Optical Simulation and Experimental Assessment with Time–Walk Correction of TOF–PET Detectors with Multi-Ended Readouts

As a commonly used solution, the multi-ended readout can measure the depth-of-interaction (DOI) for positron emission tomography (PET) detectors. In the present study, the effects of the multi-ended readout design were investigated using the leading-edge discriminator (LED) triggers on the timing performance of time-of-flight (TOF) PET detectors. At the very first, the photon transmission model of the four detectors, namely, single-ended readout, dual-ended readout, side dual-ended readout, and triple-ended readout, was established in Tracepro. The optical simulation revealed that the light output of the multi-ended readout was higher. Meanwhile, the readout circuit could be triggered earlier. Especially, in the triple-ended readout, the light output at 0.5 ns was observed to be nearly twice that of the single-ended readout after the first scintillating photon was generated. Subsequently, a reference detector was applied to test the multi-ended readout detectors that were constructed from a 6 × 6 × 25 mm3 LYSO crystal. Each module is composed of a crystal coupled with multiple SiPMs. Accordingly, its timing performance was improved by approximately 10% after the compensation of fourth-order polynomial fitting. Finally, the compensated full-width-at-half-maximum (FWHM) coincidence timing resolutions (CTR) of the dual-ended readout, side dual-ended readout, and triple-ended readout were 216.9 ps, 231.0 ps, and 203.6 ps, respectively.

Spectral Calibration of the SLSTR Focal Plane Assemblies

<p>We describe a novel technique – Fourier transform spectroscopy – that we have developed to characterise the spectral and polarisation responses of the Sentinel-3 SLSTR optical channels. Our method has a number of advantages over conventional approaches employing a grating monochromator, including excellent spectral registration and resolution, intrinsic rejection of self-emission from the test setup and fast measurement times. Our measurements are traceable, through the spectral responsivity of a reference detector and the wavelength of a HeNe laser, to national standards.</p><p>We illustrate our method with sample results from the spectral calibrations of the four SLSTR focal plane assemblies tested to date. </p>

STUDIES ON THE DETERMINATION OF THE TOTAL HARDNESS OF THE DRINKING WATER COMING FROM THE "FÂNTÂNILE RECI" SPRING IN MARAMUREŞ

The paper showcases research conducted in order to determine the total hardness of the drinking water coming from the "Fântânile Reci" spring, located at the edge of the DN18 road, at the end of the Mara town, in Maramures, Romania. A HI97735 advanced portable photometer was used for this experiment. The photometer can perform low, medium and high range measurements of the total hardness of the water samples. The counter comes equipped with a superior optical system which uses a reference detector and a narrowband interference filter used for extremely quick and repeatable measurements. The values obtained as the result of the experiment are: 204 mg/l CaCO 3 (Total Hardness MR), 15,2 °E, 12,2°dH and 21,7°f. The LED light sources are superior compared to the tungsten lamps. LED lights are more efficient, providing more light while using less energy, and they produce little heat, which could otherwise affect the electrical balance.

Optically resonant structures for the enhancement of polycrystalline PbSe photoconductors

The mid-wave infrared (MWIR) regime of the electromagnetic spectrum is attractive for long-range imaging systems due to the atmospheric window between 3 and 5 [mu]m. Due to ambient thermal background, it is often necessary to operate sensor systems below room temperature to achieve an adequate signal-to-noise ratio (SNR). This cooling requirement adds size, weight, and complexity to systems in which these parameters are at a premium. In this work I investigated two methods for optically enhancing the absorptive properties of lead selenide (PbSe) photoconductive films to increase the operating temperature up to 290 K, thereby mitigating system cooling requirements. By employing surface plasmon resonant (SPR) and embedded reflective structures, we were able to demonstrate enhanced responsivity and raise the operating temperature to room-temperature. Sensitivity was observed to increase by a factor of three for SPR enhanced detectors, and up to two-times at room temperature in detectors with an embedded Pt back reflector. Moreover, PbSe detectors with SPR discs operating at room temperature were observed to have responsivity comparable to reference detectors at 230 K. Photoconductors with the embedded Pt back reflector had a performance at room temperature that was similar to the reference detector at 250 K. Herein, I discuss my design process, as well as the fabrication of these resonant structures. Also discussed are the measurement and test results I obtained from surface plasmon and embedded reflector enhanced PbSe detectors. In this dissertation, I present results that demonstrate the viability of SPR and interference structures as mechanisms for increasing the operating temperature of PbSe MWIR photodetectors up to 290 K

VERIFICATION OF THE SENTINEL-4 FOCAL PLANE SUBSYSTEM

The Sentinel-4 payload is a multi-spectral camera system which is designed to monitor atmospheric conditions over Europe. The German Aerospace Center (DLR) in Berlin, Germany conducted the verification campaign of the Focal Plane Subsystem (FPS) on behalf of Airbus Defense and Space GmbH, Ottobrunn, Germany. The FPS consists, inter alia, of two Focal Plane Assemblies (FPAs), one for the UV-VIS spectral range (305 nm … 500 nm), the second for NIR (750 nm … 775 nm). In this publication, we will present in detail the opto-mechanical laboratory set-up of the verification campaign of the Sentinel-4 Qualification Model (QM) which will also be used for the upcoming Flight Model (FM) verification. The test campaign consists mainly of radiometric tests performed with an integrating sphere as homogenous light source.<br><br> The FPAs have mainly to be operated at 215 K ± 5 K, making it necessary to exploit a thermal vacuum chamber (TVC) for the test accomplishment. This publication focuses on the challenge to remotely illuminate both Sentinel-4 detectors as well as a reference detector homogeneously over a distance of approximately 1 m from outside the TVC. Furthermore selected test analyses and results will be presented, showing that the Sentinel-4 FPS meets specifications.