Hardware simulator for photon correlation spectroscopy

We present a hardware simulator ideal for testing digital correlators in photon correlation spectroscopy. By using a PCI-6534 National Instrument I/O board, a personal computer (1.5 GHz Pentium 4), and an original algorithm developed in LabVIEW (National Instrument(TM)), we realized an instrument capable of delivering a continuous stream of transistor-transistor logic pulses with the desired statistical properties over one or more channels'. The pulse resolution could be set to values multiple of the clock period Deltat = 50 ns available on the board. When a single channel is used, the maximum count rate at Deltat = 50 ns was (I) similar to 350 kHz. With two channels,we obtained (I) similar to80 kHz at Deltat = 50 ns and (I) similar to 120 kHz at Deltat = 100 ns. Pulse streams with Gaussian statistics and in the presence of shot noise were simulated and measured with a commercial hardware correlator. Photodetector defects, such as the presence of afterpulses, Were also simulated and their elimination by cross correlation techniques was checked. The simulator works also as a general purpose pulse pattern generator (PPG). Compared with commercial PPGs, our simulator is slower, but permits a continuous output of the pulse stream (not allowed in PPGs). At the same time it offers many other nontrivial advantages related to its flexibility, relatively low cost, and easy adaptability, to future technology developments. (C) 2003 American Institute of Physics.