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Image of Flex2K-12x2.  The dimension of the external enclosure is approximately 2.75x2.5.0.8".

Functions:

Flex2K-12x2 is a photon counting digital hardware that can be used as

1. Fast real time multiple tau digital correlator with x2 technology.  Minimum sample time 12.5ns.

2. One channel photon history recorder.  System clock speed: 60MHz. Average intensity limit: 910KHz

In photon auto correlation mode, it works like an ordinary multiple tau correlator.  It calculates the correlation function(s) in real time covering delay times from the minimum sample time to about an hour with more than 288 data points. 

In photon cross correlation mode, it works like two multiple tau correlators.  It calculates the correlation function for both channel A x channel B and channel B x channel A in real time covering delay times from the minimum sample time to about an hour with more than 288x2 data points.  This achieves two times efficiency for short time channels where the noise is limited by the photon shot noise.

In photon history recorder mode, it records the time between successive photon events.  This is measured by counting the number of ticks of the system clock between the photon events.  This time is then transferred to the host personal computer via high speed Universal Serial Bus (USB).   The amount of information to be transferred is proportional to the count rate of the incoming photons.  Using a lossless compression technique, Flex2K-12x2 transfers complete time series without gaps for average count rate from 0 to approximately 910 kcps in one channel mode.  At high count rates the overflows are displayed in real time.

Flex2K-12x2 hardware specifications:

1. Input signal: standard TTL pulses.
2. Two BNC connectors
3. One USB connector.
4. Easy to use FlexWindows software and software for Windows98 libraries included.

Correlation mode specifications:

1. Single multiple tau channel layout ( sample time denoted at T, data width W):

1. Auto/cross correlations.
2. 12.5 ns minimum sample.
3. 288x2 real time channels.
4. Delay time range: 12.5ns to 1 hour in multiple tau channel layout.
5. First 17 channels: T = 12.5ns, W = 1 bits, delay times 0 to 16*T;
6. Second 8 channels: T = 2*12.5ns, W = 2 bits, delay times 9*T to 16*T
7. Third 8 channels: T = 4*12.5ns, W = 3 bits, delay times 9*T to 16*T;
8. Fourth 8 channels: T = 8*12.5ns, W = 4 bits, delay times 9*T to 16*T;
9. Sample time doubles every 8 channels and data width increment 1 bit to prevent overflow.
10. The longest delay time is about one hour.

Photon history recorder mode specifications:

1. System clock: 60 MHz in one channel mode.
2. 16.7 ns pulse pair resolution.
3. Complete time series recorded on a PC hard drive for average count rate up to 910 KHz in one channel mode.  The maximum count rate is somewhat host PC dependent.

More about multiple tau theory.

Multiple tau theory was invented by Klaus Schätzel.  The following papers discuss the theory and the advantage of the multiple tau scheme.

1. Klaus Schätzel. Single Photon Correlation Techniques. Dynamic Light Scattering: The method and some applications, Edit by Wyn Brown, Clarendon Press, Oxford, P 76, 1993.
2. Klaus Schätzel et.  Noise on Multiple-Tau Photon Correlation Data.   SPIE Vol. 1430, P109, Photon Correlation Spectroscopy: Multicomponent Systems, 1991.
3. Klaus Schätzel. New Concept in Correlator Design. Inst. Phys. Conf. Ser. No. 77, P175, 1985.
4. Klaus Schätzel et.  Photon Correlation Measurements at Large Lag Times.  Journal of Modern Optics, Vol. 35, No. 4, P711, 1988.

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Last modified: October 25, 2006