Imaging low-energy positron beams in real-time with unprecedented resolution

Abstract

Particle beams focused to micrometer-sized spots play a crucial role in forefront research using low-energy positrons. Their expedient and wide application, however, requires highly-resolved, fast beam diagnostics. We have developed two different methods to modify a commercial imaging sensor to make it sensitive to low-energy positrons. The first method consists in removing the micro-lens array and Bayer filter from the sensor surface and depositing a phosphor layer in their place. This procedure results in a detector capable of imaging positron beams with energies down to a few tens of eV, or an intensity as low as $${35}\,{\hbox {e}^+/\hbox {s/mm}^{2}}$$ 35 e + / s/mm 2 when the beam energy exceeds 10 $${\hbox {keV}}$$ keV . The second approach omits the phosphor deposition; with the resulting device we succeeded in detecting single positrons with energies upwards of $${6}\,{\hbox {keV}}$$ 6 keV and efficiency up to 93%. The achieved spatial resolution of 0.97 $$\upmu \hbox {m}$$ μ m is unprecedented for real-time positron detectors.

Integrated anti-electronics for positron annihilation spectroscopy

“…Given that imaging through a PMA does not entail rastering, the inclusion of deflector coils in the microscopic optics is not mandatory and their addition is only contingent on the necessity of correcting the beam trajectory being expected. Moreover the active nature of the PMA allows the correction of spherical aberrations at the source, within the resolution of the PMA; this requires characterizing the aberrations, which can be performed by using a CMOS detector to directly measure the secondary positron beam, as shown in a previous work [24].…”

“…This often results in the expenditure of comparable beam time in the setup of the apparatus and the actual measurement. While we have recently proposed a possible solution based on direct imaging with CMOS sensors [24], it unfortunately does not extend to the submicrometer scale. The knife edge technique is ultimately a counting experiment, and as such the speed at which it can achieve a given precision is determined by the intensity of the beam employed.…”

“…The possibility of sculpting the beam into arbitrary shapes allows the use of grids in place of a single knife edge, thus exploiting the entire sample surface to determine the beam focusing, which would be orders of magnitude faster than a traditional knife edge. In addition, a micrometric grid printed onto a sensor similar to those in [24] would allow to test in parallel the alignment and focusing of the beam at different points of the desired target surface by observing the formation of Moiré patterns. Feature isolation: Modern PAS techniques are increasingly moving towards in operando measurements, that is, measurements in which, during the course of a PAS measurement, a sample is manipulated mechanically, thermally, chemically or through the exposure to light or slowly varying electromagnetic fields.…”