(Color online) Scheme of the eight-channel coincidence unit. The device can be grouped into three different parts: A first fast part for coincidence detection and event capturing, followed by a FIFO to buffer the patterns, and a third, slower part, containing the microcontroller for histogramming. The unit is connected via a serial interface to a personal computer (PC) for final data processing.
Simplified circuit diagram of the fast part of the coincidence unit, relevant for the coincidence detection. The left side shows the eight input channels, for the eight detector signals (NIM), we start off with. The eight detector pulses are first turned into ECL pulses allowing fast signal processing. The whole signal processing is triggered by the output signal of an eight-channel OR gate, indicating a detection event, which is captured by an latch. P1–P4 denote four adjustable one shots, which are used to guarantee the exact timing sequence. After the correct event recognition, the data byte representing all possible single and coincidence events is written into a FIFO buffer for further processing.
(Color online) Fast side timing of the coincidence unit. The coincidence registration is initiated by a detection signal, which is denoted by DS. The output of the last OR gate is labeled by 4OR. The output signals of the four one shots providing the correct timing sequence are labeled by P1 to P4. The pattern is written into the FIFO on the rising edge of the WCLK signal (inverted and level-shifted P4 signal).
(Color online) Timing of the coincidence window. D1 and D8 denote two exemplary detector signals. The output pulse of the last OR gate is labeled by 4OR. P1 and P2 denote the output pulses of the first two one shots, allowing to tune the coincidence window. The theoretical expected average coincidence window with the present setup is .
(Color online) Experimental setup to demonstrate the operation of the multichannel coincidence counter (LBO: lithium triborate crystal, BBO: beta barium borate crystal, C: fiber coupler, F: narrow bandwidth filter , BS: beam splitter, PBS: polarizing beam splitter, and D1-D8: single-photon detectors). In different orders of the parametric down-conversion process photon pairs are created. The multiphoton emission is analyzed with the eight-channel coincidence counter presented here.
(Color online) All possible 70 fourfold coincidences between the eight detectors D1-D8. The theory predicts the registration of 18 different fourfold coincidences with two different detection probabilities. Labeled are the two fourfold coincidences corresponding to the first two terms in Eq. (3). The registration of this coincidences should be four times higher than the registration of all other events.
Analysis of the multiphoton emission of the pulsed parametric down-conversion source. Shown is, on logarithmic scale, the sum of all possible single detection events and -fold coincidence detection events registered in an overall measurement time of . The experimental results are compared with the theory. This measurement indicates that the developed multichannel coincidence unit is able to process all possible 255 different detection events at the same time, and therefore clearly demonstrates the powerful and efficient operation of this type of instrument.
Article metrics loading...
Full text loading...