Ashish

The Z-scan experiment is in an simplified version the transit of a material through the focal point of a converging lens and look for changes in amplitude. Therefore by conception Z-scan is the simplest nonlinear characterization technique and has only that significance. That is it : measures nonlinearities (CW, pulsed - thermal, orientational, excited state, Kerr, ...).

Ashish, of course the z-scan can be used in many different ways, and not only to measure nonlinear optical properties of materials. Imagine for example that you have a LINEAR layer slightly focusing layer, especially if it made of "soft matter" and its properties are modulated or affected by any external action, for example, by heat. mechanical vibration  or acoustical wave, shock wave, other radiation, etc. And of course, the focus of the probe radiation will me moving, so that you can use it as a detector of those perturbations, if you chose a very long-focus thin lens as a layer (In fact more than 50 years ago, I used it as an acoustical detector, without any laser, and it was very sensitive.)  By the way, actually the very first paper on using a nonlinear layer for "external self-focusing" (i. e. essentially z-scanning) with full theory including both nonlinear focusing and diffraction was published long before the papers cited by most of people; here is the link:

http://psi.ece.jhu.edu/~kaplan/PUBL/AEK.pubs/RUSS/10.pdf

In addition to the points mentioned above:

You can use z-scan also to determine multi-photon absorption strengths (which is of course also a nonlinear process). One example you can find here:

http://pubs.acs.org/doi/abs/10.1021/jp910010g

In z-acan method we can measuring the nonlinear refraction(close aperture) and also nonlinear absorbtion(open aperture) instantanously.

hi

you can use it to measure the sign and magnitude of nonlinear absorption coefficient and nonlinear refractive index , real and imaginary part of susceptibility also in biology or biochemistry you can use to measure the concentration of any spices.