An LED PLD based controller for experimental characterization of an optical fibre sensor system for measurement of x-ray radiation in clinical linacs

Advanced characterization of an optical fibre sensor system based on an MPPC detector for measurement of X-ray radiation in clinical linacs

“…value, the software only registers a count when 2 photons are detected simultaneously by the MPPC, if 1 photon or more than 2 photons are detected by the MPPC, the event is ignored by the software and no count is registered. While the software is clearly sensitive to the preset threshold value (it can be set too high or too low) the analogue voltage output is not subject to any such restriction, but its value must maintained in the range 0 to 3 Volts to avoid saturation effects of the detector [14].…”

“…1 illustrates the system consisting of the LED light source driven by an arbitrary waveform generator (AWG) and the readout system, including a 20 m long plastic optical fibre (POF, provide manufacturer name and fibre type as previously deployed by Chen et al [14]), an optical attenuator and MPPC detector, which is connected to a digital storage oscilloscope (DSO) and a laptop. In this work, the LED was driven using an AWG (also referred to as the signal generator (SG), Teledyne LeCroy WaveStation 2012) which replaced the in-house developed field programmable gate array (FPGA) based system previously deployed by Chen et al [14]. In comparison with the SG, the FPGA based system is flexible and good for operation outside the laboratory e.g.…”

“…In this investigation, the SG was preferred to the FPGA system. Firstly, the response of the MPPC to different pulse periods was fully investigated in [14] and hence the duty cycle limitation of the SG was not a factor in this investigation. Secondly, the pulse train of X-ray beam delivered from a medical linear accelerator (linac) is typically an ideal rectangular signal with a pulse width less than 3 ± 0.2 µs and the in-house developed FPGA system was not capable of producing an ideal rectangular pulse with a pulse width less than 3 µs.…”

“…The device of choice in this case is the multi pixel photon counter (MPPC) (C11208-01) by Hamamatsu. It comprises an array of high speed, high sensitivity avalanche photodetectors and has previously been identified by the authors of this article [14] as a highly suitable device for the challenging detection requirements of this measurement. The time resolved response of the analog signal output (voltage) and digital signal (photon counts) of the MPPC to a range of different dynamic response tests based on a pulsed light emitting diode (LED) source has been fully investigated by Chen et.…”

“…The time resolved response of the analog signal output (voltage) and digital signal (photon counts) of the MPPC to a range of different dynamic response tests based on a pulsed light emitting diode (LED) source has been fully investigated by Chen et. al [14]. In the investigation described in this article, the performance of the MPPC has been further investigated, including identifying a unique relationship between the analog and digital output signals under the correct exposure conditions of the detector.…”