Dark-field Z-scan imaging technique

• Dark-field Z-scan is a new method associating Z-scan with dark-field microscopy.
• Imaging technique of the induced nonlinear phase shift.
• Preventing collapse for high order NL coefficient estimation.
• Potential applications in laser scanning microscopy.

We report on Dark-Field Z-scan (DFZ-scan) as a new imaging technique combining Z-scan method with Dark-field microscopy in order to measure optical refraction nonlinearity. Numerical and experimental results are provided to validate this concept. The image of the induced phase shift is spatially resolved without introducing a complex interferometric setup. Moreover, the experimental results show almost 3 times increase of the sensitivity when compared to the conventional Z-scan method. New perspective of microscope laser scanning is introduced.