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Wigner transform approach to dynamic-variable partially coherent laser beam characterization

Jabczyński J., Gontar P., Gorajek Ł.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2020

Vol. 68, nr 1

141--146

1) Background: the modeling, characterization, transformation and propagation of high-power CW laser beams in optical (including fiberoptic) trains and in the atmosphere have become hot topics in laser science and engineering in the past few years. Single-mode output is mandatory for high-power CW laser applications in the military field. Moreover, an unstationary, dynamic operation regime is typical. Recognized devices and procedures for laser-beam diagnostics could not be directly applied because of dynamic behavior and untypical non-Gaussian profiles. 2) Methods: the Wigner transform approach was proposed to characterize dynamically variable high-power CW laser beams with significant deterministic aberrations. Wavefront-sensing measurements by means of the Shack-Hartmann method and decomposition into an orthogonal Zernike basis were applied. 3) Results: deterministic aberration as a result of unstationary thermal-optic effects depending on the averaged power of the laser output was found. Beam quality determined via the Wigner approach was changed in the same way as the measurements of the beam diameter in the far field. 4) Conclusions: such an aberration component seems to be the main factor causing degradation in beam quality and in brightness of high-power CW laser beams.

Investigation of structural, optical and lasing properties of YAG:Yb single crystals

Świrkowicz M., Skórczakowski M., Jabczyński J., Bajor A., Tymicki E., Kaczmarek B., Łukasiewicz T.

Opto-Electronics Review

2005

Vol. 13, No. 3

213-220

Single crystals of yttrium aluminium garnet (YAG) doped with ytterbium ions of up to 30 at.% were grown by the Czochralski method. Using the growth rate from 1 to 3 mm/h, and the rotation rate from 15 to 30 rpm, single crystals with diameters of up to 22 mm and lengths up to 85 mm were obtained. Using the inductively coupled plasma n optical emission spectroscopy (ICP-OES) method, Yb distribution coefficient was determined to be equal to 1.10±0.02. The following methods: optical absorption spectroscopy, plane and circular polariscope, electron probe microanalysis (EPMA) to determine the radial distribution of Yb ions, X-ray diffraction methods to determine the lattice constant were used. Etch pit density distribution and lasing properties were also investigated. Samples of YAG:Yb crystals with Yb ions contents of 3, 5, 7, and 10 at.% were pumped by 940 nm laser diode for their lasing properties. The best lasing slope efficiency of 40% with respect to the absorbed pump power was achieved at 5 at.% Yb content. The lowest threshold of 2.5 W of the absorbed pump power was observed, however, for a 7 at.% Yb doped sample in quasi hemispherical resonator configuration. These investigations have been found to be in good agreement with polariscopic observations, showing a certain decrease in optical homogeneity with increase in Yb content.