defining the marking plane. It will also highlight the difficulties to be encountered by those who choose to process, using these new higher power and higher-mode lasers, outside the optimal focal plane.