Polarization Dependence of Two-Photon Absorption in Si Avalanche Photodiodes

The polarization dependence of two-photon absorption (TPA) in Si avalanche photodiodes was investigated experimentally at room and low temperatures. Cross-TPA was selectively detected by using a lock-in amplifier that detects photocurrent that is synchronized to the sum frequency of two mechanical choppers. The polarizations of the two beams were independently controlled. Polarization dependence is discussed in terms of the non-diagonal elements of the third-order nonlinear susceptibility tensor. When one of two beams is circularly polarized, the dependence of the TPA efficiency on the polarization of the other beam was very weak. However, the dependence becomes greater at low temperatures as a result of the temperature dependence of the nonlinear susceptibility tensor.