Recent Advancements in Optical Harmonic Generation Microscopy: Applications and Perspectives.

Area of Science:

• Biomedical Optics
• Microscopy
• Biophotonics

Background:

• Second harmonic generation (SHG) and third harmonic generation (THG) are nonlinear optical phenomena enabling label-free imaging of biological tissues.
• These techniques offer complementary contrast mechanisms, revealing structural and refractive index information, respectively.
• Simultaneous SHG and THG imaging can be achieved with modified multiphoton microscopes.

Purpose of the Study:

• To review the instrumentation and theoretical principles of SHG and THG microscopy.
• To highlight recent advances and applications of SHG and THG in biological and medical research.
• To discuss future perspectives and challenges in the field.

Main Methods:

• Discussion of instrumentation for simultaneous SHG and THG data acquisition.
• Explanation of the underlying physics of SHG and THG contrast generation in tissues.
• Overview of applications utilizing polarization-resolved SHG and machine learning.

Main Results:

• SHG microscopy effectively visualizes collagen alterations in the extracellular matrix, aiding studies in cancer, fibrosis, and corneal research.
• THG microscopy reveals refractive index variations, crucial for developmental biology and skin cancer investigations.
• Polarization-resolved SHG and machine learning enhance structural information extraction.

Conclusions:

• SHG and THG microscopies are versatile tools for structural analysis of biological tissues.
• These techniques have significant applications in understanding diseases and advancing tissue engineering.
• Future development requires miniaturization and microendoscopy for broader clinical translation.