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.
A time-resolved, spectroscopic, diffuse optical tomography device was assembled for clinical applications like brain
functional imaging. The entire instrument lies in a unique setup that includes a light source, an ultrafast time-gated
intensified camera and all the electronic control units. The light source is composed of four near infrared laser diodes
driven by a nanosecond electrical pulse generator working in a sequential mode at a repetition rate of 100 MHz. The
light pulses are less than 80 ps FWHM. They are injected in a four-furcated optical fiber ended with a frontal light
distributor to obtain a uniform illumination spot directed towards the head of the patient. Photons back-scattered by the subject are detected by the intensified CCD camera. There are resolved according to their time of flight inside the head. The photocathode is powered by an ultrafast generator producing 50 V pulses, at 100 MHz and a width corresponding to a 200 ps FWHM gate. The intensifier has been specially designed for this application. The whole instrument is controlled by an FPGA based module. All the acquisition parameters are configurable via software through an USB plug and the image data are transferred to a PC via an Ethernet link. The compactness of the device makes it a perfect device for bedside clinical applications. The instrument will be described and characterized. Preliminary data recorded on test samples will be presented.
The paper describes the realization of a complete optical imaging device to clinical applications like brain functional
imaging by time-resolved, spectroscopic diffuse optical tomography. The entire instrument is assembled in a unique
setup that includes a light source, an ultrafast time-gated intensified camera and all the electronic control units. The light
source is composed of four near infrared laser diodes driven by a nanosecond electrical pulse generator working in a
sequential mode at a repetition rate of 100 MHz. The resulting light pulses, at four wavelengths, are less than 80 ps
FWHM. They are injected in a four-furcated optical fiber ended with a frontal light distributor to obtain a uniform
illumination spot directed towards the head of the patient. Photons back-scattered by the subject are detected by the
intensified CCD camera; there are resolved according to their time of flight inside the head. The very core of the
intensified camera system is the image intensifier tube and its associated electrical pulse generator. The ultrafast
generator produces 50 V pulses, at a repetition rate of 100 MHz and a width corresponding to the 200 ps requested gate.
The photocathode and the Micro-Channel-Plate of the intensifier have been specially designed to enhance the
electromagnetic wave propagation and reduce the power loss and heat that are prejudicial to the quality of the image. The
whole instrumentation system is controlled by an FPGA based module. The timing of the light pulses and the
photocathode gating is precisely adjustable with a step of 9 ps. All the acquisition parameters are configurable via
software through an USB plug and the image data are transferred to a PC via an Ethernet link. The compactness of the
device makes it a perfect device for bedside clinical applications.
When optimizing equipment in which 'fast grating' is used, it is important to discriminate between the 'speed' of the module and the speed of the electrical gate-pulse unit. D.E.P. has therefore developed a method to measure the speed of the module independently of the gate- pulse unit. D.E.P. measures, during the switching on of the module, the time delay between the center and the edge of the module, which we call the iris delay. Even with an electrical gate-pulse of 3 nsec rise-time, we can measure an iris delay down to 0.2 nsec. The shortest pulse-width for which a module can be used is about 2 or 3 times the iris delay. This measurement is done with a pulsed solid state laser. The laser is fired with a variable delay with respect to the gate pulse on the tube.
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