Gaseous photodetectors with solid photocathodes

Abstract

Remarkable properties of gas photodetectors make them attractive for application in high energy physics, astrophysics, and medical imaging. This review presents the results of research and development of gaseous photodetectors with solid photocathodes (GPDs). In particular, efficient photocathodes for the ultraviolet (mainly CsI) and the visible ranges, including photocathodes with protective dielectric nanofilms, are described. Some problems of the physics of gaseous photodetectors and photocathodes are considered: photoelectron backscattering in gas, photoemission amplification in an electric field, photoelectron transport through nanofilms, protective properties of nanofilms, and photon and ion feedback. A separate section is devoted to GPDs based on gas electron multipliers (GEMs), including sealed GPDs and cryogenic two-phase avalanche detectors with CsI photocathodes.

Liquid noble gas detectors for low energy particle physics

“…Considerable effort has been put into trying to couple a photocathode to an electron multiplication system, which can be operated in gas (ideally, in the liquid too). This concept is usually referred to in the literature as the 'gaseous photomultiplier' (see, for example, review papers [321,322]). …”

Electron emission properties of two-phase argon and argon-nitrogen avalanche detectors

“…It should be remarked that the electron backscattering effect in two-phase systems (step 5) was not taken into account in previous works. On the other hand, the electron backscattering effect for electrons emitted from photocathodes in gas media is well known: see for example a recent review [35]. This effect is particularly strong in noble gases and thus should certainly manifest itself in two-phase noble gas systems.…”

Advances in gaseous photomultipliers

“…The effective quantum efficiency (QE) is dictated by the photocathode material and by the photoelectron's extraction efficiency into gas (backscattering). The latter depends on the gas and on the electric field; in Ar/5%CH 4 , CH 4 and CF 4 respective extraction efficiencies of the order of 65%, 75%, and 85% were reached (compared to vacuum) at fields of 0.5Kv/cm in 1atm [28] (Fig. 5a); much lower values were measured and estimated in noble gases [29] (Fig.…”

“…In those devices the considerable ion-feedback at the PC, already seen at a gain of couple of hundreds, limited the gain to values <1000 (spark limit) [9]. In such a device the stable high-gain operation was reached by implementing an active ion-gating electrode [15]: a pulsed alternatingbias wire-plane, introduced within the cascaded-GEM structure suppressed the avalanche IBF to the PC by factor of ~10 4 . This has brought about the next significant landmark: a gated 4-GEM bialkali-GPM ( fig.…”

“…GPMs have been employed since a few decades for relativistic-particle identification, measuring Cherenkov light; particularly, they have been playing an important role in single-photon imaging in Ring Imaging Cherenkov (RICH) systems. Details on the different applications and past GPM techniques can be found in the proceedings of RICH Workshops [1] and in recent reviews [2,3,4].…”