Abstract

The recent introduction of the Z-scan technique[1-3] has provided a simple and versatile method of determining the real and imaginary parts of a materials third-order nonlinearity, χ⁽³⁾ or n₂. A two-beam modification of the technique [2] allows one to also investigate nondegenerate components of the nonlinearity. The high sensitivity of the Z-scan method is due to the fact that a small phase distortion introduced by the material nonlinearity corresponds to relatively large intensity variations as measured with a small diameter aperture in the far field. We suggest that this principle can be utilized in a pump-probe geometry with lock-in detection of intensity variations to improve the sensitivity. In the suggested geometry it is also possible to perform fully time-resolved measurements using picosecond or femtosecond laser pulses. Additionally, one can investigate the dependence of the nonlinearity on the spatial frequency of the induced phase or amplitude distortion. Finally, as in the original Z-scan, there is a way of separating the real and imaginary parts of the nonlinearity.

© 1993 Optical Society of America