Investigation and modeling of UV band-pass-filtering white compound materials for potting or embedding in micro-optical applications

A novel white compound material with spectral band pass filtering was proposed and demonstrated in the UV region for wavelengths smaller than 310 nm. This compound material can be obtained by dispersing CaF2 in polydimethylsiloxane (PDMS). Refractive index matching (RIM) of the compound material resulted in transmittance of up to 80% at RIM wavelength. In no-RIM wavelength region, refractive index difference about 0.005 could result in transmittance of down to 30% due to intense Rayleigh isotropic scattering. A good reproducibility of the transparent wavelength can be obtained with the specific CaF2 particle and PDMS matrix in this study. Meanwhile, simple calculation based on Rayleigh-Gans-Debye approximation [J. Am. Ceram. Soc. 86(3), 480 (2003)] in the soft diffusion model can explain the CaF2: PDMS compound film transmittance spectrum in the UV region, and the bandwidth narrowing condition.