Comprehensive optical monitoring of photopolymer curing for additive manufacturing of diffractive elements

Area of Science:

• Optics and Photonics
• Materials Science
• Additive Manufacturing

Background:

• Diffractive optical elements (DOEs) have diverse applications, including beam shaping and augmented reality.
• Additive manufacturing via photopolymerization offers a low-cost route to customizable DOEs.
• Monitoring the dynamic, spatial evolution of photopolymer curing is crucial for fabricating precise DOEs.

Purpose of the Study:

• To develop and demonstrate an all-optical monitoring platform for in-situ characterization of photopolymer curing processes.
• To investigate the spatio-temporal evolution of refractive index during DOE fabrication.
• To explore the potential of tunable local refractive index changes for fabricating DOEs on a single photopolymer.

Main Methods:

• Utilized a "focused line refractive index microscopy" (FLRIM) technique for dynamic, in-situ refractive index measurements.
• Employed a "lateral-shearing interferometric microscopy" (LIM) technique for quantitative 2D structure analysis via transmitted phase.
• Used an ultraviolet "digital micromirror device" (DMD) projector for pixelated photopolymerization.

Main Results:

• Successfully monitored the in-situ curing process of photopolymer structures during local and global post-curing steps.
• Obtained quantitative spatio-temporal refractive index data during photopolymerization.
• Demonstrated the feasibility of fabricating DOEs by exploiting tunable local refractive index changes.

Conclusions:

• The proposed all-optical monitoring platform provides essential in-situ characterization for photopolymer-based DOE fabrication.
• FLRIM and LIM techniques offer dynamic and sensitive measurements of curing evolution and structural properties.
• Tunable local refractive index control presents a promising avenue for advanced, single-material DOE manufacturing.