Title:

Development of High-Precision microlenses for enhanced Solar Neutron Tracking

The detection of solar neutrons is crucial for understanding high-energy particle acceleration at the Sun. NASA’s Solar Neutron Tracker (SONTRAC) employs silicon photomultipliers (SiPMs), but optical crosstalk between adjacent detectors limits performance. This project explores microlenses as a passive solution to reduce crosstalk by focusing scintillation light more directly onto individual SiPMs. Plano-convex microlenses were optimized in Code V for minimal spot size and short back focal length (BFL), targeting the 400–500 nm spectral range. The final design achieved a simulated spot size of 0.18 mm, a 0.46 mm BFL, and an intensity-weighted RMS radius of 0.066336 mm. Lenses were fabricated using stereolithography with Clear V4 resin (n ≈ 1.51 at 635 nm), followed by custom mandrel polishing to reduce surface roughness. Optical validation with collimated red laser light (635 nm) and CMOS sensors confirmed focal spot formation at 0.46 mm. Experimental results showed a maximum spot size of 0.14 mm and an RMS radius of 0.07 mm after applying a 30% intensity threshold. This work lays the foundation for precision optics in space-based neutron detectors and demonstrates the feasibility of stereolithography for prototyping custom micro-optics.

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