Effects of laser polarization and interface orientation in harmonic generation microscopy

Area of Science:

• Nonlinear optics
• Microscopy
• Materials science

Background:

• Second harmonic generation (SHG) and third harmonic generation (THG) are nonlinear optical phenomena used in microscopy.
• Understanding the influence of experimental parameters like laser polarization and sample orientation is crucial for optimizing SHG and THG microscopy.

Purpose of the Study:

• To systematically investigate the effects of laser polarization and interface orientation on SHG and THG microscopy.
• To explore the potential of harmonic generation microscopy in novel imaging geometries and applications.

Main Methods:

• Experimental setup for SHG and THG microscopy.
• Varying laser polarization states (e.g., linear, circular).
• Altering interface orientation relative to the incident laser beam.

Main Results:

• Laser polarization had no significant effect on THG signal strength or resolution.
• SHG signal strength and resolution were highly dependent on laser polarization direction.
• Both SHG and THG signal strength and imaging resolution were strongly influenced by interface orientation.
• Harmonic signals were observed even from surfaces parallel to the laser beam's optical axis.

Conclusions:

• Laser polarization is a critical parameter for SHG microscopy but not THG microscopy.
• Interface orientation is a key factor influencing both SHG and THG imaging performance.
• The ability to generate strong harmonic signals from surfaces parallel to the optical axis opens new possibilities for harmonic microscopy.
• Third harmonic microscopy was demonstrated for monitoring microfluidic flow in lateral cuts, showcasing its application potential.