Determination of nonlinear refractive index by an iterative phase retrieval method.

Area of Science:

• Nonlinear optics
• Optical metrology

Background:

• Accurate measurement of nonlinear optical properties is crucial for developing advanced optical materials and devices.
• Existing techniques for measuring the nonlinear refractive index can be complex or require specialized setups.

Purpose of the Study:

• To present a simple, robust, and lensless technique for measuring the nonlinear refractive index.
• To validate the method through simulations and experimental investigations.

Main Methods:

• Utilizing an iterative phase retrieval algorithm combined with a pump-probe system.
• Introducing controlled phase modulations to the probe beam and recording diffraction intensity patterns.
• Reconstructing the pump-induced phase on the probe beam from recorded intensity patterns.

Main Results:

• The nonlinear refractive index is accurately extracted from the reconstructed phase.
• The method demonstrates robustness against complex-valued probe fields and non-Gaussian pump beams.
• Successful validation of the technique under noisy conditions and with non-smooth beam profiles.

Conclusions:

• The proposed iterative phase retrieval method provides a straightforward and effective approach for nonlinear refractive index measurement.
• The lensless setup and tolerance to complex beam characteristics offer significant advantages over conventional methods.
• This technique has broad applicability in materials science and optical engineering.