Three-dimensional second-harmonic generation imaging with femtosecond laser pulses

Area of Science:

• Nonlinear Optics
• Optical Microscopy
• Materials Science

Background:

• Second-harmonic generation (SHG) is a nonlinear optical phenomenon.
• Optical microscopy is crucial for characterizing material microstructure.
• Characterizing local second-order nonlinearity requires advanced imaging techniques.

Purpose of the Study:

• To present a novel three-dimensional reflectance scanning optical microscope.
• To utilize the nonlinear optical phenomenon of second-harmonic generation for imaging.
• To characterize the distribution of second-order nonlinearity and microstructure in nonlinear materials.

Main Methods:

• A mode-locked Ti:sapphire laser generating <90-fs pulses at ~790 nm was employed.
• Object scanning relative to a focused laser spot enabled image construction.
• Dichroic and interference filters separated SHG light (~395 nm) for photodiode detection.

Main Results:

• The 3D reflectance scanning optical microscope successfully imaged nonlinear materials.
• The distribution of second-order nonlinearity was characterized.
• The microstructure of lithium triborate was successfully mapped.

Conclusions:

• The developed SHG-based optical microscope is effective for 3D imaging of nonlinear optical properties.
• This technique provides valuable insights into the microstructure and nonlinear characteristics of materials.
• The method demonstrated its capability in characterizing lithium triborate.