A novel design of a compact, freeform-based condenser lens for use with photomultiplier tubes to achieve high collection efficiencies

For many applications using Photomultiplier tubes (PMT) that require an efficient measurement of very weak light, it is a continuous challenge to collect as much light as possible. Regarding the improvement of the collection efficiency, there are some possible solutions, e.g., using a detector with a larger effective area or adding a large optical lens. However, there is also a demand to miniaturize detectors in certain application fields such as immunoassay analysis and underwater wireless optical communications. To overcome this challenge, we have developed a novel freeform condenser lens which shows a drastic size reduction and high light collection efficiency simultaneously. The lens has a very high collection efficiency to collect not only collimated light but also diffused light, which is usually difficult to collect for common detectors with a limited entrance aperture and acceptance angle. In this paper, we present the design and characteristics of this lens. We also present exemplary applications of the developed freeform condenser lens in an immunoassay analyzer and in underwater wireless optical communication by combining developed lens with a PMT.