Abstract

We have measured the nonlinear refractive index of CS₂ in the 9-11-μm spectral region. We employed the same technique used in Ref. ¹, which is to monitor the onset of whole beam self-focusing by observing the photoacoustic signal in an optically thick cell of room temperature, liquid CS₂. The departure of the acoustic signal from linear growth with incident power marks the critical power for the onset of nonlinearity. It is experimentally verified that the phenomenon is power dependent as expected from self-focusing. The value of n₂ is then calculated from the theoretical model² of self-focusing. In all measurements the intensity on the axis was smaller than the calculated threshold intensity for Brillouin scattering. The backreflection is also monitored to make sure the Brillouin scattering is not playing a role in the phenomenon. Our previous¹ measurement of n₂ in CS₂at 10.6 μm was an order of magnitude larger than the reorientational n₂ in the visible and near infrared. In this series of experiments we find the maximum n₂ to be [0.9 ± 0.2] × 10⁻⁹esu at 10.24 μm which is about five times greater than n₂ at 10.6 μm. Such large dispersions are indicative of resonance processes. Further experimental studies are required to understand the microscopic processes responsible for the observed dispersion in n₂.

© 1986 Optical Society of America