Nuclear Instruments and Methods in Physics Research A 471 (2001) 125–130 Optical readout of GEMs F.A.F. Fraga*, L.M.S. Margato, S.T.G. Fetal, M.M.F.R. Fraga, R. Ferreira Marques, A.J.P.L. Policarpo Departamento de F! ısica, LIP–Coimbra, Universidade de Coimbra, 3000 Coimbra, Portugal Abstract We present an overview of results from our recent studies on the use of the visible and NIR scintillation emitted by the gas electron multiplier (GEM) and on the possibility of using detectors operated with cascaded GEMs to build tracking chambers. r 2001 Elsevier Science B.V. All rights reserved. 1. Introduction and motivation Most of the published research done in the use ofgaseousscintillatorswascarriedonintheVUV and UV zone of the spectrum, using photon counting techniques and high efficiency mixtures, and many detectors were developed. However many imaging applications can be found for integrating devices, that operate by accumulation ofthelevelofirradiationforaframeperiodwitha sequent dead time for read-out. The image plates and CCDs are examples of this type of detector. This last device has been perfected during the last decade,andcurrenthighperformanceCCDdigital cameras show high sensitivity and low noise for a reasonable price without need of special fluid cooling systems. AlthoughthemorerecentdevelopmentsinCCD technology have achieved high quantum efficiency down to 120nm using back illuminated sensors, these devices are still expensive and of critical use. Systems using this zone of the spectrum are awkward to design and operate, needing special opticsandwindowstocouplethescintillationlight to the CCD with acceptable losses. Considering that common glass optics have good transmission in the range of standard CCDs and that electron avalanches in appropriate gas mixtures can result in the emission of light in the visible and NIR band covered by this devices, our group has been investigating the emissions of visible and NIR light by microstructures. In the visible region we have been considering thestudyofscintillationemittedbymicrostructure detectors, but only during the last three years we have been developing a large activity on the subject. The purpose of this paper is to report our studies in the application of CCDs and conditions of operation of gaseous mixtures for efficient light emission between 400 and 1000nm. 2. Previous work A particularly high emission of light was reported by Oed and Geltembort in 1991 [1]. The *Corresponding author. Tel.: +351-39-833-465; fax: +351- 39-822358. E-mail address: francisco@lipc.fis.uc.pt (F.A.F. Fraga). 0168-9002/01/$-see front matter r 2001 Elsevier Science B.V. All rights reserved. PII:S0168-9002(01)00972-X