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.
Interaction of laser radiation with gold metal film deposited onto the lithium niobate substrate was investigated by means of piezoelectric resonance spectroscopy. Such metal-dielectric heterostructure has eigenmodes which can be excited by application of the probe radiofrequency electric field due to the piezoelectric nature of lithium niobate. Frequencies of these piezoelectric resonances are extremely sensitive to the temperature. During interaction with laser radiation the temperature of the film is determined as a solution of the nonstationary heat conduction equation relying on the experimentally measured induced shifts of piezoelectric resonance frequencies, which were preliminary calibrated in uniform heating conditions.
A novel method of optical image registration using matrix of piezoelectric crystals is introduced. This technique allows measurement of beam profiles without using attenuation systems even at high power levels of incident radi- ation. Each element of the sensor matrix is the crystal piezoelectric resonator that has its own set of eigenmodes, which frequencies strongly depend on temperature. Due to an inverse piezoelectric effect the eigenmodes can be excited noncontactly via the application of the probe radiofrequency electric field providing that its frequency corresponds to any of the crystal eigenmode frequencies. Due to the residual optical absorption each element is heated in compliance with the incident radiation power. A calibration procedure is preliminary performed by transmitting collimated laser radiation separately through each single matrix element.
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