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Description
The Barcelona Raman LIDAR (BRL) system, which is being developed for the Cherenkov Telescope Array Observatory (CTAO) relies on photomultiplier tubes (PMTs) to detect weak optical signals backscattered by atmospheric molecules and aerosols. As aerosol transmission constitutes a major source of systematic uncertainty, efficient photon detection in the LIDAR receiver is essential to achieve the calibration accuracy and sensitivity required by CTAO.
We present an experimental study of the Hamamatsu PMT Module H11526 – a PMT coupled to a freeform-based condenser lens designed to enhance photon collection efficiency. Using a dedicated optical setup, a clear dependence of the detected signal on both the illumination position and the angle of incidence was revealed, highlighting non-uniformities in the effective collection efficiency. This work constitutes a first experimental assessment of freeform condenser lens optics for Raman LIDAR applications and demonstrates their potential to enhance photon collection in compact detector systems, such as BRL.