The measurement of time to very high precision is a prerequisite in many fields of science and technology. A new optical sensor, the Radio Frequency Photomultiplier Tube (RFPMT), capable of ps resolution for single photon detection at high rates, is under development jointly by physicists from the Alikhanyan National Science Laboratory and the University of Glasgow. The RFPMT operates similarly to a conventional photomultiplier, but includes a set of radio-frequency powered deflection electrodes. These convert the arrival times of photoelectrons, produced by photons incident on the cathode, to a time-dependent position which is detected at the anode. Currently the first prototype sealed-vacuum tube, produced by Photek UK Ltd., which has a single deflector and resistive-sea anode, is under verification. However tests are also underway using a demountable vacuum chamber, of a dual deflector setup which will increase the time range of the device beyond a single RF period. Eventually this dual RFPMT will use a high spatial resolution pixelated anode, which can resolve the more complex spatial loci produced by two deflectors, and also allow detection of multiple single photons spaced at intervals of the order 1 ps.

The RFPMT will has a number of potential applications, two of which are outlined here.

  • In Positron Emission Tomography (PET), measurement of the arrival time difference of the gamma-ray pair provides extra position information and improved image quality. Equipped with RFPMTs a PET scanner could potentially achieve better than 10 ps time resolution which would represent a breakthrough in terms of imaging quality.
  • In high-resolution fluorescent optical microscopy the ps timing capabilities of the RFPMT and the ability to resolve single-photon arrival times at the (sub)ps level would be enormously beneficial to time correlated single photon counting techniques. RFPMT-level performance has the potential not only to improve spatial resolution at the molecular level, but also to provide dynamical information on molecular processes as they take place.

Verification of the RFPMT performance is making excellent progress at Alikhanyan National Science Laboratory, the CANDLE institute in Yerevan and the University of Glasgow. With the above applications in mind, ways to further improve the timing resolution, shrink the size, and increase the data throughput are already under investigation. The collaboration between Yerevan and Glasgow has already proved to be extremely fruitful and we look forward to developing the RFPMT technology to the level where it is available commercially for use in medicine, life sciences and the physical sciences.

Amur