Nonlinear optical properties of bulk cuprous oxide using single beam Z-scan at 790 nm

Abstract

The two-photon absorption (TPA) coefficient β and the nonlinear index of refraction n2 for bulk cuprous oxide (Cu2O) direct gap semiconductor single crystal have been measured by using a balance-detection Z-scan single beam technique, with an excellent signal to noise ratio. Both coefficients were measured at 790 nm using a 65 fs laser pulse at a repetition rate of 90.9 MHz, generated by a Ti:Sapphire laser oscillator. The experimental values for β were explained by using a model that includes allowed-allowed, forbidden-allowed, and forbidden-forbidden transitions. It was found that the forbidden-forbidden transition is the dominant mechanism, which is consistent with the band structure of Cu2O. The low value for β found in bulk, as compared with respect to thin film, is explained in terms of the structural change in thin films that result in opposite parities of the conduction and valence band. The n2 is also theoretically calculated by using the TPA dispersion curve and the Kramers-Kronig relations for nonlinear optics.

Thickness dependency of nonlinear optical properties in ITO/Sn composite films

“…where L eff = 1 − e −α 0 L =α 0 is the effective path length, in which z is the vertical separation from the focal point to the sample, z 0 is the diffraction length of the beam, I 0 is the laser strength of this beam waist, and L is the thickness of the test sample [35] .…”

Ultrafast carrier dynamics of Cu2O thin film induced by two-photon excitation*

“…This initiates studies that focused on the two-photon absorption properties of Cu 2 O, demonstrating considerable applications in optical limiting, ultrafast all-optical modulation, and so on. [11][12][13] As is known, understanding the carrier dynamics is essential for semiconductor optoelectronic devices. It has been proved that the carrier distribution generated by two-photon excitation is more uniform than that by one-photon excitation, due to the former has relatively weaker absorption coefficient.…”

Two-photon absorption coefficient determination using the differential F-scan technique

“…To enhance the sensitivity of the technique Xia et al [4] replaced the far-field aperture in the standard Z-scan by an obscuration disk that blocks most of the beam, while Zhao et al [5] used a top-hat beam instead of a Gaussian beam, and Martinelli et al [6] measure the reflected beam from the sample in a Brewster angle configuration. To improve the signal to noise ratio some authors have used balance-detection systems [7,8], while Ménard et al [9] introduce the differential Z-scan where a piezo-transducer device generates an oscillatory motion to induces a periodic modulation of the beam intensity at the sample, which in turn produces a modulation of the transmitted light proportional to the spatial derivative of the transmitted light, and therefore provides a background-free measurement. More recently, a new technique, that is a variation of Z-scan, was proposed.…”