Using femtosecond laser pulses to study the nonlinear optical properties of rhodamine 6G dissolved in water

Abstract

Using the Z- scan method, we studied the nonlinear absorption coefficient of rhodamine 6G dissolved in water. With laser pulses of 100 fs, the nonlinear absorption coefficient was measured at different excitation wavelengths and incident powers for both water and R6G. Water behavior showed saturable absorption (SA) at high power (>0.8 W) but at low laser power (<0.8 W) does not exhibit any nonlinearity whatever of the wavelength of excitation. At high laser power, the nonlinear absorption coefficient of the water increases as the wavelength decreases. A transition from saturable absorption to reverse saturable absorption (RSA) was observed when R6G was added to the water. In the case of R6G solution, the nonlinear absorption coefficient was found to be sensitive to both excitation wavelength and power. The two photon absorption cross-section was obtained from the nonlinear absorption coefficient of rhodamine 6G solution and was found to increase with increasing excitation wavelength while increasing with decreasing laser power. The nonlinear absorption coefficient β and nonlinear refractive index n2 of rhodamine 6G solution were found to be concentration dependent. Based on its RSA behaviour, the optical limiting of rhodamine 6G solution was measured and found to be concentration dependent. The higher concentration of rhodamine 6G solution has better optical limiting characteristics.