Thanks to a large set of available photocathodes with first in class QE, high gain, high collection efficiency, high dynamic range while keeping low dark count rate and single photon resolution capability with excellent timing, MCP-PMTs have emerged as candidates for LIDAR receivers. We present results of Ageing tests and Radiation tests carried out with Photonis and Airbus Defence & Space on High QE, and High linearity MCP-PMT for UV LIDAR receivers. Ageing of the photocathode is usually due to electron-induced ion feedback and molecule desorption from the MCP and anode, causing degradation of the photocathode layer leading to a progressive loss of QE related to the quantity of electron charges generated along lifetime. Expected Coulomb charges generated along a typical and worst-case mission were estimated from the atmosphere profiles. Thanks to a design change of the MCP-PMT and the implementation of Long-Lifetime MCP technology, ageing of the photocathode was drastically reduced. The new design showed no Quantum Efficiency nor Collection Efficiency degradation up to 20 C. Proton radiation tests were performed to evaluate false signal generated, end-of-life impact on performance, loss of transmission depending on the photocathode glass substrate as well as cathodoluminescence and photoluminescence at the photocathode. Quantum Efficiency, Collection Efficiency, PHD shape, Gain, and Linearity were found to be unchanged for fluences of 5x1011 p+/cm² with 60 MeV protons. Only small increase of DCR for about 120 cps/cm² was recorded about 8 weeks after the radiation.
In this paper the focus is on the implementation of Photonis MCP-PMTs with single photon counting capability for LIDAR applications. In particular we are presenting our MCP-PMTs based on HI-QE photocathodes optimized for different spectral ranges (UV, Blue, Green with typical QE<30%) and for fixed laser wavelength of 355 nm and 532 nm [1]. In addition to the high QE, those photocathodes demonstrate low dark rates, typically below 50 Hz/cm2, property that is important for low-rate signal detection. The collection efficiency of the MCP is also improved to reach almost 100%, allowing to increase the detective QE by a factor of 1.5 compared to conventional MCP-PMTs [2]. The timing performance for MCP-PMTs operated at low and high rate photon fluxes are also studied. Non-linearity effects for high rate of illumination are analyzed and MCP-PMTs with extended linearity are presented. All these improved detection properties can be combined with the possibility of fast triggering and extended life time technology making these devices unique for future atmospheric and altimetry LIDAR missions.
A fast timing MCP-PMT detector has been developed and characterized for LIDAR applications. A field of application for which it is needed to demonstrate the capability to measure photon fluxes in single photon counting mode at low and high rates on one hand, and on the other hand to detect high intensity peaks, containing up to thousands photons within a ns-time window, as it is the case in the response signal of highly reflective surfaces. Based on high quantum efficiency (above 30% in peak) and low dark rates (about 30 Hz/cm2) s-20 photocathodes from our Hi-QE series optimized for 200-550 nm spectral range, our fast MCP-PMT detectors are demonstrating efficient single photon counting from very low rates and up to few GHz for burst pulses. Thanks to the implementation of high linearity MCPs the linear detection range is extended up to several 100 MHz of averaged photon fluxes. The detection of high intensity peak is a challenge for devices optimized for single photon counting mode; here we propose a two-channel detection scheme that allows performing accurate measurements in photon counting mode and in parallel that is enabling the detection and counting intense multi-photon pulses with sub-ns time resolution.
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