Microchannel plate based photon counting at UV wavelengths for astronomy applications

Photon counting in the far and extreme ultraviolet (FUV and EUV from 40 to 200 nm) is an important technique in various astronomic fields, such as solar physics, planetary atmosphere and surface, stellar formation and galaxies evolution studies. Thanks to their solar blindness, good efficiency at UV wavelengths and low dark count rates, microchannel plates (MCPs) are typically utilized to build imaging and spectroscopic space-based astronomical instruments. In this framework, the major limitations of microchannel plates are represented by limited dynamic range and lifetime. Both parameters can benefit from the use of ALD-MCPs and the ability to operate the MCP at low gain. However, this requires the development of new readout systems that do not themselves limit the system’s performance. To fully leverage the properties of the new MCPs, operating them at low gain, we have proposed to couple the MCP to a custom readout circuit, composed of a bi-dimensional anode matrix with a pitch of 35 µm; each pixel features a charge acquisition and discriminating chain with an extremely low readout noise. This allows attaining single-photon detection together with a high-dynamic range up to 100 kcps per pixel and a high spatial resolution. A first prototype of the detector with a 32x32 readout circuit has been developed and assembled in an ultra-high vacuum custom chamber. The first measurements demonstrate good spatial resolution and linearity; further tests are currently being performed to fully characterize the detector performance. Future works envision instead a possible extension of the prototype to a higher dimension matrix to cover the whole active area of the MCP.