Anisotropy Of Two-photon Absorption Research Articles

Anisotropy of two-photon absorption and free-carrier effect in nonpolar GaN

We reported a systematic study about the anisotropic optical nonlinearities in bulk m-plane and a-plane GaN crystals by Z-scan and pump-probe with phase object methods under picosecond at 532 nm. The two-photon absorption coefficient, which was measured as a function of polarization angle, exhibited oscillation curves with a period of π/2, indicating a highly polarized optical third-order nonlinearity in both nonpolar GaN samples. Furthermore, free-carrier absorption revealed stronger hole-related absorption for E⊥c than for E//c probe polarization. In contrast, free-carrier refraction was found almost isotropic due to electron-related refraction in the isotropic conduction bands.

Anisotropy of two-photon absorption in [110]-cut nearly-intrinsic silicon crystal

以沿[110]晶向切割的近本征硅单晶为样品，通过研究样品对连续波固体激光器所产生的1.3 μm的近红外光的双光子吸收所诱导的光电流对入射光偏振方向的依赖关系，研究了双光子吸收的各向异性.测得了硅单晶对该波长的光的三阶极化率张量χ(3)的各向异性系数为-0.25，两个独立分量的比值χxxxx/χxxyy的幅度为2.4，并基于前期工作所得的χxxyy的结果，进而确定了另一分量χxxxx的值大约为1.49×10-19 m2/V2.

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

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.

Anisotropy of two-photon absorption in BBO at 264 nm

Femtosecond pulses at λ=264 nm were used to measure the two-photon absorption (TPA) coefficient in β-BaB 2O 4 (BBO) crystal. It was found that nonlinear absorption in BBO depends significantly on crystal cut and/or beam polarization. For an ordinary beam propagating along the optical axis (∥ c) and perpendicular to it (⊥ c) the similar values of TPA coefficient were obtained, namely (68±6)×10 −11 and (66±7)×10 −11 cm/W. For an extraordinary beam (⊥ c) the TPA coefficient is significantly smaller, (47±5)×10 −11 cm/W.

Anisotropy of two-photon absorption in cubic direct-band-gap semiconductors.

The two-photon absorption (TPA) cross section in zinc-blende-structure semiconductors has been analyzed, both analytically and numerically. The warping of the valence band is shown to result in a dependence of the TPA on the orientation of the polarization plane of the light with respect to the crystal axes, i.e., in a linear dichroism. In InSb and GaAs, the relative differences in the TPA cross sections for light polarized along 〈100〉 and 〈111〉 axes, depending on the light wavelength, are 0.02--0.05 and 0.13--0.20, respectively. The linear-circular dichroism of TPA, even in narrow-band-gap semiconductors, is noticeably influenced by the presence of a split-off valence subband.

Anisotropy of two-photon absorption in GaAs and CdTe

The anisotropy in the two-photon absorption coefficient for GaAs and CdTe is reported for the first time. Variations of the order of 15% are observed at room temperature in the magnitude of the nonlinear absorption, and are seen to increase at 85\ifmmode^\circ\else\textdegree\fi{}K, as the angle of the polarization vector of the incident 1.06-\ensuremath{\mu}m light is changed with respect to the crystal axes. The variation agrees with the predictions of nonlinear optics and a simple three-band model (neglecting excitons), but is too large at 85\ifmmode^\circ\else\textdegree\fi{}K to be accounted for by the band model.