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Image of Flex99R-480 and with a notebook computer.  The dimension of the external enclosure is 2.5"x2.75"x0.8".

Functions:

Flex99R-480 is a photon counting digital hardware that can be used as

1. Moderate speed real time multiple tau digital correlator.  Minimum sample time 480 ns.

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

In photon correlation mode (mode 1), it works like an ordinary hardware real time 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 256 data points.  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, Flex99R-480 transfers complete time series without gaps for average count rate from 0 to approximately 910 kcps.  At high count rates the overflows are displayed in real time.

Flex99R-480 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. 480 ns minimum sample.
3. 264 real time channels.
4. Delay time range: 48ns to 1 hour in multiple tau channel layout.
5. First 16 channels: T = 480ns, W = 5 bits, delay times T to 16*T;
6. Second 8 channels: T = 2*480ns, W = 6 bits, delay times 9*T to 16*T
7. Third 8 channels: T = 4*480ns, W = 7 bits, delay times 9*T to 16*T;
8. Fourth 8 channels: T = 8*480ns, W = 8 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.

Intensity limits:

Flex99R-480 is designed with sufficient hardware resource to prevent overflow at any reasonable intensities.  However, in extreme situations, clipping and overflow could happen.  The intensity limits are following:

1. Maximum intensity integrated over 480ns: 64.6 MHz.  Clipping will happen if the input intensity exceeds the maximum.
2. Maximum intensity integrated over 126ms: 11.8 MHz.  Overflow will happen if the maximum is exceeded.

Photon history recorder mode specifications:

1. System clock: 60 MHz.
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.   The count rate limit may depend on the performance of the host PC. 

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