Optical diffraction tomography of second-order nonlinear structures in weak scattering media: theoretical analysis...

Area of Science:

• Optics and Photonics
• Materials Science
• Imaging Techniques

Background:

• Computed tomography (CT) provides high-resolution imaging.
• Optical diffraction tomography (ODT) extends CT to the optical domain.
• Imaging nonlinear optical structures is crucial for materials characterization.

Purpose of the Study:

• To present the theoretical framework for ODT of second-order nonlinear structures.
• To explore experimental considerations for implementing this technique in weak scattering media.
• To enable high-resolution, polarization-sensitive imaging of nonlinear material properties.

Main Methods:

• Derivation of the relationship between second harmonic waves and anisotropic nonlinear tensors in the spatial frequency domain.
• Application of the first-order Born approximation.
• Analysis of 2D spatial spectra of the second harmonic field in relation to Ewald spheres.
• Numerical phantom testing to validate the proposed method.

Main Results:

• The 2D spatial spectra of the second harmonic field are linked to the inverse lattice of nonlinear structures on Ewald sphere shells.
• Ewald sphere parameters are determined by incident fundamental wavevector and second harmonic wavevector.
• The spectra represent a superposition of Ewald spheres corresponding to different components of the nonlinear tensor.
• Feasibility demonstrated using a numerical phantom with proposed polarization control strategies.

Conclusions:

• The proposed ODT method allows for high-resolution, wide-field, and polarization-sensitive imaging of nonlinear structures.
• Controlling fundamental and second harmonic polarizations is key to solving the inverse problem.
• This technique holds significant potential for applications in nonlinear microscopy and materials analysis.