Comprehensive simulation study and preliminary results on various shapes of nanopatterns for light extraction improvement in scintillation crystal

Abstract

Positron Emission Tomography (PET) systems with high spatial resolution and sensitivity suffer from reduced photon transmittance due to the high aspect ratio of scintillation crystals and the large refractive index (RI) difference at the crystal-photosensor boundary. This study aimed to enhance light extraction from the scintillation crystal to the photosensor by applying various nanopatterns on the crystal surface. Various nanopattern shapes, including line, circular, hexagonal, and tapered pyramid, were designed and simulated using Monte Carlo and finite-difference time-domain (FDTD) methods. The optimization focused on the nanostructure's diameter, width, height, period ratio, and RI. Light extraction gain was evaluated against a reference dataset with a 100 nm thick airgap between the crystal and photosensor. Nanopatterns significantly improved light transmission at the crystal-photosensor boundary, especially for scintillation photons entering at angles larger than the critical angle. Hole-type patterns showed superior performance with lower heights, larger period ratios, and RIs between 1.7 and 1.9. A maximum light extraction gain of 1.46 was achieved with a hole-type circular nanopattern with an RI of 1.7. Furthermore, our simulation results were experimentally validated through the preliminary development of a nanopattern applied to the GAGG crystal. Nanopattern on the crystal surface can effectively enhance light extraction to the photosensor. These findings were experimentally validated, confirming the potential of nanopatterns in improving PET system performance.