Fig. 1. Experimental setup.

Fig. 2. Principle and internal configuration of the SPD.

Fig. 3. Pulses output simultaneously from the two SPDs. a1: SPD1, a2: SPD2, b1 and b2 are the details of the waveforms in a1 and a2, respectively.

Fig. 4. Envelope diagram of counts (logarithm) vs. delayed time under different total count rates (a–d: 1.5 Mcps, 150 kcps, 15 kcps, and 1.5 kcps).

Fig. 5. Coincidence counting spectra with details (inside) under different total count rates (a–d: 1.5 Mcps, 150 kcps, 15 kcps, and 1.5 kcps).