Anisotropy of two-photon absorption in gallium selenide at 1064 nm

The Bridgman method is used to grow single crystals of epsilon-GaSe. The two-photon absorption (TPA) coefficient beta was measured for especially un-doped crystals at room temperature for the ordinary o-ray (beta(perpendicular to)) and extraordinary e-ray (beta(parallel to)) using single-wavelength excitation by a Nd:YVO4 laser at 1.064 mu m with a pulse duration of 10 ps and a repetition rate of 81 MHz. No large anisotropy was observed for the TPA coefficients between the two geometries. The TPA coefficients were found to be beta(perpendicular to) = 1.07 x 10(-9) cm/W and beta(parallel to) = 1.88 x 10(-9) cm/W. It was found that doping slightly increases the TPA coefficient. The value of the TPA for crystals doped with 0.5 at.% of Tl is perpendicular to = 7.56 x 10(-9) cm/W. (C) 2005 Elsevier B.V. All rights reserved.