Broadband femtosecond nonlinear optical properties of silver nanowire films

Abstract

In this report, we present results from the investigation of femtosecond (fs) nonlinear optical (NLO) behaviour of silver nanowires (Ag NWs) films. High quality Ag NWs (10 μm length, diameter 50 nm in isopropyl alcohol) were utilzied for the NLO studies employing the standard Z-scan technique in both open and closed aperture configurations at wavelengths of 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, and the corresponding NLO coefficients were estimated from theoretical fits to the experimental data. Nonlinear absorption in the Ag NWs at 800 nm demonstrated a pure reverse saturable absorption (RSA) with a strong two-photon absorption (TPA) coefficient. At 800 nm, intensity dependent Z-scan studies were performed at different peak intensities of 190 MW/cm2, 210 MW/cm2, 260 MW/cm2 and observed that the TPA coeffieicent (~10−5 cm/W) increased significantly as a function of peak intensity. Interestingly, the nonlinear absorption of Ag NWs films demonstrated a complex behavior of saturable absorption (SA), reverse saturable absorption (RSA) and switching from RSA within SA depending on excitation wavelength even though the studies were performed at similar peak intensities. The estimated NLO coefficients were IS = 30 MW/cm2 (βsa = 0), βTPA = 1.6 × 10−5 cm/W, IS = 92 MW/cm2 (βeff = 1.4 × 10−5 cm/W) and IS = 60 MW/cm2 (βsa = 1.72 × 10−5 cm/W) for the wavelengths of 700 nm, 750 nm, 850 nm and 900 nm, respectively. The nonlinear refraction studies at the wavelength 800 nm, investigated by closed aperture Z-scan, demonstrated a positive sign (compared to the studies at other wavelengths) and the obtained intensity dependent nonlinear refractive index was ~1.6 × 10−9 cm2/W.