Ultrafast optical imaging at 2.0  μm through second-harmonic-generation-based time-stretch at 1.0  μm

Area of Science:

• Optical Imaging
• Spectroscopy
• Biomedical Optics

Background:

• Ultrafast time-stretch imaging performance is limited at long wavelengths (>1.5 μm) by optical fiber losses.
• Low detection sensitivity hinders applications in spectral regions with unique optical absorption contrast.

Purpose of the Study:

• To develop an ultrafast optical imaging system with enhanced detection sensitivity at 2.0 μm.
• To enable time-stretch imaging at longer wavelengths by overcoming fiber loss limitations.

Main Methods:

• Utilized second-harmonic generation (SHG) to convert 2.0-μm signals to 1.0 μm.
• Employed highly sensitive time-stretch detection at 1.0 μm.
• Achieved spectral encoding of the sample at 2.0 μm, followed by temporal mapping via a dispersive fiber.

Main Results:

• Demonstrated an ultrafast optical imaging system with a line scan rate of approximately 19 MHz at 2.0 μm.
• Achieved a superior dispersion-to-loss ratio of ~53 ps/nm/dB at 1.0 μm, ~50 times greater than standard fibers at 2.0 μm.
• Successfully translated time-stretch technology to longer wavelengths while maintaining high detection sensitivity.

Conclusions:

• The developed system overcomes sensitivity limitations of long-wavelength time-stretch imaging.
• This advancement allows leveraging unique optical absorption contrasts at longer wavelengths.
• The approach benefits from high detection sensitivity typically found at shorter wavelengths.