High-intensity rectangular fiber-coupled diode laser array for solid-state laser pumping

A high-power diode laser bar coupling scheme with rectangular optical fibers is proposed, and the concept is tested on a scale version: an individual diode laser array and a single rectangular fiber. 60% of the power from a 1-W cw, 213-µm-wide 20-stripe diode array is coupled into a 216 µm × 28 µm 0.66 numerical aperture optical fiber, which produces intensities at the fiber output face of 9.9 kW cm(-2). The elliptical, dual-lobed far-field intensity pattern of the diode laser output, with divergence of 39° × 13° FWHM is converted on passing through the fiber into a single-lobed, nearly circular pattern with a FWHM divergence of 21° × 22°. The beam quality is reduced by only a factor of 30 when this coupling method is used. Alignment tolerances in the three planes of movement are measured and found to be in excess of 10 µm.