Pump power dependence of the spatial gating properties of femtosecond optical Kerr effect measurements

The pump power dependence of the spatial gating properties of femtosecond optical Kerr gate (OKG) was investigated using coaxial two-color optical Kerr measurements in CS2. As the pump power increased, the spatial pattern of the optical Kerr signals changed from a Gaussian spot to a ring form, and then a spot surrounded by a concentric ring, successively. By comparing the experimental data with the calculation results and measuring the pump power dependence of the OKG signal intensity, we demonstrated that the spatial variation of OKG transmittance could be attributed to the non-uniform spatially distributed phase change of the probe beam, due to the transient birefringence effect induced by pump beam with transverse mode of a Gaussian distribution.