Abstract

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. Modern materials processing applications demand ever higher delivered beam qualities (as measured by a parameter such as M ²) to achieve greater machining precision and efficiency, a demand that is currently in conflict with the desire to utilize the convenience and flexibility of large-core fiber-optic beam delivery. We present a detailed experimental investigation of the principal beam-quality degradation effects associated with fiber-optic beam delivery and use numerical modeling to aid an initial discussion of the causes of such degradation.

© 2000 Optical Society of America

Preparation of fiber optics for the delivery of high-energy high-beam-quality Nd:YAG laser pulses

Andreas Kuhn, Paul French, Duncan P. Hand, Ian J. Blewett, Mark Richmond, and Julian D. C. Jones
Appl. Opt. 39(33) 6136-6143 (2000)

Delivery of 10-MW Nd:YAG laser pulses by large-core optical fibers: dependence of the laser-intensity profile on beam propagation

B. Richou, I. Schertz, I. Gobin, and J. Richou
Appl. Opt. 36(7) 1610-1614 (1997)

Bend loss in large core multimode optical fiber beam delivery systems

Alvaro A. P. Boechat, Daoning Su, D. R. Hall, and J. D. C. Jones
Appl. Opt. 30(3) 321-327 (1991)

Beam delivery by large-core fibers: effect of launching conditions on near-field output profile

Daoning Su, Alvaro A. P. Boechat, and Julian D. C. Jones
Appl. Opt. 31(27) 5816-5821 (1992)

Dependence of output near-field beam profile on launching conditions in graded-index fibers used in delivery systems for Nd:YAG lasers

Alvaro A. P. Boechat, Daoning Su, and Julian D. C. Jones
Appl. Opt. 32(3) 291-297 (1993)