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

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The Bridgman method is used to grow single crystals of ε-GaSe. The two-photon absorption (TPA) coefficient β was measured for especially un-doped crystals at room temperature for the ordinary o-ray (β⊥) and extraordinary e-ray (β∥) using single-wavelength excitation by a Nd:YVO4 laser at 1.064μm with a pulse duration of 10ps and a repetition rate of 81MHz. No large anisotropy was observed for the TPA coefficients between the two geometries. The TPA coefficients were found to be β⊥=1.07×10−9cm/W and β∥=1.88×10−9cm/W. It was found that doping slightly increases the TPA coefficient. The value of the TPA for crystals doped with 0.5at.% of Tl is β⊥=7.56×10−9cm/W.