I would like to do a two-photon cross correlation measurement. Hardware auto correlators and cross correlators are available but expensive. It seems many other users have come up with the idea of using the 80 or 100 MHz clocks into the counter input for each desired channel, starting the counters simultaneously, and putting each photon channel into the gate of the corresponding counter. Then each photon triggers the counter to store the clock count in its internal register, i.e., the time stamp for that photon. Since overflows on a 32 bit counter running at 100 MHz only occur every 42 seconds, and average photon rates will be at least 100 Hz, overflows should be easily recognized and corrected in post processing. So let's assume all we have to do is get the counter readings into a memory buffer. There can be bursts of photons with arrival separations as small as few clock cycles. Average rates might be a few hundred kHz or more on each channel. We can adjust this rate by turning the laser power up or down---the source for the scatterer that produces the correlated photon stream. I suspect many others would like to know what system is better for these kinds of measurements, the 6602 or the X-Series. If FPGA is a good solution, we should maybe start a new thread on that. But for 6602 or X-Series: What is the fastest they can do this for short bursts (how fast for how long) and what is the sustainable rate? I realize the sustained rate will depend on hardware. I thought I saw that the PXI beats the PCI bus in this kind of application. So are the PXI versions any better? In particular, what are the effects of the 128 sample FIFO on the X-Series versus the 2 sample buffer on 6602. And I saw something about the speed of the front end for these two choices might be an issue in this regard. TTL (photon) pulses on the gate will have 10-50 nsec widths.
↧