Characterization of the transient thermal-lens effect using top-hat beam Z-scan

The transient thermal-lens effect in a solution is investigated by using the top-hat beam Z-scan technique. The numerical results show that the sensitivity of the top-hat beam Z-scan measurements is about 3.5 times greater than the Gaussian beams for the transient thermal-lens effect when the phase shift is small, which is greater than that for the Kerr effect and the steady-state thermal-lens effect. The reasons are also discussed in detail.