which is proportional to the original time spectrum I(t) except a slight temporal spread determined by the bit period T0 .In SSTR, the detected response R(t) is acquired directly from the linear output of a photodetector, while the PRSPC method utilize single photon counting to accumulate the photon numbers in various time slots. The total number of time slots is the number of bit in the excitation sequence, and the width of each slot is identical to the bit period. The excitation sequence and pulse detection are synchronized with a universal clock signal.