Improving the beam quality factor (M2) by phase-only reshaping of structured light

Laser brightness is crucial in many optical processes, and is optimized by high power, high beam quality (low M-2) beams. Here we show how to improve the laser beam quality factor (reducing the M-2) of arbitrary structured light fields in a lossless manner using continuous phase-only elements, thus allowing for the increase in brightness by a simple linear optical transformation. We demonstrate the principle with four high M-2 initial beams, converting each to a Gaussian (M-2 approximate to 1) with a dramatic increase in brightness of >10 x. This work puts a new (to the best of our knowledge) perspective on the old debate of improving laser beam quality with binary diffractive optics, while providing a practical approach to enhancing laser brightness for arbitrary input beams. (C) 2020 Optical Society of America