Objective: The main goal of the proposed project is to develop, construct, and test a new radio frequency (RF) timing processor - the RF Timer for keV energy electrons. The RF Timer is a THz timing processor, based on vacuum-tube technology and can be used to time photoelectrons or secondary electrons with picosecond resolution over a time interval of a few tens of ns. It has potential applications in accelerator technology and material science, life science, high energy nuclear physics experiments among other fields. The activities of the project include theoretical and experimental studies and developments of the following parts: RF spiral scanning deflector; microchannel plate based electron detector; multi-pixel readout anode; readout electronics; data acquisition software package; power supplies for operation of electron optics and electron detector; RF synthesizer for spiral scanning deflector; air resistive photocathodes; electron optics studies; vacuum tube. In addition the existing experimental setup could be modified to operate and test each part of the timer and an entire system, including development of an RF synchronized keV energy pulsed electron source.
State of the art: Precise time measurement is a frequent requirement in science and technology. Classic areas of scientific application are in physics, astronomy, geodesy, medical and biomedical imaging, and chemistry. In technology and industrial metrology, the key applications are in dynamic testing of integrated circuits and high-speed optical components for data storage and fiber optic telecommunication. Further applications of picosecond timing are found in laser ranging and depth imaging (see e.g. [1, 2] and references therein).
The most common requirement is a repeated time difference measurement with high precision, e.g. the time difference between two photon pulses or between a clock and photon pulse. The difficulty lies in the requirement of picosecond resolution. Even though modern digital circuits can operate at very high clock speeds, in some cases tens of GHz, they are not yet fast enough to directly count at the ps level. Nevertheless, high-speed digital circuits typically called time-to-digital converters (TDCs) are frequently used for time measurement. There are many variants of TDC (see e.g. [3–5]). The simplest is a digital counter running at the speed of a fast crystal locked clock. Suitable counter implementations in fast semiconductor technologies can in principle be operated at clock rates as high as 40 GHz, thereby directly providing time resolutions of 25 ps. However, there is a solution that allows the time resolution to be increased beyond the clock period. The real-world limitations come into play with the instrumental dead time. When striving for high resolution of, e.g., 1 ps, we must currently accept a TDC dead time of 80 ns, as a result of the used complicated electronics, and for 25 ps resolution, we have about 25 ns dead time [6, 7]. However, there are other limitations to state-of-the art timing processors. Even if a 1 ps resolution dead-time-less TDC existed, photon detector technology would also impose a time dispersion and dead time. At present, the detection of optical signals, down to the single-photon level, is carried out with Avalanche Photodiodes (APD), vacuum Photomultiplier Tubes (PMT), or Hybrid Photon Detectors (HPD). The time resolution limit of current APD, PMT or HPD for single photo-electron detection is about 100 ps FWHM. The dead time limit of these devices is few ten ns.
Project and Expected Scientific Technological Progress: An ideal electronic timing processor would have 1 ps timing resolution, 1 THz bandwidth, 1 Tbit/s sampling rate and virtually unlimited dynamic range. It can in principle be realized by using the spiral scanning RF timing technique, implemented as a Streak Camera or RFPMT. We propose to develop a GHz RF spiral scanning deflector based on a recently developed RF circular scanning system [9-11] that is capable of real-time conversion of a sequence of electrons into a two-dimensional spatial image. It will be the basis of an ultrafast timing processor, where a temporal sequence of keV energy electrons may be directly encoded on to a spatial locus, producing a two-dimensional (2D) image which reflects the time of arrival of the electrons. The single electrons will be multiplied in a position-sensitive microchannel plate (MCP) system and then detected on a pixelated anode. This high-resolution pixel detector, along with fast readout and data acquisition, is being developed in parallel, by our collaborators from Glasgow University, UK, lead by Dr. John Annand. The combination of the spiral scanning system, PS electron multiplier, high-resolution pixel detector and ultrafast readout electronics will produce a THz bandwidth and dead-time free device which is capable of 1 Tbit/s sampling rate and 1 ps time resolution over few hundreds of ns time range. This will be a totally new, nearly ideal timing technology which will have potential applications in many fields. In particular it will lead to the development of a new types of photon detector based on RF Streak Camera or RF PMT technology. In addition we intend to develop air resistant photocathodes, which in turn will allow manufacturing of a cost effective, demountable RF Timer in Yerevan.
