Z-Scan Measurement

definition:
A method based on self focusing effect for measuring the Kerr nonlinear strength of materials

ZScanning measurement technology is commonly used to measure the Kerr nonlinear intensity (i.e. nonlinear refractive index) of optical materialsn2）. The principle is to move the material sample to be tested through the focus of the laser beam and measure the beam radius (or intensity on the optical axis) at a certain point behind the sample. Due to the effect of self focusing, these quantities will change, thus obtaining a function of the beam radius (or intensity on the optical axis) with respect to the position of the sample.
As shown in the figureoneAs shown, it is a commonZScanning measuring device. If the nonlinear refractive index is positive and the sample is placed behind the focal point, the self focusing effect will reduce the divergence of the beam, thereby increasing the signal strength of the detector. If the sample is placed in front of the focal point, the focal point will move to the left, and the strong beam divergence after focusing will reduce the signal intensity of the detector. The magnitude of the nonlinear refractive index can be calculated from the functional relationship between the measured detector signal intensity and the sample position.

(picture1)ZScanning measurement experimental setup diagram. By measuring the light intensity after passing through the aperture and determining its relationship with the position of the sample, the nonlinear refractive index can be calculatedn2The detector in the upper left corner is commonly used to detect the intensity of incident light.
It should be noted that some nonlinear absorption (such as two-photon absorption) may also affect the measured signal. However, this can be corrected by additionally recording all transmitted beam powers.