Measurement of the intensity profile of the high-power laser radiation using the matrix of the copper-coated optical fibers

In this paper we introduce a novel approach for the measurement of the intensity profile of high-power laser radiation, which does not require any preliminary attenuation. It is based on the application of the matrix made of multimode passive copper-coated optical fibers. It is well known, that laser radiation experiences Rayleigh and Mie scattering while transmitting along an optical fiber. Radiation scattered inside the fiber core is completely absorbed by the outer copper layer leading to its heating. The temperature change of the metal coating proportional to the transmitted optical power is determined directly by measuring its electrical resistance. A matrix sensor was assembled for measuring the transverse intensity distribution of the laser beams. It comprised nineteen 660 μm (core diameter 600 μm) multimode copper-coated optical fibers. Intensity profile measurements were carried out for the 67 W single-mode Yb-doped fiber laser and 72 W multimode laser diode sources. The laser radiation was directed into the polished end faces of the fiber matrix elements. Optical power transmitted through each fiber was proportional to the incident optical intensity at corresponding location of the fiber end face. The transverse intensity profile of the laser beam was evaluated by measuring the resistance change of the copper coating of each fiber. Preliminary the calibration of the resistance dependence on the incident optical power was separately conducted for all 19 fibers. An introduced technique can be also applied for the determination of the radiation beam quality factors such as M² and BPP.