The Hamamatsu S8550 4×8 pixel APD matrix has high quantum efficiency at a broad visible wavelength range, but its fill factor is only ~50%. This means half of the light is lost where the detector is used in a direct imaging setup. To improve the situation a small lens matrix is manufactured by Fusion Instruments which can focus light from the whole detector surface into the sensitive pixel areas. The device consists of two 2×8 high precision plastic lens matrices, which are fixed permanently to the carefully pre-polished detector surface, matching the exact position of the two 2×8 pixel sub-arrays of the S8550 detector.
With the ML-S8550 lens matrix mounted onto the detector surface the detection efficiency is improved close to 100% if the light reaches the lenses within a ±30 degree cone. Uncoated or broadband anti-reflection coated versions are available and custom coating requests can also be fulfilled.