World Space Observatory Ultraviolet (WSO-UV) is a major Russian-led international collaboration to develop a large Space-borne 1.7 m Ritchey-Chrétien telescope and instrumentation to study the Universe in the ultraviolet wavelengths. The WSO-UV WUVS spectrograph consists of three channels: two high resolution channels (R=50000) with spectral ranges of 115-176 nm and 174-310 nm, and a low resolution (R=1000) channel with a spectral range of 115-305 nm. Each of the three channels has an almost identical custom detector consisting of a CCD inside a vacuum Enclosure, and drive electronics with associated cables. The main challenges of the WUVS detectors are to achieve high quantum efficiency in the FUV-NUV range, to provide low readout noise (≤3 e- at 50 kHz) and low dark current (≤ 12 e- /pixel/hour), to operate with integral exposures of up to 10 hours, and to provide good photometric accuracy. Teledyne e2v has designed three variants of a custom CCD272-64 sensor with different UV AR coatings, optimised for each WUVS channel. The custom vacuum Enclosure, also designed by Teledyne e2v, prevents contamination and maintains the CCD at the operating temperature of -100oC, while the temperature of the WUVS optical bench is +20oC. STFC RAL Space has developed the Camera Electronics Box (CEB) which houses the CCD drive electronics. Digital correlated double sampling technology provides extremely low readout noise and also enables flexibility to optimise readout noise against pixel frequency for a number of normal and binned pixel readout modes. This paper presents the general trade-offs of the WUVS detector design, methods for extending the service life of the CCD sensors working with low signals in a Space radiation environment, and a summary of the measured and calculated key parameters of the WUVS detectors.
We have measured the spectral quantum efficiency of several digital detectors in two spectral ranges, namely vacuum ultraviolet (VUV, 115-310 nm) and extreme ultraviolet (EUV, 10-58 nm) wavebands. We used monochromatic synchrotron radiation from the VEPP-4M storage ring (INP, Novosibirsk) to investigate the spectral response of GSENSE400BSI-GP CMOS which have been specially designed for optimum VUV sensitivity, as well as the WSO-UV project’s custom deep cooled CCD272-64 sealed within a hermetic contaminant-protective stainless-steel enclosure with a VUV-transparent entrance window. The CMOS GSENSE400BSI-GP sensitive surface has four types of different pretreatment: (i) small boron implantation dose, weak annealing; (ii) small boron implantation dose, strong annealing, (iii) large boron implantation dose, weak annealing; (iv) large boron implantation dose, strong annealing. These VUV optimised CMOS sensors have higher spectral sensitivity and higher quantum efficiency in the 112-180 nm spectral range, compared to a commercial CMOS which is typically optimised for the best performance at visible wavelengths, but at longer wavelengths GSENSE400BSI-GP sensitivity decreases. The measurements have revealed that stronger annealing can slightly increase the CMOS spectral sensitivity, while large boron implantation dose decreases the sensitivity of the CMOS sensors. With relation to quantum efficiency figures, CCD still prevails in the VUV while recent advances in CMOS technology could make CMOS more preferable in the EUV range.
Vladimir Zabrodsky, Pavel Aruev, Vladimir Filimonov, Nikolay Sobolev, Evgeniy Sherstnev, Viktor Belik, Anton Nikolenko, Denis Ivlyushkin, Valery Pindyurin, Nikita Shadrin, Artem Soldatov, Mikhail Mashkovtsev
This work presents the results of long-term observation of the silicon photodiodes spatial profile response and the silicon photodiodes dark current after their exposure to 10.2 eV quanta and in the spectral range of 150–300 eV. Exposure of the photodiodes to quanta of an energy of 10.2 eV was repeated. Several other photodiodes have been irradiated in the spectral range of 700-1800 eV with a dose of 8 J/cm2. The spatial profile of the irradiated photodiodes was studied with 3.49 eV, 10.2 eV and 100 eV quanta. The effect of the recovery of the response spatial profile has been proved for the p+-n diode. An additional useful method of visualization of irradiated photodiode area is also presented.
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