Cascade upconversion: a strategy enabling four-photon lithography in weak light intensity

Area of Science:

• Materials Science
• Optics and Photonics
• Nanotechnology

Background:

• Multiphoton lithography achieves submicron 3D printing but requires high laser intensity, limiting photon counts.
• Existing methods face challenges with feature size reduction and laser power requirements.

Purpose of the Study:

• To introduce a cascade upconversion strategy for achieving four-photon photopolymerization.
• To enable high-resolution 3D polymer structure fabrication using low-intensity lasers.

Main Methods:

• Combined excited state absorption upconversion (Ho3+/Yb3+ nanoparticles) with triplet-triplet annihilation upconversion.
• Utilized a low-cost continuous wave 980 nm laser at low intensity (10^5 W/cm^2).

Main Results:

• Achieved a two-orders-of-magnitude reduction in feature size compared to conventional methods.
• Fabricated 3D polymer structures with high quality, speed, and design freedom.
• Overcame nanoparticle luminescence diffusivity for improved resolution.

Conclusions:

• The cascade upconversion strategy enables efficient four-photon and potentially six-photon multiphoton lithography.
• This approach offers a general method for high-resolution 3D printing with weak light intensity.
• Demonstrated a viable pathway for advanced submicron 3D printing applications.